Investigation of heat transfer augmentation and friction factor in triangular duct solar air heater due to forward facing chamfered rectangular ribs: A CFD based analysis

Abstract

The rib provided over absorber plate can improve the performance of solar air heater (SAH). The effect of forward chamfered ribbed absorber plate is studied in the present article. Two new roughness parameters named as rib aspect ratio (e/w) and rib chamfered height ratio (e′/e) has been defined and their influence on the performance of triangular duct SAH is simulated using commercial ANSYS software for fixed range of Reynolds number (Re) which varies from 4000 to 17000. The e/w, relative roughness height (e/D) and e′/e ranges from 0.24 to 1.5, 0.018 to 0.043 and 0 to 1.0, respectively. The ribbed side of duct is heated with constant heat flux of 1000 Wm-2. The three-dimensional model of SAH is developed for the analysis and results are simulated using finite volume approach. The numerical methodology is validated by comparing predicted results with the available results and a close match is seen between friction factor (f) and Nusselt number (Nu). A remarkable change in f and Nu value is observed by varying both Re and roughness parameters. The maximum increase in Nu is observed in case of e/w, e/D and e′/e value of 1.5, 0.043 and 0.75, respectively, at Re value of 17000 and it is of the order of 2.88. The maximum increase of friction penalty is seen in case of e/D value of 0.043 which is of the order of 3.52 times the without ribbed duct at Re value of 4000. With the help of numerically predicted results, a generalized correlation is developed for Nu and f.