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Produced by the NASA Center for Aerospace Information (CASI)
NASA CONTRACTOR REPORT 166538

b ' Ig,^o^^p

Electrochemical Carbon Dioxide Concentrator

Subsystem Development - Final Report

(SkSA-CE- 166538) LLECUUCUMICAL CARBON

DIOXIDE CONCLAXIATOR SUESYSTEM DEVELOPMENT

Final Report (Life Systems, Inc., Cleveland,

Ohio.) 73 p HC A04/MF A01 CSCL 06K

N84- 17857

Unclas

G3/54 11755

D.B. Heppner

M.J. Dahlhausen

F.H. Schubert

CONTRACT NAS2— 11129

November, 1983
NASA CONTRACTOR REPORT 166538

Electrochemical Carbon Dioxide Concentrator

Subsystem Development - Final Report

D.B. Heppner

M.J. Dahlhausen

F.H. Schubert

Life Systems, Incorporated

Cleveland, OH 44122

Prepared for

Ames Research Center

under Contract NAS-2-11129

ROM

National Aeronautics and

Space Administration

Ames Research Center

Moffett Field, California 94035
FOREWORD

The development work described herein was conducted by Life Systems, Inc. at

Cleveland, Ohio under Contract NAS2-11129, during the period of December, 1981

through November, 1983. The Program Manager was Dr. Dennis B. Heppner. The

personnel contributing to the program and their responsibilities are outlined

below:

Personnel Area of Responsibility

Mike J. Dahlhausen Control and Monitor Instrumentation Software and

Computer Hardware

Tim H. Hallick Program Testing, Data Reduction, Module/Cell

Configurations, Fabrication and Assembly

Dennis B. Heppner, Ph.D. Program Manager, System Design and Analysis

Don W. Johnson Control and Monitor Instrumentation Fabrication

and Electronic Device Design, Assembly and

Checkout

Ray Klimas Control and Monitor Instrumentation Hardware

Design

Eugene P. Koszenski Product Assurance, Electrode/Matrix Development

Joel B. Lantz, Ph.D. TRRHS Concept Review, Trade Studies and Design

Brian N. Livaich Mechanical Component/System Assembly and

Checkout, Data Recording

Franz Schubert System Integration and Electrochemical Design

The contract's Technical Monitor is P. D. Quattrone, Chief, Advanced Life

Support Office, NASA Ames Research Center, Moffett Field, CA.
TABLE OF CONTENTS

PAGE

LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

LISTOF ACRONYMS . . . . . . . . . . . . . . . . . . . . . . . . . . . v

SUMMARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

PROGRAM ACCOMPLISHMENTS . . . . . . . . . . . . . . . . . . . . . . . . 2

INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Program Objectives . . . . . . . . . . . . . . . . . . . . . . . . 6

Report Organization . . . . . . . . . . . . . . . . . . . . . . . 6

ADVANCEDEDC CELL AND MODULE . . . . . . . . . . . . . . . . . . . . . 6

Unitized Core Fabrication . . . . . . . . . . . . . . . . . . . . 7

Composite Cell Fabrication . . . . . . . . . . . . . . . . . . . . 7

Advanced EDC Module . . . . . . . . . . . . . . . . . . . . . . . 8

ONE-PERSON CO2 REMOVAL SUBSYSTEM . . . . . . . . . . . . . . . . . . . 13

General Description . . . . . . . . . . . . . . . . . . . . . . . 13

Application . . . . . . . . . . . . . . . . . . . . . . . . . 13

Specifications . . . . . . . . . . . . . . . . . . . . . . . 13

Mechanical / Electrochemical Assembly . . . . . . . . . . . . . . . 13

Fluids Control Assembly . . . . . . . . . . . . . . . . . . . 19

Coolant Control Assembly . . . . . . . . . . . . . . . . . . 19

Current Controller . . . . . . . . . . . . . . . . . . . . . 19

M/E A Packaging . . . . . . . . . . . . . . . . . . . . . . 25

Control and Monitor Instrumentation . . . . . . . . . . . . . . . 25

General Description . . . . . . . . . . . . . . . . . . . . . 30

Hardware Description . . . . . . . . . . . . . . . . . . . . 30

TESTSUPPORT ACCESSORIES . . . . . . . . . . . . . . . . . . . . . . . 38

CS-1 TSA . . 38

EDC Component TSA 38

continuedi

^ 
ii

Table of Contents - continued

PAGE

TESTING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

CS-1 Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Shakedown Testing . . . . . . . . . . . . . . . . . . . . . . 47

