Patent Publication Number: US-11650016-B2

Title: Method of installing a heat pipe wick into a container of differing thermal expansion coefficient

Description:
GOVERNMENT CONTRACT 
     This invention was made with government support under Contract DE-NE0008853 awarded by the Department of Energy. The government has certain rights in the invention. 
    
    
     BACKGROUND 
     This invention relates generally to heat pipes used in heat transfer systems, and more particularly, to wicks within the heat pipes that are configured to transfer the working fluid of the heat pipe from a condenser region of the heat pipe to an evaporator region. 
     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.  1   , as an example, illustrates a heat pipe  100  comprising the aforementioned evaporator section  102  and condenser section  106 , along with an adiabatic section  104  extending therebetween. The heat pipe  100  further includes a working fluid (such as water, liquid potassium, sodium, or alkali metal) and a wick  108 . In operation, the working fluid is configured to absorb heat in the evaporator section  102  and vaporize. The saturated vapor, carrying latent heat of vaporization, flows towards the condenser section  106  through the adiabatic section  104 . In the condenser section  106 , the vapor condenses into a liquid pool  110  and gives off its latent heat. The condensed liquid is then returned to the evaporator section  102  through the wick  108  by capillary action. The aforementioned flow path of the working fluid is illustrated by segmented arrows in  FIG.  1   . 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 U.S. Pat. Nos. 5,684,848, 6,768,781, and U.S. Patent Application Publication No. 2016/0027536, all of which are incorporated by reference in their entirety. 
     Another example use for heat pipes in nuclear systems is with micro-reactors, which are nuclear reactors that generate less than 10 MWe 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 (&gt;850° C.) 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  112  from a different material than the wick  108 . As an example, it may be important to maintain good mechanical properties of the container  112 , 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  108 . In addition, the outside of the container  112  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  112  material that is not compatible with the working fluid on the inside thereof. 
     Generally during assembly of the heat pipe  100 , a container lid  114  (that is comprised of same material as the container  112 ) is utilized to seal the wick  108  and working fluid within the container  112  of the heat pipe  100 . The container lid  114  includes an end plug  116  extending therefrom that is configured to couple to the wick  108  at an interface  118 . It is necessary to maintain a seal at the interface  116  between the end plug  116  of the heat pipe  100  and the evaporator section  102  of the wick  108 . Methods of directly coupling the wick  108  and the end plug  116  at the interface  118  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  100  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  108 , which are typically on the order of 10 micrometers. Therefore, utilizing dissimilar wick  108  and container lid/end plug  116  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. 
     SUMMARY 
     In various embodiments, a heat pipe is disclosed includes a container, a container lid including a groove defined therein, a wick, and an end plug operably coupled to the wick. The end plug includes a pin extending therefrom. The groove of the container lid is configured to receive the pin. 
     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 includes a wick and an end plug coupled to the wick. The end plug includes a rod extending therefrom. The rod is configured to be inserted into a recess defined in the container lid. 
     In various embodiments, a heat pipe is disclosed including a container, a wick, and an end plug coupled to the wick. The container includes a first material and a lid including a recess defined therein. The wick includes a second material. The second material is different that the first material. The end plug includes a shaft extending therefrom. The recess of the lid is configured to receive the shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG.  1    illustrates a heat pipe having a container lid with an end plug extending therefrom. 
         FIG.  2    illustrates a heat pipe having a container lid and an end plug, according to one aspect of the present disclosure. 
         FIG.  3    illustrates a heat pipe having two container lids and end plugs, according to one aspect of the present disclosure. 
     
    
    
