PDA

View Full Version : a new method of magnet refrigeration: just an idea







Ximing Huang
29-12-2011, 07:00 AM
I would introduce an invention on magnet electrics refrigeration or generation.
In this invention, you may place two pieces of different magnet materials connectted to each other and make a loop.
Place a DC coil around one piece.
Then the two contacts may be one cold one hot.
See attached, please.

yinmorrison
29-12-2011, 07:25 PM
I see a donut.

install monkey
29-12-2011, 07:48 PM
its not new
Thermoelectric cooling uses the Peltier effect (http://www.refrigeration-engineer.com/wiki/Peltier_effect) to create a heat (http://www.refrigeration-engineer.com/wiki/Heat) flux between the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric (http://www.refrigeration-engineer.com/wiki/Thermoelectric) heat pump is a solid-state active heat pump (http://www.refrigeration-engineer.com/wiki/Heat_pump) which transfers heat from one side of the device to the other side against the temperature gradient (from cold to hot), with consumption of electrical energy (http://www.refrigeration-engineer.com/wiki/Electrical_energy). Such an instrument is also called a Peltier device, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC). The Peltier device is a heat pump: when direct current runs through it, heat is moved from one side to the other. Therefore it can be used either for heating or for cooling (refrigeration), although in practice the main application is cooling. It can also be used as a temperature controller that either heats or cools.[1] (http://www.refrigeration-engineer.com/forums/#cite_note-0)
This technology is far less commonly applied to refrigeration than vapor-compression refrigeration (http://www.refrigeration-engineer.com/wiki/Vapor-compression_refrigeration) is. The main advantages of a Peltier cooler (compared to a vapor-compression refrigerator) are its lack of moving parts or circulating liquid, and its small size and flexible shape (form factor). Its main disadvantage is that it cannot simultaneously have low cost and high power efficiency. Many researchers and companies are trying to develop Peltier coolers that are both cheap and efficient. (See Thermoelectric materials (http://www.refrigeration-engineer.com/wiki/Thermoelectric_materials).)
A Peltier cooler is the opposite of a thermoelectric generator (http://www.refrigeration-engineer.com/wiki/Thermoelectric_generator). In a Peltier cooler, electric power is used to generate a temperature difference between the two sides of the device, while in a thermoelectric generator, a temperature difference between the two sides is used to generate electric power. The operation of both is closely related (both are manifestations of the thermoelectric effect (http://www.refrigeration-engineer.com/wiki/Thermoelectric_effect)), and therefore the devices are generally constructed from similar materials using similar designs.[citation needed (http://www.refrigeration-engineer.com/wiki/Wikipedia:Citation_needed)]


Contents [hide (http://www.refrigeration-engineer.com/forums/#)]

1 Performance (http://www.refrigeration-engineer.com/forums/#Performance)
2 Uses (http://www.refrigeration-engineer.com/forums/#Uses)
3 See also (http://www.refrigeration-engineer.com/forums/#See_also)
4 References (http://www.refrigeration-engineer.com/forums/#References)
5 External links (http://www.refrigeration-engineer.com/forums/#External_links)



[edit (http://www.refrigeration-engineer.com/w/index.php?title=Thermoelectric_cooling&action=edit&section=1)] Performancehttp://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Peltierelement.png/300px-Peltierelement.png (http://www.refrigeration-engineer.com/wiki/File:Peltierelement.png)http://bits.wikimedia.org/skins-1.18/common/images/magnify-clip.png (http://www.refrigeration-engineer.com/wiki/File:Peltierelement.png)
Peltier element schematic. Thermoelectric legs are thermally in parallel and electrically in series.


http://upload.wikimedia.org/wikipedia/commons/thumb/8/88/Peltierelement_16x16.jpg/220px-Peltierelement_16x16.jpg (http://www.refrigeration-engineer.com/wiki/File:Peltierelement_16x16.jpg)http://bits.wikimedia.org/skins-1.18/common/images/magnify-clip.png (http://www.refrigeration-engineer.com/wiki/File:Peltierelement_16x16.jpg)
Peltier element (16x16 mm)


