Boundary Layer Analysis of Boundary Layer Analysis of Flow through a Single Flow through a Single Channel PEM Fuel CellChannel PEM Fuel Cell

Viscous FlowsViscous Flows

Dr. KirkDr. Kirk

By Chris JojolaBy Chris Jojola

IntroductionIntroduction

How They WorkHow They Work

UsesUses

Small voltage for each cell.Small voltage for each cell. They must be stacked in series for They must be stacked in series for

automotive purposes.automotive purposes.

My ResearchMy Research

The effect of channel path on PEM The effect of channel path on PEM fuel cell performance.fuel cell performance.

Several different configurations, Several different configurations, including square, serpentine, and including square, serpentine, and spiral.spiral.

For this project the serpentine For this project the serpentine configuration was chosen.configuration was chosen.

My Research cont.My Research cont.

Sample ResultsSample Results

~ 2 million cells

ProblemProblem

The goal of this project was to The goal of this project was to resolve the boundary layer along the resolve the boundary layer along the inside of the channels to improve the inside of the channels to improve the accuracy of computations.accuracy of computations.

Once accomplished, the next goal Once accomplished, the next goal was to determine if the improved was to determine if the improved accuracy was worth the extra accuracy was worth the extra computational time and power.computational time and power.

Splitting the Problem in TwoSplitting the Problem in Two

The cell has nearly 2 million cells.The cell has nearly 2 million cells. Adding more points and using Adding more points and using

Fluent’s PEM module could take an Fluent’s PEM module could take an entire day per case.entire day per case.

Instead I performed two different Instead I performed two different tests for three cases (6 total)tests for three cases (6 total)

Part OnePart One

For the first test, I reduced the cell to For the first test, I reduced the cell to a single channel and ran hot air a single channel and ran hot air through it.through it.

Part One – Cont.Part One – Cont.

The goal was to observe the change The goal was to observe the change in velocity, temperature, and in velocity, temperature, and pressure profiles.pressure profiles.

The overall pressure drop was also The overall pressure drop was also taken into consideration.taken into consideration.

Part TwoPart Two

The second part was to reduce the The second part was to reduce the cell to a single sweep and run using cell to a single sweep and run using the full PEM module.the full PEM module.

The velocity, pressure, etc. were also The velocity, pressure, etc. were also observed, but the main goal was to observed, but the main goal was to see how the change affected see how the change affected electrical parameters such as cell electrical parameters such as cell voltage and current density.voltage and current density.

Part Two – Cont.Part Two – Cont.

OriginalCourse Fine

ConditionsConditionsParameterParameter ValueValue UnitUnit

Inlet TempInlet Temp 353353 KK

Mass flow rate, H2Mass flow rate, H2 8 x 108 x 10-7-7 kg/mkg/m33

Mass flow rate, O2Mass flow rate, O2 8 x 108 x 10-6-6 kg/mkg/m33

Channel Dim.Channel Dim. 3.125 x 3.125 x 3.1253.125

mmmm

Cell VoltageCell Voltage 0.650.65 VV

ViscosityViscosity 2.09 x 102.09 x 10-5-5 kg/(ms)kg/(ms)

ReRe 120120 11

ResultsResults

The results for both tests showed The results for both tests showed that the grid change did very little to that the grid change did very little to improve the accuracy of the test.improve the accuracy of the test.

Results – Part OneResults – Part One

Grid refinement had an almost Grid refinement had an almost negligible change on the pressure negligible change on the pressure drop over the entire channel.drop over the entire channel.

However, the time needed for However, the time needed for convergence increased dramatically convergence increased dramatically (close to 50%)(close to 50%)

Results – Part One Cont.Results – Part One Cont.C

ours

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rigin

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Fine

Pressure Velocity Velocity (Zoom)

Results – Part 1 Cont.Results – Part 1 Cont.

CaseCase ∆∆pp % % DifferenceDifference

CourseCourse 18.3 Pa18.3 Pa 2.7%2.7%

OriginalOriginal 18.8 Pa18.8 Pa 0%0%

FineFine 19.0 Pa19.0 Pa 1.1%1.1%

Results – Part TwoResults – Part Two

The grid refinement on the small section The grid refinement on the small section of the cell running the full PEMFC of the cell running the full PEMFC software led to less than 1% change in software led to less than 1% change in pressure and current density.pressure and current density.

Since two channels had a significant Since two channels had a significant number of cells added, the number of cells added, the computational time increased computational time increased dramatically for the refined grid.dramatically for the refined grid.

Results – Part Two Cont.Results – Part Two Cont.

CaseCase Current Current DensityDensity

% Diff% Diff Time/ Time/ IteratioIterationn

RatioRatio

CourseCourse .0814 .0814 A/cmA/cm33

0.47%0.47% 2.3 s2.3 s 2/32/3

OriginOriginalal

.0818 .0818 A/cmA/cm33

0%0% 3.6 s3.6 s 11

FineFine .0820 .0820 A/cmA/cm33

0.27%0.27% 32.4 s32.4 s 99

Results – Part Two Cont.Results – Part Two Cont.C

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rigin

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Fine

ConclusionsConclusions

The boundary layer within the anode The boundary layer within the anode and cathode channels is sufficiently and cathode channels is sufficiently large to be captured by the current large to be captured by the current grid.grid.

Increasing the cell count would add Increasing the cell count would add considerable computing with a considerable computing with a minimal effect on the results.minimal effect on the results.

QuestionsQuestions

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