What Is Magnetic refrigeration

What Is Magnetic refrigeration
he magnetocaloric effect (MCE, from magnet and calorie) is a magneto-thermodynamic phenomenon in which a temperature change 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 demagnetization. In that part of the refrigeration process, a decrease in the strength of an externally applied magnetic field allows the magnetic domains of a 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 (re)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 of a ferromagnetic material, 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 increases when it enters certain magnetic fields. When it leaves the magnetic field, the temperature drops. The effect is considerably stronger for the gadolinium alloy (Gd
5Si
2Ge
2).[8] Praseodymium alloyed with nickel (PrNi
5) has such a strong magnetocaloric effect that it has allowed scientists to approach to within one milliKelvin, one thousandth of a degree of absolute zero.[9]

1. MAGNETIC REFRIGERATION Group Members Ehtisham Ahsan BSME 01153113 Hafiz Usama Akhtar BSME 01153120 Zain ul Abideen BSME 01153130 Asjad Ahmed Khan BSME 01153143 Hafiz Shahreyar Raza BSME 01153115

2. EHTISHAM AHSAN BSME 01153113

3. INTRODUCTION A compressor is a mechanical device like a pump that is used in various different applications. Basically it is a refrigerant gas pump in which the evaporator supplies gaseous refrigerant at a low pressure and increases it to a greater pressure. Upon being compressed, the temperature and pressure of the vapor are increased. The gaseous refrigerant is delivered to the condenser at a pressure at which condensation occurs at an appropriate temperature. COMPRESSOR

4. TYPES OF COMPRESSOR There are basically 5 types of air conditioner compressor that are commonly used in the HVAC industry: Reciprocating Scroll Screw Rotary Centrifugal

5. MAGNETIC REFRIGERATION It is a cooling technology based on the magneto caloric 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. It is a physical process that exploits the magnetic properties of certain solid materials to produce refrigeration.

6. The refrigerant is often a paramagnetic salt, such as cerium magnesium nitrate. It gives cooling nearest to absolute zero than any other method hence it made liquification of gases easier. At the same time it does not emit any CFC or HCFC compounds hence it never affects our environment specially OZONE layer.

7. HISTORY Magneto caloric effect was discovered in pure iron in 1881 by E. Warburg. Debye (1926) & Giauque (1927) proposed a improved technique of cooling via adiabatic demagnetization independently. The cooling technology was first demonstrated experimentally in 1933 by chemist Nobel Laureate William F.Giauque & his colleague Dr.D.P. MacDougall for cryogenic purposes. In 1997,Prof. Karl A. Gscheidner, Jr. by the lowa State University at Ames Laboratory demonstrated the first near room temperature proof of concept magnetic refrigerator.

8. MAGNETIC CALORIC EFFECT MCE is a magneto-thermodynamic phenomenon in which a reversible change in temperature of a suitable material is caused by exposing the material to changing magnetic field. All magnets bears a property called Currie effect i.e. If a temperature of magnet is increased from lower to higher range at certain temperature magnet looses the magnetic field.

9. Currie temperature Depends on individual property of each material. As Energy input to the magnet is increased the orientation of them magnetic dipoles in a magnet starts loosing orientation. And vice a versa at curie temperature as magnet looses energy to the media it regains the property.

10. Zain ul Abideen BSME 01153130

11. WORKING PRINCIPLE

12. THERMODYNAMIC CYCLE

13. VIDEO

14. DETAILS OF THERMODYNAMIC CYCLE Process is similar to gas compression and expansion cycle as used in regular refrigeration cycle Steps of thermodynamic Cycle Adiabatic Magnetization Isomagnetic Enthalpy Transfer Adiabatic demagnetization Isomagnetic Entropic Transfer

15. ADIABETIC MAGNETIZATION Substance placed in insulated environment. Magnetic field +H increased. This causes the magnetic dipoles of the atoms to align. The net result is that total Entropy of the item is not reduced and item heats up (T + ΔTad ).

16. ISOMAGNETIC ENTHALPY TRANSFER Added heat removed by a fluid like water or helium (-Q). Magnetic Field held constant to prevent the dipoles from reabsorbing the heat. After a sufficient cooling Magneto caloric material and coolant are separated (H=0).