Thermoelectric junctions are generally only around 5–10% as efficient as the ideal refrigerator (http://www.refrigeration-engineer.com/wiki/Refrigerator) (Carnot cycle (http://www.refrigeration-engineer.com/wiki/Carnot_cycle)), compared with 40–60% achieved by conventional compression cycle systems (reverse Rankine (http://www.refrigeration-engineer.com/wiki/Rankine_cycle) systems using compression/expansion). Due to the relatively low efficiency, thermoelectric cooling is generally only used in environments where the solid state nature (no moving parts (http://www.refrigeration-engineer.com/wiki/Moving_parts), maintenance-free, compact size) outweighs pure efficiency.
Peltier (thermoelectric) cooler performance is a function of ambient temperature, hot and cold side heat exchanger (heat sink (http://www.refrigeration-engineer.com/wiki/Heat_sink)) performance, thermal load, Peltier module (thermopile) geometry, and Peltier electrical parameters.[citation needed (http://www.refrigeration-engineer.com/wiki/Wikipedia:Citation_needed)]
[edit (http://www.refrigeration-engineer.com/w/index.php?title=Thermoelectric_cooling&action=edit&section=2)] UsesPeltier devices are commonly used in camping (http://www.refrigeration-engineer.com/wiki/Camping) and portable coolers and for cooling electronic components and small instruments. Some electronic equipment intended for military use in the field is thermoelectrically cooled. The cooling effect of Peltier heat pumps can also be used to extract water from the air in dehumidifiers (http://www.refrigeration-engineer.com/wiki/Dehumidifier).
Peltier elements are a common component in thermal cyclers (http://www.refrigeration-engineer.com/wiki/Thermal_cyclers), used for the synthesis of DNA by polymerase chain reaction (PCR (http://www.refrigeration-engineer.com/wiki/PCR)), a common molecular biological technique which requires the rapid heating and cooling of the reaction mixture for denaturation, primer annealing and enzymatic synthesis cycles.
The effect is used in satellites (http://www.refrigeration-engineer.com/wiki/Satellite) and spacecraft (http://www.refrigeration-engineer.com/wiki/Spacecraft) to counter the effect of direct sunlight (http://www.refrigeration-engineer.com/wiki/Sunlight) on one side of a craft by dissipating the heat over the cold shaded side, whereupon the heat is dissipated by thermal radiation (http://www.refrigeration-engineer.com/wiki/Thermal_radiation) into space.
Photon detectors such as CCDs (http://www.refrigeration-engineer.com/wiki/Charge-coupled_device) in astronomical telescopes (http://www.refrigeration-engineer.com/wiki/Telescopes) or very high-end digital cameras (http://www.refrigeration-engineer.com/wiki/Digital_camera) are often cooled down with Peltier elements. This reduces dark counts due to thermal noise (http://www.refrigeration-engineer.com/wiki/Thermal_noise). A dark count occurs when a pixel generates an electron because of a thermal fluctuation rather than because it has received a photon. On digital photos taken at low light these occur as speckles (or "pixel noise").[citation needed (http://www.refrigeration-engineer.com/wiki/Wikipedia:Citation_needed)]
Thermoelectric coolers can be used to cool computer components (http://www.refrigeration-engineer.com/wiki/Computer_cooling) to keep temperatures within design limits, or to maintain stable functioning when overclocking (http://www.refrigeration-engineer.com/wiki/Overclocking). However, due to low efficiency, much more heat is generated than normally, necessitating a very large and noisy fan or a liquid cooling system. In fiber optic applications, where the wavelength of a laser or a component is highly dependent on temperature, Peltier coolers are used along with a thermistor in a feedback loop to maintain a constant temperature and thereby stabilize the wavelength of the device. A Peltier cooler with a heat sink (http://www.refrigeration-engineer.com/wiki/Heat_sink) or waterblock (http://www.refrigeration-engineer.com/wiki/Waterblock) can cool a chip to well below ambient temperature.
http://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/USB_Beverage_Cooler.jpg/220px-USB_Beverage_Cooler.jpg (http://www.refrigeration-engineer.com/wiki/File:USB_Beverage_Cooler.jpg)http://bits.wikimedia.org/skins-1.18/common/images/magnify-clip.png (http://www.refrigeration-engineer.com/wiki/File:USB_Beverage_Cooler.jpg)
A USB-powered beverage cooler


