phasechange

Phase change is the transition of matter between states of matter—solid, liquid, and gas—driven by temperature and pressure changes. Each transition occurs at a characteristic temperature on a phase diagram and involves latent heat, the energy absorbed or released without a change in temperature.

Common processes include melting (solid to liquid), freezing (liquid to solid), vaporization (liquid to gas), condensation (gas to liquid), sublimation (solid to gas), and deposition (gas to solid). At a fixed pressure, phase boundaries separate the states; the critical point marks where liquid and gas become indistinguishable. Kinetics, impurities, and confinement can affect the transitions.

Phase-change materials are substances that store and release large amounts of latent heat during phase transitions, providing compact thermal energy storage. They are used in buildings, textiles, electronics cooling, and solar energy systems. Popular PCMs include organic paraffins and fatty acids, and inorganic hydrates or salt mixtures. Selection depends on transition temperature, latent heat, cycling stability, and compatibility.

In engineering, challenges include cost, material stability, subcooling, and heat transfer limitations. Effective use often requires encapsulation and integration with conductive paths. Phase change remains a central concept in thermodynamics and materials science, underpinning energy storage, thermal regulation, and climate control technologies.