17. Hafiz Usama Akhtar BSME 01153120

18. ADIABETIC DEMAGNETIZATION Substance returned to another adiabatic(insulated) condition Entropy remains constant Magnetic field is decreased Thermal Energy causes the Magnetic moments to overcome the field and sample cools(adiabatic temperature change) Energy transfers from thermal entropy to magnetic entropy(disorder of the magnetic dipoles)

19. ISOMAGNETIC ENTROPIC TRANSFER Material is placed in thermal contact with the Environment being refrigerated. Magnetic field held constant to prevent material from heating back up. Because the working material is cooler than the refrigerated environment, heat energy migrates into the working material (+Q) Once the refrigerant and refrigerated environment are in thermal equilibrium, the cycle continuous.

20. Construction Components required for construction :- Magnets Hot Heat exchanger Cold Heat Exchanger Drive Magneto caloric wheel

21. WORKING MATERIALS MCE is an intrinsic property of a magnetic solid Ease of application and removal of magnetic effect is most desired property of material Alloys of gadolinium produce 3 to 4 K per tesla of change in magnetic field are used for magnetic refrigeration or power generation purposes. Ferro magnets, antiferromagnets and spin glass systems are not suitable for this application. Gd5(SixGe1 − x)4, La(FexSi1 − x)13Hx and MnFeP1 − xAsx alloys are some of the most promising substitutes for Gadolinium and its alloys

22. Asjad Ahmed Khan BSME 01153143

23. REGENERATORS Magnetic refrigeration requires excellent heat transfer to and from the solid magnetic material. Efficient heat transfer requires the large surface areas offered by porous materials. When these porous solids are used in refrigerators, they are referred to as “Regenerators”

24. Typical regenerator geometries include: Tubes Perforated plates Wire screens Particle beds

25. SUPER CONDUCTING MAGNETS Most practical magnetic refrigerators are based on superconducting magnets operating at cryogenic temperatures (i.e., at -269 C or 4 K) These devices are electromagnets that conduct electricity with essentially no resistive losses. The superconducting wire most commonly used is made of a Niobium-Titanium alloy

26. SUPER CONDUCTING MAGNETS

27. AMR A regenerator that undergoes cyclic heat transfer operations and the magneto caloric effect is called an Active Magnetic Regenerator. An AMR should be designed to possess the following attributes:- High heat transfer rate High magneto caloric effect Sufficient structural integrity Low thermal conduction in the direction of fluid flow Affordable materials Ease of manufacture

28. BENEFITS TECHNICAL High Efficiency Reduced Operating Cost Compactness Reliability SOCIO-ECONOMIC Competition in Global Market Low Capital Cost Key Factor to new technologies

29. Hafiz Shahreyar Raza BSME 01153115

30. FUTURE APPLICATIONS Some of the future applications are:- Magnetic household refrigeration appliances Magnetic cooling and air conditioning in buildings and houses Central in spacecraft and laboratory applications Refrigeration in medicine Cooling in food industry and storage Cooling in transportation Cooling of electronic equipments

31. ADVANTAGES Purchase cost may be high, but running costs are 20% less than the conventional chillers. Thus life cycle cost is much less. Ozone depleting refrigerants are avoided in this system, hence it more eco-friendly. Energy conservation and reducing the energy costs are added advantages. The efficiency of magnetic refrigeration is 60% to 70% as compared to Carnot cycle. Magnetic refrigeration is totally maintenance free & mechanically simple in construction.

32. DISADVANTAGES As every coin has 2 sides, this technique also posses some drawbacks to be worked on The initial investment is more as compared with conventional refrigeration. The magneto caloric materials are rare earth materials hence their availability also adds up an disadvantage in MAGNETIC REFRIGERATION.

33. CONCLUSION It is a technology that has proven to be environmentally safe. Computer models have shown 25% efficiency improvement over vapor compression Systems. In order to make the magnetic refrigerator commercially Viable, scientists need to know how to achieve larger temperature swings and also permanent magnets which can produce strong magnetic fields of order 10 tesla. There are still some thermal and magnetic hysteresis problems to be solved for the materials that exhibit the MCE to become really useful.