Microencapsulation of Molten Salt in Titanium Shell for High-Temperature Latent Functional Thermal Fluid

Herein, a water-limited sol–gel method is applied to fabricate microencapsulated phase change materials (MEPCMs) which have a sodium nitrate (NaNO 3 ) core and a titanium dioxide (TiO 2 ) shell. The MEPCM has a high melting temperature of 306.5 °C and a solidification temperature of 296.7 °C, which shows a potential usage as a high-temperature compatible thermal storage medium for industrial waste heat recovery and concentrated solar power (CSP). The MEPCM is demonstrated to be thermally stable for 200 thermal cycles with a high latent heat of 135.3 J g −1 . The high-temperature latent functional thermal fluid (HT-LFTF) is prepared by dispersing the NaNO 3 @TiO 2 MEPCMs into thermal oil. The test results show that MEPCMs provide an 18.4% effective thermal conductivity enhancement and 131.7% effective specific heat enhancement compared with base thermal oil. The rheological test indicates that the MEPCMs added in the thermal oil enhance the viscosity of the suspension and it increases with the MEPCM concentration. This work provides a new type of thermal oil–based functional thermal fluid containing high-temperature MEPCM and paves the way for the application of LFTF in high-temperature heat storage and transfer.