Non-Darcian forced convection heat transfer over a horizontal flat plate in a porous medium of spherical particles has been studied experimentally. With air as the working fluid, the effects of particle diameter and particles materials of different thermal conductivities were examined. The heat transfer measurements were obtained by heating the test plate under the condition of constant heat flux. The experiments have been made for Reynolds numbers ranging from 10 5 to 10 6 based on the test plate length. The porous media used in the experiments were made of glass, rock, and steel covering a wide range of solid thermal conductivity. Particles diameters of 2.7 mm, 4.2 mm, 5.6 mm, 8.1 mm, and 11 mm for rock material and 11 mm particle diameter for glass and steel materials were used. It was found that higher heat transfer coefficients were obtained with larger particle size and higher particle thermal conductivity. (C) 2013 Ain Shams University. Production and hosting by Elsevier B. V. All rights reserved.