In-situ fill fraction adjustment of oscillating heat pipe

Abstract

A switchable oscillating heat pipe (OHP) system that comprises an OHP device comprising a plurality of OHP microchannels, a switching control fluid reservoir fluidly connected to the OHP device by a fluid transfer conduit, and a reservoir temperature control device. The reservoir temperature control device is structured and operable to selectively adjust a temperature of the switching control fluid reservoir to create a pressure differential between the switching control fluid reservoir and the OHP device. The pressure differential will generate movement of a working fluid between the switching control fluid reservoir and the OHP device to in-situ change a working fluid fill fraction of the OHP device to selectively switch OHP device between an ON state and an OFF state.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 770,424, filed on Mar. 12, 2025. The disclosure of the above application is incorporated herein by reference in its entirety.FIELD

[0002] The present teachings relate to controlling a working fluid fill fraction within an oscillating heat pipe (OHP), and more particularly to a system and method for controlling the transition of the OHP device from an operating state to a non-operating state by controlling the a working fluid fill fraction within the oscillating heat pipe (OHP).BACKGROUND

[0003] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0004] Oscillating heat pipes (OHPs) devices are typically filed with a predetermined amount of working fluid that dictates the performance (i.e., cooling efficiency) of the OHP device. In various instances it is desirable to adjust the performance of the OHP device based on changing temperature differences between the heat absorption portion(s) and the heat rejection portion(s) of the OHP device. In order to adjust the performance of the OHP device in such instances the amount of working fluid within the OHP device (i.e., the working fluid fill fraction) can be adjusted while the OHP device is disposed in an operational environment and setting (i.e., in-situ adjustment of the working fluid fill fraction). However, there can be situations where the in-situ adjustment of the working fluid must be stopped to prevent damage to the OHP device and / or the device(s), system(s) or object(s) the OHP device is cooling. For example, in some OHP device applications, to avoid damage to a heat source the temperature of the heat source (i.e., the device(s), system(s) or object(s) the OHP device is cooling) cannot exceed an upper limit and / or also cannot exceed a lower limit.SUMMARY

[0005] To address the scenario described above, the present disclosure provides an OHP system for controlling the operation of an oscillating heat pipe (OHP) device. In various embodiments the OHP system comprises an OHP device having OHP microchannels with a working fluid disposed therein, a switching control fluid reservoir fluidly connected to the OHP microchannels via a fluid transfer tube, and a reservoir temperature control mechanism. The reservoir temperature control device is configured to, in-situ, adjust the temperature of the switching control fluid reservoir to create a differential pressure between the OHP device and the switching control fluid reservoir, thereby causing the working fluid to move between the switching control fluid reservoir and the OHP microchannels to adjust the fill fraction of the OHP device in-situ, which in turn adjusts the temperature differential between heat absorption portion(s) and the heat rejection portion(s) of the OHP device. More particularly, the reservoir temperature control device is configured to, in-situ, stop or pause the operation of the OHP device by adjusting the temperature of the switching control fluid reservoir to create a differential pressure between the OHP device and the switching control fluid reservoir sufficient to change the working fluid fill fraction within the OHP device to a level that is below minimal operational fill-factor. This will controllably stop or pause the operation of the OHP device when further adjustment of the temperature differential between the heat absorption portion(s) and the heat rejection portion(s) of the OHP device would damage the device(s) the OHP device is cooling and / or the OHP device.

[0006] For example, in various embodiments, the present disclosure provides a switchable oscillating heat pipe (OHP) system that comprises an OHP device comprising a plurality of OHP microchannels, a switching control fluid reservoir fluidly connected to the OHP device by a fluid transfer conduit, and a reservoir temperature control device. The reservoir temperature control device is structured and operable to selectively adjust a temperature of the switching control fluid reservoir to create a pressure differential between the switching control fluid reservoir and the OHP device. The pressure differential will generate movement of a working fluid between the switching control fluid reservoir and the OHP device to in-situ change a working fluid fill fraction of the OHP device to selectively switch OHP device between an ON state and an OFF state.

[0007] In various other embodiments, the present disclosure provides a method of selectively switching an oscillating heat pipe (OHP) device between an ON state and an OFF state, wherein the method comprises fluidly coupling an OHP device comprising a plurality of OHP microchannels to a switching control fluid reservoir via a capillary fluid transfer conduit, wherein there is a two-phase working fluid disposed within the OHP microchannels and the switching control fluid reservoir. The method additionally comprises selectively adjusting a temperature of a switching control fluid reservoir via a reservoir temperature control device to create a pressure differential between the switching control fluid reservoir and the OHP device. The method further comprises transferring working fluid between the OHP device and the switching control fluid reservoir via the created pressure differential to change a fill fraction of the OHP device to selectively switched the OHP device between an ON state and an OFF state.

[0008] This summary is provided merely for purposes of summarizing various example embodiments of the present disclosure so as to provide a basic understanding of various aspects of the teachings herein. Various embodiments, aspects, and advantages will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. Accordingly, it should be understood that the description and specific examples set forth herein are intended for purposes of illustration only and are not intended to limit the scope of the present teachings.BRIEF DESCRIPTION OF DRAWINGS

[0009] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present teachings in any way.

[0010] FIGS. 1A, 1B and 1C are exemplary block diagrams generically illustrating a switchable oscillating heat pipe (OHP) system structured and operable to in-situ switch between an ON state and an OFF state based on the temperature of one or more heat sources the OHP system is configured to cool, in accordance with various embodiments of the present disclosure.

[0011] FIG. 2 is an exemplary block diagram illustrating the switchable oscillating heat pipe (OHP) system generically illustrated in FIGS. 1A, 1B and 1C wherein a reservoir temperature control device of the switchable oscillating heat pipe (OHP) system comprises a separate and independent device that is mounted to and in thermal contact with a switching control fluid reservoir of the switchable oscillating heat pipe (OHP) system, in accordance with various embodiments of the present disclosure.

[0012] FIG. 3 is an exemplary block diagram illustrating switchable oscillating heat pipe (OHP) system generically illustrated in FIGS. 1A, 1B and 1C wherein the reservoir temperature control device comprises a portion of an OHP device of the switchable oscillating heat pipe (OHP) system generically, in accordance with various embodiments of the present disclosure.

[0013] FIG. 4 is an exemplary block diagram illustrating a control valve that is structured and operable to control a flow of working fluid between switching control fluid reservoir and the OHP device, in accordance with all embodiments of the present disclosure.

[0014] FIG. 5A is an exemplary cross-sectional view of the switching control fluid reservoir illustrating an internal cavity configuration of the switching control fluid reservoir in accordance with various embodiments of the present disclosure.

[0015] FIG. 5B is an exemplary cross-sectional view of the switching control fluid reservoir illustrating the internal cavity configuration of the switching control fluid reservoir in accordance with various other embodiments of the present disclosure.

[0016] FIG. 5C is an exemplary cross-sectional view of the switching control fluid reservoir illustrating the internal cavity configuration of the switching control fluid reservoir in accordance with various embodiments of the present disclosure.

[0017] Corresponding reference numerals indicate corresponding parts throughout the several views of drawings.DETAILED DESCRIPTION

[0018] The following description is merely exemplary in nature and is in no way intended to limit the present teachings, application, or uses. Throughout this specification, like reference numerals will be used to refer to like elements. Additionally, the embodiments disclosed below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art can utilize their teachings. As well, it should be understood that the drawings are intended to illustrate and plainly disclose presently envisioned embodiments to one of skill in the art, but are not intended to be manufacturing level drawings or renditions of final products and may include simplified conceptual views to facilitate understanding or explanation. As well, the relative size and arrangement of the components may differ from that shown and still operate within the spirit of the invention.

[0019] As used herein, the word “exemplary” or “illustrative” means “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other implementations. All of the implementations described below are exemplary implementations provided to enable persons skilled in the art to practice the disclosure and are not intended to limit the scope of the appended claims.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an”, and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises”, “comprising”, “including”, and “having” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps can be employed.

[0021] When an element, object, device, apparatus, component, region or section, etc., is referred to as being “on”, “engaged to or with”, “connected to or with”, or “coupled to or with” another element, object, device, apparatus, component, region or section, etc., it can be directly on, engaged, connected or coupled to or with the other element, object, device, apparatus, component, region or section, etc., or intervening elements, objects, devices, apparatuses, components, regions or sections, etc., can be present. In contrast, when an element, object, device, apparatus, component, region or section, etc., is referred to as being “directly on”, “directly engaged to”, “directly connected to”, or “directly coupled to” another element, object, device, apparatus, component, region or section, etc., there may be no intervening elements, objects, devices, apparatuses, components, regions or sections, etc., present. Other words used to describe the relationship between elements, objects, devices, apparatuses, components, regions or sections, etc., should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.).

[0022] As used herein the phrase “operably connected to” will be understood to mean two are more elements, objects, devices, apparatuses, components, etc., that are directly or indirectly connected to each other in an operational and / or cooperative manner such that operation or function of at least one of the elements, objects, devices, apparatuses, components, etc., imparts or causes operation or function of at least one other of the elements, objects, devices, apparatuses, components, etc. Such imparting or causing of operation or function can be unilateral or bilateral.

[0023] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. For example, A and / or B includes A alone, or B alone, or both A and B.

[0024] Although the terms first, second, third, etc. can be used herein to describe various elements, objects, devices, apparatuses, components, regions or sections, etc., these elements, objects, devices, apparatuses, components, regions or sections, etc., should not be limited by these terms. These terms may be used only to distinguish one element, object, device, apparatus, component, region or section, etc., from another element, object, device, apparatus, component, region or section, etc., and do not necessarily imply a sequence or order unless clearly indicated by the context.

[0025] Moreover, it will be understood that various directions such as “upper”, “lower”, “bottom”, “top”, “left”, “right”, “first”, “second” and so forth are made only with respect to explanation in conjunction with the drawings, and that components may be oriented differently, for instance, during transportation and manufacturing as well as operation. Because many varying and different embodiments may be made within the scope of the concept(s) taught herein, and because many modifications may be made in the embodiments described herein, it is to be understood that the details herein are to be interpreted as illustrative and non-limiting.

[0026] As used herein, the term “integrally formed” will be understood to mean formed from or as a single piece.

