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i

NASA/TP—2013–217477

Closeout Report for the Refractory Metal 

Accelerated Heat Pipe Life Test Activity

J. Martin, R. Reid, E. Stewart, R. Hickman, and O. Mireles

Marshall Space Flight Center, Huntsville, Alabama

January 2013

National Aeronautics and

Space Administration

Marshall Space Flight Center • Huntsville, Alabama 35812
ii

Available from:

NASA Center for AeroSpace Information

7115 Standard Drive

Hanover, MD 21076 –1320

301–621–0390

This report is also available in electronic form at

<https://www2.sti.nasa.gov>

TRADEMARKS

Trade names and trademarks are used in this report for identification only. This usage does not constitute an official

endorsement, either expressed or implied, by the National Aeronautics and Space Administration.
iii

TABLE OF CONTENTS

1. INTRODUCTION .......................................................................................................................... 1

1.1 Laboratory Layout ................................................................................................................... 3

1.2 Hardware Procurements........................................................................................................... 3

2. WATER-COOLING SYSTEM CONSIDERATIONS ................................................................... 5

2.1 Thermal Analysis for Loss of Facility Coolant Flow Condition ............................................. 5

2.2 Thermal Analysis for Loss of Recirculation Coolant Flow Condition ................................... 8

3. CALORIMETER CONSIDERATIONS......................................................................................... 12

3.1 Use of Standard Tube Sizes to Meet Calorimeter Performance ............................................. 12

3.2 Alternate Calorimeter Design .................................................................................................. 15

3.3 Calorimeter Power Measurement Uncertainty Estimate ......................................................... 16

4. RADIO FREQUENCY HEATING SYSTEM................................................................................ 18

5. HEAT PIPE DEVELOPMENT ACTIVITY................................................................................... 20

5.1 Mo-44.5%Re Material General Welding Development .......................................................... 20

5.2 Heat Pipe Wick and Envelope Development/Manufacture Activity........................................ 24

6. SODIUM PURITY EVALUATION USING VANADIUM 

WIRE EQUILIBRATION............................................................................................................... 28

6.1 Basic Hardware Setup ............................................................................................................. 28

6.2 General Preparation and Operations........................................................................................ 29

7. SUMMARY ................................................................................................................................ 31

APPENDIX A—LAMINAR FLOW WATER CALORIMETER 

UNIT SPECIFICATION ....................................................................................... 32

APPENDIX B—TWO-BAND OPTICAL PYROMETER SPECIFICATION ................................... 39

APPENDIX C—WATER-COOLING PALLET SPECIFICATION.................................................... 41

APPENDIX D—WATER FLOW METER SPECIFICATION ........................................................... 44
iv

TABLE OF CONTENTS (Continued)

APPENDIX E—INERT GAS PURIFIER SPECIFICATION........................................................... 48

APPENDIX F—WATER AND GAS SYSTEM HAND VALVE SPECIFICATION........................ 50

APPENDIX G—VACUUM PUMP UNITS SPECIFICATION........................................................ 53

APPENDIX H—FORTRAN 90 SOURCE CODE LISTING—LOSS OF COOLANT

TRANSIENT ANALYSIS ................................................................................... 56

APPENDIX I— HEAT PIPE CALORIMETER GEOMETRY—STANDARD 

TUBE SIZES .......................................................................................................... 59

APPENDIX J— CALORIMETER POWER EXTRACTION PERFORMANCE 

WORKSHEET FOR STANDARD TUBING ........................................................ 61

APPENDIX K—SIMPLIFIED CALORIMETER UNCERTAINTY ANALYSIS............................ 63

APPENDIX L—RADIO FREQUENCY INDUCTIVE COIL ASSEMBLY 

CONTRACTOR REPORT..................................................................................... 71

APPENDIX M—MO-44.5%RE PLATE MATERIAL ANALYSIS.................................................. 87

APPENDIX N—MO-44.5%RE CLEANING PROCEDURE FOR WELDING.............................. 95

APPENDIX O—MO-44.5%RE 0.5-INCH-DIAMETER ROD STOCK 

MATERIAL ANALYSIS........................................................................................ 96

APPENDIX P—MO-44.5%RE 0.625-INCH-DIAMETER ROD STOCK 

MATERIAL ANALYSIS........................................................................................ 104

APPENDIX Q—CHEMICALS USED FOR VANADIUM WIRE EQUILIBRATION

MATERIAL CLEANING....................................................................................... 112

APPENDIX R—VANADIUM WIRE EQUILIBRATION OPERATIONAL 

PROCEDURE ........................................................................................................ 113

APPENDIX S—VANADIUM AND MOLYBDENUM WIRE SAMPLE

PREPARATION RESULTS ................................................................................... 129

REFERENCES ................................................................................................................................. 132
v

LIST OF FIGURES

 1. Heat pipe cross section with ancillary test systems ........................................................... 2

 2. General laboratory layout for accelerated heat pipe life testing: 

(a) Proposed laboratory setup and (b) photograph of floor

space prior to hardware setup ............................................................................................ 3

 3. Equilibrium temperature and volume of water required to cool 16 kg 

of Mo-44.5%Re where initial temperature of Mo-44.5%Re is 1,400 K ............................ 6

 4. Heat pipe calorimeter geometry ......................................................................................... 8

 5. Calorimeter transient soak-back temperatures for the baseline heat 

pipe geometry ..................................................................................................................... 11

 6. Calorimeter transient soak-back temperatures for three times the baseline 

heat pipe Mo-Re mass ........................................................................................................ 11

 7. An alternate design—electric resistance heater element calorimeter design...................... 15

 8. Brazing development testing for coil-type calorimeter design .......................................... 16

 9. Micrographs of PM Mo-44.5%Re plate ............................................................................. 22

10. EB welding fixture and sample setup ................................................................................. 22

11. Bend test configuration ...................................................................................................... 24

12. Mo-5%Re screen material .................................................................................................. 25

13. Room-temperature swaged wick element sample .............................................................. 26

14. Hot isostatic pressed wick element sample ........................................................................ 27

15. Vanadium wire support and insertion concept using a Mo-alloy bow ............................... 28

16. Layout of V wire/Na sampling test setup ........................................................................... 29

17. Oxygen concentrations: Na initial, Na final, and V wire ................................................... 30
vi

18. Conceptual calorimeter design ........................................................................................... 33

19. Conceptual process application/calorimeter with mounting setup ................................... 33

20. Calorimeter tube layout nomenclature .............................................................................. 34

21. Initial calorimeter concept—engineering design layout ................................................... 35

22. Initial calorimeter concept—engineering design parts detail ........................................... 35

23. Calorimeter cluster arrangement ....................................................................................... 38

24. General layout RF inductive coil assemblies (cluster with five positions) ....................... 72

25. General dimensional layout of a single RF inductive coil position .................................. 72

26. Magnetic field lines (a) with and (b) without a neighboring inductor 

for a three-turn coil with Fluxtrol 50 magnetic flux controller ......................................... 73

27. Magnetic field lines (a) with and (b) without a neighboring inductor 

for a three-turn coil without a magnetic flux controller .................................................... 73

28. Axial power-density distribution in the heat pipe ............................................................. 74

29. DC breakdown voltages in various atmospheres .............................................................. 75

30. Relationship between voltage and frequency for various coupling gaps .......................... 76

31. Heat transferred from heat pipe to induction coil (curves based upon 

calculations and information provided by Jim Martin from NASA 

for 1,373 K heat pipe temperature) ................................................................................... 77

32. Conceptual layout of the heat pipe inductive coil assembly ............................................. 79

33. Conceptual layout of the RF inductor assembly 3 ............................................................ 82

34. Conceptual induction coil head cross section ................................................................... 83

35. Conceptual layout of the RF inductor assembly 4 ............................................................ 85

36. Typical Ni tube .................................................................................................................. 113

LIST OF FIGURES (Continued)
vii

37. Fume hood and associated pickling equipment ................................................................ 114

38. Branson ultrasonic cleaners .............................................................................................. 114

39. Valve prepared for pickling ............................................................................................... 114

40. Ni tubes postprocessing .................................................................................................... 116

41. Typical electropolishing apparatus ................................................................................... 116

42. Buehler® Electromet III electropolisher/etcher ................................................................ 116

43. Typical as-received V wire sample ................................................................................... 117

44. Methanol-filled beaker in ice bath .................................................................................... 117

45. Vanadium wire suspension loop and sample wire ............................................................ 117

46. Anode and cathode positioning ......................................................................................... 118

47. Mitutoyo CD 12-in digital calipers ................................................................................... 118

48. Denver Instruments M–220D analytical balance .............................................................. 119

49. Vacuum bakeout system .................................................................................................... 120

50. Vacuum tube assembly ...................................................................................................... 120

51. Roughing pump ................................................................................................................. 120

52. Turbopump (a) and with controller (b) ............................................................................. 120

53. Ion gauge ........................................................................................................................... 121

54. Multigauge reader ............................................................................................................. 121

55. Leak detector ..................................................................................................................... 121

56. He source .......................................................................................................................... 121

57. Vacuum tube in furnace .................................................................................................... 122

LIST OF FIGURES (Continued)
viii

58. Thermocouple reader ........................................................................................................ 122

59. Ar glove box .................................................................................................................... 122

60. SS valves after vacuum bake ........................................................................................... 123

61. Wire bow .......................................................................................................................... 123

62. Bow with tube .................................................................................................................. 123

63. Assembled sample tube .................................................................................................... 124

64. Tube test configuration ..................................................................................................... 124

65. Tube processing—crimp .................................................................................................. 125

66. Tube processing—EB weld ............................................................................................. 126

67. Tube processing—cutoff .................................................................................................. 126

68. Tube processing—furnace heating ................................................................................... 126

69. Tube processing—wire removal ...................................................................................... 127

LIST OF FIGURES (Continued)
ix

LIST OF TABLES

 1. Baseline heat pipe life test matrix conditions (water coolant) ........................................... 1

 2. Heat pipe calorimeter parameters for a film gap width of 0.015 in ................................... 7

 3. Average heat pipe and calorimeter model parameters ....................................................... 8

 4. Heat pipe calorimeter drawn tubing requirements (all dimensions are in inches) ............. 12

 5. Standard tube sizes identified ............................................................................................. 13

 6. Calorimeter assembly layout with standard tube sizes—machining of channel 

tube only (all dimensions are in inches) ............................................................................ 14

 7. Calorimeter parameters for a film gap width of 0.0135 in ................................................. 14

 8. Summary of calorimeter power uncertainty with various 

instrumentation configurations ........................................................................................... 16

 9. Baseline heat pipe life test matrix ...................................................................................... 18

10. Summary of RF inductive coil assembly layouts .............................................................. 19

11. Chemical composition of the Mo-44.5%Re plate .............................................................. 21

12. General EB weld development matrix ............................................................................... 23

13. Final Mo-44.5%Re test matrix ........................................................................................... 23

14. Tube sizes required for calorimeter layouts (all dimensions are in inches) 

for tubing material produced by drawn technique (or other) ............................................. 37

15. Guaranteed delivered gas purity at flow rate ..................................................................... 49

16. Heat pipe calorimeter geometry based on standard tubing dimensions ............................. 60

17. Calorimeter geometry and performance for a cooling film annulus of 0.0135 in .............. 62

18. Results of two-dimensional simulation for 5/8-in OD Mo-Re heat pipe tube 

with 0.05-in wall thickness ................................................................................................ 74
x

LIST OF TABLES (Continued)

19. Electrical parameters per meter for 3-in-tall busswork carrying 1,450 A 

at 50 kHz .......................................................................................................................... 78

20. Electrical parameters of RF inductor assembly 1 ............................................................. 80

21. Description of RF assembly 3 heat pipes ......................................................................... 81

22. Parameters of RF assembly 3 ........................................................................................... 83

23. Electrical parameters of RF inductor assembly 3 ............................................................. 85

24. Recalculating five-turn inductor for use in RF assembly 4 configuration ........................ 85

25. Electrical parameters of RF inductor assembly 4 ............................................................. 85

26. Data sheet for V wire samples .......................................................................................... 129

27. Data sheet for V wire test segments ................................................................................. 130

28. Data sheet for Mo wire test holders ................................................................................. 131
xi

LIST OF ACRONYMS AND SYMBOLS

AMM Advanced Methods and Materials, Inc.

Ar argon

ARO after receipt of order

ASTM American Society for Testing and Materials

CH3CH2OH ethanol

CH3OH chilled methanol

DBTT ductile-to-brittle transition temperature

EB electron beam

Fe iron

GDMS glow discharge mass spectroscopy

GTA gas tungsten arc

HCL hydrogen chloride

HDPE high-density polyethylene

He helium

HIP hot isostatic pressing

HNO3 nitric acid

H2O2 hydrogen peroxide

H2SO4 sulfuric acid

ID inner/inside diameter

LDPE low-density polyethylene

Mo-Re molybdenum-rhenium
xii

MSFC Marshall Space Flight Center

N nitrogen

Na sodium

NaCL sodium chloride

NaOH sodium hydroxide

Nb niobium

NH3 ammonia

Ni nickel

OD outer/outside diameter

PM powder metallurgy

PTFE polytetrafluoroethylene

RF radio frequency

RFP radio frequency power

RT room temperature

SS stainless steel

TFE tetrafluoroethylene

Ti titanium

TIG tungsten inert gas

TP Technical Publication

UV ultraviolet

V vanadium

VAC Vacuum Atmospheres Company

LIST OF ACRONYMS AND SYMBOLS (Continued)
xiii

VHN Vickers hardness number

Zr zirconium

LIST OF ACRONYMS AND SYMBOLS (Continued)
xiv

NOMENCLATURE

A area

Co(v) oxygen concentration in vanadium

Cp specific heat

Cp,h2o specific heat of water (J/kg·K)

Cp,hp specific heat of heat pipe (J/kg·K)

Cp,j specific heat of element j (J/kg·K)

D diameter

Di diameter of inner wall

Do diameter of outer wall

d density

f function

hcond effective conduction heat transfer coefficient (W/K)

hrad effective radiation heat transfer coefficient (W/K)

htot effective total heat transfer coefficient (W/K) (heff=hcond+hrad)

j element number

k thermal conductivity

kgas thermal conductivity of He-Ar gas (W/m·K)

kj thermal conductivity of element j (W/m·K)

L axial length (m)

m flow rate
xv

mh2o mass of water (kg) (mh2o=ρh2oVh2o)

mhp mass of heat pipe (kg)

Q power

qcond conduction heat transfer rate (W)

qrad radiation heat transfer rate (W)

qtot total heat transfer rate (W) (qtot=qcond+qrad)

ri inner radius (m)

ro outer radius (m)

s gap thickness (m) (s=ro–ri)

T temperature

Ti, initial temperature (K)

Ti,h2o initial temperature of water (K)

Ti,hp initial temperature of heat pipe (K)

Ti,j initial temperature of element j (K)

To outside temperature (K)

Tsink sink temperature or temperature of vacuum chamber inner wall (K)

Tss steady-state temperature (K)

Tss,h2o steady-state temperature of water (K)

Tss,hp steady-state temperature of heat pipe (K)

t thickness

V volume; velocity

NOMENCLATURE (Continued)
xvi

Vh2o volume of water (m3) (Vh2o=mh2o/ρh2o)

Vj volume of element j (m3)

∆T temperature difference (K) (∆T=Ti–To)

∆Th2o temperature difference of water (K) (∆Th2o=Tss,h2o–Ti,h2o)

∆Thp temperature difference of heat pipe (K) (∆Thp=Tss,hp–Ti,hp)

∆t time step (s)

ε emissivity

εi emissivity of inner wall

εo emissivity of outer wall

ρ density

ρh2o density of water (kg/m3)

ρj density of element j (kg/m3)

σ Stefan-Boltzman constant (5.67×10–8 W/m2K4)

NOMENCLATURE (Continued)
1

TECHNICAL PUBLICATION

CLOSEOUT REPORT FOR THE REFRACTORY METAL ACCELERATED HEAT PIPE 

LIFE TEST ACTIVITY

1. INTRODUCTION

The primary goal of the accelerated heat pipe life testing activity was to focus on an experimental 

investigation of aging effects, using a series of 16 molybdenum-rhenium (Mo-Re) alloy heat pipes. To 

accelerate the response rate of potential life-limiting factors, an increase in both temperature and mass 

flux was imposed. Specific test conditions for each of the heat pipes are summarized in table 1. The first 

set of seven tests, referred to as the G Series, is based on the American Society for Testing and Materials 

(ASTM) G68–80 and examines time-dependent corrosion by holding constant temperature and mass 

fluence boundary conditions over the operating interval.1 The second set of nine tests, referred to as the

F Series (Fisher central composite F(–4) to F(4)), imposes variations in both operating temperature and 

mass fluence, with the intent of providing insight into the cross correlation of these parameters with 

respect to corrosion rates. Detailed documentation covering the approach, design, and layout of the heat 

pipes and test support systems was previously reported.2–4 Due to a change in program direction and 

funding, the heat pipe project was terminated prior to build and testing. 

Table 1. Baseline heat pipe life test matrix conditions (water coolant).

Test 

Identifier

Power 

Level (W)

Heat Pipe 

Temp. (K)

Gas Gap 

Mixture

Gas Gap

Width (in)

Coolant Flow 

(gpm)

Coolant

Delta Temp. (K)

Number of 

Heat Pipes

G Series

F(–4)

F(–3)

F(–2)

F(–1)

F(0)

F(1)

F(2)

F(3)

F(4)

3,000

5,000

1,000

3,000

3,000

3,000

2,000

4,000

2,000

4,000

1,273

1,273

1,273

1,373

1,173

1,273

1,223

1,223

1,323

1,323

He-32%Ar

He-6%Ar

He-32%Ar

He-32%Ar

He-32%Ar

He-32%Ar

He-32%Ar

He-32%Ar

He-32%Ar

He-32%Ar

0.025

0.025

0.103

0.031

0.021

0.025

0.037

0.017

0.046

0.020

0.61

0.77

0.11

0.56

0.65

0.61

0.54

0.67

0.50

0.63

18.8

24.6

35.2

21.1

17.6

18.8

13.9

22.8

15.2

24.0

7

1

1

1

1

1

1

1

1

1
2

The 16 heat pipe envelopes were to be constructed of Mo–44.5%Re material, formed using the 

powder metallurgy (PM) process by Rhenium Alloys, Inc., and assembled by Advanced Methods and Materials, Inc. (AMM). The heat pipes were designed with an active length of ≈12 in (3-in evaporator and 9-in 

condenser) and an outer diameter (OD) of 0.625 in. The proposed wick structure was an annular crescent 

design fabricated from seven layers of Mo-5%Re 400 × 400-mesh cloth (average 0.001-in-diameter 

wire). The final cylindrical wick structure had an OD of ≈0.48 in and a wall thickness of 0.014 in, resulting 

in an annular flow gap of ≈0.022 in. The wick tube was equipped with a bonded plug at the evaporator end 

while the condenser end remained open, sealed by the excess liquid sodium (Na) that pools at the end of 

the condenser section. The evaporator end plug was fitted with a zirconium- (Zr-) based getter pack to irreversibly trap impurities collected in the evaporator pool during normal operation. Power transfer into and 

out of the heat pipe would be provided by noncontact methods to minimize the potential for introducing 

impurities. Power was to be supplied using a radio frequency (RF) induction coil on the evaporator section 

and removed from the condenser using a low-pressure static gas (helium (He) and argon (Ar) mixture) 

gap coupled water calorimeter. Each heat pipe temperature was to be monitored with a single, noncontact 

optical pyrometer, sighted at the evaporator exit just upstream of the calorimeter assembly. Figure 1 illustrates the basic layout of the heat pipe with attached support hardware.

Evaporator Plug 

and Support

Getter Pack

RF Feed 

Busswork

Wick Plug Wick Structure

Static Gas Gap (0.02 in to 

0.1 in Depending on Test)

Condenser Plug

Cooling 

Water 

Feeds

Fill Stem and Plug

Heat Pipe 

Envelope Closeout Support

Inductive Heater 

Coil Assembly (x3) Heat Pipe/Calorimeter 

Support Bracket

Laminar Flow

Water Calorimeter

Closeout and 

Support Tubes

Heat Pipe

Figure 1. Heat pipe cross section with ancillary test systems.

The planned evaluation activity would require around-the-clock operation of the heat pipes with

a goal of accumulating up to 3 years of test time. During this test time, at approximately 6-mo intervals, the heat pipes would be removed and examined by a combination of nondestructive and destructive

methods to assess the accelerated effects of aging on both the wick and heat pipe envelope.
3

1.1 Laboratory Layout

To accomplish the outline testing, a portion of the floor space within the NASA Marshall Space 

Flight Center (MSFC) Building 4655 high-bay area was designated to house the setup and operation. This 

location is in close proximity to both facility water and power interfaces, while minimizing interference 

with normal day-to-day operations. Geometric constraints were developed for each of the primary test 

support systems, such that an approximate laboratory layout could be generated. 

Figure 2(a) illustrates the proposed laboratory setup and figure 2(b) is a photograph of the floor 

space prior to hardware setup. The illustration does not include two 19-in instrumentation racks and the 

table to house the data acquisition/control hardware and computers. Also omitted are tubing runs for the 

water cooling and gas systems, power wiring runs for all equipment, and the RF distribution busswork.

(a) (b)

Proposed Location for Accelerated 

Heat Pipe Life Testing Activity

Test Chambers

 Large (5 Heat Pipes Each) (3)

 Small (Single Heat Pipe) (1)

RF Power Supplies

 50-kW Units (3)

 1 15-kW Unit (1)

Facility 

Water 

Supply

Water 

Recirculation 

System

Gas Purification 

Pallet (2)

Power Distribution 

Panel

Figure 2. General laboratory layout for accelerated heat pipe life testing: 

(a) Proposed laboratory setup and (b) photograph of floor space prior to 

hardware setup.

Although this project was terminated prior to setting up the hardware support systems within the 

laboratory, the environmental test chambers and the inert gas purification pallets, two of the basic support 

systems, were already in fabrication and have been completed.

1.2 Hardware Procurements

A majority of the test support systems have been detailed and the specifications developed to 

support the procurement process. Once final vendor submissions were received, selection was based on 

combined cost and technical evaluation criteria. Several of the large hardware components were detailed 

in previous reports that covered the heat pipe material and fabrication specifications and the RF inductive 

coil fabrication and performance specifications. Since that time, specifications for many of the remaining 

hardware components have been developed and procurements initiated. Appendices A–G provide details 

for many of the larger components that were procured.
4

Many smaller purchases for items such as tubing, relief valves, fittings, raw materials, vacuum 

system components, etc. have also been made and are not listed individually. With termination of the 

project, all procurements underway were cancelled using the most logical approach, which was finishing 

those that were nearing completion while descoping others that were at suitable break points. Many of the 

early hardware orders for off-the-shelf items had already been completed and material goods received. 

A number of procurements that were underway and were adjusted included the following: 

• Heat pipe wick structure fabrication—Development activity for the wick structure was completed and 

successfully demonstrated. This activity was then terminated to recoup remaining funds. Since the 

screen mesh material is an extremely limited and expensive commodity, to complete the fabrication of 

the wicks would be an unnecessary waste of material.

• Heat pipe envelope/assembly fabrication—Material for the heat pipe envelopes has been procured, rod 

stock completed, and tubing stock nearing completion. It was elected to complete the material fabrication and accept delivery of the raw stock. Weld development activity and component fabrication such 

as getter packs was also terminated.

• RF power system—Modeling analysis of the inductive coil assemblies and RF busswork for the 

required test geometries was completed. No material procurement or hardware fabrication had been

initiated on the inductive coils, making this a logical break point to terminate the contract.

• Environmental test chambers—A contract was in place, materials had been acquired, and fabrication in 

process, therefore cancellation would have resulted in a significant loss. The chambers were completed.

• Laminar flow water calorimeters—The procurement process had been initiated with specification posted and potential vendors contacted. The solicitation was canceled prior to closure of the procurement 

posting cycle and no vendor quotes were received.

• Inert gas purifier units—A contract award had been made and fabrication initiated. The contract was 

descoped to a single unit with a minor price impact.

• Two-band optical pyrometers—A contract award had been made and fabrication was underway. The 

contract was descoped from 17 to 8 units.

• Water circulation pump pallet—The initial procurement cycle had been completed with vendor quotes 

received and evaluated. The solicitation was canceled prior to making an award with no penalty.

• Magnetic flow meters—The procurement had been posted and potential vendors contacted. The solicitation was canceled prior to receiving final vendor quotes.
5

2. WATER-COOLING SYSTEM CONSIDERATIONS

During specification and layout of the calorimeter cooling system, concerns regarding loss of 

coolant conditions were identified. This situation appeared especially relevant due to the nature of the 

proposed testing, operating around the clock for up to 6 months at a time. Undoubtedly unexpected power 

outages, hardware failure, and computer software errors would occur, resulting in system shutdowns. To 

examine potential effects, thermal analyses were performed to assess the potential temperature rise within 

the heat pipe calorimeters due to two failure scenarios. The first case examined was where facility water 

was lost but the recirculation loop water continued to circulate (power was not lost). The assumption was 

made that RF input power to the heat pipes would be turned off immediately, and as a worst case, all of the 

heat contained within the heat pipes at operational temperature would be absorbed by the water. Results 

indicate that sufficient water volume exists within the system to safely absorb the energy without boiling. 

The second failure scenario case examined was where power was lost, resulting in a loss of recirculation 

coolant flow. This analysis required an unsteady assessment of the transient temperature rise within the 

stagnant calorimeter. Results indicate that portions of the water will likely exceed its boiling temperature. 

