US-12618618-B2 - Planar bridging-droplet thermal diodes

US12618618B2US 12618618 B2US12618618 B2US 12618618B2US-12618618-B2

Abstract

This disclosure provides a thermal diode including a first plate having a first surface defining a wick structure. The thermal diode can include a second plate having a smooth surface facing the wick structure, the smooth surface and the wick structure defining a chamber for accommodating a phase-change liquid. The thermal diode also can include a separator positioned between the first plate and the second plate to separate the wick structure from the smooth surface by a gap that is less than a capillary length of the phase-change liquid.

Inventors

Jonathan B. Boreyko
Mojtaba EDALATPOUR
Kevin R. Murphy
Ranit MUKHERJEE

Assignees

VIRGINIA TECH INTELLECTUAL PROPERTIES, INC.

Dates

Publication Date: 20260505
Application Date: 20210625

Claims (15)

1 . A thermal diode, comprising: a smooth condensing surface; a wicked evaporating surface substantially parallel to the condensing surface, wherein the wicked evaporating surface and the condensing surface are separated by a predetermined distance to form a chamber therebetween; and a phase-change liquid within the chamber, wherein the predetermined distance between the wicked evaporating surface and the condensing surface is less than or equal to a critical distance, and wherein the critical distance is defined as the largest distance between the wicked evaporating surface and the condensing surface at which, when a droplet of the phase-change liquid condenses on the condensing surface, the droplet can grow to a height to bridge a gap between the wicked evaporating surface and the condensing surface.
2 . The thermal diode according to claim 1 , further comprising an insulating gasket separating the wicked evaporating surface and the condensing surface and defining the predetermined distance therebetween and forming insulating walls on edges of the chamber.
3 . The thermal diode according to claim 2 , wherein one or both of the wicked evaporating surface and the condensing surface comprise copper, silicon, aluminum, steel, titanium, or a combination thereof.
4 . The thermal diode according to claim 1 , wherein the phase change liquid comprises water or a mixture thereof.
5 . The thermal diode according to claim 1 , wherein the smooth condensing surface comprises a hydrophobic coating.
6 . The thermal diode according to claim 5 , wherein the hydrophobic coating comprises a hydrophobic thiol coating or a hydrophobic polymer coating.
7 . The thermal diode according to claim 1 , wherein the smooth condensing surface has a surface roughness about 5 nm, about 1 nm, about 0.5 nm, or less.
8 . The thermal diode according to claim 1 , wherein the wicked evaporating surface comprises a plurality of micro-scale pillars, micro-scale dimples, a micro-mesh, or a sintered copper surface.
9 . The thermal diode according to claim 1 , wherein the thermal diode has a diodicity of at least 10, at least 20, at least 40, or at least 60 and up to about 150 or 300 at a temperature of about 20° C. to about 90° C.
10 . The thermal diode according to claim 1 , wherein a diodicity of the thermal diode varies by 25% or less with changes in orientation of the thermal diode in relation to the gravitational field.
11 . The thermal diode according to claim 1 , wherein a shortest straightline distance between the smooth condensing surface and the wicked evaporating surface is about 500 μm or less, about 300 μm or less, or about 100 μm or less.
12 . The thermal diode according to claim 1 , wherein the thermal diode has an aspect ratio defined as either a length or a width over a height of greater than 2, such that the thermal diode is essentially two-dimensional.
13 . The thermal diode according to claim 2 , wherein the insulating gasket provides fluidic sealing of the chamber and prevents or reduces thermal conduction during operation of the thermal diode.
14 . The thermal diode according claim 1 , wherein the thermal diode is attached to a body selected from at least one of an electronic device, a biological system, a medical implant, a dwelling, a construction material, a window, a motorized land or water vehicle, a satellite, an aerospace vehicle, a spacecraft, a chemical processing plant, a power plant, a mechanical machine, an electromechanical system, an energy harvesting device, a nuclear reactor, and an energy storage system.
15 . A method of rectifying heat flow, the method comprising providing a thermal diode according to claim 1 .

