Patent Description:
A heat pipe is a hermetically sealed, two-phase heat transfer component used to transfer heat from a primary side (evaporator section) to a secondary side (condenser section). <FIG>, as an example, illustrates a heat pipe <NUM> comprising the aforementioned evaporator section <NUM> and condenser section <NUM>, along with an adiabatic section <NUM> extending therebetween. The heat pipe <NUM> further includes a working fluid (such as water, liquid potassium, sodium, or alkali metal) and a wick <NUM>. In operation, the working fluid is configured to absorb heat in the evaporator section <NUM> and vaporize. The saturated vapor, carrying latent heat of vaporization, flows towards the condenser section <NUM> through the adiabatic section <NUM>. In the condenser section <NUM>, the vapor condenses into a liquid pool <NUM> and gives off its latent heat. The condensed liquid is then returned to the evaporator section <NUM> through the wick <NUM> by capillary action. The aforementioned flow path of the working fluid is illustrated by segmented arrows in <FIG>. The phase change processes and two-phase flow circulation continues as long as the temperature gradient between the evaporator and condenser sections is maintained. Due to the very high heat transfer coefficients for boiling and condensation, heat pipes are highly effective thermal conductors.

In nuclear systems, heat pipes are utilized by placing the evaporator section of the heat pipe within the reactor core containing nuclear fuel and the condenser section is placed near heat exchangers. The nuclear fuel vaporizes the working fluid and heat exchangers absorb the latent heat at the condenser section. Example heat pipes in nuclear applications are described in <CIT>, <CIT>, and <CIT>.

<CIT> discloses a heat storage container with a tubular body, a chemical heat storage material accommodated in the tubular body, and a flow channel that penetrates the tubular body in a longitudinal direction.

Another example use for heat pipes in nuclear systems is with micro-reactors, which are nuclear reactors that generate less than 10MWe and are capable of being deployed for remote applications. These micro-reactors can be packaged in relatively small containers, operate without active involvement of personnel, and operate without refueling/replacement for a longer period than conventional nuclear power plants. One such micro-reactor is the eVinci Micro Reactor system, designed by Westinghouse Electric Company. The eVinci system is a heat pipe cooled reactor power system that utilizes heat pipes to act as passive heat removal devices that efficiently move thermal energy out of the reactor core to heat exchangers.

The heat pipes used in the micro-reactors experience extreme operating temperatures (><NUM>) and requires an internal wick that is made from materials that can withstand these temperatures and are compatible with the working fluid. This wick can be constructed from a wire mesh that is rolled and diffusion bonded together into a tube-like structure. The wick tube allows for the working fluid within the heat pipe to pass through it radially (such as after the latent heat is given off and the working fluid is absorbed by the wick) and along its axis (transferring the working fluid back toward the evaporator section with capillary action) while remaining rigid.

In some instances, it is desirable to fabricate the heat pipe container <NUM> from a different material than the wick <NUM>. As an example, it may be important to maintain good mechanical properties of the container <NUM>, such as ability to withstand high operating pressures of the heat pipe, to mitigate structural concerns. These same mechanical requirements are not imposed on the wick <NUM>. In addition, the outside of the container <NUM> will be exposed to a different environment that may see a large range of material and chemical interactions. This may necessitate the use of a container <NUM> material that is not compatible with the working fluid on the inside thereof.

Generally during assembly of the heat pipe <NUM>, a container lid <NUM> (that is comprised of same material as the container <NUM>) is utilized to seal the wick <NUM> and working fluid within the container <NUM> of the heat pipe <NUM>. The container lid <NUM> includes an end plug <NUM> extending therefrom that is configured to couple to the wick <NUM> at an interface <NUM>. It is necessary to maintain a seal at the interface <NUM> between the end plug <NUM> of the heat pipe <NUM> and the evaporator section <NUM> of the wick <NUM>. Methods of directly coupling the wick <NUM> and the end plug <NUM> at the interface <NUM> includes welding, diffusion bonding and brazing. These methods are not ideally suited to bonding dissimilar metals that are susceptible to different thermal expansion properties (differential thermal coefficients (DTE)). Repeated thermal cycling of materials with DTE will lead to failure over time, which short circuits the heat pipes <NUM> ability to perform its intended function. In this case, failure is any defect that results in a pore size greater than the pores within the wick <NUM>, which are typically on the order of <NUM> micrometers. Therefore, utilizing dissimilar wick <NUM> and container lid / end plug <NUM> materials runs the risk of failure over time.

It is the goal of the present disclosure to provide a heat pipe that includes a heat pipe container and a wick that are comprised of dissimilar materials and avoid failures mechanisms associated with DTE and dissimilar material compatibility.

