Hydrothermal performance and entropy generation analysis for mixed convective flows over a backward facing step channel with baffle

Abstract

In this work, we numerically investigate the thermo-hydraulic characteristics and entropy generation for mixed convective flow through a backward facing step channel with baffle. The effect of baffle geometry is studied by considering three different shapes for the baffle viz. square, triangular and elliptical and two different baffle sizes viz. hb × wb = 1 × 1 and hb × wb = 2 × 2 designated as B1 and B2 configuration respectively. Parametric studies are also carried out to analyse the effects of baffle to step obstruction distance, number of baffles and arrangement of baffles in inline and staggered order on the fluid flow, heat transfer and entropy generation characteristics. Local and average Nusselt number, pressure drop and entropy generation are computed for all the configurations at a fixed Reynolds number Re = 100 and for a range of Richardson number Ri = 0.1–1. Our study reveals that the reattachment length decreases with the addition of the baffle inside the channel and the length is inversely proportional to the size of the baffle. Peaks of local Nusselt number are observed in the region near the baffle and the magnitude of these peaks are dependent on the baffle shape and size. It is observed that local entropy generation is minimum within the re-circulation zone while the same is maximum at the reattachment point. The larger the distance of baffle from step, the smaller is the total irreversibility associated with it and its magnitude is the least in case of elliptical baffle for both the configurations. For any baffle shape having B1 configuration, the average Nusselt number, the average pressure drop and the total entropy generation are minimum for two baffles both mounted on the top wall, while these parameters predict an increasing trend with increasing number of baffles for B2 configuration. In case of pair of baffles mounted both on the top and bottom walls, inline arrangement of baffles always incur higher heat transfer performance, pressure drop penalty and entropy generation as compared to staggered arrangement. For all the number of pairs of baffles in staggered arrangement, elliptical baffles always provide the highest heat transfer performance, least pressure drop penalty and least entropy generation among all the baffle geometries and as such in staggered arrangement, elliptical baffles in backward facing step channel is an optimum design choice from the perspective of both the thermo-hydraulic performance and entropy generation.