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Реферат: Untitled Essay Research Paper Cryogenics and the

Название: Untitled Essay Research Paper Cryogenics and the
Раздел: Топики по английскому языку
Тип: реферат Добавлен 10:37:57 31 октября 2010 Похожие работы
Просмотров: 2 Комментариев: 11 Оценило: 1 человек Средний балл: 5 Оценка: неизвестно     Скачать

Untitled Essay, Research Paper

Cryogenics and the Future 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 measurement 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 Superfluidity. Cryogenics first came about in 1877, when a Swiss Physicist named Rasul

Pictet and a French Engineer named Louis P. Cailletet liquefied oxygen for the first time.

Cailletet created liquid oxygen in his lab using a process known as adiabatic expansion,

which 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"(Vance 26).

At the same time Pictet used the "Joule-Thompson Effect," a thermodynamic

process that states that the "temperature of a fluid is reduced in a process

involving expansion below a certain temperature and pressure"(McClintock 4). After

Cailletet and Pictet, a third method, known as cascading, was developed by Karol S.

Olszewski and Zygmut von Wroblewski in Poland. At this point in history Oxygen was now

able to be liquefied at 90 K, then soon after liquid Nitrogen was obtained at 77 K, and

because of these advancements scientist all over the world began competing in a race to

lower the temperature of matter to Absolute Zero (0 K) [Vance, 1-10]. Then in 1898, James DeWar mad a major advance when he succeeded in

liquifying hydrogen at 20 K. The reason this advance was so spectacular was that at 20 K

hydrogen is also boiling, and 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, which 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 they

would have to have better holding containers. So, scientists came up with insulation

techniques that we still use today. These techniques include expanded foam materials and

radiation shielding. [McClintock 43-55] 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 physicists 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 , their are two subjects that are also closely related to

cryogenics called Superconductivity and Superfluidity. 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,…"(Tilley 11). This unusual behavior was also discovered by Heike

Kamerlingh Onnes. It 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. However, almost all elements and compounds have Tc’s between 1 K and 15 K (or -457.68

(F and -432.67 (F) so they would not be very useful to us on a day to day basis[McClintock

208-226]. 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, in 1987, scientists at the University of

Houston and the University of Alabama discovered YBCO, a compound with a Tc of 95 K. This

discovery made superconductivity possible above the boiling point of liquid Nitrogen, so

now the 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 compund 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. Some applications are demonstrated by magnetically

levitated trains, energy storage, motors, and Zero-Loss Transmission Lines. 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 as you can see and will probably keep growing. The second subject related to cryogenics is Superfluidity.

Superfluidity is a strange state of matter that is most common in liquid Helium, when it

is below a temperature of 2.17 K. Superfluidity means that the liquid "…discloses

no viscosity when traveling through a capillary or narrow slit…"(Landau 195) and

also flows "…through the slit disclosing no friction…"(Landau 195) That this

means is that when Helium reaches this state it can flow, without any friction, through

the smallest holes and in between atoms in a compund. If the top is off the beaker it is

also possible for the liquid Helium to flow up the side of the baker and out of the beaker

until all the liquid helium is gone. It was then 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

Superfluidity is much more complex, and is not completely understood by today’s

physicists.[McClintock 103-107] Cryogenics also consists of many smaller sciences, including

Cryobiology, which is "the study of the effects of low-temperatures on materials of

biological origin."(Vance 528) 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.

Another field is Cryopumping. Cryopumping is the process "of condensing gas or vapor

on a low-temperature surface."(Vance 339) This is done by extracting gas from a

vacuum vessel by conventional methods then freezing the remaining gas on low temperature

coils. This process has been useful when trying to simulate the properties that the vacuum

in outerspace will have on electronic circuitry. Cryogenics has also been a part of many modern advances including:

The transportation of energy in the form of a liquefied gas.

Processing, handling, and providing food by cryogenic means has become a large business,

providing both frozen and freeze-dried food.

Liquid Oxygen powers rockets and propulsion systems for space research.

Liquid Hydrogen is used in high-energy physics experiments.

Using cryogenic drill bits so drilling for oil and other gases is easier.

Chemical synthesis and catalysis.

Better fire fighting fluids.

Gas separation.

Metal Fabrication. As you can see by now 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. However, its full potential will probably not be understood for quite a while.

Though, as you can see, if we can grasp the concepts of cryogenics we will have a tool

that will allow us to do things ranging from making better drill bits to exploring the

universe. The future of cryogenics can best be summed up by Krafft A. Ehricke, a rocket

developer, when he said, "It’s centeral goal is the preservation of

civilization."ReferencesKhalatnikov, I. M., An Introduction to the Theory of Superfluidity (New York: W.A.

Benjamin Inc., 1965).

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

Tilley, David R. and Tilley, John, Superfluidity and Superconductivity (New York: John

Wiley and Sons, 1974)

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

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