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Cryogenics Engineering
by Vikas Tripathi Bookmark and Share
 

Abstract

Cryogenics Engineering is one of the key technologies of the modern era. It is widely used in research and has many applications in industry and last but not least in medicine. In research, cryogenics engineering and its applications are omnipresent from the smallest laboratories to fusion reactors, huge detectors and accelerators. This engineering research field involves knowledge, capabilities and practices associated with aerospace cryogenic systems (particularly for use in propulsion), life support, refrigeration and laboratory processes. This research area includes handling characteristics, material properties, system safety, and system unique requirements for the safe and effective usage of cryogenic fluids for research, development, design, analysis, test, operation and/or evaluation of cryogenic fluids storage and transfer systems for both fuels and oxidizers.

Introduction

The intention of presenting this paper is to study the various aspects of cryogenics engineering and knowing about the history behind cryogenics programme as well as the applications of it in various fields. Cryogenics is the science that addresses the production and effects of very low temperatures. The word originates from the Greek words 'kryos' meaning "frost" and 'genic' meaning "to produce." Under such a definition it could be used to include all temperatures below the freezing point of water (0°C). However, Prof. Kamerlingh Onnes of the University of Leiden in the Netherlands first used the word in 1894 to describe the art and science of producing much lower temperatures. He used the word in reference to the liquefaction of permanent gases such as oxygen, nitrogen, hydrogen, and helium. Oxygen was liquefied at -183 °C a few years earlier (in 1887), and a race was in progress to liquefy the remaining permanent gases at even lower temperatures. The techniques employed in producing such low temperatures were quite different from those used somewhat earlier in the production of artificial ice. In particular, efficient heat exchangers are required to reach very low temperatures. 

Over the years, the term cryogenics has generally been used to refer to temperatures below approximately -150 °C. There are several trends today that can help us look into the future of cryogenics materials. These include: computationally designed materials and processing; unique nanophase materials systems for new applications at low temperatures; smart materials and systems based on new alloys; durability and performance, quality assurance and testing etc. According to the laws of thermodynamics, there exists a limit to the lowest temperature that can be achieved, which is known as absolute zero. Molecules are in their lowest, but finite, energy state at absolute zero. Such a temperature is impossible to reach because the input power required approaches infinity. However, temperatures within a few billionths of a degree above absolute zero have been achieved. 

Absolute zero is the zero of the absolute or thermodynamic temperature scale. It is equal to -273.15 °C or -459.67 F. The metric or SI (International System) absolute scale is known as the Kelvin scale whose unit is the kelvin (not Kelvin) which has the same magnitude as the degree Celsius. The symbol for the Kelvin scale is K, as adopted by the 13th General Council on Weights and Measures (CGPM) in 1968, and not °K. Thus, 0 °C equals 273.15 K. The English absolute scale, known as the Rankine scale, uses the symbol R and has an increment the same as that of the Fahrenheit scale. In terms of the Kelvin scale the cryogenic region is often considered to be that below approximately 120 K (-153 °C). Such liquids are known as cryogenic liquids or cryogens. When liquid helium is cooled further to 2.17 K or below, it becomes a super-fluid with very unusual properties associated with being in thequantum mechanical ground state. For example, it has zero viscosity and produces a film that can creep up and over the walls of an open container, such as a beaker, and drip off the bottom as long as the temperature of the container remains below 2.17 K.

A person who studies elements under extremely cold temperature is called a cryogencist. Rather than the relative temperature scales of Celsius and Fahrenheit, cryogencists use the absolute temperature scales. These are Kelvin (SI units) or Rankin scales (Imperial & US units.

History of Cryogenics:

In early 19th century, people used to freeze their things only by natural ice. This was the only technique to keep the things cool. But later, the demand of artificial-cooling started increasing, because the butchers, the brewers and later the industrialists felt the need of keeping their things cool. Meats and fishes could be kept fresh for a long time with the help of ice. People used to keep the natural ice in big caves so that they could use it on a long basis. Refrigerated Rail Road Cars also came in use afterwards. The successful liquefaction of Oxygen was announced at the meeting of the Académie de Sciences in Paris on December 24th, 1877 by the physicist Louis Paul Cailletet from Paris. Louis Paul Cailletet presented Cailletet’s Apparatus by which the liquefaction of the oxygen was possible. In this apparatus, following process was being followed-

  1. Compression to 200 bars in a glass tube with a hand-operated jack, using water and mercury for pressure transmission,
  2. Pre-cooling of the glass tube with liquid ethylene to -103°C,
  3. Expansion to atmosphere via a valve.

Milestones in the History of Cryogenics:

The cryogenics programme started in 1904 when Congress appropriated funds to purchase the two-litre per-hour hydrogen liquefier exhibited at the St. Louis World’s Fair by the British Oxygen Company. It was rarely used until 1925, when F. G. Brickwedde, and later Russell Scott, started producing liquid hydrogen for research and as a coolant to liquefy helium. In the early 1930s, Harold C. Urey of Columbia University set out to prove experimentally the existence of an isotope of hydrogen which we now call deuterium. He asked Brickwedde to liquefy hydrogen and, by distillation, to concentrate isotopes for spectroscopic analysis. Urey found deuterium present in the sample and was awarded the Nobel Prize.

