Tech Briefs Magazine - October 2023 - Comsol-13A

RESEARCH SPOTLIGHT
" Engineers might prefer to use
straight channels with no side
branching, but nature chooses
the 'reaction design'. "
- YUQING ZHOU, RESEARCH SCIENTIST, TRINA
FIGURE 5 A machined metal prototype flow field plate
based on one of TRINA's generated designs.
pore individually designed.
We need to install walls
and channels to direct fluid
through the pores in ways
that approximate the ideal.
To generate this design, we
use COMSOL Multiphysics®
to solve a customized partial
differential equation (PDE)
for pattern generation. The
software also gives us plotting
functions we can use to
visualize the results. "
Two of the formal
options created by TRINA's
dehomogenization equations
are shown in Figure 4.
Their guiding performance
objectives are to reduce
resistance to reactant flow
and to enhance reactant
supply and reaction
uniformity across the entire
plate. These objectives are
represented by governing
variables in the model's
PDE. By assigning different
weighting factors to these
two objectives, Zhou and
his team can induce the
model to generate different
design options. They can
then evaluate the relative
merits of each option and
make adjustments to produce
further iterations.
Of the design shown in
Figure 4 at left, Zhou says,
" We call this the 'flow design'
because it leads to the
smallest pressure drop across
the entire flow field surface.
The model generated paths
that are relatively parallel and
straight, without much side
branching. "
While this design effectively
moves fluid across the plate,
it does less well at distributing
reactant evenly through
the porous material layer.
Simulation shows lower
reactant concentration on the
outlet side of the design, which
can limit reaction uniformity
and the resulting power
output from the fuel cell.
If the weighting factors
in the governing equation
were adjusted to prioritize
reaction uniformity, the
model would then generate
a design like the one shown
in Figure 5, which Zhou calls
the " reaction design " . High
reactant concentrations
(shown in red and orange
in the bottom image) now
predominate, indicating
that a larger share of the
available reactant is being
put to work. The intricate
forms of the " reaction design "
microchannels may seem
familiar to students of biology.
" Most commercial
microreactors would use a
design somewhat similar
to the 'flow design', " says
Zhou. But naturally occurring
systems that distribute fluid
reactants - such as leaves,
lungs, and blood vessels -
more closely resemble the
forms of Figure 4 at right.
" Engineers might prefer
to use straight channels
with no side branching, but
nature chooses the 'reaction
design', " Zhou says. The
TRINA team's research paper
notes that while some have
previously experimented with
natural-looking, fractal, or
hierarchical forms selected a
priori for flow field channels,
" this is the first time that such
large-scale branching flow
fields have been discovered
using an inverse design
approach without assuming
prescribed layouts. "
» RATHER THAN
TRYING TO PREDICT
THE FUTURE, CREATE IT
Along with the " flow versus
reaction " comparison
illustrated earlier, TRINA
produced two further designs
(not shown) that combined
attributes of those in Figure
4. Every one of TRINA's four
iterations outperformed
baseline conventional designs
across key reaction-fluid
performance metrics. An
additional design that was
fabricated and experimentally
tested by the TRINA team is
shown in Figure 5.
So, what is the ideal design
for a flow field plate? There is
no such thing, just as there is
not a single ideal technology
for replacing gasolinepowered
automobiles. " From
our point of view, we succeed
by providing multiple good
options for our engineers to
consider, " Zhou says. Yuqing
Zhou shares some advice that
guides him and his colleagues:
" Our chief scientist has said:
'We must stop trying to
predict the future, and just
work on trying to create it.' "
Four core contributors to the project. From left to right:
Ercan M. Dede, Tsuyoshi Nomura, Yuqing Zhou, and
Danny J. Lohan. Nomura is affiliated with Toyota Central
R&D Labs in Japan, while the others work at Toyota
Research Institute of North America.
COMSOL NEWS 13a
Tech Briefs Magazine - October 2023

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