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

• Published in: International journal of heat and mass transfer 2018-10, Vol.125, p.525-542
• Main Authors: Boruah, Manash Protim, Randive, Pitambar R., Pati, Sukumar
• Format: Article
• Language: English
• Subjects: Backward facing step channel; Backward facing steps; Baffle; Baffles; Bejan number; Computational fluid dynamics; Configurations; Convective flow; Entropy; Entropy generation; Flow velocity; Fluid flow; Fluid mechanics; Heat transfer; Mixed convection; Numerical analysis; Nusselt number; Pressure drop; Reynolds number; Richardson number
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2018.04.094

•Effect of baffle structure on mixed convective flow through backward-facing step channel is studied.•Effects of baffle size, baffle to step obstruction distance, number of baffles and arrangement of baffles are analysed.•Shortest reattachment length is for the channel with square baffle.•Transport characteristics strongly vary with baffle size and shape.•In staggered arrangement, elliptical baffle is an optimum design choice. 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.