Cryogenic-Applications
Author:
Alok D. Bhatt
V.V.P. Engineering College,
Virda-Vajdi, Kalavad Road,
Rajkot – 360 005.
E-mail: [email protected]
Index
- Abstract
- History
- The ‘Joule-Thomson’ effect
- Cryogenic Tempering
- Cryogenics in space research
- Cryogenics in missile launching
- For personal protection in fuel handling
- As auxiliary power source
- As propellants
- Nuclear rockets
- Space simulation
- Cryogenics in biology
- In blood preservation
- Tissue preservation
- In treatment of skin diseases
Abstract:
Cryogenics
is a branch of physics concerned with very low temperatures- how to produce the
lowest temperatures possible (below minus 300 F), and what effects these low
temperatures have on organisms or materials. The prefix Cryo is derived from the Greek word kryos, meaning "cold."
Cryogenics is a term
normally associated with low temperatures. However, the location on the
temperature scale at which refrigeration generally ends and cryogenics begins
has never been well defined. Most scientists and engineers working in this field
restrict cryogenics to a temperature below -235°F (225°R) because the normal
boiling points of most of the permanent gases (e.g., helium, hydrogen, neon,
nitrogen, argon, oxygen, and air) occur below this temperature. The National
Bureau of Standards has suggested that the term cryogenics can be applied to
all temperature below -150°C.
This branch of physics
has come a long way since initial work started way back in 1823 by Sir Humphrey
Davy and Michael Faraday. From research work to human usable technology, today
Cryogenics is applied in various fields such as: space research, missile
launching, rocket launching technology, propellants, power sources, food
preservation and superconductivity. There are wide applications of cryogenics
in the field of biology, called cryobiology. From preserving blood and tissues,
treating skin diseases to preserving human bodies, cryogenics will surely prove
to be a promising technology in the coming years.
This paper talks about
the term ‘cryogenics’ and its possible applications in various human endeavors.
History:
Pioneering work in low temperature physics by the
British chemists Sir Humphrey Davy and Michael Faraday, between 1823 and 1845,
prepared the way for development of cryogenics and cryogenic tempering. Davy
and Faraday generated gases by heating an appropriate mixture at one end of a
sealed tube shaped like an inverted ‘V’. The other end was chilled in a salt
and ice mixture. The combination of reduced temperature and increased pressure
caused the evolved gases to liquefy. When the tube was opened, the liquid
evaporated rapidly and cooled to its normal boiling point. By evaporating solid
carbon dioxide mixed with ether, at low pressure, Faraday finally succeeded in
reaching a temperature of about 163°K (about
-110°C or -166°F).
If a gas
initially at moderate temperature is expanded through a valve, its temperature
increases. But if its initial temperature is below the inversion temperature,
the expansion will cause a temperature reduction as result of what is called
the ‘Joule-Thomson’ effect. The inversion temperature of hydrogen an helium,
two primary cryogenic gases, are extremely low, and to achieve a temperature
reduction through expansion, these gages must be first precooled below their
inversion temperature, the hydrogen by liquid air and helium by liquid
hydrogen. This method is generally not able to bring about liquefaction in one
step. However, by cascading the effects, the French physicist Louis Paul
Cailletet (1832-1913) and the Swiss scientist Raoul Pierre Pictet (1846-1929)
were able in 1877 to produce droplets of liquid oxygen.
The
Dutch physicist Heike Kamberlingh Onnes was able to setup the first liquid air
plant in 1894 using the cascade principle. The British chemist Sir James Dewar
first liquefied hydrogen in 1898 and Kamberlingh Onnes liquefied helium, the
most difficult of the gases to liquefy in 1908. Since then increased attention
has been given to studying phenomena at lower temperatures.
The ‘Joule-Thomson’ effect:
It is
the phenomenon by which a cooling effect is produced by passing a high-pressure
gas, through a restriction, to a low pressure. Its fundamental principal is
that is of using ‘internal work’ to cool a gas. This work results from the fact
that molecules separate further as the gas expands.
