Investigations on Evacuated Glass tube solar Collector as an Air Heater

Abstract

Energy is the significant force for economic and sustainable development of any country. Energy demand has increased drastically due to rapid industrialization and population growth. Extensive use of fossil fuels to fulfill present energy demand makes it empty one fine day. Second issue to use of fossil fuels is higher CO2 emissions which leads to environmental issues like global warming. Looking towards the limitations of conventional energy sources, renewable energy sources are becoming popular to fulfill present and future energy demand. Solar energy is one of the best renewable energy sources, as it is clean and inexhaustible, and universally available source without any environmental issues. India has added advantage with a plentiful amount of solar energy because of its geographical position. Solar energy is the best alternative to fossil fuels due to its variety of applications such as water heating, air heating, water distillation, refrigeration and air conditioning etc., for domestic and industrial purposes. Several solar energy technologies have been developed since last few decades. One of the promising technology is solar air heating for the numerous applications of hot air. Present study deals with investigation on evacuated glass tube solar collector with external parabolic and flat segmented reflector of different concentration ratios. Air is used as working fluid to extract heat from the collector. Helical wiry structured insert is used as turbulator to increase the convective heat transfer coefficient between absorber of the collector and air. A thermal model is developed to predict the performance of evacuated glass tube solar collector for different concentration ratios of parabolic and flat segmented reflector. Heat balance equations for various components of the collector were considered to compute the useful heat gain and efficiency of the solar collector with and without turbulator. Effect of various parameters like solar radiation, concentration ratio, and mass flow rate on solar collector