The belief is that some localized dryout will occur but with no damage to the system (temperatures do not 

exceed copper melting point). Care should be taken to allow the calorimeters to cool down prior to restarting the system, minimizing the potential for water-hammer-like pressure spikes. Both of these analyses are 

low-order assessments; however, the results are believed to be conservative.

2.1 Thermal Analysis for Loss of Facility Coolant Flow Condition

The objective of this analysis was to estimate the temperature rise of the heat pipe calorimeter 

resulting from the loss of facility water, assuming that the RF input power is turned off simultaneously. 

Under this scenario, the recirculation water continues to flow but is no longer able to reject heat into the 

facility water. The issue becomes, what volume of water is required to absorb the heat contained within 

the heat pipes and maintain a water temperature below some allowable maximum temperature, e.g., the 

boiling temperature of water? More specifically, does the expansion tank need to be oversized to facilitate 

this heat soak-back? A low-order assessment was performed, which is simply a steady-state balance of 

thermal energy. The resulting temperature rise is given by the following equations:

mh2oCp,h2oΔTh2o = mhpCp,hpΔThp , (1)

ρh2oVh2oCp,h2o (Tss,h2o − Ti,h2o ) = mhpCp,hp (Ti,hp − Tss,hp ) , (2)

and

Vh2o = mhpCp,hp (Ti,hp − Tss)

ρh2oCp,h2o (Tss − Ti,h2o ) ,

(3)
6

where at steady state, Tss,h2o=Tss,hp=Tss, and Ti,hp ≥ Tss ≥ Ti,h2o (i.e., the heat pipe cools and the water 

warms to the same temperature). The analysis should overpredict the water temperature because there are 

additional masses that will absorb heat (e.g., calorimeter metal, support structures, piping, etc.) that are 

not taken into account. Equation (3) was assessed with a spreadsheet analysis, producing the results in figure 3 for required water volumes (Vh2o) as a function of steady-state temperature (Tss). Water properties 

(ρh2o) and (Cp,h2o) are calculated at a pressure of 0.414 MPa and a temperature of (Tss+Ti,h2o)/2.5 The 

Mo-44.5%Re heat pipe properties, mhp and Cp,hp, are specified as 16 kg and 250 J/kg K, respectively, for 

the plotted results. The initial heat pipe temperature (Ti,hp) is set equal to 1,400 K (a maximum value).

50

40

30

20

10

0

Required Water Volume (gal)

Steady-State Temperature (K)

320 330 340 350 360 370 380 390 400

Ti, H2O=310 K

Ti

, H2O=320 K

Ti

, H2O=330 K

Ti

, H2O=340 K

Ti

, H2O=350 K

Figure 3. Equilibrium temperature and volume of water required 

to cool 16 kg of Mo-44.5%Re where initial temperature 

of Mo-44.5%Re is 1,400 K.

As stated, the final steady-state temperature (Tss) will be greater than the initial water temperature 

(Ti,h2o), and as indicated by figure 3, as Tss approaches Ti,h2o, the required water volume (Vh2o) approaches infinity. At the assumed operating pressure, 0.414 MPa, the boiling temperature of water is 418 K. Figure 3 illustrates that for an initial water temperature (Ti,h2o) as high as 350 K, 10 gal of water will absorb 

the thermal energy and produce a steady-state temperature (Tss) of <380 K. For the planned system, over 

15 gal of water are contained in the 50 ft of 0.5-in-diameter tubing, 20 ft of 4-in-diameter piping, and the 

water circulation pallet reservoir. Therefore, sizing the expansion tank to provide sufficient water for heat 

soak-back does not appear necessary. 

Table 2 provides the design parameters calculated for the various heat pipe calorimeter test series.

The maximum water outlet temperature is 335 K, which is the maximum bulk or average temperature of 

the recirculating water. Using this value as the initial water temperature (Ti,h2o) in these calculations is 

conservative, because the majority of the water in the recirculation loop will very likely be at or near the 

inlet temperature of 300 K. Table 2 also indicates that the calorimeter inner wall temperatures may be as 
7

high as 396 K (for case F(– 4)), and as a result, the water temperature near the wall will approach this value. It is believed that in the transient, following shutdown of the RF power supplies, the wall temperature 

will drop rapidly as the heat flux decays across the calorimeter inner wall, even with the subsequent rise 

in the average water temperature.

Table 2. Heat pipe calorimeter parameters for a film gap width of 0.015 in.

Film Cooling Water 

Inlet Temperature

300 K

Film Gap Width 0.015 in

Calorimeter Heat 

Extraction Length

9.25 in

Calorimeter Total Length 13 in

Test Condition Units G Series F(–4) F(–3) F(–2) F(–1) F(1) F(2) F(3) F(4) F(0)

Power W 3,000 5,000 1,000 3,000 3,000 2,000 4,000 2,000 4,000 3,000

Heat Pipe to Calorimeter 

Gas Gap Width

in 0.025 0.025 0.103 0.031 0.021 0.037 0.017 0.046 0.02 0.025

Heat Pipe Temperature K 1,273 1,273 1,273 1,373 1,173 1,223 1,223 1,323 1,323 1,273

Calorimeter Channel 

Wall Temperature

K 360 396 338 360 360 340 380 340 380 360

Log Mean Temp. 

Difference (Wall to Fluid)

K 502 83.3 13.8 49.5 50.9 32.7 68.2 32 67.5 50.2

Cooling Film Flow DT

(Outlet-Inlet)

K 18.8 24.6 35.2 20.1 17.6 13.9 22.8 15.2 24 18.8

Cooling Flow Outlet 

Temperature

K 318.6 324.4 335 319.9 317.4 313.8 322.6 315 323.8 318.6

Cal. Film Flow ID in 0.795 0.794 0.951 0.806 0.786 0.818 0.777 0.836 0.785 0.795

Cal. Film Flow OD in 0.825 0.824 0.981 0.836 0.816 0.848 0.807 0.866 0.815 0.825

Water Film Flow Rate Gal/min 0.6 0.77 0.11 0.56 0.65 0.54 0.67 0.5 0.63 0.6

Heat Transfer Coef k W/m2K 4,009.09 4,035.15 4,075.22 4,014.7 4,004.1 3,986.03 4,027.64 3,991.38 4,032.91 4,009.09

Reynolds No. 1,651.62 2,234.2 289.99 1,542.72 1,760.48 1,369.09 1,936.03 1,244.12 1,842.06 1,651.62

Calorimeter Pressure 

Drop

psi 3.7 4 0.5 3.3 4 3.5 3.8 3.1 3.5 3.7
8

2.2 Thermal Analysis for Loss of Recirculation Coolant Flow Condition

The objective of this analysis was to estimate the temperature rise of the calorimeter resulting 

from the loss of recirculating water flow, i.e., the water has no velocity but remains within the system and 

assumes that the RF input power is turned off simultaneously. While a first-look, steady-state assessment 

analogous to that performed in section 2.1 is useful, the issue is the transient temperature rise within the 

calorimeter. Following shutdown of the RF power supplies, the energy within the heat pipes dissipates 

into the calorimeter, producing a temporary rise in temperature due to the stagnate calorimeter’s reduced 

ability to remove the heat. The low-order assessments performed here are based on the geometry given 

in figure 4, where the total calorimeter length (L) is equal to 0.33 m. The material parameters are listed in 

table 3.

Copper

Mo-Re

He-Ar

Sodium

Water

D1

D2

D3

D4

D5

D6

D7

D8

 Diameter (in) Diameter (m)

D1 0.555 0.014097

D2 0.629 0.015977

D3 0.679 0.017252

D4 0.795 0.020198

D5 0.825 0.020960

D6 0.941 0.023906

D7 1.191 0.030256

D8 1.307 0.033203

Calorimeter Cover

Water Return Gap

Calorimeter Shell

Water Film Gap

Calorimeter Channel

Gas Conduction Gap

Heat Pipe

Figure 4. Heat pipe calorimeter geometry.

Table 3. Average heat pipe and calorimeter model parameters.

Element Material

ID 

(m)

OD

(m)

ρ

(kg/m3)

Cp

(J/kg-K)

k

(W/m-K)

Ti

(K)

1

2

3

4

5

6

Mo-Re

Copper

Water

Copper

Water

Copper

0.014097

0.017252

0.020198

0.02096

0.023906

0.030256

0.015977

0.020198

0.02096

0.023906

0.030256

0.033203

13,800

8,900

985

8,900

985

8,900

250

380

4,200

380

4,200

380

90

400

0.65

400

0.65

400

1,273

400

325

325

325

325
9

Using the parameters in table 3 to perform a steady-state energy balance analogous to that performed in 

section 2.1 yields a steady-state temperature equal to 392 K. The equation governing this is as follows:

Tss =

ρ jVjCp, jTi, j

j=1

6

∑

ρ jVjCp, j

j=1

6

∑

, (4)

where the subscript j corresponds to the element number in table 3. The steady-state temperature (392 K) 

is well below the melting point of copper (≈1,300 K) and even the boiling point of water (418 K) at the 

assumed pressure of 0.414 MPa. This is especially good since additional heat absorption masses and/or 

heat leak paths have been neglected in this assessment. However, the transient temperature response is the 

concern here, and ideally any temperature spike would not cause the water to boil, much less cause the 

copper to soften. The following equations6 are used to perform the transient assessment: 

ρ jVjCp, j

∂Tj

∂t = qcond, j∂Aj

0

Aj

∫ + qrad, j∂Aj

0

Aj

∫ , (5)

qcond,j∂Aj

0

Aj

∫ = 2πLk j

ln Do, j ( /Di, j)

(Ti, j − To, j) , (6)

and

qrad, j∂Aj

0

Aj

∫ = π Di, jLσ

1

εi, j

+

1− εo, j

εo, j

Di, j

Do, j

⎛

⎝

⎜

⎞

⎠

⎟

Ti, j

4 − To, j4 ( ) .

(7)

The equations are coded into the Fortran 90 program, listed in appendix H, which solves them numerically 

using an explicit time-stepping approach. The equations solved are as follows:

T1

t+Δt = T1t − Δtπ L

ρ1V1Cp,1

⎛

⎝

⎜

⎞

⎠

⎟

2kgas

ln

D3

D2 ( )

(T1 − T2 ) +

D2σ

1

ε1

+

1− ε2

ε 2

D2

D3

⎛

⎝

⎜

⎞

⎠

⎟

T1

4 − T24 ( )

⎡

⎣

⎢

⎢

⎢

⎢

⎤

⎦

⎥

⎥

⎥

⎥

t

, (8)

 

T2

t+Δt = T2t − Δtπ L

ρ2V2Cp,2

⎛

⎝

⎜

⎞

⎠

⎟ ×
10

2k3

ln D4 + D5

2D4 ( )

(T2 −T3 ) − 2kgas

ln D3

D2 ( )

(T1 −T2 ) − D2σ

1

ε1

+

1− ε2

ε2

D2

D3

⎛

⎝

⎜

⎞

⎠

⎟

T1

4 −T24 ( )

⎡

⎣

⎢

⎢

⎢

⎢

⎢

⎤

⎦

⎥

⎥

⎥

⎥

⎥

t

,

(9)

T3

t+Δt = T3t − 2Δtπ L

ρ3V3Cp,3

⎛

⎝

⎜

⎞

⎠

⎟ k3

ln

2D5

D4 + D5 ( )

(T3 − T4 ) − k3

ln

D4 + D5

2D4 ( )

(T2 − T3)

⎡

⎣

⎢

⎢

⎢

⎤

⎦

⎥

⎥

⎥

t

, (10)

T4

t+Δt = T4t − 2ΔtπL

ρ4V4Cp,4

⎛

⎝

⎜

⎞

⎠

⎟ k5

ln D6 + D7

2D6 ( )

(T4 − T5 ) − k3

ln

2D5

D4 + D5 ( )

(T3 − T4 )

⎡

⎣

⎢

⎢

⎢

⎤

⎦

⎥

⎥

⎥

t

, (11)

T5

t+Δt = T5t − 2Δtπ L

ρ5V5Cp,5

⎛

⎝

⎜

⎞

⎠

⎟ k5

ln 2D7

D6 + D7 ( )

(T5 − T6 ) − k5

ln

D6 + D7

2D6 ( )

(T4 − T5 )

⎡

⎣

⎢

⎢

⎢

⎤

⎦

⎥

⎥

⎥

t

, (12)

and

T6

t+Δt = T6t − ΔtπL

ρ6V6Cp,6

⎛

⎝

⎜

⎞

⎠

⎟ D8σε3 T6

4 −Tsin k4 ( ) − 2k5

ln 2D7

D6 + D7 ( )

(T5 −T6 )

⎡

⎣

⎢

⎢

⎢

⎤

⎦

⎥

⎥

⎥

t

. (13)

where the superscripts t+  ∆t and t indicate that values are specified at the next time step and the current 

time step, respectively. The motivation for actually writing the software, rather than using existing thermal 

software programs (e.g., SINDA), was the desire to incorporate this type of analysis into a spreadsheet 

approach that is commonly used for preliminary design trades. It is emphasized here that the analysis is 

low order, and higher fidelity thermal software could be used to further assess the localized effects and/

or potentially provide a higher degree of accuracy. Calculated results are illustrated in figures 5 and 6, 

and again may be seen as conservative from the perspective that additional heat-absorbing masses are 

neglected. Heat is allowed to escape the calorimeter via thermal radiation from the external surface, but 

not through the water piping or solid supports. Figure 6 differs from figure 5 in that the Mo-Re element’s 

wall thickness was tripled to assess the sensitivity to the total heat stored in the heat pipe. The motivation 

is that the results of figure 5 only use the heat pipe Mo-Re shell layer and neglect the heat stored within the 

wick screen and Na. It is believed that increasing the Mo-Re wall thickness by a factor of 3 is conservative, 

in that more than the actual stored heat is added to the analyses. 
11

600

550

500

450

400

350

300

Temperature (K)

Time (s)

0 10 20 30 40 50 60 70 80 90

Mo-Re

Inner Copper

Inner Water

Mid Copper

Outer Water

Outer Copper

Figure 5. Calorimeter transient soak-back temperatures 

for the baseline heat pipe geometry.

600

550

500

450

400

350

300

Temperature (K)

Time (s)

0 10 20 30 40 50 60 70 80 90

Mo-Re

Inner Copper

Inner Water

Mid Copper

Outer Water

Outer Copper

Figure 6. Calorimeter transient soak-back temperatures for three times 

the baseline heat pipe Mo-Re mass.

In all cases examined, the maximum temperature reached by the copper is below 550 K. Results 

indicate that portions of the water will likely exceed its boiling temperature of 418 K. However, the belief 

is that some localized dryout will occur, but with no damage to the system (i.e., copper temperatures do not 

exceed melting temperatures) as long as care is taken to allow the calorimeters to cool below the boiling 

point prior to restarting the system, the potential for water-hammer-like pressure spikes will be minimized.
12

3. CALORIMETER CONSIDERATIONS

During this project alternate calorimeter designs were identified to potentially reduce material cost 

and simplify fabrication requirements. In addition, to verify that the selected instrumentation could accurately assess the heat pipe power (calorimeter coolant flow and temperature rise) a simplified uncertainty 

assessment was performed.

3.1 Use of Standard Tube Sizes to Meet Calorimeter Performance

The original heat pipe calorimeter layout made use of drawn copper tube material to form the three 

coaxial tube elements (channel, shell, and cover) requiring unique tubing sizes for each of the proposed 

test setups. At that time, a company was identified that indicated it could provide the specified material; 

however, due to a combination of cost, availability, and minimum order requirements, the drawn tubing 

option was revisited with an eye on using readily available standard sizes. Table 4 lists the original drawn 

tubing dimensions that would be required to satisfy operational requirements. The basic assumption with 

the drawn stock approach was that the material could be drawn to any given ID and OD while holding

a fixed tube wall thickness of 0.058 in. These values were used as a basis to begin the selection of standard 

tube sizes.

Table 4. Heat pipe calorimeter drawn tubing requirements (all dimensions are in inches).

Calorimeter Geometry (Elements) G F(–4) F(–3) F(–2) F(–1) F(1) F(2) F(3) F(4) F(0)

Quantity

Heat Pipe OD

Gas Conduction Gap Width

7

0.625

0.027

1

0.625

0.027

1

0.625

0.105

1

0.625

0.033

1

0.625

0.023

1

0.625

0.039

1

0.625

0.018

1

0.625

0.048

1

0.625

0.022

1

0.625

0.027

Calorimeter Channel Tube ID

Calorimeter Channel Tube OD

Calorimeter Channel Tube Wall Thickness

0.679

0.795

0.058

0.678

0.794

0.058

0.835

0.951

0.058

0.69

0.806

0.058

0.67

0.786

0.058

0.702

0.818

0.058

0.661

0.777

0.058

0.72

0.836

0.058

0.669

0.785

0.058

0.679

0.795

0.058

Calorimeter Shell Tube ID

Calorimeter Shell Tube OD

Calorimeter Shell Tube Wall Thickness

Water Film Flow Gap

0.825

0.941

0.058

0.015

0.824

0.94

0.058

0.015

0.981

1.097

0.058

0.015

0.836

0.952

0.058

0.015

0.816

0.932

0.058

0.015

0.848

0.964

0.058

0.015

0.807

0.923

0.058

0.015

0.866

0.982

0.058

0.015

0.815

0.931

0.058

0.015

0.825

0.941

0.058

0.015

Calorimeter Cover Tube ID

Calorimeter Cover Tube OD

Calorimeter Cover Tube Wall Thickness

Water Return Path Gap

1.191

1.307

0.058

0.125

1.19

1.306

0.058

0.125

1.347

1.463

0.058

0.125

1.202

1.318

0.058

0.125

1.182

1.298

0.058

0.125

1.214

1.33

0.058

0.125

1.173

1.289

0.058

0.125

1.232

1.348

0.058

0.125

1.181

1.297

0.058

0.125

1.191

1.307

0.058

0.125
13

The use of standard tubing was expected to simplify the overall design by minimizing the differences between each calorimeter, and reducing the number of unique tubes required. Using this approach, 

the width of the gas conduction gap between the heat pipe and channel tube would be controlled by selecting a sufficiently thick-walled calorimeter channel tube section to allow for internal boring. No machining 

was planned for either the shell or cover tube elements. The standard tubing sizes identified in the initial 

calorimeter assessment are listed in table 5 and were selected to roughly meet the gas gap, water film flow 

gap, and water return flow gap requirements. 

Table 5. Standard tube sizes identified.

Calorimeter Element Tube OD (in) Tube Wall Thickness (in)

Channel Tube—Requires Three Sizes 0.875 by 0.109

by 0.095

by 0.083

Shell Tube—Requires Three Sizes 1.000

 1.125

by 0.049

by 0.083

by 0.049

Cover Tube—Requires Two Sizes 1.500 by 0.083

by 0.065

The dimensions for each of the 16 calorimeters are provided in table 6, which was generated from 

a simple sizing spreadsheet (app. I) based on the initial gas conduction gaps set by the original drawn tubing analysis. The use of standard tubing requires that the water film flow gap be set to a width of 0.0135 in, 

slightly tighter than the 0.015 in width calculated in the original analysis. This is not expected to present 

any difficulties. In addition, the water return path is opened up slightly from 0.125 in to 0.167 in for all but 

the F(–3) case. The final weight of a completed calorimeter unit is estimated at 3.7 lb.

As a quick check, the selected standard tube sizes were used in the simplified calorimeter sizing 

spreadsheet developed at the beginning of this project. The results follow expected trends with an increase 

in coolant temperature rise and a corresponding drop in flow rate (the smaller film gap improves the heat 

transfer); pressure drop is approximately the same due to the lower flow rate. Table 7 provides tabulated 

values for each of the calorimeter configurations and appendix J contains the full spreadsheet used in the 

assessment. 
14

Table 6. Calorimeter assembly layout with standard tube sizes—machining of 

channel tube only (all dimensions are in inches).

Calorimeter Geometry (Elements) G F(–4) F(–3) F(–2) F(–1) F(1) F(2) F(3) F(4) F(0)

Quantity

Heat Pipe OD

Gas Conduction Gap Width

7

0.625

0.027

1

0.625

0.027

1

0.625

0.105

1

0.625

0.033

1

0.625

0.023

1

0.625

0.039

1

0.625

0.018

1

0.625

0.048

1

0.625

0.022

1

0.625

0.027

Calorimeter Channel Standard Tube OD

Calorimeter Channel Tube Standard Wall Thickness

Wall Material to be Machined (From the Radius)

Calorimeter Channel Final Tube ID

0.875

0.109

0.011

0.679

0.875

0.109

0.011

0.679

1

0.083

0.005

0.835

0.875

0.095

0.03

0.691

0.875

0.109

0.07

0.671

0.875

0.095

0.09

0.703

0.875

0.109

0.02

0.661

0.875

0.083

0.06

0.721

0.875

0.109

0.06

0.669

0.875

0.109

0.011

0.679

Calorimeter Shell Standard Tube OD

Calorimeter Shell Tube Standard Wall Thickness

Calorimeter Shell Standard Tube ID

Final Water Film Flow Gap

1

0.049

0.902

0.013

1

0.049

0.902

0.013

1.125

0.049

1.027

0.013

1

0.049

0.902

0.013

1

0.049

0.902

0.013

1

0.049

0.902

0.013

1

0.049

0.902

0.013

1

0.049

0.902

0.013

1

0.049

0.902

0.013

1

0.049

0.902

0.013

Calorimeter Cover Tube Standard OD

Calorimeter Cover Standard Tube Wall Thickness

Calorimeter Cover Standard Tube ID

Final Water Return Path Gap

1.5

0.083

1.334

0.167

1.5

0.083

1.334

0.167

1.5

0.065

1.370

0.123

1.5

0.083

1.334

0.167

1.5

0.083

1.334

0.167

1.5

0.083

1.334

0.167

1.5

0.083

1.334

0.167

1.5

0.083

1.334

0.167

1.5

0.083

1.334

0.167

1.5

0.083

1.334

0.167

Table 7. Calorimeter parameters for a film gap width of 0.0135 in.

Test Condition Units G Series F(–4) F(–3) F(–2) F(–1) F(1) F(2) F(3) F(4) F(0)

Power W 3,000 5,000 1,000 3,000 2,000 2,000 4,000 2,000 4,000 3,000

Heat Pipe to Calorimeter 

Gas Gap Width

in 0.025 0.025 0.104 0.031 0.037 0.037 0.017 0.046 0.02 0.025

Heat Pipe Temperature K 1,273 1,273 1,273 1,373 1,223 1,223 1,223 1,323 1,323 1,273

Calorimeter Channel 

Wall Temperature

K 355 390 332 355 337 340 373 338 373 355

Log Mean Temperature 

Difference 

(Wall to Fluid)

K 40.8 66.9 11.9 40.8 27.5 32.7 53.9 27.4 53.9 40.8

Cooling Film Flow DT

(Outlet-Inlet)

K 26 42.2 29.5 26 17.6 13.9 34.8 19.3 34.8 26

Cooling Flow Outlet Temp. K 325.8 342 329.3 325.8 317.4 313.8 334.7 319.1 334.7 325.8

Cal Film Flow ID in 0.875 0.875 1 0.875 0.875 0.818 0.875 0.875 0.875 0.875

Cal Film Flow OD in 0.902 0.902 1.027 0.902 0.902 0.848 0.902 0.902 0.902 0.902

Water Film Flow Rate gal/min 0.44 0.45 0.13 0.44 0.43 0.54 0.43 0.39 0.43 0.44

Heat Transfer Coef k W/m2K 4,484.26 4,558.33 4,497.51 4,484.27 4,442.6 3,986.03 4,525.64 4,451.28 4,525.64 4,484.27

Reynolds No. 1,171.24 1,403.8 312.43 1,171.17 1,058.46 1,369.09 1,271.02 981.78 1,271.02 1,171.17

Calorimeter Pressure Drop psi 3.2 2.6 0.9 3.2 3.5 3.5 2.8 3.2 2.8 3.2

Film Cooling Water Inlet 

Temperature

300 K Film Gap Width 0.0135 in Calorimeter Heat

Extraction Length

9.25 in Calorimeter Total Length 13 in
15

3.2 Alternate Calorimeter Design

Another calorimeter concept was developed to support electric resistance heater testing. This calorimeter layout also makes use of a static gas gap technique to provide a noncontact thermal transport 

boundary, and may offer a potential alternative to the heat pipe three-tube calorimeter assembly currently 

baselined. This alternate concept incorporates a central copper tube, sized to set the required gas conduction gap width, which is covered on its outer surface with a spiral-wrapped copper tube containing the 

coolant flow. This tightly wound cooling tube is brazed to the surface of the central tube. Figure 7 illustrates this concept for a six-coil arrangement (the layout for testing electric resistance heater elements) 

mounted in parallel to the inlet and outlet coolant manifolds. During coil brazing, sufficient braze material 

should be provided to fill a majority of the gaps between adjacent coils and the central tube. However, due 

to the high thermal conductivity of copper and the close packing of the cooling coils, complete filling of 

the gaps would not be necessary to achieve the required performance levels. Figure 8 illustrates a typical 

wound coil on a central tube section and a postbraze cross section showing partially filled braze gaps. Possible benefits include a potentially simpler fabrication process, fewer required materials, and the ability to 

place viewing holes along the condenser, between coolant coils, should additional temperature measurements be required. The use of several parallel cooling coils along the length of the heat pipe calorimeter 

would minimize variations in temperature.

