The use of gas working fluids in parabolic trough collectors - An energetic and exergetic analysis

The use of gas working fluids in concentrating solar collectors is an easy way to operate in high temperature levels. This study is an energetic and exergetic comparison of various gas working fluids in a commercial parabolic trough collector (PTC). Air, nitrogen, carbon dioxide, helium, neon and argon are the examined working fluids. The objective of this study is to determine the optimum operating conditions for every working fluid and to make a parametric comparison among the examined gasses. Mass flow rate and fluid inlet temperature are the examined parameters in order to predict which combination of these leads to maximum exergetic efficiency. The final results proved that helium is the best working fluid for inlet temperature up to 700 K, while carbon dioxide is the most appropriate solution for higher temperature levels. The global maximum of the exergetic efficiency is achieved with helium operating to 640 K inlet temperature and 0.035 kg/s mass flow rate. Moreover, it is essential to state that the optimum mass flow rate depends on the operating temperature level for every examined working fluid. For this study, a detailed numerical model is developed in Engineering Equator Solver (EES), including all the proper energetic and exergetic equations.