Thermal performance of parabolic trough collector using oil-based metal nanofluids

Applying nanofluids in heat transfer systems is an innovative approach to improve the weak thermal characteristics of thermal oils. In this work, the thermal performance of a parabolic trough solar collector using Dowtherm A oil-based nanofluid along with Pd, Au, and NiO nanoparticles as an operating fluid within the receiver tube was numerically investigated from the Finite Volume Method and turbulent flow condition. Originally, we considered the real thermophysical properties of stable nanofluids that were experimentally evaluated. Furthermore, the simulations are carried out using the state turbulence k-epsilon RNG model for various thermal flow conditions. The collector performance parameters such as static temperature, velocity magnitude, and dynamic pressure were assessed while taking into account the influence of nanofluid properties, heat flux, nanoparticle concentration, receiver tube diameter, nanofluid inlet temperature, and nanofluid inlet velocity. A MATLAB-based computational model is developed to investigate the outlet thermal energy efficiency of PTC considering all prior parameter impacts. The results show that the type, length, diameter, and concentration of the nanoparticles significantly impact the PTC performance such as outlet temperature and thermal energy efficiency. Thus, the Au-based nanofluid reached the greatest outlet temperature, with a maximum gain of around 8 % from 320 K to 347.5 K. Furthermore, the temperature difference and inlet velocity of nanofluid are the key factors influencing the thermal energy efficiency of PTC. A high-temperature difference of around 40 K was achieved with Au-based nanofluid at an inlet temperature of 298 K and a high inlet velocity of 0.5 m/s resulting in high outlet thermal energy efficiency of 50 %. Analysis of the performance evaluation criteria shows that Dowtherm A containing 0.0097 wt% of Au nanoparticles is the optimal nanofluid achieving the highest static temperature and PTC thermal energy efficiency.