Entropy generation of pure mixed convection from double circular cylinders rotating inside a confined channel

Abstract

In this article, numerical investigations have been done on mixed convective laminar flow in a confined horizontal rectangular channel, considering air as the flowing fluid. The channel is provided with two hot solid cylinders rotating about their axes, placed vertically in a side-by-side configuration. A convection current is supplied by inducing a fully developed forced flow at a low temperature through the channel's inlet across the clockwise or counterclockwise rotating cylinders. Steady, two-dimensional Navier-Stokes and heat energy equations govern the transport phenomena within the flow domain. These equations have been simulated using the Galerkin finite element technique with appropriate boundary and interface conditions. Parametric studies have been conducted for Reynolds number based on the mean flow speed over a range of 31.62 ≤ Re ≤ 316.23, and Grashof number within the range of 103 ≤ Gr ≤ 105, while Richardson number is maintained unity (Ri = 1) indicating pure mixed convection. Variations of the geometrical configurations are considered in terms of the cylinders' blockage ratio (λ = 0.05, 0.1, 0.2) and gap ratio (γ = 0.25, 0.50, 0.75). The cylinders' rotational direction impacts are also analyzed by altering the rotational Reynolds number (Reω = 10, −10). Then, a configuration that maximizes the heat transfer rate is obtained by evaluating the flow and thermal properties and the accompanying entropy generation. It is found that maximum heat transfer and lower entropy generation occur when the cylinders rotate in opposite directions to each other. Moreover, the thermal performance criterion improves with a smaller cylinder size, and decreasing the gap ratio increases the Nusselt number and lowers entropy generation.