The Analysis Of Internal Mass Transfer Of PEMFC And The Optimized Design Of Water Management In PEM Fuel Cell Based On CFD Methods

A proton exchange membrane fuel cell(PEMFC)is an electrochemical energy conversion device that converts chemical energy into electrical energy directly.Due to its attractive features,including zero pollution,high energy efficiency,compact structure and fast start & stop ability,PEMFCs have been widely regarded as potential future power source for stationary,automotive and mobile applications.To improve the cell performance,an effective water management is highly desired,since water behavior significantly affects the performance.For instances,if the water content in the membrane electrode assemble(MEA)is too high,it will cause flooding,leading to huge concentration loss.If the water content is too low,it will leads to the dehydration of membrane and the Nafion ionomer,which in turn decreases the proton conductivity and increases the ohmic loss significantly.In order to solve this problem,the internal mass transfer of PEMFC is simulated and experimentally studied in this study.The counterflow strategy is put forward for low humidity conditions and two optimized flow field designs are proposed to achieve stable water content in membrane,lower proton resistivity,and ultimately enhance the performance of the cell.The main contents of this paper are as follows:In the first chapter,we introduced the basic knowledge of fuel cells and the research progress of cell water management,flow channels and selfhumidification in recent years.In the second chapter,the CFD model describing the internal flow phenomena of fuel cells was introduced.Then,the Butler-Volmer equation and corresponding current conservation equations which can describe the electrochemical reaction inside the PEMFC are introduced.And mass transfer model was established to analyze the phenomenon of osmotic drag and back diffusion,and to analyze the effects of two diffusion phenomenon for proton conductivity of the membrane in PEMFC.In the third chapter,firstly the counter flow strategy is introduced which has self-humidification effect on the cell.Through experiment and simulation,the influence of counterflow strategy on the cell performance was analyzed,and the conclusion is drawn that it has good self-humidification performance at low humidity conditions.In the fourth chapter,we introduced two kinds of new flow channels were designed to solve drainage problem under high current density.One is the depth-changed flow field and the other is the width-changed flow field.The influence of newly designed flow field on the parameters was obtained.It is concluded that the depth-changed flow field and the width-changed flow field have better performance and reasonable liquid water saturation distribution compared to the traditional flow channel.And the new flow fields are proved that they have better drainage performance.Comparing to depth-changed flow field,the width-changed flow field achieved the overall performance advantage due to the relatively low pressure drop.In the fifth chapter,the simulation model of hydrogen circulation for dry conditions was introduced.The effects of hydrogen circulation on the average humidity of the anode,water content of the membrane and the current density were investigated.Compared with the steady-state condition without circulation,hydrogen circulation makes the anode average humidity,membrane water content and current density be improved significantly,and the response is very fast.But hydrogen supplementation will impact anode average humidity and current density,so in real time operations attention is needed.