Cooling Coils (x6)

Electric Resistance Heater Element Calorimeter Design

Gas Gap Coupling (Heater Element to Calorimeter)

Water-Cooling Flow for Power Extraction

Copper Construction With Brazed Cooling Coils

Cooling Coils in Parallel Configuration

Coil Gap 

(Instrumentation)

Moly Sheathed 

Heater Element

Water Outlet 

Manifold

Water Inlet 

Manifold

Central Tube

Figure 7. An alternate design—electric resistance heater element

calorimeter design.
16

4-in Cooling Coil Segment 

(Before Brazing)

Partial Coil Cross Section 

After Brazing

Filled Gap Region 

Between Tubes

Partial Void 

Gap Region

Calorimeter Coil Wrapping and Brazing Tests

Figure 8. Brazing development testing for coil-type calorimeter design.

3.3 Calorimeter Power Measurement Uncertainty Estimate 

To examine the uncertainty impacts of the flow meter and temperature instrumentation on measured heat pipe power, a rough uncertainty analysis was performed. The objective was to verify that readily available off-the-shelf hardware components could be used to obtain data with an uncertainty level of 

5% or better. Details of this analysis are provided in appendix K, which compares various configurations 

including the use of paddle-wheel and magnetic-type meters for flow measurement, and single-point thermocouples and differential temperature meters for temperature measurement. The paddle-wheel/thermocouple configuration represents the cheapest approach, whereas the magnetic meter/differential temperature is the most expensive. Table 8 summarizes the results of this initial assessment, which indicates that 

an uncertainty of better then 5% is achieved for all instrumentation configurations examined.

Table 8. Summary of calorimeter power uncertainty 

with various instrumentation configurations.

Instrumentation Configuration

Uncertainty in Calorimeter 

Power (%)

Paddle Wheel With Thermocouples

Paddle Wheel With Differential Temperature

Magnetic Flow Meter With Thermocouples

Magnetic Flow Meter With Differential Temperature

4.2

3.3

2.9

1.3
17

The final selection of measurement devices was performed based on a combination of cost 

and durability (capable of lasting up to 3 years). Paddle-wheel-type flow meters cost approximately

$1,400 each, magnetic meters cost up to $2,400 each. Differential temperature measurement units can 

range from $1,000 to $2,000 each, depending on range and accuracy. The paddle-wheel-type flow meters 

also offer an integrated temperature and pressure measurement in a single package. The final decision was 

to use magnetic flow meters with thermocouples to determine the calorimeter coolant temperature rise. 

This approach provides a low uncertainty without undue cost impact and good long-term reliability (no 

moving parts).
18

4. RADIO FREQUENCY HEATING SYSTEM

A contract was awarded to Fluxtrol, Inc. for the RF design, engineering details, and fabrication 

of both the inductive coil assemblies and interconnecting busswork. The contract was terminated at the 

completion of the inductive coil RF design and just prior to starting the detailed engineering; no hardware components were procured. A closeout summary detailing the RF design for each of the four coil 

assemblies is provided in appendix L. The RF inductive coil assemblies were required to provide the heat 

pipe evaporator nominal power levels, specified in table 9, while operating in a reduced pressure (75 torr) 

ultra-high-purity He/Ar environment for a period exceeding 3 years. 

Table 9. Baseline heat pipe life test matrix.

Test 

Identifier

Power Level 

(W)

Heat Pipe 

Temp (K)

Gas Gap 

Mixture

Gas Gap 

Width (in)

Number of Heat 

Pipe Units

RF Coil Cluster 

Assembly

G-Series

F(–4)

F(–3)

F(–2)

F(–1)

F(0)

F(1)

F(2)

F(3)

F(4)

3,000

5,000

1,000

3,000

3,000

3,000

2,000

4,000

2,000

4,000

1,273

1,273

1,273

1,373

1,173

1,273

1,223

1,223

1,323

1,323

He-32%Ar

He-6%Ar

He-32%Ar

He-32%Ar

He-32%Ar

He-32%Ar

He-32%Ar

He-32%Ar

He-32%Ar

He-32%Ar

0.025

0.025

0.103

0.031

0.021

0.025

0.037

0.017

0.046

0.02

7

1

1

1

1

1

1

1

1

1

1 and 2

4

3

2

2

2

3

3

3

3

It was noted that three of the four assemblies were comprised of five inductive coil elements, forming a cluster arranged in a pentagonal series configuration. The interaction between these 

coils and neighboring components was modeled with Flux 2D software (marketed by CEDRAT 

Technologies). As a baseline, all coils are equipped with flux concentrators (Fluxtrol 50 material) 

to minimize coupling between neighboring coils and components, such as the calorimeter. The 

flux concentrator also provides a more symmetric and uniform power profile in the heat pipe evaporator, both axially and circumferentially. While the RF inductive coils provide the heat pipe 

evaporator power input, the final heat pipe operating temperature is set by the water calorimeter 

unit, which regulates the temperature using a static gas gap and coolant flow to maintain a specific 

power balance. An additional parameter affecting the power balance of RF cluster assemblies 2 and 

3 is a variation in thermal loss due to different heat pipe operating temperatures. However, this loss 

is estimated to be approximately 2% of the total power load and not worth complicating the design 

of the inductive coils to compensate. A summary of the operational conditions for each of the RF

assemblies is listed in table 10.
19

Table 10. Summary of RF inductive coil assembly layouts.

Configuration

Number 

of Heat 

Pipes

Total

Heat Pipe 

Power (W)

Required RF Power 

With Estimated 

Loss (W)

Maximum 

Voltage (V)

Heat Pipe Power and 

Inductor Turns

Assembly 1

Assembly 2

Assembly 3

Assembly 4

5

5

5

1

15,000

15,000

13,000

5,000

26,476

26,476

23,713

8,190

180

180

212

60.6

3,000 W—three turns

3,000 W—three turns

1,000 W—three turns

2,000 W—four turns

4,000 W—five turns

5,000 W—five turns

To simplify both fabrication and setup of the inductive coils, the layout was standardized to three 

baseline coil geometries that included designs for three-, four-, and five-turn configurations. The number 

of inductor turns was minimized to reduce the required voltage to drive the RF coils; cluster assembly 3 

had a maximum voltage drop of 212 V due to the mixture of three-, four-, and five-turn coils. The design 

gap width between the inductive coil and the heat pipe was set to 6.4 mm for all assemblies, providing

a factor of 2 against the breakdown voltage estimated at ≈450 V (discussed in app. L). Powering each of 

the three five-coil RF assemblies would be a 50-kW Inductoheat SP16 solid-state RF power supply. The 

single-coil RF assembly would be powered by a Flexitune 15-kW RF power supply. A closed-loop water 

circulation system provided waste heat removal for the power supplies, busswork, and inductive coils.
20

5. HEAT PIPE DEVELOPMENT ACTIVITY

The development process for the Mo-Re refractory metal heat pipes was a two-step process:

(1) Selection of a vendor for fabrication of heat pipe wicks and envelopes, and (2) final assembly of the 

complete units. The second step would involve heat pipe filling and closeout operations to be conducted 

at MSFC. 

As part of this process, tube, rod, and plate stock material was procured to both develop welding 

procedures and fabricate the final components. As expected, the Mo-44.5%Re material baselined for this 

project has a long lead time with plate and rod stock requiring 8 to 12 weeks for delivery and drawn tube 

stock (formed with tube shells) requiring up to 20 weeks.

5.1 Mo-44.5%Re Material General Welding Development

To perform the final heat pipe closeout activity at MSFC, it was necessary to establish reliable and 

repeatable electron beam (EB) welds using in-house equipment. There are a total of three circumferential 

welds identified in the planned heat pipe closeout approach. The most critical of these is a single weld 

pass used to cap the severed heat pipe fill stem, sealing the internal heat pipe volume after Na is added. 

The remaining two welds attach the secondary containment cap and support tube. A general EB welding 

development plan was assembled to address relevant equipment settings using bead-on-plate type weld 

samples, formed from PM Mo-44.5%Re material. 

Welding characteristics are a key concern for the fabrication of refractory metal components.

Molybdenum and its alloys tend to be significantly less ductile in the as-welded condition.7 This phenomenon is generally attributed to interstitial impurity segregation to the grain boundaries (higher Re content 

alloy) and to the large recrystallized grain structure (low Re content Mo). Ductility improvements have 

been demonstrated for high Re content Mo-Re alloys (>41%Re) but very little property data exist for 

welded material.

Electron beam welding has received considerable attention for the joining of Mo alloys. Electron 

beam welding is performed in a consistently controlled high-vacuum chamber, so there is less opportunity 

for interstitial contamination. Tungsten inert gas (TIG) welding in an inert atmosphere represents a considerably more complex monitoring problem. Electron beam welding also inputs significantly lower amounts 

of heat into the base metal, which minimizes thermal stress and grain growth. Fine control of the EB diameter and the focused high power allows much smaller heat-affected zones and weld metal, as compared to 

gas tungsten arc (GTA) welding. Ammon and Buckman reported a ductile-to-brittle transition temperature 

(DBTT) of 180 K for GTA welded Mo-50%Re, as compared to 80 K for the base metal material.8 The difference between the base metal and welded material in DBTT was thought to be controlled predominantly 

by the large grain size. Morito reported considerable bend properties at 77 K for EB welded Mo-50%Re.9

Kramer and Moore both reported successful EB welding of Mo-41% to 44.5%Re for space-based power 

systems.10,11
21

The initial weld development was to examine microstructure, chemistry, and bend testing to determine the DBTT. Data on refractory metal alloys have shown that welding has a pronounced effect on the 

DBTT and that bend testing is an excellent criterion for assessing the low-temperature ductility. Tests were 

to be performed on Mo-44.5%Re plate material (0.04-in thick) fabricated by Rhenium Alloys, Inc. using 

the PM processes. Table 11 lists the chemical composition of the Mo-44.5%Re plate. The plate material 

average grain size of 6 was determined in accordance with ASTM E3–95 and E112–96, shown in the 

figure 9 micrographs. Microhardness was performed in accordance with ASTM E3–84 using a Vickers 

diamond indentor with a 500-g load for 15 s. The average microhardness was 282.3±3.8 Vickers hardness 

number (VHN). This material information was supplied by Rhenium Alloys, Inc., and the full description 

is provided in appendix M.

Table 11. Chemical composition of the Mo-44.5%Re plate.

Element Impurity Element Impurity Element Impurity

H*

Li

Be

B

C**

N*

O**

F

Na

Mg

Al

Si

P

S

Cl

K

Ca

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

2.53

<0.005

<0.005

<0.005

17

4

12.5

<0.05

1.1

<0.01

2.1

0.43

0.11

0.13

0.05

15

0.63

<0.005

<10

0.09

10

0.89

9.5

0.25

6.7

0.65

Zn

Ga

Ge

As

Se

Br

Rb

Sr

Y

Zr

Nb

Mo

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te

I

Cs

Ba

La

Ce

<0.1

<0.05

<0.05

<0.05

<0.05

<0.05

0.05

<0.1

<0.1

<0.1

<0.1

55.85 wt%

<0.01

<0.01

<0.01

<1

<1

<0.1

0.17

0.05

<0.01

<0.01

<0.01

<0.5

<0.01

<0.01

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Hf

Ta

W

Re

Os

Ir

Pt

Au

Hg

Tl

Pb

Bi

Th

U

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<50

80

Balance

<0.01

<0.01

<0.05

<0.5

<0.05

<0.01

<0.01

<0.01

0.007

0.13

 * Determined by inert gas fusion-thermal conductivity.

** Determined by combustion-infrared absorbance.

Unless otherwise indicated, elements were analyzed by glow discharge mass spectroscopy 

 (GDMS). 

Results in ppm (ppm = parts per million = mg/Kg); 0.1000% by wt = 1,000 ppm unless otherwise 

 indicated.

Methods: ASTM E 1937-04, ASTM E 1409-97, ASTM E 1447-01, ASTM E 1941-98, and GDMS.
22

100 μm 50 μm

Figure 9. Micrographs of PM Mo-44.5%Re plate.

To perform EB welding evaluations, a series of bead-on-plates trials were planned, followed by 

bend testing of the samples. The weld fixture was ≈1.5 in long and consisted of a base block and two 

clamps, as illustrated in figure 10. The Mo-44.5%Re test samples were prepared by electrodischarge 

machining into blanks, measuring 0.5 in wide by 1 in long, followed by a chemical cleaning process as 

described in appendix N. The approach was to evaluate welding parameters over a range of values (such 

as current, voltage, spot size, and speed) by adjusting them with respect to as-welded ductility, microstructure, hardness, and chemistry. The effect on ductility will be measured by the maximum bend angle (up to 

90 deg) at 77 K until failure occurs. Chemistry and microstructure results, such as grain size of the weld 

metal and heat-affected zone, will be evaluated as needed to optimize parameters. If necessary, subsequent 

postweld annealing and tensile testing would be conducted on optimized welds with the best ductility and 

microstructure. Due to project cancellation, this activity was terminated after fabrication of the test specimens and holding fixture; no welding trials were performed. 

Stainless Steel

Clamps and 

Fixture

Mo-44.5%Re Sample

0.25 in

0.06 in

(a) (b)

Sample Clamps

Base Fixture

Mo-44.5%Re 

Weld Sample

Figure 10. EB welding fixture and sample setup.
23

Sample weld testing was to be conducted using a general matrix, such as that shown in table 12, in 

which the parameters are varied about a previous experience base. Typical EB weld parameters found in 

the literature9 are as follows: 

• Accelerating voltage: 50 kV

• Primary beam current: 50 mA

• Welding speed: 30 mm/s. 

Table 12. General EB weld development matrix.

Trial

Voltage 

(kV)

Current 

(mA)

Speed

(mm/s)

Response Factors

Bend Angle 

@ 77 K Microstructure Chemistry

1

2

3

4

5

6

7

8

1

2

1

2

1

2

1

2

1

1

2

2

1

1

2

2

1

1

1

1

2

2

2

2

–

–

–

–

–

–

–

–

As Needed

As Needed

As Needed

As Needed

As Needed

As Needed

As Needed

As Needed

As Needed

As Needed

As Needed

As Needed

As Needed

As Needed

As Needed

As Needed

To eliminate a variable, the EB focus would be set at the smallest possible spot size for each of 

the trials. After determination of the best welding parameters, a final set of material evaluations would 

be made at higher temperatures with weld comparison to base metal performance. The use of potential 

heat treatment could also be examined at this point. Table 13 provides a general test matrix outlining this 

approach.

Table 13. Final Mo-44.5%Re test matrix.

Sample

DBTT

(Bend Test)

Tensile Testing

RT 1,473 K Chemistry Hardness Microstructure

Base Metal

Base Metal + Anneal

As-Welded

As-Welded + Anneal

As Needed

As Needed

As Needed

As Needed

2

2

2

2

2

2

2

2

1

1

1

–

1

1

1

1

1

1

1

1

Figure 11 shows the setup of the base metal and as-welded samples that were to be bend tested using 

procedures developed by the Materials Advisory Board for ductile refractory metal alloys, as reported by 

Ammon and Buckman.8 The base metal specimen and weld bead will be perpendicular to the rolling direction of the plate and axis of bending. The topside of the weld bead will be placed in tension. Base metal 

and optimized weld samples would be tested at multiple temperatures to determine the DBTT.
24

Base Bend Test Weld Bend Test

Thickness, t = 0.04 mm

Width = 12 t

Length = 24 t

Test Span = 15 t

Punch Speed = 0.4 mm

Punch Radius = 1 t

DBTT = Lowest Temperature for 90 deg + Bend Without Cracking

Figure 11. Bend test configuration.

For this project, it was planned to conduct bend test evaluations for both the base metal and welded 

samples onsite at MSFC and at Pittsburgh Materials and Technology, Inc. 

5.2 Heat Pipe Wick and Envelope Development/Manufacture Activity

Manufacture of the refractory metal heat pipes was awarded via competitive procurement to 

Advanced Methods and Materials, Inc. (AMM), which included development and fabrication activities 

to produce the wick element, envelope, cleaning, and final assembly with installed wick. As a part of this 

activity, AMM was to procure all Mo-44.5%Re material and the government was to provide the wick 

screen material. Due to project cancellation, all contracts were terminated and procured raw material

supplied to MSFC.

Prior to cancellation, AMM forcused on developing a method suitable for forming the cylindrical wick element from seven layers of 400 × 400 weave screen material, with a Mo-5%Re composition 

and a wire diameter of 0.001 in. This mesh material, shown in figure 12, was on hand from a previous 

government program. After receipt of the material, several chemical composition tests were performed to 

determine base material impurities in the as-received condition, after chemical cleaning, and lastly after 

vacuum hot isostatic pressing (HIP). 

Analytical results of the Mo-5%Re screen mesh show that, for the ‘as received condition,’ there 

is an oxygen weight percent (wt%) of 0.37 and nitrogen wt% of 0.136 for the material. After chemically 

cleaning the screen material, the oxygen wt% was reduced to 0.08 and the nitrogen to 0.031, indicating 

that a majority of these elements were absorbed on the surface. After the HIP process to form the wick 

structure, material chemistry shows that the final wt% concentration of oxygen is 0.08 and that of nitrogen 

is 0.01.
25

Mo-5% Re Screen Material

 -400 x 400 Weave

 -Wire Diameter 0.001 in

Weave Closeup Weave Closeup

Mo-5%Re Screen Material

 -400 x 400 Weave

 -Wire Diameter 0.001 in

Figure 12. Mo-5%Re screen material.

AMM identified several approaches to fabricate the wick, ranging from a room temperature (RT) 

swaging/drawing technique to HIP. A HIP procedure was successfully used to bond stainless steel (SS) 

and niobium (Nb)1%Zr heat pipes, fabricated for MSFC on a prior program. The initial direction was to 

start with low-temperature techniques to minimize the chance of ductility loss due to recrystallization, 

which raises the DBTT for this alloy (an issue resulting from the low Re content of the 5% material).

A number of trial tests were performed by swaging/drawing short wick sections, using mandrel and sheath 

materials such as Zr, titanium (Ti), and mild steel. After drawing, acid was used to dissolve the mandrel 

material from the final wick. The type of acid depended on the mandrel/sheath material—hydrofluoric 

acid for Ti, and Zr and hydrochloric acid for mild steel. Although Ti would be a preferred mandrel material, especially if using high processing temperatures since it would getter oxygen and other impurities from 

the screen material, the initial drawing/swaging trials indicated that mild steel provided a better final wick 

product. All three encapsulant metals—iron (Fe), Zr, and Ti—produced similar quality wicks; however, a 

very slight reduction in weight was observed for Ti and Zr, suggesting some interdiffusion between the Ti/

Zr and the Mo-Re wick material. Because there was no interaction between the mild steel and the Mo-Re, 

the steel was selected over the two reactive metals. Results of the low-temperature forming techniques 

indicate that a strong mechanical bonding between the screen layers was formed; however, there was 

no diffusion bonding of the material to keep it from fraying or pulling apart. Figure 13 shows one of the 

drawn/swaged samples that was produced.
26

Drawn/Swaged Heat Pipe Wick Assembly

 - Mo-5%Re Mesh (400x 400 Weave)

 - 7 Mesh Layers

 - Outside Diameter ~0.5 in

 - Thickness ~0.14 in

Drawn/Swaged Heat Pipe Wick Assembly

 - Mo-5%Re Mesh (400x 400 Weave)

 - 7 Mesh Layers

 - Outside Diameter ~0.5 in

 - Thickness ~0.14 in

Figure 13. Room-temperature swaged wick element sample.

The layers were tightly packed, retaining considerable ductility and allowing the assembly to be 

flexed/deformed to a considerable extent. The surface was fairly smooth with the exception of a lengthwise ripple pattern, an artifact of the drawing processing which could be resolved. It was noted that the 

layers could be separated if small tools were used to pry apart and grasp the exposed layer edges. This 

could be a concern when considering the long-term operation of the heat pipes for this project (thermal 

cycling and possible chemical attack loosening the bonds between the layers). It was therefore decided 

that a HIP technique would be evaluated to examine if a diffusion bond could be achieved without

a significant loss of ductility.

A 6-in-long wick sample was fabricated to evaluate the HIP technique. The mesh material was 

wrapped on a mild steel mandrel with sheath and initially drawn to achieve the required wick thickness 

(≈0.014 in). The mandrel was evacuated, sealed by EB welding, and placed in a HIP chamber. This HIP 

process included a 1.5-hr ramp to a temperature of 950 °C and a pressure of 30,000 psi, at which it was 

held for 1 hr. The pressure was released and the furnace turned off to cool over ≈2 hr. The HIP temperature 

was kept as low as possible to minimize the amount of recrystallization (maximize ductility) yet still provide a satisfactory diffusion bond. The mandrel and sheath assembly were dissolved using hydrochloric 

acid. The final wick product is shown in figure 14. The outer surface still retains a slight pattern (artifact 

of the drawing process). This wick assembly is significantly more rigid when compared to the drawn/

swaged version and behaves more like a solid piece of tubing, with no visible bond line on the external 

surface (outer layer). The tube can be flexed very slightly if squeezed, so some ductility has been retained 

(the wick was not flexed to failure); however, it cannot be deformed to the extent demonstrated by the

drawn/swaged sample.
27

HIP Heat Pipe Wick Assembly

 - Mo-5%Re Mesh (400x 400 Weave)

 - 7 Mesh Layers

 - Outside Diameter ≈0.5 in

 - Thickness ≈0.012 in

HIP Heat Pipe Wick Assembly

 - Mo-5%Re Mesh (400x 400 Weave)

 - 7 Mesh Layers

 - Outside Diameter ≈0.5 in

 - Thickness ≈0.012 in

Figure 14. Hot isostatic pressed wick element sample.

A concern with the HIP process was that it could completely close off the screen pores, resulting 

in a solid cylindrical tube rather then a porous wick structure. To verify the product, it was evaluated by 

bubble-point testing to determine final pore size. The bubble-point test made use of ethyl alcohol and 

high-purity He, with results indicating an ≈22-μ wick pore radius, well within the required specification 

of 16 to 32 μ. 

Overall, the final HIP wick element had good geometric consistency and was vastly superior to 

the RT swaged version, which has the potential to unravel since it is only mechanically bonded. The HIP 

wick produced in this test was approximately half the length of what would be required for the life test 

heat pipes. No issues or problems are expected with proceeding to the full-length wick, and the success 

of the HIP technique was a major project accomplishment. The PM Mo-1 44.5%Re rod stock supplied by 

Rhenium Alloys, Inc., was provided to MSFC; chemical composition is provided in appendices O and P.
28

6. SODIUM PURITY EVALUATION USING VANADIUM WIRE EQUILIBRATION

An investigation into the experimental assessment of Na purity in heat pipes has been undertaken. 

The vanadium (V) wire equilibration method has been identified as the technique of choice to evaluate Na 

purity within the heat pipe by means of a high-temperature oxygen equilibration process. To support the 

application of this technique, procedural development governing the processing steps and checkout testing 

operations for the V wire setup were undertaken with consideration of previous investigations.12–14 In 

addition, acquisition of the hardware components and chemicals required to prepare the samples according to the V wire equilibration technique, per ASTM C 997–83,15 were completed. The Na stock currently 

in-house at MSFC will be used for all evaluations, as this material was baselined for use with the accelerated life test heat pipes.

6.1 Basic Hardware Setup

In the current approach, the V wire element is sized to fit within the volume constraint of the heat 

pipe fill stem. The V wire selected has a diameter of 0.25 mm and requires a length of 100 mm to achieve 

the desired oxygen content sensitivity. The V wire is mounted to an Mo alloy wire bow that is inserted 

into the fill stem. The bow is held in place by a combination of spring force and a hook (holding tab) that 

is positioned between the valve body and the end of the fill stem. Figure 15 shows the wire bow layout 

and a typical installation (a window cut from the sample 0.25-in-diameter fill stem to allow viewing of the

V wire). 

Vanadium Wire Element

Mo-Re Bow Element

Flattened Bow Sections 

to Hold Wire Vanadium 

Wire Position

Mo-Re Bow Element

Fill Stem Cutaway

Heat Pipe Fill Stem

Heat Pipe 

Condenser Plug

Vanadium Wire

Installed Vanadium Wire Sampling Bow

Fill Valve

Figure 15. Vanadium wire support and insertion concept using a Mo-alloy bow.

For the Vanadium wire evaluation testing, a nickel (Ni) sample tube was selected to simulate the 

Mo-44.5%Re fill stem. (Nickel was identified as the containment material in the ASTM specification.)

Figure 16 shows the final sample fixture setup, configured for verification testing. The assembly consists 
29

Known Volume Segment

Connection To 

Sodium Fill Macine

Isolation Valves

Thermocouple 

Locations

Test Sample Segment

Figure 16. Layout of V wire/Na sampling test setup.

of three isolation valves and seven thermocouples to control and monitor the quantity and position of the 

Na in the test segment. The Na is initially loaded into the known volume segment, so a precise charge can 

be determined, and then transferred into the test sample segment. The sample segment has additional void 

volume to account for Na expansion during heating to the 750 °C equilibration temperature; the Na would 

be transferred at a temperature of ≈150 °C during filling to minimize oxygen solubility. Prior to filling, 

all components undergo an extensive cleaning and vacuum bakeout process to minimize the possibility of 

contamination.

6.2 General Preparation and Operations

To test the operational procedures for this technique, a number of components were processed up 

to the point of filling the test segments with Na. The initial step was to chemically clean all components 

(SS valves, Ni tubing, and Mo wire) with pickling procedures to remove surface oxide layers and organics. 

