Simulation and experimental investigation of fluid flow in porous and non-porous solar air heaters

The porous absorber in the solar air heater gives considerable temperature increment which is shown by computational fluid dynamic simulation and verified experimentally. Experimental analysis on porous (wire screen) and non-porous solar air heaters were carried out to study the heat transfer and friction factor characteristics. The analysis encompasses the investigation on effect of mass flow rate on air temperature increment, thermal efficiency and pressure drop across the test section. The heat transfer parameter is established in terms of Colburn (J(h)) factor for porous bed solar air heaters. The effect of friction factor on different geometries for a range of operating Reynolds number (194-591) is presented. Two wire screen matrix (WSM) solar air heater WSM-I and WSM-II were investigated which has different diameter, pitch and porosity. Thermal efficiency increased on introducing the packed wire-screen matrix diagonally in the air flow path. The increase in thermal efficiency for WSM-I and WSM-II were found to be 5-17% and 5-20% respectively with the mass flow rate ranging from 0.01 kg/s to 0.055 kg/s. The collector heat removal factor was found to be 0.95 +/- 0.021 for wire mesh absorber and 0.72 +/- 0.0073 for conventional type. The pressure drop across the length of the duct was studied to be in the range of 15 +/- 0.28 Pa to 17 +/- 0.28 Pa and 7 +/- 0.16 Pa to 11 +/- 0.28 Pa for WSM-I and WSM-II respectively and for conventional type it was between 5 +/- 0.20 Pa and 10 +/- 0.28 Pa.