MATERIAL LOSSES AND HEAT EXCHANGES: A UNIFIED THERMODYNAMIC APPROACH TO COOLING EFFICIENCY

To achieve highly efficient cooling devices using caloric materials, it is necessary to engineer a system where electric/magnetic field and the heat transfer are fully mastered. The active substance, the source of the field and the thermal switches can all introduce additional losses that need to be considered when estimating the system's efficiency upper bound. At the same time, all cooling systems either use the regenerative approach or they rely on cascade thermodynamic cycles to amplify the temperature variation of the material in order to achieve the required temperature span. The thermodynamic approach we present here provides guidance to understand the regenerative thermodynamic cycle (Brown, 1976; Steyert, 1978) and to design future devices. After describing regenerative and cascaded cycles, the analysis will consider heat transfer within the frame of the finite time thermodynamics. Different approaches for maximizing efficiency will be presented. Finally, additional losses are introduced to illustrate the design challenges.