Appendix Q lists the chemicals, concentrations, and mixtures used for each of the materials. Chemical cleaning was followed by vacuum bakeout of the Ni tubing using a small vacuum furnace system at a pressure 

in the 10–6 torr range and a temperature of 750 °C, the projected equilibration temperature. The SS transfer 

valves were vacuum baked to 225 °C at a pressure of 10–6 torr; this temperature is sufficient due to the low 

operating temperature during transfer. (The valves will not be attached during equilibration.) The V and Mo 

wire samples were prepared using an electroetching unit; the V wire was not vacuum baked to avoid gettering 

oxygen. Vanadium wire samples were etched from an initial diameter of 0.25 to 0.22 mm, producing a clean 

and oxide-free, lustrous surface appearance. The Mo wire diameter was not monitored, since it functions 

only as a structural support element. An outline of the operations used for preparation and equilibration 

testing is provided in appendix R. A total of seven sample V wire segments were processed to test the 

operations and promote familiarity with the equipment and handling. It was planned that three complete 

Na equilibration tests would be performed; therefore, an additional three V wire samples and three Mo 

bow wires were also prepared. All of these items were stored in clean, inert-gas-filled, sealed containers. 

The results of this activity are documented in appendix S. 

To accurately determine the oxygen increase in the V wire resulting from being immersed in a 

quiescent liquid-Na bath at high temperature, an analysis of the initial and final oxygen concentration in 

the V wire would be required. The LECO Corporation analysis technique was identified in the ASTM
30

specification as the appropriate test method. For the heat pipe application, the analysis must be accomplished using a minimal amount (20–30 mg) of V wire. The length of V wire is proportioned to the volume 

of Na used in the test. This poses an operational concern for the LECO method, which has an industry 

standard minimum mass requirement of 1 g. Discussions with the LECO Corporation indicate that the 

preferred 1-g mass provides guaranteed accuracies of 0.05 ppm Na and 0.05 ppm O. Smaller material 

quantities can be used, however, the measurement uncertainty increases. For materials quantities in the 

range of interest for the heat pipe Na equilibration, testing accuracy will drop into the 10 to 20 ppm O 

range. This resolution should be sufficient, because the V-O concentration is expected to increase on the 

order of 100 to 1,000 ppm during equilibration. For example, (from fig. 17) an initial Na-O concentration

(CO(Na)I) of 20 ppm equilibration produces a final Na-O concentration (CO(Na)F) of ≈0.04 ppm and a 

final V wire oxygen concentration (CO(V)) of ≈900 ppm. This analysis was performed assuming that the 

V wire segment is immersed and equilibrated in Na using a configuration geometrically consistent with 

the heat pipe fill stem. 

CO(Na) F (ppm)

CO(V) (wt%)

CO(Na)I (ppm)

1

0.1

0.01

0.001

1

0.1

0.01

0.001

0.1 1 10 100

Figure 17. Oxygen concentrations: Na initial, Na final, and V wire.

To evaluate the LECO method, two V wire control samples were prepared and sent to LECO to 

undergo oxygen determination analysis. These samples, identified as control 6 and control 7 (as listed in 

app. S), had masses of 23 and 26 mg, respectively. The project was terminated prior to performing material 

analysis on these samples.

Prior to implementing the approach on actual heat pipes, it was planned that three complete test 

cycles (Na fill, equilibration, and LECO analysis) would be performed using the samples identified as test 

1, test 2, and test 3 (as listed in app. S). Once the operations were found to provide satisfactory results, 

a complete SS test heat pipe unit would be evaluated. However, due to termination of this project, all

activity has been closed out prior to filling the first Ni test units with Na.
31

7. SUMMARY

The accelerated heat pipe life test project was cancelled due to program selection of a gas-cooled 

reactor concept. As a result, all activities have been closed out using the most logical approach to terminate procurements and recover costs where possible. A majority of the hardware procurements had 

been placed for the laboratory equipment required to perform the tests, including fabrication of the 

Mo-44.5%Re heat pipe units. This Technical Publication (TP) provides details for the specific test systems 

that included calorimeters, RF inductive heaters, and Na oxide impurity activity. Significant progress was 

made related to the heat pipe fabrication procurement. The vendor, AMM, had procured material (rod, 

tube, and plate stock) and successfully manufactured an annular wick structure. This wick was fabricated 

from Mo-5%Re screen material (existing NASA stock) by a HIP technique (950 °C for 1 hr at 30,000 

psi). The final product had a pore radius of 22 μm, and still retained significant ductility. Low-temperature 

drawing/swaging techniques were also tested, producing wick structures in which the screen layers were 

only mechanically bonded. This simple technique was found to be unacceptable because there is a risk 

of layer separation; this was not an issue with the HIP approach. At the time of project termination, no 

technical showstoppers were encountered, either with heat pipe development or laboratory equipment procurement/layout. The planned focus for this test project was to implement a methodology to establish heat 

pipe material system life expectancy consistent with a limited schedule, budget, and material availability 

while conducting comparatively few tests (16 units for this project) to study key variables. Data were 

expected early in the program (within 6 months of starting the first heat pipe), providing early indications 

of the aging effect. Additional data obtained over the course of the planned 3-year operation would build 

confidence in extrapolationing corrision and provide insight into possible random manufacturing and processing defects.
32

APPENDIX A—LAMINAR FLOW WATER CALORIMETER UNIT SPECIFICATION 

Request for Information for Materials and Fabrication of Calorimeter Assemblies

Integrated Financial Management Program Procurement

Delivery 6–8 weeks after receipt of order (ARO)

Quantity—16 units

Title—Copper Alloy Laminar Flow Water Calorimeter Units for use in a Vacuum/High-Purity Inert Gas 

Environment. Request information for both fabrication materials, as well as complete manufacturing of 

the calorimeter units. 

Specification for Water Circulation System

Laminar flow water calorimeter units fabricated from a copper alloy are used to absorb heat energy 

from a research application. The calorimeters consist of three concentric tubes forming the primary water 

film flow gap/path and the water return path, shown in figures 18–20. The calorimeter surrounds a process 

component that operates at high temperature, providing the heat load. Power is transferred to the calorimeter from the process component, a small noncontact gas conduction gap that allows for a large temperature 

gradient in a short distance. Critical calorimeter dimensional constraints necessary to meet test power and 

temperature requirements include the following:

• The gas gap distance between the process component surface and the ID of the calorimeter channel tube 

regulates the power transfer between the process component and the calorimeter. The low-temperature 

calorimeter cannot come into physical contact with the high-temperature process component, hence the 

required dimensional tolerances.

• The water film flow gap between the OD of the calorimeter channel tube and the ID of the shell tube 

controls the water flow regime, maintaining laminar conditions.

• The outermost cover tube should have sufficient ID to provide a water return path approximately an 

order of magnitude larger than the water film flow gap.
33

Figure 18. Conceptual calorimeter design.

Figure 19. Conceptual process application/calorimeter with mounting setup.
34

Figure 20. Calorimeter tube layout nomenclature.

The initial engineering drawings of a calorimeter unit are shown in figures 21 and 22. 

The calorimeter unit is 11–13 in long and currently planned to be fixed at the clamped end with the 

free-cantilevered section supported by a collar. Specific specifications include the following:

• High-strength (durable) alloy with good thermal conductivity and an excellent ability to hold tolerance. 

Copper alloy C122 is an option, but other alloys should be suggested for consideration.

• The unit will be operated in a very clean test chamber with either vacuum or low-pressure purified inert gas (He/Ar) environments; therefore, it should have a good, clean external finish 

(32–64 μin) with no virtual leaks and minimal outgassing properties. Internal coolant will be filtered 

water with a conductivity between 1 and 40 μS/cm to support operation of a magnetic-type flow meter.

• The calorimeter will be assembled with an all-welded construction to minimize the potential for leakage. This welding should be performed in an inert environment to minimize oxidation and potential for 

trapping of contaminants in the calorimeter welds. During the assembly process, the primary flow gap 

width and ID of the channel tube will be monitored to verify compliance with the required sizes. Small 

tabs that will not interfere with the fluid flow can be used in the primary coolant flow path, between 

the channel and shell tubes, to assist in maintaining the dimension. The ID of the channel tube will be 

honed, if necessary, after welding to achieve the required ID.

• Leak checking will be performed to verify leak tightness of all calorimeter assemblies. The assemblies 

will be checked with an He mass spectrometer leak detector with a sensitivity capable of detecting leak 

rates of 1×10–10 std-cc/s of He or lower. All components (100% of the calorimeter units) will be leak 

tested and any defective units rejected. 
35

Figure 21. Initial calorimeter concept—engineering design layout.

Figure 22. Initial calorimeter concept—engineering design parts detail.
36

• Water feed lines will be 0.37-in OD by 0.35-in wall nominal copper feed lines with 36-in stub lengths. 

Feeds are welded to the calorimeter manifolds. 

• Material stock and final assembly of the calorimeter should conform to the following target requirements:

– Tubing wall thickness variation: ±0.001 in.

– Tubing diameter variation: ±0.002 in. 

– Tubing diameter ovality variation: Cannot exceed ±0.002 in at any cross section.

– Permissible straightness: 0.002 in over the length of the calorimeter.

The calorimeter length is estimated at 11 to 13 in, based on preliminary design analysis. The calorimeter unit is supported, in cantilever fashion, at one end with a support and at the other end, as indicated 

in figures 18 and 19, by a 1-in extension of the inner channel tube. Tight tolerances are required to prevent 

the calorimeter from touching the very hot process component. There are 10 different calorimeter geometry 

types required to meet the research objectives. Each is composed of a single-channel tube, shell tube, and 

cover tube with dimensions and quantity as provided in table 14. The following assumptions were made in 

performing the thermal analysis and generating this table:

• Current design makes use of a constant wall thickness tube for all calorimeter tubes (baseline wall 

thickness 0.058 in). This approach assumes that the tube manufacturing process is a drawing 

technique, in which the draw dies can be adjusted to provide the required OD/ID dimensions.

• The primary coolant film flow gap width baseline for all calorimeters is held at 0.015 in.

• The return coolant flow gap width baseline for all calorimeters is held at 0.125 in.

• Inspection/cleaning—Each completed calorimeter unit should be tested for straightness and dimensional 

consistency along the inner bore (diameter/ovality). Any final machining to bring units into tolerance, remove burrs, finalize the surface, etc., should be performed. Each of the calorimeter units will be cleaned 

externally and internally by flushing, to remove debris and surface contaminants.

• Operational duty—Calorimeters will be operated in an around-the-clock fashion for 3–5 years.

• Other considerations for tubing selection and dimensions—The use of standard or specialized tube sizes 

with machining to meet the final geometry is also an acceptable option. If standard/specialized sizes are 

used, some additional variation can be allowed in the gap widths for the water film flow gap/path and 

water return path as follows: 

– Water film flow gap (between the OD of the calorimeter channel tube and the ID of the shell tube) can 

range between 0.010 and 0.015 in.

– Water return path can range to provide approximately a factor of 10 increase over the film flow gap 

width.Table 14. Tube sizes required for calorimeter layouts (all dimensions are in inches) for tubing 

material produced by drawn technique (or other).
37

Table 14. Tube sizes required for calorimeter layouts (all dimensions are in inches) for tubing 

material produced by drawn technique (or other).

Calorimeter Geometry G F(–4) F(–3) F(–2) F(–1) F(1) F(2) F(3) F(4) F(0)

Quantity 7 1 1 1 1 1 1 1 1 1

Process Component OD 0.625 0.625 0.625 0.625 0.625 0.625 0.625 0.625 0.625 0.625

Gas Conduction Gap Width 0.027 0.027 0.105 0.033 0.023 0.039 0.018 0.048 0.022 0.027

Calorimeter Channel Tube ID 0.679 0.678 0.835 0.690 0.670 0.702 0.661 0.720 0.669 0.679

Calorimeter Channel Tube OD 0.795 0.794 0.951 0.806 0.786 0.818 0.777 0.836 0.785 0.795

Calorimeter Channel Tube 

Wall Thickness

0.058 0.058 0.058 0.058 0.058 0.058 0.058 0.058 0.058 0.058

Calorimeter Shell Tube ID 0.825 0.824 0.981 0.836 0.816 0.848 0.807 0.866 0.815 0.825

Calorimeter Shell Tube OD 0.941 0.940 1.097 0.952 0.932 0.964 0.923 0.982 0.931 0.941

Calorimeter Shell Tube Wall 

Thickness

0.058 0.058 0.058 0.058 0.058 0.058 0.058 0.058 0.058 0.058

Calorimeter Cover Tube ID 1.191 1.190 1.347 1.202 1.182 1.214 1.173 1.232 1.181 1.191

Calorimeter Cover Tube OD 1.307 1.306 1.463 1.318 1.298 1.330 1.289 1.348 1.297 1.307

Calorimeter Cover Tube Wall 

Thickness

0.058 0.058 0.058 0.058 0.058 0.058 0.058 0.058 0.058 0.058

However, the gas conduction gap between the process component and the calorimeter channel tube 

ID must remain fixed as specified in table 14; therefore, the selection of the size used for the calorimeter 

channel tube must be able to meet the required dimensions after machining.

• The following information provides operational specifics regarding the expected flow and temperature 

conditions for the calorimeter, based on research requirements and a thermal analysis:

– Water flow rates: Ranging from 0.1 to 1 gpm, depending on thermal load.

– Power capacity: 1,000 to 5,000 W range.

– Water temperature inlet: Expected range 15–30 °C.

– Water temperature rise: Expected up to 40 °C.

– Process component temperature: From 1,100 to 1,400 K.

– Inert gas gap environment: He/Ar mixture at 1 to 2 psia.

– Process component material: Mo-Re refractory metal.

– Packaging: Calorimeter must be a modular design, since they will be packaged to test component 

clusters (fig. 23).
38

Figure 23. Calorimeter cluster arrangement.

• Additional information sought:

– Copper alloy materials that provide a robust and durable calorimeter unit to better meet the goal.

– Alternate calorimeter-type cooling designs that will provide the same function in a similar package 

(commercial). 

– Enhancement to the water film flow gap cooling channel design (improved heat transfer) with 

predicted thermal performance with known correlations. 

– Low-cost welded transition elements from copper alloy to SS to simplify routing the calorimeter 

water feeds out of the test chamber and avoid the use of mechanical fittings.
39

APPENDIX B—TWO-BAND OPTICAL PYROMETER SPECIFICATION

Specification for Procurement for Optical Pyrometer Temperature Sensors 

Integrated Financial Management Program Procurement

Estimated delivery 4–6 weeks ARO

Title—Turnkey Two-Band Optical Pyrometer Temperature Sensors

Vendors:

• Ircon, Inc.

7300 N. Natchez Ave.

Niles, IL 60714

Telephone: 847–967–5151

POC: Randy Cutrara

Telephone: 704–604–4165

• PEI Group

2815 Winterberry Way

Hampton Cove, AL 35763

POC: William Burnette

Telephone: 256–534–5949

• Mikron Infrared, Inc.

16 Thornton Road

Oakland, NJ 07436

POC: Korhan Gazi

Telephone: 201–405–0900

• Uni-Tech Engineering

983 Yeager Parkway

P.O. Box 510

Pelham, AL 35124

Telephone: 205–999–7983

• Omega Engineering

One Omega Drive

P.O. Box 4047

Stamford, CT 06907

Telephone: 203–359–1660

Quantity—17 complete units
40

Specification for Two-Band Pyrometer Units

Turnkey two-band optical pyrometer units, such as the Ircon® series/model 5R–1410 complete 

system or equivalent with the following specifications:

• Temperature range: 600–1,400 °C.

• Mode: Operates in one- or two-color (ratio) mode.

• Wavelength: Ratio mode (0.75–1.05 and 1–1.1 mm range). Single-color 1–1.15 mm.

• Focusing range: 13 in to infinity. 

• Measurement spot size: 0.13-in diameter at 13 in and 0.24-in diameter at 24 in.

• Sighting method: Through lens, no filter.

• Response time: 10 μs to 60 s.

• Analog output: 4–20 mA.

• Analog input: 4–20 mA.

• Digital input/output: RS–485.

• Accuracy: 0.5% of reading plus 2 °C.

• Resolution: 1 K.

• Emissivity slope: 0.8 to 1.2.

• Repeatability: 0.1% of full-scale plus 1 digit (25 °C). 

• Sensor rear panel control: Temperature, setup display, and keypad for independent configuration and 

operation.

• Operating voltage: 24 VDC.

• Operating temperature: Ambient 0–55 °C.

• Cable assembly: 25 ft.

• Weight: Under 4 lb.

• Mount: Universal two-axis support.

• Operators manual: Included.

• Normal operation: No cooling required.
41

APPENDIX C—WATER-COOLING PALLET SPECIFICATION

Procurement Specification for Water-Cooling Recirculation System

Integrated Financial Management Program Procurement

Estimated delivery 6 weeks ARO

Title—Turnkey Water-to-Water Heat Exchanger System (Recirculation Flow Separated from Plant 

Service Cooling Water) to Remove up to 100 kW from Test Hardware

Vendors:

• Thermo Electron Corporation

Control Technologies Division

25 Nimble Hill Road

Hewington, NH 03801

POC: Kathy Payne

Telephone: 972–867–9769

• Fluid Flow of Georgia

1135 Powers Place

Alpharetta, GA 30004

POC: Jeff Norford

Telephone: 800–849–5947

• Advantage Engineering

525 East Stop 18 Road

Greenwood, In 46142

POC: Kip Kelly

Telephone: 317–887–0729

Quantity—1 complete unit

Specification for Water Circulation System

Complete turnkey recirculation water-cooling system, such as the Sentry closed-water isolation 

skid or the NESLAB recirculating system, with water-to-water heat exchanger to dump waste heat to

a plant cooling water system. Nonrefrigerated system with the following specifications:
42

• Temperature range: 5–40 °C.

• Temperature stability: ±2 °C.

• Cooling capacity: 90 kW or more.

• Operating voltage: 440–480 VAC 3–P (preferred) or 208–240 VAC 3–P.

• Power consumption: 2–5 kVA.

• Pumping capacity: 40 gpm or more.

• Maximum operating press: 100 psi or better.

• Pump pressure rise: 40 psig or better.

• Reservoir/expansion tank: Included.

• Inlet/outlet fitting type: Pipe connections.

• Unit controller: Easy to use, programmable control capability for automatic, closed-loop control, 

regulation of recirculation water temperature with modulating valves. User-selectable temperature 

set points, limits, and alarms. High temperature, low level, and loss of flow indicators, alarms, and 

interlocks. Display with keypad entry for user to input settings. Automatic restart capability should 

power fail.

• Isolation valves: As necessary on recirculation and plant cooling connections.

• Heat exchanger: Heavy-duty SS construction with provisions for cleaning with minimal system impact. 

• Make-up water: Allocation for introducing clean treated water into system.

• Instrumentation: Pressure, temperature, and flow-on recirculation.

• Material: Recirculation system piping, etc. should be made of SS parts and other materials that will not 

rust or slough off debris into the clean water flow (steel should not be used).

• Plant water: Untreated nonpotable water.

• Recirculation water: Capable of long-duration operation with clean filtered water and a nominal resistive in the 0.05 to 1 MΩ/cm range. Maximum return water temperature of 40° (from process).

• Operational duty: 24/7 operation for 3–5 years. Unit is located on the floor of an environmentally controlled high bay.
43

Include the following options in the quote, if possible, and break out as separate costs:

(1) Dual heat exchanger and/or oversized heat exchanger to deal with potential fouling on 

plant water side.

(2) Dual pump unit to serve as backup should the primary fail (with switchover capability).

(3) Inline filter unit on the recirculation side, downstream of the pumps to stop any potential debris 

from reaching the process.

(4) Bacteria/algae control options, using treatment or inline ultraviolet (UV) filter.

(5) Allocation to deaerate the recirculation system water to remove dissolved gases.
44

APPENDIX D—WATER FLOW METER SPECIFICATION

Specification for Procurement of Magnetic-Type Flow Meters 

Integrated Financial Management Program Procurement

Estimated delivery 4–6 weeks ARO

Title—Turnkey Magnetic-Type Flow Meters for Both Small- and Large-Line Sizes With No 

Moving Parts and No Flow Restrictions, Ready for Inline Water Service

Vendors:

• Total Temperature Instrumentation, Inc.

8 Leroy Road

P.O. Box 1073

Williston, VT 05495

POC: Lou Phelps

Telephone: 802–863–0085

• Trinova, Inc.

P.O. Box 2806

Mobile, AL 36601

POC: Chad Green

Telephone: 251–378–7837

• Rosemount Inc.

8200 Market Blvd

Chanhassen, MN 55317

POC: Sales

Telephone 800–999–9307

Quantity—17 low-flow range units

Specification for Small Magnet Flow Meter Units

Complete ready-to-use magnetic flow meters, providing no flow restriction, with no moving parts to include the flow element, converter, or other assemblies as required with the following

specifications:

• Flow range: 0.03 to 2 gpm water.

• Overrange capability: Up to 4 gpm water.
45

• Water temperature range: Room temperature to 100 °C.

• Flow accuracy: ±0.5% or better.

• Operating pressure: 150 psi or more.

• Operating voltage: 120 VAC.

• Line size: Suitable for 0.25 to 0.5-in-diameter line.

• Inlet/outlet fitting type: Compression, pipe-type fittings, flanges.

• Signal output: 4–20 mA.

• Flow meter setup: Unit has a display window, attached or remote position, that can be used to set up the 

meter and also provides display of current flow in user-selected units.

• Material: All wetted surface should be made of SS or other materials that will not rust or contribute 

debris to the clean water flow (steel should not be used).

• Water type: Capable of long-duration operation with clean filtered water and a nominal conductivity in 

the 1–20 μS/s range.

• Operational duty: Around-the-clock operation for 3–5 years.

• Calibration data: Provided for water flow measurement (covering high- and low-flow conditions).

• Options for consideration with the units—break out as separate costs:

– Embedded temperature and pressure measurement that provides water flow media conditions.

– Internal provisions for self-cleaning the meter electrodes.

– Suggested water specifications for long-term operation. Also, water treatment or conditioning if 

the nominal conductivity of the water is out of range, and meter to indicate conductivity problems

impacting accuracy of the measurement.

– 485 digital communication interface.

– Calibration interval and how it is accomplished.

Quantity—Two high-flow rate units.
46

Specification for Large-Magnet Flow Meter Units

Complete ready-to-use magnetic flow meters, providing no flow restriction, with no moving parts 

to include the flow element, converter, or other assemblies as required with the following specifications:

• Flow range: 10 to 100 gpm water.

• Over range capability: Up to 150 gpm water.

• Water temperature range: Room temperature to 100 °C.

• Flow accuracy: ±0.5% or better.

• Operating pressure: 150 psi or more.

• Operating voltage: 120 VAC.

• Line size: Suitable for 2-in-diameter line.

• Inlet/outlet fitting type: Compression, pipe type fittings, flanges.

• Signal output: 4–20 Ma.

• Flow meter setup: Unit has a display window, attached or remote position, that can be used to set up the 

meter and also provides a display of current flow in user-selected units.

• Material: All wetted surface should be made of SS or other materials that will not rust or contribute 

debris to the clean water flow (steel should not be used).

• Water type: Capable of long-duration operation with clean filtered water and a nominal conductivity in 

the 1–20 μS/s range.

• Operational duty: Around-the-clock operation for 3–5 years.

• Calibration data: Provided for water flow measurement, covering high- and low-flow conditions.

• Options for consideration with the units—break out as separate costs:

– Embedded temperature and pressure measurement that provides water flow media conditions.

– Internal provisions for self-cleaning the meter electrodes.
47

– Suggested water specifications for long-term operation. Also, water treatment or conditioning if 

the nominal conductivity of the water is out of range, and meter to indicate conductivity problems 

impacting accuracy of measurement.

– 485 digital communication interface.

– Calibration interval and how it is accomplished.
48

APPENDIX E—INERT GAS PURIFIER SPECIFICATION

Specification for Procurement of an Inline Inert Gas Purifier Unit 

Integrated Financial Management Program Procurement

Estimated delivery 6 weeks ARO

Title—Inert Gas Purifier Unit for Use with He and Ar in a Closed-Loop Gas Circulation System

Vendors:

• SAES Pure Gas Inc.

4175 Santa Fe Road

San Luis Obispo, CA 93401

POC: Greg Perry

Telephone: 805–786–2130

• Johnson Matthey USA

Gas Purification Technology Group

1397 King Road

West Chester, PA 19380

Telephone: 610–232–1900

• NuPure III

67 Iber Road, Unit 107 

Ottawa ON K2S 1E7 Canada

Telephone: 1–613–836–0336 

Quantity—Two complete units

Specification for Turbopump Unit

Complete turnkey heated getter purifiers (getter material irreversibly binds with impurities) for 

rare gas (He and Ar). SAES® MonoTorr PS4–MT3–R1 complete turnkey system or equivalent with the 

following specifications:

• Setup: Device contained in an enclosure.

• Surface mountable: Enclosure can be mounted.

• Cooling: Fan unit in enclosure.
49

• Voltage: 120 VAC. 

• Power consumption: Less than 400 W.

• Operating temperature: 400 °C.

• Operating pressure: Vacuum to 150 psig.

• Maximum flow rate: 50 slpm.

• Nominal flow rate: 20 slpm.

• Fittings: VCR type.

• Tubing internal roughness: 10-μin finish for low outgassing.

• Filter: 0.003-mm metal filter.

• Valves: SS diaphram type.

• Valve actuation: Air (80–100 psig).

• Pressure drop: Low-pressure drop unit at nominal flow rate.

• Life and status sensor: Included.

• Bypass assembly: Included.

• Control: Thermocouple interface with multifunction controller.

Table 15. Guaranteed delivered gas purity at flow rate.

