Heat transfer and friction in solar air heater duct with W-shaped rib roughness on absorber plate

Artificial roughness in form of ribs is convenient method for enhancement of heat transfer coefficient in solar air heater. This paper presents experimental investigation of heat transfer and friction factor characteristics of rectangular duct roughened with W-shaped ribs on its underside on one broad wall arranged at an inclination with respect to flow direction. Range of parameters for this study has been decided on basis of practical considerations of system and operating conditions. Duct has width to height ratio (W/H) of 8.0, relative roughness pitch (p/e) of 10, relative roughness height (e/Dh) 0.018–0.03375 and angle of attack of flow (α) 30–75°. Air flow rate corresponds to Reynolds number between 2300–14,000. Heat transfer and friction factor results have been compared with those for smooth duct under similar flow and thermal boundary condition to determine thermo-hydraulic performance. Correlations have been developed for heat transfer coefficient and friction factor for roughened duct.

► Paper presents experimental investigation of heat transfer and friction factor characteristics of solar duct roughened with W-shaped ribs.
►  Maximum enhancement of Nusselt number and friction factor as result of providing artificial roughness is 2.36 and 2.01 times respectively to that of smooth duct.
► Thermo-hydraulic performance is maximum for angle of attack of 60°. W-ribs are thermo-hydraulically superior to V-ribs.
►  Correlations have been developed for heat transfer coefficient and friction factor for W- rib roughened duct.