seminar-on-magn-refr-1233144769599259-1 (2)

7/29/2019 seminar-on-magn-refr-1233144769599259-1 (2)

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SEMINAR ON

MAGNETIC REFRIGERATION

PRESENTED BY

GANESH PRALHAD BHARAMBE

UNDER THE ABLE GUIDANCE OF

PROF. A. M. PATIL.

DEPARTMENT OF MECHANICAL ENGINEERING,

PADMABHUSHAN VASANTRAODADA PATIL INSTITUTE OF TECHNOLOGY,

BUDHAGAON, DIST. SANGLI. MAHARASHTRA.


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ACKNOWLEDGEMENT

THE AUTHOR OF THIS SEMINAR ISTHANKFUL TO PROF. A.M. PATIL ANDPROF. DANGE FROM MECHANICALDEPARTMENT FOR GIVING VALUABLEGUIDANCE FOR PREPARING THISSEMINAR. THEIR INSPIRATIONS HAVESUCCEEDED IN GIVING A FULL FORMAND SHAPE OF THIS SUBJECT INDEPTH.

GP BHARAMBE


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CONTENTS

>Basic principles of magnetic refrigeration

>Thermodynamic cycle

>Materials : Working materials, Developmentin materials and Nano compositswhich can play important role inupgradin the efficiency of materials

>Commercial aspects

>Historical background


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MAGETIC REFRIGERATION

AIMS OF SEMINAR :

To understand the principle and mechanism for generating

cooling effect using the magnet.

Materials and process

Commercial aspects .

Nano technology

History

Practical cases of equipment building


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Introduction : Principle

Mageto calorific effect is the basic principle on which the coolingis achieved.

All magnets bears a property called Currie effect i.e. If a

temperature of magnet is increased from lower to higher range atcertain temperature magnet looses the magnetic field.

Currie temperature. Depends on individual property of eachmaterial.

As Energy input to the magnet is increased the orientation of themagetic dipoles in a maget starts loosing orientation. And vice aversa at currie temperature as maget looses energy to the media itregains the property.


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Thermo dynamic cycle


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DETAILS OF THE THERMODYNAMIC CYCLE

PROCESS IS SIMILAR TO GAS COMPRESSION ANDEXPANSION CYCLE AS USED IN REGULAR

REFRIGERATION CYCLE.

Steps of thermodynamic cycle -

Adiabatic magnetization

Isomagnetic enthalpic transfer

Adiabatic demagnetization

Isomagnetic entropic transfer


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Adiabatic magnetization

Procedure to be followed :

> Substance placed in insulated environment.

> Magnetic field +H increased.

> Magnetic dipoles of atoms to align, thereby

material decreases.

> Total Entropy of the item is not reduced, anditem heats up


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Isomagnetic enthalpic transfer

> Added heat removed by fluid, gas gaseous or

liquid helium

> Magnetic field held constant to prevent the dipolesfrom reabsorbing the heat.

> After a sufficient cooling magnetocaloric material

and coolant are seperated


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Adiabatic 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 )


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Isomagnetic entropic transfer

> Material is placed in thermal contact with theenvironment being refrigerated.

> Magnetic field held constant to prevent fromheating back up

> Because the working material is cooler than therefrigerated environment, heat energy migratesinto the working material ( +Q )

*****Once the refrigerent and refrigeratedenvironment are in thermal equillibrium, the cyclebegins a new


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Advantages of Magnetic Refrigeration

> Purchase cost may be high, but running costsare 20% less than the conventional chillers

> Thus life cycle cost is much less.

> Ozone depleting refrigerants are avoided in thissystem, hence it more eco-friendly.

> Energy saving would lessen the strain on ourhousehold appliances

> Energy conservation and reducing the energycosts are added advantages.


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Working Materials

> Magneto caloric effect is an intrinsic porperty ofmagnetic solid.

> Ease of application and removal of magneticeffect is most desired propery of material. It isindividual characteristics and strongly dependson :

Curie temperature, Degree of freedom for magnetic dipoles during

ordering and randomization of particals.

> ferrimagnets, antiferromagnets and spin glass

sytems are not suitable for this application

Alloys of gadolinium producing 3 to 4 K per teslaof change in magnetic field are used for magneticrefrigeration or power generation purposes.


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xxxxx AsandMnfePHSiFeLa 11 ,13)(

Development in Working Materials

> Recent research on materials exhibit a giant entropychange showed. Alloys of gadolinium are promising

materials as below as compared to existing stocks.

Gd5(Six Ge1 x )4, La(FexSi1 x)13Hx

> These are some of the most promising substitute for

Gadolinium.

Such materials are called as magnetocaloric effect materials


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Magnetic refrigeration works in the vicinity of a materials Curie

temperature

The range of operation is = +/- 20

In 1950s MRC operated near by 1 to 30 K, in 1976 this range had

expanded to 80 C around the Curie temperature.

1997 lead this activity to built commecial and industrial use.

Using the Ericcsons cycle system refrigerator was built and used for

1500 hrs continuously.

Gd alloys, most notably Gd alloy, most notably Gd5(Si2Ge2), due to

simultaneous magnetic and crystallographic first order transition, the

adiabatic temperature rise was 30% higher than that of Just Gd and

200 600 % than previous refrigerent materials.


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Material Dy0.5Er0.5)Al2 has paramagnetic to ferromagnetic

transition at 40 k where the large peak occur.

Similar is Gd5(Si0.33Ge3.67) shows enormous peak

It is possible to predict weight to mass ratio of components which

produce maximum constant magnetic entropy. This techniqueallows one to find a suitable material composition which has a

constant slope on MCE vs temperature plot. It should have good

magnetocaloric effect and could withstand the process of cooling.

Gadolinium silicon germanium ternary system ( Gd-Si-Ge ), withstoichiometry of Gd5(SixGe1-x)4

Transition temperatures of the alloys formed by Gd, Tb, Dy, Ho, Er,

Tm and Lu shows transitions with transitions above 180 k.


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10 Amorphous materials shows high

resistivity and improved corrosion

resistance which aids the process of

magnetic refrigeration.

Amorphous alloys may be able to fill up the

gaps between 100 to 200 k

Gd0.54Er0.46)NiAl has 11 top effects, is

currently being implemented inErriccson cycle refrigerators.

seminar-on-magn-refr-1233144769599259-1 (2)

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