The rising cost of energy has made the need for the design of energy-efficient thermal equipment a necessity. It was therefore the purpose of this study to experimentally determine the heat transfer and pressure drop during the forced convective turbulent flow of water in a horizontal concentric annular flow passage with various prescribed uniform wall heat fluxes. Unilateral heating from either the inner or outer wall of the annulus, as well as bilateral heating on both walls simultaneously, were considered. Compared to unilateral heating conditions, bilateral heating resulted in enhanced heat transfer coefficients. When the difference in temperature between the fluid and the walls was considered, the factors of diabatic friction were correlated to within 1%.