In various embodiments, a wick assembly for use with a heat pipe assembly including a container and a container lid is disclosed, the wick assembly being as claimed in claim <NUM>.

The wick of the wick assembly may comprise a first material and the end plug of the wick assembly a second material, wherein the first material is substantially identical to the second material. The rod of the wick assembly may comprise a first cross-sectional shape and the recess of the wick assembly a second cross-sectional shape, wherein the first cross-sectional shape and the second cross-sectional shape are substantially identical.

In various embodiments, a heat pipe assembly is disclosed including a container, a wick, and an end plug coupled to the wick, the heat pipe assembly being as claimed in claim <NUM>. The rod may be configured to center the wick within the container. The rod may be slidable within the recess based on growth and shrinkage of the wick.

Various features of the embodiments described herein, together with advantages thereof, may be understood in accordance with the following description taken in conjunction with the accompanying drawings as follows:.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate various embodiments of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

Numerous specific details are set forth to provide a thorough understanding of the overall structure. function, manufacture, and use of the embodiments as described in the specification and illustrated in the accompanying drawings. Well-known operations, components, and elements have not been described in detail so as not to obscure the embodiments described in the specification. The reader will understand that the embodiments described and illustrated herein are non-limiting examples, and thus it can be appreciated that the specific structural and functional details disclosed herein may be representative and illustrative. Variations and changes thereto may be made without departing from the scope of the claims.

<FIG> illustrates a heat pipe <NUM> accordingly at least one aspect of the present disclosure. The heat pipe <NUM> includes an evaporator section <NUM>, a condenser section <NUM>, and an adiabatic section <NUM> extending therebetween. The heat pipe <NUM> further includes a working fluid (such as water, liquid potassium, sodium, or alkali metal) and a wick <NUM> positioned within a container <NUM>. In operation, the working fluid is configured to absorb heat in the evaporator section <NUM> and vaporize. The saturated vapor, carrying latent heat of vaporization, flows towards the condenser section <NUM> through the adiabatic section <NUM>. In the condenser section <NUM>, the vapor condenses into a liquid pool <NUM> and gives off its latent heat. The condensed liquid is then returned to the evaporator section <NUM> through the wick <NUM> by capillary action. The aforementioned flow path of the working fluid is illustrated by segmented arrows in <FIG>. The phase change processes and two-phase flow circulation continues as long as the temperature gradient between the evaporator and condenser sections is maintained.

The wick <NUM> material is selected such that the wick <NUM> is compatible with the working fluid of the heat pipe <NUM> (such as alkali metal), as well as is able to withstand the high operating temperatures of the heat pipe <NUM> (><NUM>). In operation, the wick <NUM> can expand and contract based on the thermal expansion properties of the wick <NUM>. As an example, a wick <NUM> fabricated from <NUM> series stainless steel has high thermal expansion properties, leading to large fluctuations in size during operation of the heat pipe <NUM>.

The heat pipe <NUM> further includes an end plug <NUM> that can interface and couple to the wick <NUM> at an interface <NUM>. The wick <NUM> can be coupled to the end plug <NUM> by any suitable coupling method, such as with welding, diffusion bonding, brazing, fasteners, adhesive, or any suitable form of coupling. The end plug <NUM> further includes a centering pin <NUM> extending therefrom.

The end plug <NUM> can be constructed with the same, or at least substantially the same, material as the wick <NUM> such that the thermal expansion properties of the wick <NUM> and the end plug <NUM> are the same, or at least substantially the same. The end plug <NUM> being fabricated from the same, or at least substantially the same, material as the wick <NUM> avoids failure mechanisms associated with DTE and dissimilar material compatibility between the wick <NUM> and the end plug <NUM>. In other embodiments, the wick <NUM> and end plug <NUM> can comprise dissimilar materials that include similar, or at least substantially similar thermal expansion coefficients such that the wick <NUM> and end plug <NUM> expand and contract at similar rates, while also mitigating failures associated with DTE.

The heat pipe <NUM> further including a container lid <NUM>. Unlike the heat pipe <NUM> illustrated in <FIG>, the container lid <NUM> and the end plug <NUM> are separate and distinct components. The container lid <NUM> includes a groove or recess <NUM> defined therein that can receive the pin <NUM> extending from the end plug <NUM>. thereby coupling the end plug <NUM> to the container lid <NUM>. The pin <NUM> and the groove <NUM> are configured to center the wick <NUM> within the container <NUM>, which is important for the thermal performance of the heat pipe <NUM>. In addition, the groove <NUM> comprises a length that is the same, or at least substantially the same, as the length of the pin <NUM>. Other embodiments are envisioned where the length of the groove <NUM> and the length of the pin <NUM> are different.