Design Verification Testing . . . . . . . . . . . . . . . . . 47

Endurance Test . . . . . . . . . . . . . . . . . . . . . . . 47

Parametric Tests . . . . . . . . . . . . . . . . . . . . . . 50

EDC Component Endurance Testing . . . . . . . . . . . . . . . . . 50

EDCM Endurance Testing . . . . . . . . . . . . . . . . . . . 50

FCAEndurance Testing . . . . . . . . . . . . . . . . . . . . 50

CCAEndurance Testing . . . . . . . . . . . . . . . . . . . . 58

SUPPORTINGTECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . 58

TRRHS Preliminary Design . . . . . . . . . . . . . . . . . . . . . 58

Space Station CO2 Removal Subsystem Mockup . . . . . . . . . . . . 63

CONCLUSIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
LIST OF FIGURES

PAGE

iii

1 EDC Sngle-cell Schematic . . . . . . . . . . . . . . . . . 4

2 EDC Functional Schematic With Reactions . . . . . . . . . . 5

3 CS-1 T !nitized Core and Composite Cell . . . . . . . . . . . 9

4 Composite Cell EDC Module for CS-1 . . . . . . . . . . . . . 10

5 CS-1 Process Block Diagram . . . . . . . . . . . . . . . . . 14

6 Central Air Humidity Specification Ranges . . . . . . . . . . 16

7 CS-1 Mass and Energy Balance . . . . . . . . . . . . . . . . 17

8 CS-1 Mechanical Schematic . . . . . . . . . . . . . . . . . . 18

9 Fluids Control Assembly . . . . . . . . . . . . . . . . . . . 20

10 Coolant Control Assembly . . . . . . . . . . . . . . . . . . 21

11 CS-1 Current Controller . . . . . . . . . . . . . . . . . . . 22

12 CS-1 Current Controller.-Disassembled . . . . . . . . . . . . 23

13 CS-1 Current Controller/Heat Sink . . . . . . . . . . . . . . 24

14 CS-1 Mechanical/Electrochemical Assembly . . . . . . . . . . 26

15 Multi-Person EDC CO Removal Subsystems . . . . . . . . . . . 27

16 CS-1 Modes and Alloiable Mode Transitions . . . . . . . . . . 31

17 Model 220 C/M I (Front View) . . . . . . . . . . . . . . . . 33

18 Model 220 C/M I (Rear View) . . . . . . . . . . . . . . . . . 34

19 Model 220 C/M I (Internal Packaging) . . . . . . . . . . . . 35

20 Model 220 C/M I Illustrating Major Assemblies . . . . . . . . 36

21 Series 100 versus 200 C/M I Size Comparison . . . . . . . . . 40

22 CS-1 C/M I Actuator Overrides . . . . . . . . . . . . . . . . 41

23 CS-1 TSA-Gas/Coolant Supply . . . . . . . . . . . . . . . . . 42

24 CS-1 TSA-Gas Sample Analysis . . . . . . . . . . . . . . . . 43

25 Liquid-Cooled EDCM Test Stand . . . . . . . . . . . . . 44

26 Coolant Control Assembly Test Stand . . . . . . . . . . . . 45

27 Fluids Control Assembly Test Stand . . . . . . . . . . . . 46

28 CS-1 Performance . . . . . . . . . . . . . . . . . . . . . 49

29 CS-1 Performance (pCO Variation) . . . . . . . . . . . . . . 51

30 CS-1 Performance (Current Density Variation) . . . . . . . . 52

31 CS-1 Performance (RH Variation) . . . . . . . . . . . . . . 53

32 Long-Term EDCM Endurance Test . . . . . . . . . . . . . . . . 54

33 FCA Endurance Test Performance . . . . . . . . . . . . . 57

34 CCA Endurance Test Performance . . . . . . . . . . . . . . . 59

35 Conceptual TRRHS . . . . . . . . . . . . . . . . . . . . . . 62

36 Four Person CO 2 Removal Subsystem Mockup . . . . . . . . . . 64
LIST OF TABLES

TABLE PAGE

1 CS-1 EDCM Weight Summary . . . . . . . . . . . . . . . . . . 12

2 CS-1 Design Specifications . . . . . . . . . . . . . . . . . 15

3 CS-1 Current Controller/Heat Sink Characteristics

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

4 Characteristics of EDC CO Removal Subsystems . . . . . . . . 28

5 CS-1 Mechanical Component 2Weight, Power and

Heat Rejection Summary . . . . . . . . . . . . . . . . . . . 29

6 CS-1 Mode Definitions . . . . . . . . . . . . . . . . . . . . 32

7 Model 220 C/M I Design Characteristics . . . . . . . . . . . 37

8 Model 220 C/M I Weight, Size and Power Consumption Summary . 39

9 Nominal Test Conditions . . . . . . . . . . . . . . . . . . . 48

10 TRRHS Specifications . . . . . . . . . . . . . . . . . . . . 60

iv

P
LIST OF ACRONYMS

A/D Analog/Digital

BID Built-in Diagnostic

CCA Coolant Control Assembly

C/M I Control/Monitor Instrumentation

CPU Central Processing Unit

CS-1 One-Man Person EDC CO Removal Subsystem

DVT Design Verification Tist

EDC Electrochemical Depolarized CO2 Concentrator

EDCM EDC Module

EPROM Erasable Programmable Read-Only Memory

FCA Fluids Control Assembly

M/E A Mechanical/Electrochemical Assembly

NASA National Aeronautics and Space Administration

POR Power on Reset

RAM Random Access Memory

RH Relative Humidty

RTV Resistive Thermal Device

TRRHS Triple Redundant RH Sensor

TSA Test Support Accessories

v

N
SUMKARY

Regenerative carbon dioxide removal techniques are needed to sustain man in

space for extended periods of time. The most promising concept for a

regenerative carbon dioxide removal system is the Electrochemical Depolarized

Carbon Dioxide Concentrator. This device allows for the continuous, efficient

removal of carbon dioxide from the spacecraft cabin and delivery of the carbon

dioxide premixed with hydrogen to a carbon dioxide reduction subsystem for

subsequent oxygen recovery.

The objectives of this program for the Electrochemical Carbon Dioxide

Concentrator subsystem were to (1) achieve high level of performance of a

one-person electrochemical carbon dioxide concentrator subsystem with the

ability to operate over wide ranges in relative humidity and H,, back

pressure, (2) demonstrate reliability by endurance testing the`major

components of an electrochemical concentrator subsystem, (3) demonstrate

achievement of reproducible electrochemical cell and module performance and

subsystem simplification concepts through extensive testing and (4) continue

to improve and develop needed ancillary components. These objectives were

successfully met. The program included (1) the fabrication, assembly and

testing of an advanced one-person carbon dioxide removal subsystem based on a

new electrochemical cell and module concept and unitized core composite

cells, (2) endurance testing of the three major components of an electrochemical concentrator, i.e., a six-cell module with unitized composite cores,

a Coolant Control Assembly and a Fluids Control Assembly, (3) test support

accessories required for subsystem testing, and (4) a preliminary design for a

triple redundant relative humidity sensor with in situ calibration. A

detailed mockup of an electrochemical concentrator subsystem as would be

applicable for the Space Station was also developed.

A one-person electrochemical concentrator subsystem was fabricated, assembled

and tested. The electrochemical module consists of six cells of a new

::onstruction. The new construction permitted the fabricatior of any size

midules without having to alter process air inlet and outlet duct work. All

ancillary components fit onto an end plate which is easily adaptable to any

size subsystem. A newly developed microcomputer based instrumentation, which

is roughly 75% smaller in weight, volume and power than the previous series of

instrumentation, was fabricated and used to control the one-person subsystem.

The one-person system consistently demonstrated high level, repeated performance

over 1,800 hours of operation and relative humidity variations between 30 an.,

85%. Average carbon dioxide removal efficiency was typically between 90 and

1002 (versus the 85% design point) at a nominal carbon dioxide partial pressure

of 400 Ps (3.0 mm of Hg). The cell voltages averaged 0.42 V. The module

nominally sustained 35 kPa (5 psig) H 2-to-air differential pressures.

Endurance testing of three electrochemical carbon dioxide removal. subsystem

components was continued under the program. Over 11,000 h of additional

operation was achieved on the six-cell module having the unitized composite

core construction. Average carbon dioxide removal efficiency was typically

greater than 70% at nominal carbon dioxide partial pressures of 400 Pa 0 mm

of H6;. Cell voltages averaged 0.35 V.
A Fluids Control Assembly with its test stand performed for a total of

9,500 additional hours, which included over 10,000 test cycles. No failure of

the Fluids Control Assembly was observed. The Coolant Control Assembly

performed at or above its design point levels for over 9,400 additional hours

(18,800 typical test cycles) Satisfactory mechanical performance was achieved

on both of these devices.

A concept for a triple redundant relative humidity sensor based on directly

sensing the moisture content of air was designed. The design incorporates in

situ calibration with a repeatable gas pressure calibration source.

PROGRAM ACCOMPLISHMENTS

The key program accomplishments were as follows:

• Completed the fabrication of pi one-person Electrochemical Depolarized

carbon dioyide (CO ) Concentrator (EDC) subsystem incorporating

advanced electrochemical, mechanical and control and monitor instrumentation (C/M I) concepts. This subsystem, called the CS-1,

included the design of an advanced, liquid-cooled unitized core/

composite cell EDC module (EDCM) that features superior performance

stability, inlet air relative humidity (RH) range tolerance. pressure

capability and thermal characteristics and lower unit weight and

volume relative to prior modules.

• Completed over 1.800 h of testing of the CS-1 with CO 2 removal

efficiencies between 90 and 100%

• Designed and fabricated two new molds for injection molding

polysulfone cell frame parts. The cell frames together with a new

unitized core assembly permitted the assembly of six cell frames for

the CS-1.

• Completed endurance testing of a prototype Fluids Control Assembly

(FCA) which integrates 11 gas handling components required by the

CS-1 into a single unit.

• Completed endurance testing of r prototype Coolant Control Assembly

(CCA), which integrates a coolant pump, diverter valve and a liquid

accumulator into a single unit.

• Modified a test stand which provided all the fluid, electrical and

shutdown requirements for long-term, unattended testing of the CS-1.

• Developed a four-person EDC mockup. This mockup is useful to

demonstrate the size of the CO

2

 removal subsystem as would be

developed for a Space Station.

• Completed a preliminary design of a triple redundant RH sensor

(TRRHS), which will have in situ calibration and which will be

miniature relative to the present RH or dew point sensor.

2
INTRODUCTION

Regenerative processes for revitalization of spacecraft atmospheres are essential

for making long-term manned space missions a reality. An important air revitalization step is the collection and concentration of metabolically produced CO2

for subsequent oxygen (0 ) recovery. This report discusses development of an

electrochemically-based lubsystem which performs that function.

Background

The EDC technique is the most promising technique for concentrating low level

CO from the air without incurring large weight and volume penalties. The EDC

removes CO continuously from low CO partial pressure in a flowing air

stream. Re CO exhaust, premixed with H 2 , can be sent to a CO reduction

subsystem for recovery of the 0 2 from the CO2 or vented, as required. The EDC

also generates electrical power which can be used in other life support

processes (e.g., 0 2 generation by water electrolysis) if that is desired.

The CO2

 removal process takes place in a module consisting of a series of

electrochemical cells. Each cell corsists of two electrodes separated by a

matrix containing an aqueous carbonate electrolyte solution. Plates adjacent

to the electrodes provide passageway4 for distribution of gases and electrical

current. Figure 1 shows the functional schematic of the EDC cell. Figure 2

details the specific electrochemical and chemical reactions which occur at the

electrodes. As shown in Figure 7, the overall reaction is

02 + 2 CO2 + 2 H 2 a 2 CO2 + 2 H2O + electrical energy + heat (1)

A theoretical maximum of two moles of CO 2

 can be transferred for one mole of

0 consumed. The observed ratio of CO2

 transferred to 0 2 consumed represents

tie process removal efficiency. A defined efficiency of 100% occurs when 2.75

kg (6.05 lb) of CO 2 is removed for each kg (2.2 lb) of 0 2 consumed.