Peltier devices are used in recent products that chill beverages. Some products can also reverse the current to heat the beverage. Products such as the one pictured draw power from the USB (http://www.refrigeration-engineer.com/wiki/USB) port found on computers. However, these products' ability to heat and cool is limited, as the USB 2.0 standard guarantees (http://www.refrigeration-engineer.com/wiki/USB#Power) only 500 mA of current (900 mA in the USB 3.0 standard). sourced from wikepedia

stufus
29-12-2011, 07:52 PM
If I want to refrigerate a magnet , I stick it in the fridge ,simples:D
Cheers
Stu

Brian_UK
29-12-2011, 11:13 PM
I see a doughnut with stripey cream coating, mmmmmm

Tesla
29-12-2011, 11:49 PM
It's not Thermo-Electric refrigeration it is Magnetic cooling used since 1933 to reach initially down to 0.53K absolute. Has been used as a standard method to reach temperatures near to absolute zero. A book called The Quest for Absolute Zero has good description of how it works.

Magoo
30-12-2011, 01:45 AM
I think its called a peltier bridge, the russian space program refined the process.

install monkey
30-12-2011, 11:02 AM
this maybe?
Magnetic refrigerationFrom Wikipedia, the free encyclopedia
(Redirected from Magnetic cooling (http://www.refrigeration-engineer.com/w/index.php?title=Magnetic_cooling&redirect=no))
Jump to: navigation (http://www.refrigeration-engineer.com/forums/#mw-head), search (http://www.refrigeration-engineer.com/forums/#p-search)
http://upload.wikimedia.org/wikipedia/commons/thumb/0/08/Magnetocaloric_effect1_04a.svg/400px-Magnetocaloric_effect1_04a.svg.png (http://www.refrigeration-engineer.com/wiki/File:Magnetocaloric_effect1_04a.svg)http://bits.wikimedia.org/skins-1.18/common/images/magnify-clip.png (http://www.refrigeration-engineer.com/wiki/File:Magnetocaloric_effect1_04a.svg)
Gadolinium alloy heats up inside the magnetic field and loses thermal energy to the environment, so it exits the field cooler than when it entered.


Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This technique can be used to attain extremely low temperatures (http://www.refrigeration-engineer.com/wiki/Temperature) (well below 1 K (http://www.refrigeration-engineer.com/wiki/Kelvin)), as well as the ranges used in common refrigerators (http://www.refrigeration-engineer.com/wiki/Refrigerator), depending on the design of the system.
The effect was first observed by the German physicist Emil Warburg (http://www.refrigeration-engineer.com/wiki/Emil_Warburg) (1880) and the fundamental principle was suggested by Debye (http://www.refrigeration-engineer.com/wiki/Peter_Debye) (1926) and Giauque (http://www.refrigeration-engineer.com/wiki/William_Giauque) (1927).[1] (http://www.refrigeration-engineer.com/forums/#cite_note-0) The first working magnetic refrigerators were constructed by several groups beginning in 1933. Magnetic refrigeration was the first method developed for cooling below about 0.3 K (a temperature attainable by 3He (http://www.refrigeration-engineer.com/wiki/Helium-3) refrigeration, that is pumping on the 3He vapors).


Contents [hide (http://www.refrigeration-engineer.com/forums/#)]

1 The magnetocaloric effect (http://www.refrigeration-engineer.com/forums/#The_magnetocaloric_effect)

1.1 Thermodynamic cycle (http://www.refrigeration-engineer.com/forums/#Thermodynamic_cycle)
1.2 Applied technique (http://www.refrigeration-engineer.com/forums/#Applied_technique)

2 Working materials (http://www.refrigeration-engineer.com/forums/#Working_materials)

2.1 Paramagnetic salts (http://www.refrigeration-engineer.com/forums/#Paramagnetic_salts)
2.2 Nuclear demagnetization (http://www.refrigeration-engineer.com/forums/#Nuclear_demagnetization)

