Nusselt number and friction factor correlation development for arc-shape apex upstream artificial roughness in solar air heater.

In the present work, an outdoor experimental investigation for solar air heater with arc-shape apex upstream flow by the use of circular cross-sectional wires as roughness elements has been carried out. The roughness elements have been expressed in non-dimensionalizing geometric parameters as relative roughness pitch (P/e), relative roughness height (e/D), and flow attack angle (α/60), and the range of these parameters varies from 8 to 15, 0.0454, and 0.75 to 1.25, respectively. For evaluation of performance of the roughened SAH, a novel parameter has been proposed and introduced in the present investigation which is thermo-hydraulic improvement parameter (THIP). With the use of present roughness geometry, considerably, Nusselt number enhancement ratio (NNER) and friction factor enhancement ratio (FFER) have been observed. The maximum NNER and FFER values obtained experimentally are about 2.83 and 1.79 times, respectively, while the maximum THIP obtained is 157.49% higher than the smooth SAH. Using the experimental results, correlations for the output parameters (Nusselt number and friction factor) as a function of input parameters (flow and roughness) have been developed.