magnetic refrigeration full report

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Magnetic Refrigeration
1.0 ABSTRACT
The objective of  this effort is to study the Magnetic Refrigeration which uses solid materials as
the   refrigerant.  These   materials  demonstrate  the  unique  property  known  as  magneto caloric
effect,   which   means   that   they   increase   and   decrease   in   temperature   when
magnetized/demagnetized.  This   effect   has   been  observed  for  many  years  and  was   used  for
cooling   near   absolute   zero.   Recently  materials   are   being   developed   which   have   sufficient
temperature and entropy change to make them useful for  a wide range temperature applications.
Benefits of magnetic refrigeration are lower cost, longer life, lower weight and higher efficiency
because it only requires one moving part-the rotating disc on which the magneto caloric material
is  mounted. The unit uses no gas  compressor, no pumps, no working fluid, no valves and no
ozone   destroying   chlorofluorocarbons/hydro   chlorofluorocarbons.   potential   commercial
applications   include   cooling   of   electronics,   super   conducting   components   used   in
telecommunications equipment, home and commercial refrigerator ,heat pumps, air conditioning
for homes, offices and automobiles and virtually any places where refrigeration is needed.
2.0   INTRODUCTION
Magnetic   refrigeration  is   a   cooling   technology   based   on   the  magnetocaloric   effect.   This
technique can be used to attain extremely low temperatures (well below 1 kelvin), as well as the
ranges used in common refrigerators, depending on the design of the system.
2.1 HISTORY
The  effect  was  discovered in pure  iron in 1881 by  E. Warburg. Originally, the cooling effect
varied between 0.5 to 2 K/T.
Major  advances first appeared in the late 1920s when cooling via adiabatic demagnetization was
independently proposed by two scientists: Debye (1926) and Giauque (1927).
The process was demonstrated a few years later  when Giauque and MacDougall in 1933 used it
to reach a temperature of 0.25 K. Between 1933 and 1997, a number of advances in utilization of
the MCE for cooling occurred.
This   cooling  technology  was  first   demonstrated   experimentally   by  chemist   Nobel  Laureate
William F. Giauque and his colleague Dr. D.P. MacDougall in 1933 for cryogenic purposes (they
reached 0.25 K)
Between 1933 and 1997, a number  of  advances occurred which have been described in some
reviews.
In   1997,   the   first   near   room   temperature  proof   of   concept  magnetic   refrigerator   was
demonstrated   by   Prof.  Karl   A.   Gschneidner,   Jr.  by   the  Iowa   State   University  at  Ames
Laboratory. This event attracted interest from scientists  and companies  worldwide that started
developing new kinds of room temperature materials and magnetic refrigerator designs.
Refrigerators based on the magnetocaloric effect have been demonstrated in laboratories, using
magnetic fields  starting  at  0.6 T  up to  10  teslas. Magnetic  fields  above  2 T  are  difficult to
produce with permanent magnets and are produced by a superconducting magnet (1 tesla is about
20,000 times the Earth's magnetic field).
2.2   MAGNETO CALORIC EFFECT
The   Magneto  caloric  effect   (MCE,  from  magnet  and  calorie)   is   a  magneto-thermodynamic
phenomenon in which a reversible change in temperature  of  a suitable material is caused by
exposing   the   material   to   a   changing   magnetic   field.   This   is   also   known   as  adiabatic
demagnetization  by   low   temperature   physicists,   due   to   the   application   of   the   process
specifically  to  affect  a  temperature  drop.  In that  part  of  the  overall  refrigeration  process, a
decrease in the strength of an externally applied magnetic field allows the magnetic domains of a
chosen (magnetocaloric) material to become disoriented from the magnetic field by the agitating
action of  the thermal energy (phonons) present in the material. If the material is isolated so that
no energy is allowed to (e) migrate into the material during this time (i.e. an adiabatic process),
the  temperature drops  as  the domains absorb the thermal energy to perform their  reorientation.
The randomization of the domains occurs in a similar  fashion to the randomization at the curie
temperature, except that magnetic dipoles overcome a decreasing external magnetic field while
energy   remains   constant,   instead   of   magnetic   domains   being   disrupted   from   internal
ferromagnetism as energy is added.
One  of  the  most  notable  examples  of   the  magnetocaloric  effect  is  in the  chemical  element
gadolinium  and some of  its  alloys. Gadolinium's  temperature is  observed to increase  when it
enters  certain magnetic fields.  When  it  leaves  the  magnetic  field,  the  temperature  returns  to
normal. The effect is considerably stronger  for the gadolinium alloy Gd5(Si2Ge2). Praseodymium
alloyed with nickel (Pr
  Ni
  5) has such a strong magnetocaloric effect that it has allowed scientists
to approach within one thousandth of a degree of absolute zero.
Magnetic Refrigeration is also called as Adiabatic Magnetization.
3.0 CONSTRUCTION AND WORKING
3.1 COMPONENTS REQUIRED
1. Magnets
2. Hot Heat exchanger
3. Cold Heat Exchanger
4. Drive
5. Magneto caloric wheel