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i

NASA/TP—2013–217487

Testing of an Annular Linear Induction Pump 

for the Fission Surface Power Technology 

Demonstration Unit

K.A. Polzin, J.B. Pearson, and K. Webster

Marshall Space Flight Center, Huntsville, Alabama

T.J. Godfroy

Maximum Technology Corporation, Huntsville, Alabama

J.A. Bossard

BSRD, LLC/Yetispace, Inc., Huntsville, Alabama

August 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

443–757–5802

This report is also available in electronic form at

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

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 Fission Surface Power Technology Development .......................................................... 1

1.2 Nonnuclear Testing at Marshall Space Flight Center .................................................... 2

2. ANNULAR LINEAR INDUCTION PUMP TEST CIRCUIT SETUP ........................... 3

2.1 Overview of Components Unchanged From Previous Annular Linear 

Induction Pump Test Circuit Experiments .................................................................... 3

2.2 Components in the System Changed for the Present Work ........................................... 4

3. PERFORMANCE TEST DATA ........................................................................................ 8

4. CONCLUSIONS ................................................................................................................ 14

APPENDIX A—IMMERSION HEATER PRESSURE DROP ANALYSIS ......................... 15

A.1 Flow Model ................................................................................................................. 15

A.2 Computational Results ................................................................................................ 16

APPENDIX B—HEATER ELBOW ASSEMBLY .................................................................. 20

REFERENCES ....................................................................................................................... 21
iv
v

LIST OF FIGURES

 1. Schematic of the ALIP test circuit configured for TDU ALIP testing ......................... 3

 2. Three-dimensional view of elbow heater section .......................................................... 5

 3. Raw data from operation at NaK temperatures of 125 oC and pump frequencies 

of (a) and (b) 40 Hz, (c) and (d) 55 Hz, and (e) and (f) 70 Hz operating on either 

the VFD (black markers) or VFS (gray markers) ......................................................... 9

 4. Raw data from operation at NaK temperatures of 325 oC and pump frequencies 

of (a) and (b) 40 Hz, and (c) and (d) 55 Hz operating on the VFD .............................. 10

 5. Raw data from operation at NaK temperatures of 525 oC and pump frequencies 

of (a) and (b) 40 Hz, (c) and (d) 55 Hz, and (e) and (f) 70 Hz operating on either 

the VFD (black markers) or VFS (gray markers) ......................................................... 11

 6. Raw efficiency data from sweeps of the throttling valve during operation

at NaK temperatures of 525 °C for frequencies from (a) 45–60 Hz 

and (b) 63–78 Hz ......................................................................................................... 12

 7. Data over several cycles of the throttling valve showing (a) applied

line-to-neutral RMS voltages on all three input lines to the ALIP

and (b) the resulting RMS currents for all three phases ............................................... 13

 8. Immersion heater GFSSP model ................................................................................. 16

 9. Across the heater section as a function of flow rate: (a) Pressure change 

and (b) flow coefficient ................................................................................................. 19

10. Heater elbow assembly drawing for the ATC ................................................................ 20
vi
vii

LIST OF TABLES

1. Two-chassis power supply unit specifications ............................................................... 6

2. Summary of equivalent diameters and lengths for various immersion 

heater geometries ......................................................................................................... 16

3. Results from two-element computations ...................................................................... 17

4. Results from three-element computations .................................................................... 17

5. Results from four-element computations ..................................................................... 17
viii

LIST OF ACRONYMS AND SYMBOLS

AC alternating current

ALIP annular linear induction pump

ATC ALIP test circuit

DAQ data acquisition

DC direct current

EM electromagnetic

FSP fission surface power

GFSSP Generalized Fluid System Simulation Program

He helium

ID inner diameter

INL Idaho National Laboratory

MSFC Marshall Space Flight Center

NaK sodium potassium

RMS root mean square

SS stainless steel

TDU technology demonstration unit

TP Technical Publication

VFD variable frequency drive

VFS variable frequency power supply
ix

NOMENCLATURE

ARMS line current in amperes (RMS)

Cp specific heat 

Cv flow coefficient

D0 ATC tube inside diameter

Dequiv equivalent diameter

Dr heater element diameter

l physical immersion heater length

l

equiv equivalent tube length

n number of heater elements

PIN total electrical power to the pump

VLL input voltage, line-to-line

VLN output voltage, line-to-line

v volumetric flow rate

γ ratio of specific heats

Dp change in pressure

ρ density 

η efficiency
x
1

TECHNICAL PUBLICATION

TESTING OF AN ANNULAR LINEAR INDUCTION PUMP FOR THE FISSION 

SURFACE POWER TECHNOLOGY DEMONSTRATION UNIT

1. INTRODUCTION

Fission surface power (FSP) systems could be used to provide power on the surface of the 

Moon, Mars, or other planets and moons of our solar system, as they are capable of providing 

excellent performance at any location, including those near the poles or other permanently shaded 

regions, and offer the capability to provide on-demand power at any time, even at long distances from 

the Sun. Fission-based systems also offer the potential for outposts, crew, and science instruments 

to operate in a power-rich environment while maintaining a relatively small footprint for the reactor 

system. NASA has been exploring technologies with the goal of reducing the cost and technical risk 

of employing FSP systems. A reference 40-kWe option has been devised that is cost competitive with 

alternatives while providing more power anywhere on the lunar surface for less mass. The reference 

FSP system is also readily extensible for use on Mars. On Mars, the system would be capable of operating through global dust storms and providing year-round power at any Martian latitude.

