Design And Experimental Research On Porous Carbon Plate Humidifier For PEMFC

The water content in the membrane of PEMFC directly affects the proton conduction and membrane mechanical strength, and further affects the fuel cells performance. So it is very important to maintain an appropriate membrane wetting. The humidification is essential for PEMFC because it is difficulty to maintain water balance for an operation PEMFC. The humidification method most widely used in PEMFC is the external-humidification. In this thesis, an external-humidification technology selected porous carbon plate as the key material in PEMFC humidifier was researched. The appropriate hunmidifier was designed and the performance of the hunmidifier was experimentally studied.Firstly, The humidification demand of the fuel cell stack was theoretical calculated under different conditions. The design process of the porous carbon plate humidifier was proposed (PCP humidifier). A PCP humdifier was designed and fabricated for a 5kW fuel cell system. According to the design parameters, the pressure drop in the humidifier flow channels was calculated, and the results showed that the pressure drops of air and water channels in the humdifier are very small. The design of flow field in the humidifier is verified to meet the requirements.Secondly, the factors which infuence the water permeability of the PCP humidifier were experimentally researched. And the matching test between the humidifier and fuel cell stack was carried out to verify the rationality of the humidifier design. The experimental result showed that:(1) The water permeability of porous carbon plate humidifier is mainly affected by the pressure difference on both sides of the carbon plate and the circulating water temperature. The water permeability increases linearly with the increases of the pressure difference on both sides of the carbon plate. With the circulating water temperature rising, the water permeability increases, but in a diminishing growth rate.(2) In a low air flow, the humidifier water permeability increased with the rising of air flow rate, however, when the air flow exceeds a certain value, the water permeability of the humidifier reminds stable without noticedable fluctuation. (3) The flow rate of circulating water has little effect on the water permeability of humidifier; (4) The fuel cell stack achieves the best performance when the cathode inlet temperature reach the level of the fuel cell stack operating temperature. Therefore, taking the fuel cell stack cooling circulating water as the humidification medium improves the performance of the humidifier and the performance of the fuel cell stack significantly improves also.Finally, A three-dimensional model of air flow on PCP humidifier was developed by STAR-CD software. CFD analysis of air flow on the PCP humidifier was carried out, the influence of the air intake box height on the distribution of air and pressure drops was analyzed. Based on the numerical calculation, the parameters of humidifier were optimized, that is, the number of carbon plate group was decreased by 1/5, the intake box height was reduced by 1/3, and the pressure difference on both sides of the carbon plate was increased. As a consequence, the water permeability remained unchanged while the volume of PCP humidifier decresses markedly without a significantly increased of the pressure drops.