[0027] Generally, an oscillating heat pipe device (OHP device) is a passive heat transfer device (e.g., OHP device 14 shown in attached Figures) that transports heat using a saturated two-phase working fluid hermetically sealed within the capillary-sized OHP channels (e.g., microchannels 22 shown in the attached Figures) formed internally within and completely enclosed internally within a body (e.g., body 26 shown in the attached Figures) of the OHP device. The hydraulic diameter of the OHP microchannels is small enough and the surface tension of the working fluid is great enough such that the OHP microchannels have a capillary effect on the working fluid causing the working fluid to disperse itself throughout the interior area of the OHP microchannels in discrete liquid plugs and vapor bubbles. Generally, the OHP microchannels have a meandering path traveling between areas of the body in thermal contact with one or more heat source (e.g., heat source(s) 30 shown in FIG. 1, e.g., an electronic device such as an integrated circuit semiconductor device, or other heat generating device that is provided, disposed, integrally formed with, or fabricated on the body) and areas of the body in thermal contact with one or more heat sink or cooling zone (e.g., heat sink 34 shown in FIG. 1). When heat from one or more heat source(s) is / are absorbed by the working fluid, a resulting working fluid evaporation and condensation process, as described below, creates pressure imbalances within the OHP microchannels that, coupled with the random distribution of liquid plugs and vapor bubbles, generates motion of the two-phase mixture within the OHP microchannels.

[0028] More specifically, the OHP microchannels are integrally formed and enclosed internally within the body and pass near and / or adjacent and / or in close proximity (e.g., within approximately one to thousands of microns) to heat absorption regions of the body (e.g., areas of the body having the heat source(s) disposed thereon or integrally formed therewith) and also pass near and / or adjacent and / or in close proximity (e.g., within approximately one to thousands of microns) to heat rejection regions of the body (e.g., areas of the body absent the heat source(s) and / or in thermally conductive contact with a heat sink or cooling device / system). As heat is absorbed from heat absorption regions (also known as evaporator regions) by the working fluid within the OHP microchannels, evaporation of the working fluid occurs and the capillary dimensions of the OHP microchannels (e.g., from hundreds of nanometers to tens of thousands of microns, and in some instances up to approximately 1.0 inch) forces the working fluid into a train of liquid plugs and vapor bubbles. The train of liquid plugs and vapor bubbles creates a pressure imbalance within the OHP microchannels. This pressure imbalance forces the working fluid to move within the OHP microchannels, thereby transferring the heat (e.g., both latent and sensible heat) from the heat absorption region(s) (also known as evaporator region(s)) to the heat rejection region(s) of the body (also known as condenser region(s)) where the heat of the vapor phase working fluid is rejected into the ambient air and / or heat sink or cooling device / system. When the heat of the vapor phase working fluid is rejected the vapor phase working fluid converts back to liquid phase, which then moves back to the heat absorption region(s) of the body to repeat the evaporation-condensation cycle to continuously remove heat from, and cool, the heat sources and the OHP device overall.

[0029] Referring now to FIGS. 1A, 1B and 1C, in various embodiments, the present disclosure provides a switchable oscillating heat pipe (OHP) system 10 that comprises an OHP device 14, a switching control fluid reservoir 18 fluidly connected to the OHP device 14 and a reservoir temperature control device 20 (e.g., a heater and / or a heat sink or cold plate). The switching control fluid reservoir 18 is fluidly connected to the OHP device via a hermetic fluid transfer conduit 24. The fluid transfer conduit 24 can be any conduit such as a tube, hose, channel, etc. In various embodiments the fluid transfer conduit 24 can be a microchannel capillary sized conduit such as a microchannel capillary sized tube, hose, channel, etc. The OHP device 14 is structured and operable to transport heat away from one or more heat source 30 (e.g., one or more electronic device such as an integrated circuit semiconductor device, or other heat generating device) to a heat sink 34 when the OHP device 14 in in an ON state as described below. The heat source(s) 30 is / are physically and / or thermally connected to a body 26 of the OHP device. Specifically, the heat source(s) 30 is / are provided, disposed, integrally formed with, or fabricated on a body 22 of the OHP device 14 such that the heat source(s) 30 is are thermally connected to a plurality of the OHP microchannels 22 formed internally within and completely enclosed internally within the OHP device body 26.

[0030] The system 10 is structured and operable to switch the operational status of the OHP device 14 in-situ between an ON state wherein the OHP device 14 transports heat away from the heat source(s) 30 via the oscillation of the two-phase working fluid within the microchannels 22 as described above, and an OFF state wherein the OHP device 14 ceases to transport heat away from the heat source(s) 30 via the oscillation of the two-phase working fluid within the microchannels 22. As used herein, in-situ will be understood to mean when the OHP device 14 is disposed in an operational environment and setting, that is disposed within a system, apparatus, device or mechanism, wherein the OHP device 14 is operational to transport heat away from the heat source(s) 30 that are thermally connected thereto. Generally, control between the ON state and the OFF state is done by controlling a temperature difference between the switching control fluid reservoir 18 and the OHP device 14. This can be achieved by applying heat and / or removing heat from the switching control fluid reservoir 18 and / or the OHP device 14. However, for exemplary purposes the following description will refer to heat being applied to and / or removed from the switching control fluid reservoir 18 via the reservoir temperature control device 20. The method of heating and / or cooling the switching control fluid reservoir 18 can be conduction, convection, and / or radiation (i.e., any heat transfer mechanism). The temperature control device 20 can be any active or passive device, apparatus or system that is structured and operable to put heat into or extract heat from the switching control fluid reservoir 18.

[0031] As described above, generally the interior volume of the OHP device microchannels 22 are filled with a specific amount of working fluid (i.e., a specific ratio of working fluid volume to the microchannels 22 interior volume) referred to as the fill fraction. Particularly, the OHP device microchannels are filled with a specific fill fraction of working fluid. Adjusting the fill fraction of the OHP device 14 alters the performance of the OHP device 14. More specifically, by changing the fill fraction below a certain minimum operating value that is specific to the respective OHP device(s) 14 or above a certain maximum operating value that is specific to the respective OHP device(s) 14 will render the OHP device 14 non-operational. Therefore, the OHP device 14 can be controllably and selectively switched from the ON state to the OFF state by controllably and selectively adjusting the fill fraction to be above the maximum operating value and / or controllably and selectively adjusting the fill fraction to be below the minimum operating value. When in the OFF state (e.g., non-operational state), the OHP device 14 stops operating to transport heat away from the heat source(s) via the oscillation of the two-phase working fluid within the microchannels 22 as described above, and merely transports heat at a rate substantially equal to or close to the heat transport rate of just the structure material of the body 26 of the OHP device 14 (e.g., metal, ceramic, plastic, etc.).

[0032] The switching control fluid reservoir 18 can be any structure of any shape having an internal cavity (in various embodiments the internal cavity can comprise one or more internal microchannels, as described below) having sufficient interior volume to controllably and selectively retain at least a transition amount of working fluid. The transition amount of working fluid is equal to or greater than an amount of working fluid that would alter the fill fraction of the OHP device 14 sufficiently to disable the OHP device 14 if the transition amount of working fluid were removed from the OHP device 14 in-situ, thereby switching the OHP device 14 from the ON state to the OFF state. For example, the switching control fluid reservoir 18 can be any round, square, rectangular, oval, etc., shaped cannister, container, flask, tank, bellows, diaphragm, etc., having an internal cavity with an interior volume sufficient to controllably and selectively retain at least the transition amount of working fluid. In various embodiments, the interior volume of the switching control fluid reservoir 18 can be sufficient to hold a base amount of working fluid plus the transition amount of working fluid. In various embodiments, the fluid can be vapor only (no liquid), as long as the vapor is at the correct temperature and connected to the OHP device 14 volume, the pressure will be determined by the thermodynamic state. If it is all vapor in the switching control fluid reservoir 18, and the switching control fluid reservoir 18 has reached equilibrium with the OHP device 14, the pressure of the vapor is higher than the pressure in the OHP device 14. The base amount of working fluid is a predetermined amount of working fluid that generally remains within the switching control fluid reservoir 18 to generate pressure differentials between the OHP device 14 and the switching control fluid reservoir 18 that control of the transfer of the transition amount of working fluid between the OHP device 14 and the switching control fluid reservoir 18, as described below. More specifically, the internal cavity of the switching control fluid reservoir 18 must have an interior volume at least large enough to hold an amount of working fluid that is known to transition the OHP device 14 from the ON state to the OFF state when the transition amount of working fluid is transferred from the OHP device 14 to the switching control fluid reservoir 18 (e.g., 50% to 100% of the OHP working fluid) as described below. More particularly, transferring working fluid between the OHP device 14 and the switching control fluid reservoir 18 comprises heating the switching control fluid reservoir 18 to cause the two-phase working fluid within the switching control fluid reservoir to change phase to generate movement of the working fluid within the switching control fluid reservoir that will cause the working fluid to flow from the switching control fluid reservoir 18 to the OHP device 14.

[0033] As used herein, the OFF state can be considered to be when the performance or thermal conductivity of the OHP device 14 is reduced to approximately the natural thermal conductivity of the empty OHP device body 26 (e.g., there is no working fluid in the OHP device body 26). Said another way, the OFF state can be considered to be when the working fluid volume within the OHP device 14 (e.g., the fill fraction) is altered sufficiently (e.g., reduced) such that the thermal conduction of the OHP device 14 is reduced to less than 50% greater than (e.g. 1% to 49%) the natural thermal conductance of the empty OHP device body 26. Accordingly, when the transition amount of working fluid is transferred from the OHP device 14 to the switching control fluid reservoir 18, as described below, the heat transfer motion of the oscillating two-phase working fluid within the microchannels 22 ceases, thereby switching the OHP device 14 to the OFF state and resulting in a significant loss of heat transfer capability of the OHP device 14. In various instances some working fluid will remain within OHP device microchannels 22 and working fluid motion can occur, but such motion will be restricted to locally moving back and forth, and will not fully flow along the microchannel path.

[0034] In an initial static disposition, the switchable OHP system 10 will comprise at least a predetermined operational amount of working fluid. The operational amount of working fluid is an amount of working fluid that is known to provide efficient operation of the OHP device 14 for cooling the heat source(s) 30 as desired when the operational amount of working fluid is disposed within the OHP device 14 (e.g., within the OHP microchannels 22). When the operational amount of working fluid is disposed within the OHP device 14 the oscillating motion of the working fluid within the microchannels 22 will cause the conductivity of the OHP device 14 to increase significantly above the natural conductance of the OHP device body 26.

[0035] When the OHP system 10 is in the initial static disposition the operational amount of working fluid can entirely within the OHP device 14, or partially within the OHP device 14 and partially within the switching control fluid reservoir 18. For example, in various embodiments, when in the initial static disposition, the OHP system 10 can comprise only the operational amount of working fluid disposed therein such that when switched to the ON state all the working fluid is disposed within the OHP device 14. Alternatively, in various embodiments, when in the initial static disposition, the OHP system 10 can comprise the operational amount of working fluid plus the base amount of working fluid (described above).

