Liquid helium is not commonly used in most refrigeration systems due to several practical and economic reasons:
Cost: Helium is relatively rare on Earth and expensive to produce and store. It is typically extracted from natural gas deposits, and its scarcity makes it significantly more costly than other common refrigerants.
Low Boiling Point: Helium has an extremely low boiling point of around -268.93°C (-452.07°F) at standard atmospheric pressure. Operating refrigeration systems at such low temperatures requires specialized and expensive equipment, which adds to the overall cost.
Safety Concerns: Helium is an asphyxiant, meaning it can displace oxygen in the air and create an oxygen-deficient environment, which can be hazardous to humans if leaked. Special safety precautions and systems would be required to handle and store helium safely.
Efficiency: While liquid helium can achieve extremely low temperatures, it may not be the most efficient choice for many refrigeration applications. Other refrigerants, such as hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs), can provide adequate cooling at less extreme temperatures and are more energy-efficient.
Availability: Due to its rarity and cost, there may be limited availability of liquid helium for widespread use in commercial or industrial refrigeration systems.
Gaseous State at Room Temperature: Helium remains in a gaseous state at room temperature and standard atmospheric pressure. This makes it impractical for many common refrigeration applications, as the refrigerant needs to be in a liquid state to efficiently absorb and release heat during the refrigeration cycle.
Instead of liquid helium, refrigeration systems commonly use other refrigerants like hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), hydrocarbons (HCs), or ammonia (NH3). These refrigerants are more readily available, safer to handle, and can be used in a wide range of temperatures and applications while providing good efficiency and performance. However, it's worth noting that there is growing interest in finding alternative refrigerants that have lower global warming potential (GWP) and ozone depletion potential (ODP) to mitigate their environmental impact.