refrigeration

Refrigeration is the process of removing heat from a space or substance to lower its temperature, enabling preservation, comfort, or industrial processing. It relies on a cycle that transfers heat from a low-temperature reservoir to a warmer environment by doing work on a circulating refrigerant. In the common vapor-compression cycle, the refrigerant absorbs heat in an evaporator, is compressed to higher pressure and temperature, releases heat in a condenser, and expands back to a low-pressure state through an expansion device.

Key components are a compressor, condenser, evaporator, and expansion device, with controls and safety devices monitoring temperature, pressure, and refrigerant charge. Refrigerants are chosen for thermodynamic properties and environmental impact; past substances such as CFCs and HCFCs damaged the ozone, leading to phased replacements under the Montreal Protocol. Modern systems often use low-GWP refrigerants, including specific HFCs, or natural options like carbon dioxide, ammonia, or hydrocarbons. Efficiency is expressed as COP or EER, with higher values indicating less energy per unit cooling.

Applications include household refrigerators and air conditioning, commercial cold storage, food processing, and industrial process cooling. Absorption refrigeration uses heat rather than mechanical work and can employ waste heat or solar energy, useful where electricity is limited. Cryogenic refrigeration achieves very low temperatures for science and manufacturing.

Environmental and safety considerations include refrigerant leakage, flammability, toxicity, and lifecycle management. Ongoing research aims to reduce climate impact, improve efficiency, and expand the use of low-GWP refrigerants and advanced cycles.