Lattice structures for two-phase cooling

Abstract

Methods and configurations for lattice structured parts for two-phase cooling. Embodiments include a part comprising a flow path configured for two-phase fluid flow and a lattice structure defining at least a portion of the flow path within the part, wherein the lattice structure is configured to have a hydraulic diameter that varies dynamically along the flow path to increase internal volume for vapor phase. Some embodiments include the manufacture of lattice structured parts via laminated object manufacturing methods.

Description

ALY-016PCLATTICE STRUCTURES FOR TWO-PHASE COOLINGCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of and priority to each of United States Provisional Application No. 63 / 677,110, filed on July 30, 2024, PCT Application No. PCT / US2025 / 032985, filed on June 10, 2025, and United States Provisional Application No. 63 / 791,225, filed on April 18, 2025. The entire disclosure of each of these applications is hereby incorporated by reference as if set forth in its entirety herein.TECHNICAL FIELD

[0002] Embodiments described herein generally relate to methods and apparatus for fabricating metal object parts, and more specifically to the manufacture of lattice structured parts for two-phase cooling.BACKGROUND

[0003] Effective thermal management is crucial in a wide range of high-performance systems, including power electronics, computing devices, and aerospace components. Specially manufactured parts such as lattice structured and micro-channeled parts may be used to improve heat transfer performance. These geometries are particularly advantageous in two-phase cooling systems, where both liquid and vapor phases of a fluid are used to remove heat with high efficiency.

[0004] Forming such geometries, however, poses challenges for traditional manufacturing techniques such as milling or drilling. Traditional techniques are often incapable of producing complex void patterns and other internal structures required for optimized two-phase cooling. As a result, traditional techniques may fall short in forming appropriate lattice structured parts for two-phase cooling.

[0005] Accordingly, a need exists for improved methods of manufacturing lattice structured parts for two-phase cooling.SUMMARY

[0006] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description section. This summary is not intended to identify or exclude 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.ALY-016PC

[0007] In some embodiments, the techniques described herein relate to a part for use in two- phase cooling, including: a flow path configured for two-phase fluid flow; and a lattice structure defining at least a portion of the flow path within the part, wherein the lattice structure is configured to have a hydraulic diameter that varies dynamically along the flow path to increase internal volume for vapor phase transport.

[0008] In some embodiments, the lattice structure includes at least one of a gyroid, Schwarz - diamond, other triply periodic minimal surface (TPMS), or tessellated pattern.

[0009] In some embodiments, the wetted surface of the part along the flow path is microscopically textured or patterned to selectively promote and distribute nucleation boiling within the part.

[0010] In some embodiments, the surface texture or patterns have features on the order of tens of nanometers to hundreds of microns.

[0011] In some embodiments, the surface texture or patterns are configured to prevent overboiling in a region of the part.

[0012] In some embodiments, the part is configured such that during its use the fraction of vapor flow to liquid flow is less than 20%.

[0013] In some embodiments, the hydraulic diameter increases along the flow path.

[0014] In some embodiments, the lattice structure has a minimal surface.

[0015] In some embodiments, the part is a cold plate or a heat exchanger.

[0016] In some embodiments, the lattice structure includes a dense network of small hydraulic diameter pores and channels.

[0017] According to another aspect, the techniques described herein relate to a method of manufacturing a part for two-phase cooling, the method including: providing a plurality of patterned sheets; and bonding the plurality of patterned sheets together via a laminated object manufacturing (LOM) technique to form a part including a lattice structure defining at least a portion of a flow path, wherein the lattice structure is configured to have a hydraulic diameter that varies dynamically along the flow path to increase internal volume for vapor phase transport.

[0018] In some embodiments, bonding is accomplished via at least one of solid-state diffusion bonding, semi-solid state diffusion bonding, or transient liquid-phase bonding.

