Mass Transfer Analysis And Optimization Of Counter-Flow Flow Field In PEMFC

Proton exchange membrane fuel cell(PEMFC)uses hydrogen as fuel,and the product is only water,which is pollution-free and environmentally friendly.The fuel cell directly converts the chemical energy of the fuel and oxidant into electrical energy under the action of a catalyst,and is not restricted by the Carnot cycle.In addition to the advantages of other fuel cells,PEMFC also has the characteristics of fast cold start and high energy density,and is very suitable for use as a portable power source.Since the performance of PEMFC is greatly affected by the hydration state of PEMFC,a humidifier is generally added before the air intake to ensure sufficient hydration of the membrane.With the advancement of material science,the thickness of PEMFC is gradually reduced,and the performance of the membrane is gradually improved.More and more manufacturers begin to use the water generated by the battery itself for self-humidification instead of using humidifiers.In this paper,three-dimensional models of channels and a new type of bionic flow channel single cell are established,and they are meshed using professional meshing software.Based on the designed single cell model and the existing experimental conditions,a total of four types of bipolar plates with flow channels are designed and processed for experiments.On the basis of the experimental data,numerical simulation is carried out using CFD analysis software to explore the internal mass transfer mechanism and water transfer phenomenon of the battery.Based on experiments and three-dimensional simulations,the effects of co-flow and counter-flow on battery performance under different working conditions are explored through serpentine flow channels,parallel flow channels and interdigitated flow channels.The results show that the interdigital flow channel is less improved by the counter-flow strategy due to its structural characteristics;the serpentine flow channel and the parallel flow channel can be improved by the counter-flow strategy under different working conditions.The serpentine flow channel is most significantly increased by countercurrent in dry conditions,and the voltage increase can reach up to 95 m V.Parallel flow channel has the best performance under counter-flow,the peak power density is increased by 39.23%,and the voltage is increased by up to 205 m V.Under the co-flow strategy,the battery performance is greatly affected by humidity.The serpentine flow channel performs better under medium and high humidity,while the parallel flow channel performs better under low humidity due to its characteristics of easy accumulation of water.Under the counter-flow strategy,both the serpentine channel and the parallel channel achieve the best performance under high humidity.At the same time,the battery performance under the counter-flow strategy is less affected by the intake humidity,so the counter-flow can effectively reduce the battery’s dependence on the intake humidity,and achieve good self-humidification effect under low humidity.At the same time,when working under high humidity and current density,counter-flow strategy can greatly improve the performance of parallel channel and achieve the effect of alleviating flooding.As the operating temperature rises,the battery performance under the co-flow strategy changes less,while the counter-flow strategy decreases performance due to the weakening of the anti-diffusion ability;as the working pressure rises,the battery performance under both co-flow and counter-flow is improved.By studying the performance of the lung-shaped channel under different working conditions,the results show that the bionic structure of the lung-shaped channel can bring better water and gas management capabilities,and is especially suitable for operation under high humidity and high current density conditions.Under medium and high humidity,the lung-shaped flow channel has a voltage increase of 98 m V compared to the interdigital flow channel at high current density,which is only 15 m V away from the serpentine flow channel which has the best performance.Compared with the traditional interdigital flow channel,its reaction gas concentration distribution and water distribution are more uniform,which can effectively improve the working performance of the membrane electrode;its current density distribution is also more uniform,which can inhibit the generation of local hot spots and is beneficial to the membrane working performance.When working under high humidity and high current density,its drainage capacity is better than the interdigital flow channel,and the pressure drop is smaller,which can reduce the burden on the air intake system.