A CFD Analysis on the Influence of Upstream Surface Geometry Modifications of Clerestory Shaped Rib on Heat Transfer Characteristics of Solar Air Heater

Abstract

Two-dimensional numerical analysis is conducted to determine the influence of upstream surface modifications of a novel clerestory shaped rib turbulator on thermal performance augmentation. The upstream surface of the rib is divided into two parts where the upper rib surface is always normal to the incoming flow and the lower rib surface, which is inclined to the flow. The elevation of the vertical surface is varied using non-dimensional approach length (h/e=0, 0.25, 0.5 and 0.75), and the inclination of the lower surface is varied using the rib angle (θ=15°, 45° and 90°). The relative roughness height and pitch of rib is fixed as 0.0421 and 12.5, respectively. RNG k-ϵ turbulence model is used in the analysis, and Reynolds number is varied from 8000-20000. The results reveal that the combined effect of flow impingement and the suppression of formation of recirculation zone leads to increased heat transfer. Lower values of non-dimensional approach length and rib angle provides a higher thermal enhancement factor. The highest increase in Nusselt number is found to be about 1.82 times that of the smooth duct at Re=8000 for h/e=0.25 and rib angle of 15°. The maximum thermal enhancement factor is found to have a range of 1.6-1.45 for an approach length of 0.25 and a rib angle of 15°.