TOWARDS A VIRTUAL REALITY

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Nov 14, 2013 (3 years and 8 months ago)

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Institute for Chemical Process and Environmental Technology

TOWARDS A VIRTUAL REALITY
PROTOTYPE


FOR FUEL CELLS




Steven Beale Ron Jerome

National Research Council

Anne Ginolin

Institut Catholique d’Arts et Métiers

Martin Perry, Dave Ghosh

Global Thermoelectric Inc.








Institute for Chemical Process and Environmental Technology

Introduction


Fuel Cells convert chemical energy (hydrogen and oxygen)
to electrical energy


Potential replacement for IC engines


National Fuel Cells Initiative: Kyoto summit


Three main parts: Anode, cathode, electrolyte


Solid Oxide Fuel Cells (SOFC’s) can use methane/natural
gas in place of hydrogen


Built in stacks of 10
-
50 cells: Connected in parallel
hydraulically; electrically in series


Institute for Chemical Process and Environmental Technology

Introduction


SOFC’s operate at up to 1000 ºC


If supply of fuel and air non
-
uniform, reaction rates and
hence temperatures will vary


Temperature uniformity important: If too cold, cell reaction
shuts down; Too hot, mechanical failure


Current work to model fluid mechanics (mechanical
design). Goal: Uniform delivery of air and fuel to the
membrane
-
electrode assembly


Chemistry not considered at present time



Institute for Chemical Process and Environmental Technology

Introduction


Single cell model


Stack model: 10
-
50 cells. Two approaches


Direct Numerical Simulation (DNS).


Distributed Resistance Analogy (DRA)


For the DNS require large amounts of storage and memory


Certain details lost with the DRA


Several different DRA implementations are possible


Institute for Chemical Process and Environmental Technology

DRA approach












F
is a ‘distributed resistance’ obtained from theory,
experiments, or detailed numerical simulations.
r
i
are

volume fractions of air and fuel.





i
i
i
i
i
i
i
i
i
u
Fr
p
r
u
u
r
t
u
r






2
;















0








i
i
i
u
r
t
r


U
F
p




u
r
U



velocity
l
Superficia

U

velocity
al
Interstiti

u

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Determination of resistance term


Many internal flows are correlated in the form;




where the Reynolds number is written in terms of a
“hydraulic diameter”



The distributed resistance is just,

Re
a
f




u
D
h
Re
2
2
h
D
r
a
F


Institute for Chemical Process and Environmental Technology

Example: Plane duct

For a plane duct:











For more complex geometries must use numerical
integration empirical correlations

Hu
u
f
w






12
2
2
1
P
H
r

3
12
H
P
F


3
2
12
12
nBH
Q
L
H
u
L
p






Institute for Chemical Process and Environmental Technology

PHOENICS settings



Used PHOENICS VR to construct SOFC stack model


Diffusion terms turned off using Group 12 patches
GP12DFE etc. for DRA


Source term with PATCH type PHASEM in momentum
equations, and Coefficient
C

=

F
/
r


2
-
D flow imposed in core (
w
= 0)


Institute for Chemical Process and Environmental Technology

Results

Source:
http://www.globeinvestor.com/

Phase 1 CFD
modelling begins

Phase 1 ends

Phase 2 CFD
modelling begins

Institute for Chemical Process and Environmental Technology

Results


Results of flow calculations for 24 designs were displayed
as 3
-
D VRML files using a secure web site to the client in
Calgary across internet.


This allowed us to work together “at a distance”


Images were also displayed locally to client in Ottawa
using NRC Virtual Reality (VR) wall


SOFC stack completely redesigned as a result of this work




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Results

FLOW IN

Exit manifold

Inlet manifold

FLOW OUT

Fuel cell stack

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NRC Virtual Reality Wall

Institute for Chemical Process and Environmental Technology

Pressure in SOFC manifolds and
stack

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Velocity vectors in manifolds and
stack

NB: Vector scale different in
stack from in manifolds

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Discussion


Geometry

is

quite

simple,

but

flow

in

inlet

manifold

complex
;

Pressure

maximum

at

front

of

step
.

Due

to

horizontal

inlet


Flow

within

the

core

of

this

SOFC

stack

is

uniform,

i
.
e
.
,

design

is

good
.

Little

variation

in

vectors,

in

spite

of

inlet

design


Core

flow

is

a

low

Reynolds

number

(creeping)

flow,

driven

primarily

by

the

pressure

gradient



Pressure

drops

consistent

with

values

based

on

theory


Flow

in

outlet

manifold

is

less

complex

than

inlet
:

Size

and

form

less

critical
.


Institute for Chemical Process and Environmental Technology

Discussion


Gradient across stack is uniform horizontal.


In manifolds gradient is relatively small and decreases with
height
-

due to injection/suction


Manifold losses are in many cases quite significant, with
substantial variations observed, depend on particular
configuration under consideration.


For uniform flow the ratio of

P
stack
/

P
manifolds

should be
large.


Parametric studies identified which parameters important
-

allowed for the stack design to be optimised.


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Comparison of DRA and DNS

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Comparison of DRA and DNS
approaches


DRA

and

DNS

results

are

similar

with

minor

systematic

deviations
.



Details

of

velocity

profile

lost

with

the

DRA
.


If core resistance is small, inertial effects become
significant: Pressure and velocity less uniform.


For tall stacks need large pressure gradient within core, so
inertial effects due injection/suction of working fluid from
manifolds does not lead to starvation at top of core.


Various DRA approaches are possible. Minor differences
occur due to convection terms.

Institute for Chemical Process and Environmental Technology

Conclusions


DRA

model

may

be

used

as

an

engineering

tool

to

design

SOFC's

with

a

measure

of

confidence
:

Certain

details

of

flow

field

are

lost
.

However

combines

computational

speed

with

accuracy


Certain

SOFC

models

superior
.



Back

pressure

across

stack

should

be

large

to

maintain

uniformity

of

pressure

and

velocity

across

core
.



Geometric

features

by

which

this

may

be

achieved

were

identified

using

parametric

studies


SOFC

design

re
-
configured

as

a

result

of

CFD
.



Institute for Chemical Process and Environmental Technology

Future (current) work


SOFC’s

with

more

complex

passages
.



Flow

of

two

working

fluids,

combined

with

inter
-
fluid

heat

transfer

and

Ohmic

heating
.


Initial

anlysis

suggests

the

conventional

DRA

for

heat

transfer

may

need

to

be

modified

due

to

low

Reynolds

number

effects
.


Concurrent

display

and

manipulation

of

graphics

data,

locally

on

VR

walls,

and

across

the

country

via

CA*net

3
.


Experimental

facilities

to

gather

empirical

data

and

conduct

flow

visualisation

studies

for

model

validation
.