1. MAGNETIC REFRIGERATION PRESENTED BY SHRADDHA DHAJEKAR MAGNETIC REFRIGERATION PRESENTED BY SHRADDHA DHAJEKAR UNDER THE ABLE GUIDANCE OF PROF. K. BHUYAR DEPARTMENT OF CHEMICAL ENGINEERING, PRIYADARSHINI INSTITUTE OF ENGINGGRING AND TECHNOLOGY, NAGPUR, MAHARASHTRA.

2. ACKNOWLEDGEMENT THE AUTHOR OF THIS SEMINAR IS THANKFUL TO PROF. K. BHUYAR FROM CHEMICAL DEPARTMENT FOR GIVING VALUABLE GUIDANCE FOR PREPARING THIS SEMINAR. THEIR INSPIRATIONS HAVE SUCCEEDED IN GIVING A FULL FORM AND SHAPE OF THIS SUBJECT IN DEPTH. SHRADDHA DHAJEKAR

3. >Basic principles of magnetic refrigeration >Thermodynamic cycle >Materials : Working materials, Development in materials and Nano composits which can play important role in upgradin the efficiency of materials >Commercial aspects >Historical background CONTENTS

4. MAGETIC REFRIGERATION 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

5. Introduction : Principle Mageto calorific effect is the basic principle on which the cooling is achieved. 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. Currie temperature. Depends on individual property of each material. As Energy input to the magnet is increased the orientation of the magetic dipoles in a maget starts loosing orientation. And vice a versa at currie temperature as maget looses energy to the media it regains the property.

6. Thermo dynamic cycle

7. DETAILS OF THE THERMODYNAMIC CYCLE PROCESS IS SIMILAR TO GAS COMPRESSION AND EXPANSION CYCLE AS USED IN REGULAR REFRIGERATION CYCLE. Steps of thermodynamic cycle -  Adiabatic magnetization  Isomagnetic enthalpic transfer  Adiabatic demagnetization  Isomagnetic entropic transfer

8. 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, and item heats up

9. Isomagnetic enthalpic transfer > Added heat removed by fluid, gas – gaseous or liquid helium > Magnetic field held constant to prevent the dipoles from reabsorbing the heat. > After a sufficient cooling magnetocaloric material and coolant are seperated

10. 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 )

11. Isomagnetic entropic transfer > Material is placed in thermal contact with the environment being refrigerated. > Magnetic field held constant to prevent from heating back up > Because the working material is cooler than the refrigerated environment, heat energy migrates into the working material ( +Q ) Once the refrigerent and refrigerated environment are in thermal equillibrium, the cycle begins a new

12. Advantages of Magnetic Refrigeration > 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 saving would lessen the strain on our household appliances > Energy conservation and reducing the energy costs are added advantages.

13. Working Materials > Magneto caloric effect is an intrinsic porperty of magnetic solid. > Ease of application and removal of magnetic effect is most desired propery of material. It is individual characteristics and strongly depends on : 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 tesla of change in magnetic field are used for magnetic refrigeration or power generation purposes.

14. Development in Working Materials > Recent research on materials exhibit a giant entropy change showed. Alloys of gadolinium are promising materials as below as compared to existing stocks. Gd 5 (Si x Ge 1 – x ) 4, La(FexSi1 – x)13Hx > These are some of the most promising substitute for Gadolinium. Such materials are called as magnetocaloric effect materials

15. Development in Working Materials Magnetic refrigeration works in the vicinity of a material’s Curie temperature The range of operation is = +/- 20 In 1950’s 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 Ericcson’s 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.

16. Development in Working Materials 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 technique allows 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 ), with stoichiometry 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.

17. Development in Working Materials 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 in Erriccson cycle refrigerators.

18. NUCLEAR DEMAGNETIZATION This type is one of the variant that continues to find substantial research application. It follows the same principle, but in this case the cooling power arises from the magnetic dipoles of the nuclei of refrigent atoms rather than their electronic configuration. Since these dipoles ar of much smaller magnitude, they are less prone to self alignment and have lower intrinsic minimum field. This allows NDR to cool the nuclear spin system to very low temperatures, often 1 micro kelvin. Magnetic fields of 3 telsa or greator are often needed for the intial mgneization step of NDR

19. NANO MATERIALS FOR REFRIGERATION New research shows that nanocomposites from metallic glasses could make promising magnetic refrigeration materials, > These materials are as good as the best currenly available magnetic refrigerants with added adavantages. > This leads to environmental friendly and more efficient than the existing devices that rely on a vapour cycle.  Energy effiiciency reaches upto 60 %. This saves 40% energy.  Working temperatures and operating range can be tailored by tuning the composition and manipulating the microstructure.  Properties are similar to crystallized and amorphous materials due to unique microstructure

20. NUCLEAR DEMAGNETIZATION This type is one of the variant that continues to find substantial research application. It follows the same principle, but in this case the cooling power arises from the magnetic dipoles of the nuclei of refrigent atoms rather than their electronic configuration. Since these dipoles ar of much smaller magnitude, they are less prone to self alignment and have lower intrinsic minimum field. This allows NDR to cool the nuclear spin system to very low temperatures, often 1 micro kelvin. Magnetic fields of 3 telsa or greator are often needed for the intial mgneization step of NDR

21. NUCLEAR DEMAGNETIZATION Nano composite made of gadolinium nanocrystallites embedded in a gadolinium-aluminium-manganese (Gd60Al10Mn30) metallic glass matrix. These materials exhibits unique properties of hysteric and hard magnetic behaviour, which reduces the efficiency of cooling process. Structural changes in these materials promote crack nucleation and propogation that can cause severe damage to the refrigerant material during cycling. Disadvantage of material.