ELDHOSE KURIAN 10TH05F

CONTENTS INTRODUCTION WORKING PRINCIPLE THERMODYNAMIC CYCLE REQUIREMENTS APPLICATIONS MERITS CONCLUSION REFERENCES

INTRODUCTION Magnetic refrigeration is a cooling technology based on the magneto caloric effect. Invented by Emil Warburg in 1880 Used to attain cryogenic temperatures well below 1 o K with the help of magnetic fields

PRINCIPLE OF MAGNETIC REFRIGERATION Magneto caloric effect is the basic principle on which the cooling is achieved. Magneto caloric effect 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 called adiabatic demagnetisation.

THERMODYNAMIC CYCLE

STEPS OF THERMODYNAMIC CYCLE Adiabatic magnetisation Isomagnetic enthalpic transfer Adiabatic demagnetization Isomagnetic entropic transfer

REQUIREMENTS FOR PRACTICAL APPLICATIONS Magnetic Materials Regenerators Super Conducting Magnets Active Magnetic Regenerators(AMR’s)

MAGNETIC MATERIALS Magnetocaloric effect is an intrinsic property of a substance Gadolinium and its alloys are the best materials available for magnetic refrigeration They can reach ultra low temperatures

REGENERATORS Efficient heat transfer requires large surface areas offered by porous materials When these porous materials are used in refrigerators they are referred to as regenerators

SUPER CONDUCTING MAGNETS The magnetic field is created by superconducting magnets Most practical magnetic refrigerators are based on super conducting magnets operating at cryogenic temperatures Commonly used is made of a Niobium-Titanium alloy

ACTIVE MAGNETIC REGENERATORS A regenerator that undergoes cyclic heat transfer operations and magneto caloric effect is called Active Magnetic Regenerator It should be designed to possess: high heat transfer rate high magneto calorific effect affordable materials ease of manufacture

APPLICATIONS Liquefaction purposes in the case of hydrogen,nitrogen and helium Also focuses on many future applications like magnetic household refrigeration,cooling in transportation,cooling electronic circuits etc.

MERITS High efficiency Reduced operating cost Reliability

CONCLUSIONS Magnetic refrigeration is a technology that has proven to be environmentally safe 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

REFERENCES refrigeration A text book on Refrigeration and Air conditioning by C P Arora and Domkundwar A text book on Cryogenic Engineering by Thomas M. Flynn

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