Enhancement of conjugate mixed convection heat transfer in a long horizontal channel with multiple rotating cylinders

Two-dimensional, laminar, steady mixed convection heat transfer in a long horizontal channel has been investigated numerically with flow modulation through periodically distributed heat conducting rotating cylinders. The upper wall of the channel is maintained at constant low temperature and the lower wall is maintained at constant high temperature. A series of heat conducting rotating cylinders is placed periodically along the centerline of the channel with a spacing between two successive cylinders being equal to the height of the channel. The mathematical model of the present problem is governed by two-dimensional continuity, momentum and energy equations. The governing equations are then transformed to non-dimensional forms that are solved by using Galerkin finite element method with triangular discretization system. Water, air and liquid Gallium are considered as the working fluids. Numerical simulation is performed for case of pure mixed convection heat transfer characterized by a Richardson number of unity. Parametric simulation is carried out for a wide range of Reynolds numbers (1 ≤ Re ≤500) based on the dynamic condition of the rotating cylinder. Numerical results are presented and analyzed in terms of the distribution of streamline and isotherm patterns, local and average Nusselt number variation along the hot wall for different parametric conditions. It is found that, presence of heat conducting rotating cylinder increases the heat transfer significantly particularly in the lower range of Reynolds numbers considered in the present study and enhancement of heat transfer occurs as the Prandtl number increases. Thus, dynamic condition of the rotating cylinder and the thermophysical properties of working fluid play dominant roles for enhancing the heat transfer characteristics and flow behavior within the long horizontal channel.