29-09-2008, 10:43 AM
The efficiency of fuel cell is higher than the Carnot engine. To date, cost is the daunting factor for making the proton exchange membrane fuel cells (PEMFC) commercially viable in appliances. Over the years, a significant research activity has been witnessed in cutting down the cost that is involved in making the individual components of a fuel cell. However, relatively fewer efforts have been put into minimization of the cost of integrating a PEM fuel cell (PEMFC) system. This work is focused on the reduction in cost of PEMFC stack system (stack with auxiliaries). The efforts have been made in reducing the cost involved mainly in (i) humidifying the H2, (ii) increasing the temperature of exit coolant water and (iii) elimination of air flow meter used for reactant flow control on cathode side. A novel design is proposed for humidifying the H2 gas on continuous basis using stack exit coolant water. As a result the cost involved in cooling the stack coolant water can be reduced. Further, the results obtained for stack power with humidified H2 are shown to be high about 5 - 15 % when compared with dry conditions. A control orientated thermal model is developed and is used for studying effect of heat transfer area on increasing the exit coolant water temperature. This is studied by increasing the number of coolant plates to be kept in the stack. The results show that 58 % of total numbers of single cells in a stack are required to reach the exit water temperature near the stack temperature. An alternate method is used for controlling the air flow rate instead of using the direct measurements. The proposed idea involves the use of stack voltage as a controlled variable in place of the air flow rate. This eliminates the use of mass flow controller so that the cost associated with the PEMFC system can be reduced by a significant amount. Results obtained for air flow rate from these studies are found to be encouraging to the extent of supporting the proposed idea as a good cost reducing alternative for controlling the air flow rate.