Study on Effect of Number of Transparent Covers and Refractive Index on Performance of Solar Water Heater

Liquid flat plate collector (solar flat plate collector) is one of the important applications in solar thermal system. The development in solar photovoltaic is an emerging challenge for the solar thermal system. In the current work an attempt has been made to optimize the number of transparent covers and refractive index to improve the optical efficiency and thermal efficiency for the collector. Performance of the liquid flat plate collector at VIT University Vellore has been simulated numerically for January 21st at an interval of half an hour with different numbers of transparent covers (0–3) and different refractive index values ranging from 1.1 to 1.7. The formulation and solutions are developed with simple software Microsoft Office Excel to result the performance characteristics. The result shows that the efficiency of the flat plate collector increases with an increase in number of covers and decreases after an optimum number of covers. It also decreases with an increase in refractive index. The combination of optimum number (two) and lower refractive index (1.1) results improved useful heat. 1. Introduction The selection of number of transparent covers and refractive index of transparent cover, in a liquid flat plate collector, will affect the performance of the flat plate collector, thus it’s important in finding an optimum number of cover and an effective refractive index, for achieving higher efficiency irrespective of solar insulation and location. The flat plate collector is the heart of all solar energy thermal system designed for working at low temperature range of ambient to 60°C. The flat plate collector is basically a heat exchanger which transfers the radiant energy of the incident sunlight to the sensible heat of a working fluid—liquid or air. The solar liquid flat plate collector for water heating was invented by Saussure [1], a Swiss scientist, during 1767, as reported by Ackermann in the year 1915. However the use of flat plate collector became more popular in 1900s at United States and at California. During the past fifty years researchers and scientist from all over the world have done many contribution in this field, in building and testing different types of liquid flat plate collector. Among these works, the literature in number of transparent covers and has been reviewed on contributions in refractive index and transparent cover’s properties. Lampert [2] discussed in detail the properties of optical materials and coatings, which would predominantly increase the performance of the solar thermal system. He highlighted that for