The primary characteristic of a chemical used as a refrigerant is its ability to undergo phase transitions between gas and liquid at relatively low temperatures. This property is crucial for the refrigeration cycle, which is the fundamental process that allows refrigerators and air conditioning systems to function effectively.
The refrigeration cycle involves four main stages: compression, condensation, expansion, and evaporation. During compression, the refrigerant is compressed to a high-pressure gas, which raises its temperature. The hot, high-pressure gas then moves to the condenser coils, where it releases heat to the surrounding environment and condenses into a high-pressure liquid.
Next, the high-pressure liquid refrigerant passes through an expansion valve or device, causing its pressure to drop significantly. As a result, the refrigerant becomes a low-pressure, low-temperature liquid. This low-pressure liquid then enters the evaporator coils, where it absorbs heat from the surrounding environment, such as the inside of a refrigerator or a room.
Finally, the refrigerant evaporates into a low-pressure gas as it absorbs heat, completing the cycle. The gas is then returned to the compressor to start the process again.
The refrigerant's ability to efficiently undergo these phase transitions while maintaining stable thermodynamic properties is critical for effective cooling and heat transfer within the refrigeration system. Additionally, refrigerants should have low toxicity, be non-flammable, and have minimal impact on the environment, as refrigerants can have significant implications for climate change and ozone depletion if they escape into the atmosphere. This is why there has been a continuous effort to develop and use refrigerants that are more environmentally friendly, such as hydrofluorocarbons (HFCs) with lower global warming potential (GWP) or natural refrigerants like ammonia, hydrocarbons, or carbon dioxide.