Unconventional solar air heater with triangular flow-passage: A CFD based comparative performance assessment of different cross-sectional rib-roughnesses

Roughness is one of the effective and promising method to improve heat transfer through the solar air heater. The cross-sectional shape of roughness provided on the absorber plate shows a strong influence on solar air heater performance. In this work, the influence of various roughness-elements (such as semi-circular, circular, triangular, square, rectangular) has been investigated on flow dynamics as well as thermal characteristics of solar air heater and these geometries were investigated in triangular passage solar air heater. Commercial software is used for simulating heat and flow dynamics of roughened solar air under steady-state conditions. At Reynolds number of 18.7 x 10(3) , the best thermohydraulic perfor-mance parameter (TPP) obtained is 2.75 for forward-chamfered rectangular rib (with e/w = 2). The maximum value of TPP obtained for various roughness geometries decrease in the order of 2.68, 2.57, 2.45, 2.06, 1.79, and 1.60 for backward-chamfered rectangular rib (with e/w = 2), rectangular rib (with e/ w = 2), rectangular rib (with e/w = 0.67), square rib, semi-circular rib, and circular ribs, respectively. (C) 2021 Elsevier Ltd. All rights reserved.