The EDC concept utilizing alkaline metal carbonate electrolytes has evolved at

Life Systems, Inc. (LSI) under the National Aeronautics and Space Administration

(NASA) spontTEOP through Contracts NAS2-6118, NAS2-6478, NAS2-8666 and

NAS2-10204. The concept has progressed from operation of single EDC

cells to fabrication and testing of one-, three-, four- and six-person selfcontained subsystems. These previous research and development activities

resulted in demonstrated performance improvements in the electrodes, the

electrolyte and the electrolyte retaining matrix. These programs also include

development of unique peripheral components and advancement of technology

relating to EDC subsystem integration with other spacecraft air revitalization

svl-yetems.

(1-12) References cited at the end of this report.

3
Process Air

Inlet

ORIGINAL PAQL W

OF POOR QUALITY

H, + CO,

Outlet

Liquid

Coolant

Inlet

Cathode

Anode

Coolant

Cavity

Electrolyte/

Coolant Matrix

Cavity

Separator

PolysuHom

Parts

H,

Inlet

Liquid

Coolant

Outlet

Process Ali

Outlet

FIGURE 1 EDC SINGLE-CELL SCHEMATIC

4
ORIGINAL PAGE 11

OF POOR QUALITY Stat/Siop Switch:

Lad Control ,

4"^^40144-

2H2O

4H2O^^

2H2O

2H2

Oz

220 H

2CO3 =

2CO2

2003

--- — -- — Carbonate ..- —.. — -

- — — — Electrolyte — —.

Cathode

Cathode Pisa kx*:

02 + 2H2O + 4e- = 4OH4OH- + 2CO2 - 2H2O + 2CO3 =

Anode Reactions:

2H2 + 4CH- 4H2O + 4edIC:03 = + 21-12O = 4OH- + 2CO2

Overall Reaction:

02 + 2CO2 + 2H2 z 2CO2 + 2H2O + Electrical Energy + Hest

FIGURE 2 EDC FU.4CTIONAL SCHEMATIC WITH REACTIOWS

5
Program Objectives

The objectives of this program were to:

1. Using newly designed hardware, including cell frames and composite

cores, fabricate and test a one-person liquid cooled EDC subsystem

(the CS-0.

2. Demonstrate achievement of reproducible electrochemical module

performance and subsystem simplification concepts through extensive

testing.

3. Simplify and increase EDC subsystem reliability by design of a

TRRHS.

4. Achieve reproducible and predictable high level EDC performance over

ranges of relative humidity, H 2 backpressure and inlet CO2 partial

pressure for the CS-1 subsystem wider than previously demonstrated.

5. Continue to improve EDC subsystem performance.

The objectives of the program were met.

Report Organization

This Final Report covers the work performed during the period December, 1981

through November, 1983. The following major sections of this report present

the technical results grouped according to:

• Advanced EDC cell and module

0 One-person CO2 removal subsystem

• Test support accessories

• Testing

• Supporting activities

These sections ore followed by conclusions and recommendations based upon the

work performed and by the references cited in the text.

ADVANCED EDC CELL AND MODULE

The hear' of the F.DC CO Removal Subs ystem is the EDCM and considerable

attention was giver to improving the dividual cells and the overall module.

The objectives of the composite cell th unitized core development were to

achieve reproducible and predictable high level EDC performance over extended

ranges of differential cell pressure and process air RH. The unitized core

concept enables such improvements by providing permanently bonded, versus

mechanically sealed, cell construction. This technology prevents gas leakage

across the edges of a cell matrix and therefore permits operation at higher

H -to-air differential pressures. It also provides uniformed matrix support

and thickness both up to and including the edges, resulting in uniform

electrolyte distributi-n and a superior RH tolerance range. The following

subsections describe ,4e core design and fabrication, the cell fabrication and

the advanced EDC module.

6
Uritized Core Fabrication

Since a major driver for composite EDC cell construction was to enhance

pressure differential and broaden RH capabilities, primary emphasis was

directed toward selection of compatible materials and the fabrication technique

for the unitized core, the heart of the cell. Following material selection,

preliminary methodology and equipment were defined for fabricating the building

blocks of the unitized core (matrix, gas cavity spacers and electrodes) and

assembly of the core. Initial fabrication procedures were then written, and

fixtures were fabricated to allow building of a breadboard 7.3 x 7.3 cm 0 x. 3 in) cell. This activity was performed on a prior program and showed

that the fabrim fon procedures could be used to successfully develop a

unitized core. Under the present program these procedures and fixtures

were upgraded to permit the fabrication of a unitized cote for the new CS-1

cell design, which has an active area of 465 cm ` (0.5 ft ). Six of these

unitized core assemblies were fabricated for the CS-1 and none failed

throughout the testing of this subsystem.

The unitized core combines the following five major elements of the

electrochemical cell: (1) Process air gas cavity spacer, (2) the airside

electrode (cathode), (3) the cell matrix, (4) the hydrogen side electrode

(anode) and (5) the H2 gas cavity spacer. Fabrication of the unitized core

involves, first, the application of epoxy rims around the perimeters of the

process gbs cavity spacers and the cell matrix. This creates three

subassemblies. These subassemblies are then combined with the electrodes,

using more epoxy, to form the unitized core. This approach provides a uniform

support of the cell matrix over its entire area, thereby avoiding edge

distortion, maximizing gas pressure sealing characteristics of the

electrochemical cell and promoting uniform response of the electrolyte to

humidity changes.

The key structural material selected for the unitized core fabrication is an

epoxy resin. It forms the frames around the matrix and the expanded metal gas

cavity spacers and provides final sealing of the various building blocks to

form the unitized core. This material is compatible with the environment,

exhibits sufficient strength and has the needed flexibility. Critical

requirements of the fabrication process include maintainirg proper epoxy

thickness and uniformity and excluding air bubbles and pockets in the cured

epoxy rim. These parameters are controlled using combinations of heat,

pressure and vacuum applications. Care must be taken to ensure that all

components of the core are properly aligned with respect to the gas inlet and

outlet areas, that the cell matrix and electrode active areas are free from

epoxy, and that an effective epoxy seal is achieved around the edge of the

unitized core.

Composite Cell Fabrication

The overall concept for the composite EDC cell design and fabrication consists

of the unitized core as discussed above, injection-molded polysulfone plastic

frames for manifolding and distributing the process gases and internal

I
coolant, and current collectors for delivering current to the cell. The

composite cell polysulfone cell frame is fabricated as two sections - an air

frame and an H frame. These are so named because of the process fluids, air

and H, that t9ey come in contact with. A coolant cavity cover is epoxied to

the air frame and then the cathode current collector is laser-welded to the

current tabs. The H frame, with the anode current collector laser-welded to

its current tab, is hen epoxied together with the air frame. This

fabrication process provides an isolated internal liquid coolant cavity for

the EDC cells.

Process fluid isolation is accomplished by an arrangement of 0-rings that

provide seals between each composite cell in the module stack. A molded

O-ring was designed and fabricated to provide intercell sealing around the

entire periphery of the cell frame. This provided sealing of process air from

Internal to external of the module.

Figure 3 shows the unitized core and composite cell elements. Under this

program, five molds were designed, fabricated and used to make cell parts.

Two large molds were used to make the two polysulfone cell frame parts. The

H frame, in particular, was the most difficult to iniection mold because of

its large size and thickness. Several trial and error molding injection

attempts were made until the parts came out satisfactorily. Nonetheless, the

molds were very precise: the parts (air and H 2 frames) from the two separate

molds fit together almost perfectly. Three smaller molds were developed for a

large sealing 0-ring and two types of silver tabs (one for each type of frame)

used to transfer the current to the silver foil current collectors. All other

cell parts were machined or purchased as commercially available parts.

Advanced EDC Module

The advanced EDCM is designed as a liquid-cooled module, composed of six

unitized core composite cells for superior performance and differential

pressure capability. Each composite cell consists of the electrochemical

elements described above. The selected number of cells, six, was based on the

one-person 2 CO removal rate of 1.0 kg/d (2.2 lb/d) and a current density of

21.3 mA/cm (19.8 ASF). The module has additional CO. removal capacity if

operated at higher current density.

