Cryogenics: The Science of Extreme Low Temperature

Having just watched the fifth episode of series 3 of "The Flash" where Cathelyn Snow absorbed a lot of heat in an experiment with her mother in a bid to answer some questions about her "frosty superability", I was reminded of the field of Engineering that many are unaware of and I was compelled to share with you.

I am sure you are aware of what refrigeration is even if it is just a slight idea. We all have refrigerators in our homes, We buy frozen foods, We take ice-creams, We ride in vehicles with Air conditioning unit. So in one way or the other we have encountered refrigeration.

In simple words simply put that Refrigeration is the science and engineering that deals with the extraction of heat from substances through work input from an external source. However, that definition will be ambiguous as there is another allied and intertwined field of Engineering that also deals with heat extraction from substances. This is called Cryogenics.

The obvious questions here now are: What is cryogenics? How does it differ from ordinary Refrigeration? What are some of its application? Do read on to find out.

CC0 Public Domain: Ice at Low temperature

DEFINITION
Cryogenics is coined from the Greek word "cryo" meaning cold and "genic" meaning production. It is thus an Engineering field which deals with the production of substances at extremely low temperatures. Cryogenics does not only produce extreme low temperatures, it studies the effect of this low temperature on the material.

DIFFERENCE BETWEEN CRYOGENICS AND REFRIGERATION

Cryogenics and Refrigeration are both concerned with the removal of heat from a substance. However, there is a distinction between them. This distinction is the attainable temperature of each. Although a clear dividing line (single temperature) is yet to be drawn between them, scientists take the temperature of 123 K as demarcation. Thus, the term Refrigeration is applicable up to a temperature of 123 K, while cryogenics applies from 123 K to absolute zero temperature.

Furthermore, another dividing line is drawn by the National Institute of Standard and Technology,
based on the fact that most cryogens (Cryogens are fluids which are used for cryogenic applications. Examples of such include: Oxygen, Nitrogen and Helium) have boiling points lower than 93 K. They thus consider the dividing line to be 93 K.

In any case we can easily conclude that cryogenics is capable of achieving very low temperatures which are impossible using ordinary refrigeration processes.

APPLICATIONS OF CRYOGENICS

• Cryotherapy

Cryotherapy is any medical treatment that is rendered with the aid of low temperature. One example is in treating Malignant, a type of skin cancer as well as the precancerous condition (Wart). The ease of administering cryotherapy along side low cost and good cosmetic results make it advantageous over other means of treating cancer. Liquefied Nitrogen is usually used in cryotherapy, but any other cryogen may be used. This cryogen is applied over the concerned area of the skin. From elementary physics, evaporation of the cryogen takes place and the same time freezing of the concerned area i. e. evaporation by cooling. The rapid transfer of heat between the treated area of the skin and the cryogen and subsequent thaw destroys the infected cells.

• Production and storage of liquefied gases

Cryogenics is employed to condense real gases in order to convert them into liquid. The temperature of the gas is lowered until a temperature below its boiling point. Cryocoolers are employed for this. One type of Cryocooler is the sterling Cryocooler which is based on the reverse sterling engine (See the post by @churchboy here for more on sterling engines). Example of such liquefied gases includes oxygen, nitrogen and helium. Gases are liquefied for easy transportation and storage of larger volume and safety as they are non pressurized in this state. One very important example of this is Liquefied Natural Gas (LNG).

• Fractional distillation of air.

Fractional distillation is the separation of a substance into its constituents. Fractional distillation is carried out in a chamber known as fractionating column. The principle of fractional distillation is based on the fact each constituent of the substance have different boiling temperatures. Air is known to contain 79% Nitrogen and 21% Oxygen by volume. Nitrogen has a boiling point of 77 K while that of Oxygen is 90 K.

To achieve the separation, air is cooled to about 73 K and is then passed into the fractionating column where the separation occurs. Nitrogen is tapped from the top and liquid oxygen is tapped from the bottom of the fractionating column.

• Research

The advent of cryogenics and its improvement has enhanced research. Through Cryogenics, the study of the behavior of a material under low temperature is possible. This had led to the discovery of superconductivity and its study. Superconductivity is a phenomenon which occur in some materials when their temperature is lowered below a critical value. At this point their resistance to electricity becomes zero.

CONCLUSION
Cryogenics is a field that deals with extreme low temperature. It is related to refrigeration but it is capable of much lower temperatures. It has found widespread application in many areas.

By now I believe you understand what cryogenics is all about.
Was this insightful? Do drop your comments and contribuions.

REFERENCES

• Wikipedia: Cryogenics

• MedScape: Cryotherapy

• CERN: Superconductivity

• BBC-GCSE Bitesize: Fractional Distillation of Liquid Air

• Liquid Oxygen. Safetygram 6. Air Products and Chemicals, Inc., 2015 (38983) 900-13-078-US-May17

• A. M. Papadopoulos and C. J. Koroneos, (2004), REFRIGERATION AND CRYOGENIC
  SYSTEMS, in Air Conditioning - Energy Consumption and Environmental Quality, [Ed. Matheos
  Santamouris], in Encyclopedia of Life Support Systems (EOLSS), Developed under the Auspices of the UNESCO, Eolss Publishers, Oxford ,UK, [http://www.eolss.net] [Retrieved February 6, 2012]