In the 1940s, the emphasis in the field of cryogenics changed dramatically from research to engineering, which stimulated great improvements in system performance. Some of the engineering applications that evolved over the next decades included storage and shipment of gases such as oxygen, nitrogen, hydrogen, helium, and natural gas in liquid form; production of oxygen for making steel; rocket and aircraft fuels; energy transport and storage; electronics; and facilities for high-energy physics. NBS was one of the few U.S. laboratories with equipment, personnel and experience to meet the national need for information and data. In 1953, the NBS staff (Brickwedde, Scott, Baird, Birmingham, Chelton, Freeman, Gifford, Goddard, Johnson, Kropschot, Powell, and Vander Arend) was awarded Gold Medal by the Department of Commerce ffor ‘the design, construction and operation of large and unique hydrogen and nitrogen liquefiers.’

Applications of Cryogenics Engineering:

Cryogenic treatment works on Reamers (carbide or HSS), Tool Bits, Tool Punches (carbide or HSS), Carbide Drills, Carbide Cutters, Milling Cutters, Files, Shaping Equipment, Scissors, Razors, Clippers, Knives, Band Saw Blades, Saw Blades, Reciprocating Blades, Sabre Saw, Steel Woodworking and Form Tooling, Cutting Tools and Dies. In all cases, this treatment will result a stronger and more wear resistant metal.

Cryogenics is used to treat many types of sports equipment also, the most common being golf clubs, because cryogenics increases the molecular density of treated materials. It improves the distribution of energy (in this case kinetic energy) through the object. The treatment also increases the rigidity of the metal, which in this case might affect the shaft of the golf club. Combined, the increases in kinetic energy distribution and rigidity of the shaft make for a longer and straighter drive. Basically, the club has significantly less give, so the performance increases. This type of treatment can be used on many other types of sports equipment where the same energy and rigidity characteristics would benefit the user. It is also used to treat musical instruments.

Liquefied gases, such as liquid nitrogen and liquid helium, are used in many cryogenic applications. Liquid nitrogen is the most commonly used element in cryogenics and is legally purchasable around the world. Liquid helium is also commonly used and allows for the lowest attainable temperatures to be reached. These liquids are held in either special containers known as Dewar flasks, which are generally about six feet tall (1.8 m) and three feet (91.5cm) in diameter, or giant tanks in larger commercial operations. Dewar flasks are named after their inventor, James Dewar, the man who first liquefied hydrogen.

Magnetic resonance imaging (MRI) is a method of imaging objects that uses a strong magnetic field to detect the relaxation of protons that have been perturbed by a radio-frequency pulse. This magnetic field is generated by electromagnets, and high field strengths can be achieved by using superconducting magnets. Traditionally, liquid helium is used to cool the coils because it has a boiling point of around 4 K at ambient pressure. Cheap metallic superconductors can be used for the coil wiring. So, high-temperature superconducting compounds can be made to super-conduct with the use of liquid nitrogen which boils at around 77 K.

It is difficult to transmit power by overhead cables in big cities, so underground cables are used. But underground cables get heated and the resistance of the wire increases leading to waste of power. Superconductors are frequently used to increase power throughput, requiring cryogenic liquids such as nitrogen or helium to cool special alloy-containing cables to increase power transmission.

Cryogenic gases are used in transportation of large masses of frozen food. When very large quantities of food must be transported to regions like war zones, earthquake hit regions, etc. they must be stored for a long time, so cryogenic food freezing is used. Cryogenic food freezing is also helpful for large scale food processing industries.

Conclusion:

In a nutshell, it is concluded that “Cryogenics Engineering” has become the basic need of every industry and human being. It helps to store the raw materials so that they can be used for a long time. Cryogencists are developing new techniques to advance the efficiency of the work with the help of cryogenics engineering. Superconductors are the result of these researches. Enhancement in the field of cryogenics engineering made the maglev trains to be possible to run on a very high speed after achieving a very low temperature with the help of cryogenic tools and materials. The main development in this field was done by the British Oxygen Company. In a general opinion, the father of the cryogenics engineering is “Louis Paul Cailletet”, because he was the first person to liquefy the oxygen in 1877. At old times, the people were not capable to store their products for long times. Fishers who used to do fishing in the widest sea were not able to keep their dead fishes for many days. Hence they developed freezing-machines to store them on larger amounts. This type of refrigeration was the first attempt of human being in the field of cryogenics. They also used to keep the ice in large caves. The road rail vehicles came in use and the butchers became capable of storing their meats and fishes on a long basis.

Days passed by and the researches in this field made this modern era to be facilitated with the lots of physical things to make our world more easier to survive and utilize it at its fullest. Cryogenics is one of field in which some specific materials play a very important role in its advancement. Cryogenics-based technologies have applications in wide variety of areas as metallurgy, chemistry, power industry, medicine, rocket propulsion and space simulation, food processing by refrigeration, etc. Next century has several aspects to it. First, is to look at the history of the development of cryogenics materials. Secondary, is to evaluate where we are today in this science and to look at research and development trends in this area which can give us some clues to future developments. To the extent possible, this paper will deal with the past, the present and the future of cryogenics materials for the 21st century.

Image (c) Gettyimages.com
  

24-Mar-2013
More by :  Vikas Tripathi
 
Views: 1476
Article Comment Educative, thanks.
BS Murthy
03/28/2013
 
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