In operation, as the wick <NUM> expands and contracts due to fluctuating operating temperatures experienced by the heat pipe <NUM>, the pin <NUM> can slide within the groove <NUM>, accommodating the axial movement of the wick <NUM> and end plug <NUM>. The groove <NUM> can include a sufficient length such that the pin <NUM> abuts the end <NUM> of the groove <NUM> at the same, or at least substantially the same, time as the end plug <NUM> contacts the container lid <NUM>. In another embodiment, the groove <NUM> can include a length such that the pin <NUM> abuts the end <NUM> of the grove <NUM> prior to the end plug <NUM> contacting the container lid <NUM>. In another embodiment, the end plug <NUM> can contact the container lid <NUM> prior to the pin <NUM> abutting the end <NUM> of the groove <NUM>. The use of the pin <NUM> / groove <NUM> allows the container <NUM> and the container lid <NUM> to be constructed or manufactured from materials dissimilar to the wick <NUM> and the end plug <NUM>. By isolating the sealing interface <NUM> as a separate part that can move with respect to the container <NUM> and container lid <NUM>, failure mechanisms associated with DTE in a bonded plug/heat pipe design are eliminated. Existing methods of forming annular heat pipe wicks, as described with respect to <FIG>, require the wick to be bonded to the container / end plug.

The pin <NUM> and the groove <NUM> can include any suitable cross-sectional shape such that the pin <NUM> can axially slide through the groove <NUM> based on growth and shrinkage of the wick <NUM>. In one embodiment, the pin <NUM> and the groove <NUM> can include circular cross-sectional shapes. The use of circular cross-sectional shapes allows the pin <NUM> to be slidable within the groove <NUM>, but allows the end plug <NUM> to be rotatable relative to the container lid <NUM>. In other embodiments, the pin <NUM> and the groove <NUM> can include a square cross-sectional shape. The use of a square cross-sectional shape allows the pin <NUM> to be slidable within the groove <NUM>, while also preventing the end plug <NUM> from rotating relative to the container lid <NUM>. Other suitable cross-sectional shapes are envisioned, such as oval, star, pentagon, or octagon cross-sectional shapes, as examples. The small diameter or cross-sectional shape of the pin <NUM> allows for tight part tolerances even considering a large DTE between the wick <NUM> material and container lid <NUM> material or container <NUM> material.

The above-described invention applies to heat pipe materials with larger or smaller thermal expansion coefficients compared to the wick. The container groove <NUM> is be designed to accept growth or shrinking of the wick <NUM> length (relative to the heat pipe container <NUM>) by properly sizing the groove <NUM> dimension and also properly setting the initial position of the pin <NUM>.

While <FIG> illustrates a heat pipe <NUM> with one container lid <NUM> / groove <NUM> / end plug <NUM> / pin <NUM>, other heat pipes are envisioned wherein the heat pipe, such as heat pipe <NUM> illustrated in <FIG>, includes a container lid <NUM> / groove <NUM> / end plug <NUM> / pin <NUM> on both ends of the heat pipe. The use of more than one container lid <NUM> / groove <NUM> / end plug <NUM> / pin <NUM> allows the wick to thermally expand in more than one direction.

Various aspects of the subject matter described herein are set out in the following examples.

Example <NUM> - A heat pipe comprising a container, a container lid comprising a groove defined therein, a wick, and an end plug operably coupled to the wick. The end plug comprises a pin extending therefrom. The groove of the container lid is configured to receive the pin.

Example <NUM> - The heat pipe of Example <NUM>, wherein the wick comprises a first material. The end plug comprises a second material. The first material is substantially identical to the second material.

Example <NUM> - The heat pipe of Example <NUM>, wherein the wick comprises a first material. The container comprises a second material. The first material and the second material are different.

Example <NUM> - The heat pipe of Example <NUM>, wherein the end plug comprises the first material.

Example <NUM> - The heat pipe of any one of Examples <NUM>-<NUM>, wherein the pin comprises a first cross-sectional shape. The groove comprises a second cross-sectional shape. The first cross-sectional shape and the second cross-sectional shape are substantially identical.

Example <NUM> - The heat pipe of any one of Examples <NUM>-<NUM>, wherein the pin is configured to center the wick within the container.

Example <NUM> - The heat pipe of any one of Examples <NUM>-<NUM>, wherein the pin is slidable within the groove based on growth and shrinkage of the wick.

Example <NUM> - A wick assembly for use with a heat pipe assembly comprising a container and a container lid. The wick assembly comprises a wick and an end plug coupled to the wick. The end plug comprises a rod extending therefrom,. The rod is configured to be inserted into a recess defined in the container lid.

Example <NUM> - The wick assembly of Example <NUM>. wherein the wick comprises a first material. The end plug comprises a second material. The first material is substantially identical to the second material.

