Variation of the cross-sectional area of a channel affects the flow field and, therefore, convective heat transfer between the fluid and channel walls. In this paper, a geometrical model is proposed for a wavy channel carrying steady laminar flow of an incompressible fluid. The two-dimensional channel is modeled as a combination of a number of subsonic diffusers and nozzles. Effects of the geometrical characteristics such as length, boundary shape and symmetry of the channel, which describe the shape of these nozzles and diffusers, are investigated. Numerical studies at Re=200 show that the shape of the wall does not dramatically affect the convection heat transfer rate in the steady laminar regime. However, optimization studies can be carried out to change the shape of the channel and improve the average Nusselt number to some extent. It is shown that the average Nusselt number increases with the increase of the length of the diffuser part, but the asymmetry of the channel might increase or decrease the average Nusselt number. Finally, a genetic algorithm is introduced and used to optimize the geometrical parameters which describe the aforementioned nozzles and diffusers and, hence, the shape of the channel.