H=50 mm 4. The PEMFC single cell shown in the figure uses a 50mmx50mm MEA and generates 20W in electrical power and 25W in heat rate. The membrane must operate in a moist state in order to conduct hydrogen protons. However, the liquid water formed in the cathode side may block the oxygen from reaching the catalyst layer and result in failure of W-50 the fuel cell. Therefore, it is critical to control temperature of the fuel cell, To, so that the cathode side contains saturated water vapor. Saturated water vapor conditions exist in the fuel cell is corresponding to T =80C and the ambient temperature is T,=25 C. Consider two situations: (a) An external air flow driven by a fan is used to maintain the PEMFC temperature of the fuel cell. The relationship between the external cooling air velocity V and the convection heat transfer coefficient his h = 20.V0.8 where h is in W/(m2.C) and Vin m/s. Determine the external cooling air velocity needed to maintain the steady-state temperature conditions. T= 25C (The edges are assumed to be insulated.) (b) Alternatively, the heat rate could be removed by air entering the cathode side with a stoichiometry 2.. If air temperature jump is 55 C and Cp of air is 1004 J/kg-K, determine the value of 2. to main the same conditions. H=50 mm 4. The PEMFC single cell shown in the figure uses a 50mmx50mm MEA and generates 20W in electrical power and 25W in heat rate. The membrane must operate in a moist state in order to conduct hydrogen protons. However, the liquid water formed in the cathode side may block the oxygen from reaching the catalyst layer and result in failure of W-50 the fuel cell. Therefore, it is critical to control temperature of the fuel cell, To, so that the cathode side contains saturated water vapor. Saturated water vapor conditions exist in the fuel cell is corresponding to T =80C and the ambient temperature is T,=25 C. Consider two situations: (a) An external air flow driven by a fan is used to maintain the PEMFC temperature of the fuel cell. The relationship between the external cooling air velocity V and the convection heat transfer coefficient his h = 20.V0.8 where h is in W/(m2.C) and Vin m/s. Determine the external cooling air velocity needed to maintain the steady-state temperature conditions. T= 25C (The edges are assumed to be insulated.) (b) Alternatively, the heat rate could be removed by air entering the cathode side with a stoichiometry 2.. If air temperature jump is 55 C and Cp of air is 1004 J/kg-K, determine the value of 2. to main the same conditions