3 Commercial development (http://www.refrigeration-engineer.com/forums/#Commercial_development)

3.1 Current and future uses (http://www.refrigeration-engineer.com/forums/#Current_and_future_uses)

4 History (http://www.refrigeration-engineer.com/forums/#History)

4.1 Room temperature devices (http://www.refrigeration-engineer.com/forums/#Room_temperature_devices)

5 See also (http://www.refrigeration-engineer.com/forums/#See_also)
6 References (http://www.refrigeration-engineer.com/forums/#References)
7 Further reading (http://www.refrigeration-engineer.com/forums/#Further_reading)
8 External links (http://www.refrigeration-engineer.com/forums/#External_links)



[edit (http://www.refrigeration-engineer.com/w/index.php?title=Magnetic_refrigeration&action=edit&section=1)] The magnetocaloric effectThe magnetocaloric effect (MCE, from magnet (http://www.refrigeration-engineer.com/wiki/Magnet) and calorie (http://www.refrigeration-engineer.com/wiki/Calorie)) is a magneto-thermodynamic (http://www.refrigeration-engineer.com/wiki/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 by low temperature physicists as adiabatic (http://www.refrigeration-engineer.com/wiki/Adiabatic_process) demagnetization, due to the application of the process specifically to create 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 (http://www.refrigeration-engineer.com/wiki/Phonon)) present in the material. If the material is isolated so that no energy is allowed to (re)migrate into the material during this time, i.e., an adiabatic process, the temperature (http://www.refrigeration-engineer.com/wiki/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 (http://www.refrigeration-engineer.com/wiki/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 (http://www.refrigeration-engineer.com/wiki/Ferromagnetism) as energy is added.
One of the most notable examples of the magnetocaloric effect is in the chemical element gadolinium (http://www.refrigeration-engineer.com/wiki/Gadolinium) and some of its alloys (http://www.refrigeration-engineer.com/wiki/Alloys). Gadolinium's temperature is observed to increase when it enters certain magnetic fields. When it leaves the magnetic field, the temperature drops. The effect is considerably stronger for the gadolinium alloy (http://www.refrigeration-engineer.com/wiki/Alloy) Gd (http://www.refrigeration-engineer.com/wiki/Gadolinium)5(Si (http://www.refrigeration-engineer.com/wiki/Silicon)2Ge (http://www.refrigeration-engineer.com/wiki/Germanium)2).[2] (http://www.refrigeration-engineer.com/forums/#cite_note-Ames-1) Praseodymium (http://www.refrigeration-engineer.com/wiki/Praseodymium) alloyed with nickel (http://www.refrigeration-engineer.com/wiki/Nickel) (Pr (http://www.refrigeration-engineer.com/wiki/Praseodymium)Ni (http://www.refrigeration-engineer.com/wiki/Nickel)5) has such a strong magnetocaloric effect that it has allowed scientists to approach within one thousandth of a degree of absolute zero (http://www.refrigeration-engineer.com/wiki/Absolute_zero).[3] (http://www.refrigeration-engineer.com/forums/#cite_note-2)
[edit (http://www.refrigeration-engineer.com/w/index.php?title=Magnetic_refrigeration&action=edit&section=2)] Thermodynamic cyclehttp://upload.wikimedia.org/wikipedia/commons/c/cb/MCE.gif (http://www.refrigeration-engineer.com/wiki/File:MCE.gif)http://bits.wikimedia.org/skins-1.18/common/images/magnify-clip.png (http://www.refrigeration-engineer.com/wiki/File:MCE.gif)
Analogy between magnetic refrigeration and vapor cycle or conventional refrigeration. H = externally applied magnetic field; Q = heat quantity; P = pressure; ΔTad = adiabatic temperature variation


The cycle is performed as a refrigeration cycle (http://www.refrigeration-engineer.com/wiki/Refrigeration_cycle), analogous to the Carnot cycle (http://www.refrigeration-engineer.com/wiki/Carnot_cycle), and can be described at a starting point whereby the chosen working substance is introduced into a magnetic field (http://www.refrigeration-engineer.com/wiki/Magnetic_field), i.e., the magnetic flux density is increased. The working material is the refrigerant, and starts in thermal equilibrium with the refrigerated environment.