In
separating they are moving against Vander Wall’s force of attraction between
them, the energy for this motion is obtained at the expense of the kinetic
energy. The loss of kinetic energy results in decrease in internal energy of
the gas and thus decreases in temperature.
The
effect of the volume of the molecules is to cause the gas to heat instead of
cooling during expansion. Thus the net temperature effect of the expansion is
the result of two processes, one that tends to cool the gas and other that
tends to heat it. Since the changes in temperature in two processes are not the
same, there is inversion at which the effect is zero - below the temperature,
the gas cools and expands, and while above inversion temperature it gets
heated.
At room
temperature, air, H2 and He are above their inversion temperature, and
therefore get warmed when expanded. All other common gases are cooled by
expansion at room temperature. Therefore if throttling of these gases is to be
used to accomplish refrigeration, it is first necessary to cool them below the
inversion temperature by other means.
Cryogenic
Tempering:
Cryogenic
Tempering is an offshoot of Cryogenics. This industry has specialized in
increasing the durability and performance characteristics of metals by
subjecting them to -300°F and
heating to +300°F.
Deep
cryogenic tempering is operated at -240°F to
-320°F. Deep cryogenic tempering is
the process of cooling (using liquid nitrogen) inert materials (primary metals)
at a controlled rate until the material reaches –300°F. These parts are then maintained at this temperature for
a predetermined time period after which they are returned to ambient
temperature. But this is not the end; the materials are then subsequently
tempered in a series of heating cycles.
Shallow
cryogenic, would be the process of cooling the temperature from -110°F to -239°F. Researchers
have found that the effect of shallow cryogenic tempering (-110°F) is minimal unless it is performed as a part of the
initial heat treatment cycle. Heat-treating is what gives steel its hardness as
well as its toughness, wear resistance and ductility. Even performed properly,
heat-treating cannot remove all of the retained austenite (large, unstable
particles of carbon dioxide) from steel. Proper heat-treating is a key part in
increasing part toughness, durability, wear resistance, strength and Rockwell
hardness.
The
beneficial changes that occurs as a result of the heat-treat process do not
actually take place during the heating, but, rather from cooling or ‘quenching’
from the high temperature (the benefits of quench do not shop at room
temperature as many alloys will continue to show significant improvement as the
quench temperature nears absolute zero). While it is impossible to actually
achieve –459.67°F, deep cryogenic
temperatures are very efficient and cost effective in increasing dimensional
stability, wear resistance and performance of most alloys.
Cryogenics
in space research:
By
simple observation we find that in space in space research high temperatures
are produced during rocket launching and in many other processes. All of these
high temperature phenomena seem a far cry from the world of low temperature.
However,
space research is a major consumer of the cryogenics fluids, using oxygen as a
chemical reactant, hydrogen both as a chemical fuel and also as a working
medium for nuclear rockets, nitrogen for pre-cooling, flushing an cold flow
testing of rockets on the stands and for cooling of space simulator chamber,
and helium for cryopumping of space simulator chamber.
Cryogenics
in missile launching:
Cryogenic
fluids are the most important factors in a successful missile bunch, aside from
the missile engine itself and the control mechanism. While solid propellants
have been subject of much discussion and certainly will find application in
tactical weapons for use in the field, liquid propellants still moves most of
missiles.
Cryogenics
liquids are used to test, precool and flush the piping in typical rocket test
stand
For
personal protection in fuel handling:
During
earl days the first problem was the development of clothing to protect liquid
fuel handler from harmful effects. A major development was the totally
enclosed, impermeable suit, equipped
with gloves but problem is of cooling the wears within the suit to relieve the
stress, and supplying a source of pure air for breathing.
These
problem were solved by a back-pack containing, liquid air as shown in figure.
This device cools the suit furnishes, oxygen for breathing, maintains a
positive pressure within the suit to keep toxic fumes from entering, and
prevents fogging on the face of the mask.
