Investigations of Physical Processes in Microgravity

National Aeronautics and Space Administration

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Investigations of Physical Processes in Microgravity

Relevant to Space Electrochemical Power Systems

Dr. Vadim F. Lvovich, Dr. Robert Green, and Ian Jakupca

NASA Glenn Research Center

Cleveland, OH 44135

6th International Symposium on Physical Sciences in Space, Kyoto, Japan

September 15, 2015


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Regenerative Fuel Cells

• Develop Components and Integrated Systems

– kW-size Fuel Cell stacks with advanced water removal

– Balanced-pressure passive liquid-feed, vapor-feed or hybrid Electrolyzer

– Advanced MEAs for both Fuel Cells and Electrolyzers

– Compact, efficient balance-of-plant components

– Advanced manufacturing processes for high-pressure operation and reduced mass,

volume and cost

– Discrete Fuel Cell and Electrolyzer systems to optimize efficiency of each

Regenerative Fuel Cell with Array

Electrolyzer

Fuel Cell

H2 O2H2O

kWe

kWe

Main Power Bus

Photovoltaic Array

kWe

Electrical

Loads

Regenerative Fuel Cell

Electrolyzer Stack

FC

Stack

MEA

BOP

Components developed to

create system

Non-Flow-Through Fuel Cell

Shuttle Flow-Through Fuel Cell

Heat

2

Regenerative Fuel Cell with Array


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Shuttle

“Active BOP”

Alkaline

“Active BOP”

PEM

GlennResearch Center

JohnsonSpace Center

17 - 20 psia

BULKHEAD FITTING

TAP WATER

T FITTING

ACCUMULATOR

PTTP

PT

PT5

PT6

TP

TP5

TP6TP PT

PT3TP3TP PT

M1RV1

COOLANT

OXYGEN PURGE 3/4" **

AS4395-12 Male flare

fitting

OXYGEN* Supply to 3/8" **

AS4395-06 Male flare fitting

PR1

PR2

FC1

WT1

PT

PT1

PT2

PRODUCT WATER 1/4"


19 psia +/- 3CATHODE

HYDROGEN* Supply to 1/4" **


TP

TP1

TP2

SV1

SV2

ANODE

FACILITYPOWERPLANT

T1Accumulator

with bellows

MV1

H1

HYDROGEN PURGE 1/2" **


SV3

RV2

TP PT

SV4

AIR

DI WATER

HYDROGEN

LEGEND PRESSURE REGULATING VALVE

SOLENOID VALVE (NO)

SOLENOID VALVE (NC) WATER SEPARATOR

FILL PORT

CIRCULATION PUMP

PRESSURE TRANSDUCERPPT

TEMPERATURE PROBETTP

COOLANT PUMP

MIXING VALVEELECTRIC HEATER

HEAT EXCHANGER HEAT EXCHANGERRELIEF VALVE

PT4TP4

M2

WT2

HX2

MV2

100 - 275 psia

Temp > 10 C

21 psia +/- 2

19 psia +/- 3

19 psia +/- 3

21 psia +/- 3

17 psia

21 psia +/- 2 100 - 275 psia

Temp > 10 C

17 - 20 psia

50 - 56 deg C

17 -20 psia

44 - 50 deg C

3/4" Primary Coolant Loop

30 psia +/- 2

32 psia +/- 2

45 psia +/- 2

PT

PT

PT7

PT8

M3

Secondary Coolant Loop

HX1

PRIMARY COOLANT INLET 3/4"


PRIMARY COOLANT OUTLET 3/4"


25 +/- 10 deg C

50 - 56 deg C

44 - 56 deg C

17 - 20 psia

PRODUCT WATER 1/4"

AS4395-04 Male flare fitting44 - 56 deg C

Hydrogen pressure manifold

Oxygen pressure manifold

Flow-Through Flow-Through


“Passive BOP”

PEM

Flow-Through

“Passive BOP”

