Patent Publication Number: US-2023164953-A1

Title: Systems and methods for three-dimensional vapor chambers in immersion-cooled datacenters

Description:
BACKGROUND 
     Background and Relevant Art 
     Computing devices can generate a large amount of heat during use. The computing components can be susceptible to damage from the heat and commonly require cooling systems to maintain the component temperatures in a safe range during heavy processing or usage loads. Different computing components produce different amounts of thermal energy and require different amounts of thermal management. Conventional thermal management systems cool the entire device uniformly, which may insufficiently cool the high-capacity components and/or waste energy cooling components that may not need the thermal management. 
     BRIEF SUMMARY 
     In some embodiments, a vapor chamber includes a main body, a first vertical structure, and an enhanced boiling surface. The main body has a first surface and defines a first portion of an interior volume. The first vertical structure protrudes transverse to the main body and defines a second portion of the interior volume. The enhanced boiling surface is on at least a portion of the first vertical structure. 
     In some embodiments, a vapor chamber includes a main body and a first vertical structure. The main body has a first surface and defining a first portion of an interior volume. The first vertical structure protrudes transverse to the main body and defines a second portion of the interior volume. The first vertical structure has a first end having first width and a second end having a second width that is less than the first width. 
     In some embodiments, a vapor chamber includes a main body, a first vertical structure, and a wicking structure. The main body has a first surface and defining a first portion of an interior volume. The first vertical structure protrudes transverse to the main body and defines a second portion of the interior volume. The wicking structure is in the interior volume. 
     In some embodiments, a thermal management system includes a heat-generating component, a vapor chamber, and an immersion working fluid. The vapor chamber is thermally connected to the heat-generating component to conduct thermal energy from the heat-generating component. The vapor chamber includes a main body, at least one vertical structure, and an enhanced boiling surface. The main body is substantially parallel to the heat-generating component, and the vapor chamber defines an interior volume containing a vapor chamber working fluid. The at least one vertical structure of the vapor chamber containing at least a portion of the interior volume and vapor chamber working fluid, and the vertical structure protruding transverse to the main body. The enhanced boiling surface located on at least a portion of the vertical structure. The immersion working fluid contacts at least a portion of the vapor chamber. 
     In some embodiments, a thermal management system includes a heat-generating component, a vapor chamber, and an immersion working fluid. The vapor chamber is thermally connected to the heat-generating component to conduct thermal energy from the heat-generating component. The vapor chamber includes an interior volume, a main body, a plurality of vertical structures, and an enhanced boiling surface. The interior volume contains a vapor chamber working fluid. The main body contains at least a portion of the interior volume and vapor chamber working fluid, and a plane of the main body is oriented in a direction of gravity and substantially parallel to the heat-generating component. The plurality of vertical structures contains at least a portion of the interior volume and vapor chamber working fluid, and the vertical structures protrude transverse to the main body and define at least one channel. The enhanced boiling surface located on at least a portion of the vertical structures and main body in the channel. The immersion working fluid contacts at least a portion of the vapor chamber. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     Additional features and advantages will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the teachings herein. Features and advantages of the disclosure may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. Features of the present disclosure will become more fully apparent from the following description and appended claims or may be learned by the practice of the disclosure as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to describe the manner in which the above-recited and other features of the disclosure can be obtained, a more particular description will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. For better understanding, the like elements have been designated by like reference numbers throughout the various accompanying figures. While some of the drawings may be schematic or exaggerated representations of concepts, at least some of the drawings may be drawn to scale. Understanding that the drawings depict some example embodiments, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG.  1    is a side schematic representation of an immersion cooling system, according to at least one embodiment of the present disclosure; 
         FIG.  2    is a side schematic representation of an immersion cooling system with an external condenser, according to at least one embodiment of the present disclosure; 
         FIG.  3 - 1    is a perspective view of a vapor chamber, according to at least one embodiment of the present disclosure; 
         FIG.  3 - 2    is a perspective view of another vapor chamber, according to at least one embodiment of the present disclosure; 
         FIG.  4    is a cross-sectional view of a vapor chamber, according to at least one embodiment of the present disclosure; 
         FIG.  5    is a schematic representation of a vapor chamber with an enhanced boiling surface, according to at least one embodiment of the present disclosure; 
         FIG.  6    is a front view of a vapor chamber immersed in immersion working fluid, according to at least one embodiment of the present disclosure; 
         FIG.  7    is a front view of another vapor chamber immersed in immersion working fluid, according to at least one embodiment of the present disclosure; 
         FIG.  8    is a front view of yet another vapor chamber immersed in immersion working fluid, according to at least one embodiment of the present disclosure; 
         FIG.  9    is a front view of a further vapor chamber immersed in immersion working fluid, according to at least one embodiment of the present disclosure; and 
         FIG.  10    is a cross-sectional view of a vapor chamber with varying interior volume height, according to at least one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates generally to systems and methods for thermal management of electronic devices or other heat-generating components Immersion chambers surround the heat-generating components in a liquid working fluid, which conducts heat from the heat-generating components to cool the heat-generating components. As the working fluid absorbs heat from the heat-generating components, the temperature of the working fluid increases. In some embodiments, the hot working fluid is circulated through the thermal management system to cool the working fluid and/or replace the working fluid with cool working fluid. In some embodiments, the working fluid vaporizes, introducing vapor into the liquid of the working fluid which rises out of the liquid phase, carrying thermal energy away from the heat-generating components in the gas phase via the latent heat of boiling. 
     In large-scale computing centers, such as cloud-computing centers, data processing centers, data storage centers, or other computing facilities, immersion cooling systems provide an efficient method of thermal management for many computing components under a variety of operating loads. In some embodiments, an immersion cooling system includes a working fluid in an immersion chamber and a heat exchanger to cool the liquid phase and/or a condenser to extract heat from the vapor phase of the working fluid. The heat exchanger may include a condenser that condenses the vapor phase of the working fluid into a liquid phase and returns the liquid working fluid to the immersion chamber. In some embodiments, the liquid working fluid absorbs heat from the heat-generating components, and one or more fluid conduits direct the hot liquid working fluid outside of the immersion chamber to a radiator, heat exchanger, or region of lower temperature to cool the liquid working fluid. 
     In some embodiments, a high-capacity component of the computing devices or systems in the immersion cooling system requires a large amount of thermal management. The heat generated by the high-capacity component may be transferred to the immersion working fluid by a heat spreader. In some embodiments, the heat spreader includes a vapor chamber including three-dimensional surface features and/or surface treatments to increase heat transfer and/or boiling of the immersion working fluid on a surface of the vapor chamber. 
     Whether the immersion cooling system is a two-phase cooling system (wherein the working fluid vaporizes and condenses in a cycle) or a one-phase cooling system (wherein the working fluid remains in a single phase in a cycle), the heat transported from the heat-generating components outside of the immersion chamber is further exchanged with an ambient fluid to exhaust the heat from the system. 
     An illustrative immersion cooling system  100 , shown in  FIG.  1   , includes an immersion tank  102  containing an immersion chamber  104  and a condenser  106  in the immersion chamber  104 . The immersion chamber  104  contains an immersion working fluid that has a liquid working fluid  108  and a vapor working fluid  110  portion. The liquid working fluid  108  creates an immersion bath  112  in which a plurality of heat-generating components  114  are positioned to heat the liquid working fluid  108  on supports  116 . 