As
auxiliary power source:
Cryogenic
liquids can be used to power two different kind of auxiliary power source. One
type is a liquid nitrogen hydraulic system, in which nitrogen is heated and
used to drive a motor. The motor in turn drives nitrogen pump and also
furnishes power for other purpose.
A second
type of auxiliary power source using cryogenic liquid is the fuel cell, in
which both fuel and oxidizer are liquids, such as liquid hydrogen and liquid
oxygen. A useful by product is the pint of drinking water produced for every
kilowatt-hour of operation to augment the water supply carried in the
spacecraft.
As
propellants:
The
concept of using a cryogenic liquid, as rocket propellant is attractive for
several reasons:
Storage and handling as a
compact liquid is the easiest and most efficient way of handling a material
which is to generate many times its volume of propellant gas.
Liquid propellants motor offer
higher specific impulse values than solid propellant motors.
The material with the most
desirable characteristics are liquids only at cryogenic temperatures, hydrogen
for instances.
The possibility of new exotic
propellant based molecular species will certainly necessitate their handling
and storage at cryogenic temperatures for reasons of stability.
Nuclear
rockets:
Liquid
hydrogen also finds its place as a propellant in nuclear rockets. A schematic
diagram of a nuclear propulsion unit is show in figure. Energy is transferred
from the reactor to the propellants. The propellant temperature and pressure
are increased to high values, and the propellant is exhausted through the
nozzle at a high velocity.
Space
simulation:
In space
research much testing must be done on components and even on complete
spacecraft under condition duplicating the environments of a given mission.
One of
the most important of this condition is that of temperature the near vacuum
pressure of deep space where the temperature of a body depends on the heat losses
by radiation from its surface and the heat it gains from radiation entering it.
The
pressure of space is produced by cryopumps cooled by gaseous helium backed by
diffusion pump to remove non condensable. The temperature of space is simulated
by means liquid nitrogen. The irradiation is provided by mercury xenon lamp and
quartz lens system.
Cryogenics
in biology:
The use
of cold in biology has given birth to a new sub science “Cryobiology”. There
are wide applications of cryobiology that are discussed in the further topics.
In blood
preservation:
Two
techniques of cryogenic blood storage have been investigated:
Freezing red blood cells in
mixture with protective agents.
Rapid freezing of whole blood to
cryogenic temperatures.
In the
first case the separation from blood of red cells, addition to them of glycerol
freezing and storage -80°C. When
blood is needed and the cells are suspended in plasma. The equipment is complex
and costly, so that central hospitals and other large institutions should best
adapt the method.
The
second method of blood storage involves immersing the whole blood in a bath of
liquid nitrogen to freeze the blood in less than 1 minute at -320°F. A protective additive, such as polyvinyl pyrrolidone
(PVP), is often used to reduce red blood cells mortality. In contrast to
glycerol, PVP need not to be removed from the blood before transfusion. When
the blood is needed, it is thawed as rapidly as it was frozen.
Successful
transfusion of bone marrow in human patients may soon become possible reality,
due to application cryogenics. The same of quick-freezing methods, which proved
successful with blood, are now being tested for application to bone marrow.
Tissue
preservation:
Preservation
of tissue and cells at cryogenic temperatures is also possible. Tissue that has
been the subject of many preservation studies is the cornea of eye.
Considerable success has been achieved in transplanting corneal tissues from
cadavers to individual whose corneas have been damaged. Sophisticated
freeze-drying techniques have been applied successfully to corneal tissue
grafts in both man and animal.
In treatment of skin diseases:
Liquid
nitrogen may be used in the treatment of warts and of scarring caused by acne.
It is applied by an ordinary cotton swab, when the lesion is touched, freezing
occurs almost instantly. Contact time may be 10 to 60 seconds, the aim being to
initiate the formation of a blister just sufficient to separate the wart from
the surroundings tissues. The blister appears 6 to8 hours after treatment,
exfoliation of the undesired area occurs and the final cosmetic result is good.
I hope that this paper would
prove to be helpful to those students who are preparing their academic seminars
and would not face not much problems, which I have faced. For any further
information and suggestions please do mail.
–Alok