Direct numerical simulation (DNS) is performed to solve the governing equations for fluid flow and heat transfer around a sphere which is placed on the bottom wall of a flume. Two way coupling is used to account for the effect of the sphere on the structure of the near-wall turbulence and on the main stream. The calculation of the thermal field is done with the same grid system used for the velocity field. Water and transformer oil were used as test fluids, with the Prandtl numbers Pr = 5.4 and Pr = 55, respectively. The heat transfer calculations were carried out at the constant mean heat flux along the bottom. For both Prandtl numbers the DNS results indicate enhancement of heat transfer coefficient associated with a flow motion toward the wall. The thermal pattern around the sphere is obtained and the effect of Prandtl number is discussed.