Numerical analyses were performed for the effect of inclined angle on the mixing flow in a square channel with uniform temperature walls (T-w = 30 degrees C) and inlet temperature (T-o = 10 degrees C). Three-dimensional governing equations were solved numerically for Re = 100, Pr = 0.72 and various inclined angles (from -90 degrees to 90 degrees). Three-dimensional behavior of fluid in a channel was examined for each angle. Thermal performance was evaluated using the relationship between Nusselt number ratio and pressure loss ratio with and without buoyancy induced flow as a parameter of inclined angles. High heat transfer and low pressure loss region was from -15 degrees to -60 degrees in thermal performance using mean Nusselt number ratio. (C) 2008 Elsevier Ltd. All rights reserved.