Heat transfer and friction factor correlations of solar air heater ducts artificially roughened with discrete V-down ribs

Abstract

The heat and fluid flow characteristics of rectangular duct having its one broad wall heated and roughened with periodic ‘discrete V-down rib’ are experimentally investigated. Reynolds number (Re) has been varied from 3000–15000 with relative gap width ( g/ e) and relative gap position ( d/ w) range of 0.5–2.0 and 0.20–0.80 respectively. The respective variation in relative roughness pitch ( P/ e), angle of attack ( α) and relative roughness height ( e/ D h ) have been 4–12, 30°–75° and 0.015–0.043. The effect of roughness parameters on Nusselt number (Nu) and friction factor ( f) has been determined and the results obtained were compared with those of smooth duct. The maximum increase in Nu and f over that of smooth duct was 3.04 and 3.11 folds respectively. The rib parameters corresponding to maximum increase in Nu and f were d/ w = 0.65, g/ e = 1.0, P/ e = 8.0, α = 60° and e/ D h = 0.043. Correlations for the Nu and f in terms of Re and rib parameters have been developed.