Adiabatic magnetization: A magnetocaloric substance is placed in an insulated environment. The increasing external magnetic field (+H) causes the magnetic dipoles (http://www.refrigeration-engineer.com/wiki/Magnetic_dipole) of the atoms to align, thereby decreasing the material's magnetic entropy (http://www.refrigeration-engineer.com/wiki/Entropy) and heat capacity (http://www.refrigeration-engineer.com/wiki/Heat_capacity). Since overall energy is not lost (yet) and therefore total entropy (http://www.refrigeration-engineer.com/wiki/Entropy) is not reduced (according to thermodynamic laws), the net result is that the item heats up (T + ΔTad).


Isomagnetic enthalpic transfer: This added heat can then be removed (-Q) by a fluid or gas — gaseous or liquid helium (http://www.refrigeration-engineer.com/wiki/Helium), for example. The magnetic field is held constant to prevent the dipoles from reabsorbing the heat. Once sufficiently cooled, the magnetocaloric substance and the coolant are separated (H=0).


Adiabatic demagnetization: The substance is returned to another adiabatic (insulated) condition so the total entropy remains constant. However, this time the magnetic field is decreased, the thermal energy causes the magnetic moments to overcome the field, and thus the sample cools, i.e., an adiabatic temperature change. Energy (and entropy) transfers from thermal entropy to magnetic entropy (disorder of the magnetic dipoles).


