Magnetic refrigeration enhanced by magnetically-activated thermal switch: An experimental proof-of-concept

In the era of energy transition and climate change, environmentally safe refrigeration technologies are of utmost importance. Magnetocaloric refrigeration (MCR) is one of the most promising alternatives to the existing vapor -compression systems. Overcoming the primary challenges of the low heat dissipation and elevated device production costs is imperative for MCR development. This work provides the first demonstration of an MCR prototype that combines the magnetocaloric material (MCM) gadolinium with a ferrofluidic thermal switch (TS). The performance was assessed using dispersions of MnFe 2 O 4 /Ethylene Glycol:Water and Fe 3 O 4 /paraffin oil. For the first time, a strategic asymmetry was introduced into MCR cycles. The inclusion of the TS did not uncover any advantages in the Gd-alone system by using symmetrical cycles. However, by applying/removing the magnetic field asymmetrically, a remarkable temperature span of up to 0.6 degrees C was achieved within the TS+MCM prototype. This represents a substantial improvement, reaching up to 60% compared to the Gd-alone configuration. The prototype ensures that a single magnetic field, responsible for driving the magnetocaloric effect, also activates the TS, thereby streamlining system operability and improving performance. To validate our findings, we developed a 1D numerical model, which consistently confirmed that system optimization can be achieved through the exclusive use of asymmetric cycles. Consequently, the application of magneticallyactivated fluidic TSs and asymmetric cycles emerge as important strategies for enhancing MCR across a diverse range of systems.