     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. 
     DETAILED DESCRIPTION 
     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.  2    illustrates a heat pipe  200  accordingly at least one aspect of the present disclosure. The heat pipe  200  includes an evaporator section  202 , a condenser section  206 , and an adiabatic section  204  extending therebetween. The heat pipe  200  further includes a working fluid (such as water, liquid potassium, sodium, or alkali metal) and a wick  208  positioned within a container  212 . In operation, the working fluid is configured to absorb heat in the evaporator section  202  and vaporize. The saturated vapor, carrying latent heat of vaporization, flows towards the condenser section  206  through the adiabatic section  204 . In the condenser section  206 , the vapor condenses into a liquid pool  210  and gives off its latent heat. The condensed liquid is then returned to the evaporator section  202  through the wick  208  by capillary action. The aforementioned flow path of the working fluid is illustrated by segmented arrows in  FIG.  2   . 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  208  material is selected such that the wick  208  is compatible with the working fluid of the heat pipe  200  (such as alkali metal), as well as is able to withstand the high operating temperatures of the heat pipe  200  (&gt;850° C.). In operation, the wick  200  can expand and contract based on the thermal expansion properties of the wick  208 . As an example, a wick  208  fabricated from 300 series stainless steel has high thermal expansion properties, leading to large fluctuations in size during operation of the heat pipe  200 . 
     The heat pipe  200  further includes an end plug  216  that can interface and couple to the wick  208  at an interface  218 . The wick  208  can be coupled to the end plug  216  by any suitable coupling method, such as with welding, diffusion bonding, brazing, fasteners, adhesive, or any suitable form of coupling. The end plug  216  further includes a centering pin  220  extending therefrom. 
     The end plug  216  can be constructed with the same, or at least substantially the same, material as the wick  208  such that the thermal expansion properties of the wick  208  and the end plug  216  are the same, or at least substantially the same. The end plug  216  being fabricated from the same, or at least substantially the same, material as the wick  208  avoids failure mechanisms associated with DTE and dissimilar material compatibility between the wick  208  and the end plug  216 . In other embodiments, the wick  208  and end plug  216  can comprise dissimilar materials that include similar, or at least substantially similar thermal expansion coefficients such that the wick  208  and end plug  216  expand and contract at similar rates, while also mitigating failures associated with DTE. 
     The heat pipe  200  further including a container lid  214 . Unlike the heat pipe  100  illustrated in  FIG.  1   , the container lid  214  and the end plug  216  are separate and distinct components. The container lid  214  includes a groove or recess  222  defined therein that can receive the pin  220  extending from the end plug  216 , thereby coupling the end plug  216  to the container lid  214 . The pin  220  and the groove  222  are configured to center the wick  208  within the container  212 , which is important for the thermal performance of the heat pipe  200 . In addition, the groove  222  comprises a length that is the same, or at least substantially the same, as the length of the pin  220 . Other embodiments are envisioned where the length of the groove  222  and the length of the pin  220  are different. 
     In operation, as the wick  208  expands and contracts due to fluctuating operating temperatures experienced by the heat pipe  200 , the pin  220  can slide within the groove  222 , accommodating the axial movement of the wick  208  and end plug  216 . The groove  222  can include a sufficient length such that the pin  220  abuts the end  224  of the groove  222  at the same, or at least substantially the same, time as the end plug  216  contacts the container lid  214 . In another embodiment, the groove  222  can include a length such that the pin  220  abuts the end  224  of the grove  222  prior to the end plug  216  contacting the container lid  214 . In another embodiment, the end plug  216  can contact the container lid  214  prior to the pin  220  abutting the end  224  of the groove  222 . The use of the pin  220 /groove  222  allows the container  212  and the container lid  214  to be constructed or manufactured from materials dissimilar to the wick  208  and the end plug  216 . By isolating the sealing interface  218  as a separate part that can move with respect to the container  212  and container lid  214 , 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.  1   , require the wick to be bonded to the container/end plug. 
     The pin  220  and the groove  222  can include any suitable cross-sectional shape such that the pin  220  can axially slide through the groove  222  based on growth and shrinkage of the wick  208 . In one embodiment, the pin  220  and the groove  222  can include circular cross-sectional shapes. The use of circular cross-sectional shapes allows the pin  220  to be slidable within the groove  222 , but allows the end plug  216  to be rotatable relative to the container lid  214 . In other embodiments, the pin  220  and the groove  222  can include a square cross-sectional shape. The use of a square cross-sectional shape allows the pin  220  to be slidable within the groove  222 , while also preventing the end plug  216  from rotating relative to the container lid  214 . 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  220  allows for tight part tolerances even considering a large DTE between the wick  208  material and container lid  214  material or container  212  material. 
     The above-described invention applies to heat pipe materials with larger or smaller thermal expansion coefficients compared to the wick. The container groove  222  is be designed to accept growth or shrinking of the wick  208  length (relative to the heat pipe container  212 ) by properly sizing the groove  220  dimension and also properly setting the initial position of the pin  220 . 
     While  FIG.  2    illustrates a heat pipe  200  with one container lid  214 /groove  222 /end plug  216 /pin  220 , other heat pipes are envisioned wherein the heat pipe, such as heat pipe  300  illustrated in  FIG.  3   , includes a container lid  214 /groove  222 /end plug  216 /pin  220  on both ends of the heat pipe. The use of more than one container lid  214 /groove  222 /end plug  216 /pin  220  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 1—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 2—The heat pipe of Example 1, 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 3—The heat pipe of Example 1, wherein the wick comprises a first material. The container comprises a second material. The first material and the second material are different. 
     Example 4—The heat pipe of Example 3, wherein the end plug comprises the first material. 
     Example 5—The heat pipe of any one of Examples 1-4, 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 6—The heat pipe of any one of Examples 1-5, wherein the pin is configured to center the wick within the container. 
     Example 7—The heat pipe of any one of Examples 1-6, wherein the pin is slidable within the groove based on growth and shrinkage of the wick. 
     Example 8—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 9—The wick assembly of Example 8, 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 10—The wick assembly of Example 8, wherein the wick comprises a first material. The container comprises a second material. The first material and the second material are different. 
     Example 11—The wick assembly of Example 10, wherein the end plug comprises the first material. 
     Example 12—The wick assembly of any one of Examples 8-11, 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 13—The wick assembly of any one of Examples 8-12, wherein the rod is configured to center the wick within the container. 
     Example 14—The wick assembly of any one of Examples 8-13, wherein the rod is slidable within the recess based on growth and shrinkage of the wick. 
     Example 15—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 16—The heat pipe of Example 15, wherein the end plug comprises a third material substantially identical to the second material. 
     Example 17—The heat pipe of Examples 15 or 16, 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 18—The heat pipe of any one of Examples 15-17, wherein the shaft is configured to center the wick within the container. 
     Example 19—The heat pipe of any one of Examples 15-18, 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&#39;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. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. 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. 
     Any patent application, patent, non-patent publication, or other disclosure material referred to in this specification and/or listed in any Application Data Sheet is incorporated by reference herein, to the extent that the incorporated materials is not inconsistent herewith. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein will only be incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material. 
     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 1, 2, 3, or 4 standard deviations. In certain embodiments, the term “substantially”, “about”, or “approximately” means within 50%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.05% of a given value or range. 
     In summary, numerous benefits have been described which result from employing the concepts described herein. The foregoing description of the one or more forms has been presented for purposes of illustration and description. It is not intended to be exhaustive or limiting to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The one or more forms were chosen and described in order to illustrate principles and practical application to thereby enable one of ordinary skill in the art to utilize the various forms and with various modifications as are suited to the particular use contemplated. It is intended that the claims submitted herewith define the overall scope.