     Referring now to  FIG.  2   , an immersion cooling system  200  according to the present disclosure includes an immersion tank  202  defining an immersion chamber  204  with an immersion working fluid positioned therein. In some embodiments, the immersion working fluid transitions between a liquid phase  208  of the immersion working fluid and a vapor phase  210  of the immersion working fluid to remove heat from hot or heat-generating components  214  in the immersion chamber  204 . The liquid phase  208  of the immersion working fluid more efficiency receives heat from the heat-generating components  214  and, upon transition to the vapor phase  210  of the immersion working fluid, the vapor phase  210  of the immersion working fluid is optionally removed from the immersion tank  202 , cooled and condensed by the condenser  206  (or other heat exchanger) to extract the heat from the immersion working fluid, and the liquid phase  208  of the immersion working fluid is optionally returned to the liquid immersion bath  212 . 
     In some embodiments, a server computer or other computing device is positioned inside an immersion tank  202  for cooling. The immersion tank  202  houses a liquid phase  208  of the immersion working fluid that cools the server computer by absorbing heat from the components of the server computer. In some embodiments, the immersion bath  212  of the liquid phase  208  of the immersion working fluid has a plurality of heat-generating components  214  positioned in the liquid phase  208  of the immersion working fluid. The liquid phase  208  of the immersion working fluid surrounds at least a portion of the heat-generating components  214  and other objects or parts attached to the heat-generating components  214 . In some embodiments, the heat-generating components  214  are positioned in the liquid phase  208  of the immersion working fluid on one or more supports  216 . The support  216  supports one or more heat-generating components  214  in the liquid phase  208  of the immersion working fluid and allows the working fluid to move around the heat-generating components  214 . In some embodiments, the support  216  is thermally conductive to conduct heat from the heat-generating components  214 . The support(s)  216  may increase the effective surface area from which the liquid phase  208  of the immersion working fluid removes heat through convective cooling. 
     In some embodiments, the heat-generating components  214  include electronic or computing components or power supplies. In some embodiments, the heat-generating components  214  include computer devices, such as an individual personal computer or a server computer (e.g., a server blade computer). In some embodiments, the high-capacity components of the server computer, such as a CPU, GPU, or other components generate large amounts of heat. In some embodiments, one or more of the heat-generating components  214  includes a heat sink or other device attached to the heat-generating component  214  to conduct away thermal energy and effectively increase the surface area of the heat-generating component  214 . In some embodiments, the heat sink of the heat-generating component  214  is a vapor chamber with one or more three-dimensional structures to increase surface area. 
     As described, conversion of the liquid phase  208  of the immersion working fluid to a vapor phase requires the input of thermal energy to overcome the latent heat of vaporization and may be an effective mechanism to increase the thermal capacity of the working fluid and remove heat from the heat-generating components. In use, the liquid phase  208  of the immersion working fluid is vaporized into a vapor phase  210  of the immersion working fluid which rises in the tank toward a condenser  206 . Because the vapor phase  210  of the immersion working fluid rises in the liquid phase  208  of the immersion working fluid, the vapor phase  210  of the immersion working fluid is extracted from the immersion chamber  204  in an upper vapor region of the chamber, in some embodiments. A condenser  206  cools part of the vapor phase  210  of the immersion working fluid back into a liquid phase  208  of the immersion working fluid, removing thermal energy from the system and reintroducing the working fluid into the immersion bath  212  of the liquid phase  208  of the immersion working fluid. The condenser  206  radiates or otherwise dumps the thermal energy from the working fluid into the ambient environment or into a conduit to carry the thermal energy away from the cooling system. 
     In some examples, an immersion cooling system  200  includes an air-cooled condenser  206 . An air-cooled condenser  206  may include fans or pumps to force ambient air over one or more heat pipes or fins to conduct heat from the condenser to the air. 
     In some embodiments of immersion cooling systems, a liquid-cooled condenser is integrated into the immersion tank and/or the chamber to efficiency remove the thermal energy from the working fluid. In some embodiments, an immersion cooling system  200  for thermal management of computing devices allows at least one immersion tank  202  and/or chamber  204  to be connected to and in fluid communication with an external condenser  206 . In some embodiments, an immersion cooling system  200  includes a vapor return line  218  that connects the immersion tank  202  to the condenser  206  and allows vapor phase  210  of the immersion working fluid to enter the condenser  206  from the immersion tank  202  and/or chamber  204  and a liquid return line  220  that connects the immersion tank  202  to the condenser  206  and allows liquid phase  208  of the immersion working fluid to return to the immersion tank  202  and/or chamber  204 . 
     The vapor return line  218  may be colder than the boiling temperature of the working fluid. In some embodiments, a portion of the vapor phase  210  of the immersion working fluid condenses in the vapor return line  218 . The vapor return line  218  can, in some embodiments, be oriented at an angle such that the vapor return line  218  is non-perpendicular to the direction of gravity. The condensed working fluid then drains either back to the immersion tank  202  or forward to the condenser  206  depending on the direction of the vapor return line  218  slope. In some embodiments, the vapor return line  218  includes a liquid collection line or valve, such as a bleeder valve, that allows the collection and/or return of the condensed working fluid to the immersion tank  202  or condenser  206 . 
     In some embodiments, the circulation of immersion working fluid through the immersion cooling system  200  causes liquid phase  208  of the immersion working fluid to flow past one or more heat-generating components  214 . In embodiments where a heat-generating component  214  has a vapor chamber heat sink, the dynamics of liquid phase  208  of the immersion working fluid are used to move vapor chamber working fluid within the vapor chamber and/or the boiling of the immersion working fluid by the vapor chamber drives flow of the immersion working fluid. 
     In some embodiments, a vapor chamber heat sink transfers heat to the immersion working fluid to boil the liquid phase of the immersion working fluid, and the fluidic drag of the vapor bubbles further induces flow of the immersion working fluid across a surface of the vapor chamber. 
     In some embodiments, the heat-generating components, supports, or other elements of the immersion cooling system positioned in the working fluid have nucleation sites on a surface thereof that promote the nucleation of vapor bubbles of the working fluid at or below the boiling temperature of the working fluid. 
     Immersion working fluid is recycled through the immersion cooling system and, in some embodiments, the working fluid is a dielectric fluid or other fluid that is expensive. An immersion cooling system that uses less working fluid and/or uses the working fluid more efficiently allows for cost savings in the working fluid. In some embodiments, a vapor chamber heat sink according to the present disclosure allows for cooling of the high-capacity components in a larger cooling volume of the immersion working fluid, more efficiently utilizing the available immersion working fluid. 
     In some embodiments, the liquid phase of the immersion working fluid receives heat in a cooling volume of immersion working fluid immediately surrounding the heat-generating components. The cooling volume is the region of the immersion working fluid (including both liquid and vapor phases) that is immediately surrounding the heat-generating components and is responsible for the convective cooling of the heat-generating components. In some embodiments, the cooling volume is the volume of immersion working fluid within 5 millimeters (mm) of the heat-generating components. A larger cooling volume, therefore, can therefore provide a larger thermal mass to conduct heat away from the heat-generating component. 
     The immersion working fluid has a boiling temperature below a critical temperature at which the heat-generating components experience thermal damage. For example, the heat-generating components may be computing components that experience damage above 100° Celsius (C). In some embodiments, the boiling temperature of the immersion working fluid is less about 90° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the immersion working fluid is less about 80° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the immersion working fluid is less about 70° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the immersion working fluid is less about 60° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the immersion working fluid is at least about 35° C. at 1 atmosphere of pressure. 
