A numerical study on performance optimization of a micro-heat pipe arrays-based solar air heater

Solar air heater is a simple and convenient technology to utilize solar thermal energy. In this paper, an optimization study was carried out for a micro-heat pipe arrays-based solar air heater, aiming to derive the optimal operation conditions and geometrical parameters of the solar air heater. A 3-D CFD model was developed based on the physical heat transfer processes in the solar air heater and validated by the experimental results. The ambient temperature, air flow rate, air layer thickness, air duct aspect ratio and fins geometrical parameters (height and spacing) were selected as the parameters and their effects on the system efficiency and thermal-hydraulic performance of air flow were investigated. The results indicate that the inlet velocity of 3.3 m/s was determined to be the optimal flow velocity of the air heater, enabling a maximum thermal efficiency of 66.5%. The air layer thickness of 25 mm was determined as the optimal value, which is able to minimize the heat loss from the glass cover to the surrounding. The results also indicate the optimal aspect ratio, fin height and fin spacing among the values studied in the paper, which are 0.25, 12 mm and 6 mm, respectively.