Fluid Flow and Heat Transfer of Combined Forced and Natural Convection over Upward-Facing, Horizontal Heated Wedge Placed in Uniform Downward Flow of Forced Convection

Abstract

Experimental investigations have been carried out on combined forced and natural convective flows induced around upward-facing, horizontal heated wedges placed in a uniform vertical downward flow of air. A keen interest was directed to the thermal instability of the laminar boundary layer flows over the wedge and its effect on the heat transfer from the wedges. For the sake of this, comprehensive flow visualization experiments and measurements of the local heat transfer coefficients have been conducted with the wedges of various angles θ from 180°(horizontal plate) to 0° (vertical plate). The results showed that longitudinal vortices appear over the wedges of 180°<θ<135° with increasing buoyancy force and they enhance the heat transfer from the wedges. While, a separation of the boundary layer occurs over the wedges of 110°<θ<0° and the heat transfer was deteriorated significantly. It is also found that the onsets of these thermal instabilities as well as the heat transfer variations are predicted well with the non-dimensional parameter (Gr_L^*/Re_L^2.5).