[0036] Once the OHP system 10 is in an operational disposition and it is desirable to place the OHP device 14 in the ON state, the reservoir temperature control device 20 is operated to adjust (e.g., increase) the temperature of the switching control fluid reservoir 18 is to change the internal pressure and / or the saturation pressure of any amount of working fluid with in the switching control fluid reservoir 18 relative to the saturation pressure of the working fluid within the OHP device 14. The resulting differential pressure between the OHP device 14 and the switching control fluid reservoir 18 will cause fluid to move between the switching control fluid reservoir 18 and the OHP device 14 (more particularly the microchannels 22). For example, if switching control fluid reservoir 18 is heated via the reservoir temperature control device 20 whereby the pressure differential is such that pressure and / or saturation pressure the working fluid within the switching control fluid reservoir 18 and / or the one or more internal microchannels of the switching control fluid reservoir 18 is greater than that of the saturation pressure of the working fluid within the OHP device 14, working fluid will flow from the switching control fluid reservoir 18 into the OHP device 14 (e.g., into the OHP device microchannels 22). Thereafter, the temperature of the switching control fluid reservoir 18 is increased, via the reservoir temperature control device 20, thereby transferring more working fluid from the switching control fluid reservoir 18 into the OHP device 14 until the OHP device 14 has the operational amount of working fluid disposed therein. Thereafter, the switching control fluid reservoir 18 is maintained at a temperature that will keep the operational amount of working fluid within the OHP device and hence maintain the OHP device in the ON state, whereby the OHP device is cooling the heat source(s) 30. More specifically, when the switching control fluid reservoir 18 is at a higher temperature than the OHP device 14, via control of the reservoir temperature control device 20, the working fluid will move from the switching control fluid reservoir 18 into the OHP microchannels 22 and the OHP device 14 will efficiently transport heat from the heat source(s) 30 to the heat sink (e.g., ON state).

[0037] Conversely, if switching control fluid reservoir 18 is at a temperature (e.g., cooled via the reservoir temperature control device 20) whereby the pressure differential is such that pressure and / or saturation pressure the working fluid within the switching control fluid reservoir 18 and / or the one or more internal microchannels of the switching control fluid reservoir 18 is less than that of the saturation pressure of the working fluid within the OHP device 14, working fluid will flow from the OHP device 14 (e.g., from the OHP device microchannels 22) into the switching control fluid reservoir 18. Thereafter, the temperature of the switching control fluid reservoir 18 can be maintained or further decreased, via the reservoir temperature control device 20, to transfer more working fluid from the OHP device 14 into the switching control fluid reservoir 18 until at least the transition amount of working fluid within OHP device 14 has been transferred to the switching control fluid reservoir 18 whereby the OHP device is in placed the OFF state. Thereafter, the switching control fluid reservoir 18 is maintained at a temperature that will retain at least the transition amount of working fluid within the switching control fluid reservoir 18 and hence maintain the OHP device in the OFF state, whereby the OHP device 14 ceases to cool the heat source(s) 30 via the oscillation of the via the oscillation of the two-phase working fluid within the microchannels 22. More specifically, when the switching control fluid reservoir 18 is at a lower temperature than the OHP device 14, the working fluid will move from the OHP microchannels 22 into the switching control fluid reservoir 18. Therefore, when the temperature of the switching control fluid reservoir 18 is sufficiently lower than the temperature of the OHP device 14 at least the transition amount working fluid will move from the OHP microchannels 22 into the switching control fluid reservoir 18 such that the OHP device will not have sufficient fluid to operate (e.g., Off state)-operational mode). As set forth above, when in the OFF state the effective thermal conductivity of the OHP device 14 is the same or nearly the same as the thermal conductivity of just the material of the OHP device body 26.

[0038] Therefore, if during in-situ operation of the OHP system 10 the heat source(s) 30 are at a temperature such that cooling of the heat source(s) 30 via the oscillation of the two-phase working fluid within the microchannels 22 is no longer desirable, the OHP device 14 can be switched in-situ from the ON state to the OFF state as described above. Particularly, the OHP device 14 can be switched in-situ from the ON state to the OFF state by controllably and selectively changing the temperature of the switching control fluid reservoir 18 (e.g., lowering the temperature) such that pressure and / or saturation pressure the working fluid within the switching control fluid reservoir 18 and / or the one or more internal microchannels of the switching control fluid reservoir 18 is less than that of the saturation pressure of the working fluid within the OHP device 14. As described above, such a pressure differential will transfer at least a transition amount of working fluid from the OHP device 14 to the switching control fluid reservoir 18, and thereby in-situ switch the OHP device from the ON state to the OFF state.

[0039] As described above in various embodiments, the switching control fluid reservoir 18 can comprise a bellows or diaphragm. In such embodiments, the internal cavity of the switching control fluid reservoir 18 can have an adjustable volume. In such embodiments, the adjustment of the physical volume of the internal cavity will change the amount of working fluid in the OHP device 14 (e.g., the fill fraction of the OHP device 14) For example, when the switching control fluid reservoir 18 is disposed in a neutral state the internal cavity of the switching control fluid reservoir 18 will have a volume (referred to herein as a neutral volume) such that the internal pressure of the switching control fluid reservoir 18 is substantially the same as the OHP device 14 saturation pressure, the working fluid will be distributed approximately equally between the OHP device microchannels 22, and the switching control fluid reservoir 18. However, if the switching control fluid reservoir 18 is compressed such that volume of the internal cavity is reduced to less than the neutral volume, the working fluid within the switching control fluid reservoir 18 will be transferred to the OHP device 14 until the fill fraction of the OHP device 14 comprises at least the operational amount of working fluid, whereby the OHP device 14 will be placed in the ON state. Conversely, if the switching control fluid reservoir 18 is expanded such that volume of the internal cavity is increased to greater than the neutral volume, the working fluid within the OHP device 14 will be transferred to the switching control fluid reservoir 18 until at least the transition amount of working fluid is removed from the OHP device 14, whereby the OHP device 14 is placed in the OFF state..

[0040] The switching control fluid reservoir 18 and the OHP device 14 can have any physical configuration with regard to location and orientation relative to each other that is suitable for the respective application and installation of the OHP system 10. For example, as illustrated in FIG. 1A, in various embodiments, the switching control fluid reservoir 18 can be a separate and independent structure from the OHP device 14 and not be in physical or thermal contact with the OHP device 14. In such embodiments, the hermetic fluid transfer conduit 24 connecting the internal cavity of the switching control fluid reservoir 18 with the OHP device microchannels 22 can be an external (e.g., external to the OHP device 14 and the switching control fluid reservoir 18) hose, tube or channel that physically and fluidly connects the switching control fluid reservoir 18 with the OHP device 14.

[0041] In various other embodiments, as exemplarily illustrated in FIG. 1B, the switching control fluid reservoir 18 can be a separate and independent structure from the OHP device 14 that is in physical or thermal contact with the OHP device 14. In such embodiments, the switching control fluid reservoir 18 can be in physical or thermal contact with the OHP device 14 at any desired location of the OHP device 14. In such embodiments, the switching control fluid reservoir 18 can be connected to or mounted to or joined with the OHP device body 26 via any suitable connecting / mounting / joining means such as welding, soldering, clueing, etc. In such embodiments, the hermetic fluid transfer conduit 24 connecting the internal cavity of the switching control fluid reservoir 18 with the OHP device microchannels 22 can be a fluid channel formed interiorly within the OHP device body 26 and / or the switching control fluid reservoir 18.

[0042] In yet other embodiments, as exemplarily illustrated in FIG. 1C the switching control fluid reservoir 18 can be formed internally within the OHP device body 26. In such embodiments, the hermetic fluid transfer conduit 24 connecting the internal cavity of the switching control fluid reservoir 18 with the OHP device microchannels 22 can be a fluid channel formed interiorly within the OHP device body 26.

[0043] Referring now to FIGS. 1A, 1B, 1C and 2, in various embodiments the reservoir temperature control device 20 (e.g., a heat source and / or heat sink such as an electric heater, a radiator, a cold plate, etc.) can be a separate and independent device that is mounted to and in thermal contact with the switching control fluid reservoir 18, and is not in thermal contact with the OHP device 14 (i.e., the reservoir temperature control device 20 is thermally mounted to the switching control fluid reservoir 18). The reservoir temperature control device 20 is controllable via any suitable control mechanism, device or means to controllably and selectively alter the temperature in the switching control fluid reservoir 18 to in-situ switch the OHP device 14 between the ON state and the OFF state by controlling the fill fraction of the OHP device 14 via transfer of the working fluid between the OHP device 14 and the switching control fluid reservoir 18, as described above. The reservoir temperature control device 20 can be actively controlled or passively known to be at a known temperature to switch the OHP device 14 between the ON and OFF states when desired. Although this embodiment is exemplarily illustrated in FIG. 2 having the OHP device 14 and the switching control fluid reservoir 18 as separate and independent structures that are not in physical or thermal contact with each other, it will be understood that any of the generic embodiments shown in FIGS. 1A, 1B and 1C can comprise the reservoir temperature control device 20 being a separate in independent device that is mounted to and in thermal contact with the switching control fluid reservoir 18.

[0044] Referring now to FIGS. 1A, 1B, 1C and 3, in various embodiments the reservoir temperature control device 20 can comprise a portion of the OHP device 14. That is, the temperature of the switching control fluid reservoir 18 can be controlled by thermal connection (and in various instances physical connection) to a portion or section of the OHP device 14. This is a passive configuration, wherein the temperature at the thermal connection of the switching control fluid reservoir 18 to the OHP device 14 (i.e., the temperature control device 20) is not actively controlled. Rather, the temperature at the location of the connection between the switching control fluid reservoir 18 and OHP device 14 (i.e., the temperature of the temperature control device 20) controls the flow of working fluid between the OHP device 14 and the switching control fluid reservoir 18, thereby controlling operation of the switching control fluid reservoir 18 to in-situ switch the OHP device 14 between the ON state and the OFF state by controlling the fill fraction of the OHP device 14 via transfer of the working fluid between the OHP device 14 and the switching control fluid reservoir 18, as described above.

[0045] For example, as the temperature at the thermal connection of the switching control fluid reservoir 18 to the OHP device 14 (i.e., the temperature of the temperature control device 20) increases working fluid will flow from the switching control fluid reservoir 18 into the OHP device 14, as described above. Conversely, as the temperature at the thermal connection of the switching control fluid reservoir 18 to the OHP device 1414 (i.e., the temperature of the temperature control device 20) decreases working fluid will flow from the OHP device 14 into the switching control fluid reservoir 18, as described above. the thermal link between the switching control fluid reservoir 18 into the OHP device 14 can be a direct contact between the switching control fluid reservoir 18 into the OHP device 14, a thermal interface material, a metallic structure, etc.