Flow Rate

Impurity 0–20 slpm 20–50 slpm

O2

H2O

CO

CO2

N2

H2

CH4

<1 ppb

<1 ppb

<1 ppb

<1 ppb

<1 ppb

<1 ppb

<1 ppb

<1 ppb

<1 ppb

<1 ppb

<1 ppb

<10 ppb

<10 ppb

<10 ppb
50

APPENDIX F—WATER AND GAS SYSTEM HAND VALVE SPECIFICATION

Specification for Procurement of Stainless Steel Hand-Valve Hardware for Water and Purified Gas 

Systems Integrated Financial Management Program Procurement

Estimated delivery 4–6 weeks ARO

Title—SS Hand Valves for Water and High-Purity Gas Systems

Vendors:

• Alabama Fluid Systems (primary)

237 Cahaba Valley Parkway 

Pelham, AL 35124 

Telephone: 205–988–4812 

• Hile Controls

311 Applegate Parkway 

Pelham, AL 35124

Telephone: 205–620–4000

• Parker Hannifin Corporation

6035 Parkland Boulevard

Cleveland, OH 44124-4141 USA

Telephone: 1–800–272–7537

Deliverables and Specifications

• Six 2-in SS hand-operated ball valves, Swagelok® SS–68TSW32T or equivalent with the following 

specifications:

– Reinforced polytetrafluoroethylene (PFTE) seats.

– Manual operation.

– Operating temperature rating up to 200 °C.

– Working pressure of 880 psi at 120 °C.

– 2-in diameter with SS construction. 

– Tube socket weld connections.
51

• Five 1-in SS hand-operated ball valves, Swagelok SS–65TS16 or equivalent with the following

specifications:

– Reinforced PFTE seats.

– Manual operation.

– Operating temperature rating up to 200 °C.

– Working pressure of 1,150 psi at 120 °C.

– 1-in diameter with SS construction.

– Swagelock compression connections.

• Twenty-two 1⁄2-in SS hand-operated ball valves, Swagelok SS–63TS8 or equivalent with the following 

specifications:

– Reinforced PFTE seats.

– Manual operation.

– Operating temperature rating up to 200 °C.

– Working pressure of 1,150 psi at 120 °C, 1⁄2-in diameter with SS construction.

– Swagelock compression connections.

• Twenty 1⁄2-in all SS straight bellows valves with compression fittings, Swagelok SS–8BW or equivalent 

with the following specifications:

– Completely welded bellows valve design.

– Manual operation.

– Temperature rated to at least 900 °F continuous operation.

– Pressure rated to at least 200 psig (at full temperature).

– All SS wetted surfaces.

– 1⁄2-in Swagelok connection. 
52

• Fifteen 1⁄2-in all SS straight bellows valves with VCR fittings, Swagelok SS–8BW–V47 or equivalent 

with the following specifications:

– Completely welded bellows valve design.

– Manual operation.

– Temperature rated to at least 900 °F continuous operation.

– Pressure rated to at least 200 psig (at full temperature).

– 1⁄2-in VCR female connection. 

– All SS wetted surfaces.

– Handles may be rated to less than 900 °F if they are removable.

• Eight 3/8-in all SS straight bellows valves with compression fittings, Swagelok SS–6BW or equivalent 

with the following specifications:

– Completely welded bellows valve design.

– Manual operation.

– Temperature rated to at least 900 °F continuous operation.

– Pressure rated to at least 200 psig (at full temperature).

– All SS wetted surfaces.

– Handles may be rated to less than 900 °F if they are removable.

– 1⁄2-in Swagelok connection. 
53

APPENDIX G—VACUUM PUMP UNITS SPECIFICATION

Specification for Procurement of Stainless Steel Hand-Valve Hardware for Water and Purified Gas 

Systems Integrated Financial Management Program Procurement

Estimated delivery 6 weeks ARO

Title—Turbopump System (Turbopump With Controller) Varian V–301 Navigator Complete 

System or Equivalent Unit. Dry rough pump unit Alcatel model ACP40 or equivalent unit

Vendors:

• Varian Vacuum Technologies

121 Hartwell Ave.

Lexington, MA 02173

POC: Thomas J. Drisgill

Telephone: 407–366–8602

• Alcatel Vacuum Products

67–T Sharp St

Hingham, MA 02043

Sales: 781–331–4200

• Osaka Vacuum Ltd.

911 Bern Court, Suite 140

San Jose, CA 95112

Telephone: 408–441–7658

• Leybold Vacuum Inc.

5700 Mellon Road

Export, PA 15632

Sales: 724–327–5700

• BOC Edwards

301 Ballardvale St.

Wilmington, MA 01887

Sales: 978-658-5410

• Pfeiffer Vacuum Inc.

24 Trafalgar Sq.

Nashua, NH 03063

Sales: 603–578–6500

Quantity—two units.
54

General Specification for Turbopump Unit

Turbopump system (turbopump with controller) Varian V–301 navigator complete system or 

equivalent with the following specifications:

• Cooling: Natural air convection.

• Protective screen: Inlet screen factory installed. 

• Pumping speed: 250 L/s N, 200 L/s H, 220 L/s He.

• Compression ratio: 7×108 for N.

• Ultimate pressure: 8×10–10 mbar or less.

• Operating voltage: 120 VAC.

• Bake-out temperature: Up to 120 °C on the inlet flange.

• Startup time: 2 to 5 min.

• Installation position: Any.

• Ambient temperature: Up to 40 °C (for operation).

• Inlet flange: 6-in conflat.

• Outlet flange: KF25.

Quantity—1 unit 

General Specification for Rough Pump

Alcatel model ACP40 equivalent with the following specifications:

• Oil-free pumping.

• 500 L/min pumping speed or better.

• Operating pressure range from atmospheric to less than 10–2 torr.

• NW40 inlet flange.

• 120 VAC single phase.
55

• Air-cooled.

• Operating temperature 5–40 °C.

• Gas ballast fitting provided.

• Noise level 68 dB or lower.

• Time between overhauls >20,000 hr.
56

APPENDIX H—FORTRAN 90 SOURCE CODE LISTING—LOSS OF COOLANT 

TRANSIENT ANALYSIS

A Fortran code was developed to assess the transient calorimeter heating trends during a loss of 

recirculation coolant condition.

**********************************************************************************************************************************

** trans_anular.f90 (4-7-2005)

**********************************************************************************************************************************

** Eric Stewart

** (256) 544-7099

** Eric.T.Stewart@nasa.gov

**********************************************************************************************************************************

PROGRAM trans_anular

 IMPLICIT NONE

 INTEGER :: lumps=6,id,pc,jd

 REAL, DIMENSION(1:6) :: vol=0.,cp=0.,k=0.,rho=0.,t1,to,heff=0.,rvc=0.,dtrvc=0.

 REAL, DIMENSION(1:8) :: diam=0.

 REAL :: em1=.2,em2=.2,em6=.2,length=0.33,pi,to=0,dt=.0001,kgas=.205,sig=5.67E-08,qin=5000.

 REAL :: dr23,dr32,pi,qrad,qcon,time,ts=290.

 REAL :: c1,d1,e1,c2,d2,e2,c3,d3,e3,c4,d4,e4,c5,d5,e5,c6,d6,e6,energy,energyo

 pi = 4.0*ATAN(1.0)

 diam(1) = .014097

 diam(2) = .015977

! diam(1) = diam(2)-3.*(diam(2)-diam(1))

 diam(3) = .017252

 diam(4) = .020198

 diam(5) = .020960

 diam(6) = .023906

 diam(7) = .030256

 diam(8) = .033203

 to(1) = 1273.

 to(2) = 400.

 to(3) = 325.

 to(4) = 325.

 to(5) = 325.

 to(6) = 325.

 t1 = to

 vol(1) = 0.25*pi*(diam(2)*diam(2)-diam(1)*diam(1))*length

 vol(2) = 0.25*pi*(diam(4)*diam(4)-diam(3)*diam(3))*length

 vol(3) = 0.25*pi*(diam(5)*diam(5)-diam(4)*diam(4))*length

 vol(4) = 0.25*pi*(diam(6)*diam(6)-diam(5)*diam(5))*length

 vol(5) = 0.25*pi*(diam(7)*diam(7)-diam(6)*diam(6))*length

 vol(6) = 0.25*pi*(diam(8)*diam(8)-diam(7)*diam(7))*length

 cp(1) = 250.

 cp(2) = 380.

 cp(3) = 4200.

 cp(4) = 380.

 cp(5) = 4200.

 cp(6) = 380.

 rho(1) = 13800.

 rho(2) = 8900.

 rho(3) = 985.

 rho(4) = 8900.
57

 rho(5) = 985.

 rho(6) = 8900.

 k(1) = 90.

 k(2) = 400.

 k(3) = 0.65

 k(4) = 400.

 k(5) = 0.65

 k(6) = 400.

 rvc(1) = rho(1)*vol(1)*cp(1)

 rvc(2) = rho(2)*vol(2)*cp(2)

 rvc(3) = rho(3)*vol(3)*cp(3)

 rvc(4) = rho(4)*vol(4)*cp(4)

 rvc(5) = rho(5)*vol(5)*cp(5)

 rvc(6) = rho(6)*vol(6)*cp(6)

 dtrvc = dt/rvc

!***********************************************************************************************************************************

 dr23 = diam(2)/diam(3)

 dr32 = diam(3)/diam(2)

 qrad = (t1(1)-t1(2))*sig*pi*diam(2)*length*(to(1)+to(2))*(to(1)*to(1)+to(2)*to(2))/(1./em1+(1-em2)*dr23/em2)

 qcon = (t1(1)-t1(2))*(2.*pi*length*kgas)/LOG(dr32)

 WRITE(6,’(/,» t of mo-re is «,3E15.8)’) to(1),qcon,qrad

 WRITE(6,’(/,» mass is «,6E15.8)’) rho(1)*vol(1),rho(2)*vol(2),rho(3)*vol(3),rho(4)*vol(4),rho(5)*vol(5),rho(6)*vol(6)

 WRITE(6,’(/,» rvc is «,6E15.8)’) rvc(1),rvc(2),rvc(3),rvc(4),rvc(5),rvc(6)

!***********************************************************************************************************************************

 OPEN(UNIT=81,FILE=’temperature.txt’,STATUS=’REPLACE’,FORM=’FORMATTED’)

 WRITE(81,’(4X,»time»,7X,»temp1»,6X,»temp2»,6X,»temp3»,6X,»temp4»,6X,»temp5»,6X,»temp6»,5X,»energy»)’)

 time = 0

 energyo = 0.

 DO jd=1,6

 energyo = energyo + to(jd)*rvc(jd)

 ENDDO

 WRITE(81,’(8E11.3)’) time,to(1),to(2),to(3),to(4),to(5),to(6),energyo

 c1 = dtrvc(1)*(sig*pi*diam(2)*length/(1./em1+(1-em2)*(diam(2)/diam(3))/em2))

 d1 = dtrvc(1)*(2.*pi*length*kgas/LOG(diam(3)/diam(2)))

 c2 = dtrvc(2)*(sig*pi*diam(2)*length/(1./em1+(1-em2)*(diam(2)/diam(3))/em2))

 d2 = dtrvc(2)*(2.*pi*length*kgas/LOG(diam(3)/diam(2)))

 e2 = dtrvc(2)*(2.*pi*length*k(3)/LOG((diam(5)+diam(4))/(2.*diam(4))))

 c3 = dtrvc(3)*(2.*pi*length*k(3)/LOG((diam(5)+diam(4))/(2.*diam(4))))

 d3 = dtrvc(3)*(2.*pi*length*k(3)/LOG((2.*diam(5))/(diam(5)+diam(4))))

 c4 = dtrvc(4)*(2.*pi*length*k(3)/LOG((2.*diam(5))/(diam(5)+diam(4))))

 d4 = dtrvc(4)*(2.*pi*length*k(5)/LOG((diam(7)+diam(6))/(2.*diam(6))))

 c5 = dtrvc(5)*(2.*pi*length*k(5)/LOG((diam(7)+diam(6))/(2.*diam(6))))

 d5 = dtrvc(5)*(2.*pi*length*k(5)/LOG((2.*diam(7))/(diam(7)+diam(6))))

 c6 = dtrvc(6)*(2.*pi*length*k(5)/LOG((2.*diam(7))/(diam(7)+diam(6))))

 d6 = dtrvc(6)*(sig*pi*diam(8)*length*em6)

 pc = 0

 DO id=1,1000000

 pc = pc + 1

 time = time + dt

 t1(1) = to(1) - c1*(to(1)**4-to(2)**4) - d1*(to(1)-to(2))

 t1(2) = to(2) + c2*(to(1)**4-to(2)**4) + d2*(to(1)-to(2)) - e2*(to(2)-to(3))

 t1(3) = to(3) + c3*(to(2)-to(3)) - d3*(to(3)-to(4))

 t1(4) = to(4) + c4*(to(3)-to(4)) - d4*(to(4)-to(5))

 t1(5) = to(5) + c5*(to(4)-to(5)) - d5*(to(5)-to(6))

 t1(6) = to(6) + c6*(to(5)-to(6)) - d6*(to(6)**4-ts**4)

 IF(pc == 1000)THEN

 energy = 0.

 DO jd=1,6

 energy = energy + t1(jd)*rvc(jd)

 ENDDO
58

 WRITE(81,’(8E11.3)’) time,t1(1),t1(2),t1(3),t1(4),t1(5),t1(6),energy

 pc = 0

 ENDIF

 to = t1

 ENDDO

 CLOSE(UNIT=81)

*********************************************************************************************************************************

END PROGRAM trans_anular
59

APPENDIX I—HEAT PIPE CALORIMETER GEOMETRY—STANDARD TUBE SIZES

Due to difficulty obtaining quotes for drawn tubing, an assessment, shown in table 16, was made 

using standard copper tube sizes. Machining of the inner diameter would be required.
60

Table 16. Heat pipe calorimeter geometry based on standard tubing dimensions.

56

APPENDIX I HEAT PIPE CALORIMETER GEOMETRY – STANDARD TUBE 

SIZES

Due to difficulty obtaining good quotes for drawn tubing, an assessment was made using 

standard copper tube sizes and machining the inner surface as necessary. 

Fabrication of Copper Alloy Heat Pipe Calorimeters Using Standard Tubing Sizes

Standard Sizes Taken From Parker Instrument Tubing Selection Guide Bulletin 4200-TS (June 2004)

Actual Sizes may vary based on Vendors and Alloys - Will Require Slight Adjustments

Possible Copper Alloys include C122 and Beryllium Copper C172

Calorimeter Geometry G F(-4) F(-3) F(-2) F(-1) F(1) F(2) F(3) F(4) F(0)

Quantity 7 1 1 1 1 1 1 1 1 1

Process Component (OD) 0.625 0.625 0.625 0.625 0.625 0.625 0.625 0.625 0.625 0.625

Gas Conduction Gap Width 0.027 0.027 0.105 0.033 0.023 0.039 0.018 0.048 0.022 0.027

Calorimeter Channel Tube

Std Tube OD 0.875 0.875 1.000 0.875 0.875 0.875 0.875 0.875 0.875 0.875

Std Tube Wall 0.109 0.109 0.083 0.095 0.109 0.095 0.109 0.083 0.109 0.109

Caloirmeter Channel Tube OD 0.875 0.875 1.000 0.875 0.875 0.875 0.875 0.875 0.875 0.875

Calorimeter Channel Tube ID 0.679 0.679 0.835 0.691 0.671 0.703 0.661 0.721 0.669 0.679

Calorimeter Channel Tube Wall -Target 0.098 0.098 0.0825 0.092 0.102 0.086 0.107 0.077 0.103 0.098

Std Tube Wall Material to Remove 0.0110 0.0110 0.0005 0.0030 0.0070 0.0090 0.0020 0.0060 0.0060 0.0110

Calorimeter Shell Tube

Water Film Flow Gap - Target 0.0135 0.0135 0.0135 0.0135 0.0135 0.0135 0.0135 0.0135 0.0135 0.0135

Std Tube OD 1.000 1.000 1.125 1.000 1.000 1.000 1.000 1.000 1.000 1.000

Std Tube Wall 0.049 0.049 0.049 0.049 0.049 0.049 0.049 0.049 0.049 0.049

Caloirmeter Shell Tube OD 1.000 1.000 1.125 1.000 1.000 1.000 1.000 1.000 1.000 1.000

Calorimeter Shell Tube ID 0.902 0.902 1.027 0.902 0.902 0.902 0.902 0.902 0.902 0.902

Calorimeter Shell Tube Wall -Target 0.049 0.049 0.049 0.049 0.049 0.049 0.049 0.049 0.049 0.049

Std Tube Wall Material to Remove 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

Calorimeter Cover Tube

Water Return Path Width - Target 0.135 0.135 0.135 0.135 0.135 0.135 0.135 0.135 0.135 0.135

Std Tube OD 1.500 1.500 1.500 1.500 1.500 1.500 1.500 1.500 1.500 1.500

Std Tube Wall 0.083 0.083 0.065 0.083 0.083 0.083 0.083 0.083 0.083 0.083

Caloirmeter Cover Tube OD 1.500 1.500 1.500 1.500 1.500 1.500 1.500 1.500 1.500 1.500

Calorimeter Cover Tube ID - Target 1.27 1.27 1.395 1.27 1.27 1.27 1.27 1.27 1.27 1.27

Calorimeter Cover Tube Wall -Target 0.115 0.115 0.0525 0.115 0.115 0.115 0.115 0.115 0.115 0.115

Std Tube Wall Material to Remove -0.0320 -0.0320 0.0125 -0.0320 -0.0320 -0.0320 -0.0320 -0.0320 -0.0320 -0.0320

Water Return Path Width - No Machining 0.167 0.167 0.1225 0.167 0.167 0.167 0.167 0.167 0.167 0.167

Calorimeter Cover Tube ID - No Machining 1.334 1.334 1.37 1.334 1.334 1.334 1.334 1.334 1.334 1.334

For Calorimeters G, F(-4), F(-1), F(2), F(4) and F(0)

Channel Tube Notes:

Std Tubing OD = 0.875 1) Wall thickness for the Channel Tube is approx. 2X that of the baseline drawn case.

Std Tubing Wall Thickness = 0.109 For Copper this should be no issue due to the high themal conductivity.

Shell Tube 2) The size and wall thickness of the Shell Tube are adjusted to achieve a film flow gap

Std Tubing OD = 1.000 width which is between 0.010 and 0.015 inch so that no machining is required.

Std Tubing Wall Thickness = 0.049 3) The size and wall thickness of the Cover Tube is adjusted so that it is approx.

Cover Tube 10 times the film flow gap width. It is suggested that no machining be performed on this

Std Tubing OD = 1.500 tube and the ID/OD are used as is (machined amount is very small).

Std Tubing Wall Thickness = 0.083 4) Total of 8 different types of tubing material are required to build all calorimeters.

5) The calorimeter cover tube could potentially be reduced to save weight possible to 

For Calorimeters F(-3) a 1-3/8" diameter tube with a 0.065 wall if available. This would provide a water flow

Channel Tube return path of approx. 0.122" and an cover tube mass reduction of approx 0.5 lbs.

Std Tubing OD = 1.000

Std Tubing Wall Thickness = 0.083

Shell Tube Approximate Weight per Calorimeter

Std Tubing OD = 1.125 Copper Density 0.323 lb/in^3

Std Tubing Wall Thickness = 0.049 Calorimeter length 14 in

Cover Tube

Std Tubing OD = 1.500 Channel Tube 1.08 lb

Std Tubing Wall Thickness = 0.065 Shell Tube 0.67 lb

Cover Tube 1.67 lb (1.5" OD x 0.083 wall)

For Calorimeters F(-2) and F(1) Cover Tube 1.21 lb (1.3755" OD x 0.065 wall)

Channel Tube

Std Tubing OD = 0.875 Manifold End Caps 0.24 lb

Std Tubing Wall Thickness = 0.095

Shell Tube Total 3.66 lb (with 1.5" OD cover)

Std Tubing OD = 1.000

Std Tubing Wall Thickness = 0.049

Cover Tube

Std Tubing OD = 1.500

Std Tubing Wall Thickness = 0.083

For Calorimeters F(3)

Channel Tube

Std Tubing OD = 0.875

Std Tubing Wall Thickness = 0.083

Shell Tube

Std Tubing OD = 1.000

Std Tubing Wall Thickness = 0.049

Cover Tube

Std Tubing OD = 1.500

Std Tubing Wall Thickness = 0.083
61

APPENDIX J—CALORIMETER POWER EXTRACTION PERFORMANCE WORKSHEET 

FOR STANDARD TUBING

The full spreadsheet, shown in table 17, was used in assessing the calorimeter configuration based 

on standard size tubing holding this water film flow gap at 0.0135 in.
62

Table 17. Calorimeter geometry and performance for a cooling film annulus of 0.0135 in.

57

APPENDIX J CALORIMETER POWER EXTRACTION PERFORMANCE WORK 

SHEET FOR STD TUBING

Table 1. Calorimeter Geometry and Performance for a Cooling Film Annulus = 0.0135” For NRPCT Work Item #2 Updated on 5-15-2005 for Std Tubing inputs 

Water Calorimeter Quick Assessment for Heat pipe life time testing

Assumes: helium/argon gas flooded test chamber at low pressure to improve coupling to calorimeter

 - Direct Input Value

 - Value Carried From Other Input Location

Heat pipe Inputs parameters of interest

Heat pipe length 0.3048 12 inch ratio Cond/Evap

Evaporator length 0.06985 m 2.75 inch

Adiabatic length 0 m 0 inch

Condenser length 0.23495 m 9.25 inch

Diameter 0.015875 m 0.625 in OD

Calorimeter Inputs

length of calorimeter 0.3302 m 13 inch

Calorimeter Area 0.01171167 m^2 18.153125 inch^2 covering heat pipe

Calorimeter Area 0.004747974 m^3 7.359375 inch^3 covering support

Nominal Inlet Temperature 299.8166667 K 80 deg F

Nominal Flow rate 0.027491492 kg/sec 0.435 gallons/min

inlet water pressure 446599 Pa 65 psi

Target Surface Temp (ID) 351 K 172.13 F on the ID surface exposed to hot heat pipe (boiling = 420 K at 65psia)

Channel Wall thickness 0.0014732 m 0.058 inch inner tube exposed to hot heat pipe

Shell Wall thickness 0.0014732 m 0.058 inch middle tube creating the film flow path

Cover Wall thickness 0.0014732 m 0.058 inch outer tube sealing the return path

film flow Gap 0.0003429 m 0.0135 inch water flow gap on inner annulus (outlet flow) next to heat pipe - this absorbs the heat

Return Flow Gap 0.0042418 m 0.167 inch water flow gap on outer annulus (inlet flow)

Test Condition ---> G series F(-4) F(-3) F(-2) F(-1) F(1) F(2) F(3) F(4) F(0)

Variables Units

Power (W) W 3000 5000 1000 3000 3000 2000 4000 2000 4000 3000

Heat Pipe Surface Temperature K 1273 1273 1273 1373 1173 1223 1223 1323 1323 1273

Average Gas Gap Temperature K 814 831.5 802.5 864 764 780 798 830.5 848 814

Calorimeter Channel ID Temperature K 355 390 332 355 355 337 373 338 373 355

Calorimeter Channel Wall OD Temperature K 353.48 387.46 331.64 353.58 353.41 336.12 370.76 337.23 370.85 353.48

Calorimeter Channel Wall Delta Temp K 1.52 2.54 0.36 1.42 1.59 0.88 2.24 0.77 2.15 1.52

Dimensions (meters)

Heat Pipe OD at Room Temperature m 0.01588 0.01588 0.01588 0.01588 0.01588 0.01588 0.01588 0.01588 0.01588 0.01588

Heat Pipe OD at Temperature m 0.01597 0.01597 0.01597 0.01598 0.01595 0.01596 0.01596 0.01597 0.01597 0.01597

Condenser Length m 0.23495 0.23495 0.23495 0.23495 0.23495 0.23495 0.23495 0.23495 0.23495 0.23495

Gas Gap Width - HP OD to Calorimeter ID m 0.000646 0.000631 0.002638 0.000782 0.000531 0.000942 0.000423 0.001166 0.000508 0.000646

Calorimeter Channel Wall ID m 0.01725 0.01725 0.02121 0.01755 0.01704 0.01786 0.01679 0.01831 0.01699 0.01725

Calorimeter Channel Wall OD m 0.02223 0.02223 0.02540 0.02223 0.02223 0.02223 0.02223 0.02223 0.02223 0.02223

Calorimeter Channel Wall Thickness m 0.00249 0.00249 0.00210 0.00234 0.00259 0.00218 0.00272 0.00196 0.00262 0.00249

Calorimeter Shell Wall ID m 0.02291 0.02291 0.02609 0.02291 0.02291 0.02291 0.02291 0.02291 0.02291 0.02291

Calorimeter Shell Wall OD m 0.02540 0.02540 0.02858 0.02540 0.02540 0.02540 0.02540 0.02540 0.02540 0.02540

Calorimeter Shell Wall Thickness m 0.00124 0.00124 0.00124 0.00124 0.00124 0.00124 0.00124 0.00124 0.00124 0.00124

Calorimeter Cover Wall ID m 0.03388 0.03388 0.03480 0.03388 0.03388 0.03388 0.03388 0.03388 0.03388 0.03388

Calorimeter Cover Wall OD m 0.03810 0.03810 0.03810 0.03810 0.03810 0.03810 0.03810 0.03810 0.03810 0.03810

Calorimeter Cover Wall Thickness m 0.00211 0.00211 0.00165 0.00211 0.00211 0.00211 0.00211 0.00211 0.00211 0.00211

