Study On Liquid Water Transport Mechanism In PEMFC Gas Channel And Interaction With The Channel Surface

Proton exchange membrane fuel cell(PEMFC)is a promising energy conversion device.PEMFC has the characteristics of high energy conversion efficiency and pollution-free.Water management is one of the key factors affecting the performance and reliability of PEMFC.It is necessary to study transport mechanism in the channel and the interaction between liquid water and the channel wall.In this paper,the two-phase flow in PEMFC gas channel is investigated.The growth,accumulation,detachment and impact of liquid water in PEMFC channel are studied by numerical simulations.Based on the static wetting model,the mechanism of droplet impact on the channel wall is discussed,and the movement patterns of droplet under different conditions are considered.This paper simulates and analyzes the process of liquid water growing on the GDL surface,detaching from and impinging on the wall of the channel,and the flow pattern in the channel under the high-speed water mode is recognized.Based on the static wetting model,this paper takes the dynamic contact models into consideration,and makes comparisons among the models.The main work of this paper includes:1.Study on the motion mechanism of small-scale droplets impacting on the wall of the channel.When droplets impinge vertically on the wall,the effects of impact velocity,droplet size,wall contact angle and temperature in the interaction process between droplets and the wall are explored.The causes of droplet spreading,retraction,splash and rebound were analyzed to enrich the mechanism of liquid water impingement in the channel.When droplets impact the wall at an inclined angle,the effects of impact angle,impact velocity and contact angle during the spreading and sliding process of droplets after impact are investigated.When droplets impact on liquid film vertically,large impact velocity and small thickness of liquid film are beneficial to the jet and splash process.Large impact velocity and contact angle,small impact angle and liquid film thickness are beneficial to the removal of liquid water from the wall.2.Discussion on high speed water emerging from GDL pore,the process of droplet growth and detachment of GDL,transport in the channel and its interaction with the wall of U-shaped channel.The flow pattern of liquid water movement in the channel is recognized.The results show that larger airflow velocity and higher water emerging velocity lead to water removal from the GDL surface.Hydrophily and hydrophobicity result in water removal from the GDL surface and the channel,respectively.3.Comparisons among static contact angel model and dynamic contact angle models.The applicable conditions to different models are discussed,and the transport process of liquid water along the channel is further analyzed.The non-slip boundary conditions on the wall bring about larger wall shear force,which is unreasonable under high velocity.The effect of excessive wall shear force can be effectively removed by considering the slip boundary conditions.