The. advanced composite cell frames incorporated into the CS-1 feature integral

process air manifolds. These are apparent in the module drawing, Figure 4.

This design simplifies interfacing with the process air; only one set of inlet

and outlet ducts are required to interface the process air no matter how many

cells are in the module. It also enhances module storage life by permitting

capping of the manifolds to avoid dryout (versus sealing the module in plastic

bag). Most importantly, it allows vacuum charging of the total module (versus

one cell at a time) with electrolvte. This ensures uniform charging of all

cells, allows isolation of the cells from the atmosphere after they are charged

(since they are already assembled into a module) and saves considerable time.

The advanced, composite cell frame design provided vastly improved (from prior

cell designs), permanently sealed coolant cavities. The! several advantages of

this design were proven during testing:

8
'-D 

Composite Cell 

, 

Coolant C

Cover 

FIGURE J CS-l UNITIZED CORE AND COMPOSITE CELL 
in.

-^,-- 5.0 --^

in.

ORIGINAL PAGE 18

OF POOR QUALITY

Hz orFN^From

Coolant From CCA

Mob to Air/Liquid H To FCA ppHx N2 To FCA Vent From FCA

Coolant Inlet

t_

Module HZ Inlet

from Airlliquid Hx

Coolant J=^- -- -

CCA to Hx i

a

Air i Air G

Inlet O o Outlet

O

^

0

p O

p

Coolant p

Hx to CCA

-- ----- - — 

-.15.50

In.

^ i

FIGURE 4 COMPOSITE CELL EDC MODULE FOR CS-1

10
e First, the coolant cavity design significantly improved thermal

conduction from the cathode, where most of the heat is produced,

because the thickness of plastic between it and the coolant was

minimized. Heat removal and cell temperature regulation was

therefore improved. Conversely, the new design reduced thermal

conduction from the anode, where water is produced, since there now

exists an increased thickness of insulating plastic and a foil

current collector. This provides desirably higher anode

temperatures. The effect was to provide improved cooling and

temperature regulation at the primary point of heat production and

promote water removal at the point of water generation.

Second, when cell operation ceases, the anode temperature drops to

the coolant temperature at the same time water production stops, and

cell dryout is avoided. Conversely, the coolant temperature is not

so low as to permit condensation. This was again borne out in the

testing; approximately 15 applications of current ( startup) occurred

with no problems. This approach also should avoid damage to cells

that electrically are isolated by any in situ cell. maintenance

techniques that jumper out inactive cells.

e The bonded cavity seal proved to be more reliable than the prior

mechanical ( 0-ring) seals. Throughout the testing there were no

leaks from the internal H cavity to the external atmosphere or

across the matrix from thl H22 to the air side. The module held

pressure at 34 . 5 kPa ( 5 psigl from the beginning of the testing to

the end.

e The coolant is intrinsically electrically isolated from the cell,

eliminating the need to electrically isolate coolant components.

Indeed, in the CS-1 design the coolant is distilled water. There

was no need to use specialized nonconducting `rlaiis as in the past.

There were no electrical grounding problems associated with the

CS-1.

The CS-1 EDCM component weight summary is shown in Table 1. It should be

noted that the top and bottom end plates used in the CS-1 were made from

stainless steel and naturally were heavy. Stainless steel was selected for

severe: reasons. First, the material was inexpensive and machining costs were

fairly minimal. Secondly, the top end plate and, to a certain extent the

bottom, contain fluid pathways and structural strength was required to ensure

no breakthrough of these pathways. For instance, the top end plate has nine

separate channels drilled into it. With stainless steel, these channels could

be drilled and then plugged and welded on the outside. With other materials

the sealing would be more difficult. Another reason was the unavailability of

the desired alternate material ( glass-filled polysulfone) in the size required

to make the end plates. Even though the stainless steel was a convenient and

at this point, necessary material it is recognized that the top and the bottom

end plates presently comprise almost 80% of the total CS-1 EDCM weight.

Probably a 60 to 70% reduction in this area can be achieved with alternate

materials. However, these have to be evaluated in terms of structural strength

and their ability to support the various internal passages without other

impacts ( such as significantly increased thickness).

11

^
TABLE 1 CS-1 EDCH WEIGHT SUMMARY

Unit Weight, Total Weight

Part Oty kg (lb) kg (Ib)

Top End Plate Assembly 1 16.40 (36.00) 16.40 (36.00)

Bottom End Plate Assembly 1 20.10 (44.20) 21.10 (44.20)

Top Insulation Plate 1 0.91 (2.00) 0.91 (2.00)

Bottom Insulation Plate 1 1.00 (2.20) 1.00 (2.20)

H2 Frame 7 0.30 (0.67) 2.13 (4.69)

Air Frame 7 0.08 (0.17) 0.54(l.19)

Unitized Core 6 0.33 (0.73) 1.99 (4.38)

Coolant Cavity Cover 7 0.09 (0.20) 0.64(l.40)

Molded 0-ring 9 0.01 (0.03) 0.12 (0.27)

H 2 Frame Current Collector 6 0.05 (0.12) 0.33 (0.72)

Air Frame Current Collector 6 0.06 (0.13) 0.35 (0.78)

FCA Adapter Plate 1 0,60(l.32) 0.60(l.32)

CCA Adapter Plate 1 0.71(l.57) 0.71(l.57)

Bolts, Washers, Nuts, Epoxy Misc. 0-55(1.20) 0-55(1.20)

Total 46.33 (101.92)(x)

a. A flight unit, with lightweight end plates, would weigh 20.8 kg (45.8 lb)

a

12
ONE-PERSON CO2 REMOVAL SUBSYSTEM

The major achievement under this program was the fabrication, assembly and

successful testing of a one-person CO removal subsystem, the CS This

section describes the design and fabrication of the CS-1. Testing is covered

in a subsequent section. This section includes a general description including

specifications and a schematic, a description of the Mechanical/Electrochemical

Assembly (M/E A) and a description of the C/M I.

General Description

The overall CO,, removal process and control scheme is shown in Figure S. The

WE A includes ` s six-cell EDCM and all components required to sense and

control gaseous and liquid fluid flows to and from this module. The C/M I

controls overall subsystem operation through the sensors and actuators located

on the M/E A. The C/M I also monitors end interprets subsystem operational

parameters and through the use of a communication link can display values on a

separate video monitor. It can also, through the communication link, provide

for appropriate changes in operational modes in response to operator inputs or

subsystem malfunctions.

Application

Two applications were considered for the CS-1. They include use in the

Shuttle Orbiter as a replacement of the existing lithium hydroxide (LiOH)

CO2 removal function. The second application is part of a central air

revitalization system as would be found in the Space Station. Because of

increased interest in the Space Station recently, the CS-1 was tested

extensively in the central application range.

Specifications

General design specifications are listed in Table 2. The RH/temperature range

projected for the Space Station application is shown in Figure 6. Overall

fluid, electrical and thermal inputs and outputs for the CS-1 are further

illustrated in Figure 7.

Mechanical/Electrochemical Assembly

The WE A is illustrated schematically in Figure S. The four primary

components are:

• The EDCM, which is the CO2 concentration element

ti An FCA, which regulates EDCM back pressure and N 2 and H2 flows

e The CCA, which in conjunction with the liquid/liquid heat exchanger

permits temperature regulation of the EDCM

e A current controller (liquid-cooled), which regulates the current to

the EDCM
I

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URIGINAL PAGE IS

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Air Outlet

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FIGURE S CS-1 PROCESS BLOCK DIAGRAM

14
ORIGINAL PAGE 13

OF POOR QUALITY

TABLE 2 CS-1 DESIGN SPECIFICATIONS

Application

Central Shuttle

1 1

1.0 (2.2) 1.0 (2.2)

400 (3.0) 667 (5.0)

667(5-0) 1.013 (7.6)

22.1 (3.2) 22.1 (3.2)

286 to 297 291 to 302

(60 to 75) (65 to 84)

277 to 286 277 to 289

(40 to 60) (39 to 61)

101 (14.7) 101 (14.7)

See Figure 6 20-80

280(45) 275 to 295 (35 to 71)

432 (950) 432 (950)

0.007 (0.014) 0.0024 (0.0053)

2.9 Stoichiometric 1.2 Stoichiometric

(at 9.9A) (at 9.OA)

