UB researchers develop a new refrigeration cycle based on magnetic materials

The refrigeration cycle the researchers carried out consists of six steps. In the first one, the magnetic field is applied and materials cool; then the field is taken out so that materials are magnetized thanks to hysteresis. In the third step, a mechanical pressure is applied to the material, which allows the modification of its crystal structure and it can be brought back to its original state while the material warms up. The refrigeration effect takes place during the fourth step, when the material absorbs the heat. In the fifth step, pressure is removed and material is kept in this new state, demagnetized. Last, the alloy brings heat in the environment and the cycle is finally closed. Image: T. Gottschall et al.
The refrigeration cycle the researchers carried out consists of six steps. In the first one, the magnetic field is applied and materials cool; then the field is taken out so that materials are magnetized thanks to hysteresis. In the third step, a mechanical pressure is applied to the material, which allows the modification of its crystal structure and it can be brought back to its original state while the material warms up. The refrigeration effect takes place during the fourth step, when the material absorbs the heat. In the fifth step, pressure is removed and material is kept in this new state, demagnetized. Last, the alloy brings heat in the environment and the cycle is finally closed. Image: T. Gottschall et al.
Research
(03/10/2018)

About 17 % of the global energy consumption is assigned to domestic and industrial refrigeration. This consumption is skyrocketing mainly in emerging countries, and the refrigeration use is expected to exceed the one that is now dedicated to warming, mainly due climate change. Moreover, current technology is based on the use of fluorocarbons, gases that cause greenhouse effect and which should be replaced over the next years.

The refrigeration cycle the researchers carried out consists of six steps. In the first one, the magnetic field is applied and materials cool; then the field is taken out so that materials are magnetized thanks to hysteresis. In the third step, a mechanical pressure is applied to the material, which allows the modification of its crystal structure and it can be brought back to its original state while the material warms up. The refrigeration effect takes place during the fourth step, when the material absorbs the heat. In the fifth step, pressure is removed and material is kept in this new state, demagnetized. Last, the alloy brings heat in the environment and the cycle is finally closed. Image: T. Gottschall et al.
The refrigeration cycle the researchers carried out consists of six steps. In the first one, the magnetic field is applied and materials cool; then the field is taken out so that materials are magnetized thanks to hysteresis. In the third step, a mechanical pressure is applied to the material, which allows the modification of its crystal structure and it can be brought back to its original state while the material warms up. The refrigeration effect takes place during the fourth step, when the material absorbs the heat. In the fifth step, pressure is removed and material is kept in this new state, demagnetized. Last, the alloy brings heat in the environment and the cycle is finally closed. Image: T. Gottschall et al.
Research
03/10/2018

About 17 % of the global energy consumption is assigned to domestic and industrial refrigeration. This consumption is skyrocketing mainly in emerging countries, and the refrigeration use is expected to exceed the one that is now dedicated to warming, mainly due climate change. Moreover, current technology is based on the use of fluorocarbons, gases that cause greenhouse effect and which should be replaced over the next years.

One of the change options is the creation of refrigeration systems based on solid state, and inside it, materials that are based on the use of cooling magnetic fields are one of the top listed alternatives. In this line, a study has been carried out in the Department of Condensed Matter Physics of the UB, published in Nature Materials, and led by professors Lluís Mañosa and Antoni Planes, and PhD student Adrià Gràcia, in collaboration with Professor Oliver Gutfleisch, from the Technische Universität Darmstadt (Germany), and Doctor Tino Gottschall, from Helmholtz-Zentrum Dresden-Rossendorf (HZDR). These researchers have designed a cooling cycle in six steps based on the “magnetic memory” of certain alloys.

“When certain types of alloys are under a magnetic field, these remain magnetized -even when the field is taken out- and during this process, materials cool”, says Lluís Mañanosa. “What we found out with this study -he adds- is that by applying an external pressure we can reverse the magnetization effect and take the system back to its original state. This step is necessary to set a closed cycle”.

The refrigeration cycle the researchers carried out consists of six steps. In the first one, the magnetic field is applied and materials cool; then the field is taken out so that materials are magnetized thanks to hysteresis. In the third step, a mechanical pressure is applied to the material, which allows the modification of its crystal structure and it can be brought back to its original state while the material warms up. The refrigeration effect takes place during the fourth step, when the material absorbs the heat. In the fifth step, pressure is removed and material is kept in this new state, demagnetized. Last, the alloy brings heat in the environment and the cycle is finally closed.  

 

 

For this research, experts used a magnetocaloric alloy of nickel, manganese, and indium (Ni-Mn-In) which allows working at room temperature. In addition, materials that build up the alloy are easily accessible, unlike the ones that are currently used.

Due technological reasons, the magnetic refrigeration cycle needs to use permanent magnets. These are based on rare soils, minerals which are extremely expensive and which are obtained through polluting processes.

“Thanks to this step we included in the refrigeration cycle, the size of the required magnets is considerably reduced, gaining competitiveness. The new cycle is more competitive, since it only requires half the magnet, while now for each part of cooling materials we need four times the amount of the magnet”, notes Antoni Planes. “Another important element -continues the researcher- is that this cycle uses the phenomenon of hysteresis, which usually involves a loss of energy”.
There is now a certain consensus regarding the idea that these magnetocaloric materials can be more efficient than current systems, and that devices based on these materials could replaces those equipments that do not need intense temperature drops, of about 15 and 20 ºC, such as air conditionings.

Referència de l'article:

T. Gottschall, A. Gràcia-Condal, M. Fries, A. Taubel, L. Pfeuffer, L. Mañosa, A. Planes, K.P. Skokov, O. Gutfleisch: “A multicaloric cooling cycle that exploits thermal hysteresis”, Nature Materials, AOL 10 September 2018. Doi: 10.1038/s41563-018-0166-6