[0019] In some embodiments, the patterned sheets include metal sheets of different thicknesses layered into the part to create surface features on the same length scale as the thickness of the metal sheet.ALY-016PC

[0020] In some embodiments, the method further includes cutting features into at least one of the patterned sheets with a cutting tool prior to bonding to form at least part of the lattice structure.

[0021] In some embodiments, the cutting tool is a laser cutter. In some embodiments, the method further includes roughening at least part of a surface of at least one patterned sheet using the laser cutter.

[0022] In some embodiments, the lattice structure includes at least one of a gyroid, Schwarz - diamond, other triply periodic minimal surface (TPMS), or tessellated pattern.

[0023] In some embodiments, the method further includes microscopically texturing or patterning a wetted surface of the part.

[0024] In some embodiments, the texturing or patterning is performed as part of the LOM manufacturing process or in a post-production step.BRIEF DESCRIPTION OF DRAWINGS

[0025] Non-limiting and non-exhaustive embodiments of this disclosure are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified:

[0026] Figure 1 depicts a lattice structure used in pool boiling;

[0027] Figure 2 depicts the same lattice structure as in Figure 1, magnified to show surface microstructure;

[0028] Figure 3 depicts a layer of a pool boiling part with a lattice structure;

[0029] Figure 4 depicts a schematic of a tapered channel with varying hydraulic diameter;

[0030] Figure 5 depicts a schematic of a fin with holes configured to promote rewetting;

[0031] Figure 6 depicts a channel with rewetting features;

[0032] Figure 7A depicts a channel with a laser-ablated surface;

[0033] Figure 7B depicts a cross-section of the channel of Figure 7A, assembled; and

[0034] Figure 8 presents a flowchart of a method of manufacturing a part for two-phase cooling.DETAILED DESCRIPTION

[0035] Various embodiments are described more fully below with reference to the accompanying drawings, which form a part hereof, and which show specific exemplary embodiments. However, the concepts of the present disclosure may be implemented in manyALY-016PC different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided as part of a thorough and complete disclosure, to fully convey the scope of the concepts, techniques and implementations of the present disclosure to those skilled in the art. Embodiments may be practiced as methods, systems or devices. The following detailed description is, therefore, not to be taken in a limiting sense.

[0036] Reference in the specification to “one embodiment” or to “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least one example implementation or technique in accordance with the present disclosure. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

[0037] In addition, the language used in the specification has been principally selected for readability and instructional purposes and may not have been selected to delineate or circumscribe the disclosed subject matter. Accordingly, the present disclosure is intended to be illustrative, and not limiting, of the scope of the concepts discussed herein.Definitions

[0038] Unless otherwise specified, the following terms as used herein shall have the meanings as provided below:

[0039] The term “laminated object manufacturing” (LOM) refers to a method of manufacturing a part, containing additive and subtractive steps, beginning with contiguous sheets of material, and processing sheets sequentially to form a part.

[0040] The term “bonding” refers to the process through which the contiguous sheets of material are formed into a part. The workpiece is subjected to a combination of heat and applied force which form covalent and / or metallic bonds between the sheets of material, forming an object.

[0041] The term “build volume” refers to the geometric volume enclosed by the external faces of the stack of patterned metal sheets.

[0042] The term “layer” refers to an individual sheet in the stack of patterned metal sheets.

[0043] The term “part” refers to a cold plate, heat exchanger, or other object manufactured with internal flow paths through LOM.

[0044] The term “workpiece” refers to a stack of metal sheets to be bonded into at least one part and at least one corresponding support structure.

[0045] The term “metal sheet” refers to a metal sheet or foil that is stacked in the workpiece. Each metal sheet may be patterned to contain part regions and support structure regions. In someALY-016PC embodiments, the metal sheet may comprise at least one of aluminum, copper, magnesium, titanium, aluminum alloy, magnesium alloy, and / or titanium alloy.

[0046] The term “sheet” refers generally to a metallic layer between 25 pm and 10 cm in thickness.