Film Flow Gap Thickness m 0.00034 0.00034 0.00034 0.00034 0.00034 0.00034 0.00034 0.00034 0.00034 0.00034

Return Flow Gap Thickness m 0.00424 0.00424 0.00312 0.00424 0.00424 0.00424 0.00424 0.00424 0.00424 0.00424

Film Hydraulic Diameter (Douter-Dinner) m 0.000686 0.000686 0.000686 0.000686 0.000686 0.000686 0.000686 0.000686 0.000686 0.000686

Dimensions (inches)

Heat Pipe OD at Room Temperature in 0.6250 0.6250 0.6250 0.6250 0.6250 0.6250 0.6250 0.6250 0.6250 0.6250

Heat Pipe OD at Temperature in 0.6286 0.6286 0.6286 0.6290 0.6281 0.6283 0.6283 0.6288 0.6288 0.6286

Condenser Length in 9.2500 9.2500 9.2500 9.2500 9.2500 9.2500 9.2500 9.2500 9.2500 9.2500

Gas Gap Width - HP OD to Calorimeter ID in 0.0254 0.0248 0.1038 0.0308 0.0209 0.0371 0.0166 0.0459 0.0200 0.0254

Calorimeter Channel Wall ID in 0.6790 0.6790 0.8350 0.6910 0.6710 0.7030 0.6610 0.7210 0.6690 0.6790

Calorimeter Channel Wall OD in 0.8750 0.8750 1.0000 0.8750 0.8750 0.8750 0.8750 0.8750 0.8750 0.8750

Calorimeter Channel Wall Thickness in 0.0980 0.0980 0.0825 0.0920 0.1020 0.0860 0.1070 0.0770 0.1030 0.0980

Calorimeter Shell Wall ID in 0.9020 0.9020 1.0270 0.9020 0.9020 0.9020 0.9020 0.9020 0.9020 0.9020

Calorimeter Shell Wall OD in 1.0000 1.0000 1.1250 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000

Calorimeter Shell Wall Thickness in 0.0490 0.0490 0.0490 0.0490 0.0490 0.0490 0.0490 0.0490 0.0490 0.0490

Calorimeter Cover Wall ID in 1.3340 1.3340 1.3700 1.3340 1.3340 1.3340 1.3340 1.3340 1.3340 1.3340

Calorimeter Cover Wall OD in 1.5000 1.5000 1.5000 1.5000 1.5000 1.5000 1.5000 1.5000 1.5000 1.5000

Calorimeter Cover Wall Thickness in 0.0830 0.0830 0.0650 0.0830 0.0830 0.0830 0.0830 0.0830 0.0830 0.0830

Film Flow Gap Thickness in 0.0135 0.0135 0.0135 0.0135 0.0135 0.0135 0.0135 0.0135 0.0135 0.0135

Return Flow Gap Thickness in 0.1670 0.1670 0.1230 0.1670 0.1670 0.1670 0.1670 0.1670 0.1670 0.1670

Film Hydraulic Diameter (Douter-Dinner) in 0.0270 0.0270 0.0270 0.0270 0.0270 0.0270 0.0270 0.0270 0.0270 0.0270

Material Emissivity

Emissivity Mo-44.5Re @ Temp 0.16 0.16 0.16 0.17 0.15 0.16 0.16 0.16 0.16 0.16

Emissivity Copper C122 0.44 0.44 0.44 0.44 0.44 0.44 0.44 0.44 0.44 0.44

Effective Emissivity 0.13 0.14 0.13 0.14 0.13 0.13 0.13 0.14 0.14 0.13

Heat Transfer Gas Gap

Radiation Heat Transfer Gap W 235.23 234.72 235.60 333.91 160.73 195.53 194.99 281.53 280.99 235.23

Conduction Heat Transfer Gap W 2764.77 4765.28 764.40 2666.09 2839.27 1804.47 3805.01 1718.47 3719.01 2764.77

Gas Gap Composition Helium -Argon 32% Ar 6% Ar 32% Ar 32% Ar 32% Ar 32% Ar 32% Ar 32% Ar 32% Ar 32% Ar

Helium Thermal conductivity @ Avg Temp W/m-K 0.31 0.32 0.31 0.33 0.30 0.30 0.31 0.32 0.32 0.31

Gas Gap Compensation factor 0.51 0.88 0.51 0.51 0.51 0.51 0.51 0.51 0.51 0.51

Effective Gas Gap Thermal Conductivity W/m-K 0.1588 0.2783 0.1572 0.1658 0.1517 0.1540 0.1565 0.1611 0.1636 0.1588

Calorimeter Material copper C122 copper C122 copper C122 copper C122 copper C122 copper C122 copper C122 copper C122 copper C122 copper C122

Calorimeter Channel Wall Thermal Conductivity W/m-K 339.0 339.0 339.0 339.0 339.0 339.0 339.0 339.0 339.0 339.0

Calorimeter Cooling Fluid Water Water Water Water Water Water Water Water Water Water

Avg Temp Used for Fluid Properties K 312.8 320.9 314.6 312.8 312.8 308.6 317.2 309.5 317.2 312.8

Water Flow Rate kg/sec 0.028 0.028 0.008 0.028 0.028 0.027 0.027 0.025 0.027 0.028

Water Flow Rate gal/min 0.436 0.449 0.128 0.436 0.436 0.430 0.435 0.392 0.435 0.436

Inlet Water Pressure Pa 446599 446599 446599 446599 446599 446599 446599 446599 446599 446599

Inlet Water Pressure psi 65.00 65.00 65.00 65.00 65.00 65.00 65.00 65.00 65.00 65.00

Water Inlet Temperature K 299.82 299.82 299.82 299.82 299.82 299.82 299.82 299.82 299.82 299.82

Log mean Water Film Flow temp Wall to Fluid K 40.80 66.90 11.87 40.80 40.80 27.46 53.91 27.40 53.91 40.80

Average Water Film Flow Temperature K 312.82 320.90 314.57 312.82 312.82 308.61 317.23 309.47 317.23 312.82

Water film flow temp delta (inlet to outlet) K 26.02 42.17 29.51 26.02 26.02 17.59 34.83 19.31 34.83 26.02

Water Outlet Temperature K 325.83 341.99 329.32 325.83 325.83 317.41 334.65 319.13 334.65 325.83

Water specific heat Cp J/kg-K 4180.28 4180.26 4180.15 4180.28 4180.28 4180.86 4180.09 4180.71 4180.09 4180.28

Water thermal conductivity k W/m-K 0.63 0.64 0.63 0.63 0.63 0.62 0.63 0.62 0.63 0.63

water density rho kg/m3 993.64 990.52 992.99 993.64 993.64 995.12 991.98 994.82 991.98 993.64

Water Absolute Viscosity mu kg/m-s 0.000665 0.000570 0.000642 0.000665 0.000665 0.000725 0.000610 0.000712 0.000610 0.000665

Log Mean Temperature Difference Wall to Fluid K 40.80 66.90 11.87 40.80 40.80 27.46 53.91 27.40 53.91 40.80

Heat Transfer To Cooling Fluid

Channel Flow Tube surface smooth smooth smooth smooth smooth smooth smooth smooth smooth smooth

Shell Flow Tube surface smooth smooth smooth smooth smooth smooth smooth smooth smooth smooth

Type of flow (Re<2300 = Laminar) Laminar Laminar Laminar Laminar Laminar Laminar Laminar Laminar Laminar Laminar

Film Flow Area m^2 2.43E-05 2.43E-05 2.77E-05 2.43E-05 2.43E-05 2.43E-05 2.43E-05 2.43E-05 2.43E-05 2.43E-05

Film Flow Velocity m/sec 1.14 1.18 0.29 1.14 1.14 1.12 1.14 1.02 1.14 1.14

Reynolds Number 1171.24 1403.80 312.43 1171.24 1171.24 1058.46 1271.16 981.78 1271.16 1171.24

Nusselt Number 4.89 4.89 4.89 4.89 4.89 4.89 4.89 4.89 4.89 4.89

Convective heat Transfer Coeff h W/m^2-K 4484.26 4558.33 4497.51 4484.26 4484.26 4442.60 4525.62 4451.28 4525.62 4484.26

 Check on power balance -convection side W 3000.00 5000.00 1000.00 3000.00 3000.00 2000.00 4000.00 2000.00 4000.00 3000.00

Check power balance - water flow side W 3000.00 5000.00 1000.00 3000.00 3000.00 2000.00 4000.00 2000.00 4000.00 3000.00

Pressure Drop in Film Channel

viscosity ratio (mu-bulk to mu-wall) 1.87 2.50 1.35 1.87 1.87 1.64 2.13 1.63 2.13 1.87

annular passage dia ratio dinner/douter 0.970 0.970 0.974 0.970 0.970 0.970 0.970 0.970 0.970 0.970

annular passage adjustment factor 1.49998 1.49998 1.49998 1.49998 1.49998 1.49998 1.49998 1.49998 1.49998 1.49998

factor for #/Re expression 82.0 76.3 89.1 82.0 82.0 84.9 79.5 85.0 79.5 82.0

friction factor f smooth channel 0.070 0.054 0.285 0.070 0.070 0.080 0.063 0.087 0.063 0.070

Calorimeter Length m 0.330 0.330 0.330 0.330 0.330 0.330 0.330 0.330 0.330 0.330

Delta pressure in Film Channel Pa 21873.3 18009.0 5914.0 21873.3 21873.3 24303.4 19398.4 21768.7 19398.4 21873.3

Delta pressure in Film Channel psi 3.2 2.6 0.9 3.2 3.2 3.5 2.8 3.2 2.8 3.2

Delta Pressure/Inlet Pressure 0.049 0.040 0.013 0.049 0.049 0.054 0.043 0.049 0.043 0.049
63

APPENDIX K—SIMPLIFIED CALORIMETER UNCERTAINTY ANALYSIS

Water Calorimeter Power Assessment—Simple Uncertainty Analysis

Water flow calorimeter was selected as the method to assess the heat pipe condenser power output 

for accelerated heat pipe life tests. This power is assessed using measurement of the water temperature 

increase (∆T), specific heat (Cp), and flow rate ( ) per the following formulation:

Q = mCpΔT . (14)

The temperature difference (∆T) is based on thermocouple readings taken both upstream and 

downstream of the calorimeter as,

ΔT = To − Ti . (15)

The mass flow rate is based on the measured water flow velocity (V), density (ρ), and area (A) of 

the flow meter duct as,

m = ρVA . (16)

The flow rate is measured with a flow meter that has an accuracy ranging from 0.3% to 3% depending on the type (magnetic meter or paddle wheel-style). The temperature difference is based on the reading 

of two thermocouples, with accuracy on the order of 2%. Fluid properties are assessed based on standard 

water tables at the flow meter temperature, with accuracy typically of 0.5%.

General Uncertainty Equations

The expression in equation (14) is used for the current uncertainty analysis. The power can be 

expressed as a function of the following terms:

Q = f (m ,Cp,ΔT ) . (17)

The propagation of errors results in,

dQ = ∂Q

∂m

dm +

∂Q

∂Cp

dCp +

∂Q

∂ΔT

dΔT . (18)
64

Squaring, expanding, and setting all correlated terms to zero results in the following final expression:

dQ2 = ∂Q

∂m

⎛

⎝

⎜ ⎞

⎠

⎟

2

dm 2 +

∂Q

∂Cp

⎛

⎝

⎜

⎞

⎠

⎟

2

dCp

2 +

∂Q

∂ΔT

⎛

⎝

⎜ ⎞

⎠

⎟

2

dΔT 2 . (19)

Defining all partial derivatives listed in equation (19) by using equation (14):

∂Q

∂m = CpΔT , (20)

∂Q

∂Cp

= m ΔT , (21)

and

∂Q

∂ΔT = mCp .

(22)

Substituting equations (20), (21), and (22) into equation (19) results in,

dQ2 = (CpΔT )

2

dm 2 + (m ΔT )

2 dCp

2 + (mCp )

2

dΔT 2 . (23)

Rearranging each derivative term in equation (23) by dividing it by its square results in the following:

dQ2 = (CpΔTm )

2 dm

m

⎛

⎝

⎜ ⎞

⎠

⎟

2

+ (m ΔTCp )

2 dCp

Cp

⎛

⎝

⎜

⎞

⎠

⎟

2

+ (mCpΔT )

2 dΔT

ΔT

⎛

⎝

⎜ ⎞

⎠

⎟

2

. (24)

Further rearrangement results in the following: 

dQ2 = (CpΔTm )

2 dm

m

⎛

⎝

⎜ ⎞

⎠

⎟

2

+

dCp

Cp

⎛

⎝

⎜

⎞

⎠

⎟

2

+

dΔT

ΔT

⎛

⎝

⎜ ⎞

⎠

⎟

⎡ 2

⎣

⎢

⎢

⎤

⎦

⎥

⎥ . (25)

Each of the derivative terms dm

m , 

dCp

Cp

, and dΔT

ΔT

 must now be determined. 
65

Mass Flow Rate Uncertainty Determination

For the mass flow rate expression, given in equation (16), a propagation of errors must be evaluated. For this formulation, the flow meter produces a flow velocity, while the flow area is measured and 

the density is taken from the water property tables as follows:

dm 2 = ∂m

∂ρ

⎛

⎝

⎜

⎞

⎠

⎟

2

dρ2 +

∂m

∂V

⎛

⎝

⎜ ⎞

⎠

⎟

2

dV2 +

∂m

∂A

⎛

⎝

⎜ ⎞

⎠

⎟

2

dA2 . (26)

Find all partial derivatives listed in equation (26) by using equation (16) as follows:

∂m

∂ρ = VA , (27)

∂m

∂V = ρA , (28)

∂m

∂A = ρV . (29)

Substitute the partials from equations (27), (28), and (29) into equation (26) resulting in the following:

dm 2 = (VA)

2 dρ2 + (ρA)

2 dV2 + (ρV )2 dA2 . (30)

Rearrange each derivative term in equation (30) by dividing it by its square, resulting in the following:

dm 2 = (VAρ)

2 dρ

ρ

⎛

⎝

⎜

⎞

⎠

⎟

2

+ (ρAV )

2 dV

V

⎛

⎝

⎜ ⎞

⎠

⎟

2

+ (ρVA)

2 dA

A

⎛

⎝

⎜ ⎞

⎠

⎟

2

. (31)

Factor out the term ρVA = m , and divide both sides of the expression by it, resulting in this final form, 

dm

m

⎛

⎝

⎜ ⎞

⎠

⎟

2

= dρ

ρ

⎛

⎝

⎜

⎞

⎠

⎟

2

+

dV

V

⎛

⎝

⎜ ⎞

⎠

⎟

2

+

dA

A

⎛

⎝

⎜ ⎞

⎠

⎟

2

.

(32)

Each of these terms can now be determined as follows:

• dV

V

⎛

⎝

⎜ ⎞

⎠

⎟ = uncertainty in determining velocity (0.3%=0.003 to 3%=0.03 depending on the magnitude

of the flow rate).
66

• dA

A

⎛

⎝

⎜ ⎞

⎠

⎟ = uncertainty in determining the duct area, which is assumed to be a negligible error (0%).

• dρ

ρ

⎛

⎝

⎜

⎞

⎠

⎟ = uncertainty in determining the density, which is composed of two components:

– Uncertainty over a temperature range of 300 to 350 K (2%=0.02), assuming a single average density

value is used to cover this temperature range.

– Uncertainty in the reference density data (0.5%=0.005).

 

The uncertainty of the density term can be reduced considerably by curve fitting the referenced 

density data as a function of temperature, and replacing the single average value. A more suitable density 

value can be determined by using the measured temperature at the flow meter. This density value will have 

an associated uncertainty that is approximately that of the reference data, as temperature measurement 

uncertainty is relatively small over the range. 

For the flow rate, the uncertainty term can be approximated assuming maximums as,

dm

m

⎛

⎝

⎜ ⎞

⎠

⎟

2

= (0.03)

2 + (0.02)

2 + (0.0)

2 , (33)

dm

m

⎛

⎝

⎜ ⎞

⎠

⎟ = 0.036 or 3.6% . (34)

If the density is assumed to be found as a function of the temperature, with uncertainty approximating the 

reference data, the overall uncertainty tracks that of the flow meter.

Specific Heat Uncertainty Determination

The specific heat (Cp) assessment is calculated from the tabulated water data. The value of Cp varies by approximately 0.3% over the expected flow temperature range of 300 to 350 K. For conservatism 

and simplicity in this exercise, uncertainty is based on a combination of temperature affect and reference 

accuracy:

•

dCp

Cp

= Uncertainty based on a temperature range of 300 to 350 K (0.3%=0.003), assuming that 

a single-average (Cp) value is used to cover this temperature range.

•

dCp

Cp

= Uncertainty from the reference Cp data (0.5%=0.005).
67

As with the density calculation, uncertainty in the specific heat term can be reduced by curve fitting the referenced specific heat data, and using the measured temperature at the flow meter to determine 

a more suitable density value. This approach reduces the overall uncertainty by eliminating the use of a 

single average value. However, it is seen that there is only a small uncertainty in the Cp value as a function 

of temperature, on the order of that for the reference data; therefore, the use of a single value is not a bad 

approach.

The specific heat uncertainty term can be approximated with maximum values by,

dCp

Cp

⎛

⎝

⎜

⎞

⎠

⎟

2

= (0.003)

2 + (0.005)2 , (35)

dCp

Cp

⎛

⎝

⎜

⎞

⎠

⎟ = 0.0058 or 0.58% . (36)

Temperature Difference Uncertainty Determination

The temperature difference across the calorimeter (∆T) is assessed using the expression from 

equation (15) and propagating errors. This measurement is strictly based on two thermocouple measurements as follows:

dΔT 2 = ∂ΔT

∂To

⎛

⎝

⎜

⎞

⎠

⎟

2

dTo

2 +

∂ΔT

∂Ti

⎛

⎝

⎜

⎞

⎠

⎟

2

dTi

2 . (37)

Find all partial derivatives listed in equation (37) by using equation (15):

∂ΔT

∂To

= 1 (38)

and

∂ΔT

∂Ti

= −1 . (39)

Substitute the partials from equations (38) and (39) into equation (37), resulting in the following:

dΔT 2 = (1)

2 dTo

2 + (−1)

2 dTi

2 . (40)

Divide both sides by the temperature difference, resulting in the following:

dΔT

ΔT

⎛

⎝

⎜ ⎞

⎠

⎟

2

= dTo

(To − Ti)

⎛

⎝

⎜

⎞

⎠

⎟

2

+

dTi

(To − Ti)

⎛

⎝

⎜

⎞

⎠

⎟

2

. (41)
68

Each of these terms can now be determined as,

• dTo

(To − Ti)

⎛

⎝

⎜

⎞

⎠

⎟

2

= uncertainty in thermocouple measurement at outlet (2%=0.02)

• dTi

(To − Ti)

⎛

⎝

⎜

⎞

⎠

⎟

2

= uncertainty in thermocouple measurement at inlet (2%=0.02).

The flow rate uncertainty term is

 dΔT

ΔT

⎛

⎝

⎜ ⎞

⎠

⎟

2

= (0.02)

2 + (0.02)2 , (42)

 

dΔT

ΔT

⎛

⎝

⎜ ⎞

⎠

⎟ = 0.028 or 2.8% . (43)

The uncertainty value for each of these independent thermocouples is based on the combined accuracy of 

both the thermocouple probe/wire and the reading device. This uncertainty can be improved if the thermocouples are used in a differencing mode with a common reading device, because the accuracy of the 

device is related to its ∆T (a small number) rather than to the accuracy of each absolute and independent 

measurement (large numbers). A typical ∆T measurement can have an accuracy approaching 1%, half that 

of a single thermocouple.

Overall Uncertainty Assessment

Collecting all the dm

m , 

dCp

Cp

, and dΔT

ΔT terms and substituting them into equation (25) results in 

the following expression:

dQ

Q

⎛

⎝

⎜

⎞

⎠

⎟

2

= dρ

ρ

⎛

⎝

⎜

⎞

⎠

⎟

2

+

dV

V

⎛

⎝

⎜ ⎞

⎠

⎟

2

+

dA

A

⎛

⎝

⎜ ⎞

⎠

⎟

2

+

dCp

Cp

⎛

⎝

⎜

⎞

⎠

⎟

2

+

dTo

(To − Ti)

⎛

⎝

⎜

⎞

⎠

⎟

2

+

dTi

(To − Ti)

⎛

⎝

⎜

⎞

⎠

⎟

⎡ 2

⎣

⎢

⎢

⎤

⎦

⎥

⎥ . (44)

In the case of a paddle-wheel-style flow meter setup (3%) with thermocouples for temperature 

measurement (2%), taking reference uncertainties for both Cp and ρ, and assuming curve fits, the overall 

uncertainty in power is as follows:

dQ

Q

⎛

⎝

⎜

⎞

⎠

⎟

2

= (0.005)

2 + (0.03)2 + (0.0)2 + (0.0058)2 + (0.02)2 + (0.02)2 ⎡

⎣ ⎤⎦ (45)
69

dQ

Q

⎛

⎝

⎜

⎞

⎠

⎟ = 0.042 or 4.2% . (46)

In the case of a magnetic-style flow meter setup (0.3%) with thermocouples for temperature measurement (2%), the overall uncertainty in power is

dQ

Q

⎛

⎝

⎜

⎞

⎠

⎟

2

= (0.005)

2 + (0.003)2 + (0.0)2 + (0.0058)2 + (0.02)2 + (0.02)2 ⎡

⎣ ⎤⎦ , (47)

dQ

Q

⎛

⎝

⎜

⎞

⎠

⎟ = 0.029 or 2.9% . (48)

The uncertainty bars for the setup using a paddle-wheel flow meter are approximately 45% wider 

than those for the magnetic meter configuration. If the thermocouples used to measure the temperature are 

configured in a delta temperature arrangement (1%), the uncertainty for the paddle-wheel configuration is 

reduced as given by the following:

dQ

Q

⎛

⎝

⎜

⎞

⎠

⎟

2

= (0.005)

2 + (0.03)2 + (0.0)2 + (0.0058)2 + (0.01)2 ⎡

⎣ ⎤⎦ , (49)

dQ

Q

⎛

⎝

⎜

⎞

⎠

⎟ = 0.033 or 3.3% . (50)

The uncertainty is reduced by approximately 20%, a small value since the overall uncertainty is 

dominated by the flow meter velocity calculation. A similar assessment for the magnetic flow meter can 

be performed as follows: 

dQ

Q

⎛

⎝

⎜

⎞

⎠

⎟

2

= (0.005)

2 + (0.003)2 + (0.0)2 + (0.0058)2 + (0.01)2 ⎡

⎣ ⎤⎦ , (51)

dQ

Q

⎛

⎝

⎜

⎞

⎠

⎟ = 0.013 or 1.3% . (52)

Since the temperature term carries the largest weight of any of the factors, there is nearly a 60% reduction 

in the overall uncertainty.
70

Summary

For all the cases examined, flow meter and temperature types, the maximum overall uncertainty 

in the calorimeter power is expected to be on the order of 5%, which translates to 50 W out of 1,000 W 

for the low-powered test case, and 250 W out of 5,000 W for the high-powered case. An error of this 

magnitude is certainly acceptable for the level of operation expected for the heat pipe evaluations; therefore, the final selection of measurement devices should be performed based on a combination of cost 

and durability (lasting up to 3 years). Paddle-wheel-type flow meters cost approximately $1.4k each and 

have the benefit of including both a temperature and pressure measurement, while magnetic meters cost 

up to $2.4k each for the planned heat pipe system. 
71

APPENDIX L—RADIO FREQUENCY INDUCTIVE COIL ASSEMBLY 

CONTRACTOR REPORT

Fluxtrol® Inc.

1388 Atlantic Blvd.

Auburn Hills, MI 48326

Telephone: 248–393–2200/Fax: 248–393–0277

Date: June 3, 2005

Project name: Radio Frequency Induction Coil Assembly

Customer: NASA MSFC

Project type: Induction coil development

Process type: Heating for device validation 

Author: Robert Goldstein

Background

This report contains the results of the computer simulation design phase. The report is for “Final 

Modeling of the Configuration of the RF Inductive Coils.” This modeling should be used as a basis for 

engineering and manufacturing induction coils that fit the project specifications.

Fluxtrol, Inc. is an induction company specializing in advanced induction coil design including 

computer simulation, induction coil manufacturing, and magnetic flux control. Fluxtrol manufactures 

Fluxtrol and Ferrotron products, which are the primary materials used for RF induction heating magnetic 

flux control. 

The induction coil assemblies for the heat pipe testing should be reliable to meet the stringent demands of the testing procedure. The test coils should run maintenance-free for a period of 

3 years in a low-pressure environment, with or without a load. This means that careful calculation of the 

power that needs to be removed from the induction coil is required to ensure reliable performance.

Design Considerations

Computer Modeling and the Role of Magnetic Flux Controllers

The heat pipe test configuration, shown in figures 24 and 25, maximizes space utilization within 

the test chamber and minimizes the number of test chambers required. To accomplish this, the following 

issues must be considered:
72

Figure 24. General layout RF inductive coil assemblies (cluster with five positions).

Figure 25. General dimensional layout of a single RF inductive coil position.

• Variation in azimuthal power-density distribution, due to mutual inductance of adjacent inductors.

• Variation in azimuthal power-density distribution, due to proximity to the chamber wall.