[0046] Although the switching control fluid reservoir 18 is exemplarily illustrated in FIG. 3 to be thermally connected to the OHP device at the heat sink portion / section of the OHP device 14, the switching control fluid reservoir 18 can be thermally connected to any portion / section of the OHP device 14 (e.g., the heat source portion / section or the adiabatic portion / section between the heat source portion / section and the heat sink portion / section) and function as described above. Additionally, although this embodiment is exemplarily illustrated in FIG. 3 having the OHP device 14 and the switching control fluid reservoir 18 as separate and independent structures that are thermally and physically connected, it will be understood that the thermal connection of the switching control fluid reservoir 18 to the OHP device 14 can be equally applicable to any of the generic embodiments shown in FIGS. 1A, 1B and 1C.

[0047] Referring now to FIGS. 1A, 1B, 1C, 2, 3 and 4, all of the embodiments described above exemplarily illustrate the fluid transfer conduit 24 as being an open conduit (e.g., absent a flow control valve) such that the amount of working fluid within the OHP device 14 and the switching control fluid reservoir 18, and the flow of the working fluid therebetween, is controlled and maintained via control of the temperature of the reservoir temperature control device 20. For example, in various embodiments, the switching control fluid reservoir 18 must be held at a temperature higher than the OHP device 14 to maintain operation of the OHP device 14 via the oscillation of the via the oscillation of the two-phase working fluid within the microchannels 22. It can take considerable energy to maintain this temperature differential. In various applications of the OHP system 10 it can be desirable to conserve this energy. Therefore, in all embodiments described herein, a control valve 38 can be disposed within the fluid transfer conduit 24 to further control the flow of working fluid between the OHP device 14 and the switching control fluid reservoir 18. Particularly, the control valve 38 is structured and operable to isolate the working fluid in a selected distribution between the OHP device 14 and the switching control fluid reservoir 18 once it has moved between the OHP device 14 and the switching control fluid reservoir 18 to place the OHP device in ON state and in the OFF state. Accordingly, the temperature differential between the OHP device 14 and the switching control fluid reservoir 18 only needs to be maintained while the valve is Open and the working fluid is flowing therebetween. Once the desired amount of working fluid has reached its destination, the control valve 38 can be closed such that the operational status of the OHP device 14 (e.g., either the ON state or the Off state or any state therebetween) can be maintained without using energy to heat the reservoir temperature control device 20.

[0048] Referring now to FIGS. 1A, 1B, 1C, 2, 3, 4 and 5A, as described above, the switching control fluid reservoir 18 can be any structure of any shape having an internal cavity having sufficient interior volume to controllably and selectively retain at least the transition amount of working fluid. For example, as exemplarily illustrated in FIG. 5A, in various embodiments the switching control fluid reservoir 18 can comprise an internal cavity 42. The internal cavity 42 is a single open space having no structure disposed within the single open space, wherein the single open space is sized to have an internal volume sufficient to controllably and selectively retain at least the transition amount of working fluid, as described above.

[0049] Referring now to FIGS. 1A, 1B, 1C, 2, 3, 4 and 5B, by increasing the contact surface area of fluid within the switching control fluid reservoir 18, the vapor within the switching control fluid reservoir 18, and hence the pressure differential between the OHP device 14 and the switching control fluid reservoir 18, can be generated more quickly (it will generally require a higher heat flux). The contact surface area of the fluid within the switching control fluid reservoir 18 will be understood to mean the surface area of the switching control fluid reservoir 18 with which the fluid is in thermal contact. Any means, element, device or feature that will increase the contact surface area of the fluid within the switching control fluid reservoir 18 will have this result. For example, the interior of the switching control fluid reservoir 18 can comprise a plurality of microchannels, solid foams, finned structures, and / or any other means, element, device or feature of increasing internal surface area of the switching control fluid reservoir 18, and hence the surface contact area of the fluid. For example, as exemplarily illustrated in FIG. 5B, in various embodiments the switching control fluid reservoir 18 can comprise and plurality of capillary sized reservoir microchannels 46, similar to the OHP microchannels 22. The cumulative internal volume of the plurality of the reservoir microchannels 46 is sufficient to controllably and selectively retain at least the transition amount of working fluid, as described above. In such embodiments, the working fluid within the reservoir microchannels 46 will behave similarly to the behavior of the working fluid within the OHP microchannels 22, as described above. That is, controllably and selectively heating the switching control fluid reservoir 18 using the reservoir temperature control device 20 will cause the two-phase working fluid within the reservoir microchannels 46 to change phase, thereby generating movement of the working fluid within the reservoir microchannels. This generated movement will cause the working fluid to flow from the switching control fluid reservoir 18 to the OHP device 14 until the fill fraction of the OHP device 14 comprises at least the operational amount of working fluid, whereby the OHP device 14 will be placed in the ON state. Heating the switching control fluid reservoir 18, via the reservoir temperature control device 20, to generate movement of the working fluid within the reservoir microchannels 46 and push the working fluid into the OHP device 14 will expend much less energy than open cavity embodiments described above.

[0050] Referring now to FIGS. 1A, 1B, 1C, 2, 3, 4 and 5C, since the working fluid within the entire OHP system 10 consists of both vapor and liquid, it will require less overall energy if the working fluid flow between the OHP device 14 and the switching control fluid reservoir 18 is liquid, as opposed to vapor. Therefore, as exemplarily illustrated in FIG. 5C, in various embodiments, the switching control fluid reservoir 18 can comprise an interior cavity 50 and a porous wick 54 disposed on and lining the walls of the cavity 50 and at least partially fills the internal lumen of the fluid transfer conduit 24. The wick 54 lining the walls of the cavity 50 defines a chamber 58 therebetween. The diameter of the pores within the wick 54 is smaller than width L of the chamber 58. This will result in the liquid phase working fluid being absorbed by the wick 54 such that gaseous phase working fluid will be prevented from transferring between the switching control fluid reservoir 18 and the OHP device 14 and only liquid phase working fluid is transferred between the switching control fluid reservoir 18 and the OHP device 14. If the wick exists all the way through the connecting tube to the OHP, or the connecting tube is smaller than the OHP channel, then the tube will preferentially transport liquid to the reservoir. It is envisioned that having the wick 54 disposed within the entire length of the fluid transfer conduit 24 will improve transport of only liquid phase working fluid through the fluid transfer conduit 24.

[0051] In summary, the present disclosure provides the switchable oscillating heat pipe (OHP) system 10 that controls the operation of the OHP device 14 by adjusting the fill factor the OHP device 14, in-situ. The switchable oscillating heat pipe (OHP) system 10 is structured and operable to, in-situ, controllably and selectively switch the OHP device 14 between the ON state and the OFF state by changing the fill fraction of the OHP device 14. Particularly, the OHP system 10 is structured and operable to limit the heat rejection of the heat source(s) 30 being cooled by the OHP device 14 in order to prevent failure of the heat source(s) 30 and / or the OHP device 14. More particularly, the OHP system 10 is structured and operable to in-situ switch between an ON state and an OFF state based on the temperature of one or more heat sources the OHP system is configured to cool, thereby preventing damage to the heat source(s). For example, the OHP system 10 can be configured to be in the ON state, wherein an OHP device 14 operates to cool the heat source(s) 30, when the heat source(s) 30 is / are above a first temperature threshold that is specific to the respective heat source(s) 30, and to switch to the OFF state, wherein the OHP device 14 stops operating to cool the heat source(s) 30, when the heat source(s) 30 is / are below a second temperature threshold that is specific to the respective heat source(s) 30. The first and second temperature thresholds can be different temperature values or the same temperature value. The OHP system 10 can be utilized in many different applications. For example, the OHP system 10 can be particularly useful for OHP systems installed on satellites due to the wide environmental temperature ranges during an orbital cycle and the heat loads from the sun, earth, etc.

[0052] The description herein is merely exemplary in nature and, thus, variations that do not depart from the gist of that which is described are intended to be within the scope of the teachings. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and / or functions, it should be appreciated that different combinations of elements and / or functions can be provided by alternative embodiments without departing from the scope of the disclosure. Such variations and alternative combinations of elements and / or functions are not to be regarded as a departure from the spirit and scope of the teachings.

Examples

Embodiment Construction

[0018]The following description is merely exemplary in nature and is in no way intended to limit the present teachings, application, or uses. Throughout this specification, like reference numerals will be used to refer to like elements. Additionally, the embodiments disclosed below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art can utilize their teachings. As well, it should be understood that the drawings are intended to illustrate and plainly disclose presently envisioned embodiments to one of skill in the art, but are not intended to be manufacturing level drawings or renditions of final products and may include simplified conceptual views to facilitate understanding or explanation. As well, the relative size and arrangement of the components may differ from that shown and still operate within the spirit of the inven...

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 770,424, filed on Mar. 12, 2025. The disclosure of the above application is incorporated herein by reference in its entirety.FIELD

[0002] The present teachings relate to controlling a working fluid fill fraction within an oscillating heat pipe (OHP), and more particularly to a system and method for controlling the transition of the OHP device from an operating state to a non-operating state by controlling the a working fluid fill fraction within the oscillating heat pipe (OHP).BACKGROUND

[0003] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0004] Oscillating heat pipes (OHPs) devices are typically filed with a predetermined amount of working fluid that dictates the performance (i.e., cooling efficiency) of the OHP device. In various instances it is desirable to adjust the performance of the OHP device based on changing temperature differences between the heat absorption portion(s) and the heat rejection portion(s) of the OHP device. In order to adjust the performance of the OHP device in such instances the amount of working fluid within the OHP device (i.e., the working fluid fill fraction) can be adjusted while the OHP device is disposed in an operational environment and setting (i.e., in-situ adjustment of the working fluid fill fraction). However, there can be situations where the in-situ adjustment of the working fluid must be stopped to prevent damage to the OHP device and / or the device(s), system(s) or object(s) the OHP device is cooling. For example, in some OHP device applications, to avoid damage to a heat source the temperature of the heat source (i.e., the device(s), system(s) or object(s) the OHP device is cooling) cannot exceed an upper limit and / or also cannot exceed a lower limit.SUMMARY

[0005] To address the scenario described above, the present disclosure provides an OHP system for controlling the operation of an oscillating heat pipe (OHP) device. In various embodiments the OHP system comprises an OHP device having OHP microchannels with a working fluid disposed therein, a switching control fluid reservoir fluidly connected to the OHP microchannels via a fluid transfer tube, and a reservoir temperature control mechanism. The reservoir temperature control device is configured to, in-situ, adjust the temperature of the switching control fluid reservoir to create a differential pressure between the OHP device and the switching control fluid reservoir, thereby causing the working fluid to move between the switching control fluid reservoir and the OHP microchannels to adjust the fill fraction of the OHP device in-situ, which in turn adjusts the temperature differential between heat absorption portion(s) and the heat rejection portion(s) of the OHP device. More particularly, the reservoir temperature control device is configured to, in-situ, stop or pause the operation of the OHP device by adjusting the temperature of the switching control fluid reservoir to create a differential pressure between the OHP device and the switching control fluid reservoir sufficient to change the working fluid fill fraction within the OHP device to a level that is below minimal operational fill-factor. This will controllably stop or pause the operation of the OHP device when further adjustment of the temperature differential between the heat absorption portion(s) and the heat rejection portion(s) of the OHP device would damage the device(s) the OHP device is cooling and / or the OHP device.

