NUMERICAL STUDY ON THE THERMAL BEHAVIOR OF POROUS MEDIA AND NANOFLUID AS VOLUMETRIC ABSORBERS IN A PARABOLIC TROUGH SOLAR COLLECTOR

In this paper, a combination of Monte Carlo ray tracing (MCRT) and finite volume method (FVM) was utilized to numerically investigate the application of CuO/water nanofluid and porous media (as volumetric absorber agents) in a direct absorption parabolic trough solar collector (DAPTC). The main purpose of this study is the numerical eval-uation of the effect of the nanofluid and porous media (separately and simultaneously) to compare their influences on the efficiency of DAPTCs using Ansys Fluent software. The effects of volume fraction, porosity, pore diameter, input temperature, and flow rate on the collector thermal performance are also examined. The results indicated 40.5% and 49.9% improvement in the thermal efficiency of the collector due to the use of nanofluid and porous media, respectively. Thermal efficiency showed a reduction with increasing the inlet temperature as well as decreasing the flow rate. Ap-plying the porous media can reduce the temperature concentration near the absorber tube wall, which will decrement the heat loss. However, using full porous media as a volumetric absorber leads to a great pressure drop. Results showed that the use of porous media enhanced the friction factor of pure water without metal foam 1500-1750 times. Therefore, nanofluids and partially filled porous media can be simultaneously used for their synergistic benefits. The combina-tion of direct absorbers can increment the thermal efficiency up to 69.5%. The numerical simulation is validated with available experimental data.