In this study the mixed convection heat transfer process in a square cross section cavity with a bottom groove heated from three side walls (left, right, and bottom) with vertically unheated baffle is investigated numerically and experimentally. In the numerical part the in-house CFD commercial code of ANSYS-FLUENT-V.16.0 based on finite volume method has been used to solve the 2D governing equations. The results are represented in terms of wall temperature profiles and Nusselt numbers of the heated wall. For the experimental work, a test rig were built to determine the effect of heater position, baffle height ratio (h/H), the baffle angle for the range of 300