     In some embodiments, the immersion working fluid includes water. In some embodiments, the immersion working fluid includes glycol. In some embodiments, the immersion working fluid includes a combination of water and glycol. In some embodiments, the immersion working fluid is an aqueous solution. In some embodiments, the immersion working fluid is a non-conductive fluid. In some embodiments, the immersion working fluid is an electronic liquid, such as FC-72 available from 3M. 
       FIG.  3 - 1    is a perspective view of a vapor chamber  324  according to the present disclosure. In some embodiments, a vapor chamber  324  has a main body  326  with one or more vertical structures  328  protruding from the main body  326  in a direction transverse to the main body  326 . In the illustrated embodiment of  FIG.  3   , the main body has six vertical structures  328  protruding from the main body  326  substantially perpendicular to a plane of the main body  326 . In some embodiments, the vertical structures  328  extend at least partially perpendicular to the plane of the main body  326 . In other embodiments, at least one of the vertical structures  328  protrudes at a non-perpendicular angle to the main body  326  or have a curved surface or non-planar surface that is non-perpendicular to the main body  326 , but the dimensions of vertical structure  328  include a transverse component such that the vertical structure  328  protrudes in a perpendicular direction. In at least one example, the vertical structure  328  protrudes from the main body  326  at approximately a 45° angle, and the vertical structure  328  projects in the direction of the plane of the main body  326  an equal amount to projecting in the perpendicular direction of the plane of the main body  326 . 
       FIG.  3 - 2    is a perspective view of an embodiment of a vapor chamber  324  with vertical structures  328 - 1 ,  328 - 2  that are non-perpendicular to a plane  329  of the main body  326  but extend at least partially perpendicular to the plane  329  of the main body  326 . A first vertical structure  328 - 1  includes a curved portion  331  where a base of the first vertical structure  328 - 1  is wider than a top of the first vertical structure  328 - 1 . The second vertical structure  328 - 2  has planar and parallel sides, and the second vertical structure  328 - 2  extends at a 45° angle to the plane  329  of the main body  326 . 
     In some embodiments, the main body  326  varies in thickness across the plane  329  of the main body  326 . In some embodiments, a thickness  333  of the main body  326  changes between a first edge of the main body  326  and a second edge of the main body  326 . In at least one embodiment, the thickness  333  of the main body  326  decreases from a bottom edge  335  to a top edge  337  of the main body  326 . 
     In embodiments with a plurality of vertical structures  328 , the vertical structures  328  of the vapor chamber  324  define channels  330  therebetween. In the illustrated embodiment of  FIG.  3 - 1   , the vertical structures  328  of the vapor chamber  324  are substantially parallel to one another and define channels  330  of constant dimension(s) (e.g., depth and/or width). As will be described herein, the vertical structures  328  have, in some embodiments, other dimensions or orientations that define channels  330  with varying dimensions. In some embodiments, an immersion working fluid flows through the channels  330  to absorb and remove heat from the surface of the vapor chamber  324 . 
       FIG.  4    is a cross-sectional view of an embodiment of a vapor chamber  424  positioned on a heat-generating component  414 . In some embodiments, the heat-generating component  414  is a high-capacity component of a server computer, such as a CPU, a GPU, or other component that requires greater thermal management than other heat-generating components of the server computer. For example, a vapor chamber  424  according to the present disclosure may be applied to a CPU while system memory modules are cooled by the immersion cooling fluid without a vapor chamber heat sink. 
     In some embodiments, the vapor chamber  424  has an interior volume  432  inside the main body  426  and the vertical structures  428 . The vapor chamber  424  has a vapor chamber working fluid  434  positioned therein. In some embodiments, the vapor chamber  424  includes a wicking structure through which the vapor chamber working fluid  434  moves, as will be described in more detail herein. The wicking structure assists in moving the vapor chamber working fluid  434  through the interior volume  432  by capillary effects. A porosity of the wicking structure balances the capillary effect with a permeability of the wicking structure. 
     The vapor chamber working fluid has a boiling temperature below a critical temperature at which the heat-generating components experience thermal damage. In some embodiments, the boiling temperature of the vapor chamber working fluid is less than a critical temperature of the heat-generating components. In some embodiments, the boiling temperature of the vapor chamber working fluid is less about 90° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the vapor chamber working fluid is less about 80° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the vapor chamber working fluid is less about 70° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the vapor chamber working fluid is less about 60° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the vapor chamber working fluid is at least about 35° C. at 1 atmosphere of pressure. 
     In some embodiments, the vapor chamber working fluid includes water. In some embodiments, the vapor chamber working fluid includes glycol. In some embodiments, the vapor chamber working fluid includes a combination of water and glycol. In some embodiments, vapor chamber the working fluid is an aqueous solution. In some embodiments, the vapor chamber working fluid is a non-conductive fluid. In some embodiments, the vapor chamber working fluid is an electronic liquid, such as FC-72 available from 3M. 
     The vapor chamber  424  is thermally connected to a heat-generating component  414 . In some embodiments, the vapor chamber  424  is coupled directly to the heat-generating component  414 . In some embodiments, the vapor chamber  424  is coupled to a thermal interface material (TIM)  436 , which is coupled to the heat-generating component  414 . In some examples, the TIM  436  is a thermal paste between the main body  426  of the vapor chamber  424  and the heat-generating component  414 . When pressed between the main body  426  of the vapor chamber  424  and a surface of the heat-generating component  414 , the TIM  436  conforms to the two surfaces providing a continuous thermally conductive connection therebetween. 
     In some embodiments, the vapor chamber  424  includes, in the interior volume  432 , a vapor chamber working fluid  434  with a boiling temperature below a peak operating temperature of the heat-generating component  414 . For example, if the heat-generating component  414  has a peak operating temperature of 60° C., the boiling temperature of the vapor chamber working fluid  434  is below 60° C. Upon receiving heat from the heat-generating component  414  (either directly or indirectly through the TIM), the liquid phase  438  of the vapor chamber working fluid rises in temperature and vaporizes into a vapor phase  440  of the vapor chamber working fluid. In some embodiments, the vapor phase  440  of the vapor chamber working fluid expands through a wicking structure of the vapor chamber  424 . 
     In some embodiments, the vapor phase  440  of the vapor chamber working fluid is condensed by rejection of thermal energy to the immersion working fluid outside the vapor chamber  424 . In some embodiments, the main body  426  and/or the vertical structures  428  of the vapor chamber  424  are substantially surrounded by a liquid phase  408  of the immersion working fluid, which receives heat from the vapor chamber  424  to cool the vapor chamber working fluid  434  therein. 
     In some embodiments, movement of the vapor chamber working fluid  434  within the interior volume  432  is driven by or assisted by the boiling and condensing of the vapor chamber working fluid  434 . Therefore, efficient transfer of the heat through the walls  442  of the vapor chamber  424  is needed to efficiently circulate the vapor chamber working fluid  434 . The thermal transfer from the vapor chamber working fluid  434  to the immersion working fluid is increased by maintaining the largest thermal gradient possible. Some embodiments of vapor chambers according to the present disclosure include internal features and/or external features to increase the thermal transfer from the vapor chamber working fluid to the immersion cooling fluid. 