One key technology associated with the FSP system is the pump that circulates liquid-metal 

coolant through the reactor system. An annular linear induction pump (ALIP) was designed to support a quarter-scale, end-to-end technology demonstration unit (TDU) where 50 kW of simulated 

nuclear thermal power will be converted to 10 kW of electrical power. The ALIP was designed to 

support the TDU requirements and was tested in a stand-alone environment at representative reactor operating conditions. This Technical Publication (TP) details the performance testing of this 

prototypic TDU ALIP. 

1.1 Fission Surface Power Technology Development

NASA and the Department of Energy are pursuing long-lead technology development for 

potentially supporting future integrated FSP systems. The major effort in the FSP technology project 

has been focused on a reference mission and concept. The reference mission is to provide electrical 

power to habitats on the lunar surface. The requirements derived from this mission are 40 kWe delivered to the habitat over a design lifetime of 8 years. Although many options exist, NASA’s current 

reference FSP system uses a fast spectrum, pumped liquid sodium potassium- (NaK-) cooled reactor coupled to a Stirling power conversion subsystem. The reference system uses technology with 

significant terrestrial heritage that can perform at any location on the surface of the Moon or Mars. 

Detailed development of the FSP concept and the reference mission are documented in various 

other reports.1–4
2

The objectives of the FSP technology project are as follows:5

• Develop FSP concepts that meet expected surface power requirements at reasonable cost with 

added benefits over other options.

• Establish a nonnuclear hardware-based technical foundation for FSP design concepts to reduce 

overall development risk.

• Reduce the cost uncertainties for FSP and establish greater credibility for flight system cost 

estimates.

• Generate the key nonnuclear products to allow Agency decision makers to consider FSP as a viable 

option for potential future flight development.

The pump must be compatible with the liquid NaK coolant and have adequate performance 

to enable a viable flight system. Idaho National Laboratory (INL) was tasked with the design and 

fabrication of an ALIP suitable for the FSP reference mission. Under the program, a quarter-scale 

FSP technology demonstration is under construction to test the end-to-end conversion of simulated 

nuclear thermal power to usable electrical power intended to raise the entire FSP system to Technology Readiness Level 6. An ALIP for this TDU was fabricated under the direction of the INL and 

shipped to NASA Marshall Space Flight Center (MSFC) for testing at representative operating conditions. This pump was designed to meet the requirements of the TDU experiment. The ALIP test 

circuit (ATC) at MSFC, previously used to conduct performance evaluation on another ALIP6 was 

used to test the present TDU pump for the FSP Technology Development program.

1.2 Nonnuclear Testing at Marshall Space Flight Center

The Early Flight Fission Test Facility was established by MSFC to provide a capability for 

performing hardware-directed activities to support multiple in-space nuclear reactor concepts by 

using a nonnuclear test methodology.7,8 This includes fabrication and testing at both the module/

component level and near prototypic reactor components and configurations, allowing for realistic 

thermal-hydraulic evaluations of systems. In the present testing, the ATC was slightly modified from 

the previous configuration6 to provide more controllable heating of the NaK working fluid. The 

system and changes incorporated in this iteration are described in section 2, followed by measured 

performance results on the TDU ALIP.
3

2. ANNULAR LINEAR INDUCTION PUMP TEST CIRCUIT SETUP

The ATC apparatus, shown schematically in figure 1, was fabricated to allow for performance 

testing of liquid-metal induction pumps. The majority of the components of the test circuit are 

described in detail in “Performance Testing of a Prototypic Annular Linear Induction Pump for Fission Surface Power.”6 A brief overview of those unchanged components is provided in this section, 

with the balance of the section devoted to a discussion of the upgrades implemented for the testing 

described in this TP.

Accumulator

ALIP

Heat Exchanger

Throttling

Valve

Immersion Heaters

Electromagnetic

Flowmeter

Flow Direction

Pump Pressure (∆p)

Flow Direction

F1

Figure 1. Schematic of the ALIP test circuit configured for TDU ALIP testing.

2.1 Overview of Components Unchanged From Previous Annular Linear 

Induction Pump Test Circuit Experiments

The test circuit consists of a large pipe (3-in, schedule 10, stainless steel (SS)) configured in 

a closed-loop shape with components positioned at different locations along the path. The large pipe 

size is employed to minimize the viscous pressure loss in the pipe, leaving the liquid NaK free to 

flow in the loop. Each of the components in the loop that are briefly mentioned in this subsection is 

described in greater detail in reference 6.
4

The throttling valve is included to provide an active control of the flow resistance in the loop. 

It is a gate valve that translates into and out of the flow, changing the flow impedance over a large 

range from minimal flow resistance to almost complete stagnation of the flow.

A gas-to-NaK counterflow concentric tube heat exchanger is employed to provide cooling 

and temperature control for the loop. The heat exchange medium is gaseous nitrogen with the heat 

exchanger sized to provide 10 kW of cooling. 

The volumetric flow rate of NaK in the loop is measured using an electromagnetic flowmeter. 

It consists of two neodymium-iron-boron magnets opposing each other on opposite sides of the 

pipe, with magnetically permeable material forming the magnetic flux return. The flowmeter output 

is a voltage that arises from the motion of the conductive liquid metal across the magnetic field lines. 

That voltage is measured across the pipe and is proportional to the volumetric flow rate.

One of the two methods used to apply power to the pump was to employ an Allen Bradley 

PowerFlex 400 variable frequency drive (VFD), which permits testing up to 60 Hz. The VFD uses 

pulse-width modulation to produce a current waveform at the desired frequency that is approximately sinusoidal. Sine wave filtering of the three-phase waveform produces a voltage waveform that 

is also approximately sinusoidal, making it easier for the data acquisition (DAQ) system to measure 

the current, voltage, and power. When the VFD is used, the power to the pump is measured using an 

Ohio Semitronics two-meter wattmeter (model P-144D), which gives a voltage output proportional 

to the measured power, assuming the input current and voltage are sinusoidal waveforms.

