Phase-Change Materials: Thermal Batteries That Store Heat by Melting and Freezing
Phase-change materials absorb and release thermal energy during melting/solidifying, acting as passive thermal buffers in buildings, cold chains, and electronics cooling.
Phase-change materials (PCMs) store and release large quantities of thermal energy during their transition between solid and liquid states. During melting, a PCM absorbs heat at nearly constant temperature — its latent heat of fusion — and releases the same heat upon solidifying. This allows them to act as passive thermal batteries. ## Types - **Paraffin waxes**: 20–60°C melting range, chemically stable, non-corrosive, widely used - **Salt hydrates**: Higher energy density and lower cost, but prone to supercooling and phase separation over cycles - **Fatty acids**: Bio-based, tunable melting points, used in building applications ## Applications In building construction, PCMs embedded in walls, ceilings, or panels absorb daytime heat and release it at night, reducing HVAC loads. They're also used in cold-chain logistics (maintaining temperature during shipping), electronic thermal management, and smart textiles. The key design parameter is selecting a PCM whose melting point matches the target temperature range — a PCM that melts at 23°C is ideal for room comfort, while one melting at -18°C suits frozen food transport. **See also:** Net Zero Home: Lessons and Regrets After Two Years Off-Grid