173(25) 173(25)

0to75 0to5

N2 N2

173(25) 173(25)

115, 400 Hz, 10 115, 400 Hz, 10

28 28

Crew Size

CO2 Removal Rate, kg/d (lb/d)

Cabin PCO2, Pa (mm Hg)

Daily Average

Maximum

Cabin p02, kPa (psia)

Cabin Temperature, K (F)

Cabin Dew Point, K (F)

Cabin Pressure, kPa (psia)

Process Air Humidity Range,

• Liquid Coolant

Temperature (max), K (F)

Flow Rate, kg/h (lb/h)

H2 Supply

Flow Rate, kg/h (lb/h)

Pressure, Pa (psia)

Relative Humidity, %

Purge Gas

Type

Pressure, kPa (psia)

Electrical Power

VAC

VDC

Gravity

Noise Criteria, db

0to1 Oto1

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In addition to the primary components, two of which integrata several discrete

device functions, the subsystem includes: (a) two filter/isolation valves

(inlet and outlet), (b) two dry bulb temperature sensors (c) two dew point

temperature sensors, which when combined with the dry bulb temperature sensors,

are used to measure inlet and outlet RH and (d) a liquid/liquid heat exchanger.

The principal WE A components besides the EDCM, which was discussed

previously, are described further below.

Fluids Control Assembly

The CS-1 EDCM, like its precursors. will require monitoring and control of IHP2

flow. H back pressure and N ^ purge gas flow. These functions previously

performid by 11 discrete components, have now been integrated into a single,

lightweight, low volume FCC► . This assembly, pictured in Figure 9. was

developed under a prior program and has been endurance tested for almost

20.000 hours. The CS-1 is the first application for the FCA in a subsystem.

Coolant Control Assembly

Three elements are essential for temperature control of the liquid-cooled

EDCM: a circulation pump, a diverter valve to regulate the proportions of

module coolant flowing through and around .s liquid/liquid heat exchanger

(connected to a central coolant source) and a liquid/gas accumulator to

accommodate module coolant expansion/contraction. These discrete components,

which require individual mounting and interconnecting plumbing, have been

replaced by an integrated CCA. This item, pictured in Figure 10. alr+o was

developed under a prior program and has been extensively endurance tested and

this program represents the first time it has been used in a CO 2 removal

subsystem.

Current Controller

The current controller, Figure 11, provides a regulated current sink for the

power generatee by the EDCM. For the CS-1 it is packaged as a separate

device. It is designed to be liquid cooled and lowod with the CS-1 WE A.

The central coolant source that interfaces with the CCc also removes the waste

heat from the current controller. Placement of the current controller near

the EDCM reduces the length of the electrical leads between the module and the

current controller and thereby minimises voltage drops.

The CS-1 current controller was fabricated, checked out and installed in tha

subsystem. This unit is an improvement over prior EDC current controllers,

not only in size reduction but also in the method M:.a efficiency of controlling

current and dissipating the EDCM-produced power. It uses power field effect

transistors mounted on a thermal surface (see Figure 12) and instrumentation

amplifiers for control and sensing. &is thermal surface or base of the current

controller is in direct contact (ph•sical and thermal) with a liquid-cooled

heat sink in normal operation as shown in Figure 13. The current controller

was packaged separately from the heat sink to allow removal and maintenance of

the controller without breaking into the spacecraft coolant line. Characteristics and operating conditions of the current controller and heat sink are

19
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FIGURE 10 COOLANT CONTROL ASSEMBLY

21

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FIGURE 13 CS-1 CURRENT CONTROLLER/HEAT SINK

24
given in Table 3. This current controller can accommodate multi-person EDCMs.

The maximum power dissipation capability of the current controller is 200 W.

During CS-1 testing the nominal power dissipated was 25 W.

TABLE 3 CS-1 CURRENT CONTROLLER/HEAT SINK CHARACTERISTICS SUMMARY

Current Range, A 0-25

Supply Voltages, VDC * 15, 28

Power Required, W 3

Max. Power Dissipation, W 200

Coolant Flow, dm3/min (gal/min) 0-15(0-4)

Temperature, K (F) 280-289(45-60)

Current Controller Heat Sink

Weight, kg (lb) 1.0 (2.2) 0.82 (1.?"

Volume, dm3 (in3 ) 0.62 (38) 0.26 (16)

Dimensions, cm (in) 9.9 x 9.4 x 6.6 15 x 9.9 x 1.8

(3.4 x 3.7 x 2.6) (5.9 x 3.9 x 0.7)

M/E A Packaging

The assembled CS-1 M/E A is shown in Figure 14. The major subassemblies, as

indicated, are the FCA, the CCA, the EDCM and inlet and outlet process air

ducts. Each of the latter includes an isolation/filter valve, a dew point

temperature sensor and a dry bulb temperature sensor. The dew point sensor is

a commercial chilled mirror type sensor in which the electronics were

incorporated in the C/M I. The temperature sensors are resistive thermal

device (RTD) types. In addition, the inlet duct contains an air/liquid heat

exchanger (not shown) which preconditions the process air prior to entering

the EDCM.

Figure 15 chows EDC CO 2 removal subsystems at various person capacities to

illustrate the flexibility of achieving multi-person systems with the basic

CS-1 design. It is noted that only the height dimension changes. Detailed

characteristics of one to 12 person sizes are given in Table 4. It should be

noted that the listed weights assume a light-weight end plate construction.

Table 5 summarizes the CS-1 M/E A weight, power and heat rejection

requirements.

Control and Monitor Instrumentation

The function of the CS-1 C/M I is to provide for automatic mode and mode

transition control, automatic shutdown for self-protection, monitoring of

subsystem parameters and interfacing with ground Test Support Accessories

(TSA) and data acquisition facilities. Under this program a new series of

instrumentation based on microcomputer technology was developed. The CS-1

C/M I, termed the Model 220, represents a major size reduction from the prior

series of instrumentation. The weight, volume and power consumption were

reduced by over 75%.

5
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FIGURL 14 CS-1 MECHANICAL/ELECTROCHEMICAI ASSEMBLY

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TABLE 4 CHARACTERISTICS OF EDC CO2 REMOVAL SUBSYSTEMS 

Model No. of Capacity, People @ Weight, Volume, Dimensions, em (in) 

No. eells·al 3 mm H--'I 12mm Hg kg (Ib) dm3 (fP) Ht Wd Ln 

CS·l 6 1 2 23 (50) 45 (1.6) 34.0(13.4) 39.4 (15.5) 34.3(13.5) 

CS-2 12 2 4 28(62) 54 (1.9) 40.1 (15.8) 39.4 (15.5) 34.3 (13.5) 

CS-3 18 3 6 34(74) 62 (2.2) 46.2 (18.2) 39.4 (15.5) 34.3 (13.5) 

CS-4 24 4 8 39(86) 71 (2.5) 52.3(20.6) 39.4 (15.5) 34.3 (13.5) 

CS-6 36 6 12 50 (110) 88(3.1) 65.4 (25.4) 39.4(15.5) 34.3 (13.5) 

CS-8 48 8 16 61 (134) 105(3.7) 76.7 (30.2) 39.4(15.5) 34.3(13.5) 

---- -

a. Based on 2.20 Ib C02/person·day. 

Powe

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10 

40 

70 

100 

160 

220 
ORIGINAL PAGE 18

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TABLE 5 CS-1 MECHANICAL COMPONENT WEIGHT,

POWER AND HEAT REJECTION SUMMARY

Total Total Neat

AC Power, DC Power, Rejection,

W W W

- -27 41

- 2(0) 2

75 -- 75

- 1 1

- 1 1

- 3 30(d)

75 -27 150

Unit Total

Item No. Weight!') Weight,

No. Component Req'd kg (Ib) k9 (lb)

1 EDCMibI 1 46.3 (101.9) 46.3 (101.9)

2 Assembly, Fluids Control 1 1.7( 3.8) 1.7( 3.8)

3 Assembly, Coolant Control 1 2.7( 6.0) 2.7( 6.0)

4 Heat Exchanger, Liq!Liq 1 0.8( 1.8) 0.8( 1.8)

5 Filter! Isolation Valve 2 0.7( 1.5) 1.4( 3.0)

6 Sensor, Dew Point 2 0.2( 0.5) 0.4( 1.0)

7 Sensor, Temperature 2 0.1( 0.2) 0.2( 0.4)

8 interface, Inlet Air (w!Heat) 1 2.2( 4.8) 2.2( 4.8)

9 Interface, Outlet Air 1 1.2( 2.7) 1.2( 2.7)

10 Assembly, Current Controller 1 1.8( 4.0) 1.8( 4.0)

- 58.5 (129.4)

(a) Dry weight.

