Transcript PRINCIPLES OF CRYOGENIC TECHNIQUE AND ITS APPLICATION

M.Ashok
A.Ciby
L.Srinath
INTRODUCTION
Cryogenics is the study and use of materials at extremely
low temperatures.
Such low temperatures cause changes in the physical
properties of materials that allow them to be used in
unusual engineering, industrial, and medical applications.
For example, in the cryogenic temperature range, air
becomes a liquid—or even a solid—
and living tissue freezes instantly.
Matter behaves strangely at the lowest temperatures
of the cryogenic range.
Electric currents never stop flowing, liquids run uphill, and
rubber becomes as brittle as glass.
In medicine, cryogenic cooling is used in some diagnostic
techniques, such as magnetic resonance imaging (MRI).
 Cryosurgery uses liquid nitrogen to kill unhealthy tissue by
freezing it.
 Cryogenics is expected to play an important role in the
development of better procedures for preserving human
organs for transplant.
The Cooling Process
 A substance is normally cooled by placing it next to
something colder.
 To make the substance supercold, however, heat must also be
removed and the substance must be insulated (encased).
 An important method of cryogenic supercooling involves
liquefying gases and using these gases to cool other
substances.
 One technique is to convert to liquid form a gas that can be
liquefied by pressure alone.
 Then a gas requiring a lower temperature to become a liquid
is placed in a container and immersed (dipped) in the first.
 The gas that is already liquefied cools the second and
converts it to a liquid.
 After several repetitions of this process, the targeted gas is
liquefied.
 A Dewar flask is normally used to store such very low
temperature liquefied gases.
 If the disorderly spin of electrons in a substance could
be slowed down, then the substance would cool down.
 In cooling by demagnetization, a strong magnetic
force is used to give the outside energy required to line
up the molecules of a paramagnetic substance (one
made up of paramagnetic ions). This also raises the
temperature. At the same time the substance is cooled
in liquid helium. When the substance cools down to
its starting temperature, the magnetic field is
removed.
 This causes the ions to resume their disorderly alignment
(order). The energy the ions use to move comes from the
heat energy of the substance, which causes the temperature
of the substance to drop.
 Liquid nitrogen is one of the safest cooling agents available.
In medicine it is used to kill unhealthy tissues by freezing
them. Cryogenic processes are also used to supply "banks"
storing eye corneas, blood, and sperm for future surgical
procedures. Some embryos have also been frozen and stored
for later implantation (surgical placement) in women.
Cryosurgery
 Cryosurgery is relatively bloodless because the low
temperatures used constrict the blood vessels,
stemming the flow.
 Special instruments are used that have freezing tips to
kill the damaged tissue and shields to protect
surrounding tissue.
 Cooper used cryosurgery to freeze and destroy
damaged tissue in the brains of patients with
Parkinson's disease (a degenerative illness).
 Since then, cryosurgery has found many applications.
It is used to repair detached retinas and to remove
cataracts.
 It is also used to treat liver cancer and prostate cancer.
 Cryosurgery is also widely used in the fields of
dermatology, gynecology, plastic surgery, orthopedics,
and podiatry.
 Cryosurgery has also been used successfully for more
than 30 years in veterinary medicine.
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