Certain materials heat up, when brought into a magnetic ﬁeld. This phenomenon is called the magnetocaloric effect (MCE). Materials endowing this effect are called magnetocaloric materials (MCM). Using the magnetocaloric effect, a magnetic cooling cycle near room temperature is possible.

What is the magnetocaloric effect?

The magnetocaloric effect (MCE) manifests itself as a change of thermodynamic state of a magnetic material in an external alternating magnetic field H. Depending on the conditions (isothermal or adiabatic) under which the magnetic field H is applied, either the isothermal entropy change ∆s_t or the adiabatic temperature change ∆T_ad are commonly used as numerical parameters characterizing the magnitude of the magnetocaloric effect.

How does the magnetocaloric effect (MCE) work?

An increasing field H causes the magnetic moments/spins of the magnetic material to align parallel to H decreasing the magnetic entropy S_mag. Due to adiabatic conditions within the system, the total energy of the system stays constant and the material is heated by a temperature ∆T_ad with the net temperature of the material now being T_start + ∆T_ad due to an increase in the lattice entropy S_lat.

What are magnetocaloric materials (MCM)?

Magnetocaloric materials are metals endowing the magnetocaloric effect (MCE). Such materials include pure elements such as Gadolinium or alloys such as Lanthanum-iron-silicon (LaFeSi) or Iron-phosphorus (Fe2P).

How was the effect discovered?

This effect was first theoretically postulated in the works of Langevin in 1905. He predicted that the temperature of a paramagnetic material should change as a function of magnetic field. The later called magnetocaloric effect was first observed in experiment by Weiss and Picard in the year 1917 where they could measure a temperature change on Ni among application of a magnetic field.

Magnetic Cooling Cycle

By using the magnetocaloric effect (MCE) intelligently, a magnetic cooling cycle is possible. The magnetocaloric cycle is performed analogous to the refrigeration cycle by Carnot. In contrast to the conventional compressor-based Carnot cycle not the pressure but the magnetic ﬁeld is increased and decreased. Similar to a gas compression cycle, the magnetic cooling process includes four steps.

Four steps of magnetic cooling cycle

(1) Heating the material

At the starting point (1) the magnetic material is in its paramagnetic state. The magnetocaloric material is placed in a thermally insulated (adiabatic) environment and the magnetic field is applied. The material heats up due to the above-mentioned magnetocaloric effect (2).

(2) Expelling the heat

The added heat Q is then extracted by fluid or gas heat exchange media. The magnetic field hereby is held constant. Once the material has cooled down to the temperature Tstart (3), it is brought back to adiabatic conditions and the magnetic field H is removed.

(3) Cooling the material

As the total entropy of the system is again constant and the spin entropy of the system increases and the lattice entropy decreases, the material must expel energy in the form of heat, whereas the material is cooled to a temperature of T_start – ∆T_ad.

(4) Absorbing the heat

The material is then put in contact with a thermal transfer fluid which is in contact with the environment to be refrigerated.

Iteration

In an iterative process a cooling cycle can then be realized and can be used in a magnetic cooling device for example a refrigerator or air conditioner.

Active Magnetic Regeneration (AMR)

Demonstration of active magnetic regeneration.

Benefits

HIGHLY EFFICIENT

Magnetic cooling has the capability to be up to 40% more efficient than conventional gas compression cooling and heating solutions.

F-GAS FREE

Fully compliant with all current and future EU f-gas regulation standards due to disruptive method of operation.

100% GREEN TECHNOLOGY

No GWP, no ODP, no direct CO2 emissions. With our innovative configuration of components and highly effective materials nature is no longer strained.

NEARLY NOISE FREE

Due to low pressures of max. 5 bars, the system is low in vibrations, nearly noise free and low in maintenance.

EFFICIENT SCALING

Our units can be scaled to specific temperature and power ranges without any loss in efficiency.

ALSO HEAT PUMP

With minor changes, the technology is also able to function as a highly efficient heat pump.