Isomagnetic entropic transfer: The magnetic field is held constant to prevent the material from heating back up. The material is placed in thermal contact with the environment being refrigerated. Because the working material is cooler than the refrigerated environment (by design), heat energy migrates into the working material (+Q).
Once the refrigerant and refrigerated environment are in thermal equilibrium, the cycle begins again.
[edit (http://www.refrigeration-engineer.com/w/index.php?title=Magnetic_refrigeration&action=edit&section=3)] Applied techniqueThe basic operating principle of an adiabatic demagnetization refrigerator (ADR) is the use of a strong magnetic field (http://www.refrigeration-engineer.com/wiki/Magnetic_field) to control the entropy (http://www.refrigeration-engineer.com/wiki/Entropy) of a sample of material, often called the "refrigerant". Magnetic field constrains the orientation of magnetic dipoles (http://www.refrigeration-engineer.com/wiki/Dipole) in the refrigerant. The stronger the magnetic field, the more aligned the dipoles are, and this corresponds to lower entropy (http://www.refrigeration-engineer.com/wiki/Entropy) and heat capacity (http://www.refrigeration-engineer.com/wiki/Specific_heat_capacity) because the material has (effectively) lost some of its internal degrees of freedom (http://www.refrigeration-engineer.com/wiki/Degrees_of_freedom_(physics_and_chemistry)). If the refrigerant is kept at a constant temperature through thermal contact with a heat (http://www.refrigeration-engineer.com/wiki/Heat) sink (usually liquid helium (http://www.refrigeration-engineer.com/wiki/Helium)) while the magnetic field is switched on, the refrigerant must lose some energy (http://www.refrigeration-engineer.com/wiki/Energy) because it is equilibrated (http://www.refrigeration-engineer.com/wiki/Thermodynamic_equilibrium) with the heat sink. When the magnetic field is subsequently switched off, the heat capacity of the refrigerant rises again because the degrees of freedom associated with orientation of the dipoles are once again liberated, pulling their share of equipartitioned (http://www.refrigeration-engineer.com/wiki/Equipartition_of_energy) energy from the motion (http://www.refrigeration-engineer.com/wiki/Kinetic_energy) of the molecules (http://www.refrigeration-engineer.com/wiki/Molecule), thereby lowering the overall temperature of a system (http://www.refrigeration-engineer.com/wiki/System) with decreased energy. Since the system is now insulated (http://www.refrigeration-engineer.com/wiki/Thermal_insulation) when the magnetic field is switched off, the process is adiabatic (http://www.refrigeration-engineer.com/wiki/Adiabatic), i.e., the system can no longer exchange energy with its surroundings (the heat sink), and its temperature decreases below its initial value, that of the heat sink.
The operation of a standard ADR proceeds roughly as follows. First, a strong magnetic field is applied to the refrigerant, forcing its various magnetic dipoles to align and putting these degrees of freedom of the refrigerant into a state of lowered entropy. The heat sink then absorbs the heat released by the refrigerant due to its loss of entropy. Thermal contact with the heat sink is then broken so that the system is insulated, and the magnetic field is switched off, increasing the heat capacity of the refrigerant, thus decreasing its temperature below the temperature of the helium heat sink. In practice, the magnetic field is decreased slowly in order to provide continuous cooling and keep the sample at an approximately constant low temperature. Once the field falls to zero or to some low limiting value determined by the properties of the refrigerant, the cooling power of the ADR vanishes, and heat leaks will cause the refrigerant to warm up.
[edit (http://www.refrigeration-engineer.com/w/index.php?title=Magnetic_refrigeration&action=edit&section=4)] Working materialsThe magnetocaloric effect is an intrinsic property of a magnetic solid. This thermal response of a solid to the application or removal of magnetic fields is maximized when the solid is near its magnetic ordering temperature.
The magnitudes of the magnetic entropy and the adiabatic temperature changes are strongly dependent upon the magnetic order process: the magnitude is generally small in antiferromagnets, ferrimagnets and spin glass systems; it can be substantial for normal ferromagnets which undergo a second order magnetic transition; and it is generally the largest for a ferromagnet which undergoes a first order magnetic transition.
Also, crystalline electric fields and pressure can have a substantial influence on magnetic entropy and adiabatic temperature changes.
Currently, alloys (http://www.refrigeration-engineer.com/wiki/Alloys) of gadolinium producing 3 to 4 K per tesla (http://www.refrigeration-engineer.com/wiki/Tesla_(unit)) (K/T) of change in a magnetic field can be used for magnetic refrigeration.
Recent research on materials that exhibit a giant entropy change showed that Gd5(SixGe1−x)4, La(FexSi1−x)13Hx and MnFeP1−xAsx alloys, for example, are some of the most promising substitutes for gadolinium and its alloys — GdDy, GdTb, etc. These materials are called giant magnetocaloric effect materials (GMCE).
Gadolinium and its alloys are the best material available today for magnetic refrigeration near room temperature since they undergo second-order phase transitions which have no magnetic or thermal hysteresis involved.
[edit (http://www.refrigeration-engineer.com/w/index.php?title=Magnetic_refrigeration&action=edit&section=5)] Paramagnetic saltsThe originally suggested refrigerant was a paramagnetic (http://www.refrigeration-engineer.com/wiki/Paramagnetism) salt (http://www.refrigeration-engineer.com/wiki/Salt), such as cerium (http://www.refrigeration-engineer.com/wiki/Cerium) magnesium (http://www.refrigeration-engineer.com/wiki/Magnesium) nitrate (http://www.refrigeration-engineer.com/wiki/Nitrate). The active magnetic (http://www.refrigeration-engineer.com/wiki/Magnetic_field) dipoles (http://www.refrigeration-engineer.com/wiki/Dipole) in this case are those of the electron shells (http://www.refrigeration-engineer.com/wiki/Electron_shell) of the paramagnetic atoms.
In a paramagnetic salt ADR, the heat sink is usually provided by a pumped 4He (about 1.2 K) or 3He (about 0.3 K) cryostat (http://www.refrigeration-engineer.com/wiki/Cryostat). An easily attainable 1 T magnetic field is generally required for the initial magnetization. The minimum temperature attainable is determined by the self-magnetization tendencies of the chosen refrigerant salt, but temperatures from 1 to 100 mK are accessible. Dilution refrigerators (http://www.refrigeration-engineer.com/wiki/Dilution_refrigerator) had for many years supplanted paramagnetic salt ADRs, but interest in space-based and simple to use lab-ADRs has remained, due to the complexity and unreliability of the dilution refrigerator
