Thermal Management in Caloric Devices

Caloric energy conversion is an emerging field of cooling, heat-pumping and power-generation technologies. The potentially high energy efficiency and use of environmentally friendly and safe solid-state working substances has stimulated increased research activity in the past two decades. Most of today's caloric devices use so-called active regeneration, in which the working fluid oscillates through the matrix of the caloric material - the caloric regenerator. This is associated with irreversible viscous and heat-transfer losses and limits the operating frequency and related power density of the device.<br/><br/>Thermal Control Devices (TCDs) represent an alternative thermal management technique to active regeneration processes, which are widely used as a heat transfer principle in caloric technologies. TCDs allow non-linear, switchable and active control of the heat, similar to the control of electrical current by their electrical counterparts. Their integration in the form of thermal diodes, thermal switches, thermal regulators, and thermal conductors in caloric energy conversion system has the potential to significantly increase power density through rapid and oscillatory heat transfer from/to the caloric material and the heat sink/source while maintaining high energy efficiency, thus meeting the most important market condition and facilitating the commercialization of caloric technologies.<br/>Despite some research activities on TCDs integrated in caloric technologies, research in this particular area is still at an early stage. There is a great lack of knowledge and experience regarding the operational performance of the different types of TCDs as well as their performance when integrated into caloric devices. On the other hand, the scientific community dealing with materials should focus on various possible (new) materials or their composites, whose thermal properties correspond to the desired properties of thermal diodes, and approach them systematically with proper data collection on their thermal properties.<br/><br/>In this work, we provide a critical and an up-to-date review on the research activities and applications of TCDs in all types of caloric devices, as well as an overview of various mechanisms that have not yet been applied in calorics. Based on this, we provide guidelines and target characteristics for future research activities in the field of caloric technologies.