Abstract
The thermal enhancement of parabolic trough collectors is a critical issue and numerous ideas have been applied in the literature on this domain. The objective of this paper is to investigate some usual thermal enhancement techniques for improving the performance of evacuated and non-evacuated receivers of parabolic trough solar collectors. More specifically, the use of twisted tape inserts, perforated plate inserts, and internally finned absorbers are compared with the reference case of the smooth absorber. The analysis is conducted with a developed and validated thermal model in Engineering Equation Solver. The collector is investigated for a typical flow rate of 100 L/min and for inlet temperatures between 50 °C and 350 °C with Syltherm 800 as working fluid. According to the final results, the use of internally finned absorber leads to the highest thermal efficiency enhancement, which is up to 2.1% for the non-evacuated collector and up to 1.6% for the evacuated tube collector. The perforated plate inserts and the twisted tape inserts were found to lead to lower enhancements, which are up to 1.8% and 1.5%, respectively, for the non-evacuated collector, while they are up to 1.4% and 1.2%, respectively, for the evacuated collector. Moreover, the pressure drop increase with the use of the thermal enhancement methods is investigated and the use of internally finned absorber is found again to be the superior technique with the performance evaluation criterion to be ranged from 1.5 to 1.8 for this case.
Highlights
Solar energy exploitation is one of the most promising ways for facing important issues as the fossil fuel depletion, the global warming and the increasing worldwide energy consumption [1,2].Concentrating solar collectors are technologies that can be applied in a great range of applications, such as space-heating, space-cooling, refrigeration, domestic hot water production, chemical processes, industrial heat, desalination, and electricity production [3,4,5].The most mature solar concentrating technology is the parabolic trough solar collector (PTC), which is a linear concentrating technology with a concentration ratio from 10 up to 50
The perforated plate inserts and the twisted tape inserts were found to lead to lower enhancements, which are up to 1.8% and 1.5%, respectively, for the non-evacuated collector, while they are up to
The receiver of the PTC is an evacuated tube receiver that consists of a metallic inner tube where the heat transfer fluids flow and an external cover tube made of glass
Summary
The most mature solar concentrating technology is the parabolic trough solar collector (PTC), which is a linear concentrating technology with a concentration ratio from 10 up to 50. This collector has been used in various applications for temperatures of up to 400 ◦ C with thermal oil and up to 550 ◦ C with molten salts [6]. The receiver of the PTC is an evacuated tube receiver that consists of a metallic inner tube where the heat transfer fluids flow and an external cover tube made of glass Between these materials there are vacuum conditions (extremely low pressure), and so the convection thermal losses
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