Thermal Performance Study of a Copper U-Tube-based Evacuated Tube Solar Water Heater

Abstract

In the current scenario of energy demand and environmental pollution, optimum harvesting of renewable energy resources is essentially required. Solar energy is one of the most prominent and easily available clean energy sources. With time, several techniques and devices have evolved and have been invented to harvest solar energy; nevertheless, consistent efforts are still needed to improve the performance of existing techniques and make it more convenient and approachable. The solar water heating system is certainly the most matured solar energy-based device that has been widely used in many countries and regions all over the world. Compared to a flat plate and other solar collectors, evacuated tube collectors (ETCs) are more efficient and capable of overcoming a few drawbacks associated with flat plate collectors such as higher heat losses and lesser efficiency. In order to further improve the heat transfer performance of the ETC, several amendments and reforms have been suggested in the literature. In the present work, an experimental study has been conducted on ETCs with copper U-tubes. A copper tube of 7 mm inner diameter is placed inside the ETC having outer and inner diameters of 57 and 44 mm, respectively. Liquid water flows through the copper tube at the rate of 350–1,100 mL/min. A set of experiments have been conducted with the ETC facing towards the south and kept at an inclination of 30° from horizontal. Experiments were done during March–April 2021 at NIT Uttarakhand Srinagar (Garhwal) which is located at a latitude of 30.2184° and longitude of 78.7670°. Results in terms of the heat transfer rate with varying solar radiation have been recorded and other performance parameters are evaluated for the ETC considered. It has been observed that the maximum outlet temperature of the water is being recorded to 29.97°C at a mass flow rate of 700 mL/min. For the present experimental setup and operating conditions, maximum efficiency of 53.76% is achieved at solar radiation of 895 W/m2.