Experimental mixed convection heat transfer from an isothermal horizontal square cylinder

•A setup is designed to study convection across a horizontal square isothermal cylinder.•The effects of blockage due to developed boundary layers on duct walls are studied.•New correlations for free and mixed convection are given.•A new correlation for the effect of flow attack angle on heat transfer is given. Laminar natural and mixed convection heat transfer from an isothermal horizontal square cylinder was experimentally studied. The study includes the design and construction of a test rig to fulfill the research requirements. The natural convection experiments were established for three different side lengths of the square cylinder (25, 30 and 40mm) which in atmospheric air give Grashof numbers, Gr of 9.895×104, 1.499×105 and 4.388×105. For mixed convection, using the three cylinders, Reynolds number, Re ranged from 48 to 670, and the attack angle, Ψ from 0° to 180° with steps of 30°. The experimental results gave the effects of Grashof, Reynolds and Richardson numbers on the average Nusselt number for air (Pr=0.7). The experimental results were correlated and compared with previous work.