Transcript Fuel Cell Fluid Dynamics” Topic Area: Monitoring

Multiphase Flow in Simulated PEM Fuel Cell Under
Variable Gravity Conditions
PEM Fuel Cell Team (PEMFCT)
Graduate Student Mentor:
Faculty Advisor:
NASA Advisor:
Dr. Cable Kurwitz
Dr. Fred Best
Art Vasquez
Team Member
Classification
Major
Ernie Everett
Senior
MEEN
Nikhil Bhatnagar
Junior
AERO
Christie Tipton
Junior
BMEN
Trevor Bennett
Freshman
AERO
Caitlin Riegler
Freshman
AERO
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Background
Objectives
 - NASA’s Needs
 - SEI Goals
Review of Fall Work
Preliminary Analysis
Review of Spring Work
Ground Testing
 Set Up
 Manufacturing
 PSA
Preliminary Modeling
Results
New Direction
Conclusions
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Typical fuel cells generate electricity
by combining a fuel and oxidizer in the
presence of an electrolyte
Main parts of a fuel cell
– Flow channels for fuel and oxidizer
– Anode and Cathode separated by an
electrolyte
Fuel and oxidizer react to produce
electricity and byproducts
Fluid distribution and control is a
critical issue with fuel cell operation
The parallel flow channels and parallel
plates can produce flow instabilities
leading to degraded fuel cell operation
and possible damage
Goal –Identify regions of operation
where instabilities can occur
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NASA’s Need
 Utilized fuel cells in Gemini, Apollo, and currently in Space Shuttle
 NASA plans to utilize fuel cells in Constellation program
 Technology has many other applications
▪ Vehicles, buildings, and alternative energy applications
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Purpose
 Evaluate flow conditions that lead to unstable operation within a
prototypic fuel cell geometry
 Develop a flow map that describes stable and unstable operating regions
 Provide simple modeling approach to predict transition from stable to
unstable operation
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Learning Objectives:
 Understand two-phase fluid flow
 Identify and understand the flow conditions that produce instabilities
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Literature Review
 Understood fuel cells and the flow distribution during
operation as well as flow anomalies
 Researched standard geometries and flow rates
▪ Confirmed with NASA Advisor
Developed CAD drawings of two cell geometries
Performed stress and flow analysis for both parallel
and serpentine configurations
 Built simple cells for ground testing
 Proposed testing to Microgravity University
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Parallel Plate
Gas Used:
Mass Flow Rate:
Inlet Pressure:
Inlet Temperature:
Max Channel Velocity:
Nitrogen
3 SLPM
50 psig
293.2 K
0.1 m/s
Serpentine Plate
Gas Used:
Mass Flow Rate:
Inlet Pressure:
Inlet Temperature:
Max Channel Velocity:
Nitrogen
3 SLPM
50 psig
293.2 K
0.35 m/s
Parallel Model
Gas Used:
Mass Flow Rate:
Inlet Pressure:
Inlet Temperature:
Serpentine Model
Nitrogen
3 SLPM
50 psig
293.2 K
Parallel Model Delta Pressure:
Serpentine Model Delta Pressure:
10 Pa
56 Pa
Maximum Stress: 834.9 psi
Located over channel/plenum
junction.
Maximum Displacement: <1 micron
Located at lid over the plenum.
Minimum Factor of Safety: 36
Maximum Stress: 274.3 psi
Located at center of channel/plenum
junction.
Maximum Displacement: 10.82 microns
Located over the center of the plenum.
