Optimization of Thermal Performance of Water in Glass Evacuated Tube Solar Heater

Abstract

Solar water heaters provide a cost-e cient, unlimited, and environmentally friendly approach to hot water generation. Water in glass evacuated tube solar water heater (WG-ETSWH) is one of the commonly used solar water heaters (SWHs) available in the market. Despite its widespread use, WG-ETSWH has a low thermal performance and its installation cost is very high. As a result, hot water generation in homes and industries is highly dependent on electricity, fossil fuels, and traditional biomass despite the high solar potential in Africa. That has resulted in environmental pollution, various health problems and the high cost of conventional fuels. Several research studies have been conducted to help improve the performance of water in glass evacuated tube solar collectors (WG-ETSC). The performance of WG-ETSWH is dependent on the geographic location. Additionally, for collectors with identical parameters, tilt-type collectors absorb slightly more solar irradiation than horizontal-type collectors. The optimum thickness of the polyurethane insulation to reduce heat loss from the storage tank is 50 mm. However, the e ect of collector tube length, diameter and tilt angle on the performance of WG-ETSWH has not been fully studied. This research work is focused on optimizing the performance of WG-ETSWH for water heating applications using both experimental and numerical methods under the climatic conditions in Kenya. An experimental study on the performance of WG-ETSWH was conducted under the climatic conditions in Kenya. A CFD model was developed according to the speci cations of the experimental setup and its performance was then validated against the experimental data. The validated CFD model was then used to study the in uence of geometric variables such as the collector tilt angle, collector tube diameter and the collector tube length on the performance of the system. From the experimental study, the outlet temperature of the water in glass evacuated tube solar water heater was found to be ranged from 55 oC to 69 oC given an initial temperature of 25 oC for a whole day heat collection. The daily e ciency of the water in glass evacuated tube solar water heater under the climatic conditions in Kenya ranges from 58 % to 65 %. The collector tube length, diameter and tilt angle had a signi cant in uence on the xvii performance of WG-ETSWH. The optimum collector tube length, diameter and tilt angle were found to 2000 mm, 50 mm and 28 degrees respectively. The optimized design of the WG-ETSWH enhanced the outlet temperature of the water in the storage tank by 6.0 % and the average ow velocity of water in the system by 11.8 %. The results from this research will give insight into the design of improved products of water in glass evacuated tube solar water heater for the extraction of maximum heat energy from the sun.