Heat transfer efficiency enhancement of latent functional thermal fluids through multiscale interfacial modulation

In the past decade, a novel composite fluid, i.e., microencapsulated phase change material latent functional thermal fluid (MPCM-LFTF), which consists of nano/microsized core-shell microencapsulated phase change material (MPCM) and base fluid, has attracted increasing research attention, as it is capable of facilitating rapid heat transfer by virtue of both the phase transition properties of MPCM and the flow characteristics of base fluid. To improve the heat transfer capability and promote the practical application of MPCM-LFTFs, it is essential to fully figure out the complicated process of heat transfer in the whole composite fluid. In this review, a concept of multiscale interfacial modulation in MPCM-LFTFs is firstly proposed based on their composite structures and heat transfer characteristics. Specifically, the multiscale interfaces in MPCM-LFTFs include the nanoscale interface in core-shell architecture of MPCM (Interface I), the microscale interface between MPCM and base fluid (Interface II), and the macroscale interface between the composite fluid and the internal surface of container (Interface III). The typical preparation methods of MPCMs and composite fluids are further introduced, and the significance of some typical physical property parameters in evaluating the heat transfer efficiency across the three interfaces is emphasized. Quantitative analyses from the literatures indicate that systematically optimizing these interfaces can enhance the effective thermal conductivity of MPCM-LFTFs by up to 120% compared to the base fluid, with the latent heat values of synthesized MPCMs typically ranging from 80 to 200 J/g depending on the core material and encapsulation ratio. Then, some effective strategies for enhancing the heat transfer efficiency of MPCM-LFTFs, considering the synergistic effect of multiscale interfacial modulation, are summarized. Finally, the promising applications of MPCM-LFTFs in a range of fields are presented. Overall, this review provides a state-of-the-art overview on the research progress of MPCM-LFTFs, and the discussion for future directions may help concentrate efforts on solving the key challenges in this emerging research area. Heat transfer mechanisms between multiscale interfaces in microencapsulated phase change material latent functional thermal fluids (MPCM-LFTFs) have been proposed. Heat transfer efficiency enhancement strategies of MPCM-LFTFs considering the synergistic effects between multiscale interfaces have been summarized. Typical applications of MPCM-LFTFs with elaborate structural designs have been illustrated.