Electrodeposition of charged particles onto fuel cell coolant channel walls

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Electrodeposition of charged particles onto fuel
cell coolant channel walls

• Chao Xie

EGEE 520 project presentation
5/1/2007
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Introduction

1. A fuel cell is an electrochemical energy
   conversion device that is able to covert
   externally supplied H2 to electricity with a very
   high efficiency.
2. During the operation period a huge amount of heat
   will be produced, which needs a cooling system to
   ensure fuel cells to run in an appropriate
   temperature range.
3. After long-term operation charged particles can
   leach into the coolant, and be attracted onto the
   coolant channel walls via electrodeposition. This
   phenomenon is believed to impair the cooling
   effect of the coolant.

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Governing equations
Electrodeposition is a complex multidimensional
process that include transport of charged
particles via diffusion, electromigration, and
convection in the coolant, as well as their
sorption on the coolant channel walls .
1. Coolant fluid flow Fluid flow in the
coolant channel follows Narier-Stokes equations
2. Convection, migration and diffusion of charged
particles in the coolant
3. Sorption of charged particles onto the walls
The Random Sequential Adsorption model
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Formulation
Assumptions 1. The charged particles are in a
suspension so dilute that they do not experience
significant agglomerations. 2. Given the dilute
nature of the suspension, the removal of
particles from the fluid over time is not
expected to affect the hydrodynamic properties of
the coolant.
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Solution
The charged particle concentrations in the
coolant channel (left T20 S right T 35 S)
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Validation
Electrodeposition of charged particles onto
coolant channel walls occur in two stages
The plot of depositions of charged particles
with different sizes versus deposition time.
1. The surfaces are free of charged particles
Coolant channel wall
The deposition rate is predominantly determined
by the interaction between charged particles and
the wall.
2. The surfaces are covered by particles
Coolant channel wall
1st stage
2nd stage
The charged particles already adsorbed onto the
surfaces have great influences on the subsequent
particle sorption onto the wall.
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Parametric Study
Charged particle concentrations in the channel at
different particles concentrations (left 0.5 x
10-7 M right 5 x 10-7 M)
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Conclusion
1. COMSOL Multiphysics has proven to be a
powerful tool to predict the electrodeposition
processes of charged particles onto fuel cell
coolant channel walls. 2. The predicted charged
particle deposition rates are not uniform along
the channel. More depositions occur near the
inlet region. 3. The concentration of particles
has a remarkable effect on their depositions onto
the walls, i.e., the higher the concentration of
particles in the coolant, the more the
depositions occur. 4. It was proven that charged
particle electrodeposition onto the walls is
fairly sensitive to the particle sizes. If the
particle sizes are out of nanoscale (1-100 nm),
the bulk charged particles will exhibit distinct
electrodeposition behaviors as compared with
nanosized particles.
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Questions?