[0006] For example, in various embodiments, the present disclosure provides a switchable oscillating heat pipe (OHP) system that comprises an OHP device comprising a plurality of OHP microchannels, a switching control fluid reservoir fluidly connected to the OHP device by a fluid transfer conduit, and a reservoir temperature control device. The reservoir temperature control device is structured and operable to selectively adjust a temperature of the switching control fluid reservoir to create a pressure differential between the switching control fluid reservoir and the OHP device. The pressure differential will generate movement of a working fluid between the switching control fluid reservoir and the OHP device to in-situ change a working fluid fill fraction of the OHP device to selectively switch OHP device between an ON state and an OFF state.

[0007] In various other embodiments, the present disclosure provides a method of selectively switching an oscillating heat pipe (OHP) device between an ON state and an OFF state, wherein the method comprises fluidly coupling an OHP device comprising a plurality of OHP microchannels to a switching control fluid reservoir via a capillary fluid transfer conduit, wherein there is a two-phase working fluid disposed within the OHP microchannels and the switching control fluid reservoir. The method additionally comprises selectively adjusting a temperature of a switching control fluid reservoir via a reservoir temperature control device to create a pressure differential between the switching control fluid reservoir and the OHP device. The method further comprises transferring working fluid between the OHP device and the switching control fluid reservoir via the created pressure differential to change a fill fraction of the OHP device to selectively switched the OHP device between an ON state and an OFF state.

[0008] This summary is provided merely for purposes of summarizing various example embodiments of the present disclosure so as to provide a basic understanding of various aspects of the teachings herein. Various embodiments, aspects, and advantages will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. Accordingly, it should be understood that the description and specific examples set forth herein are intended for purposes of illustration only and are not intended to limit the scope of the present teachings.BRIEF DESCRIPTION OF DRAWINGS

[0009] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present teachings in any way.

[0010] FIGS. 1A, 1B and 1C are exemplary block diagrams generically illustrating a switchable oscillating heat pipe (OHP) system structured and operable to in-situ switch between an ON state and an OFF state based on the temperature of one or more heat sources the OHP system is configured to cool, in accordance with various embodiments of the present disclosure.

[0011] FIG. 2 is an exemplary block diagram illustrating the switchable oscillating heat pipe (OHP) system generically illustrated in FIGS. 1A, 1B and 1C wherein a reservoir temperature control device of the switchable oscillating heat pipe (OHP) system comprises a separate and independent device that is mounted to and in thermal contact with a switching control fluid reservoir of the switchable oscillating heat pipe (OHP) system, in accordance with various embodiments of the present disclosure.

[0012] FIG. 3 is an exemplary block diagram illustrating switchable oscillating heat pipe (OHP) system generically illustrated in FIGS. 1A, 1B and 1C wherein the reservoir temperature control device comprises a portion of an OHP device of the switchable oscillating heat pipe (OHP) system generically, in accordance with various embodiments of the present disclosure.

[0013] FIG. 4 is an exemplary block diagram illustrating a control valve that is structured and operable to control a flow of working fluid between switching control fluid reservoir and the OHP device, in accordance with all embodiments of the present disclosure.

[0014] FIG. 5A is an exemplary cross-sectional view of the switching control fluid reservoir illustrating an internal cavity configuration of the switching control fluid reservoir in accordance with various embodiments of the present disclosure.

[0015] FIG. 5B is an exemplary cross-sectional view of the switching control fluid reservoir illustrating the internal cavity configuration of the switching control fluid reservoir in accordance with various other embodiments of the present disclosure.

[0016] FIG. 5C is an exemplary cross-sectional view of the switching control fluid reservoir illustrating the internal cavity configuration of the switching control fluid reservoir in accordance with various embodiments of the present disclosure.

[0017] Corresponding reference numerals indicate corresponding parts throughout the several views of drawings.DETAILED DESCRIPTION

[0018] The following description is merely exemplary in nature and is in no way intended to limit the present teachings, application, or uses. Throughout this specification, like reference numerals will be used to refer to like elements. Additionally, the embodiments disclosed below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art can utilize their teachings. As well, it should be understood that the drawings are intended to illustrate and plainly disclose presently envisioned embodiments to one of skill in the art, but are not intended to be manufacturing level drawings or renditions of final products and may include simplified conceptual views to facilitate understanding or explanation. As well, the relative size and arrangement of the components may differ from that shown and still operate within the spirit of the invention.

[0019] As used herein, the word “exemplary” or “illustrative” means “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other implementations. All of the implementations described below are exemplary implementations provided to enable persons skilled in the art to practice the disclosure and are not intended to limit the scope of the appended claims.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an”, and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises”, “comprising”, “including”, and “having” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps can be employed.

[0021] When an element, object, device, apparatus, component, region or section, etc., is referred to as being “on”, “engaged to or with”, “connected to or with”, or “coupled to or with” another element, object, device, apparatus, component, region or section, etc., it can be directly on, engaged, connected or coupled to or with the other element, object, device, apparatus, component, region or section, etc., or intervening elements, objects, devices, apparatuses, components, regions or sections, etc., can be present. In contrast, when an element, object, device, apparatus, component, region or section, etc., is referred to as being “directly on”, “directly engaged to”, “directly connected to”, or “directly coupled to” another element, object, device, apparatus, component, region or section, etc., there may be no intervening elements, objects, devices, apparatuses, components, regions or sections, etc., present. Other words used to describe the relationship between elements, objects, devices, apparatuses, components, regions or sections, etc., should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.).

[0022] As used herein the phrase “operably connected to” will be understood to mean two are more elements, objects, devices, apparatuses, components, etc., that are directly or indirectly connected to each other in an operational and / or cooperative manner such that operation or function of at least one of the elements, objects, devices, apparatuses, components, etc., imparts or causes operation or function of at least one other of the elements, objects, devices, apparatuses, components, etc. Such imparting or causing of operation or function can be unilateral or bilateral.

[0023] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. For example, A and / or B includes A alone, or B alone, or both A and B.

[0024] Although the terms first, second, third, etc. can be used herein to describe various elements, objects, devices, apparatuses, components, regions or sections, etc., these elements, objects, devices, apparatuses, components, regions or sections, etc., should not be limited by these terms. These terms may be used only to distinguish one element, object, device, apparatus, component, region or section, etc., from another element, object, device, apparatus, component, region or section, etc., and do not necessarily imply a sequence or order unless clearly indicated by the context.

[0025] Moreover, it will be understood that various directions such as “upper”, “lower”, “bottom”, “top”, “left”, “right”, “first”, “second” and so forth are made only with respect to explanation in conjunction with the drawings, and that components may be oriented differently, for instance, during transportation and manufacturing as well as operation. Because many varying and different embodiments may be made within the scope of the concept(s) taught herein, and because many modifications may be made in the embodiments described herein, it is to be understood that the details herein are to be interpreted as illustrative and non-limiting.

[0026] As used herein, the term “integrally formed” will be understood to mean formed from or as a single piece.

[0027] Generally, an oscillating heat pipe device (OHP device) is a passive heat transfer device (e.g., OHP device 14 shown in attached Figures) that transports heat using a saturated two-phase working fluid hermetically sealed within the capillary-sized OHP channels (e.g., microchannels 22 shown in the attached Figures) formed internally within and completely enclosed internally within a body (e.g., body 26 shown in the attached Figures) of the OHP device. The hydraulic diameter of the OHP microchannels is small enough and the surface tension of the working fluid is great enough such that the OHP microchannels have a capillary effect on the working fluid causing the working fluid to disperse itself throughout the interior area of the OHP microchannels in discrete liquid plugs and vapor bubbles. Generally, the OHP microchannels have a meandering path traveling between areas of the body in thermal contact with one or more heat source (e.g., heat source(s) 30 shown in FIG. 1, e.g., an electronic device such as an integrated circuit semiconductor device, or other heat generating device that is provided, disposed, integrally formed with, or fabricated on the body) and areas of the body in thermal contact with one or more heat sink or cooling zone (e.g., heat sink 34 shown in FIG. 1). When heat from one or more heat source(s) is / are absorbed by the working fluid, a resulting working fluid evaporation and condensation process, as described below, creates pressure imbalances within the OHP microchannels that, coupled with the random distribution of liquid plugs and vapor bubbles, generates motion of the two-phase mixture within the OHP microchannels.

[0028] More specifically, the OHP microchannels are integrally formed and enclosed internally within the body and pass near and / or adjacent and / or in close proximity (e.g., within approximately one to thousands of microns) to heat absorption regions of the body (e.g., areas of the body having the heat source(s) disposed thereon or integrally formed therewith) and also pass near and / or adjacent and / or in close proximity (e.g., within approximately one to thousands of microns) to heat rejection regions of the body (e.g., areas of the body absent the heat source(s) and / or in thermally conductive contact with a heat sink or cooling device / system). As heat is absorbed from heat absorption regions (also known as evaporator regions) by the working fluid within the OHP microchannels, evaporation of the working fluid occurs and the capillary dimensions of the OHP microchannels (e.g., from hundreds of nanometers to tens of thousands of microns, and in some instances up to approximately 1.0 inch) forces the working fluid into a train of liquid plugs and vapor bubbles. The train of liquid plugs and vapor bubbles creates a pressure imbalance within the OHP microchannels. This pressure imbalance forces the working fluid to move within the OHP microchannels, thereby transferring the heat (e.g., both latent and sensible heat) from the heat absorption region(s) (also known as evaporator region(s)) to the heat rejection region(s) of the body (also known as condenser region(s)) where the heat of the vapor phase working fluid is rejected into the ambient air and / or heat sink or cooling device / system. When the heat of the vapor phase working fluid is rejected the vapor phase working fluid converts back to liquid phase, which then moves back to the heat absorption region(s) of the body to repeat the evaporation-condensation cycle to continuously remove heat from, and cool, the heat sources and the OHP device overall.

[0029] Referring now to FIGS. 1A, 1B and 1C, in various embodiments, the present disclosure provides a switchable oscillating heat pipe (OHP) system 10 that comprises an OHP device 14, a switching control fluid reservoir 18 fluidly connected to the OHP device 14 and a reservoir temperature control device 20 (e.g., a heater and / or a heat sink or cold plate). The switching control fluid reservoir 18 is fluidly connected to the OHP device via a hermetic fluid transfer conduit 24. The fluid transfer conduit 24 can be any conduit such as a tube, hose, channel, etc. In various embodiments the fluid transfer conduit 24 can be a microchannel capillary sized conduit such as a microchannel capillary sized tube, hose, channel, etc. The OHP device 14 is structured and operable to transport heat away from one or more heat source 30 (e.g., one or more electronic device such as an integrated circuit semiconductor device, or other heat generating device) to a heat sink 34 when the OHP device 14 in in an ON state as described below. The heat source(s) 30 is / are physically and / or thermally connected to a body 26 of the OHP device. Specifically, the heat source(s) 30 is / are provided, disposed, integrally formed with, or fabricated on a body 22 of the OHP device 14 such that the heat source(s) 30 is are thermally connected to a plurality of the OHP microchannels 22 formed internally within and completely enclosed internally within the OHP device body 26.

