Why liquid helium is an ideal ultra-low temperature coolant

Helium, liquid helium

Helium is known as one of the least active elements and typically exists in gaseous form, colorless and odorless. It is very difficult to liquefy in a gaseous state and cannot solidify at standard atmospheric pressure. Due to its unique physical properties, liquid helium has become a coolant in many industries.

1、 The situation of reactor coolant

Coolant is a medium used to cool the core of a nuclear reactor and remove the heat released from the core, also known as a heat carrier. Simply put, coolant is a substance that can dissipate heat energy from high-temperature objects and cool them down. For this type of coolant, in addition to general thermal and hydraulic properties, it is also required to have a small thermal neutron absorption cross section, weak induced radioactivity, good radiation stability, and good compatibility with reactor structural materials. Common heat dissipation media include light water, heavy water, carbon dioxide, and helium.

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2、 The properties of liquid helium cooling

Liquid helium is a substance primarily used as a low-temperature source and is employed as a super coolant. The reason is that helium has a very low melting and boiling point, no triple point at room temperature, and is the only substance that does not solidify at atmospheric pressure and 0K. After repeated cooling and pressure treatment, the surface tension of liquid helium is very low, the thermal conductivity is strong, the viscosity is extremely low, and it can even reach a low temperature close to absolute zero (about -273.15 ℃). This characteristic makes helium a super coolant that no other low-temperature cold source can replace. In addition, helium has very stable chemical properties and hardly undergoes any chemical reactions with other elements. In other words, when helium is used as a refrigerant, it does not react with the cooled object, nor does it change any of its characteristics, and therefore does not cause additional losses.

3、 Liquid helium has a wide range of cooling applications.

The low-temperature cooling technology of liquid helium is widely used in various fields, such as superconducting technology. At present, all superconducting materials need to exhibit superconducting properties in a low-temperature environment below -130 ℃. However, in most cases, only liquid helium can relatively easily achieve such extremely low temperatures. Low temperature superconducting technology has been widely applied in battery related fields, such as maglev trains in the transportation industry and magnetic resonance imaging equipment in the medical field, which require the use of liquid helium. China has successfully passed the acceptance and achievement appraisal, and has completed an important scientific research equipment project - the development of a large-scale low-temperature refrigeration system from liquid helium to superfluid helium temperature zone. This project has a wide range of applications in the fields of technical analysis and application. Both liquid helium and superfluid helium temperature range large-scale low-temperature refrigeration equipment are essential infrastructure for helium resource extraction, aerospace engineering, hydrogen energy utilization, and the operation of large-scale scientific facilities. With the rapid development of the social economy, China has become a large-scale user of large-scale low-temperature refrigeration equipment. Liquid helium, as a "magical tool" for manufacturing ultra-low temperatures, is expected to have enormous market potential in the future.