Utilization of nanofluids (mono and hybrid) in parabolic trough solar collector: a comparative analysis

The application of hybrid nanofluids plays a crucial role for heat transfer enhancement in solar collectors. The utilization of conventional heat transfer fluids (water, ethylene glycol/water, thermal oils) has limitations due to their low thermal properties. Therefore, advanced heat transfer fluids such as mono and hybrid nanofluids get extraordinary attraction due to their enhanced thermophysical properties, mainly thermal conductivity, that lead to better heat transfer characteristics. The present chapter deals with the utilization of Syltherm-800-based mono and hybrid nanofluids in the parabolic trough collector (PTC). Mono nanofluids (TiO2, CuO, MWCNT, and CeO2) and hybrid nanofluids (MWCNTs-TiO2, MWCNTs-CuO, and MWCNTs-CeO2) are investigated and compared to evaluate the thermal enhancement performance of PTC absorber tubes. Thermal efficiency, exergetic efficiency, heat transfer coefficient, Nusselt number, pressure drop, and pumping power are the parameters investigated at different inlet temperatures. In addition, performance evaluation criteria examine the entire thermal enhancement variations in friction factor and Nusselt number. Thermodynamic modeling of the system is conducted in an engineering equation solver. The study reveals that PTC absorber tube with hybrid nanofluids has the highest thermal performance compared to the other examined heat transfer fluids. Specifically, MWCNTs-TiO2/Syltherm-800 has 72.61% energy efficiency, which is 1.26% greater than CuO/Syltherm-800 mono nanofluid. The exergy efficiency of MWCNTs-CuO/Syltherm-800 hybrid nanofluid is approximately 3.6% higher than pure Syltherm-800. Moreover, heat transfer coefficient of MWCNTs-TiO2/Syltherm-800 increases to approximately 67% as the temperature increases from 350K to 600K. MWCNT/Syltherm-800 has the maximum pressure drop, which is nearly 59.39% higher than the pure base fluid. The pumping power requirements are larger for the heat transfer fluids that have maximum pressure drops. Maximum mean enhancement in thermal efficiency and Nusselt number is observed for MWCNTs-TiO2/Syltherm-800, which are 0.018% and 0.936%, respectively. Analysis of the performance evaluation criteria shows that MWCNTs-TiO2/Sylther-800 hybrid nanofluid and CEO2/Syltherm-800 mono nanofluid have the highest and lowest performance evaluation criteria, respectively.