[0030] The system 10 is structured and operable to switch the operational status of the OHP device 14 in-situ between an ON state wherein the OHP device 14 transports heat away from the heat source(s) 30 via the oscillation of the two-phase working fluid within the microchannels 22 as described above, and an OFF state wherein the OHP device 14 ceases to transport heat away from the heat source(s) 30 via the oscillation of the two-phase working fluid within the microchannels 22. As used herein, in-situ will be understood to mean when the OHP device 14 is disposed in an operational environment and setting, that is disposed within a system, apparatus, device or mechanism, wherein the OHP device 14 is operational to transport heat away from the heat source(s) 30 that are thermally connected thereto. Generally, control between the ON state and the OFF state is done by controlling a temperature difference between the switching control fluid reservoir 18 and the OHP device 14. This can be achieved by applying heat and / or removing heat from the switching control fluid reservoir 18 and / or the OHP device 14. However, for exemplary purposes the following description will refer to heat being applied to and / or removed from the switching control fluid reservoir 18 via the reservoir temperature control device 20. The method of heating and / or cooling the switching control fluid reservoir 18 can be conduction, convection, and / or radiation (i.e., any heat transfer mechanism). The temperature control device 20 can be any active or passive device, apparatus or system that is structured and operable to put heat into or extract heat from the switching control fluid reservoir 18.

[0031] As described above, generally the interior volume of the OHP device microchannels 22 are filled with a specific amount of working fluid (i.e., a specific ratio of working fluid volume to the microchannels 22 interior volume) referred to as the fill fraction. Particularly, the OHP device microchannels are filled with a specific fill fraction of working fluid. Adjusting the fill fraction of the OHP device 14 alters the performance of the OHP device 14. More specifically, by changing the fill fraction below a certain minimum operating value that is specific to the respective OHP device(s) 14 or above a certain maximum operating value that is specific to the respective OHP device(s) 14 will render the OHP device 14 non-operational. Therefore, the OHP device 14 can be controllably and selectively switched from the ON state to the OFF state by controllably and selectively adjusting the fill fraction to be above the maximum operating value and / or controllably and selectively adjusting the fill fraction to be below the minimum operating value. When in the OFF state (e.g., non-operational state), the OHP device 14 stops operating to transport heat away from the heat source(s) via the oscillation of the two-phase working fluid within the microchannels 22 as described above, and merely transports heat at a rate substantially equal to or close to the heat transport rate of just the structure material of the body 26 of the OHP device 14 (e.g., metal, ceramic, plastic, etc.).

[0032] The switching control fluid reservoir 18 can be any structure of any shape having an internal cavity (in various embodiments the internal cavity can comprise one or more internal microchannels, as described below) having sufficient interior volume to controllably and selectively retain at least a transition amount of working fluid. The transition amount of working fluid is equal to or greater than an amount of working fluid that would alter the fill fraction of the OHP device 14 sufficiently to disable the OHP device 14 if the transition amount of working fluid were removed from the OHP device 14 in-situ, thereby switching the OHP device 14 from the ON state to the OFF state. For example, the switching control fluid reservoir 18 can be any round, square, rectangular, oval, etc., shaped cannister, container, flask, tank, bellows, diaphragm, etc., having an internal cavity with an interior volume sufficient to controllably and selectively retain at least the transition amount of working fluid. In various embodiments, the interior volume of the switching control fluid reservoir 18 can be sufficient to hold a base amount of working fluid plus the transition amount of working fluid. In various embodiments, the fluid can be vapor only (no liquid), as long as the vapor is at the correct temperature and connected to the OHP device 14 volume, the pressure will be determined by the thermodynamic state. If it is all vapor in the switching control fluid reservoir 18, and the switching control fluid reservoir 18 has reached equilibrium with the OHP device 14, the pressure of the vapor is higher than the pressure in the OHP device 14. The base amount of working fluid is a predetermined amount of working fluid that generally remains within the switching control fluid reservoir 18 to generate pressure differentials between the OHP device 14 and the switching control fluid reservoir 18 that control of the transfer of the transition amount of working fluid between the OHP device 14 and the switching control fluid reservoir 18, as described below. More specifically, the internal cavity of the switching control fluid reservoir 18 must have an interior volume at least large enough to hold an amount of working fluid that is known to transition the OHP device 14 from the ON state to the OFF state when the transition amount of working fluid is transferred from the OHP device 14 to the switching control fluid reservoir 18 (e.g., 50% to 100% of the OHP working fluid) as described below. More particularly, transferring working fluid between the OHP device 14 and the switching control fluid reservoir 18 comprises heating the switching control fluid reservoir 18 to cause the two-phase working fluid within the switching control fluid reservoir to change phase to generate movement of the working fluid within the switching control fluid reservoir that will cause the working fluid to flow from the switching control fluid reservoir 18 to the OHP device 14.

[0033] As used herein, the OFF state can be considered to be when the performance or thermal conductivity of the OHP device 14 is reduced to approximately the natural thermal conductivity of the empty OHP device body 26 (e.g., there is no working fluid in the OHP device body 26). Said another way, the OFF state can be considered to be when the working fluid volume within the OHP device 14 (e.g., the fill fraction) is altered sufficiently (e.g., reduced) such that the thermal conduction of the OHP device 14 is reduced to less than 50% greater than (e.g. 1% to 49%) the natural thermal conductance of the empty OHP device body 26. Accordingly, when the transition amount of working fluid is transferred from the OHP device 14 to the switching control fluid reservoir 18, as described below, the heat transfer motion of the oscillating two-phase working fluid within the microchannels 22 ceases, thereby switching the OHP device 14 to the OFF state and resulting in a significant loss of heat transfer capability of the OHP device 14. In various instances some working fluid will remain within OHP device microchannels 22 and working fluid motion can occur, but such motion will be restricted to locally moving back and forth, and will not fully flow along the microchannel path.

[0034] In an initial static disposition, the switchable OHP system 10 will comprise at least a predetermined operational amount of working fluid. The operational amount of working fluid is an amount of working fluid that is known to provide efficient operation of the OHP device 14 for cooling the heat source(s) 30 as desired when the operational amount of working fluid is disposed within the OHP device 14 (e.g., within the OHP microchannels 22). When the operational amount of working fluid is disposed within the OHP device 14 the oscillating motion of the working fluid within the microchannels 22 will cause the conductivity of the OHP device 14 to increase significantly above the natural conductance of the OHP device body 26.

[0035] When the OHP system 10 is in the initial static disposition the operational amount of working fluid can entirely within the OHP device 14, or partially within the OHP device 14 and partially within the switching control fluid reservoir 18. For example, in various embodiments, when in the initial static disposition, the OHP system 10 can comprise only the operational amount of working fluid disposed therein such that when switched to the ON state all the working fluid is disposed within the OHP device 14. Alternatively, in various embodiments, when in the initial static disposition, the OHP system 10 can comprise the operational amount of working fluid plus the base amount of working fluid (described above).

[0036] Once the OHP system 10 is in an operational disposition and it is desirable to place the OHP device 14 in the ON state, the reservoir temperature control device 20 is operated to adjust (e.g., increase) the temperature of the switching control fluid reservoir 18 is to change the internal pressure and / or the saturation pressure of any amount of working fluid with in the switching control fluid reservoir 18 relative to the saturation pressure of the working fluid within the OHP device 14. The resulting differential pressure between the OHP device 14 and the switching control fluid reservoir 18 will cause fluid to move between the switching control fluid reservoir 18 and the OHP device 14 (more particularly the microchannels 22). For example, if switching control fluid reservoir 18 is heated via the reservoir temperature control device 20 whereby the pressure differential is such that pressure and / or saturation pressure the working fluid within the switching control fluid reservoir 18 and / or the one or more internal microchannels of the switching control fluid reservoir 18 is greater than that of the saturation pressure of the working fluid within the OHP device 14, working fluid will flow from the switching control fluid reservoir 18 into the OHP device 14 (e.g., into the OHP device microchannels 22). Thereafter, the temperature of the switching control fluid reservoir 18 is increased, via the reservoir temperature control device 20, thereby transferring more working fluid from the switching control fluid reservoir 18 into the OHP device 14 until the OHP device 14 has the operational amount of working fluid disposed therein. Thereafter, the switching control fluid reservoir 18 is maintained at a temperature that will keep the operational amount of working fluid within the OHP device and hence maintain the OHP device in the ON state, whereby the OHP device is cooling the heat source(s) 30. More specifically, when the switching control fluid reservoir 18 is at a higher temperature than the OHP device 14, via control of the reservoir temperature control device 20, the working fluid will move from the switching control fluid reservoir 18 into the OHP microchannels 22 and the OHP device 14 will efficiently transport heat from the heat source(s) 30 to the heat sink (e.g., ON state).

[0037] Conversely, if switching control fluid reservoir 18 is at a temperature (e.g., cooled via the reservoir temperature control device 20) whereby the pressure differential is such that pressure and / or saturation pressure the working fluid within the switching control fluid reservoir 18 and / or the one or more internal microchannels of the switching control fluid reservoir 18 is less than that of the saturation pressure of the working fluid within the OHP device 14, working fluid will flow from the OHP device 14 (e.g., from the OHP device microchannels 22) into the switching control fluid reservoir 18. Thereafter, the temperature of the switching control fluid reservoir 18 can be maintained or further decreased, via the reservoir temperature control device 20, to transfer more working fluid from the OHP device 14 into the switching control fluid reservoir 18 until at least the transition amount of working fluid within OHP device 14 has been transferred to the switching control fluid reservoir 18 whereby the OHP device is in placed the OFF state. Thereafter, the switching control fluid reservoir 18 is maintained at a temperature that will retain at least the transition amount of working fluid within the switching control fluid reservoir 18 and hence maintain the OHP device in the OFF state, whereby the OHP device 14 ceases to cool the heat source(s) 30 via the oscillation of the via the oscillation of the two-phase working fluid within the microchannels 22. More specifically, when the switching control fluid reservoir 18 is at a lower temperature than the OHP device 14, the working fluid will move from the OHP microchannels 22 into the switching control fluid reservoir 18. Therefore, when the temperature of the switching control fluid reservoir 18 is sufficiently lower than the temperature of the OHP device 14 at least the transition amount working fluid will move from the OHP microchannels 22 into the switching control fluid reservoir 18 such that the OHP device will not have sufficient fluid to operate (e.g., Off state)-operational mode). As set forth above, when in the OFF state the effective thermal conductivity of the OHP device 14 is the same or nearly the same as the thermal conductivity of just the material of the OHP device body 26.

