Refrigeration technology is very important to our lives. However, refrigeration in use today relies almost entirely on vapor compression cycle that requires chlorofluorocarbon (CFC) or hydrofluorocarbons (HFC) to function as a heat exchanger. It is well known that CFC and HFC are the cause of global warming effect. Thus the environmentally friendly materials for refrigeration are absolutely necessary.
Magnetocaloric effect (MCE) was discovered by E. Warburg in 1881. By subjecting pure iron rod under magnetic fields at low temperature, it is found that pure iron rods release and absorb heat when magnetic fields change. MCE is a result of the change in entropy of magnetic material due to the arrangement of the magnetic moment with the external magnetic field as shown in Figure 2.1 MCE materials have been shown to have potential to be developed for use in magnetic refrigeration systems . Moreover, the theoretical study found that the system can be developed to outperform than the vapor compression cycle system. However, the applications of MCE materials for refrigeration also have the drawback that the production cost is high and requires a strong magnetic field (electromagnet or superconduction magnet). Therefore, the invention of materials that can exhibit MCE effect at the lower field will lead to great changes in the cooling technology.
The NiMnCrIn alloys exhibiting MCE effect near room temperature was synthesis by Sharma et al. . The discovery of rare earth free MCE materials is a spark in the application of MCE material for refrigeration. However, research is still needed to increase the temperature span of the MCE materials.
Permanent magnets are an important component of the MCE-based refrigerator because magnetic fields directly affect the temperature change of MCE materials. However, the high-intensity magnetic field will require high production costs as well. Although increasing the intensity of the magnetic field can be achieved by arranging permanent magnet bars. In order to meet the requirements, a large number of magnet bars are needed and make the refrigeration large and heavy. Development of MCE material that can exhibit MCE effect at the lower magnetic field will reduce the size and weight of the MCE-based refrigerator.
The soft magnetic material has special properties; it can induce a very high magnetic field when it is magnetized. The saturation induction magnetic field (Bs) of soft magnetic material is high while the coercive field is less. The Bs value 24 kOe (2.4 T) with the coercive field 8 Oe of CoFe alloy was reported by Osaka et al. .
This research project focuses on the development of low cost and low filed MCE materials for use in refrigeration applications. The MCE materials will be studied and developed to adjust the temperature span. In order to be able to apply MCE materials to refrigeration using electromagnetic field or permanent magnets, the selected materials will be coated with a soft magnetic material as shown in Figure 2.2.
Principal Investigator: Assistant Professor Dr. Pongsakorn Jantaratana 1)