Liquid NaK pressure measurements are obtained using metal diaphragm transducers manufactured by Delta Metrics. The transducers were water cooled to maintain them at a constant temperature, reducing thermal drift during the test. Independent pressure measurements were performed 

on the flow upstream and downstream of the ALIP, with the difference representing the pressure rise 

imposed on the fluid by the pump. 

Temperature measurements on the flow loop are acquired using type K thermocouples. The 

thermocouples are inserted into small copper blocks, which are contoured on one side to match 

the curvature of the pipe. When the blocks are clamped to the pipe, they possess a large surface for 

thermal conduction. The clamp-on temperature measurement method has a fast response time, with 

changes in fluid temperature owing to a variation in operating conditions showing up almost immediately in the thermocouple data. 

The DAQ and control system is based on National Instruments hardware and software. An 

in-house-developed LabVIEWTM application is used to control the experiment and acquire data from 

a PXI-1042 chassis, with an SCXI-1001 chassis used for signal conditioning. 

2.2 Components in the System Changed for the Present Work

There were changes to the ATC that were implemented either to make it possible to test 

the TDU ALIP or as a result of lessons learned from previous ALIP testing.6 These configuration 

changes are described in the remainder of this section.
5

2.2.1 Technology Demonstration Unit Annular Linear Induction Pump

The TDU ALIP consists of an annular duct surrounded by a series of electromagnetic coils. 

Three-phase power is supplied to the coils to generate an axially-traveling magnetic that induces currents in the electrically-conductive liquid NaK located within the duct. The induced currents interact 

with the externally-imposed magnetic field to generate net acceleration of the fluid in the streamwise 

direction. The flow rate and pressure developed by the pump are controlled by varying the voltage 

and frequency of the power supplied to the coils and by changing the overall NaK flow impedance in 

the loop. The pump was designed to operate nominally at 80 V and 40 Hz, producing NaK flow rates 

from 0.5 to 2.25 kg/s and developed pressures from 10 to 40 kPa. The peak operating temperature for 

the TDU and the FSP reactor systems is 800 K.

2.2.2 Immersion Heaters

In the present testing, a new immersion heating method was used to directly heat the liquid 

metal. Three graphite heaters previously designed and tested for use in other applications were placed 

in tubes directly in the flow. These heaters together are capable of delivering a theoretical maximum 

of >15 kW of thermal power (5 kW per heater) to the NaK. During operation of the ATC, about 

half of this power was required when heating to the maximum operating temperature of 525 oC. The 

heating elements are cylindrical in shape, with a diameter of about 1.9 cm (0.75 in) and a length of 

about 58.4 cm (23 in). Figure 1 shows the location of the immersion heaters in the lower left-hand 

corner of the ATC. A study, summarized in appendix A, was performed to evaluate the pressure loss 

that would result when inserting heaters into the flow. In the study, the effect of inserting two, three, 

and four pins into the flow channel was evaluated. The amount of thermal energy available to be 

delivered to the NaK increased with the number of heaters, but the pressure drop in the loop also 

increased with the number of heaters. Based on the results of the study and the anticipated range of 

flow rates during a test, three heaters were selected for a balance of the ease of installation, adequate 

heat delivery, and acceptable pressure drop. Additionally, should one of the heaters fail, there would 

still be sufficient heating capacity available with the remaining two heaters.

F2

Figure 2. Three-dimensional view of elbow heater section.
6

The immersion heaters, presented in an enlarged view in figure 2 and in appendix B, consist of 

three metal-clad cylinders shown in green with each containing a resistive heating element and filled 

with helium (He). The He allows for sufficient thermal conduction between the graphite heaters and 

the inner diameter (ID) of the cylinders, permitting even heating of the cylinders and eliminating 

local hotspots. It is important to have even heating as a hotspot can potentially lead to a material 

failure and subsequent leakage of NaK into the immersion heaters. The heaters were wired in series 

to provide the correct resistance to permit the usage of the full current and voltage range of a 15 kW 

(150 V/100 A) Lambda power supply. Additionally, the heaters were designed so the heated sections 

were completely contained within the NaK flow and there was adequate room for thermal growth 

of the various components. All electrical connections were performed in the head section on the left 

side of figure 2. In the ATC, the performance of the immersion heater design was exemplary with 

extremely good transfer of heat to the NaK.

2.2.3 Variable Frequency Power Supply

A California Instruments model 9000LS/2-3-LAN-480-ADV programmable power supply 

was used to provide power to the ALIP. Table 1 lists the specifications of this two-chassis power 

supply unit.

Table 1. Two-chassis power supply unit specifications.

Input voltage (line-to-line) 480 VLL (±5%), three-phase

Input line current 2×12 ARMS = 24 ARMS @ 456 VLL

Input line power 2×8.9 kVA = 17.8 kVA

Output voltage (line-to-neutral) 0 –135 VLN (low range) or 0–270 VLN (high range), three-phase

Output power per phase at full-scale voltage 3 kVA

Maximum output current per phase at full power 29.6 A (low range)

Maximum output current per phase at full-scale voltage 22.2 A (low range)

Frequency range 45 –1,000 Hz

All power supply setting and feedback data are communicated through an Ethernet interface. 

The AC power settings used included voltage, frequency, phase, and waveform type. The feedback 

measurements included the line-to-neutral DC and AC root mean square (RMS) components of the 

output voltage for each phase, the DC and AC RMS currents for each terminal including the neutral, 

the DC power, and the in-phase, apparent, and reactive components of the power for each output 

phase. Using this information, the power supply calculates and returns a power factor as part of the 

data. 