[0047] The term “void” refers to a volume cut out of a metal sheet in the support or part region which is fully enclosed and not fluidically connected to any other internal channel or port within the workpiece.

[0048] The term “void space” refers to a pattern of voids intentionally cut in a given volume or region.

[0049] The term “heated surface” refers to the surface of a part that is directly in contact with a heat source and includes the internal surfaces that are immediately opposite the heat source.

[0050] The term “flow path” refers to a traceable path of void space through internal channels in the part.

[0051] The term “channel” refers to at least a portion of the void space in the flow path.

[0052] The term “microchannel” refers to a channel with at least one sub -millimeter dimensional characteristic, such as channel width, channel depth, or effective channel diameter. Microchannels are typically arrayed in a regular pattern along one axis and flow parallel to other microchannels.

[0053] The term “microcapillary” refers to a channel having at least one sub -millimeter dimensional characteristic, such as a channel width, channel depth, or effective channel diameter. Whereas microchannels are arrayed in one or two rows, microcapillaries are arrayed several to hundreds of times in orthogonal directions, and may be nonplanar.

[0054] The term “lattice structure” refers to a structure that conforms to a regular pattern of at least one of gyroid, triply-periodic minimal structure (TPMS), Schwarz-diamond, ellipsoid, or another tessellated pattern such as Cassini geometry.

[0055] The term “triply periodic minimum surface” (TPMS) structure refers to a three- dimensional geometry with a repeating unit structure which has zero mean curvature.

[0056] The term “hydraulic diameter” refers to a characteristic length scale of the internal geometry of a lattice structure in a control volume. The characteristic length is calculated as the ratio of the wetted internal volume of the flow path divided by the wetted surface area along the flow path. The control volume may consist of the entire flow path or a sub-portion thereof.ALY-016PC

[0057] The term “heat exchanger” refers to a part configured to transfer heat between a heat source and at least one fluid. In some cases, the heat source may be a fluid and a heat exchanger may transfer heat between two or more fluids.

[0058] The term “cold plate” is understood to describe a subset of heat exchangers which are particularly configured to remove heat from an adjacent heat source and using at least one fluid as a coolant. The cold plate may be configured to interact with a second remote heat exchanger to regenerate the coolant, and a balance of plant to flow the coolant through the cold plate.

[0059] The terms “boiling surface” and “heat transfer surface” refer to the regions in the part where boiling, and thus the majority of heat transfer due to latent heat of vaporization, may occur.

[0060] The term “promote boiling” may refer to “reducing local superheat,” “increasing critical heat flux,” or “preventing dryout.” Boiling occurs once the fluid’s temperature exceeds its boiling point for a given ambient pressure. Because the boiling process is imperfect, the fluid near the heat source often exceeds the boiling temperature, becoming superheated. Heat transfer surfaces that promote boiling may do so by reducing the degree of superheat in the nearby fluid for a given heat flux. “Critical heat flux” occurs when nucleate boiling transitions to film boiling, thereby insulating the heat transfer surface from the coolant. This film reduces heat transfer and can cause “thermal runaway”’ where the film expands and prevents the coolant from returning to the heat transfer surface. A persistent coolant film over the heat transfer surface is called “dryout.” Therein features that promote boiling may also “prevent dryout.”Embodiments

[0061] Embodiments of this invention include configurations of lattice structured parts, such as cold plates and heat exchangers, for two-phase cooling. In embodiments of this invention, the configurations may include a part that comprises a flow path configured for two-phase fluid flow and a lattice structure defining at least a portion of the flow path within the part, wherein the lattice structure is configured to have a hydraulic diameter that varies dynamically along the flow path to increase internal volume for vapor phase transport. In some embodiments, the lattice structure may be configured to promote boiling in desired regions along the flow path. In some embodiments, the part may be manufactured using LOM or another suitable manufacturing technique.

