Although Magnetic refrigeration is a well-known method in cryogenics, it has not been commercially used at room-temperature. In this project, the possibilities with and the potentials of magnetic refrigeration system are investigated to find the most suited application for commercializing the technology.
Aims of the project
Many magnetic refrigeration prototypes with different designs and software models have been built in different parts of the world; nevertheless, there are still challenges in the way of commercialization of magnetic refrigerators. The obstacles hindering commercial production of room temperature magnetic refrigeration are both economic and technical. In this project, the possibilities with and the potentials of magnetic refrigeration system are investigated to find the most suited application for commercializing the technology.
This paper seeks to shed light on the question whether a magnetic household refrigerator with permanent magnets is more environmentally friendly than a conventional, vapor-compression refrigerator. Life cycle assessment has been used as a tool to investigate the environmental impacts associated with the life cycle of a magnetic refrigerator. The results of the assessment have been compared with those of a conventional, vapor-compression refrigerator with the same functionality. The comparison reveals that the magnetic refrigeration has higher environmental impacts mainly due to the use of rare-earth metals used in the magnet material. The possibility of compensating for this shortcoming through reuse of the magnetic materials or improving the design and efficiency of the magnetic refrigerator has been examined. In addition, the effect of the electricity mix consumed during the use phase, as one of the key factors determining the life cycle environmental impacts, has been investigated.
Monfared, B., Furberg, R., and Palm, B., 2014, "Magnetic vs. vapor-compression household refrigerators: A preliminary comparative life cycle assessment," International Journal of Refrigeration, 42(0), pp. 69-76. doi: 10.1016/j.ijrefrig.2014.02.013 .
Magnetic refrigeration, as an alternative to vapor-compression technology, has been the subject of many recent investigations. A technique to enhance the performance of magnetic refrigerators is using layers of different materials in the regenerator of such devices. In this study the choice of magnetocaloric materials in a multi-layered packed bed regenerator is investigated in order to optimize the performance. A numerical model has been developed to simulate the packed bed in this study. Optimized packed bed designs to get maximum temperature span or maximum efficiency are different. The results indicate that maximum temperature span can be achieved by choosing the materials with the highest magnetocaloric effect in the working temperature range, while maximum Carnot efficiency is achieved by choosing materials with Curie temperatures above the average layer temperature.
Monfared, B., and Palm, B., 2015, "Optimization of layered regenerator of a magnetic refrigeration device," International Journal of Refrigeration, 57, pp. 103-111. doi: 10.1016/j.ijrefrig.2015.04.019 .
Magnetic refrigeration as an alternative for vapor-compression technology has been the subject of many recent studies. Most of the studies focus on systems with limited cycle frequency in which a fluid transfers heat to and from the magnetocaloric material. A suggested solution for increasing the frequency is use of solid-state magnetic refrigeration in which thermal diodes guide the heat from the cold end to the warm end. In this work a solid-state refrigeration system with Peltier elements as thermal diodes is modeled in details unprecedented. The performance of Peltier elements and magnetocaloric materials under their transient working conditions after reaching cyclic steady state are simulated by two separate computer models using finite element method and finite volume method. The models, in parts and as a whole, are verified. The verified finite element model is used for a parametric study and the results are analyzed.
Monfared, B., 2017. "Simulation of solid-state magnetocaloric refrigeration systems with Peltier elements as thermal diodes." International Journal of Refrigeration, 74, pp. 322-330. doi: 10.1016/j.ijrefrig.2016.11.007 .
In this work a comprehensive simulation of a magnetic refrigeration device is presented, validated, and used for redesigning the regenerators of an existing prototype. The redesigning process includes choosing the magnetocaloric materials and number of layers and optimizing for particle size, flow, and operation frequency. The simulation consists of the model of the magnetic field, parasitic heat transfer and active regeneration. The model of the magnetic field and parasitic heat transfer are embedded in the 1D model of the active regeneration cycle. The detailed model of the magnetic field, taking the effect of presence of the magnetocaloric materials into account, is described and validated separately against measured magnetic field. An innovative method for including the parasitic heat transfer in the active regeneration model without compromising the accuracy is used. The influence of the properties of the binding agent on the performance of the bonded beds as regenerators are also investigated.
Monfared, B., 2018. "Design and optimization of regenerators of a rotary magnetic refrigeration device using a detailed simulation model." International Journal of Refrigeration, 88, pp. 260-274, doi: 10.1016/j.ijrefrig.2018.01.011 .
A primary motivation underlying the research on room-temperature magnetic refrigeration is reaching energy efficiency levels beyond what is achievable with vapor-compression technology. However, the goal of building commercially viable magnetic refrigeration systems with high performance and competitive price has not been achieved yet. One of the obstacles to reach this goal is the inadequate properties of the currently existing magnetocaloric materials. In this article, the needed improvements in the properties of the magnetocaloric materials are investigated. Two existing vapor-compression refrigerators are used as reference for the required performance, and magnetic refrigerators are simulated using a numerical model. Apart from the requirements such as uniformity of transition temperature for each layer, small increment in transition temperature in adjacent layers, and mechanical strength of the materials, the study shows that for the investigated cases materials with adiabatic entropy change 2.35 times larger than the existing materials are needed to outperform vapor-compression systems.
Monfared, B., and Palm, B., 2018. "Material requirements for magnetic refrigeration applications." International Journal of Refrigeration, doi: 10.1016/j.ijrefrig.2018.08.012
Background information
Although Magnetic refrigeration is a well-known method in cryogenics, it has not been commercially used at room-temperature. Brown built the first prototype magnetic refrigeration device working at room temperature in 1976. Since Brown’s successful experiments, an increasing number of prototypes have been built. Currently an increasing number of researchers are working on developing prototypes, models predicting the performance of the magnetic refrigerators, and materials used as refrigerant in magnetic refrigerators.
Working principle
The working principle of magnetic refrigerators is based on magnetocaloric effect, perceived as adiabatic temperature change or isothermal entropy change. Some materials show a significant temperature change when they are exposed to an external magnetic field. When the process of magnetizing is done adiabatically the magnetocaloric effect is observable as adiabatic temperature change, ∆Tad. However, if the heat is removed from the material to keep the temperature constant while the external magnetic field increases, the effect is seen as entropy change.
For a magnetocaloric material at thermal equilibrium with its surroundings, the increase in the external magnetic field in an adiabatic process results in an increase in the temperature of the material. Because of being at higher temperature, the magnetocaloric material can exchange heat with its surroundings to approach the surroundings’ temperature. After the heat transfer process, if the external magnetic field is reduced the temperature of the magnetocaloric material will drop below the temperature of the surroundings, and therefore, the cooling effect can be used for refrigeration purposes. There is an analogy between the magnetic refrigeration cycle and conventional cycles, esp. Joule-Brayton cycle. The analogy is shown graphically in the diagram.
