Performance enhancement of bromide salt by nano-particle dispersion for high-temperature heat pipes in concentrated solar power plants

Thermal performance of molten salts can be enhanced by nanostructured materials, which can enhance the heat transfer capacity of heat pipes and further improve the global efficiency of Concentrated Solar Power plants. In this work, a eutectic mixture of sodium bromide, potassium bromide, lithium bromide and calcium bromide acted as the base salt, into which nine SiO2 nanoparticles in three diameters were dispersed to form twenty-two nano-bromides in total. The thermodynamic properties of the base salt and nano-bromides, e.g. the thermal stability and the phase change performance were investigated experimentally and analytically. It was observed that the size and the mass concentration of the SiO2 nanoparticles exhibited significant influence on the heat of fusion and the decomposing temperature but little on the melting point. By adding 0.7 wt% of 10 nm SiO2 particles, the heat of fusion and the decomposing point of the base salt were increased by maximum 99.19% and 68.4 °C respectively. In addition, densely dendritic-like networks were observed with Scanning Electron Microscopy in the nano-bromides and considered to be responsible for the improvement of the heat of fusion and the decomposing point. The authors believed these findings would contribute to enhance the heat transfer performance of heat pipes furtherly.