SiO2-ternary carbonate nanofluids prepared by mechanical mixing at high temperature: Enhanced specific heat capacity and thermal conductivity

Abstract

Ternary carbonate (K2CO3–Li2CO3–Na2CO3, 4:4:2 mass ratio) can be used as a high-temperature heat transfer and thermal storage medium in concentrated solar power systems. Ternary carbonate nanofluids with 1.0 wt% SiO2 nanoparticles were prepared by mechanical mixing at high temperatures in order to enhance the specific heat capacity and the thermal conductivity. The effects of stirring rate (500 rpm, 750 rpm, and 1000 rpm) and stirring time (15 min, 30 min, and 60 min) on the thermal properties of the as-prepared nanofluids were analyzed. The results showed that the dispersion homogeneity of the nanoparticles in the nanofluids varied with the stirring rate and the mixing time, thereby affecting the formation of special nanostructures. The maximum enhancements in specific heat capacity and thermal conductivity at a temperature of 540 °C, stirring rate of 750 rpm and stirring time of 30 min were 38.5% and 50%, respectively. The specific heat capacity of the optimal nanofluids had no significant deterioration after the thermostatic (at 600 °C for 150 h) and thermal shock (50 cycles) experiments were conducted.