[0038] Therefore, if during in-situ operation of the OHP system 10 the heat source(s) 30 are at a temperature such that cooling of the heat source(s) 30 via the oscillation of the two-phase working fluid within the microchannels 22 is no longer desirable, the OHP device 14 can be switched in-situ from the ON state to the OFF state as described above. Particularly, the OHP device 14 can be switched in-situ from the ON state to the OFF state by controllably and selectively changing the temperature of the switching control fluid reservoir 18 (e.g., lowering the temperature) such that pressure and / or saturation pressure the working fluid within the switching control fluid reservoir 18 and / or the one or more internal microchannels of the switching control fluid reservoir 18 is less than that of the saturation pressure of the working fluid within the OHP device 14. As described above, such a pressure differential will transfer at least a transition amount of working fluid from the OHP device 14 to the switching control fluid reservoir 18, and thereby in-situ switch the OHP device from the ON state to the OFF state.

[0039] As described above in various embodiments, the switching control fluid reservoir 18 can comprise a bellows or diaphragm. In such embodiments, the internal cavity of the switching control fluid reservoir 18 can have an adjustable volume. In such embodiments, the adjustment of the physical volume of the internal cavity will change the amount of working fluid in the OHP device 14 (e.g., the fill fraction of the OHP device 14) For example, when the switching control fluid reservoir 18 is disposed in a neutral state the internal cavity of the switching control fluid reservoir 18 will have a volume (referred to herein as a neutral volume) such that the internal pressure of the switching control fluid reservoir 18 is substantially the same as the OHP device 14 saturation pressure, the working fluid will be distributed approximately equally between the OHP device microchannels 22, and the switching control fluid reservoir 18. However, if the switching control fluid reservoir 18 is compressed such that volume of the internal cavity is reduced to less than the neutral volume, the working fluid within the switching control fluid reservoir 18 will be transferred to the OHP device 14 until the fill fraction of the OHP device 14 comprises at least the operational amount of working fluid, whereby the OHP device 14 will be placed in the ON state. Conversely, if the switching control fluid reservoir 18 is expanded such that volume of the internal cavity is increased to greater than the neutral volume, the working fluid within the OHP device 14 will be transferred to the switching control fluid reservoir 18 until at least the transition amount of working fluid is removed from the OHP device 14, whereby the OHP device 14 is placed in the OFF state..

[0040] The switching control fluid reservoir 18 and the OHP device 14 can have any physical configuration with regard to location and orientation relative to each other that is suitable for the respective application and installation of the OHP system 10. For example, as illustrated in FIG. 1A, in various embodiments, the switching control fluid reservoir 18 can be a separate and independent structure from the OHP device 14 and not be in physical or thermal contact with the OHP device 14. In such embodiments, the hermetic fluid transfer conduit 24 connecting the internal cavity of the switching control fluid reservoir 18 with the OHP device microchannels 22 can be an external (e.g., external to the OHP device 14 and the switching control fluid reservoir 18) hose, tube or channel that physically and fluidly connects the switching control fluid reservoir 18 with the OHP device 14.

[0041] In various other embodiments, as exemplarily illustrated in FIG. 1B, the switching control fluid reservoir 18 can be a separate and independent structure from the OHP device 14 that is in physical or thermal contact with the OHP device 14. In such embodiments, the switching control fluid reservoir 18 can be in physical or thermal contact with the OHP device 14 at any desired location of the OHP device 14. In such embodiments, the switching control fluid reservoir 18 can be connected to or mounted to or joined with the OHP device body 26 via any suitable connecting / mounting / joining means such as welding, soldering, clueing, etc. In such embodiments, the hermetic fluid transfer conduit 24 connecting the internal cavity of the switching control fluid reservoir 18 with the OHP device microchannels 22 can be a fluid channel formed interiorly within the OHP device body 26 and / or the switching control fluid reservoir 18.

[0042] In yet other embodiments, as exemplarily illustrated in FIG. 1C the switching control fluid reservoir 18 can be formed internally within the OHP device body 26. In such embodiments, the hermetic fluid transfer conduit 24 connecting the internal cavity of the switching control fluid reservoir 18 with the OHP device microchannels 22 can be a fluid channel formed interiorly within the OHP device body 26.

[0043] Referring now to FIGS. 1A, 1B, 1C and 2, in various embodiments the reservoir temperature control device 20 (e.g., a heat source and / or heat sink such as an electric heater, a radiator, a cold plate, etc.) can be a separate and independent device that is mounted to and in thermal contact with the switching control fluid reservoir 18, and is not in thermal contact with the OHP device 14 (i.e., the reservoir temperature control device 20 is thermally mounted to the switching control fluid reservoir 18). The reservoir temperature control device 20 is controllable via any suitable control mechanism, device or means to controllably and selectively alter the temperature in the switching control fluid reservoir 18 to in-situ switch the OHP device 14 between the ON state and the OFF state by controlling the fill fraction of the OHP device 14 via transfer of the working fluid between the OHP device 14 and the switching control fluid reservoir 18, as described above. The reservoir temperature control device 20 can be actively controlled or passively known to be at a known temperature to switch the OHP device 14 between the ON and OFF states when desired. Although this embodiment is exemplarily illustrated in FIG. 2 having the OHP device 14 and the switching control fluid reservoir 18 as separate and independent structures that are not in physical or thermal contact with each other, it will be understood that any of the generic embodiments shown in FIGS. 1A, 1B and 1C can comprise the reservoir temperature control device 20 being a separate in independent device that is mounted to and in thermal contact with the switching control fluid reservoir 18.

[0044] Referring now to FIGS. 1A, 1B, 1C and 3, in various embodiments the reservoir temperature control device 20 can comprise a portion of the OHP device 14. That is, the temperature of the switching control fluid reservoir 18 can be controlled by thermal connection (and in various instances physical connection) to a portion or section of the OHP device 14. This is a passive configuration, wherein the temperature at the thermal connection of the switching control fluid reservoir 18 to the OHP device 14 (i.e., the temperature control device 20) is not actively controlled. Rather, the temperature at the location of the connection between the switching control fluid reservoir 18 and OHP device 14 (i.e., the temperature of the temperature control device 20) controls the flow of working fluid between the OHP device 14 and the switching control fluid reservoir 18, thereby controlling operation of the switching control fluid reservoir 18 to in-situ switch the OHP device 14 between the ON state and the OFF state by controlling the fill fraction of the OHP device 14 via transfer of the working fluid between the OHP device 14 and the switching control fluid reservoir 18, as described above.

[0045] For example, as the temperature at the thermal connection of the switching control fluid reservoir 18 to the OHP device 14 (i.e., the temperature of the temperature control device 20) increases working fluid will flow from the switching control fluid reservoir 18 into the OHP device 14, as described above. Conversely, as the temperature at the thermal connection of the switching control fluid reservoir 18 to the OHP device 1414 (i.e., the temperature of the temperature control device 20) decreases working fluid will flow from the OHP device 14 into the switching control fluid reservoir 18, as described above. the thermal link between the switching control fluid reservoir 18 into the OHP device 14 can be a direct contact between the switching control fluid reservoir 18 into the OHP device 14, a thermal interface material, a metallic structure, etc.

[0046] Although the switching control fluid reservoir 18 is exemplarily illustrated in FIG. 3 to be thermally connected to the OHP device at the heat sink portion / section of the OHP device 14, the switching control fluid reservoir 18 can be thermally connected to any portion / section of the OHP device 14 (e.g., the heat source portion / section or the adiabatic portion / section between the heat source portion / section and the heat sink portion / section) and function as described above. Additionally, although this embodiment is exemplarily illustrated in FIG. 3 having the OHP device 14 and the switching control fluid reservoir 18 as separate and independent structures that are thermally and physically connected, it will be understood that the thermal connection of the switching control fluid reservoir 18 to the OHP device 14 can be equally applicable to any of the generic embodiments shown in FIGS. 1A, 1B and 1C.

[0047] Referring now to FIGS. 1A, 1B, 1C, 2, 3 and 4, all of the embodiments described above exemplarily illustrate the fluid transfer conduit 24 as being an open conduit (e.g., absent a flow control valve) such that the amount of working fluid within the OHP device 14 and the switching control fluid reservoir 18, and the flow of the working fluid therebetween, is controlled and maintained via control of the temperature of the reservoir temperature control device 20. For example, in various embodiments, the switching control fluid reservoir 18 must be held at a temperature higher than the OHP device 14 to maintain operation of the OHP device 14 via the oscillation of the via the oscillation of the two-phase working fluid within the microchannels 22. It can take considerable energy to maintain this temperature differential. In various applications of the OHP system 10 it can be desirable to conserve this energy. Therefore, in all embodiments described herein, a control valve 38 can be disposed within the fluid transfer conduit 24 to further control the flow of working fluid between the OHP device 14 and the switching control fluid reservoir 18. Particularly, the control valve 38 is structured and operable to isolate the working fluid in a selected distribution between the OHP device 14 and the switching control fluid reservoir 18 once it has moved between the OHP device 14 and the switching control fluid reservoir 18 to place the OHP device in ON state and in the OFF state. Accordingly, the temperature differential between the OHP device 14 and the switching control fluid reservoir 18 only needs to be maintained while the valve is Open and the working fluid is flowing therebetween. Once the desired amount of working fluid has reached its destination, the control valve 38 can be closed such that the operational status of the OHP device 14 (e.g., either the ON state or the Off state or any state therebetween) can be maintained without using energy to heat the reservoir temperature control device 20.

[0048] Referring now to FIGS. 1A, 1B, 1C, 2, 3, 4 and 5A, as described above, the switching control fluid reservoir 18 can be any structure of any shape having an internal cavity having sufficient interior volume to controllably and selectively retain at least the transition amount of working fluid. For example, as exemplarily illustrated in FIG. 5A, in various embodiments the switching control fluid reservoir 18 can comprise an internal cavity 42. The internal cavity 42 is a single open space having no structure disposed within the single open space, wherein the single open space is sized to have an internal volume sufficient to controllably and selectively retain at least the transition amount of working fluid, as described above.

