Thermal evaluation and modeling of a double-pass solar collector for air heating

Abstract

This paper shows the experimental study of the thermal efficiency of a counter-flow double-pass solar air heater and the theoretical thermal model developed to describe its thermal behavior. The prototype was designed and manufactured at INENCO, Universidad Nacional de Salta, Argentina, The useful collection area is 2m², and a channel height of 0.025m. The edge and bottom surfaces are thermally insulated with a 0.05 m thick glass wool layer. The air flow is forced by a tangential fan installed in a 0.18m diameter pipe that is connected to the flow outlet. The collector was mounted with a slope of 40° facing north, in order to maximize the intensity of solar irradiance during winter. Experimental outdoor tests were carried out during a winter period, with maximum solar irradiance on the collector plane around 1050 W/m². A semi-empirical thermal model was developed in order to simulate the air temperature at the collector outlet under different outdoor climatic conditions and air flow. Experimental results and the predictions of the theoretical model were found to be in good agreement.