Energy, exergy, economic and environmental evaluations of a finned absorber tube parabolic trough collector utilizing hybrid and mono nanofluids and comparison

Abstract

Parabolic trough collectors (PTCs) are an important part of solar thermal power plants. Past studies have shown that the dispersion of MWCNT or Fe3O4 nanoparticles in the working fluid of PTCs improves the performance, but there has not been any study on utilization of MWCNT–Fe3O4/Therminol VP-1 hybrid nanofluid in PTCs yet. In this study, thermal, exergy, economic and environmental evaluations of a PTC with smooth and finned absorber tubes have been performed using this hybrid nanofluid and its associated mono nanofluids. The length of PTC is 7.8 (m) and its width is 5 (m). In order to model the solar heat flux a new concentration ratio has been defined. For the high volume flow rate of 150 (L/min) and irrespective of absorber type, increasing inlet temperature reduced thermal efficiency, but change of the working fluid or change of the absorber type had minor effect on thermal and exergetic efficiencies, although the hybrid nanofluid performed slightly better. However, inlet temperature increase enhanced the exergetic efficiency significantly. The levelized cost of energy (LCOE) of the PTC with internally finned absorber was higher than that of smooth absorber for all working fluids and inlet temperatures. However, for every absorber type and at any inlet temperature, utilization of mono or hybrid nanofluids did not have a significant effect on LCOE. For CO2 emission evaluation, two methods of embodied energy and life cycle have been used. Based on the method of embodied energy, the CO2 emission of the PTC with finned absorber tube was approximately 18% more than that of smooth tube for all of working fluids and inlet temperatures, while the method of life cycle predicted almost the same amount. The results showed that the method of life cycle is more accurate, since it considers all stages of PTC life time.