Cryogenics

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Cryogenics

  1. 2. Introduction <ul><li>In physics, cryogenics is the study of the production of very low temperatures (below −150 °C or 123 K) and the behaviour of materials at those temperatures. Rather than the relative temperature scales of Celsius and Fahrenheit, cryogenicists use the absolute temperature scales (Kelvin) </li></ul>
  2. 3. History <ul><li>The field of cryogenics advanced during World War II when scientists found that metals frozen to low temperatures showed more resistance to wear. </li></ul><ul><li>The life of metal tools increased by 300% </li></ul><ul><li>Cryogenic processing makes changes to the crystal structures of materials and makes them hard to wear </li></ul>
  3. 4. Dewar Flask <ul><li>A Dewar flask is a vessel designed to provide very good thermal insulation. The Dewar flask was named after its inventor, Sir James Dewar . </li></ul><ul><li>A very common use of the Dewar flask in laboratories is the storage of liquid nitrogen; in this case, the leakage of heat into the extremely cold interior of the bottle results in a slow &quot;boiling-off&quot; of the liquid. </li></ul>
  4. 5. Liquid Nitrogen <ul><li>At atmospheric pressure, liquid nitrogen boils at 77 K (−196 °C) and is a cryogenic fluid.  </li></ul><ul><li>Its ability to maintain temperatures far below the freezing point of water makes it extremely useful in a wide range of applications </li></ul>
  5. 6. Liquid Helium <ul><li>Helium exists in liquid form only at 4K. </li></ul><ul><li>Liquid helium-4 is used as a cryogenic refrigerant; it is produced commercially for use in superconducting magnets such as those used in MRI. </li></ul>Liquid helium in a cup
  6. 7. Superfluidity <ul><li>It is a state of matter in which the viscosity of a fluid vanishes, while thermal conductivity becomes infinite. So the liquid will flow uncontrollably, and also will be at exactly the same temperature throughout. </li></ul><ul><li>It still has a surface tension, so will rise up the sides of a vessel, and will move right up the sides of the constraining vessel and over the top. </li></ul>
  7. 8. Applications of Cryogenics - MRI <ul><li>An MRI machine uses a powerful magnetic field to align the magnetization of some atoms in the body, and radio frequency fields to systematically alter the alignment of this magnetization </li></ul>
  8. 9. <ul><li>Liquefied gases are sprayed on underground cables so they don’t heat up and stop transmission. </li></ul>Applications of Cryogenics – Electric Power Transmission
  9. 10. The National Physical Laboratory (INDIA) <ul><li>The NPL in New Delhi has excellent facilities to produce liquid nitrogen and hydrogen. </li></ul><ul><li>It was founded in 1952 by K.G. Ramanathan. </li></ul>
  10. 11. Thank you

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