Mixed convection flow over heat source modules mounted on a horizontal plate has been studied numerically. The present analysis is valid when the buoyancy force effects are small compared to forced convection effects. The mixed convection flow problem is formulated by two-dimensional incompressible flow with the buoyancy term represented by the Boussinesq approximation. The governing equations are solved in the stream function and vorticity formulation using high accuracy finite difference schemes. Results are reported for single and two heat source modules mounted on a horizontal plate with and without thickness. The effects of induced velocity, heat input, thickness, and location of heat source modules on heat transfer rate and thermal field in the vicinity of heat sources are reported. Results have shown that there is a decrease of maximum temperature on heat source modules with increase in free-stream velocity of the fluid. Results show that the change of location and thickness of heat source modules has a significant effect on thermal flow field characteristics. The maximum temperature and average Nusselt number on heat source modules are reported at different parameters. The reported results agreed well with experimental results available in the literature. © 2013 by Begell House. Inc.