       FIG.  5    is a schematic cross-sectional view of another embodiment of a vapor chamber  524  for immersion cooling. In some embodiments, a vapor chamber  524  includes external features, such as surface features or treatments to enhance boiling of the immersion working fluid in contact with the vapor chamber  524 . In some embodiments, the vapor chamber  524  includes an enhanced boiling surface  544  on at least a portion of the outer surface of the vapor chamber  524 . In some embodiments, the enhanced boiling surface  544  is on select portions of the vapor chamber  524 . In some embodiments, the enhanced boiling surface  544  is on the vertical structure(s)  528 . In some embodiments, the enhanced boiling surface  544  is on the main body  526  of the vapor chamber  524 . In some embodiments, the enhanced boiling surface  544  is on substantially all of the outer surface of the vapor chamber  524 . As used herein, the outer surface of the vapor chamber is the surface with which the immersion working fluid is in contact, as at least a portion of the vapor chamber is the contact area with the TIM or heat-generating component  514 . In at least one example, the enhanced boiling surface  544  is on the surface of the main body  526  and vertical structures  528  opposite the heat source or heat-generating component  514 . Boiling of the immersion working fluid between the vapor chamber  524  and a motherboard, socket, substrate, or other support of the heat-generating component  514  may create an undesirable expansion force between the main body  526  and the motherboard, socket, substrate, or other support of the heat-generating component  514 . 
     The enhanced boiling surface  544  includes suitable surface features to increase the formation of vapor bubbles on the surface. In some embodiments, the enhanced boiling surface  544  includes grooves, ridges, pockets, recesses, nucleation sites, a porous coating, other boiling enhancing surface textures, or combinations thereof to promote the formation of vapor bubbles in the immersion working fluid and lower the energy required to begin boiling of the immersion working fluid. Lowering the energy to boil the immersion working fluid allows the immersion working fluid to carry away the heat from the vapor chamber  524  more efficiently. 
     In some embodiments, the vapor bubbles in the immersion working fluid create a fluidic drag on the liquid phase of the immersion working fluid. The fluidic drag flows the liquid phase of the immersion working fluid along the surface of the vapor chamber  524 . In some embodiments, inducing a flow of liquid phase of the immersion working fluid across the vapor chamber  524  draws colder immersion working fluid in contact with the vapor chamber  524 , increasing the thermal gradient and further increasing the efficiency of thermal transfer from the vapor chamber working fluid to the immersion working fluid. 
     The enhanced boiling surface  544  of the vertical structures  528 , in some embodiments, concentrates the formation of vapor bubbles in the channels  530 , further promoting flow of immersion working fluid through the channels  530  and past the vapor chamber  524  to transfer thermal energy from the vapor chamber working fluid to the immersion cooling fluid to condense the vapor phase of the vapor chamber working fluid back into a liquid phase, further promoting the circulation of the vapor chamber working fluid to spread the heat from the heat-generating component  514 . 
     In some embodiments, the enhanced boiling surface  544  is an additive surface treatment, such as a surface treatment that is sintered to the vapor chamber  524 . In some embodiments, a powder precursor is sintered to the surface to provide a rough surface with increased surface area and nucleation sites to promote boiling of the immersion working fluid in contact with the enhanced boiling surface  544 . In some embodiments, the enhanced boiling surface  544  includes additively manufactured (e.g., 3D-printed) structures thereon. In some embodiments, the enhanced boiling surface  544  is produced with a subtractive surface treatment, such as mechanically, electrically, or chemically etching or scoring the surface of the vapor chamber  524  to provide a rough surface with increased surface area and nucleation sites to promote boiling of the immersion working fluid in contact with the enhanced boiling surface  544 . In some embodiments, the enhanced boiling surface  544  is integral to the vapor chamber  524  surface as manufactured, such as during the casting or stamping process of forming the walls  542  of the vapor chamber  524 . In at least one example, the enhanced boiling surface  544  includes a plurality of ridges and/or recesses created in the material of the vapor chamber  524  while forming the exterior walls  542  of the vapor chamber  524 . 
       FIG.  6    is a front view of an embodiment of a vapor chamber  624  immersed in immersion working fluid and oriented with the channels  630  substantially in the direction of gravity  648 . In some embodiments, the sidewalls of the channels  630  (e.g., the vertical structures  628 ) and the main body  626  cause the liquid phase  608  of the immersion working fluid to boil. The vapor bubbles  646  cause a fluidic drag on the liquid phase  608  of the immersion working fluid to draw the liquid phase  608  of the immersion working fluid through the channels  630  and across the surfaces of the vapor chamber  624 . 
     In some embodiments, the heat-generating component  614  is positioned in the lower half of the vapor chamber  624  as positioned when installed in an immersion cooling system. In some embodiments, the heat-generating component  614  is positioned in the lower third of the vapor chamber  624 . Positioning the heat-generating component  614  in the lower portion of the vapor chamber  624  when immersed in immersion working fluid may assist in circulating the vapor chamber working fluid and/or the immersion working fluid and improving thermal transfer between the vapor chamber working fluid and the immersion working fluid. In some embodiments, the vapor bubbles of the vapor chamber working fluid rise toward the upper portion of the vapor chamber, and, upon condensing into a liquid phase of the vapor chamber working fluid, the vapor chamber working fluid drips back down toward the heat-generating component  614  under the force of gravity when the channels  630  of the vapor chamber  624  are oriented substantially in the direction of gravity  648 . 
     In some embodiments, positioning the heat-generating component  614  in the lower portion of the vapor chamber  624  increases the thermal gradient proximate to the heat-generating component  614 . The fluidic drag of the upwardly moving vapor bubbles  646  of the immersion working fluid, in some embodiments, induces an upward flow of the liquid phase  608  of the immersion working fluid. The liquid phase  608  of the immersion working fluid drawn from below the vapor chamber  624  is cooler than the liquid phase  608  of the immersion working fluid above or laterally adjacent to the vapor chamber  624 , causing the channels  630  to fill with a flow of cooled liquid phase  608  of the immersion working fluid, thereby increasing the thermal gradient proximate to the heat-generating component  614 . 
       FIG.  7    illustrates another embodiment of a vapor chamber  724  according to the present disclosure. In some embodiments, the vertical structures  728  vary in at one property or dimension to further drive movement of the immersion working fluid outside of the vapor chamber  724  and/or vapor chamber working fluid inside the vapor chamber  724 . In at least one embodiment, the vertical structures  728  of the vapor chamber  724  are fins that taper in the upward direction (e.g., opposite the direction of gravity) to drive flow of the liquid phase  708  of the immersion working fluid. In some embodiments, as the vertical structures  728  taper, the channels  730  defined between the vertical structures  728  consequently widen. 
     The flow from the vapor bubbles  746  draws the liquid phase  708  of the immersion working fluid upward through the widening channels  730 . The formation of vapor bubbles  746  in the liquid phase  708  of the immersion working fluid increases pressure in the immersion working fluid. In some embodiments with channels of constant dimensions, the increased pressure can inhibit flow of the immersion working fluid through the channel. As additional vapor bubbles  746  form on the surface of the vapor chamber  724  due to the immersion working fluid  708  boiling, the flow continues upward through the widening channels  730  despite the expansion of immersion working fluid  708  vaporizing into the vapor bubbles  746 . In some embodiments, the channels  730  are at least 10% wider at a top  750  of the channel  730  than a bottom  752  of the channel  730 . In some embodiments, the channels  730  are at least 50% wider at a top  750  of the channel  730  than a bottom  752  of the channel  730 . In some embodiments, the channels  730  are at least twice as wide at a top  750  of the channel  730  than a bottom  752  of the channel  730 . 
