EGEE 520 project presentation Electrodeposition of charged particles onto fuel cell coolant channel walls Chao Xie Good evening, every one! Our topic today is heat transfer gradient through the reactor. EGEE 520 project presentation 5/1/2007

Introduction A fuel cell is an electrochemical energy conversion device that is able to covert externally supplied H2 to electricity with a very high efficiency. 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. 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.

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

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. 1. Steady-state process, 2. Ignore contact thermal resistance between each boundary, 3. Thermal conductivity for each material is constant in every direction, 4. The radiation from steel to ambient can be neglected.

Solution The charged particle concentrations in the coolant channel (left: T=20 S; right: T= 35 S)

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 The charged particles already adsorbed onto the surfaces have great influences on the subsequent particle sorption onto the wall. 1st stage 2nd stage

Parametric Study Charged particle concentrations in the channel at different particle’s concentrations (left: 0.5 x 10-7 M; right: 5 x 10-7 M)

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.

Questions?