In a series of articles SIRACH will review individual heating and cooling technologies and describe how they work, as well as who has been developing them. The article will also cover the potential benefits, applications and challenges in bringing to market. This month we will describe magnetic refrigeration.
Basic working principles
The principle of magnetic refrigeration is based on a phenomenon known as magnetocaloric effect (MCE). This was discovered by Emil Warburg in 1881 and is related to the property of some exotic materials such as Gadolinium and Dysprosium that heat up when applying a magnetic field and cool down when the magnetic field is removed.
This is illustrated in the figure below. It can be seen from the figure that by operating the magnet in four steps, it is possible to reject heat and produce cooling. The energy (E =m.Cp.ΔT) generated during each magnetocaloric cycle depends on the variation of temperature ΔT, the mass of material (m) and its specific heat capacity (Cp). This effect is maximal at a specific temperature called the Curie temperature of the material.
The principle of this cycle uses a heat transfer fluid in contact with the magnetocaloric materials (MMC) flowing from the cold side to the hot side when the MMC is heated (magnetised) and from the hot side to the cold side when the MMC is cooled down (demagnetised).
This progressively increases the temperature difference between the cold and hot source to about 20K making the system potentially suitable for commercial applications.
However, magnetic cooling can also be completely adapted to other refrigeration applications such as air conditioning, including automotive, cryogenics or in heating applications (e.g heat pumps).
In addition, the magnetocaloric cycle frequency being typically between 1 and 3 Hz, the rotation speed of the machine is slow and therefore very quiet compared to traditional compression systems.
According to recent research it has been predicted that MCE will have a significantly higher cooling efficiency (COP) than the present conventional methods, with a potential for a 30% energy saving.
- The primary one is related to the supply of magnetocaloric materials, which are scarce. Therefore reducing material content or identification of new materials would benefit.
- Possibilities for reducing production costs. According to Cooltech the fabrication process has not been optimized yet and costs are still high for allowing a large deployment scale.
- Interface optimisations (e.g Heat exchangers) between the devices and the equipment to be refrigerated have to be optimised for maximum efficiency.
- Development of prototypes for various specific applications.
Current market development
NEXTPAC (working on heat pump applications) and Cooltech, according to Cooltech after 3 years industrializing and testing its magnetic refrigeration system, Cooltech is now introducing a standard product specifically adapted to the commercial refrigeration market.
In addition other multinationals from around the world who are working on similar technologies include such as Whirlpool, Electrolux, Astronautics, GE-Appliances, Samsung, Erasteel, Sanden, Chubu, BASF, VAC etc.
On the 1st October the SIRACH Network visited Newcastle University and the Joseph Swan Centre for Energy Research. Delegates will saw the interdisciplinary research centre, known to deliver holistic, cutting-edge research and finding new ways of meeting the growing energy needs in an environmentally-friendly and sustainable way.
Current research projects include, Biofuel Micro-Trigeneration with Cryogenic Energy Storage, Building Management and Energy Demand and Low Grade Heat Driven Adsorption-Linear-Expander Cycle for Cogeneration of Power and Refrigeration. The Centre and Newcastle University are also involved in the Sustainable Thermal Energy Management Network.
For more information or to be included on the SIRACH mailing list please register at www.sirach.org.uk or email firstname.lastname@example.org