Transport phenomena in a semi-passive direct methanol fuel cell

A two-dimensional, steady state, non-isothermal, multi-fluid, two-phase flow model is presented for a semi-passive direct methanol fuel cell at which air flows through a channel at the cathode side while liquid methanol solution is fed passively at the anode. The evaporation/condensation rates are formulated in a manner to capture the non-equilibrium effects between the liquid and gas phases. The model also accounts for the methanol and water crossover through the membrane. The behavior of a semi-passive system, including the temperature, oxygen and water vapor mass fractions, and the liquid saturation at different air flow rates is well described. Capturing the thermal effect in a semi-passive system is vital, since transport variables are highly dependent on temperature. While a higher flow rate of air at the cathode channel decreases the average cell temperature, it enhances the liquid removal from the porous media at the cathode side. The results also show that a higher flow rate results in a more uniform distribution of transport variables along the channel. For a cell that does not suffer from the flooding effect, a lower air flow rate through the channel results in a higher performance of the cell due to the temperature increase.