The power supply can be programmed to regulate the output voltage using either internal or 

external sense lines. In the ATC, external sense lines were used, providing a measure of the voltage 

at the load. The output voltage range of the unit can be selected remotely, with the range of zero to 

135 VLN used in the present work. A slew rate can be specified for all programmed changes in the 

AC RMS voltage. The slew rate does not apply to changes in the DC voltage. Approximately instantaneous changes in the AC RMS voltage can be obtained by setting the slew rate to its maximum or 
7

infinity. For ATC testing, a finite slew rate was used to prevent instantaneous changes in the voltage 

level, with the DC offset voltage always set to zero.

A slew rate also can be specified for changes in the frequency of the output waveform, with 

approximately instantaneous changes obtained by setting the slew rate to its maximum or infinity. 

For ATC testing, a finite slew rate was used to prevent instantaneous changes in the frequency.

The relative phase angle of each of the three output voltage phases can be programmed independently. The phase angle is programmed in degrees relative to an internal reference. Positive and 

negative phase angles are used to program leading and lagging phases, respectively. The phase angles 

were always set 120° apart in the present work. Direction of flow can be controlled by reversing two 

of the three output phases.

In addition to sinusoidal and square output waveforms, the power supply can be programmed 

to produce arbitrary user-defined waveforms. A user-defined waveform consists of 1,024 data points 

representing one full cycle of the waveform. The first data point specifies the relative amplitude at 

the zero-degree phase reference. The data points can be in any arbitrary units since the unit rescales 

the values to an internal format that removes any DC offset and ensures that the correct AC RMS 

output voltage is achieved.

Additional data can be obtained from the power supply. These include measurement of the 

percentage of total harmonic distortion and noise in each phase of the output voltage and current and 

the crest factor, which is defined as the ratio of the peak output current to the RMS output current.
8

3. PERFORMANCE TEST DATA

Three measurements must be simultaneously acquired to calculate the performance of any 

pump, including an ALIP. Those measurements are the volumetric flow rate ( v) and the pressure 

rise in the fluid (Dp) owing to the action of the pump and the total electrical power to the pump 

(PIN). The efficiency is then defined as the net power into the fluid (equal to the volumetric flow rate 

multiplied by the pressure rise) over the total electrical power delivered to the pump: 

! = v!!p

PIN

. (1)

Data were obtained at NaK temperatures of 125 °C, 325 °C, and the nominal FSP reactor 

operating temperature of 525 °C. Data are presented for the pump operating on VFD-supplied, 

three-phase power at 40 and 55 Hz, and on the variable frequency power supply (VFS) at 55 and 

70 Hz. The pump was operated over a range of voltage levels from 30 to 120 V. Not all voltages and 

frequencies were tested for every condition.

Typically, data were acquired by first bringing the pump and loop temperature to a steadystate value. A constant pump voltage was set and the throttling valve was exercised through its entire 

range to obtain pump performance curves over a range of v and Dp values.

As in previous ALIP testing,6 the data are remarkably clean, requiring no postprocessing 

before being plotted. In this section, the data are graphed as a series of scatter plots with each plot 

encompassing the entire data set for a given operating condition. Concentrations of data points 

represent flow conditions measured at steady-state flow conditions while the throttling valve was 

stationary (approximately 30–60 s dwell time). The individual dots forming the rest of the lines represent data obtained while the valve was transitioning from one setpoint to the next. Each efficiency 

point was computed using the flow rate, ∆p , and input power as measured and recorded on the DAQ 

system. Testing with the VFD and the VFS were conducted on different days, with data corresponding to the same conditions (same temperature and a pump frequency of 55 Hz) plotted on the same 

graphs in this TP.

Pump performance data obtained at a NaK temperature of 125 °C are presented in 

figure 3. The average error bars for the pump performance data set presented in this TP are given in 

figures 3–5 to demonstrate the clean nature of the data. Data for pump operation at 325 and 525 °C 

are presented in figures 4 and 5, respectively. For completeness, the nominal design flow rate and Dp

for the TDU are plotted as plus (+) symbols in figure 5(a), (c), and (e), showing that the TDU ALIP 

underperformed relative to the nominal design point.
9

0

20

40

60

80

100

16

12

8

4

0

0 0.5

40 Hz 120 V

100 V

80 V

50 V

30 V

Avg Error Bar

1 1.5 2 2.5 3

(a) Flow Rate (L/s) (b)

(c) (d)

(e) (f)

Flow Rate (gpm)

∆p (kPa)

∆p (psi)

F3

0 10 20 30 40 50

0

1

2

3

4

5

6

0 0.5

40 Hz

120 V

80 V 100 V 30 V 50 V

Avg Error Bar

1 1.5 2 2.5 3

Flow Rate (L/s)

Flow Rate (gpm)

Efficiency (%)

0 10 20 30 40 50

0

20

40

60

80

100

16

12

8

4

0

0 0.5

55 Hz 120 V

100 V

80 V

50 V

30 V

VFD

VFS

1 1.5 2 2.5 3

Flow Rate (L/s)

Flow Rate (gpm)

∆p (kPa)

∆p (psi)

0 10 20 30 40 50

0

1

2

3

4

5

6

0 0.5

55 Hz

120 V 100 V 50 V 80 V 30 V

1 1.5 2 2.5 3

Flow Rate (L/s)

Flow Rate (gpm)

Efficiency (%)

0 10 20 30 40 50

0

20

40

60

80

100

16

12

8

4

0

0 0.5

70 Hz

120 V

1 1.5 2 2.5 3

Flow Rate (L/s)