[0062] Non-limiting examples of these configurations are further discussed below.Manufacturing

[0063] Metal parts for two-phase cooling, such as cold plates and heat exchangers, may be assembled via at least one additive or subtractive manufacturing technique. Suitable techniques may include LOM, diffusion bonding, brazing, friction stir welding, transient liquid phaseALY-016PC bonding, electroplating, electrodeposition, etching, computer numerical control (CNC) micromachining, laser cutting, stereolithography (SLA), and / or powder bed fusion. Hybrid approaches may also be employed, wherein additive techniques are used to form complex internal geometries, and other methods are used for final shaping, port formation, or surface finishing. For example, a cast outer shell may be combined with an additively manufactured core that includes the lattice structure.

[0064] In some embodiments, a metal part may be assembled via LOM. In LOM, a workpiece consisting of a plurality of metal sheets may be assembled and bonded to create the metal part. The workpiece may be assembled in a laminated fashion with the metal sheets. In this manner, the workpiece may be a layered workpiece assembled by depositing the metal sheets. The metal sheets may be patterned such that the pattern of the metal sheets partitions the workpiece into at least one support region and at least one part region.

[0065] The metal sheets may be bonded using any suitable bonding method, such as solid- state diffusion bonding, semi-solid state diffusion bonding, and / or transient liquid-phase bonding. The metal sheets may be bonded in a heated press, a more complicated bonding machine comprising a heated press and a vacuum chamber, and / or a bonding machine of any configuration appropriate for laminated object manufacturing of metal parts, such as but not limited to a metal heat exchanger. The metal sheets may be bonded by applying a mechanical force along at least one axial direction of the metal sheets.

[0066] In some embodiments, the metal sheets may be patterned and assembled to form a lattice structured part. Lattice geometries, such as gyroid structures, Schwarz diamond geometries and other triply periodic minimal surfaces (TPMS), may be particularly well suited for LOM-based assembly. These geometries provide a high degree of mechanical stability and resistance to deformation under compressive forces, making them compatible with manufacturing techniques that use applications of force such as LOM. TPMS structures may be selected for LOM assembly based on whether each distinct z-layer of the part is fully contiguous.

[0067] The metal sheets may be patterned to form the lattice structure. For example, the metal sheets may be patterned (e.g., cut into) so that material is removed from at least one part region of each metal sheet. This may create a pattern of void spaces within the workpiece. The void spaces may be formed via any appropriate cutting technique, such as drag knife cutting, laser cutting, and / or etching. The void spaces may be formed from regular, geometric patterns and / or random distributions within the workpiece. The lattice structures may be formed from the void spaces after stacking the metal sheets. The metal sheets may be patterned as part of the LOM manufacturing process (e.g., prior to bonding) or in a post-production step.ALY-016PC

[0068] Figure 1 depicts a lattice structure 101 formed of layered metal sheets. A network of structural beams 102 are formed from patterned metal sheets which are fully contiguous within each z-layer. The voids formed from the cuts generate a fluidically connected void space 103.

[0069] At least one dimension of the lattice structure may be a kerf width of the cutting tool used, such as a laser beam width. The kerf width may be as small as 10 microns to 500 microns. Larger features may be created through multiple adjacent cuts or by using broader kerf widths, with the resulting dimensions ranging from 10 microns up to greater than 1,000 microns.

[0070] In some embodiments, the metal sheets may vary in thickness, allowing the formation of surface features and flow passages with dimensions correlated to the thickness of the sheet material. For example, thinner sheets may form finer features while thicker sheets may form larger features.

[0071] Figure 2 depicts a magnified version of a regular lattice structure such as the one presented in Figure 1. The cutting pattern is configured so that the structural beams 201 are covered with small ridges 202 which increase the overall surface area per unit volume of the lattice structure. In some embodiments, the ridges are configured with at least one size dimension matched to the thickness of a single layer of the metal sheet. The layer structure is obscured throughout most of the part for visual simplicity, but some layers are depicted in 203.