     In some embodiments, the bottom portion of at least one vertical structure  728  is wider than the top portion of the vertical structure  728 . In some embodiments, the vertical structure  728 , therefore, includes more interior volume and more vapor chamber working fluid in the lower portion of the vapor chamber  724 . More vapor chamber working fluid in the lower portion allows more thermal mass of the vapor chamber  724  to be present in proximity to the cooler immersion liquid working fluid  708  drawn in at the bottom  752  of the channels  730 . 
     In some embodiments, a surface of the vertical structures  728  is tuned with an enhanced boiling surface  744  to create boiling fluid turbulence in the liquid phase  708  of the immersion working fluid, thus increasing the fluid boundary layer for enhanced cooling. In addition to the enhanced boiling surface  744 , one or more surface features, such as grooves or troughs, may be present on the surface(s) of the vertical structures  728  and/or the enhanced boiling surface  744  to induce or increase a Venturi effect. The Venturi effect on the surface of the vertical structures  728  may increase the buoyant velocity of the liquid phase  708  of the immersion working fluid. 
     In some of the described embodiments, the upper portion of the vapor chamber  724  has a lower temperature gradient than the lower portion and thermal transfer efficiently may be reduced in the upper portion. In other embodiments, one or more external or internal features of the vapor chamber  724  varies in the vertical direction to maintain or improve the thermal transfer efficiency of the vapor chamber  724 . 
       FIG.  8    is a schematic front view of varying surface features to drive more consistent rate of vapor bubble  846  formation across the vapor chamber  824 . For example, different types of enhanced boiling surfaces  844  may be positioned in different areas of the exterior of the vapor chamber  824 . In some embodiments, a first enhanced boiling surface  844 - 1  is located proximate the bottom of the vapor chamber  824  with at least a second enhanced boiling surface  844 - 2  located above the first enhanced boiling surface  844 - 1  in the direction of immersion working fluid flow  854  (e.g., opposite the direction of gravity). In at least one embodiment, a vapor chamber  824  includes three enhanced boiling surfaces  844 - 1 ,  844 - 2 ,  844 - 3  in series in the direction of immersion working fluid flow  854 . For example, each successive enhanced boiling surface  844 - 1 ,  844 - 2 ,  844 - 3  may include more nucleation sites to promote more efficient vapor bubble  846  formation as the thermal gradient between the immersion working fluid and the vapor chamber working fluid decreases in the direction of immersion working fluid flow  854 . 
     In some embodiments, interior features vary relative to the heat-generating component and/or in the direction of immersion working fluid flow.  FIG.  9    is a front view of an embodiment of a vapor chamber  924  with a varying porosity to assist vapor chamber working fluid movement and increase thermal gradient to immersion working fluid. In some embodiments, the porosity of the wicking structure in the interior volume of the vapor chamber  924  varies in relation to the heat-generating element  914  and/or the immersion working fluid flow  954  induced by the vapor bubble  946  formation. A small pore size increases capillary pumping action of the vapor chamber working fluid in the wicking structure. A larger pore size allows greater permeability in the wicking structure. 
     In some embodiments, the porosity increases in the direction of the immersion working fluid flow  954  induced by the vapor bubbles  946 . In some embodiments, the porosity increases continuously in the direction of immersion working fluid flow  954 . In some embodiments, the porosity changes in discrete regions. For example, a first portion  956 - 1  of the wicking structure has a substantially constant first porosity, and a second portion  956 - 2  has a substantially constant porosity. In some embodiments, the first portion  956 - 1  is at least 10% of the length  958  of the main body  926  of the vapor chamber  924 . In some embodiments, the first portion  956 - 1  is at least 20% of the length  958  of the main body  926  of the vapor chamber  924 . In some embodiments, the first portion  956 - 1  is at least one-third of the length  958  of the main body  926  of the vapor chamber  924 . 
     In some embodiments, the porosity increases with distance from the heat-generating component  914 . For example, the porosity increases radially away from the location of the heat-generating component  914  in contact with the vapor chamber  924 . In other examples, the porosity increases in discrete steps at certain distances from the location of the heat-generating component  914  in contact with the vapor chamber  924 . 
       FIG.  10    is a side cross-sectional view of the interior volume  1032  of an embodiment of a portion of a vapor chamber  1024 . In some embodiments, the vapor chamber  1024  includes a wicking structure  1060  in the interior volume  1032  of the main body and/or the vertical structures, and the interior volume  1032  is defined by inner surfaces of the vapor chamber walls  1042 . A distance between the inner surfaces defines the interior volume height  1062 . In some embodiments, the interior volume height  1062  is constant throughout the interior volume  1032  (such as the interior volume  1032  described in relation to  FIG.  4   ) of the main body and/or the vertical structures. In some embodiments, such as illustrated in  FIG.  10   , one or both inner surfaces opposite one another are non-planar (e.g., include at least one curve). In some embodiments, the non-planar inner surfaces produce a varying interior volume height  1062  of the main body and/or the vertical structures. In at least one example, a first inner surface is non-planar and an opposing second inner surface is planar, and the variations in the interior volume height  1062  are produced by the non-planar shape of the first inner surface. In another example, the first inner surface and second inner surface are mirrored, producing a symmetrical interior volume  1032  of the main body and/or the vertical structures that varies in height  1062 . In some embodiments, the non-planar inner surfaces are complementary to one another and produce a constant height despite the position of the interior volume  1032  moving relative to the walls  1042 . 
     In some embodiments, the varying inner surfaces create a periodic cross-sectional area of the interior volume  1032  of the main body and/or the vertical structures. In some embodiments, the periodic cross-sectional area acts as a pumping structure to assist vapor chamber working fluid  1034  movement and increase thermal gradient to immersion working fluid outside of the vapor chamber  1024 . 
     INDUSTRIAL APPLICABILITY 
     In some embodiments, a high-capacity component of the computing devices or systems in the immersion cooling system requires a large amount of thermal management. The heat generated by the high-capacity component may be transferred to the immersion working fluid by a heat spreader. In some embodiments, the heat spreader includes a vapor chamber including three-dimensional surface features and/or surface treatments to increase heat transfer and/or boiling of the immersion working fluid on a surface of the vapor chamber. 
     Whether the immersion cooling system is a two-phase cooling system (wherein the immersion working fluid vaporizes and condenses in a cycle) or a one-phase cooling system (wherein the immersion working fluid remains in a single phase in a cycle), the heat transported from the heat-generating components outside of the immersion chamber is further exchanged with an ambient fluid to exhaust the heat from the system. 
     In some embodiments, a server computer or other computing device is positioned inside an immersion tank for cooling. The immersion tank houses a working fluid that cools the server computer by absorbing heat from the components of the server computer. The liquid working fluid may vaporize into vapor working fluid which rises in the tank toward a condenser. In some embodiments, the high-capacity components of the server computer, such as a CPU, GPU, or other components generate large amounts of heat. In some embodiments, a vapor chamber heat sink transfers heat to the immersion working fluid to boil the liquid working fluid, and the fluidic drag of the vapor bubbles further induces flow of the immersion working fluid across a surface of the vapor chamber. 
     Immersion working fluid is recycled through the immersion cooling system and, in some embodiments, the immersion working fluid is a dielectric fluid or other fluid that is expensive. An immersion cooling system that uses less immersion working fluid and/or uses the working fluid more efficiently allows for cost savings in the immersion working fluid. In some embodiments, a vapor chamber heat sink according to the present disclosure allows for cooling of the high-capacity components in a larger cooling volume of the immersion working fluid, more efficiently utilizing the available immersion working fluid. A larger volume of immersion working fluid has a larger thermal mass, allowing more heat to be absorbed by the immersion working fluid. 