• Power induced in the water-cooling calorimeters.
73

Flux® 2D software was used for two-dimensional electromagnetic computer simulation 

to evaluate the level of these influences on a 5/8-in OD Mo-Re (50% Mo) heat pipe tube with a 0.05-in 

wall thickness and liquid Na inside at a temperature of 1,000 °C. Flux 2D is a two-dimensional, finite 

element code for simulation of induction heating systems. Flux 2D is written and developed by the Cedrat Group (www.cedrat.com) based in Grenoble, France. Magsoft Corporation (www.magsoft-flux.com) 

based out of Ballston Spa, NY, is the U.S. distributor of the software.

The RF frequency used for the simulation was 50 kHz. Magnetic field lines from the simulation 

demonstrate the mutual inductance between a neighboring coil 3.5-in center-to-center (fig. 26(a)), and 

without a neighbor (fig. 26(b)) using Fluxtrol 50 magnetic flux controller. Figure 27 shows the same 

conditions without a magnetic flux controller. The results, contained in table 18, indicate that without a 

magnetic flux controller the variation in power around the circumference of the heat pipe will be greater 

than 5%. With Fluxtrol 50 applied, the variation will be a very small percentage of the overall power. 

(a) (b) 

Figure 26. Magnetic field lines (a) with and (b) without a neighboring inductor 

for a three-turn coil with Fluxtrol 50 magnetic flux controller.

(a) (b) 

Figure 27. Magnetic field lines (a) with and (b) without a neighboring inductor 

for a three-turn coil without a magnetic flux controller.
74

Table 18. Results of two-dimensional simulation for 5/8-in OD Mo-Re heat pipe tube

with 0.05-in wall thickness.

Frequency 

(Hz)

Boundary 

Type

Concentrator 

Type

Electrical 

Efficiency

Cal. Losses 

(W)

Pipe Power 

(W)

Total Power 

(W)

Coil Current 

(A)

Coil Voltage 

(V)

50,000 Infinity Fluxtrol 50 66.9% 5.5 3,000 4,484 1,385 31.2

50,000 Infinity None 65.5% 61.5 3,000 4,582 1,575 30.5

50,000 Close Fluxtrol 50 66.9% 5.7 3,011 4,499 1,385 31.2

50,000 Close None 65.7% 66.3 3,179 4,841 1,575 29.7

The results also show that when Fluxtrol 50 is applied, power induced in the heat pipe reduces 

the heat induced in the calorimeter by approximately a factor of 10. It is necessary to limit and quantify 

the power induced in the calorimeter, since it will result in an error when measuring the heat pipe power 

throughput by water flow rate and temperature difference. 

Besides the value of power induced in the calorimeter, the calorimeter also shunts the power

induced in the heat pipe on the side closest to it. For a coil without a concentrator, this effect exaggerates 

the naturally occurring reduction in power density for the outer turns. When Fluxtrol 50 is applied, this 

effect is reduced and power density is more uniform along the evaporator length, nearly the same on the 

calorimeter and terminal side. Figure 28 shows the relative power density distribution in the heat pipe for 

these two cases. 

0.00E+00

2.00E-01

4.00E-01

6.00E-01

8.00E-01

1.00E+00

1.20E+00

0 10 20 30 40 50 60 70 80 90 100

Relative Power Density

Bare Coil

Fluxtrol 50 Coil

Power Density Distribution in Part Length

Terminal Side X (mm) Calorimeter

Figure 28. Axial power-density distribution in the heat pipe.
75

Voltage Breakdown

The DC voltage breakdown potential is shown in figure 29 in the form of Paschen curves. These 

curves are shown for various atmospheres at different pressure distance products. As atmospheric pressure increases, the breakdown voltage increases dramatically. Also, as the pressure distance product rises, 

breakdown voltage also increases. Voltage breakdown can be prevented either by limiting applied voltage, 

increasing the distance between components, or providing proper physical insulation of live components. 

Voltage breakdown levels are frequency dependent; however, operation at 50 kHz can be approximated as 

a DC potential. The factors that determine the voltage are as follows:

• Frequency.

• Busswork.

• Induction coil design.

• Power in the heat pipe.

100

1000

1 10 100

Breakdown Potential (V)

Helium

Argon

30%Argon

5%Argon

Pressure x Distance (torr-cm)

Figure 29. DC breakdown voltages in various atmospheres.

There will be different voltages in different areas of the heat pipe RF assembly, since all components are connected in series. The highest voltage will be at the output of the power supply, but this will be 

at one atmosphere, and the levels of acceptable voltage are much higher. Inside the chamber, the highest 

voltage will be at the feedthrough outputs/busswork input. Physical insulation should be provided for the 

busswork components to prevent breakdown; however, sufficient spacing is necessary in the connection 

areas to allow for electrical hookup.
76

The biggest determinant of the total voltage for a well-designed assembly is the induction coil 

geometry and frequency. Figure 30 illustrates the relationship between coil head voltage and frequency 

for five single-turn induction coils connected in series with selected coupling gaps as predicted by ELTA, 

a one-dimensional computer simulation program. The induction coil voltage not only depends on the 

coupling gap, but also upon the number of turns. If we assume that the system is linear, then for the same 

power the voltage will be directly proportional to the number of turns, with corresponding inverse dependence of coil current. Voltage (V)

Frequency (Hz)

Effect of Coupling Gap on Voltage

5 Single Turn Coils Connected in Series

Excludes Busswork

3.2 mm gap

6.4 mm gap

9.6 mm gap

500

450

400

350

300

250

200

150

100

50

0

1,000 10,000 100,000 1,0000,000

Figure 30. Relationship between voltage and frequency for various coupling gaps.

The final induction coil geometry should be tested with respect to the selected induction power 

supply. For example, a minimum voltage is required to properly match the coils to the induction power 

supply. At a given power level, increasing the number of coils requires higher coil head voltages and

a corresponding lower coil current, reducing losses in the power supplying the circuitry (busswork, transformer, etc.). At the same time, the breakdown voltage is strongly dependent upon chamber pressure and 

gap distance. The best compromise between coil geometry and system efficiency should be determined 

for each test chamber. 

Heat Transfer in the System

When designing the induction coils, it is important to keep in mind that the required RF power 

induced in the pipes does not include thermal losses. This is only the value that is transferred to the calorimeter in the tests. The real power necessary in a given heat pipe is the required RF power plus the heat 

transfer (loss) from the evaporator to the induction coil. Radiation and conduction are the two components 

for heat transfer to the induction coil. The heat loss values are independent of the required RF power.

There are three dominant factors that influence the thermal losses from the heat pipe to the RF 

inductor: (1) Emissivity of the coil surface, (2) coil to work piece coupling gap, and (3) temperature of the 

heat pipe. Radiant heat transfer is mainly dependent upon the coil surface emissivity, and is proportional 
77

to the 4th power of the absolute temperature. Conductive heat transfer is dependent upon the coil to work 

piece coupling gap and the evaporator to induction coil temperature difference. Figure 31 shows heat loss 

to the RF coil, as a function of gap, for a heat pipe with a temperature of 1,373 K, based upon calculations 

made by Jim Martin of NASA. Heat Loss to RF Coil (W)

Gap Width Heat Pipe to RF Inductive Coil ID (inches)

Radiation Loss (W)

Gas Conduction Loss (W)

Total Heat Loss (W)

0 0.100 0.200 0.300 0.400 0.500 0.600

2000

1750

1500

1250

1000

750

500

250

0

Figure 31. Heat transferred from heat pipe to induction coil (curves based upon 

calculations and information provided by Jim Martin from NASA 

for 1,373 K heat pipe temperature).

Design of Assemblies

RF Assembly 1

RF assembly 1 consists of all G-series heat pipes. The atmosphere in the chamber is He-32%Ar at 

75 torr. All of these heat pipes should be at 1,273 K and the power transferred to the calorimeter should 

be 3,000 W. At these conditions, the thermal losses for a 0.25-in coupling gap will be ≈250 W. This means 

the required RF power will be 3,250 W for each heat pipe.

Since the power requirement to all heat pipes is the same, all of the induction coils should be of an 

identical design. The parameters of the three-turn coil with a Fluxtrol 50 concentrator, described earlier 

in this TP, fit well to the requirements for the G-series. The system is nearly linear and required voltage 

and current are proportional to the root square of the power. To deliver the required 3,250 W of RF power 

of to the heat pipe, each individual coil will require a voltage around 33 V and carry a current of around

1,450 A. The power in each inductor head will be ≈4,910 W.
78

To design the assembly, it is also necessary to take into account the busswork. The primary 

parameters for determining busswork performance are the busswork height and the gap between adjacent 

conductors. The conductor thickness, provided it is electrically thick, influences the mechanical strength 

and weight of the assembly. 

Taller busswork and smaller gaps are beneficial for reducing voltage drop. Optimal busswork, 

in terms of voltage drop, would be infinitely tall with zero gap. This is not practical and dimensions 

are required that fit well to the system size and available space. For the busswork height, it is natural to 

initially set it equal to the coil length (3 inches). The gap between the conductors should depend upon the 

breakdown voltage in this area.

Based upon the supplied Paschen curves, breakdown voltage in the He-30%Ar chamber at various 

gaps should be approximately as follows:

• 2-mm gap—250 V

• 3-mm gap—310 V

• 6-mm gap—450 V

Table 19 shows the electrical parameters for 3-in tall busswork carrying a current of 1,450 A 

at 50 kHz. 

Table 19. Electrical parameters per meter for 3-in-tall 

busswork carrying 1,450 A at 50 kHz.

Gap

(mm)

Current

(A)

Voltage Drop 

(V/m)

Losses 

(W/m)

Reactive P

(kVA/m)

2 1,450 17 3,110 24.4

3 1,450 23 3,040 33.9

6 1,450 42 2,900 60.8

A conceptual layout of the test chamber RF coil assembly is shown in figure 32. There are different voltages at various points within the RF assembly. Because the coils are connected in series to ensure 

uniform loading and insensitivity to the presence of a heat pipe, the voltage in area 1 is the highest and 

represents the full-voltage drop on all coils and busswork inside the chamber. The voltage in area 2 is 

significantly less than in area 1, because it does not include the voltage drop for the G1 and G5 heat pipe 

inductors, plus their respective connection zones. The voltage in area 3 is lower still, representing the connection zone voltage and the individual coil head voltage. If a uniform length connection buss were used, 

the RF assembly 1 area 3 voltage would be the same at all coils.
79

Area1

Area 3

Area 2

G1 G2

G3

G5 G4

A B

Figure 32. Conceptual layout of the heat pipe inductive coil assembly.

The voltage drop, losses, and reactive power in a given section of busswork are all directly proportional to the length of that section. For this reason, it is beneficial to make all the sections of busswork as 

short as possible. From a practical sense, the following need to be considered for the respective areas:

• Area 1—Distance from chamber ceiling/floor to assembly.

• Area 2—Space between coil heads.

• Area 3—Space for making electrical and water connections.

To calculate losses for the whole assembly, each of the areas must be assessed. The first step for 

area 3 is to determine the length and acceptable portion of the connecting busswork. Based upon estimates 

from coil manufacturing specialists, a 7.5-cm distance is a reasonable estimate for minimum length. The 

individual coil head voltages are 33 V. For this level of voltage, a 2- or 3-mm gap with break down voltages of 250 V and 310 V, respectively, can be safely used. The voltage drop would be less than 2 V for 

the 7.5-cm busswork, for a total section voltage of around 35 V. Losses in this section of busswork are

≈230 W.

At point B in figure 32, the coil voltage should be around 105 V (3×35 V). This voltage is still 

relatively low, and a 2- or 3-mm gap may be used in area 2. The length of area 2 should be equal to the OD 

of an induction coil plus sufficient space for limiting mutual inductance. Figure 32 and table 20 show that 

if the length of area 2 is 3.5 in (8.9 cm), there will be minimal variation in circumferential heating of the 

heat pipe. This means the voltage drop in area 2 will be around 2 V and losses will be ≈270 W.
80

Table 20. Electrical parameters of RF inductor assembly 1.

Component

Gap

(mm)

Length

(cm) Turns

Voltage

Drop (V)

Power

(W)

Reactive

Power (kVA)

G1 Inductor 6.4 NA 3 33 4,860 47.9

G1 Buss 3.0 7.5 NA 2 230 2.9

G2 Inductor 6.4 NA 3 33 4,860 47.9

G2 Buss 3.0 7.5 NA 2 230 2.9

G3 Inductor 6.4 NA 3 33 4,860 47.9

G3 Buss 3.0 7.5 NA 2 230 2.9

G4 Inductor 6.4 NA 3 33 4,860 47.9

G4 Buss 3.0 7.5 NA 2 230 2.9

G5 Inductor 6.4 NA 3 33 4,860 47.9

G5 Buss 3.0 7.5 NA 2 230 2.9

Area 2 3.0 8.9 NA 3 270 4.4

Area 1 6.0 7.5 NA 3 230 4.4

Total Value NA NA NA 180 25,950 263

At point A in figure 32, the coil voltage should be around 177 V (5×35 V+2 V). This voltage 

is probably too high to safely use a gap of only 2 mm, but 3 mm should be sufficient. If the distance from 

point A to the chamber feedthrough is assumed to be 7.5 cm, the voltage drop in this section should be 

around 2 V and the losses ≈230 W. If a 6-mm gap was used, the voltage drop would be around 3 V and 

losses ≈230 W.

Due to the small difference, it may be better to use the larger 6-mm gap in area 1 for a breakdown 

voltage close to 450 V and a higher safety factor. Total coil voltage would be 180 V and total inductor 

power would be ≈26 kW. The values for all components are summarized in table 20.

RF Assembly 2

RF assembly 2 consists of two G-series and three F-series (0, –1, –2) heat pipes. The atmosphere 

in the chamber is He-32%Ar at 75 torr. For all of these heat pipes, the power transferred to the calorimeter should be 3,000 W. Three heat pipes should be at 1,273 K and the other two heat pipes at 1,173 and

1,373 K, respectively. 

The temperature in the heat pipe has an influence upon the required RF power, because it changes 

the thermal losses from the heat pipe to the induction coil. As stated earlier, radiation heating is proportional 

to the 4th power of temperature and convective heating should be directly proportional to the temperature 

difference. For the two G-series heat pipes and the F(0) heat pipe, thermal losses with a 1⁄4-in gap would 

be 250 W, leading to a required RF power of 3,250 W—the same as RF assembly 1. For F(–1), with a 

temperature of 1,173 K, thermal losses would be reduced to 207 W, leading to a required RF power of 

3,207 W with the same 1⁄4-in coupling gap. For F(–2) with a temperature of 1,373 K, thermal losses would 

be 295 W with a required RF power of 3,295 W. The difference between the required RF power for this 

assembly is ±45 W or around 1.5%. Based upon the magnitude of this effect, it is better to maintain 
81

consistency by using the same inductor for each case, and balance the temperature with the calorimeter 

static gas gap by a slight adjustment of the coolant flow. Therefore, the RF assembly 2 design is identical 

to RF assembly 1.

RF Assembly 3

RF assembly 3 consists of five F-series (–3, 1, 2, 3, 4) heat pipes. The atmosphere in the chamber 

is He-32%Ar at 75 torr. All five of these pipes have at least one factor (temperature or power) different 

from the others in the test chamber. The required power and temperature for these heat pipes are detailed 

in table 21. 

Table 21. Description of RF assembly 3 heat pipes.

Heat

Pipe

Calorimeter 

Power

(W)

Heat Pipe 

Temperature 

(K)

F(–3) 1,000 1,273

F(1) 2,000 1,223

F(2) 4,000 1,223

F(3) 2,000 1,323

F(4) 4,000 1,323

In RF assembly 2, there was only a relatively small change in the required RF power for a

±100 K change in temperature. Heat pipes F(1) and F(3) represent a similar situation with a ±50 K temperature difference, and the same can be said of F(2) and F(4). For this reason, these heat pipes can be 

paired up and only three unique coils designs are required to satisfy the 1,000-, 2,000-, and 4,000-W

power levels. A mean heat pipe temperature of 1,273 K will be used for the 2,000- and 4,000-W heat pipes.

A conceptual layout of the RF assembly in the test chamber is shown in figure 33. The coils are all 

connected in series to ensure insensitivity to the presence of a heat pipe, and the coil length maintained 

constant to keep power densities proportional to heat pipe power. Therefore, the three available methods 

to control the power delivered to the respective heat pipes include: (1) Number of coil turns, (2) coupling 

gap between coil and heat pipe, and (3) distance between the coil liner and heat pipe. 

When the coil length, space factor (ratio of copper length to total coil length), and coupling gap are 

held constant, the power induced in the heat pipe will be proportional to the ratio of the number of turns 

squared. This should be the primary method of power balance between the different heat pipes. 
82

Area 1

Area 3

Area 2

F2 F1

F(–3)

F4 F3

A B

Figure 33. Conceptual layout of the RF inductor assembly 3.

The coupling gap also influences the power induced in a given heat pipe, but not as strongly as the 

number of turns, since there are the same number of ampere turns. As the coupling gap is increased, the 

power will slowly decrease. The opposite will occur if the coupling gap is decreased. At the same time 

though, as the coupling gap increases, the coil voltage will dramatically increase, leading to higher reactive powers and larger gaps required for the busswork. Finally, if the coupling gap gets much larger than 

1⁄4 in, heating of the calorimeter will increase, and power-density uniformity in the coil length will decrease.

The last factor, distance between the coil liner and heat pipe, is new, and is used to match the 

required RF power to the induced power from the inductor, in effect, adjusting the thermal losses. For this, 

a new factor is introduced called the potting gap, to separate this value from the classic electromagnetic 

coupling gap. The two parameters are shown in figure 34.

An iterative process to adjust the three factors was used until a solution was achieved that balanced 

these three factors. The assumption was made that the surface temperature of the liner would be 350 K in 

all cases. This will not be the case in reality, because as the temperature difference between the coil liner 

and the coil copper ID grows, the liner temperature will increase. This will have some effect upon the 

conductive losses but the difference should be relatively small in terms of required RF power, provided 

the liner has reasonably good thermal conductivity.

The final design utilizes a three-turn inductor for the 1,000-W heat pipe (F–3), fourturn inductors for the 2,000-W heat pipes (F1 and F3), and five-turn inductors for the 4,000-W heat 

pipes (F2 and F4). The necessary design factors are shown in table 22. The desired RFP in the table is 

the required RF power based upon adding the heat pipe/calorimeter power to the thermal losses. The 

actual RFP is the value of power from the computer simulation for that geometry. The goal is for these 
83

Coupling Gap

Potting Gap

Figure 34. Conceptual induction coil head cross section.

two values to converge. The coil parameters in table 22 achieve the desired conformance within a convergence of approximately 1%. The values for the actual heat pipe RF assembly 3 will be slightly larger due 

to different heat pipe temperatures, but this can be compensated for by adjusting calorimeter properties.

Table 22. Parameters of RF assembly 3.

Cal. 

Power 

(W)

Coup. 

Gap 

(mm)

Potting 

Gap 

(mm)

Therm. 

Loss 

(W)

Desired 

RFP 

(W) Turns

Actual 

RF Power 

(W)

Ind. 

Power 

(W)

Coil I 

(A)

Coil U 

(V)

1,000 6.4 3.2 490 1490 3 1490 2190 990 22

2,000 6.4 2.0 680 2680 4 2660 3920 990 39

4,000 5.4 5.4 330 4330 5 4360 6260 990 52

The mean coil voltages for RF assembly 3 are higher due to the larger turns number. On the 

other side, the coil current is significantly lower than in RF assemblies 1 and 2 (990 A compared to 

1,450 A). This means that the voltage drop in the busswork will be lower proportionally, and the losses 

in the busswork will drop as the square of current, allowing for the use of larger gaps without significant 

penalty. 
84

The same section lengths used for RF assemblies 1 and 2 can be used to calculate the whole 

assembly. The difference in RF assembly 3 is that there are new voltages for each of the different coil 

heads. Fortunately, even the highest voltage (52.1 V) is well below the breakdown voltage for the 

2-mm gap (250 V), allowing the use of uniform area 3’s for all cases. The voltage drop in area 3 of the 

busswork will be around 1.4 V for each inductor head, due to the lower coil current. Losses in these sections of busswork are ≈110 W each.

To determine the voltage at point B in figure 33, the final arrangement of the inductors must be 

decided. Point A will see the same voltage regardless of the inductor/heat pipe arrangement. The most 

favorable arrangement for point B is to have the lowest voltage coils in the last three positions. This 

means F(–3), F(1), and F(3) heat pipes should be placed here to reduce area 2 busswork requirements. The 

voltage at point B should be around 104 V (22 V+2×39 V+3×1.4 V), which is still relatively low, and a 

2- or 3-mm gap may be used in area 2. The voltage drop in area 2 would be around 1.7 V with losses of 

≈130 W.

The point A coil voltage (fig. 33) should be around 212 V (104 V+2×1.4 V+1.7 V+2×52 V). This 

voltage is probably too high to safely use a gap of only 2 mm, but 3 mm should be sufficient. Assuming 

the distance from point A to the chamber feedthrough is 7.5 cm, the voltage drop in this section would be 

around 1.4 V and the losses ≈110 W. The voltage drop using a 6-mm gap would be around 2 V and losses 

≈110 W. 

Due to the small difference, it may be better to use the larger 6-mm gap in area 1 for a higher safety 

factor, with a breakdown voltage close to 450 V. The total coil voltage would be 214 V and the total inductor power would be ≈23 kW. Values for all of the components are summarized in table 23.

RF Assembly 4

RF assembly 4 is much simpler than the previous assemblies, because it consists of a single inductor and heat pipe (F–4) as shown in the conceptual layout in figure 35. The heat pipe power is 5,000 W 

with a He-6%Ar chamber atmosphere, instead of the He-32%Ar gas mixture used in the other test chamber setups. Breakdown voltages for this atmosphere are lower than for the other chambers, but it should 

not present a problem since only one coil and buss system are required. 

In addition, this unit is connected to a smaller power supply, where lower voltages are favorable 

for coupling. The optimal voltage for matching to this unit is in the 50–100 V range. For this reason, the 

same induction coil used for the F4 and F5 heat pipes fits well. It is only necessary to recalculate the values 

for the new power level, as shown in table 24.

To assess the losses on the complete assembly, only a single section of busswork needs to be 

evaluated. The busswork should be ≈6 in (15 cm) long to center the coil in the test chamber. Due to the 

relatively low voltage, 2- or 3-mm busswork can be used. Voltage drop in the busswork will be around 

3.1 V, and losses in these busswork sections are ≈270 W. Details of this assembly are contained in table 25.
85

Table 23. Electrical parameters of RF inductor assembly 3.

Component

Gap

(mm)

Length

(cm) Turns

Voltage Drop

(V)

Power

(W)

Reactive Power 

(kVA)

F–3 Inductor 6.4 NA 3 22 2,190 21.8

F–3 Buss 3.0 7.5 NA 1.4 110 1.4

F1 Inductor 6.4 NA 4 39 3,920 38.6

F1 Buss 3.0 7.5 NA 1.4 110 1.4

F3 Inductor 6.4 NA 4 39 3,920 38.6

F3 Buss 3.0 7.5 NA 1.4 110 1.4

F2 Inductor 5.4 NA 5 52 6,260 51.5

F2 Buss 3.0 7.5 NA 1.4 110 1.4

F4 Inductor 5.4 NA 5 52 6,260 51.5

F4 Buss 3.0 7.5 NA 1.4 110 1.4

Area 2 3.0 8.9 NA 1.7 130 1.7

Area 1 6.0 7.5 NA 1.4 110 2

Total Value NA NA NA 212 23,340 213

F(–4)

Figure 35. Conceptual layout of the RF inductor assembly 4.

Table 24. Recalculating five-turn inductor for use in RF assembly 4 configuration.

Cal. P

(W)

Coup. 

Gap

(mm)

Pot. Gap 

(mm)

Therm. 

Loss

(W) Turns

Required 

RF Power 

(W)

Electrical 

Efficiency

Ind. 

Power

(W)

Coil I

(A)

Coil U

(V)

4,000 5.4 5.4 330 5 4,360 69.6% 6,260 990 52

5,000 5.4 5.4 330 5 5,360 69.6% 7,650 1,090 57.5

Table 25. Electrical parameters of RF inductor assembly 4.

Component

Gap 

(mm)

Length 

(cm) Turns

Voltage Drop 

(V)

Power 

(W)

Reactive 

Power (kVA)

F–3 Inductor 5.4 NA 5 57.5 7,650 62.7

F–3 Buss 3.0 15 NA 3.1 270 3.4

Total Value NA NA NA 60.6 7,920 66.1
86

Summary

Four RF assemblies for heat pipe testing have been designed. The operational parameters of each 

set of RF assemblies matches well to the power supply that they are connected. The required voltages for 

all test chamber configurations are at reasonable levels and are well below, typically by a factor of 2, the 

breakdown levels predicted by the Paschen voltage breakdown curves. 

Engineering of the final assemblies is still required before fabrication can begin. Also, the design 

for connecting the power supplies to the chambers must still be finalized. This requires input from NASA 

on the complete system layout and exact RF power supply output parameters. External to the test chambers, few space restrictions should allow the power supplies to be closely coupled, lowering transmission 

losses. In addition, the projected power requirements are well within the range of the 50 kW units identified for this task.

Table 25 can be used to effectively determine the effect the busswork will have on the electrical 

parameters of RF assemblies 1 and 2. The values only need to be recalculated based upon the length. The 

RF assembly 3 voltage drop per meter and power loss per meter should be multiplied by 0.68, due to the 

lower current, while RF assembly 4 values should be multiplied by 0.75.
87

APPENDIX M—MO-44.5%RE PLATE MATERIAL ANALYSIS

Rhenium Alloys, Inc. provided the following material information for the Mo-44.5%Re plate 

material procured to support welding tests. The material consisted of two plates with dimensions of 12 in 

length by 3 in width by 0.04 in thickness.
88
89
90
91
92
93
94
95

APPENDIX N—MO-44.5%RE CLEANING PROCEDURE FOR WELDING

The typical procedures used to clean or process Mo-44.5%Re samples prior to welding are as

follows:

Pickling for Mo-Re alloys

(1) Handle with clean gloves and appropriate tools, such as tweezers, forceps, etc.