Flow Rate (gpm)

∆p (kPa)

∆p (psi)

0 10 20 30 40 50

0

1

2

3

4

5

6

0 0.5

70 Hz

120 V

1 1.5 2 2.5 3

Flow Rate (L/s)

Flow Rate (gpm)

Efficiency (%)

0 10 20 30 40 50

Figure 3. Raw data from operation at NaK temperatures of 125 oC and pump frequencies

of (a)and (b) 40 Hz, (c) and (d) 55 Hz, and (e) and (f) 70 Hz operating on either 

the VFD (black markers) or VFS (gray markers).
10

0

20

40

60

80

100

16

12

8

4

0

0 0.5

40 Hz

120 V

100 V

80 V

50 V

30 V

1 1.5 2 2.5 3

(a) Flow Rate (L/s) (b)

(c) (d)

Flow Rate (gpm)

∆p (kPa)

∆p (psi)

F4

0 10 20 30 40 50

0

1

2

3

4

5

6

0 0.5

40 Hz

120 V

30 V 50 V 80 V 100 V

1 1.5 2 2.5 3

Flow Rate (L/s)

Flow Rate (gpm)

Efficiency (%)

0 10 20 30 40 50

0

20

40

60

80

100

16

12

8

4

0

0 0.5

55 Hz

120 V

100 V

80 V

50 V

30 V

1 1.5 2 2.5 3

Flow Rate (L/s)

Flow Rate (gpm)

∆p (kPa)

∆p (psi)

0 10 20 30 40 50

0

1

2

3

4

5

6

0 0.5

55 Hz

100 V 120 V 80 V 30 V 50 V

1 1.5 2 2.5 3

Flow Rate (L/s)

Flow Rate (gpm)

Efficiency (%)

0 10 20 30 40 50

110 V

110 V

Figure 4. Raw data from operation at NaK temperatures of 325 oC and pump frequencies 

of (a) and (b) 40 Hz, and (c) and (d) 55 Hz operating on the VFD.
11

0

20

40

60

80

100

16

12

8

4

0

0 0.5

40 Hz

120 V

100 V

80 V

50 V

30 V

1 1.5 2 2.5 3

(a) Flow Rate (L/s) (b)

(c) (d)

(e) (f)

Flow Rate (gpm)

∆p (kPa)

∆p (psi)

F5

0 10 20 30 40 50

0

1

2

3

4

5

6

0 0.5

40 Hz

120 V

30 V 50 V 80 V 100 V

1 1.5 2 2.5 3

Flow Rate (L/s)

Flow Rate (gpm)

Efficiency (%)

0 10 20 30 40 50

0

20

40

60

80

100

16

12

8

4

0

0 0.5

55 Hz

120 V

100 V

100 V

100 V

80 V

50 V

30 V

VFD

VFS

1 1.5 2 2.5 3

Flow Rate (L/s)

Flow Rate (gpm)

∆p (kPa)

∆p (psi)

0 10 20 30 40 50

0

1

2

3

4

5

6

0 0.5

55 Hz

120 V

100 V

80 V

80 V

80 V

30 V 50 V

1 1.5 2 2.5 3

Flow Rate (L/s)

Flow Rate (gpm)

Efficiency (%)

0 10 20 30 40 50

0

20

40

60

80

100

16

12

8

4

0

0 0.5

70 Hz

TDU Design

Point

TDU Design

Point

TDU Design

Point

120 V

1 1.5 2 2.5 3

Flow Rate (L/s)

Flow Rate (gpm)

∆p (kPa)

∆p (psi)

0 10 20 30 40 50

0

1

2

3

4

5

6

0 0.5

70 Hz

120 V

1 1.5 2 2.5 3

Flow Rate (L/s)

Flow Rate (gpm)

Efficiency (%)

0 10 20 30 40 50

Figure 5. Raw data from operation at NaK temperatures of 525 oC and pump frequencies 

of (a) and (b) 40 Hz, (c) and (d) 55 Hz, and (e) and (f) 70 Hz operating on either 

the VFD (black markers) or VFS (gray markers).

As was previously seen in ALIP testing,6 the pump performance characteristics (achievable 

flow rate, Dp, and commensurate efficiency) all decrease as the temperature is increased. Changing 

the frequency has a large effect on the slope of the curves presenting Dp as a function of flow rate, 

but the frequency only appears to have a mild effect on the peak efficiency for a fixed temperature. 

The noticeable effect is the flow rate at which peak efficiency occurs, with the maximum occurring at 

higher flow rates as the frequency is increased. Data obtained using the VFD and the VFS operated 

at similar conditions (voltage, frequency) quantitatively agree and are relatively indistinguishable 

from each other.
12

To further investigate the effect of driving frequency on pump efficiency, the pump was operated at a constant voltage and the throttle valve was exercised through a number of cycles at different pump operating frequencies. The pump efficiency as a function of flow rate for each frequency 

is presented in figure 6. In the data set found in panel (a), the efficiency increases by small but finite 

amounts as the frequency is increased from 45 to 60 Hz. In panel (b), the efficiency begins to fall 

again above 60 Hz. However, in all cases, the change in peak efficiency does not greatly vary with 

frequency.