     In some embodiments, the liquid working fluid receives heat in a cooling volume of immersion working fluid immediately surrounding the heat-generating components. The cooling volume is the region of the immersion working fluid (including both liquid and vapor phases) that is immediately surrounding the heat-generating components and is responsible for the convective cooling of the heat-generating components. In some embodiments, the cooling volume is the volume of immersion working fluid within 5 millimeters (mm) of the heat-generating components. 
     The immersion working fluid has a boiling temperature below a critical temperature at which the heat-generating components experience thermal damage. For example, the heat-generating components may be computing components that experience damage above 100° Celsius (C). In some embodiments, the boiling temperature of the immersion working fluid is less than a critical temperature of the heat-generating components. In some embodiments, the boiling temperature of the immersion working fluid is less about 90° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the immersion working fluid is less about 80° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the immersion working fluid is less about 70° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the immersion working fluid is less about 60° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the immersion working fluid is at least about 35° C. at 1 atmosphere of pressure. In some embodiments, the working fluid includes water. 
     In some embodiments, the immersion working fluid includes glycol. In some embodiments, the immersion working fluid includes a combination of water and glycol. In some embodiments, the immersion working fluid is an aqueous solution. In some embodiments, the immersion working fluid is an electronic liquid, such as FC-72 available from 3M, or similar non-conductive fluids. In some embodiments, the heat-generating components, supports, or other elements of the immersion cooling system positioned in the immersion working fluid have nucleation sites on a surface thereof that promote the nucleation of vapor bubbles of the immersion working fluid at or below the boiling temperature of the immersion working fluid. 
     In some embodiments, a vapor chamber has a main body with one or more vertical structures protruding from the main body in a direction transverse to the main body. In some embodiments, the main body has six vertical structures protruding from the main body substantially perpendicular to a plane of the main body. In some embodiments, the vertical structures extend at least partially perpendicular to the plane of the main body. For example, at least one of the vertical structures may protrude at a non-perpendicular angle to the main body or have a curved surface that is non-perpendicular to the main body, but the dimensions of vertical structure include a transverse component such that the vertical structure protrudes in a perpendicular direction. In at least one example, the vertical structure protrudes from the main body at approximately a 45° angle, and the vertical structure projects in the direction of the plane of the main body an equal amount to projecting in the perpendicular direction of the plane of the main body. 
     In embodiments with a plurality of vertical structures, the vertical structures of the vapor chamber define channels therebetween. In some embodiments, the vertical structures of the vapor chamber are substantially parallel to one another and define channels of constant dimensions. As will be described herein, the vertical structures have, in some embodiments, other dimensions or orientations that define channels with varying dimensions. In some embodiments, an immersion working fluid may flow through the channels to absorb and remove heat from the surface of the vapor chamber. 
     In some embodiments, the heat-generating component is a high-capacity component of a server computer, such as a CPU, a GPU, or other heat-generating component that requires greater thermal management than other heat-generating components of the server computer. For example, a vapor chamber according to the present disclosure may be applied to a CPU while system memory modules may be cooled by the immersion cooling fluid without a vapor chamber heat sink. 
     In some embodiments, the vapor chamber has an interior volume inside the main body and the vertical structures. The vapor chamber has a vapor chamber working fluid positioned therein. In some embodiments, the vapor chamber includes a wicking structure through which the vapor chamber working fluid moves. The wicking structure assists in moving the vapor chamber working fluid through the interior volume by capillary effects. A porosity of the wicking structure balances the capillary effect with a permeability of the wicking structure. 
     The vapor chamber is thermally connected to a heat-generating component. In some embodiments, the vapor chamber is coupled directly to the heat-generating component. In some embodiments, the vapor chamber is coupled to a thermal interface material (TIM), which is coupled to the heat-generating component. In some examples, the TIM is a thermal paste between the main body of the vapor chamber and the heat-generating component. When pressed between the main body of the vapor chamber and a surface of the heat-generating component, the TIM conforms to the two surfaces providing a continuous thermally conductive connection therebetween. 
     In some embodiments, the vapor chamber includes, in the interior volume, a vapor chamber working fluid with a boiling temperature below a peak operating temperature of the heat-generating component. For example, if the heat-generating component has a peak operating temperature of 60° C., the boiling temperature of the vapor chamber working fluid is below 60° C. Upon receiving heat from the heat-generating component (either directly or indirectly through the TIM), the vapor chamber working fluid rises in temperature and vaporizes into a vapor phase of the vapor chamber working fluid. In some embodiments, the vapor phase of the vapor chamber working fluid may expand through a wicking structure of the vapor chamber. 
     In some embodiments, the vapor phase of the vapor chamber working fluid is condensed by rejection of thermal energy to the immersion working fluid outside the vapor chamber. In some embodiments, the main body and/or the vertical structures of the vapor chamber are substantially surrounded by a liquid working fluid of the immersion working fluid, which receives heat from the vapor chamber to cool the vapor chamber working fluid therein. 
     In some embodiments, movement of the vapor chamber working fluid within the interior volume is driven by or assisted by the boiling and condensing of the vapor chamber working fluid. Therefore, efficient transfer of the heat through the walls of the vapor chamber is needed to efficiently circulate the vapor chamber working fluid. The thermal transfer from the vapor chamber working fluid to the immersion working fluid is increased by maintaining the largest thermal gradient possible. Some embodiments of vapor chambers according to the present disclosure include internal features and/or external features to increase the thermal transfer from the vapor chamber working fluid to the immersion cooling fluid. 
     In some embodiments, a vapor chamber includes external features, such as surface features or treatments to enhance boiling of the immersion working fluid in contact with the vapor chamber. In some embodiments, the vapor chamber includes an enhanced boiling surface on at least a portion of the outer surface of the vapor chamber. In some embodiments, the enhanced boiling surface is positioned on the vertical structure(s). In some embodiments, the enhanced boiling surface is positioned on the main body of the vapor chamber. In some embodiments, the enhanced boiling surface is positioned on substantially all of the outer surface of the vapor chamber with which the immersion working fluid is in contact. In some embodiments, the enhanced boiling surface is positioned on select portions of the vapor chamber. In at least one example, the enhanced boiling surface is positioned on the surface of the main body and vertical structures opposite the heat source or heat-generating component. Boiling of the immersion working fluid between the vapor chamber and a motherboard, socket, substrate, or other support of the heat-generating component may create an undesirable expansion force between the main body and the motherboard, socket, substrate, or other support of the heat-generating component. 
     In some embodiments, the enhanced boiling surface includes grooves, ridges, pockets, recesses, nucleation sites, a porous coating, other boiling enhancing surface textures, or combinations thereof to promote the formation of vapor bubbles in the immersion working fluid and lower the energy required to begin boiling of the immersion working fluid. Lowering the energy to boil the immersion working fluid allows the immersion working fluid to carry away the heat from the vapor chamber more efficiently. 
     In some embodiments, the vapor bubbles in the immersion working fluid create a fluidic drag on the liquid phase of the immersion working fluid. The fluidic drag flows the liquid phase of the immersion working fluid along the surface of the vapor chamber. In some embodiments, inducing a flow of the liquid phase of the immersion working fluid across the vapor chamber draws colder immersion working fluid in contact with the vapor chamber, increasing the thermal gradient and further increasing the efficiency of thermal transfer from the vapor chamber working fluid to the liquid phase of the immersion working fluid. 
