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Cryogenics And The Future Essay Research Paper

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Cryogenics And The Future Essay, Research Paper

Cryogenics is a study that is of great importance to the human race and has been a major project for engineers for the last 100 years. Cryogenics, which is derived from the Greek word kryos meaning “Icy Cold,” is the study of matter at low temperatures. However low is not even the right word for the temperatures involved in cryogenics, seeing as the highest temperature dealt with in cryogenics is 100 (C (-148 (F) and the lowest temperature used, is the unattainable temperature -273.15 (C (-459.67 (F). Also, when speaking of cryogenics, the terms Celsius and Fahrenheit are rarely used. Instead scientists use a different temperature measurement scale called the Kelvin (K). The Kelvin scale for Cryogenics goes from 173 K to a fraction of a Kelvin above absolute zero. There are also two main sciences used in cryogenics, and they are Superconductivity and Superfluity.

Cryogenics first came about in 1877, when Swiss Physicist Rasul Pictet and a French Engineer named Louis P. Cailletet liquefied oxygen for the first time. Cailletet created the liquid oxygen in his lab using a process known as adiabatic expansion. Adiabatic expansion is a thermodynamic process in which the temperature of a gas is expanded

without adding or extracting heat from the gas or the surrounding system (4). At the same time Pictet used the “Joule-Thompson Effect”, which is a thermodynamic process that states that the temperature of a fluid is reduced in a process involving expansion below a certain temperature and pressure (2). After Cailletet and Pictet, a third method, known as cascading, was developed by Karol S. Olszewski and Zygmut von Wroblewski both of Poland. At this point in history, oxygen could now be liquefied at 90 K. Soon after this discovery liquid Nitrogen was obtained at 77 K, and because of these advancements scientists all over the world began competing in a race to lower the temperature of matter to Absolute Zero, or 0 K (4).

Then in 1898, James DeWar mad a major advance when he succeeded in liquefying hydrogen at 20 K. The reason this advance was so spectacular was that hydrogen is also boiling at this temperature. This presented a very difficult handling and storage problem. DeWar solved this problem by inventing a double-walled storage container known as the DeWar flask. This flask could contain and hold the liquid hydrogen for a few days. However, at this time scientists realized that if they were going to make any more advances in this field of cryogenics, they would have to have better holding containers. Scientists then came up with insulation techniques that we still use today. These techniques include expanded foam materials and radiation shielding. (2)

The last major advance in cryogenics finally came in 1908 when the Dutch physicist Heike Kamerling Onnes liquefied Helium at 4.2 and then 3.2 K. The rest of the advances in cryogenics have been extremely small since it is a fundamental Thermodynamic law that you can approach but never actually reach absolute zero. Since 1908 our technology has greatly increased and we can now freeze sodium gas to within 40 millionths of a Kelvin above absolute zero. However, in the back of every physicist?s head they want to break the Thermodynamic Law and reach a temperature of absolute zero where every proton, electron, and neutron in an atom is absolutely frozen.

Also, there are two subjects that are also closely related to cryogenics called Superconductivity and Superfluity. Superconductivity is a low-temperature phenomenon where a metal loses all electrical resistance below a certain temperature, called the Critical Temperature (Tc), and transfers to a state of zero resistance. (3) Heike Kamerlingh Onnes also discovered this unusual behavior. This Critical Temperature was discovered when Onnes and one of his graduate students realized that Mercury loses all of its electrical resistance when it reaches a temperature of 4.15 K. (2)

Then in 1986, J. Gregore Bednorz and K. Alex Muller discovered that an oxide of lanthanum, barium, and copper becomes superconductive at 30 K. This discovery shocked the world and stimulated scientists to find even more “High-Temperature Superconductors”. After this discovery in1987, scientists at the University of Houston and the University of Alabama worked together and discovered YBCO. YBCO is a compound with a Tc of 95 K. This discovery made superconductivity possible above the boiling point of liquid Nitrogen. This meant that the now relatively cheap, liquid nitrogen could replace the high priced liquid helium required for cryogenic experiments. To date the highest reported Tc is 125 K, which belongs to a compound made of Thallium, Barium, Calcium, Copper, and Oxygen. Now, with the availability of high-temperature superconductors, all the sciences, including cryogenics, have made extraordinary advances. Magnetically levitated trains, energy storage, motors, and Zero-Loss Transmission Lines demonstrate some applications. Also, superconducting electromagnets are used in Particle Accelerators, Fusion Energy Plants, and Magnetic Resonance Imaging devices (MRI’s) in Hospitals. Furthermore high-speed cryogenic computer memories and communication devices are in various stages of research. This field has grown immensely since 1986, and has continued to advance.

The second subject related to cryogenics is Superfluity. Superfluity is a strange state of matter that is most common in liquid Helium, when it is below a temperature of 2.17 K. Superfluity means that the liquid discloses no viscosity when traveling through a capillary or narrow slit, and also flows through the slit disclosing no friction. (1) That this means is that when Helium reaches this state it has the ability to flow without any friction through the smallest holes, and in between atoms in a compound. If the top is off a beaker it is also possible for the liquid Helium to flow up the side and out of the beaker until all the liquid helium is gone. It was discovered that when any liquid approaches about .2 K it has almost the exact same properties of superconducting metals, as far as specific heat, magnetic properties, and thermal conductivity. Even though both Superconducting and Superfluidic materials have similar properties, the phenomenon of Superfluity is much more complex, and is not yet completely understood by today’s physicists. (2)

Cryogenics also consists of many smaller sciences including Cryobiology. Cryobiology is the study of the effects of low-temperatures on materials of biological origin. (4) Developments in this field have led to modern methods of preserving blood, semen, tissue, and organs below the temperature that was obtained by the use of liquid nitrogen. Also, Cryobiology has led to the development of the cryogenic scalpel, which can deaden or destroy tissue with a high degree of accuracy, making it possible to clot cuts as soon as you cut them. So in theory, you could one day have surgery without having to deal with any blood.

As you can see cryogenics is still a very young science, but in the last ten years it has catapulted to being the backbone of almost every other form of science. Although unfortunately its full potential will probably not be understood for quite some time. Once we can grasp the concepts of cryogenics we will have a tool that will allow us to do things ranging from making better surgical tools to exploring the universe. The future of cryogenics can best be summed up by Krafft A. Ehricke, a rocket developer, when he said, “Its centeral goal is the preservation of civilization.”

Cryogenics and the Future

Angie Bertugli

Bibliography

References

1. Khalatnikov, I. M., An Introduction to the Theory of Superfluidity (New York: W.A. Benjamin Inc., 1965).

2. McClintock, Michael, Cryogenics (New York: Reinhold Publishing Corp., 1964).

3. Tilley, David R. and Tilley, John, Superfluity and Superconductivity (New York: John Wiley and Sons, 1974).

4. Vance, Robert W., Cryogenic Technology (London: John Wiley & Sons, Inc., 1963).




Комментарий:

Cryogenics is a study that is of great importance to the human race and has been a major project for engineers for the last 100 years. Cryogenics, which is derived from the Greek word kryos meaning “Icy Cold,” is the study of matter at low temperatures. However low is not even the right word for the temperatures involved in cryogenics, seeing as the highest temperature dealt with in cryogenics is 100 (C (-148 (F) and the lowest temperature used, is the unattainable temperature -273.15 (C (-459.67 (F).


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