Study On Output Power And Hydrothermal Characteristics Of Air-cooled PEM Fuel Cell Stack

A proton exchange membrane fuel cell is a device that converts chemical energy stored in fuel and oxidant directly into electrical energy.During operation,about 40%-50% of the energy is converted into heat and a certain amount of water is produced.Water-heat balance has an important influence on the output performance of proton exchange membrane fuel cells,which are affected by many factors,of which gravity is an important factor.Therefore,it is of great significance to analyze the influence of gravity on the water-heat balance inside the stack.This paper takes the self-made 140 W air-cooled proton exchange membrane fuel cell stack as the research object,and studies the effect of gravity on the performance of the stack through different combinations of stack placement and gravity.When the hydrogen flow path is parallel to the gravity direction,the effect of gravity on the performance of the stack is studied when the direction of hydrogen flow and the direction of gravity are in the same direction and in the opposite direction.The experimental results show that when the hydrogen flow direction is the same as the gravity direction,the local high temperature area on the surface of the stack is smaller than the local high temperature area when the hydrogen flow direction is opposite to the gravity direction,and the internal temperature uniformity of the stack is poor,and the maximum temperature difference is 4? higher than that in the opposite direction of hydrogen flow and gravity,and the output voltage is relatively low.When the direction of hydrogen flow is opposite to the direction of gravity,it is easy to cause flooding of the first unit immediately adjacent to the hydrogen inlet and outlet,and the output voltage of the stack is relatively high,and the maximum voltage can be increased by 3.4%.When the hydrogen flow channel is perpendicular to the direction of gravity,the effect of gravity on the performance of the stack is studied under the two kinds of placement modes that the hydrogen side is upper and the air side is upper.The experimental results show that the local high temperature area on the surface of the stack is mainly distributed near the hydrogen outlet at the right half of the surface of the stack when the hydrogen side is up,and the area is smaller than that in the middle part of the stack bottom when the air side is up.The output voltage of the stack is relatively low when the hydrogen side is up,and the unit at the bottom is prone to flooding.When the air side is on,the output performance of the stack is relatively good,and the voltage can be increased by 2.4%,but it is easy to cause the distribution of hydrogen concentration at the bottom of the cell is less,resulting in a large voltage difference between the voltage and other single cell voltage,the maximum difference can be up to 0.33 V.When the stack is placed at different angles,gravity can have different effects on the output performance of the stack.It can be seen from the experimental results that when the current is small,the output voltage of the stack is the largest when 0° is placed,and when the current becomes larger,there is an optimum angle of 45°.When the stack is placed at 45°,the difference between the output voltage at 45° and that at 0°decreases and output voltage of the stack gradually becomes the maximum output voltage when the stack is placed at 45°.Under the condition of large current,different placement angles have different effects on the periodic fluctuation of the stack voltage,and the voltage fluctuation of the stack is the largest when placed at 0°.