     The enhanced boiling surface of the vertical structures, in some embodiments, concentrates the formation of vapor bubbles in the channels, further promoting flow of immersion working fluid through the channels and past the vapor chamber to transfer thermal energy from the vapor chamber working fluid to the immersion working fluid to condense the vapor phase of the vapor chamber working fluid back into a liquid phase, further promoting the circulation of the vapor chamber working fluid to spread the heat from the heat-generating component. 
     In some embodiments, the enhanced boiling surface is an additive surface treatment, such as a surface treatment that is sintered to the vapor chamber. In some embodiments, a powder precursor is sintered to the surface to provide a rough surface with increased surface area and nucleation sites to promote boiling of the immersion working fluid in contact with the enhanced boiling surface. In some embodiments, the enhanced boiling surface includes additively manufactured (e.g., 3D-printed) structures thereon. In some embodiments, the enhanced boiling surface is a subtractive surface treatment, such as mechanically, electrically, or chemically etching or scoring the surface of the vapor chamber to provide a rough surface with increased surface area and nucleation sites to promote boiling of the immersion working fluid in contact with the enhanced boiling surface. In some embodiments, the enhanced boiling surface is integral to the vapor chamber surface as manufactured, such as during the casting or stamping process of forming the walls of the vapor chamber. In at least one example, the enhanced boiling surface includes a plurality of ridges and/or recesses created in the material of the vapor chamber while forming the exterior walls of the vapor chamber. 
     In some embodiments, the sidewalls of the channels and the main body cause the immersion working fluid to boil. The vapor bubbles cause a fluidic drag on the liquid phase of the immersion working fluid to draw the immersion working fluid through the channels and across the surfaces of the vapor chamber. 
     In some embodiments, the heat-generating component is positioned in the lower half of the vapor chamber. In some embodiments, the heat-generating component is positioned in the lower third of the vapor chamber. Positioning the heat-generating component in the lower portion of the vapor chamber may assist in circulating the vapor chamber working fluid and improving thermal transfer between the vapor chamber working fluid and the immersion working fluid. In some embodiments, the vapor bubbles of the vapor chamber working fluid rise toward the upper portion of the vapor chamber, and, upon condensing into a liquid phase of the vapor chamber working fluid, the vapor chamber working fluid drips back down toward the heat-generating component under the force of gravity when the vapor chamber is oriented substantially vertically. 
     In some embodiments, positioning the heat-generating component in the lower portion of the vapor chamber increases the thermal gradient proximate the heat-generating component. The fluidic drag of the upwardly moving vapor bubbles of the immersion working fluid, in some embodiments, induces an upward flow of the liquid phase of the immersion working fluid. The liquid phase of the immersion working fluid drawn from below the vapor chamber is cooler than the liquid phase of the immersion working fluid above or laterally adjacent to the vapor chamber, causing the channels to fill with a flow of the cooled liquid phase of the immersion working fluid, increasing the thermal gradient proximate the heat-generating component. 
     In some embodiments, the vertical structures vary in at one property or dimension to further drive movement of the immersion working fluid outside of the vapor chamber and/or vapor chamber working fluid inside the vapor chamber. In at least one embodiment, the vertical structures of the vapor chamber are fins that taper in the upward direction to drive flow of the liquid phase of the immersion working fluid. In some embodiments, as the vertical structures taper, the channels defined between the vertical structures consequently widen. 
     The flow from the vapor bubbles draws immersion working fluid upward through the widening channels. As additional vapor bubbles form on the surface of the vapor chamber due to the liquid phase of the immersion working fluid boiling, the flow continues upward despite the expansion of the liquid phase of the immersion working fluid vaporizing into the vapor bubbles. In some embodiments, the channels are at least 10% wider at a top of the channel than a bottom of the channel. In some embodiments, the channels are at least 50% wider at a top of the channel than a bottom of the channel. In some embodiments, the channels are at least twice as wide at a top of the channel than a bottom of the channel. 
     In some embodiments, a surface of the vertical structures is tuned with an enhanced boiling surface to create boiling fluid turbulence, thus increasing the fluid boundary layer for enhanced cooling. In addition to changing the surface treatment, one or more surface features, such as grooves for troughs, may be designed onto the surface of the vertical structures and/or the enhanced boiling surface to induce or increase a Venturi effect. The Venturi effect on the surface of the vertical structures may increase the buoyant velocity of the fluid. 
     In some embodiments, the bottom portion of at least one vertical structure is wider than the top portion of the vertical structure. In some embodiments, the vertical structure, therefore, includes more interior volume and more vapor chamber working fluid in the lower portion of the vapor chamber. More vapor chamber working fluid in the lower portion allows more thermal mass of the vapor chamber to be present in proximity to the cooler liquid phase of the immersion working fluid drawn in at the bottom of the channels. 
     In some of the described embodiments, the upper portion of the vapor chamber may have a lower temperature gradient than the lower portion and thermal transfer efficiently may be reduced. In other embodiments, one or more external or internal features of the vapor chamber may vary in the vertical direction to maintain or improve the efficiency of the vapor chamber. 
     In some examples, different types of enhanced boiling surfaces may be positioned in different areas of the exterior of the vapor chamber. In some embodiments, a first enhanced boiling surface is located proximate the bottom of the vapor chamber with at least a second enhanced boiling surface located above the first enhanced boiling surface in the direction of immersion working fluid flow. In at least one embodiment, a vapor chamber includes three enhanced boiling surfaces in series in the direction of immersion working fluid flow. For example, each successive enhanced boiling surface may include more nucleation sites to promote more efficient vapor bubble formation as the thermal gradient between the immersion working fluid and the vapor chamber working fluid decreases in the direction of immersion working fluid flow. 
     In some embodiments, interior features vary relative to the heat-generating component and/or in the direction of immersion working fluid flow. In some embodiments, a vapor chamber with a varying porosity assists vapor chamber working fluid movement and increases thermal gradient to immersion working fluid. In some embodiments, the porosity of the wicking structure in the interior volume of the vapor chamber varies in relation to the heat-generating element and/or the immersion fluid flow direction. A small pore size increases capillary pumping action of the vapor chamber working fluid in the wicking structure. A larger pore size allows greater permeability in the wicking structure. 
     In some embodiments, the porosity increases in the direction of the immersion working fluid flow. In some embodiments, the porosity increases continuously in the direction of immersion fluid flow. In some embodiments, the porosity changes in discrete regions. For example, a first portion of the wicking structure has a substantially constant first porosity, and a second portion has a substantially constant porosity. In some embodiments, the first portion is at least 10% of the length of the main body of the vapor chamber. In some embodiments, the first portion is at least 20% of the length of the main body of the vapor chamber. In some embodiments, the first portion is at least one-third of the length of the main body of the vapor chamber. 
     In some embodiments, the porosity increases with distance from the heat-generating component. For example, the porosity increases radially away from the location of the heat-generating component in contact with the vapor chamber. In other examples, the porosity increases in discrete steps at certain distances from the location of the heat-generating component in contact with the vapor chamber. 
     In some embodiments, the vapor chamber includes a wicking structure in the interior volume, and the interior volume is defined by inner surfaces of the vapor chamber walls. A distance between the inner surfaces defines the interior volume height. In some embodiments, the interior volume height is constant throughout the interior volume. In some embodiments, one or both inner surfaces opposite one another are non-planar (e.g., include at least one curve). In some embodiments, the non-planar inner surfaces produce a varying interior volume height. In at least one example, a first inner surface is non-planar and an opposing second inner surface is planar, and the variations in the interior volume height are produced by the non-planar shape of the first inner surface. In at least another example, the first inner surface and second inner surface are mirrored, producing a symmetrical interior volume that varies in height. In some embodiments, the non-planar inner surfaces are complementary to one another and produce a constant height despite the position of the interior volume moving. 
