Thermal Switch Capacitor in a Magnetocaloric Device

The quest for better performance of magnetocaloric devices has led to the development of thermal management devices such as thermal switches, thermal diodes, and thermal capacitors. These types of devices are capable of controlling the heat in a manner similar to how their electrical counterparts control electrical current. Most existing caloric devices use active caloric regeneration, in which the working fluid oscillates through the caloric regenerator compose of caloric material. The unavoidable, irreversible viscous and heat-transfer losses, associated with the active caloric regeneration principle limit the operating frequency (number of thermodynamic cycles per unit of time), which is directly related to the power density of a caloric device. Thermal management devices offer a new way to control the intensity and direction of heat flow between the magnetocaloric material and the heat source or heat sink, and therefore could improve the performance of caloric devices during high-frequency operation, which is crucial for increasing in the power density (compactness) and energy efficiency.<br/><br/>A thermal switch relies on a control parameter such as an electric field, magnetic field, or pressure to change the thermal conductance of the device. The switching ratio between the highest thermal conductance achieved (the on state) and the lowest thermal conductance achievable (the off state) represents a figure of merit for a thermal switch. Thermal switches can be either static or motional. Motional thermal switches change their thermal conductance by changing their position and making and breaking thermal contacts. Static thermal switches are always in physical contact with adjacent interfaces. The thermal capacitor, on the other hand, is a single-pole element because the other side of this element is always “grounded,” i.e., connected to a heat reservoir. It acts as a temporary heat-storage device, similar to the “self-capacitance” of an insulated electrical conductor in the electrical analogy. The operation of a thermal switch (TS) and a thermal capacitor (TC) can also be combined in a so-called thermal switch capacitor (TSC).<br/><br/>In this work, we have analyzed a novel thermal switch capacitor made of silicon operating as a solid heat transporting device. The thermal switch capacitor first stores energy and then releases it by means of the transport of heat caused by the motion of the material. We studied the impact of different design parameters and operating conditions on performance of magnetocaloric device, and based on this, established guidelines for an optimal design for further experimental studies. The proposed design provides a compact cooling solution that can be attached directly to the heat reservoir, making it attractive for a variety of applications.