Study On Water And Heat Management Of PEMFC

Proton Exchange Membrane Fuel Cell (PEMFC) is a power device which translates chemic energy contained in hydrogen and oxidant into electrical energy directly. PEMFCs have many advantages such as a low operating temperature, sustained operation at a high current density, low weight, compactness, the potential for low cost and volume, long stack life, fast start-ups and suitability for discontinuous operation. These features make PEMFCs the most promising and attractive candidate for a wide variety of power applications ranging from portable/micropower and transportation to large-scale stationary power systems for buildings and distributed generation. The heat and water management of PEMFCs Water and heat management of the fuel cell have significant influence on the performance of the PEMFC stack. There was lack of studying on temterature distribution of the fuel cell stack, and lack of a simple and effective system and method for water management. In this paper the temperature distribution in the fuel cell stack and the gravity and the exhaust condensation droplets in the cells were studied in the drain.Through numerical simulation, the temperature distribution of gas diffusion layer (GDL) surface was investigated. It indicates that the temperature increases along the gas channel in different operation condition. The inlet temperature of GDL is higer than the outlet. The temperature of GDL surface under gas channel was higher than the area which flow plate contact with GDL.The higher operation pressure of cell is benifit for the temperature uniformity of GDL. As the increasing of gas flow the inlet temperature of GDL is increasing while the oulet is decreasing.The temperature of GDL is increasing as the increasing of gas flow.Temperature mapping was measured by micro-thermocouples embedded into the cathode plate of the modeling cell. The effects of different operation conditions on temperature distribution are investigated in detail. The results show that the temperature of the stack turns on "Parabola" distribution, and the temperature increases along the flow field from the inlet to the outlet under various conditions. Temperature difference of the sigle cell in the stack increases with the increased operation current density, and decreases with the increased air flow rate. The effect of the inlet air temperature on the temperature difference can be neglected in the stack, and the temperature uniformity can be improved by increasing the mass flow rate of the coolant water.Low gas velocity in PEMFC can be occurred as gas distribution inconformity. Low gas velocity of PEMFC aided by gravity water drainage was investigated experimentally. It exhibited that gravity can help droplets separate from gas diffusion layer, which also help the liquid water drainage from PEMFC stack. The experiment revealed that the performance of stack will be the best when the cathode downward and the droplet gravity accordance to the orientation of the droplet separate from GDL; gravity drops consistent with the direction of purge gas in the PEMFC stack when the channel was vertical which improve the water management. In different orientation of PEMFC stack channel the output of stack would be increasing with the temperature rising when the reaction gas flow rate is low; the gas humidification has little effect on stack performance when the channel was vertical. The cathode of the stack should be avoided to lay horizontality and upwards during working.PEMFC stack was operated by condensing the outlet gas of the stack and the recovery water was used to humidifying the inlet gas in this paper. The effects of outlet gas condensing on stack performance and analysis of the heat release of self-humidification PEMFC stack by condensing the outlet moisture were investigated. It presented that the stack performance and water management can be improved by condensing outlet gas. In the process of condensing, the latent heat of phase change takes the principally accounts for the heat removal in the condenser. The heat removal amount increases with the increase of the stoichiometry and decreases as the increase of outlet pressure of stack. Moreover, the heat removal amount increases rapidly with the increase of the operation temperature in the condition of self-humidification of PEMFC stack.