MAGNETIC REFRIGERATION Presented By, Ananthu Sivan Feby Philip Abraham S4, Dept. of Mechanical Engineering, Mohandas College of Engineering & Technology, Anad, Trivandrum
CONTENTS • INTRODUCTION • WHAT IS MAGNETIC REFRIGERATION?? • MAGNETOCALORIC EFFECT • HOW DOES AN ADR WORK?? • MAGNETIC REFRIGERATION CYCLE • CONSTRUCTIONAL COMPONENTS • WORKING MATERIALS • GMCE MATERIALS • ALTERNATIVE TECHNIQUES • COMMERCIAL DEVELOPMENT • CONCLUSION
INTRODUCTION • Refrigeration is the process of removing heat from an enclosed space or from a substance and moving it to a place where it is unobjectionable • The primary objective of refrigeration is lowering the temperature of the enclosed space or substance and then maintaining that lower temperature.
What is Magnetic Refrigeration?? • Magnetic refrigeration is a cooling technology based on the magneto caloric effect. • It is used to attain temperature well below 1 Kelvin. • Magnetic refrigeration currently finds application in cryogenics.
Magneto-caloric Effect • Some magnetic materials heat up when they are placed in a magnetic field and cool down when they are removed from a magnetic field. This is known as the magnetocaloric effect. • The effect was discovered in pure iron in 1880 by German physicist Emil Warburg • In 1997, the first near room temperature proof of concept magnetic refrigerator was demonstrated by Prof. Karl A. Gschneidner
Illustration of the Magnetocaloric effect Gadolinium alloy heats up inside the magnetic field and loses thermal energy by irradiation, so that it exits the field cooler than when it entered.
How Does an ADR Work?? Magnetic Refrigeration Cycle • Adiabatic magnetization • Isomagneticenthalpic transfer • Adiabatic demagnetization • Isomagnetic entropic transfer
Adiabatic Magnetization • Working material is placed in an insulated environment • Increasing magnetic field is applied • Magnetic dipoles of the atoms of the material align • Decreases material’s magnetic entropy and heat capacity • Total entropy of the material remains conserved (Laws of Thermodynamics) • Results in heating up of the material (T+ΔTad)
IsomagneticEnthalpic Transfer • Heat generated in the previous process is removed by a fluid (He or H2O) • Magnetic field is held constant • After being sufficiently cooled, the magnetocaloric material and coolant are separated
Adiabatic Demagnetization • The substance is brought to another insulated environment • Magnetic field is decreased • Magnetic entropy increases, thermal entropy decreases • Material cools down
Isomagnetic Entropic Transfer • Magnetic field is held constant • Environment to be cooled is brought in contact with the magnetocaloric material • Heat transfers from space to be cooled to the magnetocaloric material
Constructional Components • Magnets • Hot Heat Exchanger • Cold Heat Exchanger • Drive • Magnetocaloric Wheel
Magnets Magnets provide the magnetic field to the material so that they can lose or gain the heat to the surrounding and from the space to be cooled respectively
Hot Heat Exchanger The hot heat exchanger absorbs the heat from the material used and gives off to the surrounding. It increases the efficiency of heat transfer
Cold Heat Exchanger The cold heat exchanger absorbs the heat from the space to be cooled and gives it to the magnetic material. It helps to make the absorption of heat efficient.
Drive Drive provides the right rotation to the Magneto caloric wheel. Due to this, heat flow in the desired direction is achieved.
Magnetocaloric Wheel It forms the base structure of the whole device. It is the fundamental element in the whole system. It joins the two magnets and ensures proper operability.
Proposed representation of a commercial system This is the picture of a proposed commercial magnetic refrigeration system which is being developed by Camfridge and Whirlpool. It is planned to be launched in the UK in the year 2012.
Working Materials • Magneto caloric effect is characteristic of the material • The ability of a material to produce a change in its temperature per Tesla of change in magnetic field, is the deciding factor. • Alloys of gadolinium can be used for magnetic refrigeration. • Paramagnetic Salts like Cerium Magnesium Nitrate
GMCE Materials • Giant Magnetocaloric Effect Materials • Exhibits GIANT change in entropy • Most promising material with respect to magnetic refrigeration, at room temperature • Examples - Gd5(SixGe1−x)4 La(FexSi1−x)13Hx MnFeP1−xAsx
Alternative Techniques • Nuclear Demagnetization Refrigeration • Working Principle remains the same • Cooling power arises from the magnetic dipoles of the nuclei of the refrigerant atoms, rather than their electron configurations. • They have much smaller magnetic dipoles • Less prone to self alignment • Lower intrinsic minimum fields • Temperatures of up to 1 µK or less, achievable
Commercial Development • Pros : • Viable in various industries and research facilities • Environmentally friendly, as it doesn’t require any polluting gases • Comparatively lower power consumption, research shows them to be 50% more efficient than conventional cooling systems • In commercial refrigeration a key cost is maintenance caused by leakage of refrigerant. By eliminating gases this maintenance cost will be removed. • In domestic refrigeration low noise is valuable; elimination of gas compression reduces noise.
Cons: • Various technical difficulties remain at large • Availability of good working material is a concern • Superconducting magnets are required to produce sufficient field • Magnetic hysteresis losses are considerable for certain materials
Conclusion 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.”
References • http://en.wikipedia.org/wiki/Magnetic_refrigeration • http://cryo.gsfc.nasa.gov/ADR/ADR_primer/ADR_primer.html • http://imagine.gsfc.nasa.gov/docs/teachers/lessons/xray_spectra/background-adr.html • http://www.physlink.com/Education/AskExperts/ae488.cfm • http://www.ameslab.gov/content/magnetocaloric-effect-magnetic-refrigeration-and-ductile-intermetallic-compounds • http:/newenergyandfuel/com/2009/05/25/progress-update-on-magnetic-refrigeration/magnetic-refrigeration-process-graph/ • http://www.camfridge.com/Pages/story.html