Eventually paramagnetic salts become either diamagnetic (http://www.refrigeration-engineer.com/wiki/Diamagnetism) or ferromagnetic (http://www.refrigeration-engineer.com/wiki/Ferromagnetism), limiting the lowest temperature which can be reached using this method.
[edit (http://www.refrigeration-engineer.com/w/index.php?title=Magnetic_refrigeration&action=edit&section=6)] Nuclear demagnetizationOne variant of adiabatic demagnetization that continues to find substantial research application is nuclear demagnetization refrigeration (NDR). NDR follows the same principle described above, but in this case the cooling power arises from the magnetic dipoles of the nuclei (http://www.refrigeration-engineer.com/wiki/Spin_(physics)#Spin_and_magnetic_moment) of the refrigerant atoms, rather than their electron configurations. Since these dipoles are of much smaller magnitude, they are less prone to self-alignment and have lower intrinsic minimum fields. This allows NDR to cool the nuclear spin system to very low temperatures, often 1 ΅K or below. Unfortunately, the small magnitudes of nuclear magnetic dipoles also makes them less inclined to align to external fields. Magnetic fields of 3 teslas or greater are often needed for the initial magnetization step of NDR.
In NDR systems, the initial heat sink must sit at very low temperatures (10–100 mK). This precooling is often provided by the mixing chamber of a dilution refrigerator or a paramagnetic salt.
[edit (http://www.refrigeration-engineer.com/w/index.php?title=Magnetic_refrigeration&action=edit&section=7)] Commercial developmentThis refrigeration, once proven viable, could be used in any possible application where cooling, heating or power generation is used today. Since it is only at an early stage of development, there are several technical and efficiency issues that should be analyzed. The magnetocaloric refrigeration system is composed of pumps, electric motors, secondary fluids, heat exchangers of different types, magnets and magnetic materials. These processes are greatly affected by irreversibilities and should be adequately considered.
Appliances using this method could have a smaller environmental impact (http://www.refrigeration-engineer.com/wiki/Environmental_impact_assessment) if the method is perfected and replaces hydrofluorocarbon (HFCs) (http://www.refrigeration-engineer.com/wiki/Haloalkane) refrigerators (some refrigerators still use HFCs (http://www.refrigeration-engineer.com/wiki/Haloalkane) which have considerable effect on the ozone layer. At present, however, the superconducting magnets that are used in the process have to themselves be cooled down to the temperature of liquid nitrogen (http://www.refrigeration-engineer.com/wiki/Liquid_nitrogen), or with even colder, and relatively expensive, liquid helium (http://www.refrigeration-engineer.com/wiki/Helium). Considering these fluids have boiling points of 77.36 K and 4.22 K respectively, the technology is clearly not cost- and energy-efficient for home appliances, but for experimental, laboratory, and industrial use only.
Recent research on materials that exhibit a large entropy change showed that alloys are some of the most promising substitutes of gadolinium and its alloys — GdDy, GdTb, etc. Gadolinium and its alloys are the best material available today for magnetic refrigeration near room temperature. There are still some thermal and magnetic hysteresis (http://www.refrigeration-engineer.com/wiki/Hysteresis) problems to be solved for them to become truly useful [V. Provenzano, A.J. Shapiro, and R.D. Shull, Nature 429, 853 (2004)] and scientists are working hard to achieve this goal. Thermal hysteresis problems is solved therefore in adding ferrite (5:4).[citation needed (http://www.refrigeration-engineer.com/wiki/Wikipedia:Citation_needed)]
Research and a demonstration proof of concept in 2001 succeeded in applying commercial-grade materials and permanent magnets at room temperatures to construct a magnetocaloric refrigerator which promises wide use.[4] (http://www.refrigeration-engineer.com/forums/#cite_note-Ames_Lab-2001-3)
This technique has been used for many years in cryogenic (http://www.refrigeration-engineer.com/wiki/Cryogenics) systems for producing further cooling in systems already cooled to temperatures of 4 K and lower. In England, a company called Cambridge Magnetic Refrigeration (http://www.cmr.uk.com/) produces cryogenic systems based on the magnetocaloric effect.
On August 20, 2007, the Risψ National Laboratory (http://www.refrigeration-engineer.com/wiki/Ris%C3%B8_National_Laboratory) at the Technical University of Denmark (http://www.refrigeration-engineer.com/wiki/Technical_University_of_Denmark), claimed to have reached a milestone in their magnetic cooling research when they reported a temperature span of 8.7 C.[5] (http://www.refrigeration-engineer.com/forums/#cite_note-4) They hope to introduce the first commercial applications of the technology by 2010.
[edit (http://www.refrigeration-engineer.com/w/index.php?title=Magnetic_refrigeration&action=edit&section=8)] Current and future usesThere are still some thermal and magnetic hysteresis (http://www.refrigeration-engineer.com/wiki/Hysteresis) problems to be solved for these first-order phase transition materials that exhibit the GMCE to become really useful; this is a subject of current research. A useful review on magnetocaloric materials published in 2005 is entitled "Recent developments in magnetocaloric materials" by Dr. Karl A. Gschneidner, et al.[6] (http://www.refrigeration-engineer.com/forums/#cite_note-5) This effect is currently being explored to produce better refrigeration techniques, especially for use in spacecraft (http://www.refrigeration-engineer.com/wiki/Spacecraft). This technique is already used to achieve cryogenic temperatures in the laboratory setting (below 10K). As an object displaying MCE is moved into a magnetic field, the magnetic spins align, lowering the entropy. Moving that object out of the field allows the object to increase its entropy by absorbing heat from the environment and disordering the spins. In this way, heat can be taken from one area to another. Should materials be found to display this effect near room temperature, refrigeration without the need for compression may be possible, increasing energy efficiency.