(b) Does not have honeycomb end plates.

(c) Steady-state operation sensors.

(d) The 27 W of EDCM power is converted to heat.

29
Four operating modes are available for the subsystem. as shown in Figure 16

with separate Normal modes corresponding to the operating conditions of either

Shuttle or Central (i.e., Space Station) application. Each mode is defined in

Table 6.

General Description

The CS-1 /M I receives and transmits signals from and to the M/E A sensors

and actuators. Through these it controls and monitors subsystem pressures,

flow rates, temperatures, cell voltages, current and valve positions in each

operating mode. It implements each mode, whether initiated automatically or

manually and provides fail-safe operational changes to protect the CS-1 if

malfunctions occur.

Internally, process operating mode control is a relatively complex operation.

It includes selection of different unit processes, selection of valve

positions, sequencing of valve positions, sequencing of actuators and checking

parametric conditions as a transition (e.g., Shutdown to Normal Central)

proceeds. However, this procedure for control is fully automated by the C/M I

so that the operator only needs to press the Mode Enable and the desired mode

buttons to initiate transition sequences.

Hardware Description

The 220 C/M I is shown in a series of photographs, Figures 17-20. These

illustrate, respectively, the front view, rear view, the total assembly

without its protective dust cover and an exploded view indicating the major

assemblies. There are five major assemblies in the 220 C/M I:

1. Computer car:! cage containing the microprocessor's central

processing unit (CPU) along with support cards (memory,

analog/digital conversion (A/D), digital input and output, etc.).

2. Power supply module for supplying ±15 V and +5 V from the input

power of +28 V.

3. Signal conditioning card cage and 11 signal conditioning cards for

conditioning the sensor outputs and providing actuator drive

signals.

4. Power assembly for supplying those sensors and actuators which

require drive current for their operation (dew point, flow, and

motor actuation)

5. Front panel assembly with status indication and mode transition

selection buttons.

Design characteristics of the :40del 220 C/M I are given in Table 7. The C/M I

uses Erasable Programmable Read-Gly Memory (EPROM) for its program storage.

It also uses some Random Access Memory (RAM) for data storage. This permits

the access of the real-time data by an external monitor through a standard

communications link.

30
ORIGINAL PAGE 19

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5 Modes

• 4 Operating Modes

• 13 Mode Transitions

• 9 Programmable, Allowed

Mode Transitions

FIGURE 16 CS-1 MODS AND ALLOWABLE MODE TRANSITIONS

31
TABLE 6 CS-1 NODE DEFINITIONS

Mode (Code) _

Shutdown (B) The EDCM is not removing CO2 . Module current is zero, the CCApump isoff and all valves are closed.

The system is powered and all sensors are working. The Shutdown Mode is called for by:

• Manual actuation

• Low EDCM individual cell voltage

• Low H2 pressure

• High H2 pressure

• Lo.r outlet process air RH

• High outlet process air RH

• Second failure of triple redundant sensors for pressure, relative humidity, temperature and

combustible gas concentration (capability only)

• Power on reset (POR) from Unpowered Mode D

• Mode transition from Shutdown Mode (B) to Normal Shuttle (A), Normal Central (F), or Purge (C)

was not successful. All transitions to the Shutdown Mode except POR and Purge include a

timed purge sequence as part of the mode transition sequence.

Normal Shuttle (A) The EDCM is operating at the constant current density of 19.4 mA/cm 2 (18.0 ASF) sized to perform

the CO2 removal function for one-person assuming an inlet pCO 2 level of 667 Pa (5.0 mm Hg). The

Normal Shuttle Mode is called for by:

• Manua: actuation

Normal Central (F) The EDCM is operating at a constant current density of 21.3 mA/cm 2 (19.8 ASF) sized to perform the

CO2 removal function for one-person assuming an inlet PCO2 level of 400 Pa (3.0 mm Hg). The

Normal Central Morse is called for by:

• Manual actuation

Purge (C) The EDC is being purged with N 2 through all H2 lines, H Z carrying module cavities and out through the

vent line. Module ci , rrent and the CCA pump are off. This is a continuous purge until a new mode is

called for. The Purge Mode is called for by:

• Manual actuation

Unpowered (D) No electrical power is applied to the EDC. Actuator positions can only be verified visually. Process air

flow is stopped. There is no N 2 or H2 flow. The Unpowered Mode is called for by:

• Manual actuation (circuit breaker)

• Electrical power failure

• C/M I failure as detected by the Built-in Diagnostic (BID) circuit and supply power to the C/M 1 is

interrupted

32
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FIGURE 19 MODEL 220 C/M I (INTERNAL PACKAGING)

35
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TABLE 7 MODEL 220 C/M I DT.ISIGN CHARACTERISTICS

Dimensions (HxWxD), cm (in) 19 x 39 x 40 (7.4 x 15.3 x 15.6)

Power Input, W 80

C/M I Power Consumption, W 67

Input Voltage, VDC 28 t 4

Computer Assembly

Bus STD-8088

Microprocessor Intel 8088

Machine Cycle Time, nsec 200 (5 MHz)

EPROM Memory, Bytes 32 K

RAM Memory, Bytes 16 K

Digital 1/0 64 TTL Lines

A/D Converter

Channels 32 single ended

Resolution 12 bits

Full Scale Ranges t 10 mV to ±10V 

D/A Converter

Channels 4 single ended

Resolution 12 bits

Full Scale Range t 10 VDC @ 5 mA

Serial Communications 1 RS232 Port

Signal Conditioning Assembly

Card Slots 12 Max.

Input Sensor Types: Differential Voltage

Wein Bridge

RTD

Reluctance Pickup (Speed)

Dew Point Sensor

LVDT

Total Number of System Inputs 19

System Outputs:

Total Number 7

Thermoelectric Cooler 2 ® 2 Amps Max.

DC Motors (28 VDC) 2

AC Motor (115 VAC @ 400 Hz) 1 on/off

Analog Current Setpoint 1 @ 0 to 5 VDC

Current Control—On/Off 1 ® 0 to 5 VDC

Communications

Front Panel

Operating Mode 5 Pushbuttons

Status 3 Indicators

Error Code 8 Digit Display

Error Code—Advance 1 Pushbutton

Communications Link 1 Asynchronous RS232 Port

Shutdown Inputs 1 0 5 VDC

Shutdown Outputs 2 ® 5 VDC

Operating Modes

Number of Operating Modes 4

Number of Allowable Mode Transitions 9

37
The size, weight and power summary of the C/M I is shown in Table 8. The

previously mentioned size reduction, of approximately 75% in weight, volume

and power, is evident in Figure 21, which compares the 220 C/M I with the

prior version Series 100 C/M I. The computer section alone represented almost

a 90% reduction in weight and power consumption with an increase in

reliability by using non-volatile (EPROM) memory versus the volatile or

magnetic core memory of the Series 100.

A separate enclosure houses controls that permit override of the actuators

during startup testing. This unit is shown in Figure 22. It was designed to

be used directly in-line with the actuator cables going to the CS-1. The

subsystem can be operated with the unit installed or not. (With the four

actuator switches in the auto position, the signals pass directly through the

unit.) Except for the very initial stages of the testing, the CS-1 was

operated with the actuator override controls removed from the subsystem.

TEST SUPPORT ACCESSORIES

Test Support Accessories (TSA) were developed and/or refurbished for the

program. This included major revisions of the TSA for the CS-1 testing and

minor upgrades to the three test stands for the EDC component endurance

testing.