[0072] In some embodiments, the part may include at least one port and / or any other surface feature for receiving and / or releasing fluid and / or gas. The port may serve as an entry and / or exit point for fluid used for two-phase cooling. The port may include a valve, septum, and / or other resealable feature that permits fluid to be received or released.

[0073] In some embodiments, the part may include features for improving heat transfer performance, such as fins, chambers, and wicks. The features may be formed during the same manufacturing process used to form the lattice structure. The features may exist solely on a single layer to increase surface area and promote boiling.

[0074] In some embodiments, the part may include features for mounting and connecting the part to at least one heat source. At least one surface of the part which is configured to contact the heat source may be termed a boiling surface or heat transfer surface. The features may be formed during the same manufacturing process used to form the lattice structure.

[0075] In some embodiments, the part may undergo at least one post-production step. For example, surface finishing operations may be applied to the part, such as sand-blasting, chemical etching, laser etching, electropolishing, and / or plasma treatments. In some examples, the ports may be sealed using welding, brazing, and / or mechanically coupled fittings after receiving a fluid.ALY-016PCTwo-Phase Cooling

[0076] In embodiments of this invention, metal cooling parts, such as cold plates and heat exchangers, may be manufactured for two-phase cooling applications. Two-phase cooling involves cooling a heat source using a fluid in both liquid and vapor phases to facilitate heat transport. Parts configured to accomplish two-phase cooling may introduce fluid via an external port, flow the fluid to a heat transfer surface, transfer heat to the fluid, evaporate at least some the fluid, remove the evaporated fluid from the heat transfer surface, and remove fluid from the part via an external port. The fluid may flow to different regions of the part (e.g., hot and cold regions) as it undergoes phase changes. The part may cool any suitable heat source, such as electronic components (e.g., CPUs, GPUs, circuit boards, etc.), battery systems, mechanical equipment (e.g., motors, actuators, etc.), and / or industrial tools.

[0077] Although nucleate boiling is an effective way to transfer heat from a surface at the boiling temperature, coolant may enter the cold plate well below the boiling temperature of the fluid. In this case, the cold plate may be improved by optimizing single-phase heat transfer in some regions of the cold plate, typically near the inlet or coolant return region, and optimizing two-phase heat transfer in other regions of the cold plate. For single-phase heat transfer within a cooling part, the Nusselt number, which represents the ratio of total heat transfer to conductive heat transfer across the fluid boundary, is approximately constant for fixed materials, cavity shape, and flow structure. The equation relating the Nusselt number and single-phase convection is: k h — Nu — w where ‘h’ is the convection coefficient, ‘k’ is the thermal conductivity of the fluid, and ‘w’ is the hydraulic diameter of the channel. This implies that the heat transfer coefficient and the hydraulic diameter have an inverse relationship. Thus, to increase single-phase heat transfer performance, it is desirable to minimize the hydraulic diameter. This makes it beneficial to manufacture lattice structures with small hydraulic diameters for cooling parts. Manufacturing parts with a dense network of pores and channels with small hydraulic diameters, however, is difficult with traditional manufacturing methods alone.

[0078] Two-phase heat transfer, by contrast, requires adequate surface area and space for vapor to escape and coolant to rewet the surface. This may conflict with the parameters for optimal single-phase cooling - particularly the motivation for small hydraulic diameters.ALY-016PC

[0079] Accordingly, some embodiments of this invention include lattice structures that are optimized for single-phase heat transfer in some regions and two-phase fluid flow in other regions. The lattice structure may define at least one flow path through regions of the part, enabling circulation of a fluid for two-phase cooling. The lattice structure may include a regular or repeating pattern of fluidically connected voids with an internal portion of a part. The remaining portions of the part may comprise part and / or support regions.