(2) Wipe with acetone/alcohol to remove grease, permanent marker, etc.

(3) Submerge in acetic, nitric, and HF using a 10:4:1 ratio to remove oxide scale (typically

<1 min, based on the level of oxidation).

(4) Submerge as needed in pure HCL to remove any visible staining (typically <1 min, based on 

visual observation).

(5) Water rinse.

(6) Acetone/alcohol rinse.

(7) Dry using heat gun or forced air.

(8) Visually inspect the part for remaining contaminants/oxide layers and if necessary, repeat 

pickling steps (2) through (7).

Degas Anneal

(1) 800–1,000 °C for 1 hr.

(2) H2 or vacuum furnace at 1×10–6 torr.

(3) Avoid having samples sit for more than a few days. Store samples in a dry, controlled

atmosphere.

(4) Wipe samples with alcohol or acetone prior to welding.
96

APPENDIX O—MO-44.5%RE 0.5-INCH-DIAMETER ROD STOCK MATERIAL ANALYSIS

Rhemium Alloys, Inc. provided the following information for the Mo-44.5%Re 0.5-in diameter 

rod stock material procured for the heat pipe envelopes: 
97
98
99
100
101
102
103
104

APPENDIX P—MO-44.5%RE 0.625-INCH-DIAMETER ROD STOCK MATERIAL ANALYSIS

Rhenium Alloys, Inc. provided the following information for the Mo-44.5%Re 0.625-in diameter 

rod stock material procured for the heat pipe envelopes:
105
106
107
108
109
110
111
112

APPENDIX Q—CHEMICALS USED FOR VANADIUM WIRE EQUILIBRATION 

MATERIAL CLEANING

Cleaning chemicals, concentration ratios, and mixtures used for each of the specific materials 

used in performing the V-wire equilibration technique.
113

APPENDIX R—VANADIUM WIRE EQUILIBRATION OPERATIONAL PROCEDURE

Raw Material Preparation

Materials required to perform the V wire equilibration analysis method: 

(1) 201 series Ni tubes: Diameter =1/4 in (0.035-in wall)×L=10 in; bent as shown in 

figure 36.

(2) 201 Ni tubes: Diameter = 1/4 in (0.035-in wall)×L = 6.35 in.

(3) Mo wires: Diameter = 0.762 mm×L=118 mm.

(4) V wires: Diameter = 0.25 mm×L=130 mm.

(5) SS–4H Swagelok SS valves; three per setup.

Figure 36. Typical Ni tube.

Pickling Procedures

The following process is applied to the experiment components to minimize the risk of 

contamination. Pickling methods, conducted in a fume hood as shown in figure 37, are necessary to 

remove surface organics and oxide scales.

Several procedural steps require ultrasonic cleaning (fig. 38) with various solutions, some of 

them being highly corrosive. To protect the ultrasonic cleaners, they are filled with deionized water and 

components are placed within glass or low-density polyethylene (LDPE) vials containing the required 

cleaning solutions. Vials are then immersed in the ultrasonic cleaner.
114

Figure 37. Fume hood and associated pickling equipment.

 

Figure 38. Branson ultrasonic cleaners.

Bellows Sealed Stainless Steel Valves

High-density polyethylene (HDPE) containers should be used, due to the caustic nature of the 

chemicals used to pickle the SS valves. Clean SS forceps should be used to manipulate the components. 

To prevent contamination, rinse forceps in distilled water after immersion in any substance before reusing 

them to manipulate the components. 

(1) Wrap the valve handle in plastic and secure with a zip tie to prevent infiltration of liquid or 

vapor into the valve handle that can react with valve lubricant (fig. 39).

Protective 

Plastic 

Sleeve

Zip Tie Fill 

Level

Figure 39. Valve prepared for pickling.
115

 (2) Immerse in Freon and ultrasonically clean for 5 min. 

 (3) Immerse in caustic solution consisting of 11 parts (by volume) deionized water, 1 part

sodium hydroxide (NaOH), and 1 part hydrogen peroxide (H2O2) and ultrasonically clean for 5 min.

 (4) Immerse in hot deionized water and ultrasonically clean for 5 min.

 (5) Repeat steps (2) and (3) three times.

 (6) Rinse in hot deionized water.

 (7) Immerse in ethanol (CH3CH2OH) and ultrasonically clean for 5 min.

 (8) Place in plastic bag and seal.

 (9) Transport plastic bag for vacuum bakeout.

(10) Vacuum bakeout at a pressure of 10–6 torr and a temperature of 200 °C for 2 to 4 hr.

201 Nickel Tubes

Due to the acidic nature of the chemicals used to pickle the Ni tubes, use glass containers and 

clean PTFE Teflon®-coated forceps to manipulate the components. Rinse forceps in distilled water after 

substance immersion before reuse to prevent contamination.

 (1) Immerse in hot water bath for 5 min to heat the components.

 (2) Immerse in solution consisting of sulfuric acid (H2SO4) (148 mL, 35 wt%), nitric acid 

(HNO3) (229 mL, 30 wt%), sodium chloride (NaCl) (3.7 g), and deionized water (H2O) (123 mL) and 

ultrasonically clean for 2 min (room temperature).

 (3) Rinse components in distilled (deionized) water.

 (4) Immerse in ammonia (NH3) for 10 s to neutralize the part.

 (5) Rinse in distilled water and allow to dry.

 (6) Place in plastic bag, seal, and transport for vacuum bakeout.

 (7) Vacuum bakeout at a pressure of 10–6 torr and a temperature of 800 °C for 4 hr in a vacuum 

baking chamber. The tubes will have a clean, lustrous finish (fig. 40). 
116

Figure 40. Ni tubes postprocessing.

Electropolishing of Molybdenum and Vanadium Wire

This process is in part based on ASTM C997–83, sections 65 to 74. The electrolysis cell consists 

of a 1,000-mL beaker with a platinum cathode (figs. 41 and 42). The lead from this electrode is insulated 

with shrink-fit tetrafluoroethylene (TFE)-fluorocarbon or polyethylene. Anode contact is made through 

spring-loaded forceps. Direct current is supplied from a power supply providing up to 4 A at 4 to 25 V.

A magnetic TFE-fluorocarbon-coated stirring bar was used. Use clean PTFE Teflon-coated forceps to

manipulate components. Rinse forceps in distilled water after substance immersion.

Clamp

Cathode

Power Supply Magnetic Stirrer

+ −

Vanadium Wire 

Sample

Electrolysis Cell

 

Figure 41. Typical electropolishing apparatus. Figure 42. Buehler® Electromet III 

electropolisher/etcher.

(1) Obtain several control lengths (L=110 mm) and several test lengths (L=130 mm) of asreceived V wire.

(2) Create a small bend in the last 3 mm using forceps (fig. 43).

(3) Store one control wire in a vial.
117

Figure 43. Typical as-received V wire sample.

(4) Create electropolishing solution by cautiously adding 200 mL of concentrated sulfuric acid 

(H2SO4) to 800 mL of chilled methanol (CH3OH) while stirring. The reaction is exothermic, therefore 

it is important to keep the methanol chilled and slowly mix the two to prevent boiling and splattering.

Figure 44 shows a beaker of methanol chilled in an ice-water bath.

Figure 44. Methanol-filled beaker in ice bath.

(5) Create a loop from V wire that will be clamped in the spring-loaded anode forceps, from which 

the sample V wire can hang, as shown in figure 45. This loop allows for the full immersion of the sample 

V wire in the electrolytic solution, significantly reducing the possibility of contamination.

V Wire Test 

Sample

V Wire 

Suspension 

Loop

Figure 45. Vanadium wire suspension loop and sample wire.
118

(6) Fill the glass electrolytic cell with electropolishing solution.

(7) Immerse each wire (four control, three test) in acetone ([CH3]2CO) (PTFE tray) and ultrasonically clean for 5 min.

(8) Remove from acetone bath and allow drying to degas.

(9) Store a second control sample in a vial.

(10) Grasp the loop with the clamp and adjust the anode position so that the loop tip is just in 

contact with the liquid and the wire is centered in the cell (fig. 46).

Fill Level

Vanadium 

Anode

Platinum 

Cathode

Figure 46. Anode and cathode positioning.

(11) With the stirrer at a low speed, apply current and adjust the voltage to provide a current of 5 

to 10 mA/mm for 0.25-mm wire. Avoid electrical sparks when electropolishing to prevent ignition of the 

polishing solution.

(12) Electropolish each wire for 3 min, 30 s to reduce the diameter from 0.25 to 0.22 mm.

(13) Remove wire from electropolish solution and allow to dry.

(14) Measure the diameter of the wire after etching using calipers, shown in figure 47.

Figure 47. Mitutoyo CD 12-in digital calipers.
119

(15) Store a third control wire in a vial.

(16) Immerse wire in deionized water beaker and ultrasonically clean for 30 s.

(17) Remove wire from deionized water bath and allow to dry.

(18) Store a fourth control wire in a vial.

(19) Immerse in methanol and ultrasonic cleaner for 30 s.

(20) Remove wire from methanol bath and allow to dry.

(21) Store a fifth control wire in a vial.

(22) Place each test wire in a vial and backfill each vial with Ar.

(23) Measure the weight of each control and test wire using an analytical balance, shown in 

figure 48.

Figure 48. Denver Instruments M–220D analytical balance.

(24) Transport test vials purge bag for vacuum degas, at room temperature.

(25) Establish a pressure of 10–6 torr for 24 hr to degas at room temperature.

(26) Repeat the complete procedure to prepare the Mo wires.

Vacuum Bakeout Procedures

The vacuum bakeout system is shown in figure 49.

Ni tubes and Mo wires are placed inside the vacuum tube (fig. 50). The process to bakeout the SS 

valves is described later.

Vacuum is achieved by linking a Varian TriScroll 300 rough vacuum pump (fig. 51) in series with 

a Varian V70 turbomolecular vacuum pump (fig. 52), an oil-free vacuum system.
120

Vacuum 

Tube

Furnace

Thermocouple 

Reader

Roughing 

Vacuum Pump

Helium Leak 

Detector

Multi Gauge 

Controller

Turbo Pump Turbo Pump Controller

Ionizing Gauge

Figure 49. Vacuum bakeout system.

Figure 50. Vacuum tube assembly.

 (a) (b) 

Figure 51. Roughing pump. Figure 52. Turbopump (a) and with controller (b).
121

Vacuum level is monitored with a Varian 564 BA ionizing vacuum gauge (fig. 53) used in

conjunction with a Varian multigauge reader (fig. 54).

 

Figure 53. Ion gauge. Figure 54. Multigauge reader.

A Varian 979 He leak detector (fig. 55) and helium source (fig. 56) were used to verify a leak-tight 

seal at all connection points.

 

 Figure 55. Leak detector. Figure 56. He source.

After components of the same material are placed in the bakeout system vacuum tube and all connections leak checked, the vacuum tube was inserted in an Omegalux® LMF–A550 furnace, as shown 

in figure 57. Since the door has to be open to accept the vacuum tube, an insulating wall was fabricated 

of Insulfrax fibrous alumina blanket material and held in place with SS wire. Vacuum tube temperature 

is monitored using two type-K thermocouples connected to an Omega HH509 hand-held thermocouple 

reader (fig. 58).

After the components have been baked, the vacuum tube isolation valve is closed and the tube is 

disconnected from the rest of the vacuum system. The tube is then transported into a glove box backfilled 

with Ar from a standard-K bottle, as shown in figure 59, to minimize oxidation and moisture absorption 

when parts are removed.
122

 

Figure 57. Vacuum tube in furnace. Figure 58. Thermocouple reader.

Figure 59. Ar glove box.

Using a temporary inert environment glove box, the vacuum baked components were removed 

from the tube assembly and placed in a purge bag. The bag was then transferred from the glove box to the 

sodium fill machine, a Vacuum Atmospheres Company (VAC) controlled atmosphere glove box. 

Prior to vacuum baking, the SS valves are connected in series using 1/4 in (0.035-in wall) 304 

SS tube stubs. One end is plugged while the other is connected to a 2.75-in ConFlat® flange with a 

compression-fitting adapter. The bakeout approach uses the same vacuum, thermal monitoring, and leak 

check system previously described.

The assembly is wrapped in heater tape and several layers of aluminum foil insulation, and then 

vacuum baked. Once the vacuum baking is completed, they are closed and disconnected from the flange 

and placed in a bag backfilled with Ar, as shown in figure 60. The valves are then transferred to the sodium 

fill machine VAC glovebox for assembly.
123

Figure 60. SS valves after vacuum bake.

Vanadium Wire Sample Assembly

(1) Weigh each component separately.

(2) Carefully bend the Mo wire so that it has a slight curve.

(3) Add two notches, 90 mm apart, by scratching the Mo wire.

(4) Wrap the V wire around the Mo wire at the notches, forming a bow, as shown in figure 61.

Figure 61. Wire bow.

(5) Ultrasonically clean in methanol for 5 min.

(6) Remove from bath and allow to dry.

(7) Place in vacuum chamber and degas at ≈5×10–8 torr for 24 hr at room temperature.

(8) Place assembled bow in inert sodium fill machine VAC glovebox.

(9) Inside the glovebox, insert the wire bow into the Ni tube, as shown in figure 62.

Figure 62. Bow with tube.
124

Sodium Vessel Sample Tube Assembly (conducted in the sodium fill machine VAC glovebox)

 (1) Assemble sample tubes, charging vessels, valves, and thermocouples as shown in figure 63.

Figure 63. Assembled sample tube.

 (2) Weigh the completed assembly.

 (3) Close all valves.

 (4) Connect the assembly to the glove box high vacuum system at V1.

 (5) Open V1 and V2 to evacuate the system into the 10–5 torr range.

 (6) Heat assembly to 200 °C, and then allow to cool to ambient temperature.

 (7) Close V1 and V2 and disconnect from vacuum system.

 (8) Connect V1 to the glove box Na fill stem.

 (9) Connect V3 to the glove box vacuum source.

(10) Wrap the assembly in two heater tapes (H1 and H2), as shown in figure 64.

Figure 64. Tube test configuration.

Sample Tube Charging With Sodium

 (1) Heat Na supply system to 150 °C in preparation of sample tube charging.

 (2) Open all valves to evacuate the system to 10–5 torr range.

 (3) Close V1.
125

(4) Note temperature: TC1_____ TC2_____.

 (5) Heat H1 to 140 °C and H2 to 125 °C.

 (6) Close all valves.

 (7) Open Na fill machine isolation valve.

 (8) Open valve V1.

 (9) Check TC1 and TC2. If TC1 and TC2 read 150 °C, the vessel is charged.

(10) Close V1.

(11) Close Na fill machine isolation valve.

(12) Open V2.

(13) Check TC3, TC4, and TC5. If TC3, TC4, and possibly TC5 read 140 to 150 °C, the wire tube 

is charged. If not, the tube should be tapped to help transfer the Na.

(14) After tapping, the Na should flow toward the end of the tube near TC6, and TC3 should cool, 

indicating that the section from TC3 to V2 is clear for crimping.

(15) Close V2.

(16) Turn off H1 and H2.

(17) Allow the sample tube to cool to ambient temperature.

(18) Disconnect the sample tube from the Na fill stem and replace fill stem plug.

(19) Weigh assembly. If additional Na is required, repeat from step (2).

(20) Remove from glove box.

(21) Using a hydraulic press, crimp both ends of the tube as shown in figure 65. (The crimp should 

allow for 0.002 in of plastic deformation.)

Figure 65. Tube processing—crimp.
126

(22) Place assembly within the EB welder, create two fusion zones on the crimps, as shown in 

figure 66 (adjust the current to achieve near-full penetration: Setting_______).

Figure 66. Tube processing—EB weld.

(23) Use the EB welder to make a third pass, cutting off the excess as shown in figure 67 (adjust 

the current to fully penetrate: Setting_____). 

Figure 67. Tube processing—cutoff.

(24) Weigh the sample tube, charge vessel, and cut off V3 end.

(25) Using a TIG welder, trace over the cut-off crimped ends created by the EB welder, building 

up the weld creating a nugget (should be performed in the VAC glove box).

(26) Weigh the sample tube.

(27) Place the sample tube into a purge bag.

(28) Transfer container to the tube furnace.

Sample Tube Heating to Equilibration Temperature

(1) Transfer the sample tube from the bag and place in the tube furnace, as shown in figure 68.

Figure 68. Tube processing—furnace heating.
127

(2) Evacuate the tube furnace to 10–6 torr.

(3) Heat the tube furnace to 750 °C for 4 hr to reach chemical equilibrium.

(4) Allow the furnace to cool to ambient temperature.

(5) Remove the sample tube from tube furnace and place in a bag.

(6) Transport to VAC glove box.

Wire Bow and Sodium Separation

(1) Inside the glove box, remove the sample tube from the bag.

(2) Cut both ends off the sample tube just past TC3 and TC4, using tube cutters.

(3) Attach the charge vessel and V3 at either end of the tube, as shown in figure 69.

Figure 69. Tube processing—wire removal.

(4) Wrap the assembly in heater tape.

(5) Close all valves.

(6) Connect V2 to the glove box vacuum source.

(7) Heat the system to 150 °C.

(8) Open V2 to evacuate the system.

(9) Close V2 once a vacuum level of 10–4 torr is established.

(10) Open V1 followed by V3 to transfer Na from tube to vessel.

(11) Vibrate/tap the surface of the sample tube to agitate the Na, causing it to flow from the bow 

and tube.

(12) Monitor thermocouple readings (TC3 and TC4 should drop, while TC1 and TC2 should 

increase, indicating that the Na has transferred from the sample tube to the charge vessel).
128

(13) Close V1 and V3.

(14) Allow system to cool to ambient temperature.

(15) Remove V3 from the tube.

(16) Remove bow from the tube using forceps. If the wire bow does not pull free easily, reheat 

it to about 150 °C and attempt again.

(17) Separate V wire from Mo wire by unraveling the V wire.

(18) Weigh each component separately.

(19) Dissolve the residual Na adhering to the V wires in about 1,000 mL of technical-grade 

ethanol. The large volume of ethanol prevents excessive heating of the wires.

(20) Rinse wires with water and allow the wires to dry.

Note: For the rest of the procedure, wires must be handled with clean ceramic forceps.

(21) Make cuts at least 3 mm from each bend (only straight portions are used for analysis).

(22) Weigh each V wire piece separately.

(23) Separate wires for archival storage from those for immediate analysis.

(24) Store the archival and test wires in capped vials that are properly identified.

(25) V wires can be submitted for LECO gas-fusion analysis to determine oxygen content.
129

APPENDIX S—VANADIUM AND MOLYBDENUM WIRE SAMPLE 

PREPARATION RESULTS

Sample of V and Mo wires were processed to evaluate the operational procedures with results, as 

listed in tables 26–28. 

Table 26. Data sheet for V wire samples.
130

Table 27. Data sheet for V wire test segments.
131

Table 28. Data sheet for Mo wire test holders.
132

REFERENCES

 1. “Standard Practice for Liquid Sodium Corrosion Testing of Metals and Alloys,” ASTM 

G68–80, ASTM International, West Conshohocken, PA, 1980.

 2. Martin, J.J.; Reid, R.S.; and Bragg-Sitton, S.M.: “Design of Refractory Metal Life Test Heat Pipe and 

Calorimeter,” NASA/TP—2010–216435, Marshall Space Flight Center, AL, August 2010.

 3. Martin, J.J.; and Reid, R.S.: “Refractory Metal Heat Pipe Life Test—Test Plan and Standard Operating Procedures,” NASA/TP—2010–216452, Marshall Space Flight Center, AL, December 2010.

 4. Martin, J.J.; Bragg-Sitton, S.M.; Reid, R.S.; et al.: “Design of Refractory Metal Heat Pipe Life 

Test Environmental Chambers, Cooling System, and Radio Frequency Heating System,” NASA/

TP—2011–216456, Marshall Space Flight Center, AL, February 2011.

 5. Verma, M.P.: “Steam Tables for Pure Water as an ActiveX Component in Visual Basic 6.0,” Computers & Geosciences, Vol. 29, pp. 1155–1163, 2003.

 6. Incoropera, F.P.; and De Witt, D.P.: Fundamentals of Heat and Mass Transfer, 2d Edition, John 

Wiley & Sons, 1985.

 7. Wadsworth, J.; Nieh, T.G.; and Stephens, J.J.: “Dilute Mo-Re Alloys—A Critical Evaluation of Their 

Comparative Mechanical Properties,” Scripta Metallurgica, Vol. 20, No. 5, Pergamon Press Ltd, 

pp. 637–642, 1986. 

 8. Ammon, R.L.; and Buckman, Jr., R.W.: “Observations on the As-Welded (GTAW) Bend Ductility 

of Mo-13% Rhenium Alloy,” Space Nuclear Power Systems 1986, M.S. El-Genk and M.D. Hoover 

(eds.), Orbit Book Company, Inc., Malabar, FL, pp. 283–289, 1987.

 9. Morito, F.: “Structures and Properties of Molybdenum-Rhenium Alloys,” Rhenium and Rhenium 

Alloys, The Minerals, Metals, & Materials Society, B.D. Bryskin (ed.), pp. 559–568, 1997.

10. Kramer, D.P.; Ruhkamp, J.D.; McNeil, D.C.; et al.: “Investigation of Mo-44.5%Re as Cell Wall 

Material in an AMTEC Based Space Power System,” Space Technology and Applications International Forum (STAIF–2000), M.S. El-Genk (ed.), American Institute of Physics, New York, NY, AIP

Conference Proceedings No. 504, Vol. 2, pp. 1402–1407, 2000.
133

11. Moore, J.P.; King, J.F.; DiStefano, J.R.; and Ohriner, E.K.: “Production and Properties of 

Mo-41%Re for AMTEC Cell Construction,” Space Technology and Applications International Forum (STAIF–2002), M.S. El-Genk (ed.), American Institute of Physics, New York, NY, 

pp. 963–971, 2002.

12. Hooper, A.J.; and Trevillion E.A.: “Oxygen Analysis of Sodium by Equilibration with Vanadium: An 

Assessment,” Journal of Nuclear Materials, Vol. 48, pp. 216–222, 1973.

13. Keough, R.F.: “Evaluation of the Vanadium Wire Equilibration Method for Determining Oxygen in 

Sodium,” Journal of Nuclear Materials, Vol. 75, pp. 294–296, 1978.

14. Smith, D.L.; and Lee, R.H.: “Characterization of the Vanadium-Wire Equilibration Method for Measurement of Oxygen Activity in Liquid Sodium,” ANL–7891, Argonne National Lab, IL, 16 pp.,1972.

15. “Standard Test Methods for Chemical and Instrumental Analysis of Nuclear-Grade Sodium and Cover 

Gas,” ASTM C 997–83 (Reapproved 1993), ASTM International, West Conshohocken, PA, 1993.
134

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Closeout Report for the Refractory Metal Accelerated Heat 

Pipe Life Test Activity

J. Martin, R. Reid, E. Stewart, R. Hickman, and O. Mireles

George C. Marshall Space Flight Center

Huntsville, AL 35812

National Aeronautics and Space Administration

Washington, DC 20546–0001

Unclassified-Unlimited

Subject Category 20

Availability: NASA CASI (443–757–5802)

Prepared by the Propulsion Research and Technology Branch, Engineering Directorate 

M–1353

Technical Publication

NASA/TP—2013–217477

alkali metal, sodium, heat pipe, refractory metal, molybdenum, rhenium, radio frequency heating, fission 

power system, nuclear, life testing

01–01–2013

UU 154

STI Help Desk at email: help@sti.nasa.gov

NASA

U

 With the selection of a gas-cooled reactor, this heat pipe accelerated life test activity was closed out and its resources redirected. The 

scope of this project was to establish the long-term aging effects on Mo-44.5%Re sodium heat pipes when subjected to space reactor temperature and 

mass fluences. To date, investigators have demonstrated heat pipe life tests of alkali metal systems up to ≈50,000 hours. Unfortunately, resources have 

not been available to examine the effect of temperature, mass fluence, or impurity level on corrosion or to conduct posttest forensic examination of heat 

pipes. The key objective of this effort was to establish a cost/time effective method to systematically test alkali metal heat pipes with both practical and 

theoretical benefits. During execution of the project, a heat pipe design was established, a majority of the laboratory test equipment systems specified, 

and operating and test procedures developed. Procurements for the heat pipe units and all major test components were underway at the time the stop 

work order was issued. An extremely important outcome was the successful fabrication of an annular wick from Mo-5%Re screen (the single, most 

difficult component to manufacture) using a hot isostatic pressing technique. This Technical Publication (TP) includes specifics regarding the heat pipe 

calorimeter water-cooling system, vendor design for the radio frequency heating system, possible alternative calorimeter designs, and progress on the 

vanadium equilibration technique. The methods provided in this TP and preceding project documentation would serve as a good starting point to 

rapidly implement an accelerated life test. Relevant test data can become available within months, not years, and destructive examination of the first 

life test heat pipe might begin within 6 months of test initiation. Final conclusions could be drawn in less than a quarter of the mission duration for a 

long-lived, fission-powered, deep space probe.

U U

STI Help Desk at: 443-757-5802

National Aeronautics and

Space Administration

IS20

George C. Marshall Space Flight Center

Huntsville, Alabama 35812