1.8

2

2.2

2.4

2.6

2.8

3

3.2

3.4

18 20 22 24 26 28 30 32 34 36

45 Hz

48 Hz

51 Hz

54 Hz

63 Hz

66 Hz

72 Hz

57 Hz 78 Hz

60 Hz

Flow Rate (gpm)

18 20 22 24 26 28 30 32 34 36

(a) (b) Flow Rate (gpm)

Flow Rate (L/s)

F6

1.2 1.4 1.6 1.8 2 2.2 1.2 1.4 1.6 1.8 2 2.2

Flow Rate (L/s)

Efficiency (%)

1.8

2

2.2

2.4

2.6

2.8

3

3.2

3.4

Efficiency (%)

Figure 6. Raw efficiency data from sweeps of the throttling valve during operation

at NaK temperatures of 525 °C for frequencies from (a) 45–60 Hz 

and (b) 63–78 Hz.

As with the FSP ALIP,6 each phase of the TDU ALIP conducted a different current value for 

a fixed line-to-neutral voltage. This phenomenon is observed clearly in figure 7, where the phase currents are graphed as a function of time. The currents exhibit a stair-step behavior up and down as the 

throttling valve is opened and closed. Furthermore, the currents all exhibit changes as the voltage is 

changed. (While only one line-to-neutral RMS voltage is plotted, the data show that all three voltage 

waveforms are coincident.) The most important thing about the data is that they demonstrate that 

the current draw for each leg of the ALIP circuit is different by several amperes per phase.
13

F7

(a)

5

10

15

20

2,000 2,500 3,000 3,500

Time (s)

RMS Phase Current (A)

(b)

74

76

78

80

82

84

2,000 2,500 3,000 3,500

Time (s)

Line-to-Neutral RMS Voltage (V)

Figure 7. Data over several cycles of the throttling valve showing (a) applied

line-to-neutral RMS voltages on all three input lines to the ALIP

and (b) the resulting RMS currents for all three phases.
14

4. CONCLUSIONS

Testing was performed to quantify the performance of the TDU ALIP. The dedicated ATC 

apparatus was used for this purpose, with minor modifications to the configuration incorporated to 

improve the operational capabilities of the system. The results of the testing lead to the following 

conclusions:

• Relative to previous ATC operation, it was much easier to bring the system to temperature using 

the new immersion heater system. Furthermore, there were no adverse flow effects or abnormally 

high pressure drops noted over the entire operating envelope.

• The pump was tested at amplitudes of up to 120 VLN input (line-to-neutral voltage) at NaK temperatures of 125 °C, 325 °C, and the nominal FSP reactor operating temperature of 525 °C.

• The pump was supplied with three-phase power from a VFD at frequencies of 40 and 55 Hz, and 

from a VFS at frequencies of 55 and 70 Hz. In addition, a scan of operation at different frequencies 

was performed using the VFS from 45 to 78 Hz.

• At the FSP reactor operating temperature of 525 °C, the performance spanned a range of flow 

rates from 0.3 to 2.75 L/s (4.8 to 43.6 gpm) and ∆p levels from <1 to 55 kPa (<0.145 psi to roughly 

8 psi). The maximum efficiency measured during this testing was approximately 3.5%.

• The efficiency of the pump decreased as the NaK temperature was increased.

• Measured performance at 55 Hz supplied by either the VFD or VFS when operating 

at comparable NaK temperatures exhibited quantitative agreement.

• The operating envelope at 525 °C fell short of the TDU design point at all frequencies.

• The pump exhibited some sensitivity to frequencies in terms of the flow rate at which the maximum 

efficiency occurred, but the maximum value of efficiency was relatively insensitive over the range of 

frequencies tested.

• For a constant line-to-neutral voltage on each phase of the pump, the phase currents differed from 

each other by several amps, indicating that the electrical loads presented by each phase of the pump 

were different. 
15

APPENDIX A—IMMERSION HEATER PRESSURE DROP ANALYSIS

In the present work, resistive heating elements immersed in the liquid NaK were added to 

heat the fluid in the ATC. These heating elements are cylindrical in shape, with a diameter of about 

1.9 cm (0.75 in) and a length of about 0.58 m (23 in). The elements are positioned within a large 

tube comprising the flow path for the ATC loop, which consists of SS tubing with an ID of 8.28 cm 

(3.26 in), and are aligned axially within the tubing as shown in figure 2 and appendix B.

The analysis detailed in this appendix was undertaken to provide a quantitative measure of 

the pressure drop the heater elements might introduce into the ATC. The Generalized Fluid System 

Simulation Program (GFSSP) computational code was used to estimate the heater-induced pressure 

loss within the ATC tubing. GFSSP is an MSFC-developed computational fluid network solver, and 

has been validated on many different fluid flow applications.9

A.1 Flow Model

The fluid properties of NaK10 were introduced using the general fluid option available in 

GFSSP. The user supplies seven specific data files to GFSSP: thermal conductivity, density, viscosity, 

ratio of specific heats (γ), enthalpy, entropy, and the specific heat (Cp). The files provide these particular fluid properties as a function of temperature. 

The flow path is constructed using a series of nodes and branches to analytically represent 

the flow path to be evaluated, in this case, the flow across a geometry representative of the immersion heater. The approach used in the present analysis was to model the geometry of the immersion 

heaters as a flow area reduction introduced by the heater elements that were represented by a squareedged reducer, where the reduced area is equal to the total cross-sectional area of the ATC tube 

minus the sum of the frontal area of the heater elements. The resulting equivalent diameter (Deqiv) 

could then be determined from

Deqiv = D0

2 ! nDr2 , (2)

where D0 is the ATC tube ID, Dr is the heater element diameter, and n is the number of heater elements. 
16

The inside surface area plays a significant role in the generation of the pressure drop through 

the immersion heater, so it was necessary to determine an equivalent tube length, such that the 

equivalent length would provide the same surface area as that of the ATC tube inside wall and the 

immersion heater rods. The equivalent tube length (l

eqiv) that would provide the same total surface 

area is

l

eqiv = l D0 ( + nDr)

D0

2 ! nDr2 ,

(3)

where l is the physical length of the immersion heater, i.e. 0.58 m (23 in). 