[0080] The flow path may be configured for two-phase cooling with the part. For example, a fluid within the part may absorb thermal energy from a heat source while near a heated surface, evaporate to a vapor, move through the flow path toward cooler regions of the part, condense back into a liquid to release the absorbed heat, and then flow to the heated surface (or another heated surface) through the flow path.

[0081] At least one of the flow path and part may be configured to enable pool boiling within the part. For pool boiling, at least one internal chamber may be configured within the part to bring the fluid in contact with the heat transfer surface. A lattice structure, fins, or any other high specific surface area structure may be configured within the internal chamber to promote heat transfer to the fluid and rewet.

[0082] Figure 3 depicts a single z-layer of a metal part 301 configured for pool boiling. The internal volume of the part is configured with a single contiguous sheet 302 with numerous voids 303 cut into the layer. The outer bound of the part features solid elements 304 which may be configured to mount the part to a heat source.

[0083] At least one of the flow path and part may be configured to enable flow boiling within the part. For flow boiling, the flow path includes at least one parallelized array of channels over the heat transfer surface. The channels are configured to promote heat transfer to the fluid and rewet. The channels may be of an arbitrary fixed or varying width, on the millimeter or micron scale.

[0084] The lattice structure may define any suitable type of flow path through the part. For example, the lattice structure may define a complete flow path that is connected to at least two externally accessible ports on the part, such as an inlet port and an outlet port. Other examples of flow paths include closed-loop flow paths, tortuous or serpentine paths, linear paths, helical paths, and / or radial paths to or from a central cavity.

[0085] The flow path may be formed from at least one channel within the part. In some embodiments, a flow path may include multiple channels that are fluidly connected. In some embodiments, the flow path may consist of multiple channels in parallel. Multiple channels mayALY-016PC merge into one or more flow paths in at least a portion of the part. A single channel may split into multiple channels in at least a portion of the part, creating branching flow paths.

[0086] In some embodiments, the flow path may be formed from a network of microchannels. The microchannels may have at least one characteristic dimension less than 1 millimeter, such as a channel width, channel height, and / or hydraulic diameter. The microchannels may have dimensions significantly smaller than other regions of the flow path. The microchannels may be of uniform or variable length, and may be straight, curved, or contoured, depending on the manufacturing technique employed and the functional requirements of the part. In some embodiments, the flow path may be formed from a network of microcapillaries.

[0087] In some embodiments, the microchannels, fins, and wicks may be configured to increase the surface area near the heat transfer surface. High specific surface area to geometric volume structures may be selected to maximize surface area that can be contacted by the fluid and maximize heat transfer.

[0088] In some embodiments, the part may include multiple flow paths. The flow paths may be arranged in a parallel fashion through the part. In other embodiments, the flow paths may cross each other (e.g., in a zig-zag fashion) along a plane of the part.

[0089] In some embodiments, the lattice structure may include a minimal surface, TPMS, and / or tessellated patterns. Examples of minimal surface geometries include but are not limited to gyroids, Schwarz-diamond geometries, Schwarz-primitive geometries, Fischer-Koch S geometries, Neovius geometries, and Infinite Periodic Wrapping geometries. Such structures are characterized by their periodicity in three orthogonal directions and minimal surface area properties. Examples of suitable tessellated geometries include but are not limited to spheres, ellipsoids, double ellipsoids, super-ellipsoids, and Cassini surfaces.

[0090] In some embodiments, the part may include multiple lattice structures. Each lattice structure may correspond to a separate region of the part. Each lattice structure may define a separate flow path. Each lattice structure may be configured to operate with a different fluid. The discrete regions of the part may be partitioned using manifolds, ribs, and / or other internal features. At least a portion of the regions may be thermally coupled but fluidically isolated. At least a portion of the regions may include restricted flow paths that control fluid exchange between the regions.

