Regulation of natural convection heat transfer for SiO2-solar salt nanofluids by optimizing rectangular vessels design

Natural convection heat transfer of molten salt is widely used in concentrated solar plants, such as the solar receiver, the single-tank thermal energy storage system, and so forth. Meanwhile, adding nanoparticles into molten salts to form nanofluids can obviously improve the thermal properties of the working medium. However, the heat transfer performance of the molten salt-based nanofluids has not been investigated extensively, and the action mechanism between base fluids and nanoparticles is still unclear. In the present work, a lattice Boltzmann model considering fluid and nanoparticles as two different phases was developed, and various interactions were taken into consideration. Meanwhile, the effects of nanoparticle concentrations, aspect ratios of the rectangular vessel, and Ra on natural convection heat transfer of solar salt-based SiO2 nanofluids were analysed. The results show that specific heat capacity contributes substantially to heat transfer for all aspect ratios, and the maximum enhancement of natural convection heat transfer is obtained with a mass fraction of 1.0%. However, increase in Ra intensifies the effect of viscosity and weakens the heat transfer enhancement. Through interaction analysis, it indicated that nanoparticles tend to be driven to the top area of the rectangular vessel by temperature difference, driving force, and drag force. Meanwhile, a Nu enhancement contour was provided to optimize the design of a single energy storage tank.