A numerical model based on a finite-element method is used to estimate the heat transfer between a solid and a fluid flow through an interface. The interface has a periodic shape, which is commonly the case in many natural phenomena or technical processes. The Navier-Stokes equations were solved with a penalty function formulation and the heat transfer equation with a classical Galerkin one. Results are presented using velocity vector plots, isotherms, and variations of the heat transfer coefficient as a function of Reynolds number and thermal conductivity ratio for a special shape of the interface.