Example <NUM> - The wick assembly of Example <NUM>, wherein the wick comprises a first material. The container comprises a second material. The first material and the second material are different.

Example <NUM> - The wick assembly of Example <NUM>, wherein the end plug comprises the first material.

Example <NUM> - The wick assembly of any one of Examples <NUM>-<NUM>, wherein the rod comprises a first cross-sectional shape. The recess comprises a second cross-sectional shape. The first cross-sectional shape and the second cross-sectional shape are substantially identical.

Example <NUM> - The wick assembly of any one of Examples <NUM>-<NUM>, wherein the rod is configured to center the wick within the container.

Example <NUM> - The wick assembly of any one of Examples <NUM>-<NUM>, wherein the rod is slidable within the recess based on growth and shrinkage of the wick.

Example <NUM> - A heat pipe comprising a container, a wick, and an end plug coupled to the wick. The container comprises a first material and a lid comprising a recess defined therein. The wick comprising a second material. The second material is different that the first material. The end plug comprises a shaft extending therefrom. The recess of the container lid is configured to receive the shaft.

Example <NUM> - The heat pipe of Example <NUM>, wherein the end plug comprises a third material substantially identical to the second material.

Example <NUM> - The heat pipe of Examples <NUM> or <NUM>, wherein the shaft comprises a first cross-sectional shape. The recess comprises a second cross-sectional shape. The first cross-sectional shape and the second cross-sectional shape are substantially identical.

Example <NUM> - The heat pipe of any one of Examples <NUM>-<NUM>, wherein the shaft is configured to center the wick within the container.

Example <NUM> - The heat pipe of any one of Examples <NUM>-<NUM>, wherein the shaft is slidable within the groove based on growth and shrinkage of the wick.

Unless specifically stated otherwise as apparent from the foregoing disclosure, it is appreciated that, throughout the foregoing disclosure, discussions using terms such as "processing," "computing," "calculating," "determining,'' "displaying," or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

One or more components may be referred to herein as "configured to," "configurable to," "operable/operative to," "adapted/adaptable," "able to," "conformable/conformed to. " etc. Those skilled in the art will recognize that "configured to'' can generally encompass active-state components and/or inactive-state components and/or standby-state components, unless context requires otherwise.

Those skilled in the art will recognize that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to claims containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations.

In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone. B alone, C alone, A and B together. A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A. B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that typically a disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms unless context dictates otherwise. For example, the phrase "A or B" will be typically understood to include the possibilities of "A" or "B" or "A and B.

With respect to the appended claims, those skilled in the art will appreciate that recited operations therein may generally be performed in any order. Also, although various operational flow diagrams are presented in a sequence(s), it should be understood that the various operations may be performed in other orders than those which are illustrated, or may be performed concurrently. Examples of such alternate orderings may include overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. Furthermore, terms like "responsive to," "related to," or other past-tense adjectives are generally not intended to exclude such variants, unless context dictates otherwise.

It is worthy to note that any reference to "one aspect," "an aspect," "an exemplification," "one exemplification," and the like means that a particular feature, structure, or characteristic described in connection with the aspect is included in at least one aspect. Thus, appearances of the phrases "in one aspect," "in an aspect," "in an exemplification," and "in one exemplification" in various places throughout the specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more aspects.

The terms "comprise" (and any form of comprise, such as "comprises" and "comprising"), "have" (and any form of have, such as "has" and "having"), "include" (and any form of include, such as "includes" and "including") and "contain" (and any form of contain, such as "contains" and "containing") are open-ended linking verbs. As a result, a system that "comprises," "has," "includes" or "contains" one or more elements possesses those one or more elements, but is not limited to possessing only those one or more elements. Likewise, an element of a system, device, or apparatus that "comprises," "has," "includes" or "contains" one or more features possesses those one or more features, but is not limited to possessing only those one or more features.

The term "substantially", "about", or "approximately" as used in the present disclosure, unless otherwise specified, means an acceptable error for a particular value as determined by one of ordinary skill in the art, which depends in part on how the value is measured or determined. In certain embodiments, the term "substantially", "about", or "approximately" means within <NUM>, <NUM>, <NUM>, or <NUM> standard deviations. In certain embodiments, the term "substantially", "about", or "approximately" means within <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% of a given value or range.

Claim 1:
A wick assembly for use with a heat pipe assembly comprising a container (<NUM>) and a container lid (<NUM>), the wick assembly comprising:
a wick (<NUM>); and
an end plug (<NUM>) coupled to the wick (<NUM>),
characterized in that
the end plug (<NUM>) comprises a rod (<NUM>) extending therefrom; and
the rod (<NUM>) is configured to be inserted into a recess (<NUM>) defined in the container lid (<NUM>).