PCMs

Phase change materials (PCMs) are substances that store and release thermal energy as they undergo phase transitions, most commonly between solid and liquid. When a PCM melts, it absorbs a large amount of latent heat at a relatively constant temperature; when it solidifies it releases that heat. This property enables the material to maintain near-constant temperatures during charging and discharging of thermal energy, making PCMs useful for thermal energy storage and temperature regulation.

PCMs are characterized by their melting and solidification points, latent heat of fusion, and heat capacity. Common categories include organic PCMs (such as paraffins and fatty acids), inorganic salt hydrates, and eutectic mixtures. Organic PCMs typically have stable cycling, high latent heat per mass, and broad chemical compatibility, but can be flammable or have lower thermal conductivity. Inorganic hydrates often offer higher latent heat and lower cost but may suffer from volume change, supercooling, and phase separation.

Applications span building energy efficiency (cooling and heating), solar thermal systems, thermal energy storage in air and water systems, electronics cooling, textiles and footwear for thermal regulation, and cold-chain logistics. PCMs are frequently used in encapsulated form to improve containment, prevent leakage during melting, and enhance heat transfer. Encapsulation methods include microencapsulation, macro-encapsulation, and form-stable composites with supporting matrices.

Challenges include subcooling, phase separation, corrosion of containment materials, limited thermal conductivity, cycling stability, and cost. Ongoing research focuses on improving heat transfer, preventing separation, exploring non-flammable and non-toxic PCMs, and tailoring transition temperatures for specific applications.