Minimum Factor of Safety: 110
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Allows undergraduate teams to carryout flight
testing of experiments in microgravity conditions
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- Submitted Proposal
- Completed Safety Analysis
- Pursued Funding
- Education Outreach
Team Proposal Turned Down
 Switch from NASA to Zero-G aircraft greatly reduced
the number of experiments
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Looked for alternative flight opportunities
 FAST Program – decided not to pursue
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Designed and fabricated a higher fidelity
prototype to more accurately reflect fuel cell
flow distribution
 Uniform liquid addition throughout each channel
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Built test loop for ground testing
Composed and submitted PSA
Performed preliminary testing and analysis
Dimensions:
20 cm x 20 cm x 1 cm
Channel Dimensions:
1 mm x 1mm
Number of Channels:
80
Wetted Surface Area:
10,700 mm^3
NASA interest fueled by these being the standard
geometries for fuel cells (based on chemical properties)
Zoomed in View
Dimensions:
Channel Dimensions:
Number of Channels:
Wetted Surface Area:
Zoomed in View
20 cm x 20 cm x 1 cm
1 mm x 1mm
20
10,700 mm^3
•Added a liquid plenum for water
introduction from the bottom
•6 mm deep
•Added holes along the channels
connecting the lumen of the channels
to the liquid plenum
•Changed water input to directly
in the center for more
uniform addition
Fuel Cell Flow Loop Schematic
Cell Plate
V-40
V-39
Legend
Nitrogen
Tank
Check Valve
Pressure
Transducer
Regulator
Plug Valve
Open Vent
Syringe Pump
CCD Camera
With LED
Pressure Relief
Valve
Flow
Meter
Back Pressure
Regulator
Output water
and gas
Drain
Specifications
• Gas provided by high pressure Nitrogen Tank
• Regulated to 50 psig
• Pressure Transducer will monitor pressure drop
• Parallel Mass flow meters will simulate excess cells
• CCD Digital Camcorders will record fluid instabilities
• Vortex Water Separator will separate fluid from gas
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Flow Loop Consists of 2 Flow Meters,
Pressure Gauge, Differential Pressure
Transducer, and CCD
Gas Flow Provided by Compressed Nitrogen
Cylinder and Water Flow Provided by Liquid
Syringe Pump
Test Stand Allows Cell Plate to be Rotated
PSA Written and Provided to Safety Officer
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Data is collected by video, flow meter and pressure
gauge
Varied flow rate on primary flow meter from 0 to 10
sLPM
Bypass Flow Rate Varied from 0 to 90% of Primary
Flow
Liquid Flow Rate 0 to 100 cc/min
Variation in gas and liquid flow rates occurred
simultaneously
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Flow instabilities occur at all flow rates tested
for parallel and serpentine channel fuel cell
plates
 Oscillations are small and focused toward exit of
channels
 Overall liquid holdup is constant for each test but
varies over range of testing with large amounts of
water held at low gas flow rates
 Some channels occluded for duration of tests (No
flow)
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Liquid holdup in channels varied with tilt
angle on test article
 Due to flow regime and hydrostatic pressure
changes
 Indicates a need for reduced gravity testing
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Two-phase flow in outlet line seemed to have
an effect on bypass flow
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Liquid pores too large allowing gas to enter
liquid plenum at high channel differential
pressure
Graded pores or a more controlled method of
adding water to better simulate water
production is needed
New test setup required to accommodate
water entering bypass flow meter
 - Engineering Skills:
▪ Analysis Tools
▪ Solid Works, Cosmos FloWorks, CosmosWorks, Microsoft Visio
▪ Analytic techniques to validate computation
▪ Analysis of test data (i.e. model fitting)
▪ Lab Skills:
▪ Machining experience
▪ Interpreting engineering drawings
▪ Developing procedures
▪ Carrying out test
▪ Education Outreach
▪ Teamwork
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Purpose:
-Evaluate flow conditions within a prototypic fuel
cell geometry
- Determine a range of stable operations for given
flow and environmental conditions
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Ground testing showed occlusions have a
great gravitational dependence and that more
work needs to be done on our test system
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Replace flow meter to complete ground test
matrix
Modify test stand to allow higher flow rates
Modify liquid addition method to provide a
more uniform liquid addition
Continue work on test loop and develop more
robust analysis techniques
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Parallel channel instability may occur when a number of channels are
connected at common headers.
Although the total flow remains constant, flow oscillations may occur in
some of the channels.
Nonlinear transient momentum equations can be used to solve for
several channels by integrating the momentum equation along each
channel.
Fluid properties used in the momentum equations are obtained from the
energy equation and the equation of state.
The modeling is very complex , the following equations convey the
complexity
After integrating the momentum equations for the channels, the
equations are solved simultaneously.
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Starting with the Momentum Equation
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Define B and C
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We Simplify
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The Total Inlet Flow
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Differentiating
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We can then Solve n Equations to Determine
the Channel Flow Rate