Thermohydraulic correlations and exergy analysis of a solar air heater duct with inclined baffles

Abstract

This paper presents the development of the Nusselt number and friction factor correlations of a solar air collector with inclined baffles on the basis of experimental data. An evaluation of the exergy performance of the collector is conducted. The inclination angle of the baffle studied ranges from 0° to 180°. The baffle pitch and size of the solar air heater duct are fixed in the current work. The maximum errors between the predictions of the correlations and the experimental data are 6% for the Nusselt number and 8.3% for the friction factor. The exergy efficiency analysis shows that the largest collector efficiency of 0.7% is reached at a baffle angle of 60° and a Reynolds number of 1500. A baffle angle of 60° causes the highest turbulence due to an increased degree of blockage. Furthermore, the baffle angle results in a smaller friction factor than the others, e.g. 45° and 120°. The thermal efficiency, effective efficiency and exergy efficiency of the collector with baffle angles of 30° and 150° are nearly equal. A baffle angle of 0° indicates the lowest efficiency. Overall, it is suggested that baffle angles from 60° to 120° should be selected to obtain high efficiencies.

Keywords

• Solar air heater
• Inclined baffle
• Heat transfer enhancement
• Linear regression
• Exergy analysis