     In some embodiments, the varying inner walls create a periodic cross-sectional area of the interior volume. In some embodiments, the periodic cross-sectional area acts as a pumping structure to assist vapor chamber working fluid movement and increase thermal gradient to immersion working fluid. 
     The present disclosure relates to systems and methods for cooling heat-generating components of a computer or computing device according to at least the examples provided in the sections below: 
     [A1] In some embodiments, a vapor chamber includes a main body, a first vertical structure, and an enhanced boiling surface. The main body has a first surface and defines a first portion of an interior volume. The first vertical structure protrudes transverse to the main body and defines a second portion of the interior volume. The enhanced boiling surface is on at least a portion of the first vertical structure. 
     [A2] In some embodiments, the enhanced boiling surface of [A1] is additionally on at least a portion of the main body. 
     [A3] In some embodiments, the enhanced boiling surface of [A1] or [A2] varies along at least a portion of a length of the vapor chamber. 
     [A4] In some embodiments, the enhanced boiling surface of any of [A1] through [A3] is an additive surface treatment. 
     [A5] In some embodiments, the enhanced boiling surface of any of [A1] through [A3] is a subtractive surface treatment. 
     [A6] In some embodiments, the vapor chamber of any of [A1] through [A5] includes a wicking structure in the interior volume. 
     [A7] In some embodiments, the first vertical structure of any of [A1] through [A6] has a width that varies along at least a portion of a length of the vapor chamber. 
     [A8] In some embodiments, an interior volume height of any of [A1] through [A7] varies along at least a portion of a length of the first vertical structure. 
     [A9] In some embodiments, the vapor chamber of any of [A1] through [A8] includes a vapor chamber working fluid in the interior volume. 
     [B1] In some embodiments, a vapor chamber includes a main body and a first vertical structure. The main body has a first surface and defining a first portion of an interior volume. The first vertical structure protrudes transverse to the main body and defines a second portion of the interior volume. The first vertical structure has a first end having first width and a second end having a second width that is less than the first width. 
     [B2] In some embodiments, the vapor chamber of [B1] includes a second vertical structure, and the first vertical structure and the second vertical structure define a channel therebetween. 
     [B3] In some embodiments, the channel of [B2] varies in width along at least a portion of a length of the first vertical structure. 
     [B4] In some embodiments, the vapor chamber of any of [B1] through [B3] includes an enhanced boiling surface on at least a portion of the first vertical structure. 
     [B5] In some embodiments, the vapor chamber of any of [B1] through [B4] includes a wicking structure in the interior volume. 
     [B6] In some embodiments, an interior volume height of the interior volume of any of [B1] through [B5] varies along at least a portion of a length of the vapor chamber. 
     [C1] In some embodiments, a vapor chamber includes a main body, a first vertical structure, and a wicking structure. The main body has a first surface and defining a first portion of an interior volume. The first vertical structure protrudes transverse to the main body and defines a second portion of the interior volume. The wicking structure is in the interior volume. 
     [C2] In some embodiments, a porosity of the wicking structure of [C1] varies along at least a portion of a length of the vapor chamber. 
     [C3] In some embodiments, the first vertical structure of [C1] or [C2] has a length and an external wall thickness that varies along the length. 
     [C4] In some embodiments, the vapor chamber of any of [C1] through [C3] includes an enhanced boiling surface on at least a portion of the first vertical structure. 
     [C5] In some embodiments, the first vertical structure of any of [C1] through [C4] has a width that varies along at least a portion of a length of the vapor chamber. 
     [D1] In some embodiments, a thermal management system includes a heat-generating component, a vapor chamber, and an immersion working fluid. The vapor chamber is thermally connected to the heat-generating component to conduct thermal energy from the heat-generating component. The vapor chamber includes a main body, at least one vertical structure, and an enhanced boiling surface. The main body is substantially parallel to the heat-generating component, and the vapor chamber defines an interior volume containing a vapor chamber working fluid. The at least one vertical structure of the vapor chamber containing at least a portion of the interior volume and vapor chamber working fluid, and the vertical structure protruding transverse to the main body. The enhanced boiling surface located on at least a portion of the vertical structure. The immersion working fluid contacts at least a portion of the vapor chamber. 
     [D2] In some embodiments, the immersion working fluid of [D1] has a boiling temperature less than a peak operating temperature of the heat-generating component. 
     [D3] In some embodiments, a majority of a contact area of the heat-generating component of [D1] or [D2] is thermally connected to the vapor chamber in a bottom half of the vapor chamber in relation to a direction of flow of the immersion working fluid across a surface of the vapor chamber. 
     [D4] In some embodiments, the vapor chamber of any of [D1] through [D3] includes a thermal interface material between the heat-generating component and the vapor chamber. 
     [E1] In some embodiments, a thermal management system includes a heat-generating component, a vapor chamber, and an immersion working fluid. The vapor chamber is thermally connected to the heat-generating component to conduct thermal energy from the heat-generating component. The vapor chamber includes an interior volume, a main body, a plurality of vertical structures, and an enhanced boiling surface. The interior volume contains a vapor chamber working fluid. The main body contains at least a portion of the interior volume and vapor chamber working fluid, and a plane of the main body is oriented in a direction of gravity and substantially parallel to the heat-generating component. The plurality of vertical structures contains at least a portion of the interior volume and vapor chamber working fluid, and the vertical structures protrude transverse to the main body and define at least one channel. The enhanced boiling surface located on at least a portion of the vertical structures and main body in the channel. The immersion working fluid contacts at least a portion of the vapor chamber. 
     [E2] In some embodiments, a width of the channel of [E1] varies along a length of the channel. 
     The articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements in the preceding descriptions. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. For example, any element described in relation to an embodiment herein may be combinable with any element of any other embodiment described herein. Numbers, percentages, ratios, or other values stated herein are intended to include that value, and also other values that are “about”, “substantially”, or “approximately” the stated value, as would be appreciated by one of ordinary skill in the art encompassed by embodiments of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable manufacturing or production process, and may include values that are within 5%, within 1%, within 0.1%, or within 0.01% of a stated value. 
     A person having ordinary skill in the art should realize in view of the present disclosure that equivalent constructions do not depart from the spirit and scope of the present disclosure, and that various changes, substitutions, and alterations may be made to embodiments disclosed herein without departing from the spirit and scope of the present disclosure. Equivalent constructions, including functional “means-plus-function” clauses are intended to cover the structures described herein as performing the recited function, including both structural equivalents that operate in the same manner, and equivalent structures that provide the same function. It is the express intention of the applicant not to invoke means-plus-function or other functional claiming for any claim except for those in which the words ‘means for’ appear together with an associated function. Each addition, deletion, and modification to the embodiments that falls within the meaning and scope of the claims is to be embraced by the claims. 
     It should be understood that any directions or reference frames in the preceding description are merely relative directions or movements. For example, any references to “front” and “back” or “top” and “bottom” or “left” and “right” are merely descriptive of the relative position or movement of the related elements. 
     The present disclosure may be embodied in other specific forms without departing from its spirit or characteristics. The described embodiments are to be considered as illustrative and not restrictive. The scope of the disclosure is, therefore, indicated by the appended claims rather than by the foregoing description. Changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.