Experimental and numerical study on heat transfer characteristic of nitrate molten salt-based nanofluids in tube with twisted tape

Nitrate molten salts are extensively applied in Concentrating Solar Power plant as high-temperature thermal energy storage and heat transfer medium. At present, the study on molten salt-based nanofluids (MSBNFs) mainly focuses on the physical properties, such as thermal conductivity, specific heat, viscosity. There is rare research on forced convection heat transfer performance of MSBNFs. In this study, the heat transfer characteristic of low melting point quaternary MSBNFs in circular tube with/without different twisted tapes are investigated. The results show the Nu number increases with the decreasing of twisted tape twisted ratio. Compared with the smooth tube, the average Nu numbers of MSBNFs in tube inserted with twisted tape Y1, Y2, Y3 increase 14.93%, 20.67%, 25.49%, respectively. The secondary flow contours by inserting twisted tape in tube increases with the decreasing of twisted ratio and reduce the temperature boundary layer. The temperature distribution in tube with twisted tape is more uniform compared with that in smooth tube. The heat transfer correlation of low melting point MSBNFs in tube inserted with different twisted tapes is fitted. The heat transfer performance of low melting point MSBNFs is compared with different convection heat transfer empirical correlations in this work.