Study On Humidification Characteristics Of Porous Plate Humidifier For PEMFC

To make sure the PEMFC operating high efficiently, one of the prerequisite is maintaining water balance inside fuel cell. It is difficult to maintain water balance by regulating operating conditions without external humidification, so the inlet stream should be properly humidified before entering the stack. A humidification system layout and humidifier design process have been proposed in this work based on a porous carbon plate humidifier. And a thermodynamic model of the humidification process has been conducted to simulate effect of operating conditions and geometry parameters of the humidifier to heat and mass transfer and humidification performance.Firstly, computational formula of the amount of water of humidification demand has been deduced to analyze the effect of operating conditions to the amount of water of humidification demand. The result showed that under the same stoichiometry and humidification demand, the air require the largest amount of water, followed by hydrogen, while oxygen require the least. The amount of water of humidification demand grows linearly with the increase of stack output power and the required humidity, and it increases exponentially with the increase of required temperature, while it declines with the increase of pressure. The computational formula of humidity of cathode exhaust stream under non-humidification condition was also deduced to calculate the humidity of cathode exhaust stream under different operating conditions. The result showed that the cathode exhaust stream humidity is either higher than100%or below80%under most operating conditions, which makes the water balance hard to maintain.Then, the design process of gas-to-gas porous carbon plate humidifier for PEMFC has been proposed based on the ratio of residence time and diffusion time and velocity of gas inside the humidifier. And a gas-to-gas porous carbon plate humidifier for a5kW fuel cell system has been designed according to the design process.Finally, a thermodynamic model of the humidification process has been conducted based on operating principle of the porous carbon plate humidifier, mass and energy conservation law and some reasonable assumption, to analyze effect of operating conditions and geometry parameters of the humidifier to heat and mass transfer and humidification perfonnance. It can be seen from the simulation result that with regard to different operating conditions, lower air flow rate, pressure and higher cathode exhaust stream temperature benefit the increase of moisture content of exhaust fresh air and water recovery ratio of the humidifier, and promoting the humidification perfonnance; with regard to different geometry parameters, thinner thickness of the porous carbon plate and larger area of the porous carbon plate are helpful to promote the humidification performance of the humidifier.