THERMAL PERFORMANCE ENHANCEMENT OF SOLAR PARABOLIC TROUGH COLLECTOR USING SECONDARY REFLECTOR

Abstract

— The slight misalignment in the focal of a parabolic trough collector (PTC) resulted in more heat losses and lower thermal efficiency due to seasonal movement of the Sun. With a negligible change in the intercept factor, the secondary reflectors are attached over the receiver to reflect the concentrated solar rays again on the receiver. Thermal performance of PTC is carried out numerical and experimentally. Use of secondary reflector improves the thermal efficiency by 10% and the heat loss from the PTC has been reduced by 0.5 kJ/s. Keyword -Solar PTC, Secondary reflectors, Receivers, Experimental work I. INTRODUCTION In solar thermal energy conversion system, which the collector absorber and concentrator are acting major to affect the performance. PTC had a simple geometry and used for medium temperature solar thermal applications. Solar collector performance investigated based on the inputs of optical properties, heat transfer fluid (HTF) properties, inlet temperature and flow rate of HTF, solar insolation, wind speed, and atmospheric temperature and outputs of collector efficiency, HTF outlet temperature, heat gain, and heat and optical losses. Abhijeet Audi et al. [1] performed the thermal tests on concentrator at various time periods and mass flow rate to investigate the variation of optical efficiency and heat loss factor. Umayal Sundari et al. [2] designed and investigated the performance solar collector with various operating parameters. Kumaresan et al. [3] investigated the storage system integrated with PTC (parabolic trough collector) for its performance during charging process. The absorber tube transfers solar radiation to the HTF (heat transfer fluid) which circulates through the tube which is connected to the storage tank. The performance of collector system improved by increasing the intensity of beam radiation. Senthil and cheralathen [4] experimentally investigated the effect of temperature distribution on the receiver. Based on obtaining results concluded that the collector efficiency improved by the configuration of solar radiation absorber. Cheng [5] investigated a PTC system that uses mirrored surfaces of a linear parabolic reflector to focus direct solar radiation on the absorber tube. The effects of various reflector parameters and receiver parameters are discussed. The analysis proves that the PTC system of different active receiver lengths or different glass cover diameters has little effects on the optical performance and little sensitivity to optical errors. Rizwan Masood et al. [6] performed the parabolic trough collector design and its feasibility for industrial applications. The simulation results show that the significant amount of high-temperature heat energy were attained which can be used for industrial applications. Ricardo et al. [7] studied the effects of working and environmental parameters on the performance of PTC using exergy analysis. Selvakumar et al. [8] presented the evacuated tube collector by using therminol D-12 working fluid integrated with PTC. The results concluded that the therminol D-12 as an HTF gives better performance compare then the water. From the literature studies, PTC collector design and its configuration of absorber and heat transfer fluid pointed as important. The present work performs the experimental performance of PTC with a secondary reflector. II. MATERIALS AND METHODS The system used is a parabolic trough collector whose function is to reflect the solar rays falling on it onto the absorber tube placed on the focus. The absorber tube is made of copper and oil flows through and is heated continuously over a specific period between which readings are taken. A secondary reflector of three different configurations is to be attached to the absorber tube to reflect the rays escaping from the absorber tube back to the absorber tube. The objective of the project is to improve the efficiency of the trough using a secondary reflector of different configurations. The Methodology is used, is that after readings are taken on the trough without any secondary reflector and the efficiency and losses are calculated for the readings. A sheet of a chosen metal is used to cut and shape into different configurations and is attached to the absorber tube on the trough. After attaching the different configurations, readings are taken, and the efficiencies and the losses are calculated ISSN (Print) : 2319-8613 ISSN (Online) : 0975-4024 P Sundaram et al. for the configurations and are then compared with the efficiency and losses of the trough and graphs are drawn. The PTC had the aperture of 1.22 m, focal length 0.61 m, depth of parabola 0.21 m, arc length 1.83 m and made up of stainless steel with mirror film. The absorber tube is made up of copper having diameter 0.0254 m and length 1.22 m respectively. The trough is tracked in a single axis. The oil circulation pump is 0.5 kW capacities. The supply and storage tanks are 10 and 28 liters respectively. The experimental test setup is constructed by Ecosense Sustainable Solutions Pvt.Ltd., New Delhi, India. The secondary reflectors considered are triangular and curved configurations. The configurations are prepared with a sheet of polished aluminum and are attached to the absorber tube one after the other as shown in fig. 1. Fig. 1. PTC test facility with secondary reflector