Numerical study on nanofluid natural convection in a vacuum tube solar collector with phase change materials

As an eternal and widespread energy source, solar energy has a low density while its intensity is changing continuously. Unavailability of the solar energy in nights and the gap between the time of radiation and its consumption are concerned as the main drawbacks of this type of energy. In applications such as domestic hot water (DHW), phase change materials (PCMs) can successfully remove this shortcoming due to their high thermal capacity and constant temperature during the phase change process. However, thermal conductivity of water is relatively low which reduces the performance of vacuum tube solar collectors. This properties can be improved substantially with the utilization of nanofluids. This paper presents a numerical study on nanofluid natural convection in a vacuum tube solar collector with phase change materials. The studied nanoparticles include copper oxide, titanium oxide, iron oxide, aluminum oxide, and graphene oxide. The obtained results show that for all of the current nanoparticles, rise in the nanoparticles volume fraction is accompanied by a decrease in the exit temperature of the collector. It is found that the highest temperature belongs to the graphene oxide nanoparticles.