Mixed convection is seen in high power devices where natural convection alone is not enough. At high temperatures radiation also contributes considerably. This work is concerned with the effect of surface radiation on mixed convection and conjugate convection in a channel with discrete heat sources. Flow is laminar and the parameters considered for this study are thermal conductivity of PCB (printed circuit board), Reynolds number, position of heat sources and emissivity of surface (emissivity of the inner surfaces of the channel are kept constant while those of the heat sources is varied). Constant fluid properties with Pr = 0.707 with Boussinesq approximation is considered. All numerical simulation has been done using FLUENT. The Reynolds number ranges from 115 to 690 (corresponding to air inlet velocity 0.25 to 1.5m/sec) and emissivity ranges from 0.1 to 0.9. Temperatures of heat sources decrease with increase in velocity, thermal conductivity of PCB and the emissivity. © Published under licence by IOP Publishing Ltd.