The fully developed laminar flow and heat transfer for ducts with rectangular and trapezoidal cross-section in fuel cells have been numerically simulated with one porous wall with a uniform mass injection or suction, the other three walls being impermeable. The new concept of thermal boundary conditions of combined constant heat flux and constant temperature on the walls was implemented. Based on the constant thermal-physical property assumption, the wall friction factor and Nusselt number for different mass transfer rates, the aspect ratios and base angles are obtained. Comparisons of these numerical results with published data are also presented.