CS-1 TSA

The CS-1 TSA provides the following:

1. Process air at the desired flow rate, dew point, temperature and

pCO2 levels

2. N2 and H2 gases at the desired pressures and flow rates

3. Coolant simulating a central spacecraft coolant source.

4. Electrical power at 28 V for the C/M I and 115 V, 400 Hz for the CCA

pump

5. Electrical circuitry to permit shutdown interface between the CS-1

and the TSA

6. Gas analysis equipment for measuring CS-1 performance.

Figure 23 shows the gas/coolant supply schematic and Figure 24 shows the

arrangement for gas sample analysis. Performance of the CS-1 based on air

side (e.g., pC0) measurements and H 2 /CO2 exhaust measurements (e.g., flow

rate) is determined with this equipment.

EDC Component TSA

Figures 25, 26 and 27 illustrate the three test stands that were used to

perform the continued endurance testing of the three major components of the

38
TABLE 8 MODEL 220 C/M I WEIGHT. SIZE AND POWER CONSUMPTION SUMMARY

Size

Assembly Weight, W, Ib _ HxWxD, cm (in) Power, W

Computer 3.0 (6.6) 17.8 x 14.5 x 20.8 31.1

(7.0x 5.7x 8.2)

Signal Conditioning 2.5 (5.4) 15.7 x 13.2 r, 24.9 10.6(•)

(6.2x 5.2x 9.8)

Power Supplies 4.0 (8.9) 16.5 x 6.4 x 22.9 16.6(b)

(+ 5, t 15 VDC) (6.5)f 2.5 x 9.0)

Power Drivers 0.9 (2.0) 17.3 x 17.8 x 6.4 11.9(x)

(6.8 x 7.0 x 2.5)

Front Panel 0.8 (1.8) 18.8 x 38.9 x 3.3 630

(7.4 x 15.3 x 1.3)

Connectors/Wiring 0.4 (1.0) - -

Enclosure 1.9 (4.1) 18.8 x 38.9 x 39.6 -

(7.4 x 15.3 x 15.6)

Total 13.5 (29.8) 18.8 x 38.9 x 39.6 76.5

(7.4 x 15.3 x 15.6)

a. With no subsystem sensors or actuators connected.

b. Represents conversion efficiency from 28 VDC supply.

c. Assumes average of two indicators on during normal operation.

39

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46

J
EDC; the liquid cooled EDCM, au FCA and a CCA. These stands were developed

under a prior ( yj?gram and were refurbish , * s required for the testing under

this program.

TESTING

Testing of the CS-1 followed fabrication of the module and the TSA. Endurance

testing of the EDC components for over 360 days was also conducted. These

tests are described below.

CS-1 Testing

A total of over 1,800 hours of CS-1 testing was achieved. versus the program

goal. of 60 days (1.440 hours). As discussed below, the performance of the

CS-1 was excellent.

Checkout Testin

During checkout testing all test stand control circuits, shutdown points and

sensor calibrations were verified. All interfaces with the TSA and CS-1 were

checked and verified.

Shakedown Testing

The shakedown test included continuous operation over 24 hours under nominal

baseline conditions. Subsequently, the shutdown and restart capabilities of

the integrated CS-1 and its test stand were verified.

Design Verification Test

The Designed Verification Test (DVT) provided data over the design range of

operating conditions to define normal operating characteristics of the module

and establish best operating conditions. These are listed in Table 9. she

established conditions were maintained during the test program unless varied

parametrically or otherwise specified.

Endurance Test

The endurance tests established the ability of the module to maintain acceptable performance while running continuously for over 1.800 hours (75 days).

Conditions were typically maintained within the ranges listed in Table 9.

Performance during the entire 1,800 hours of CS-1 operation, including the

endurance and parametric tests is plotted in Figure 28. It 1s apparent th&e

the CO2 removal efficiency averaged greater than 90% despite perturbations of

pCO2

 and process air inlet conditions. The stability of the electrochemical

cells is evidenced by essentially constant average cell voltage of 0.42 V per

cell.

J
48 

TABLE 9 NOMINAL TEST CONDITIONS

Current, A 9.9

Process Air

Flow Rate, dm3/s (cfm) 5.1 (10.8)

PCO2 , Pa (mm Hg) 400(3-0)

Relative Humidity, % 56-64

Dew Point, K (F) 283-286 (50-56)

Dry Bulb, K (F) 291-293 (64-68)

Hydrogen

Flow Rate, kg/h (lb/h) 0.006 (0.014)

Pressure, kPa (psia) 172(25)

Module Backpressure, kPa (psia) 34.5 (5.0)

Purge Gas

Type Nitrogen

Pressure, kPa (psia) 207(30)

Coolant

Temperature, K (F) 275-277 (36-40)
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Parametric Tests

The parametric tests established the effects of CO2 partial pressure (pCO2),

inlet process air RH and current density on module performance. These tests

were performed before and after the endurance test to investigate the effects

of long-term operation.

Variable CO. Partial Pressure. EDC performance at various partial pressure

levels is shown in Figure 29. The CO2 efficiency averaged approximately 100%

(well above the 85% design point) at a nominal pC0 level of 400 Pa (3.3

= Hg) and an anode exhaust (H2 ) backpressure of 3Z.5 kPa (5.0 psig).

Current Density Effects. The CS-1 performance as a function of current

density span is shown in Figure 30. This shows that excellent CO 2 removal

performance was maintained at the various current density levels.

Process Air RH Effects. The effect of variable humidity on CS-1 performance

was investigated over the range of 25 to 80% as shown in Figure 31. As seen,

the effect of RH has been minimized by the inclusion of the inlet air/liquid

heat exchanger in :he CS-1 design. This was an important finding during the

test program and verified its design function.

Conclusions of CS-1 Testing. The results of these tests verify that the CS-1

development objectives have been successfully met. Predictable, reproducible

high level performance over much wider ranges of RH and H2

 backpressure than

heretofore demonstrated, particularly at the modular level, were achieved.

This success is attributed to the development of the unitized core, liquidcooled cells and additionally to ensuring the inlet air enters the EDCM

preconditioned to module temperatures via an air/liquid heat exchanger. These

innovations shall be considered baseline for future EDCMs.

EDC Component Endurance Testing

Another task of the program was to continue endurance testing on the three

major EDC subsystem components, namely an EDCM, an FCA and a CCA.

EDCM Endurance Testing

Figure 32 shows the lmyterm EDCM endurance test. This testing was initiated

under a prior program and was continued for an additional 11,500 hours

under the current program. The total test time on this module is approximately

20,000 hours. It is seen that CO 2 removal performance and cell voltage

remained approximately constant over the test time although both values fell

off slightly.

FCA Endurance Testing

Figure 33 shows the FCA performance over approximately 9,500 hours of testing.

The parameters plotted are gas (air) inlet pressure, flow rate and residence

time. Residence time is related to how often the FCA valve is actuated or

cycled in a given period. For a residence time of 60 minutes the FCA remains

50
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57
in each of its four states for one hour before changing states, resulting in a

complete cycle every four hours or six cycles per day. Despite some shutdowns

of the test stand due to electronic failures in the FCA controller, there were

no problems with any mechanical parts of the FCA including the housing, valve

spool, seals and drive motor over the 360 day teat.

CCA Endurance Testing

Figure 34 shows the performance of the CCA over the 9,400 hours of endurance

testing under this program. The parameters selected for illustrating performance are the following: (1) total mass flow rate, (2) developed pump head

pressure, (3) temperature of the heat source which the CCA is trying to

maintain and (4) cycle time of the heater used to simulate a varying module

heat source. For the last parameter the heater is on for 30 minutes and off

for 30 minutes in the case shown. The CCA diverter valve must change its

position to divert more flow (heater on) or less flow (heater off) through an

external heat exchanger. While this is a more dynamic variation than encountered in an application, it does provide for continuous movement and "exercise"

of the CCA diverter valve assembly. The CCA pump speed war, constant at 11,000

rpm throughout the testing. At one point during the testing a new design was

tried - direct-drive coupling of the motor and the CCA pump. This proved to

be unsuccessful, and testing with the originally designed magnetic-coupled

drive was then resumed. The direct-drive coupling testing occurred over three

weeks of the total testing and was terminated because of a motor bearing

failure due to excessive shaft loads.

SUPPORTING TECHNOLOGY

Two activities were undertaken during the program as part of the EDC

advancement. These were the preliminary design of a Triple Redundant Relative

Humidity Sensor (TRRHS) and the fabrication of a EDC subsystem mockup as

applied to the Space Station.