The use of this technology for domestic refrigerators though is very remote due to the high efficiency of current Vapor-compression refrigeration (http://www.refrigeration-engineer.com/wiki/Vapor-compression_refrigeration) cycles, which typically achieve performance coefficients of 60% of that of a theoretical ideal Carnot cycle.
This technology could eventually compete with other cryogenic heat pumps for gas liquefaction purposes.
Gschneidner stated in 1999 that: "large-scale applications using magnetic refrigeration, such as commercial air conditioning and supermarket refrigeration systems, could be available within 5–10 years. Within 10–15 years, the technology could be available in home refrigerators and air conditioners."[7] (http://www.refrigeration-engineer.com/forums/#cite_note-6)
[edit (http://www.refrigeration-engineer.com/w/index.php?title=Magnetic_refrigeration&action=edit&section=9)] HistoryThe effect was discovered in pure iron (http://www.refrigeration-engineer.com/wiki/Iron) in 1880 by German physicist Emil Warburg (http://www.refrigeration-engineer.com/wiki/Emil_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, Peter Debye in 1926 and William Giauque in 1927.
This cooling technology was first demonstrated experimentally by chemist Nobel Laureate William F. Giauque (http://www.refrigeration-engineer.com/wiki/William_F._Giauque) and his colleague D. P. MacDougall (http://www.refrigeration-engineer.com/w/index.php?title=D._P._MacDougall&action=edit&redlink=1) in 1933 for cryogenic purposes when they reached 0.25 K.[8] (http://www.refrigeration-engineer.com/forums/#cite_note-7) Between 1933 and 1997, a number of advances in utilization of the MCE for cooling occurred.[9] (http://www.refrigeration-engineer.com/forums/#cite_note-8)[10] (http://www.refrigeration-engineer.com/forums/#cite_note-9)[11] (http://www.refrigeration-engineer.com/forums/#cite_note-10)[12] (http://www.refrigeration-engineer.com/forums/#cite_note-11)
In 1997, the first near room temperature proof of concept (http://www.refrigeration-engineer.com/wiki/Proof_of_concept) magnetic refrigerator was demonstrated by Karl A. Gschneidner, Jr. (http://www.refrigeration-engineer.com/w/index.php?title=Karl_A._Gschneidner,_Jr.&action=edit&redlink=1) by the Iowa State University (http://www.refrigeration-engineer.com/wiki/Iowa_State_University) at Ames Laboratory (http://www.refrigeration-engineer.com/wiki/Ames_Laboratory). This event attracted interest from scientists and companies worldwide who started developing new kinds of room temperature materials and magnetic refrigerator designs.[2] (http://www.refrigeration-engineer.com/forums/#cite_note-Ames-1) A major breakthrough came 2002 when a group at the University of Amsterdam demonstrated the giant magnetocaloric effect in MnFe(P,As) alloys that are based on earth abundant materials.[13] (http://www.refrigeration-engineer.com/forums/#cite_note-12)
Refrigerators based on the magnetocaloric effect have been demonstrated in laboratories, using magnetic fields starting at 0.6 T up to 10 T. Magnetic fields above 2 T are difficult to produce with permanent magnets and are produced by a superconducting magnet (http://www.refrigeration-engineer.com/wiki/Superconducting_magnet) (1 T is about 20,000 times the Earth's magnetic field (http://www.refrigeration-engineer.com/wiki/Earth%27s_magnetic_field)).