Thermal efficiency and exergy enhancement of solar air heaters, comparative study and experimental investigation

Abstract

This paper links the geometric design of most classical configurations of solar air heaters (SAHs), their thermal performances, and their appropriate application. The optimization concerns mainly the absorber shape and the airflow direction. Therefore, single pass and counter flow double pass SAHs with flat plate, finned, and V-corrugated absorbers and SAH with an external recycle were investigated. The overall aim is to single out the most suitable configurations for the drying process and habitation heating. Modeling of the SAHs was based on solving the energy balance equations of the SAH's components. The numerical results showed that the thermal efficiency was significantly improved by the counter flow double pass mode by about 17.01% for SAHs with a flat plate absorber and 9.03% for SAHs with a V-corrugated absorber. Furthermore, the V-corrugated shape of the absorber increases the thermal and exergy efficiencies compared to the flat plate shape, e.g., by 8.66% and 1.27% at ṁ = 0.025 kg s−1, respectively. In addition, the present study highlighted that the outlet air temperature and the thermal and exergy efficiencies could be enhanced by increasing the number of fins, and the optimal number of fins was found to be 24 per meter width of the SAH. Experimental studies were carried on a modular SAH. They showed the good capability of the developed model in predicting the thermal performances of the studied solar collectors. Finally, the SAHs were assigned to three appropriate uses, namely, aromatic and medicinal plant drying, agri-food product drying, and habitat heating.