Effect of Alterations in V-down Rib on the Performance of an Artificially Roughened Solar Air Heater Duct

Abstract

The present study is focused on the selection of a rib roughness geometry having best thermohydraulic performance among various alternatives of the V-down type configuration. The continuous V-down (type I) rib roughness pattern along with its four alternatives viz. V-down rib with two gaps (type II), V-down rib with two gaps combined with staggered ribs (type III), V-down rib with four gaps (type IV) and V-down rib with four gaps combined with staggered ribs (type V) were evaluated by calculating the Nusselt number, friction factor and thermohydraulic performance parameter values. All roughness patterns were applied on one broad wall of a high aspect ratio (12:1) solar air heater duct and data was collected by varying Reynolds number from 4000 to 12000 (5 levels) during the testing of each absorber plate. Present study used fixed values of pitch-to-rib height (P/e) ratio of 12, rib height-to-hydraulic diameter (e/D h ) ratio of 0.044, angle of attack (α) of 60°, staggered rib length to height ratio (w/e) of 4.5 and relative staggered rib pitch (p/P) of 0.65. Results revealed that, thermohydraulic performance of type II, III and V were superior as compared to the type I by 8.2-13.8%, 13.7-20.4% and 34.6-54.5% respectively, whereas the thermohydraulic performance of type IV was inferior to the type I by 1.5-14.9% for the range of Reynolds numbers evaluated.