[0049] Referring now to FIGS. 1A, 1B, 1C, 2, 3, 4 and 5B, by increasing the contact surface area of fluid within the switching control fluid reservoir 18, the vapor within the switching control fluid reservoir 18, and hence the pressure differential between the OHP device 14 and the switching control fluid reservoir 18, can be generated more quickly (it will generally require a higher heat flux). The contact surface area of the fluid within the switching control fluid reservoir 18 will be understood to mean the surface area of the switching control fluid reservoir 18 with which the fluid is in thermal contact. Any means, element, device or feature that will increase the contact surface area of the fluid within the switching control fluid reservoir 18 will have this result. For example, the interior of the switching control fluid reservoir 18 can comprise a plurality of microchannels, solid foams, finned structures, and / or any other means, element, device or feature of increasing internal surface area of the switching control fluid reservoir 18, and hence the surface contact area of the fluid. For example, as exemplarily illustrated in FIG. 5B, in various embodiments the switching control fluid reservoir 18 can comprise and plurality of capillary sized reservoir microchannels 46, similar to the OHP microchannels 22. The cumulative internal volume of the plurality of the reservoir microchannels 46 is sufficient to controllably and selectively retain at least the transition amount of working fluid, as described above. In such embodiments, the working fluid within the reservoir microchannels 46 will behave similarly to the behavior of the working fluid within the OHP microchannels 22, as described above. That is, controllably and selectively heating the switching control fluid reservoir 18 using the reservoir temperature control device 20 will cause the two-phase working fluid within the reservoir microchannels 46 to change phase, thereby generating movement of the working fluid within the reservoir microchannels. This generated movement will cause the working fluid to flow from the switching control fluid reservoir 18 to the OHP device 14 until the fill fraction of the OHP device 14 comprises at least the operational amount of working fluid, whereby the OHP device 14 will be placed in the ON state. Heating the switching control fluid reservoir 18, via the reservoir temperature control device 20, to generate movement of the working fluid within the reservoir microchannels 46 and push the working fluid into the OHP device 14 will expend much less energy than open cavity embodiments described above.

[0050] Referring now to FIGS. 1A, 1B, 1C, 2, 3, 4 and 5C, since the working fluid within the entire OHP system 10 consists of both vapor and liquid, it will require less overall energy if the working fluid flow between the OHP device 14 and the switching control fluid reservoir 18 is liquid, as opposed to vapor. Therefore, as exemplarily illustrated in FIG. 5C, in various embodiments, the switching control fluid reservoir 18 can comprise an interior cavity 50 and a porous wick 54 disposed on and lining the walls of the cavity 50 and at least partially fills the internal lumen of the fluid transfer conduit 24. The wick 54 lining the walls of the cavity 50 defines a chamber 58 therebetween. The diameter of the pores within the wick 54 is smaller than width L of the chamber 58. This will result in the liquid phase working fluid being absorbed by the wick 54 such that gaseous phase working fluid will be prevented from transferring between the switching control fluid reservoir 18 and the OHP device 14 and only liquid phase working fluid is transferred between the switching control fluid reservoir 18 and the OHP device 14. If the wick exists all the way through the connecting tube to the OHP, or the connecting tube is smaller than the OHP channel, then the tube will preferentially transport liquid to the reservoir. It is envisioned that having the wick 54 disposed within the entire length of the fluid transfer conduit 24 will improve transport of only liquid phase working fluid through the fluid transfer conduit 24.

[0051] In summary, the present disclosure provides the switchable oscillating heat pipe (OHP) system 10 that controls the operation of the OHP device 14 by adjusting the fill factor the OHP device 14, in-situ. The switchable oscillating heat pipe (OHP) system 10 is structured and operable to, in-situ, controllably and selectively switch the OHP device 14 between the ON state and the OFF state by changing the fill fraction of the OHP device 14. Particularly, the OHP system 10 is structured and operable to limit the heat rejection of the heat source(s) 30 being cooled by the OHP device 14 in order to prevent failure of the heat source(s) 30 and / or the OHP device 14. More particularly, the OHP system 10 is structured and operable to in-situ switch between an ON state and an OFF state based on the temperature of one or more heat sources the OHP system is configured to cool, thereby preventing damage to the heat source(s). For example, the OHP system 10 can be configured to be in the ON state, wherein an OHP device 14 operates to cool the heat source(s) 30, when the heat source(s) 30 is / are above a first temperature threshold that is specific to the respective heat source(s) 30, and to switch to the OFF state, wherein the OHP device 14 stops operating to cool the heat source(s) 30, when the heat source(s) 30 is / are below a second temperature threshold that is specific to the respective heat source(s) 30. The first and second temperature thresholds can be different temperature values or the same temperature value. The OHP system 10 can be utilized in many different applications. For example, the OHP system 10 can be particularly useful for OHP systems installed on satellites due to the wide environmental temperature ranges during an orbital cycle and the heat loads from the sun, earth, etc.

[0052] The description herein is merely exemplary in nature and, thus, variations that do not depart from the gist of that which is described are intended to be within the scope of the teachings. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and / or functions, it should be appreciated that different combinations of elements and / or functions can be provided by alternative embodiments without departing from the scope of the disclosure. Such variations and alternative combinations of elements and / or functions are not to be regarded as a departure from the spirit and scope of the teachings.

Examples

Embodiment Construction

[0018]The following description is merely exemplary in nature and is in no way intended to limit the present teachings, application, or uses. Throughout this specification, like reference numerals will be used to refer to like elements. Additionally, the embodiments disclosed below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art can utilize their teachings. As well, it should be understood that the drawings are intended to illustrate and plainly disclose presently envisioned embodiments to one of skill in the art, but are not intended to be manufacturing level drawings or renditions of final products and may include simplified conceptual views to facilitate understanding or explanation. As well, the relative size and arrangement of the components may differ from that shown and still operate within the spirit of the inven...

Claims

1. A switchable oscillating heat pipe (OHP) system, said system comprising:an OHP device comprising a plurality of OHP microchannels;a switching control fluid reservoir fluidly connected to the OHP device by a fluid transfer conduit; anda reservoir temperature control device structured and operable to selectively adjust a temperature of the switching control fluid reservoir to create a pressure differential between the switching control fluid reservoir and the OHP device, wherein the pressure differential will generate movement of a working fluid between the switching control fluid reservoir and the OHP device to in-situ change a working fluid fill fraction of the OHP device to selectively switch OHP device between an ON state and an OFF state.

2. The system of claim 1, wherein the reservoir temperature control device is structured and operable to increase the temperature of the switching control reservoir so that the pressure differential will increase the working fluid fill fraction within the OHP device to an operational amount and thereby selectively switch the OHP device from the OFF state to the ON state.

3. The system of claim 1, wherein the reservoir temperature control device is structured and operable to decrease the temperature of the switching control reservoir so that the pressure differential will decrease the working fluid fill fraction within the OHP device to a non-operational amount and thereby selectively switch the OHP device from the ON state to the OFF state.

4. The system of claim 1, further comprising a flow control valve disposed in the fluid transfer conduit and structured and operable to isolate the working fluid in a selected distribution between the OHP device and the switching control fluid reservoir to maintain the OHP device in each of the ON state and the OFF state.

5. The system of claim 1, wherein the switching control fluid reservoir comprises a plurality of reservoir microchannels.

6. The system of claim 1, wherein the switching control fluid reservoir comprises an internal cavity lined with a porous wick, wherein the porous wick extends at least partially into the fluid transfer conduit.

7. The system of claim 1, wherein the reservoir temperature control device is a separate and independent device that is thermally mounted to the switching control fluid reservoir.

8. The system of claim 1, wherein the reservoir temperature control device comprises portion of the OHP device.

9. The system of claim 1, wherein the switching control fluid reservoir is integrally formed within a body of the OHP device body.

10. A method of selectively switching an oscillating heat pipe (OHP) device between an ON state and an OFF state, said method comprising:fluidly coupling an OHP device comprising a plurality of OHP microchannels to a switching control fluid reservoir via a fluid transfer conduit, wherein there is a two-phase working fluid disposed within the OHP microchannels and the switching control fluid reservoir;selectively adjusting a temperature of a switching control fluid reservoir via a reservoir temperature control device to create a pressure differential between the switching control fluid reservoir and the OHP device; andtransferring working fluid between the OHP device and the switching control fluid reservoir via the created pressure differential to change a fill fraction of the OHP device to selectively switched the OHP device between an ON state and an OFF state.

11. The method of claim 10, wherein selectively adjusting the temperature comprises heating the switching control fluid reservoir so that the pressure differential will increase the fill fraction in the OHP device to an operational amount and thereby selectively switch the OHP device from the OFF state to the ON state.

12. The method of claim 10, wherein selectively adjusting the temperature comprises cooling the switching control fluid reservoir so that the pressure differential will decrease the fill fraction in the OHP device to an operational amount and thereby selectively switch the OHP device from the ON state to the OFF state.

13. The method of claim 10, further comprising isolating the working fluid in a selected distribution between the OHP device and the switching control fluid reservoir to maintain the OHP device in each of the ON state and the OFF state via a flow control valve disposed in the fluid transfer conduit.

14. The method of claim 10, wherein the switching control fluid reservoir comprises a plurality of reservoir microchannels.

15. The method of claim 10, wherein the switching control fluid reservoir comprises an internal cavity and a porous wick disposed on walls of the internal cavity and extending at least partially into the fluid transfer conduit, and wherein transferring working fluid between the OHP device and the switching control fluid reservoir comprises:heating the switching control fluid reservoir to cause the two-phase working fluid within the internal cavity to change phase;preventing gaseous phase working fluid from transferring between the switching control fluid reservoir and the OHP device via the wicktransferring only liquid phase working fluid between the switching control fluid reservoir and the OHP device via the wick.

16. The method of claim 10, wherein selectively adjusting the temperature of a switching control fluid reservoir via a reservoir temperature control device comprises thermally coupling the switching control fluid reservoir to a portion of the OHP device.

17. The method of claim 10, wherein the reservoir temperature control device is a separate and independent device and selectively adjusting the temperature of a switching control fluid reservoir via a reservoir temperature control device comprises thermally mounting the separate and independent reservoir temperature control device temperature control to the switching control fluid reservoir.

18. A method of selectively switching an oscillating heat pipe (OHP) device between an ON state and an OFF state, said method comprising:fluidly coupling an OHP device comprising a plurality of OHP microchannels to a switching control fluid reservoir via a fluid transfer conduit, wherein there is a two-phase working fluid disposed within the OHP microchannels and the switching control fluid reservoir;selectively creating a pressure differential between the switching control fluid reservoir and the OHP device; andtransferring working fluid between the OHP device and the switching control fluid reservoir via the created pressure differential to change a fill fraction of the OHP device to selectively switched the OHP device between an ON state and an OFF state.

19. The method of claim 18 wherein selectively creating a pressure differential between the switching control fluid reservoir and the OHP device comprises adjusting a reservoir temperature control device to which the switching control fluid reservoir is thermally coupled to adjust a temperature of the switching control fluid reservoir to create the pressure differential.

20. The method of claim 18 wherein the switching control fluid reservoir comprises a bellows having an adjustable volume internal cavity and wherein selectively creating a pressure differential between the switching control fluid reservoir and the OHP device comprises compressing or expanding the bellow internal cavity to create the pressure differential.

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