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In the PEM fuel cells, gas phase (air and vapour) and liquid water could simultaneously flow through the cathode Gas Diffusion Layer (GDL). On the other hand, the performance of fuel cell and the main characteristic parameters of the flow can be influenced by the interaction of these gas and liquid phases. In the present study, the main parameters of two-phase flow in the GDL such as capillary pressure, mole concentrations of gas species, gas velocity and liquid velocity have been evaluated by considering the interactional effects of the aforementioned two phases. Also, the impact of changing the value of cathode channel humidity and fuel cell temperature on the value of the mentioned parameters has been investigated. The results indicated that decreasing of relative humidity in the cathode channel causes an increase in the rate of water vaporization. Thus, this leads to a decrease in the liquid water velocity, capillary pressure gradient and saturation gradient in the GDL. Also, increasing the temperature causes an increase in the rate of water vaporization and a decrease in the gas velocity and gas pressure gradient.

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In this paper, a non - isothermal and two-phase flow in the cathode gas diffusion layer (GDL) of PEM fuel cell is modeled. To achieve more accurate boundary conditions, other components of fuel cell (membrane and anode GDL) are modeled. Governing equations including energy, mass and momentum conservation and auxiliary equations are solved by numerical method and the effect of gas mixture pressure in channels, relative humidity and effect of contact and mass exchange between two phases are investigated. Results show, it is necessary that both the contact and mass exchange between the gas and liquid phase to be considered. The performance curve and temperature distribution for single and two phase flow are compared for different amount of cathode channel humidity. The relative value of performance and temperature for single and two phase flow depends on the humidity of cathode channel. With increasing the cathode pressure from 0.5 to 5atm the value of water content in membrane and gas diffusion interface will increase about 20%. With increasing the water content in the membrane therefore the ohmic loss is reduced. With the reduction in the ohmic loss the temperature distribution along the fuel cell decreases but if the anode pressure increases the temperature distribution along the fuel cell increases. Keywords