A systematic parametric thermal analysis of nanofluid-based parabolic trough solar collectors

The objective of this work is to investigate the thermal enhancement margin with the implementation of (Syltherm 800/Cu) nanofluid in parabolic trough collectors in a systematic way. Three different collector kinds are studied; the evacuated tube receiver, the non-evacuated tube receiver and the bare tube without cover. The study is a systematic parametric investigation for different values of the following parameters: ambient temperature, solar irradiation, solar angle, wind speed, flow rate, inlet temperature, absorber emittance and nanoparticle concentration. Moreover, this study is performed by developing a mathematical model in Engineering Equation Solver which is validated with literature experimental data. The results indicate that the maximum enhancements are found for the cases with higher thermal losses and also the use of nanofluids enhances most of the performance in the bare tube. The maximum enhancements are found in small flow rates and for the cases with higher emittance. The maximum enhancement was found at 7.16% for the bare tube, 4.87% for the nonevacuated receiver and 4.06% for the evacuated receiver when the flow rate is 25 L/min and there is a cermet coating. The respective enhancement values are 17.11%, 12.30% and 12.24% for 25 L/min and for a nonselective absorber.