Numerical study of mixed convection in an annulus between concentric rotating horizontal cylinders is presented in this work by using finite volume method. The mixed convection is due to natural convection because of temperature difference of the cylinders and forced convection is because of cylinders rotation with different time functions and in different directions. Here, the effect of different cylinders motions are investigated on flow parameters such as streamlines and heat transfer parameters such as temperature contours, Nusselt numbers, along with required torque for rotation. The non-dimensionalization of the governing equations is different in this study such that the non-dimensional Reynolds number does not appear in the equations and the velocity magnitudes are Reynolds numbers themselves that can be used locally for analyzing flow in solution field. The obtained results are compared with the existing analytical and numerical of simpler cases which prove good agreements.

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