Effects of combined radiation and forced convection on a directly capturing solar energy system

In this study, the photo-thermal conversion performance of volumetrically heated solar collector with mono-nanoparticle and hybrid-nanoparticle filled fluids desired for a direct solar energy system is numerically investigated. Considering the scattering and absorption characteristics of the heat transfer fluid in the translucent medium, its thermal performance in the collector is analysed solving the radiative transport, energy, and Navier-Stokes equations. A systematic parametric study is conducted by selectively changing the fluid type, volume concentration nanoparticle, operating temperature, and collector length to evaluate their influence on the thermal capacity of the collector. The results reveal that the use of nanoparticles and the increase in volume concentration improves the solar energy absorption capacity of the heat transfer nanofluids, thus increasing the photo-thermal conversion performance. Besides, it is found that the increase in the fluid inlet temperature in-creases the heat losses, resulting in a decrease in the amount of usable heat generated from solar energy. Furthermore, although the heat gain and useful heat generation of the fluid increase as the collector length increases, the thermal performance of the collector decreases due to increasing heat losses. Moreover, it is shown that the performance evaluation criterion (PEC) of water-based Graphite, TiO2 and Ag mono nanofluids is 1.6, 1.56, and 1.43, respectively while water-based Graphite + MgO, TiO2 + MgO and Ag + MgO blended nanofluids is 1.68, 1.66, and 1.58, respectively. Because the blended nanoparticles increase the solar energy absorption capacity, both the thermal performance of the collector and the sensible energy storage capacity are enhanced. The findings of the study suggest that hybrid nanofluids can be considered as an effective heat transfer fluid that can be used in solar energy applications.

Automated summary

This study numerically investigates the photo-thermal conversion performance of volumetrically heated solar collector using mono-nanoparticle and hybrid-nanoparticle filled fluids. The thermal capacity of the collector is evaluated by analyzing the scattering and absorption characteristics of the heat transfer fluid in the translucent medium. The results show that the use of nanoparticles and the increase in volume concentration improve the solar energy absorption capacity and the photo-thermal conversion performance. Hybrid nanofluids, with blended nanoparticles, enhance the thermal performance of the collector and the sensible energy storage capacity, making them effective heat transfer fluids for solar energy applications.