Visualization Experiment And Optimization On Performance In Direct Liquid Fuel Cells

Proton exchange membrane fuel cell has the features of high energy conversion efficiency and friendly to the environment.This new energy has been considered as one of the indispensable resources in the future society.Proton exchange membrane fuel cell's structural characteristic is unique.A large amount of heat released from it can be used as power of power station and thermal power plant.This makes it become a hot spot of research.In order to deal with the problem of heat produced by the fuel cell in the process of electrochemical reaction,the researchers have carried on the deep research on the battery thermal management.To efficiently make use of this part of heat energy and electric energy,the first thing is to analyze the creation of heat energy and the affecting factors of fuel cell internal temperature.Temperature is an important parameter for the thermal management study of proton exchange membrane fuel cell.The low temperature can lead to a decrease in the performance of the battery,while the high temperature will affect the water loss of fuel cell membrane and destroy the structure of the battery so that the battery will not run properly.In this thesis,the fuel cell is simulated by the software COMSOL Multiphysics.Two-dimension and three-dimension management systems as well as heat transfer element and heat transfer calculation module are built to respectively describe the mathematical and physical models.The flow,heat transfer and chemical reaction engineering simulation involved by the proton exchange membrane fuel cell's gas-liquid-solid coupling heat transfer mechanism,with the mass conservation equation,the momentum conservation equation and the component conservation equation,to reveal the essential characteristics of the temperature field distribution in the fuel cell,the temperature variation of air cooling type cell and the flow state of cooling fluid when it cools fuel cell's internal cooling channels and influence to its temperature.The specific results of the PEMFC study are as follows:(1)Through the temperature field numerical simulation carried out in the two dimensional proton exchange membrane model,and the analysis of the relevant parameters of the temperature change to improve proton exchange membrane fuel cell's using efficiency.As the hydrogen ion of the fuel cell goes through the membrane to reach the cathode and starts the oxygen oxidation reaction,then there will be a lot of heat,so that the temperature of the cathode is higher than the anode.At the same time,to change the parameter range of the working voltage,the porosity of the battery and the exchange current density can effectively improve the working performance of the proton exchange membrane fuel cell,which makes the efficient utilization of the proton exchange membrane fuel cell.(2)The air cooling mode has a significant effect on maintaining the temperature of the battery.In the natural cooling,the three-dimensional numerical simulation model is established.The battery is kept in the best operating temperature range by controlling the changes of the factors.Both the natural cooling temperature control and the external heat transfer capacity of the battery have good dynamic characteristics,which effectively solve the problem of temperature control of natural cooling PEMFC battery.When the forced convection cooling is used,the electric,chemical and thermal energy are used to control the changes of the wind speed and the wind temperature.They can lead to different results for the temperature in the fuel cell.Reasonable changes of parameter values can make the battery achieve the purpose of efficient operation in the best operating temperature range.(3)For the first time,the physical and mathematical model of the micro compact proton exchange membrane fuel cell is established by using the multiphysics field software.It analyzes the affection on the battery's temperature by the cooling fluid's temperature,velocity and flow direction when the proton exchange membrane fuel cell's cooling fluid is in the process of heat dissipation.The flow process of the cooling water in micro-channel is established.And the internal flow field is simulated.Also,the finite element method is used to carry out the numerical simulation.The thermal simulation and thermal management of proton exchange membrane fuel cell can be obtained.It has important significance to improve the performance and durability of the battery.