PERFORMANCE ANALYSIS OF EVACUATED TUBE SOLAR COLLECTOR FOR DIFFERENT CONFIGURATIONS OF THE ABSORBER

Abstract

Solar water heaters (SWHs) are well-established and widely utilized worldwide in renewable energy technology. For low to moderate temperature applications, Flat Plate Solar Collectors are used. There are some advantages like ease to manufacture, no complex tracking devices, utilization of both the diffuse and beam solar radiation components, etc. With these advantages, there are certain limitations, i.e., conduction, convection, and radiation heat loss from the absorber plate. One can reduce the loss by providing proper insulation, incorporating a glazing cover, maintaining the vacuum between the absorber plate, and glazing (to avoid conduction and convection losses), and using a selective absorber surface (to prevent radiation losses). Though it is technically feasible, there are some practical limitations to achieving the above-said objectives (to reduce losses in an FPC). To overcome the above-mention functional limitations evacuated tube solar collectors came into existence. ETSC has two co-axial glass tubes with a selective coating over the inner tube surface and the system maintains a vacuum between tubes. As a part of the thesis, a series of experimental studies has been conducted and compared the performance of marquise shape FPC and ETSC in various modes (with & without glazing in series & parallel orientation for marquise shape FPC and with different reflectors configurations for series & parallel orientation for ETSC) in a forced circulation mode. The study on marquise shape FPC (for 1 to 7lpm, for the month of Sept-Oct 2021) shows that the first law efficiency increases (for 1 to 4lpm) and then decreases (for 4 to 7lpm). The exergy efficiency decreases as the mass flow rate increases (for 1 to 7lpm). The maximum temperature difference acquired was 14.49°C (for the series glazed system, for constant solar Irradiation value). The series glazed system shows better performance for lower lpm and the parallel unglazed system shows better performance for higher lpm. A study of ETSC and its comparison with marquise shape FPC, (for 1 to 4lpm and constant solar irradiation value for the month of March 2022, for Ac is 1m2 and for an, I value of 920W/m2) shows that the marquise shaped flat plates have acquired the maximum temperature difference up to 9.38°C (for the series glazed system) and 7.66°C for ETSCs with flat reflector. The results show that marquise shape flat plate collectors have better performance output than ETSC in forced circulation mode. The performance comparison of six different ETSC systems (without reflector, flat reflector, triangular reflector; in both series and parallel) has been carried out. The average Qu in a day (for the same inlet conditions) is getting higher for the flat reflector system with series orientation. The triangular reflector system shows better Qu than other systems when the sun is at its zenith.