[0091] In some embodiments, the lattice structure may be configured to have a small hydraulic diameter. For example, the lattice structure may have a hydraulic diameter within the range of 5 to 500 microns.ALY-016PC

[0092] In some embodiments, the hydraulic diameter may vary along the flow path. For example, the hydraulic diameter may increase progressively (e.g., to accommodate vapor expansion) and / or vary dynamically (e.g., to increase internal volume for vapor phase transport and / or control pressure drop and fluid velocity). The hydraulic diameter may increase progressively from an inlet port to an outlet port. In some embodiments, the hydraulic diameter may decrease along the flow path (e.g., to modulate fluid velocity and enhance heat transfer downstream). In some embodiments, the hydraulic diameter may vary cyclically along the flow path.

[0093] In some embodiments, the part may be partitioned into multiple regions, with each region having a particular hydraulic diameter. For example, hotter regions (e.g., regions near heated surfaces) may be configured with a smaller hydraulic diameter to enhance heat transfer performance. Colder regions may be configured with a larger hydraulic diameter.

[0094] In some embodiments, a number of channels may be configured with a small hydraulic diameter to bring liquid-phase fluid to the boiling surface, with a separate set of channels with a greater hydraulic diameter configured to remove vapor-phase fluid after it has contacted the boiling surface. These channels may be arrayed within the part to take advantage of natural convection and the tendency of the vapor phase to rise against the gravity vector.

[0095] In some embodiments, the channels or chamber along the boiling surface may be tapered to direct vapor phase flow towards channels configured to remove the vapor phase flow. In some embodiments, these channels may be tapered relative to the horizontal plane between 0° and 30°.

[0096] Figure 4 depicts a schematic cross-section 401 of a tapered channel with varying hydraulic diameter. The space between the heat transfer surface 402 and the part regions 403, 403’, and 403” form the tapered channel 404. The part regions 403, 403’, and 403” are configured with alternating small channels 405 and large channels 406 between the regions. Small channels 405 are fluidically connected to the fluid inlet to the tapered channels 404. As the fluid boils in contact with the heat transfer surface 402, bubbles rise along the tapered channel to the vapor and fluid outlet channel 406.

[0097] In some embodiments, the lattice structure may be covered with spines, pins, ridges, fins, or other microstructures. These microstructures may be configured to increase the surface area of the heat transfer surface and serve as nucleation points to promote boiling. In embodiments where the lattice structure has conical, cylindrical, wall, or wire features, the surface area may be increased by configuring disc, ridge, or pointed small features which can be stenciled in a single single z-layer may onto the surface.ALY-016PC

[0098] In some embodiments, wetted surfaces such as internal wicks, fins, channel walls, or other protrusions may be perforated with small holes to promote rewetting. Small holes may be placed throughout the microstructure where fluid modeling predicts vapor bubbles to collect. These holes may be configured to allow fluid in the liquid phase to flow into those pockets and rewet the surface. These holes may be configured to allow evaporated fluid to evacuate the boiling surface within the part, reducing the dry surface area.

[0099] Figure 5 depicts a schematic of fins with holes configured to promote rewetting. A thermally conductive feature 501, such as a part of a lattice structure, is configured with fins 502 to increase surface area and provide nucleation sites to promote boiling and reduce superheating. As the fluid boils and evaporates, some vapor may become trapped in small gap features such as the gap 503 between the adjacent fins 502. Fins and other gap regions like these may be configured with holes 504 which allow vapor to be removed from the thermally conducting feature and fluid in the liquid state to be replenished at the surfaces of 501 and 502.

[0100] Figure 6 depicts a schematic of a microchannel 601 configured with rewetting features. The channel is adjacent to a heat transfer surface 602. Fluid is flowed through inlet 603 and evaporated once in contact with the heat transfer surface 602. Vapor bubbles may become trapped in the channel 601 without secondary flow paths in the microchannel to introduce fresh fluid (604) and release vapor (605).

