Flow and heat transfer characteristics of microencapsulated phase change slurry in thermal energy systems: A review

Phase-change materials (PCMs) are good media for thermal energy storage because of their high latent heat. However, PCMs have some disadvantages such as leakage, corrosivity and instability. These problems can be solved by micro-encapsulating PCMs to form micro-encapsulated phase-change materials (MPCMs). A microencapsulated phase-change slurry (MPCS) made of MPCMs and a single-phase fluid (water) is an excellent heat-transfer and thermal storage medium. The MPCM core materials are mostly paraffin and other organic PCMs with low thermal conductivity, resulting in low storage and transportation efficiency in thermal energy systems. MPCS is also limited in practical application due to high pumping power consumption, instability and unknown durability. Many review articles mainly showed the preparation methods, thermal and physical parameters of heat transfer characteristics and flow characteristics on MPCS. At present, there is no review paper to summarize and compare the existing specific experiments and theoretical models, and there is no quantitative research. Therefore, this review summarizes the flow and heat-transfer characteristics of MPCS by combining existing models and experiments, and analyzes the heat-transfer enhancement mechanism in detail. The synthesis of MPCS and the factors influencing its stability and durability are also introduced and analyzed. Applications of MPCS in buildings, solar energy systems, photovoltaic/thermal systems, the food industry and the textile industry are also presented and summarized. This review aims to provide a reference for preparing MPCS with better performance, for promoting large-scale applications of MPCS in various thermal energy fields, and for improving thermal energy utilization efficiency.