Investigation on ETC solar water heater using twisted tape inserts

The solar water heaters are finding their application in a number of sectors such as, residential buildings, processing
industries, commercial establishments. They can be scaled based on the requirements. Among the different kind of solar water heaters, all-glass evacuated tube type (ETC) solar water heaters are considered to be the better choice for the most applications due to their efficient operations with simple design constraints compared to other type of water heaters. However, there is a large scope to boost-up the performance of the ETC type solar water heaters to the next level with the appropriate modifications in the evacuated tubes, which will help to advance the overall efficiency.The present work proposes the amalgamation of twisted tapes within the evacuated tubes (ET) of the ETC solar water heaters to attain the enhanced performance of the system. The twisted tapes with two different twist ratios of 2 and 3 were used for the investigations. The twisted tapes were made-up of copper tapes of width 15 mm. The experimental trials were conducted on a passive flow ETC solar water heater on the days having alike solar insolation and ambient conditions in three different modes namely, ETC water heater without any twisted tapes (ETC-Plain), ETC water heater with twisted tapes comprising twist ratio of 2 (ETC-Twist 2) and the ETC water heater with twisted tapes comprising twist ratio of 3 (ETC-Twist 3). The results evidenced that the twisted tapes helped to improve the evacuated tube temperature and the tank water temperature of the ETC type solar water heater. The efficiency of the ETC type solar water heater was enhanced by 6.8% and 4.6%, respectively using twisted tapes comprising twist ratio of 2 and 3. Furthermore, the twisted tape with smaller twist ratio was determined to be efficient in improving the performance of the ETC type solar water heater.