TRRHS Preliminary Design

The present method of measuring process air inlet RH to the CS-1 consists of

using a commercially available dew point temperature sensor head and a dry

bulb temperature sensor. Electronics for the chilled mirror-type dew point

sensor are fairly complex and power consuming because a thermoelectric cooler

is used that requires considerable control circuitry and power. It is desirable

to replace these two sensors with a single unit of small size and also, since

humidity measurement is critical to CS-1 operation. to make it triply redr:nuant.

A further requirement was to include in situ calibration with the TRRHS co

verify its operation and stability over a long period of time.

An extensive literature survey was conducted, from which data for 19 key

methods of dew point and RH measurement were collected, summarized and evaluated. Performance specifications defined for the TRRHS are shown in Table 10.

A semi-conductor which is responsive to RH changes was selected, as shown in

Figure 35. It has triple redundant sensing elements and the necessary

mechanical hardware and other sensors for in situ calibration based on a two

pressure calibration scheme.

58
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59
TABLE 10 TRRHS SPECIFICATIONS

OPERATIONAL CHARACTERISTICS

RH Range, % 20-95

Dew Point Temperature Range, K (F) 253-321 (-4 to 118)

Temperature Range, K (F) 273-322 (32-120)

Pressure, kPa (psla) 35-140(5-20)

Accuracy, % RH * 3 over range

Stability (at 50% RH)

Short-term, % RH change/month * 3

Long-term, % RH change/year * 10

Repeatability, % RH *2

Reproducibility. % RHM * 3

Linearity, Max. % RH Deviation from a straight 15

line over range

Response Time, sec.

Step Increase (90% FS) 45

Step Decrease (95% FS) 60

Hysteresis, % RH midrange deviation between 10

forward and reverse full range excursions

Display Resolution, I% RH 0.1

Temperature Sensitivity, % RH/K (% RH/F) 0.03 (0.05)

Air Velocity Sensitivity, % RH/m/s (%RH/ft/s) 0.03 (0.1)

Air Pressure Sensitivity, % RH/kPa (% RH/psis) 0.03 (0.2)

Shelf Life, years 5

Operating Life, years 2

Reliability (MTSF), h 10,000

Sensor Orientation Sensitivity, c/o RH * 4

In Situ Calibration

Calibration Points. % RH

Low RH Point 40

High RH Point 80

Long-Term Stability, % RH/year

Low RH Point *10

High RH Point t 8

Repeatability, % RH

Low RH Point t 3

High RH Point t 2

Accuracy, % RH

Low RH Point * 3

High RH Point t 2

Reproducibility, % RH

Low RH Point 15

High RH Point * 3

Calibration Time (complete), min 5

Calibration Frequency, No./day 1

(a) Variation from one instrument to another

continued60
Table 10 - continu&4

ELECTRICAL CHARACTERISTICS

Power (total) W 10

Power Supply Voltage, VAC 115

Power Supply Frequency, Hz 60

Front Panel Controls

Display(s) RH-3 Digit LED

Indicators Power On, In Calibration Mode

Control Adjustments Power On

Rear Panel Controls

Output TBD

• Analog'

• Alarms

• Other Digital Outputs/Relays

Control Adjustments

Sensor Cable

PHYSICAL CHARACTERISTICS

Sensor

Weight, kg (lb) 0.23 (0.5)

Volume, crn3 (in3) 340(21)

Dimensions, cm (in) 3.8 diam x 7.6

(1.5 dram x 3)

Mounting Boss--Mounted

Electronic Package

Weight, kg (lb) 4.1(9)

Volume, dm 3 (in3 ) 3.5 (216)

Dimensions, cm (in) 7.6 x 15 x 30

(3x6x12)

Meur:ting Free Standing

ENVIRONMENTAL LIMITS

Air Velocity, mis (tt/s) 0-6(0-20)

Air Pressure, kPa (psis) 35-140(5-20)

Ambient Temperature, K (F)

Sensor 273-322 (32-120)

Electronics Package 277-311 (40-100)

Shock TBD

Vibration TBD

EMI TBD

Gravity, g 0.2

MAINTAINABILITY

Line Replaceable Component Sensor, Electronics

Replacement Time, h 0.2, 0.3

Special Tools None

61
ORIGINAL PAGE 19

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FOUR PERSON CO 2 REMOVAL SUBSYSTEM MOCKUP

PRFCFDTNG PAGE P,i;ANK NOT FR.MED

L J
RECOMMENDATIONS

It is recommended that the current program be extended and focused on continued

testing of the CS-1 concept. In addition, it is recommended that an in situ

cell maintenance concept for increased EDCM reliability be incorporated into

the CS-1. This concept will include compact, automatically switched relays to

electrically isolate degraded cells. The integrated electrical design will

minimize space requirements and resistive power losses. The CS-1 composite

cell design with its allowance for a temperature difference between coolant

and anode during operation will avoid cell dry out during shutdown, during

which the temperature will drop to compensate for terminated water production.

inclusion of this capability, along with the development of a TRRHS, will then

ready the CS-1 for the stage at which it can be incorporated into the ECLSS

for the Space Station.

REFERENCES

1. Quattrone, P. D.; Babinsky, A. D. and Wynveen, R. A., "Carbon Dioxide

Control and Oxygen Generation," Paper No. 70-Av/SpT-8, ASME Conference;

Los Angeles, CA; 1970.

2. Wynveen, R. A. and Quattrone, P. D., "Electrochemical Carbon Dioxide

Concentrating Systems," Paper No. 71-Av-21, SAE/ASME/AIAA Conference; San

Francisco, CA; July, 1971.

3. Wynveen, R. A.; Schubert, F. H. and Powell, J. D., 'One-Man,

Self-Contained CO22 Concentrator Systems," Final Report, Contract

NAS2-6118, NASA CR-114426; Life Systems, Inc., Cleveland, OH; March 1972.

4. Powell, J. D., et al., "Six-Man, Self-contained Carbon Dioxide

Concentrator Subsystems," Final Report, Contract NAS2-6478, NASA

CR-11473; Life Systems, Inc., Cleveland, OH; July, 1974.

5. Schubert, F. H. and Quattrone, P. D.; "Development of a Six-Man,

Self-Contained Carbon Dioxide Collection subsystem for Spacecraft

Application, Paper No. 74-ENAs-16, Intersociety Conference on

Environmental Systems; Seattle, WA; July, 1974.

6. Schubert,-F.H.; Marshall, R. D.; Quattrone, P. D. and Wynveen, R. A.,

"Development of a Three-Man Preprototype CO 2

 Collection Subsystem for

Spacecraft Application," Paper No. 77-ENAs-19, Intersociety Conference on

Environmental Systems; San Francisco, CA; July, 1977.

7. Marshall, R. D.; Ellis, G. S.; Schubert, F. H. and Wynveen, R. A.,

"Extended Duration Orbiter Study: CO Removal and Water Recovery," Final

Report, Contract NAS9-15218, NASA CR-h0317; Life Systems, Inc.,

Cleveland, OH; May, 1979.

8. Schubert, F. H.; Heppner, D. B.; Hallick, T. M. and Woods, R. R.,

"Technology Advancement of the Electrochemical CO22 Concentrating

Process," Final Report, Contract NAS2-8666, NASA CR-152250; Life Systems,

Inc., Cleveland, OH; May, 1979.

65
9. Mashall, R. D.; Schubert, F. H. and Yang, P. Y., "EDC - A Regenerable CO

Removal Subsystem for an Enhanced Capability Orbiter," Paper No. 2

79-ENAs-34, Intersociety Conference on Environmental Systems; San

Francisco, CA; July 1979.

10. Schubert, F. H. and Lance, N., "Regenerable CO2 Collection for Spacecraft

Application," Paper 81-ENAa-28, Intersociety Conference on Environmental

Systems; San Francisco, CA; July, 1981.

11. Schubert, F. H.; Hallick, T. M. and Koszenski, E. P., "Advanced

Electrochemical Depolarized Concentrator Cell Development," Final Report,

Contract NAS2-10204, NASA CR-166141; Life Systems, Inc., Cleveland, OH;

December, 1981.

12. Heppner, D. B. and Schubert, F. H., "Electrochemical and Steam-Desorbed

Amine CO Concentration: Subsystem Comparison," Paper No. 831120,

Intersociety Conference on Environmental Systems; San Francisco, CA;

July, 1983.

66