Using these definitions, a GFSSP model was created using the computed equivalent diameters and lengths. The resulting GFSSP model, represented graphically, is shown in figure 8. The 

branch consisting of boundary nodes 5 and 6, and internal nodes 7–10 represents the immersion 

heater geometry. The contraction and expansion sections are represented by elements 78 and 910, 

with diameters given by equation (2). The length of element 89, located between the contraction and 

expansion, is found using equation (3). These equivalent diameters and lengths are summarized in 

table 2 for two, three, and four immersion heater elements.

F8

5 7 8 9 10 6

Inlet 89 Exit Contraction Expansion

78 910

Pipe

Section

Pipe

Section

Pipe

Section

Figure 8. Immersion heater GFSSP model.

Table 2. Summary of equivalent diameters and lengths for various immersion 

heater geometries.

Number

of Elements

2 3 4

cm in cm in cm in

Deqiv 7.82 3.08 7.60 2.99 7.34 2.89

l

eqiv 0.9022 35.52 1.076 42.38 1.263 49.74

A.2 Computational Results

The primary goal of this effort was to estimate the relative pressure losses induced by using 

two, three, and four elements in the immersion heater section of the ATC. With the geometry defined, 

the pressure losses were found by entering a range of supply pressures at the upstream boundary 

node (5) in the GFSSP model. Computed results for the two-, three-, and four-pin models are summarized in tables 3–5, respectively. The pressure values at nodes 5, 6, 7, and 10 are denoted, respectively, as P5, P6, P7, and P10. 
17

Table 3. Results from two-element computations.

P5

(kPa)

P6

(kPa)

P7

(kPa)

P10

(kPa)

Δp

(Pa)

Flow Rate Cv

[gpm/(psi)1/2 (kg/s) (L/min) ]

101.36 101.36 101.36 101.36 – – – –

101.39 101.36 101.39 101.36 34.5 1.2 81.8 285.4

101.43 101.36 101.43 101.36 69.0 2.4 163.4 402.8

101.70 101.36 101.70 101.36 344.8 5.9 402.9 444.4

102.05 101.36 102.05 101.36 689.5 8.6 593.5 462.8

102.39 101.36 102.39 101.36 1,034.3 10.8 743.4 473.3

102.74 101.36 102.74 101.36 1,379.0 12.6 868.3 478.8

103.43 101.36 103.43 101.36 2,068.5 15.8 1087.0 489.4

Table 4. Results from three-element computations.

P5

(kPa)

P6

(kPa)

P7

(kPa)

P10

(kPa)

Δp

(Pa)

Flow Rate Cv

[gpm/(psi)1/2 (kg/s) (L/min) ]

101.36 101.36 101.36 101.36 – – – –

101.39 101.36 101.39 101.36 34.5 0.9 65.3 227.7

101.43 101.36 101.43 101.36 69.0 0.9 133.1 328.1

101.70 101.36 101.70 101.36 344.8 4.8 328.0 361.7

102.05 101.36 102.05 101.36 689.5 7.0 481.0 375.1

102.39 101.36 102.39 101.36 1,034.3 8.8 602.8 383.8

102.74 101.36 102.74 101.36 1,379.0 10.3 705.9 389.2

103.43 101.36 103.43 101.36 2,068.5 12.8 880.8 396.6

Table 5. Results from four-element computations.

P5

(kPa)

P6

(kPa)

P7

(kPa)

P10

(kPa)

Δp

(Pa)

Flow Rate Cv

[gpm/(psi)1/2 (kg/s) (L/min) ]

101.36 101.36 101.36 101.36 – – – –

101.39 101.36 101.39 101.36 34.5 0.8 54.0 188.4

101.43 101.36 101.43 101.36 69.0 1.7 115.9 285.8

101.70 101.36 101.70 101.36 344.8 4.1 284.2 313.5

102.05 101.36 102.05 101.36 689.5 6.0 415.4 323.9

102.39 101.36 102.39 101.36 1,034.3 7.5 518.5 330.1

102.74 101.36 102.74 101.36 1,379.0 8.8 609.1 335.9

103.43 101.36 103.43 101.36 2,068.5 11.0 759.0 341.7
18

The volumetric flow rates shown in tables 3–5 are converted from the computed mass flow 

rates given in the previous column using the density of NaK (871.5 kg/m3 for this calculation). The 

flow coefficient (Cv) was found using the definition11

Cv = v!

!p

62.4

!

"

#

$

%

&

'

, (4)

where v is the volumetric flow rate in gpm, Dp is the computed pressure drop in psi, located in the 

table, and ρ is the density of NaK in lbm/ft3. The term 62.4/ρ yields the specific gravity of the fluid, 

with the resulting units on Cv being gpm/(psi)1/2. The flow coefficient is generally given in imperial 

units and is a useful way of comparing the flow capacities of different valves and flow restrictions. 

The definition of Cv is the flow capacity in gpm of 60 °F water that a valve or restriction will pass 

for a pressure drop of 1 psi.

The pressure change (Dp) across the heater section for two, three, and four heater elements 

as a function of flow rate is presented in figure 9(a). Relative to the pressures expected based upon 

previous testing with the ATC,6 the expected pressure drops for all three configurations are relatively 

small. The flow blockage and commensurate pressure drop is greater when there are more pins in the 

flow. However, for flow rates under 50 gpm, which is near the upper bound for flow rates in the ATC, 

it appears that the pressure drop will not exceed 138 Pa (0.02 psid). 

