Numerical Investigation Of Liquid Water Transport Mechanism In Novel Block Flow Channels Of Fuel Cells

Proton exchange membrane fuel cell(PEMFC)has the characteristics of compact structure,good performance and environmental friendliness,and it is a clean and efficient energy conversion device.Liquid water transport and removal is important in PEMFC for achieving good performance and durability.Block flow channel shows a promise to promote liquid water removal and mass transport,improving the PEMFC performance.The main contents for water management are investigated as follows:1.Two novel channels with different blocks,named one-block channel and twoblock channel,respectively,are designed to study their effects on water removal using the Kistler model at different cases of droplet size,air velocity,and the static contact angle of the gas diffusion layer(GDL)surface.It is found that compared with the conventional straight channel,both the one-block and two-block channels can facilitate liquid water removal.For the one-block channel,the acceleration effect of the block on the droplets plays a major role in the liquid water removal,while the two-block channel has the salient advantage that water droplet could be dragged away from the GDL surface by the adhesion force of the block surface,achieving faster water removal.The one-block channel will generate a higher pressure drop,in contrast,the pressure drop caused by the two-block channel is much smaller.Thus,the two-block channel is more potential and balanced among water removal on GDL surface and pressure drop.2.The impacts of height,width and length of the block on the water removal ability and pressure drop of the two-block channel are further analyzed by the controlled variable method.It is found that the height,width and length of the block are all decisive factors on whether droplets can be directly dragged away from the GDL surface and reach the channel top wall,achieving faster water removal.Moreover,the pressure drop is positively related to the height,width and length of the block.The two-block channel can achieve a better effect on water management,when the height of the block is 0.8mm,the width is 0.3 mm,and the length is 0.6 mm.3.The block structure parameters are optimized for the two-block channel using the artificial neural network(ANN).A total of 43 data sets including training sets and test sets are obtained using the 3D physical model.The height,width and length of blocks are considered as input variables,the water removal time(T)and the maximum pressure drop(?P)are output variables.The results show that the prediction of ANN model is in good agreement with the physical model results.Comprehensively considering the balance of water removal time and maximum pressure drop,the optimal block structure parameters are obtained of which the block length,width and height are0.8 mm,0.375 mm and 0.75 mm in the two-block channel,respectively.4.The dynamic wettability model based on the contact line shape is improved using a more accurate arc differential formula to describe the surface capillary force,and the contact angle function is adopted to describe the relationship between the azimuthal angle and the dynamic contact angle.It is found that the results of the improved dynamic wettability model(IDWM)are similar to the liquid droplet motion in the experiment results.In the IDWM and experiment results,all the droplets move like a ball,and the Height/Chord length,advancing contact angle,receding contact angle and contact angle hysteresis of droplet are all consistent with the experiment.Hence,the IDWM is quite suitable to be used to simulate the motion shape and dynamic wettability characteristics of the droplet in the flow channel.