külmutusvahendi

Külmutusvahend, also known as refrigerant or coolant, is a substance or mixture used in a refrigeration cycle to absorb heat from a cold reservoir and release it to a warmer one. The process relies on the physical properties of the substance, specifically its ability to change phase (liquid to gas and gas to liquid) at specific temperatures and pressures.

Historically, early refrigerants included ammonia, sulfur dioxide, and methyl chloride. However, due to toxicity and flammability concerns, these have largely been replaced by newer generations. Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) became popular due to their stability and non-flammability but were later phased out due to their ozone-depleting properties.

Current refrigerants are primarily hydrofluorocarbons (HFCs), which do not deplete the ozone layer. However, many HFCs have a high global warming potential (GWP). Therefore, there is a growing trend towards refrigerants with lower GWPs, such as hydrofluoroolefins (HFOs) and natural refrigerants like propane, isobutane, and carbon dioxide.

The choice of refrigerant depends on the specific application, required operating temperatures, safety considerations, environmental regulations, and cost. The refrigeration cycle typically involves compression of the refrigerant gas, condensation into a liquid, expansion through a valve, and evaporation back into a gas, thereby absorbing heat. This continuous cycle is the basis of refrigeration and air conditioning systems.