Experimental and CFD investigation of convection heat transfer in solar air heater with reverse L-shaped ribs

Abstract

A solar air heater is a thermal system which uses artificial roughness in the form of repeated ribs on the absorber plate to enhance the heat transfer rate. Forced convection heat transfer of air in a solar air heater with reverse L-shaped ribs has been carried out experimentally and numerically. Thermal performance of solar air heater is studied with design variables such as relative roughness pitch (7.14⩽P/e⩽17.86), Reynolds number (3800⩽Re⩽18,000), heat flux (1000W/m2) and constant relative roughness height (e/D=0.042). A two dimensional CFD simulation is carried out with using CFD code, ANSYS FLUENT and RNG k–ɛ turbulence model, for solving turbulence terms in governing equations. The presence of reverse L-shaped rib shows a significant effect on heat transfer and friction factor characteristics, relative to change in relative roughness pitch (P/e) and Reynolds number (Re). Thermo hydraulic performance parameter (T.H.P.P) of 1.90 considering heat transfer augmentation with same pumping power, has been evaluated for optimum configuration of the roughness element (reverse L-shaped rib) for artificially roughened solar air heater. It has been found that the numerical results are in good agreement with the experimental results for the range of parameters investigated. Correlations for Nusselt number and friction factor have been developed as a function of roughness and flow parameters.