Laminar fluid flows and heat transfers, by forced convection, in a rectangular horizontal channel, have been numerically investigated. Three blocks, simulating electronic components, have been attached to the channel bottom wall. In order to control the flow and enhance the heat transfer rate, a rectangular cross section bar, acting as a vortex generator, has been attached to the channel top wall. The Navier-Stokes and energy equations are solved using FLUENT. Velocity and temperature fields as well as local Nusselt numbers have been obtained for various imposed conditions. Our numerical simulation procedure has been validated by comparison with results of other authors. The obtained results indicate that thanks to the control element, heat transfer in the channel is enhanced. For each block, the best position of the vortex generator, which allows maximal heat dissipation, is when the control element is located above the considered block.