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is the 35 U.S.C. § 371 national stage application of PCT Application No. PCT/US2021/039106, filed Jun. 25, 2021, where the PCT claims priority to U.S. Provisional Patent Application No. 63/044,135, entitled “Planar Bridging-Droplet Thermal Diodes,” filed Jun. 25, 2020, both of which are incorporated by reference herein in their entireties. TECHNICAL FIELD This disclosure relates to heat rectifying devices, and, in particular, to thermal diodes. DESCRIPTION OF THE RELATED TECHNOLOGY Thermal diodes are devices that conduct heat more efficiently in one path compared to that in the opposite path. Thermal diodes are desirable for the smart thermal management of heat producing devices, such as, for example, electronic devices and spacecraft, as the thermal diodes can effectively dump onboard heat while also shielding from external heat sources. SUMMARY In one aspect of the disclosure, a thermal diode includes a smooth condensing surface, a wicked evaporating surface substantially parallel to the condensing surface, wherein the wicked evaporating surface and the condensing surface are separated by a predetermined distance to form a chamber therebetween, and a phase-change liquid within the chamber, where the predetermined distance between the wicked evaporating surface and the condensing surface is less than or equal to a critical distance, and where the critical distance is defined as the largest distance between the wicked evaporating surface and the condensing surface at which, when a droplet of the phase-change liquid condenses on the condensing surface, the droplet can grow to a height to bridge the gap between the wicked evaporating surface and the condensing surface. In some embodiments, the thermal diode further includes an insulating gasket separating the wicked evaporating surface and the condensing surface and defining the predetermined distance therebetween and forming insulating walls on edges of the chamber. In some embodiments, one or both of the wicked evaporating surface and the condensing surface comprise copper, silicon, aluminum, steel, titanium, or a combination thereof. In some embodiments, the phase-change liquid comprises water or a mixture thereof. In some embodiments, the smooth condensing surface comprises a hydrophobic coating. In some embodiments, the hydrophobic coating comprises a hydrophobic thiol coating or a hydrophobic polymer coating. In some embodiments, the smooth condensing surface has a surface roughness about 5 nm, about 1 nm, about 0.5 nm, or less. In some embodiments, the wicked evaporating surface comprises a plurality of micro-scale pillars, micro-scale dimples, a micro-mesh, or a sintered copper surface. In some embodiments, the thermal diode has a diodicity of at least 10, at least 20, at least 40, or at least 60 and up to about 150 or 300 at a temperature of about 20° C. to about 90° C. In some embodiments, a diodicity of the thermal diode varies by 25% or less with changes in orientation of the thermal diode in relation to the gravitational field. In some embodiments, a shortest straightline distance between the smooth condensing surface and the wicked evaporating surface is about 500 μm or less, about 300 μm or less, or about 100 μm or less. In some embodiments, the thermal diode has an aspect ratio defined as either a length or a width over a height of greater than 2, such that the thermal diode is essentially two-dimensional. In some embodiments, the gasket provides fluidic sealing of the chamber and prevents or reduces thermal conduction during operation of the thermal diode. In some embodiments, the thermal diode is attached to a body selected from at least one of an electronic device, a biological system, a medical implant, a dwelling, a construction material, a window, a motorized land or water vehicle, a satellite, an aerospace vehicle, a spacecraft, a chemical processing plant, a power plant, a mechanical machine, an electromechanical system, an energy harvesting device, a nuclear reactor, and an energy storage system. In another aspect of the disclosure, a method of rectifying heat flow includes providing a thermal diode according to any aspect discussed herein. In yet another aspect of the disclosure a thermal diode includes a first plate having a first surface defining a wick structure, a second plate having a smooth surface facing the wick structure, the smooth surface and the wick structure defining a chamber for accommodating a phase-change liquid, and a separator positioned between the first plate and the second plate to separate the wick structure from the smooth surface by a gap that is less than a capillary length of the phase-change liquid. In some embodiments, the separator is a gasket that seals the chamber and that extends along the perimeters of the first plate and the second plate. In some embodiments, the gap is less than an order of magnitude less than the capillary length. In some e