Investigation of water droplet emergence and removal in bent gas channel of PEMFC

摘要

The proton exchange membrane fuel cell (PEMFC) shows great potential as a promising candidate of alternative energy-conversion device due to its zero emission, low operating temperature, low noise and high power density. PEMFCs are also considered for a wide range of applications including stationary power systems, automobiles and other power generation units [1-3]. Combined with the operating condition, water management is one of the most important issues in PEMFCs to improve the performance. Considering from the electrochemical reaction, a high ionic conductivity requires that membrane should be well humidified [4]. On the other hand, the water flooding might be occurred due to a large number of generated water in the cathode, especially at high current density for automotive applications. The water flooding should be avoided, because it causes blocking in the gas diffusion layer (GDL), a higher pressure drop in gas channel (GC), ineffective and non-uniform heat removal, and corrosion of cell components [4, 5]. Therefore, liquid water dynamics is the key factor to high current density PEMFC. In present study, the dynamics of water droplets emerging from micro pores on the GDL into bent GC of the PEMFC is simulated numerically using the volume of fluid (VOF) method. Compared with the previous studies, the bent GC, which is so called V-flow, is introduced due to its advantages of better gas dispersion and prevention of water accumulation. The influence of the bent GC geometry is investigated by changing the bent angle, cycle, and channel height. And the effect of channel surface contact angle is taken into account. As the bent angle increases, pressure gradient increases and liquid water moves faster. As the cycle increases, the settling time increases with the longer straight part and the droplet behaviorremains'thesame. While the channel height decreases, the surface water coverage ratio and the water volume fraction increase and the water film cover the top wall quickly. The two-phase pattern changes significantly because the vertical space is not enough to form a spherical droplet. Simulation results show that the contact angle of the bipolar plate (BPP) and GDL surface also have a significant impact on the two-phase flow pattern and channel pressure drop in the bent GC. Therefore, the GC geometry and the surface contact angle may cooperate with each,..other to, determine The-performance of water management in PEMFC.