A detailed convective heat transfer study was conducted for a square cylinder subjected to uniform air and water streams at various inclination angles using a wind tunnel and a towing tank approach, respectively. Since the same test object was considered for both fluids, the comparison of the air and water heat transfer data enabled an assessment of the influence of the Prandtl number on the convective heat transfer. The reliability of the test apparatus was checked by means of mean heat transfer results obtained for air for which accurate literature data were available. The new results of the present experimental study demonstrated that the classical assumption m = 1/3 for the Prandtl number exponent in heat transfer correlations was only valid in cases where a two-dimensional boundary layer flow governed the convective heat transfer. The classical Prandtl number exponent assumption failed in the case of flow regimes dominated by separation and reattachment. The new experimental data indicated that for such threedimensional flows virtually higher values should be used for the Prandtl number exponent. (C) 2017 Elsevier Ltd. All rights reserved.