Special heat transfer mechanisms: Active and passive thermal diodes

Abstract

Many types of systems and devices require specific thermal management. For example, they can operate in such a manner that a rapid redirection of the heat flux or its intensity is required. This relates to different kinds of electronic devices, sensors, actuators, energy conversion devices, as well as some emerging technologies. The latter include ferroic energy conversion technologies based on magnetocaloric, electrocaloric, elastocaloric and other effects related to solid-state physics. With certain new design ideas it is perhaps even possible to reconsider existing systems and devices, which apply heat regenerators or require periodic heat-flux variations (i.e. Stirling devices). This chapter presents mechanisms and devices that can be applied as solid-state and (micro)fluidic thermal diodes. The thermal diode (heat “semiconductor”, thermal switch, heat valve, thermal rectifier) is a physical phenomenon, mechanism or device in which it is possible to manipulate and control the direction of the heat flux and sometimes also the intensity of the heat flux. In this chapter the characteristics of such thermal diodes are described and presented with respect to different potential applications. A careful reader of this book will realize that the application of thermal diode mechanisms can be crucial for the future development of ferroic solid-state technologies. Conventional heat transfer mechanisms, such as heat convection, are too limited by the heat transfer surface and the properties of the working fluid. In order to boost the power density of the magnetocaloric device by one order of magnitude or more, a different research direction is required that may take us out of the scope of the familiar and conventional active magnetic regeneration, which is actually based on heat convection. One solution is the introduction of thermal diode mechanisms. These can also lead to the design and construction of a new and advanced generation of magnetocaloric energy conversion or other ferroic (e.g., electrocaloric) devices.