Heat transfer analysis of double discrete arc roughness with different relative rib altitudes and relate to a single discrete arc in the solar air heater

Abstract

An artificially roughened solar air heater (SAH) with double discrete arc roughness is experimentally explored in this paper. Relative rib altitude (e/Dh ) varies from 0.018 to 0.034, while constant relative rib pitch (P/e), staggered pitch ratio (P′/P) and segment ratio (S′/S ) of 10, 0.5 and 1.6, respectively, are considered. The Reynolds number (Re) varies from 3000 to 14,000. Augmented Stanton number (St) and thermo-hydraulic performance (THPP) with a moderate friction factor (f) are reported for e/Dh of 0.034. The maximum St and f of 2.32 and 3.10 times, respectively, are the result for the rough plate related to basic configuration, while THPP of roughened SAH is augmented up to 1.60. The outcomes of the present roughness are compared with single discrete and continuous arc geometry under identical flow states and confirm the superior performance under the parameters tested. The correlations for heat transfer function (G) and roughness function (R) are also developed.