The flow coefficient (Cv) across the heater section for two, three, and four heater elements as 

a function of flow rate are presented in figure 9(b). The higher the flow coefficient at a fixed flow rate, 

the more flow can be passed for a given pressure drop. As expected, the higher blockage caused by 

the larger number of pins results in a lower flow coefficient, especially at the higher flow rates.
19

F9

0.5

0

1

1.5

2

0 2 4 6 8 10 12

Four Elements

Three Elements

Two Elements

14 16

(a) Flow Rate (kg/s)

∆p (kPa)

500

400

300

200

100

0

0 2 4 6 8 10 12 14 16

(b) Flow Rate (kg/s)

Cv (gpm/(psi)1/2)

Four Elements

Three Elements

Two Elements

Figure 9. Across the heater section as a function of flow rate: (a) Pressure change 

and (b) flow coefficient.
20

APPENDIX B—HEATER ELBOW ASSEMBLY

Figure 10 shows the heater elbow assembly drawing for the ATC.

Figure 10. Heater elbow assembly drawing for the ATC.
21

REFERENCES

 1. Nainiger, J.: “Affordable Fission Surface Power System Study Final Report,” NASA Exploration Systems Mission Directorate Report, Glenn Research Center, Cleveland, OH, October 

2007.

 2. Mason, L.S.: “A Comparison of Fission Power System Options for Lunar and Mars Surface 

Applications,” NASA/TM—2006–214120, Glenn Research Center, Cleveland, OH, February 

2006.

 3. Mason, L.S.: “A Practical Approach to Starting Fission Surface Power Development,” NASA/

TM—2006–214366, Glenn Research Center, Cleveland, OH, July 2006. 

 4. Mason, L.S.; Poston, D.; and Qualls, L.: “System Concepts for Affordable Fission Surface 

Power,” NASA/TM—2008–215166, Glenn Research Center, Cleveland, OH, January 2008.

 5. Palac, D.; Mason, L.; and Harlow, S.: “Fission Surface Power Technology Development Status,” NASA/TM—2009–215602, Glenn Research Center, Cleveland, OH, March 2009.

 6. Polzin, K.A.; Pearson, J.B.; Schoenfeld, M.P.; et al.: “Performance Testing of a Prototypic 

Annular Linear Induction Pump for Fission Surface Power,” NASA/TP—2010–216430, Marshall Space Flight Center, Huntsville, AL, May 2010.

 7. Godfroy, T.J.; Van Dyke, M.; and Dickens, R.: “Realistic Development and Testing of Fission 

Systems at a Non-Nuclear Testing Facility,” AIP Conf. Proc., Space Technologies and Applications International Forum, STAIF-2000, Vol. 504, pp. 1208–1210, 2000.

 8. Van Dyke, M.; Godfroy, T.J.; Houts, M.; et al.: “Results of a First Generation Least Expensive Approach to Fission Module Tests: Non-Nuclear Testing of a Fission System,” Space 

Technologies and Applications International Forum, STAIF-2000, AIP Conf. Proc., Vol. 504, 

pp. 1211–1127, 2000.

 9. Majumdar, A.; Steadman, T.; and Moore, R.: GFSSP Users Manual, Version 5.0, Marshall 

Space Flight Center, Huntsville, AL, February 2007.

10. Weatherford, Jr., D.W.: The Properties of Inorganic Energy-Conversion and Heat-Transfer Fluids for Space Applications, WADD-TR-61-96; Southwest Research Institute, San Antonio, TX, 

1961.

11. Flow of Fluids through Valves, Fittings, and Pipe; Technical Paper No. 410, Crane Co., Stamford, CN, 1981.
22

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Testing of an Annular Linear Induction Pump for the Fission

Surface Power Technology Demonstration Unit

K.A. Polzin, J.B. Pearson, K. Webster, T.J. Godfroy,* 

and J.A. Bossard**

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 Systems Department, Engineering Directorate

*Maximum Technology Corporation, Huntsville, AL **BSRD, LLC/Yetispace, Inc., Huntsville, AL

M–1363

Technical Publication

NASA/TP—2013–217487

ALIP, annular linear induction pump, pump performance curve, space nuclear power, fission surface power, NaK

01–08–2013

UU 36

NASA

U U U

Results of performance testing of an annular linear induction pump that has been designed for integration into a fission surface power technology demonstration unit are presented. The pump electromagnetically pushes liquid metal (NaK) through a specially-designed apparatus that 

permits quantification of pump performance over a range of operating conditions. Testing was conducted for frequencies of 40, 55, and 70 Hz, 

liquid metal temperatures of 125, 325, and 525 oC, and input voltages from 30 to 120 V. Pump performance spanned a range of flow rates from 

roughly 0.3 to 3.1 L/s (4.8 to 49 gpm), and pressure heads of <1 to 104 kPa (<0.15 to 15 psi). The maximum efficiency measured during testing 

was 5.4%. At the technology demonstration unit operating temperature of 525 oC the pump operated over a narrower envelope, with flow rates 

from 0.3 to 2.75 L/s (4.8 to 43.6 gpm), developed pressure heads from <1 to 55 kPa (<0.15 to 8 psi), and a maximum efficiency of 3.5%. The pump 

was supplied with three-phase power at 40 and 55 Hz using a variable-frequency motor drive, while power at 55 and 70 Hz was supplied using 

a variable-frequency power supply. Measured performance of the pump at 55 Hz using either supply exhibited good quantitative agreement. For 

a given temperature, the peak in efficiency occurred at different flow rates as the frequency was changed, but the maximum value of efficiency was 

relative insensitive within 0.3% over the frequency range tested, including a scan from 45 to 78 Hz.

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