Abstract
ABSTRACT Evacuated tube solar air heaters (ETSH) are efficient, easy to maintain, and have low energy losses due to the vacuum between the absorber and the outer tubes. In this study, a new ETSH with various configurations was built and experimentally tested to determine the best configuration with the highest thermal performance. The ETSH equipped with two different high thermal conductivity metal fins and coils to enhance the heat transfer between the fluid and the copper tube heat exchanger. The efficiency and temperature difference were experimentally investigated at different flow rates. It was observed that the system with aluminum fins has the highest air temperature difference at the lowest flow rate and the highest efficiency at the highest flow rate. At the highest solar irradiation of 1000 W/m2, the maximum obtained temperature difference was 88°C at a flow rate of 0.6m3/min, while the highest obtained efficiency was 37% at a flow rate of 1.25 m3/min. For the three systems, the temperature difference decreased and the efficiency increased with the increase in the flow rate.
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