PEM


an

ode

ca

thode

H2O

MEA

H2O

H2 O2

H2O

H2O

coo

lan

t

hyd

roph

ilic m

em

bra

ne

an

ode

ca

thode

H2O

MEA

H2O

H2 O2

H2O

H2O

coo

lan

t

hyd

roph

ilic m

em

bra

ne

an

ode

ca

thode

coo

lan

t

MEA

H2O

injector/ejector

passive water

separator

H2 O2

H2OH2O

O2

O2 / H2O

an

ode

ca

thode

coo

lan

t

MEA

H2O

injector/ejector

passive water

separator

H2 O2

H2OH2O

O2

O2 / H2O

Non-Flow-Through

Active Mechanical Component

(pump, active water separator)= Passive Mechanical Component

(injector/ejector, passive water separator)=

NASA Fuel Cell Technology Progression

Active coolant

pump

(coolant loop

not shown)

Active coolant

pump (coolant

loop not shown)

3


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PEM Electrolysis Systems

4

Liquid water Anode Feed• water fed on anode side, dragged to cathode side

• greatest electrical efficiency

• requires 2 phase separators, 2 pumps

• used by the Navy

Liquid water Cathode Feed• water fed on cathode side, diffuses to anode

• reduced electrical efficiency

• requires 1 phase separator, 1 pump

• used in OGA (ISS)

Highest rate and efficiency; most complex Lower rate, simpler system


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Physical Science ISS Flight Experiments

• Space Fuel Cell and Electrolysis systems management require separation

of gas/liquid multiphase streams in microgravity

• In this section, we present a quick overview of results from 2 ISS Physical

Science flight experiments

– Involves multiphase flows (i.e. gas/liquid flows)

– Has analogies to electrochemical work in microgravity

– Demonstrates maturity level needed to develop electrochemical flight

experiments of similar complexity

• Microgravity Fluid Physics discipline

– Boiling and condensation experiment

• MABE - Microheater Array Boiling Experiment

– Capillary flows experiment

• CCF – Capillary Channel Flow

5


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ISS Boiling Flight Experiments

Boiling eXperiment Facility (BXF) – 2011

• BXF included two separate pool boiling investigations:

– Microheater Array Boiling Experiment (MABE)

– Nucleate Pool Boiling Experiment (NPBX)

• Improved understanding of local boiling heat transfer

mechanisms & critical heat flux in microgravity for nucleate

and transition pool boiling.

• Detailed measurements of bubble growth, detachment and

subsequent motion of single and merged (larger) bubbles

• Developed a criteria for Boiling Transition– Buoyancy Dominated Regime (BDB)

• Heat transfer by bubble growth and departure

• Heat flux increases with gravity

– Surface Tension Dominated Regime (SDB)

• Dominated by the presence of a non-departing primary bubble

• Effect of residual gravity is very small

– Transition Criteria based on Capillary Length

• Enhanced the development of two-phase thermal

management systems, which provide isothermal control with

reduced radiator area and mass.

• Pool boiling studies are the first critical step to understanding

flow boiling in 0-g.

• A combined condensation and flow boiling experiment is

scheduled for 2018.

(Top) Paulo Nespoli installing BXF in MSG.

(Middle left) Coalescence of vapor bubbles

on NPBX wafer. (Middle right) Subcooled

nucleate boiling in g. The MABE

microheater array is colorized with actual

heat flux data. (Bottom) Transition of boiling

Heat Flux as a function of acceleration

5

0

0

W/c

m2


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Key Result from MABE Flight Investigation:

Heat Transfer Model for Varying g-levels

7

Heat flux vs. gravitational acceleration for a given TemperatureRaj, Kim, & McQuillen, Trans ASME, 2012.

• Two regimes identified– Buoyancy Dominated Regime (BDB)

– Surface tension Dominated Regime (SDB)

• Regime boundary characterized as a large

“jump” and is defined by Lh/Lc = 2.1. – where Lh = width of square heater

– and Lc = capillary length.

• Magnitude of jump requires further work.

• Slopes for SDB and BDB regimes:

ONBCHF

ONBW

TT

TTT

*


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Boiling Curves Under Varying Gravity Conditions

8

Single Phase

(natural convection)

Nucleate boiling

CHF

Film Boiling

Key results from ground-based testing:

• Boiling in microgravity is possible.

