Transport Simulation And Structure Optimization Of PEM Fuel Cells

PEMFC(Proton Exchange Membrane Fuel Cell) is a complex dynamic system of multi-physics fields,multi-phase and multi-scale.Reaction gas flows from channel to reaction zone in operation condition,and scales change from stack(meter class),to channel(millimeter class),GDL(Gas Diffusion Layer)(micron class) and catalyst layer(nano-meter class).Phenomenon and mechanism of transportation in PEMFC have not been studied thoroughly in recent research.Modeling of PEMFC using software can show the working conditions inside the PEMFC and reveal the mechanism.With structure optimization,the performance of PEMFC can be improved and the cost can be reduced.Influence of channel structure on performance of PEMFC has been studied. PEMFC operates at the best performance when the depth of channel is 0.5mm.Under low current density condition,performance improves with the decrease of ratio of width of channel to the width of shore.Road to the structure of the convection cell performance impact was studied.Condition under high current density is quite the contrary.The total performance reach peak when the width of channel equals the width of shore.As for the cross-section of channel,PEMFC has the best performance and structural intensity with cross-section of semicircle.Time of water drain out of the channel decreases with the increase of contact angle(improvement of hydropholic characteristic),and decreases little when contact angle reaches 90°.Porosity,hydrophilic and hydropholic characteristics and thickness of GDL are studied.Results show that it's better for the transfer of gas and water with the increase of porosity and decrease of contact angle and thickness when the porosity is uniform.And the gradient change in porosity is better for the transfer of liquid water. GDL with porosity spacing distribution in plane is better for the transfer of gas and water,so can improve the performance of PEMFC.The main factors influence the water transfer in the membrane of PEMFC is studied.Water content in membrane and performance of PEMFC increase with the increase of temperature,stoichiometry of air,relative humidity of react gas,operation pressure and current density,decrease of thickness of membrane.Main factors affect gas distribution in stack is studied.Results show that gas distributes even with low inlet velocity and high inlet pressure.At the meanwhile,low inlet velocity will cause problem of water drainage and high inlet pressure will cause problem of more accessory power.U-type is better than Z-type under condition of single inlet in cathode.And two inlets at the ends of cathode have the best PEMFC performance.Gas distributes even with increase of area of cross-section of main inlet or using variable cross-section.Reuse of the waste heat produce in water can also improve the performance of PEMFC.In summarization,study of PEMFC is made from micro scale to macro scale. Transfer of water in channel and gas distribution in stack is studied with the combination of micro structure of channel and macro structure of stack,which is the coupling of multi-scale.Results of study are useful for insight understanding of mechanism of PEMFC and improving of performance of PEMFC.