Performance Analysis of Evacuated Tube Collector Using Diffuse Reflectors

Solar water heaters with evacuated tube collector (ETCs) are becoming more popularly used because of their efficient operation in collecting solar energy with minimum losses compared to other types of collectors. Still, they are deficient in one way that the top half of the cylindrical tubes are only exposed to solar radiation and bottom half become inactive due to lack of whipping solar radiation. If the bottom of the tube is given an opportunity to receive a portion of the radiation, the performance of the ETCs would be improved to a definite extent. In this present work, water in glass evacuated tube was fabricated with a built-in horizontal storage tank of 100 L capacity. The performance of the ETC has been evaluated with two different geometries of the diffuse reflectors, namely diffuse flat reflector (DFR) and diffuse corrugated reflector (DCR) in Coimbatore weather conditions. The experiments have been conducted from 6 am to 6 pm during the month of February 2018. The water temperature of collector tank was observed at the end of experiment day for three cases, namely without diffuse reflector, with DFR and with DCR. The result showed that the integration of diffuse reflectors improved the performance of the ETC of solar water heaters to a substantial level. The increment in tank water temperature was noted as 6.2°C and 8.8°C with DFR and DCR, respectively.