Magnetocaloric Materials and Magnetic Refrigeration Systems

Magnetic refrigeration is an emerging energy efficient and environmentally friendly refrigeration technology. The principle of magnetic refrigeration is based on the effect of varying a magnetic field on the temperature change of a magnetocaloric material. By applying a magnetic field, the magnetic moments of a magnetic material tend to align parallel to it, and the thermal energy released in this process heats the material. Reversibly, the magnetic moments become randomly oriented when the magnetic field is removed, and the material cools down. The heating and the cooling of a magnetic material in response to a changing magnetic field is similar to the heating and the cooling of a gaseous medium in response to an adiabatic compression and expansion in a conventional refrigeration system.Room temperature magnetic refrigeration is a new highly efficient and environmentally protective technology. The purpose of my dissertation is to explore an energy efficient and environmentally friendly magnetic refrigeration system, and also study of different properties of magnetocaloric materials such as gadolinium and Heusler alloys, and study of latent heat in the magnetocaloric materials and introducing a new parameter, Cooling Factor, for interpreting the cooling performance of magnetic refrigeration systems. I have worked on developing a novel direct adiabatic temperature measurement apparatus with fully-controlled magnetic field, temperature, and time capabilities has been designed and implemented to measure the adiabatic temperature change for different materials. The initial study was upgrading the Active Magnetic Regenerator (AMR) system in the Institute for Magnetic Research (IMR) lab by adding a bath circulator and control software written in LabVIEW. Once this was accomplished, I verified system accuracy by measuring adiabatic temperature change of gadolinium, which is a generally prominent magnetocaloric material, and comparing the result with results of different literatures.A new approach of interpreting the adiabatic temperature change measurements to emphasize the reversibility of the magnetocaloric effect has been introduced. The new approach also gives the most precise measurement of a material's Curie temperature. My extensive measurement procedure paved a path for exploring the complex spin dynamics of phase transitions.Metastability near the Curie temperature of polycrystalline gadolinium, hypothesis of implicitly measuring the latent heat accompanying the phase transformations in Heusler alloy, and spin-reoriented stabilization in a Ni-Mn-In Heusler alloys has been studied. In addition the metastability in the magnetic structure of Ni-Mn-In Heusler alloy has been studied as well as gadolinium in this research. A new parameter, cooling factor, is introduced in order to provide a better understanding of magnetic refrigeration systems performance in a given temperature range. Cooling factor is defined as the area under the adiabatic temperature change curve, and is contrasted as a function of initial and average temperature.

Author

• Ghahremani, Mohammadreza

Language

• en

Keyword

• Gadolinium
• Magnetic Refrigeration
• Magnetocaloric
• MCE
• Heusler Alloy

Date created

• 2014

Type of Work

• Dissertation

License

• All rights reserved

Rights statement

• In Copyright

GW Unit

• Electrical Engineering

Degree

• Ph.D.

Advisor

• Della Torre, Edward
• Bennett, Lawrence H

Committee Member(s)

• Korman, Can E
• Provenzano, Virgil
• Zaghloul, Mona E

Persistent URL

•  https://scholarspace.library.gwu.edu/etd/db78tc22c