Environmental Engineering Reference
In-Depth Information
Chapter 6
Special Heat Transfer Mechanisms:
Active and Passive Thermal Diodes
Many types of systems and devices require speci
c thermal management. For
example, they can operate in such a manner that a rapid redirection of the heat
ux
or its intensity is required. This relates to different kinds of electronic devices,
sensors, actuators, energy conversion devices, as well as some emerging technol-
ogies. The latter include ferroic energy conversion technologies based on mag-
netocaloric, 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-
fl
ux variations (i.e. Stirling devices).
This chapter presents mechanisms and devices that can be applied as solid-state
and (micro)
fl
fl
uidic thermal diodes. The thermal diode (heat
“
semiconductor
”
,
thermal switch, heat valve, thermal recti
er) is a physical phenomenon, mechanism
or device in which it is possible to manipulate and control the direction of the heat
fl
ux. In this chapter the charac-
teristics of such thermal diodes are described and presented with respect to different
potential applications.
A careful reader of this topic will realize that the application of thermal diode
mechanisms can be crucial for the future development of ferroic solid-state tech-
nologies. Conventional heat transfer mechanisms, such as heat convection, are too
limited by the heat transfer surface and the properties of the working
ux and sometimes also the intensity of the heat
fl
uid. 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.
fl
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