Effect of nanoparticle dispersion on enhancing the specific heat capacity of quaternary nitrate for solar thermal energy storage application

Molten salt is considered to be part of the main direction for studying high temperature heat transfer and storage medium in concentrated solar power due to its good thermo physical properties. Specific heat capacity performs a significant role in increasing the overall cycle efficiency and reducing the cost of heat transfer and storage. In this paper, in order to enhance the specific heat capacity, 1 wt% SiO2 nanoparticles are added into a quaternary nitrate (Ca(NO3)2-KNO3-NaNO3-LiNO3 with a low melting point called the low melting point salt (LMPS), which are mixed through ultra-sonication. Experimental results show that the specific heat capacity can be enhanced when nanoparticles are evenly distributed in the quaternary nitrate. The optimal ultra-sonication time with a frequency of 45 kHz is researched. The average specific heat capacity of nano-LMPS can reach up to 1.87 J/(g K) and the average enhancement reaches 19.4%. There is a good linear relationship between the specific heat capacity of nano-LMPS and ultra-sonication time. Scanning electron microgram images reveal that lamellar networks with higher density phase on the solid nano-LMPS surface exist and may cause the specific heat capacity enhancement of nano-LMPS.