Steady mixed convection in a differentially heated square enclosure with an active rotating circular cylinder

Mixed convection in a square enclosure with a rotating cylinder centered within it is numerically studied. Depending on the rotation of the cylinder, the natural and forced convection effects can be combined or opposite. However, due to the complex flow structure assumed by the flow, in some conditions the combined effects do not lead to the maximum overall heat transfer crossing the enclosure. The rotating cylinder participates on both the conductive and convective heat transfer processes, and exchanges heat with the fluid naturally, without imposition of a thermal condition at its surface. It is explored the influence of the cylinder through its radius, rotating velocity, thermal conductivity and thermal capacity on the resulting mixed convection problem. Thermal field is visualized using the isotherms, the flow structure is visualized through the streamlines, and the heat transfer process is visualized through the heat-lines. For the first time, these visualization tools are applied to a moving solid. The overall thermal performance of the enclosure is analyzed through the overall Nusselt number. For a better understanding of the participation of the cylinder on the heat transfer process, the local heat exchanged between the cylinder surface and the fluid is also analyzed Results clearly show how the rotating cylinder affects the thermal performance of the enclosure, and how the thermophysical properties of the cylinder are important on the overall heat transfer process across the enclosure. (C) 2009 Elsevier Ltd All rights reserved.