Cryogenics

People commonly associate cryogenics with freezing of the corpses of rich people, whom hopes that future innovations shall make it possible for them to return to life. This is actually a branch in the field of cryogenics named Cryonics.

Cryogenics in itself is defined as the study of low-temperature phenomena e.g. how are the production and behaviour of materials affected by very low temperatures?

The dividing line between refrigeration and cryogenics is unfortunately not a well-defined point on the temperature scale, you can find different definitions in literature. The U.S. National Institute of Standards and Technology has chosen the most logical dividing line, they consider the field of cryogenics to be anything that happens at or below the temperature of -180 ⁰C (93,15 K, -292 ⁰F, 167,67 ⁰R). This temperature is below the boiling point of commonly used refrigerants and above the boiling point of the important fluids in cryogenic industry, e.g. helium, hydrogen, nitrogen, oxygen and air.

There are several very interesting applications of cryogenic fluids, for instance:

• Cryoconservation of genetic material
• Super conduction
• Air separation
• Cryotronics
• Cryosurgery

Since cryogenic systems operate at temperature much lower than the ambient temperature is heat transfer always a key factor to consider. To store a cryogenic fluid at its liquid phase demands a vessel with low heat transfer rate. Cryogenic heat exchangers on the other hand should be highly efficient e.g. have as high heat transfer rate as possible for a given heat exchanger size.

Beside this must the material in the equipment have stable mechanical properties at the temperatures in question. Cryogenic equipment therefore tends to be quite expensive, but the big cost is nearly always the energy needed to cool to cryogenic temperatures. The current trend in the cryogenic industry is development of more energy efficient systems.

Airec has been in cryogenic development projects for several years.

In one of the joint-development projects with one the leading cryogenic research institutes has a re-liquification system for helium which reduces energy consumption and costs with ca. 50 % been developed. This and other projects has given Airec valuable experience in calculating unique heat exchanger systems.