An experimental study of mixed convective transport from a protruding heat source module mounted on a vertical surface in an externally induced flow has been carried out. This problem is of particular interest in the design of thermal systems, such as the cooling of electronic circuitry and positioning of a heating element in a furnace. The temperature and velocity distributions are measured. The dependence of the heat transfer rate and of the thermal field on the mixed convection parameter and on the thickness of the heat source module, particularly in the vicinity of the source, are investigated in detail. Experimental results indicate that the flowfield and the temperature distribution in the flow over the module are substantially affected by the module thickness and also by the mixed convection parameter due to the combined effects of the forced convection flow and of the buoyancy-driven flow arising from the heat input. These, in turn, have a strong influence on the convective heat transfer from the heat source to the ambient. The thermal and viscous boundary layers as well as the variation of the surface temperature are determined and the results discussed in terms of underlying physical processes. The results obtained are also compared with those for an element of negligible thickness. Thus, the effect of a significant module thickness on the convective transport is determined.