• Bubble departure diameters in µg are

greater than 1 g, but smaller than

predictions

• CHF are also lower in µg than 1g but

higher than correlations.

• Surface tension and contact angle affect

boiling behavior.

• Bond number (Bo – relative strength of

body forces to surface tension) alone

cannot be used for correlations (regime

indicator).

Compendium of ground-based test results by Kim, Univ. of Maryland

)( fW TThq

2)( aLBo VL


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Example Boiling Results in Low and High-g Conditions

9


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Capillary Channel Flow Experiments on the ISS

ESA PI: Prof. Michael Dreyer, ZARM

Co-I: Prof. Mark Weislogel, Portland State University

PM: Robert Hawersaat, NASA GRC

PS: Robert Green, NASA GRCObjectives

– To enable design of spacecraft tanks that can supply gas-free

propellant to spacecraft thrusters, directly through capillary

vanes, significantly reducing cost and weight, while improving

reliability.– Experiment #1 (EU#1)

• Determine critical flow-rates (choking) in the capillary-inertial regime as a function of channel length for true channel and half channel.

• Probe the nature of critical behavior by introducing wave oscillation of variable amplitude and frequency for both channel configurations and variable lengths.

– Experiment #2 (EU#2)• Determine critical flow rates (choking) in the capillary-inertial,

visco-capillary, and overlap regimes for wedge channels as a function of channel length.

• Probe the nature of bubble transport, migration, and phase separation as a function of flow rate, channel length, bubble diameter and frequency.

Topics

– Experimental studies of open capillary channel flow stability.– Two experiment units with three different channel geometries.– Steady, oscillating, unsteady, and two-phase flow conditions.– Total of 50 days of effective experimental time aboard the

ISS.– Main ground station located at ZARM in Bremen, Germany.– Interactive access to the ISS for controlling and data

download.

Motivation: capillary channel flow in surface tension tanks

Capillary channels with free liquid surfaces are widely used

for propellant management in surface tension tanks. Vanes

provide channels of various shapes to transport the liquid to

the outlet. The free surfaces have to withstand the pressure

difference and prevent gas ingestion; the stability is of

significant importance for the spacecraft propulsion system.

Experimentally investigated geometries of capillary channels

Two experiment units (EU#1, EU#2) provide three different

channel geometries, each with one or two free liquid

surfaces. The plates are manufactured of glass for camera

observation and surface image analysis; a=5 mm, b=25

mm, H =30 mm, α=7.9o, variable length l =0...48 mm.

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CCF Results:

Liquid-Gas Phase Separation Regime Maps• Data reduction indicates well-defined boundaries between full and partial (or no)

gas/liquid phase separation.

• Two example regime maps are shown below for two

bubble generation frequencies ( Qg = 𝑓𝑉𝑏𝑢𝑏𝑏𝑙𝑒 ).

Flow conditions for 100% bubble separation in an open wedge channelFrom Jenson et. al., Int. J. Multiphase Flow, 2014

The Capillary Channel Flow (CCF) test section is an inverted interior corner geometry with a triangular cross-section.

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NASA Fuel Cell Stack Ground Orientation Testing

Two orientations of the stack in 1-g gravity with respect to water flow

• “baseline” (preferred for water removal)

• “inverted” (impeding water removal)


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NASA Fuel Cell Stack Ground Orientation Testing


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Conclusions

14

• Understanding of gas-liquid separation processes are very important for

effective management of advanced regenerative fuel cell systems

• Gas-liquid separation process patterns are different in 1-G and 0-G

• Boiling experiment (q vs. T) in microgravity, has analogy to electrochemical

work (I vs. V) with non-departing primary bubble resulting in both higher

wall temperature (TW) and higher voltage (V) for same heat flux (q) and

current (I).

• Capillary channel flow with “free surface” can be used for passive gas-

liquid multiphase separation in 0-G.

• Fuel cell stack orientation in 1-G experiments affects long term power

performance

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Investigations of Physical Processes in Microgravity