[0101] In some embodiments, the wetted surface of the part may be textured, etched, patterned, and / or otherwise patterned to promote heat transfer. For example, the part may be microscopically textured or patterned to include nucleation sites that promote localized boiling. The nucleation sites may be formed from features such as microcavities, ridges, protrusions, and / or surface roughness. The nucleation sites may be formed during the manufacturing process (e.g., by patterning metal sheets forming the part). The features may have dimensions ranging from tens of nanometers to hundreds of microns. The distribution of such features may be selected to prevent overboiling in at least one region of the cold plate and avoid dry-out.

[0102] In some embodiments, a cutting or texturing tool is used to texture or pattern a surface to create nucleation sites. Any type of texture or pattern die may be used.

[0103] In some embodiments, the method of texturing or patterning the surface to create nucleation sites is laser ablation. A laser is used to periodically ablate the surface of a single layer of the part to increase the surface roughness. Multiple applications of the laser may be used to further increase the surface roughness, or pattern the surface in a way to concentrate or disperse the nucleation points.ALY-016PC

[0104] Figure 7A depicts a configuration of three layers 701 to assemble a channel with a laser-ablated surface. The top and bottom layers 702 and 702’ are laser-ablated on a select region of the inwards-facing surface 703. One middle layer 704 is placed between 702 and 702’ with a void cut in the sheet corresponding to the area 703.

[0105] Figure 7B depicts a cross-section of the same three layers 701 of Figure 7A assembled and rotated. Laser ablation has further roughened the select regions 703 of Figure 7A to serve as nucleation points for boiling 705. When the three layers are bonded together, a void region 706 can be used as a channel with the characteristic width of a single z-layer, and fluidically connected to other internal volumes of the part (not depicted).

[0106] In some embodiments, the nucleation sites may be spatially distributed in a non- uniform manner. For example, hotter regions of the part may be patterned with a higher density of nucleation sites. Colder regions may have a lower density of nucleation sites and / or lack nucleation sites entirely.

[0107] In some embodiments, the part may be configured to maintain an optimum fluid quality during operation. The fluid quality may be calculated as the ratio of vapor flow to liquid flow. The part may be configured to operate with a fluid quality of less than 20%. This may improve heat transfer efficiency, flow stability, and help avoid dry-out.

[0108] Figure 8 depicts a flowchart of a method of manufacturing a part for two-phase cooling according to the present invention.

[0109] The method begins with the design of a part having a two-phase flow path (Step 800). Such a part typically has a lattice structure that at least partially defines the two-phase flow path. Representative lattice structures include, but are not limited to, gyroid patterns, Schwarz-diamond patterns, triply periodic minimal surface patterns, and tessellated patterns. The flow path itself typically has a hydraulic diameter that varies dynamically along the flow path to increase internal volume for vapor phase transport.

[0110] The design for the part is converted to a plurality of patterned sheets (Step 804). The sheets may have uniform thickness or they may have varying thicknesses, which can be useful for creating surface features on the same length scale as the sheet thickness and achieving desired heat transfer characteristics.[OHl] In some embodiments features are cut into the patterned sheets using a cutting tool, such as a laser cutter. The same or another laser cutter may also be used to roughen the surface of one or more sheets as discussed above. Microscopic texturing or patterning a wetted surface of the part is also possible during the LOM manufacturing process or as a post-production operation.ALY-016PC

[0112] The plurality of patterned sheets are bonded using a LOM technique (Step 808), such as solid-state diffusion bonding, semi-solid state diffusion bonding, or transient liquid-phase bonding, resulting in the desired two-phase cooling part having an integrated lattice structure with at least one flow path having a dynamically varying hydraulic diameter.Equivalents

[0113] The methods, systems, and devices discussed above are examples. Various configurations may omit, substitute, or add various procedures or components as appropriate. For instance, in alternative configurations, the methods may be performed in an order different from that described, and that various steps may be added, omitted, or combined. Also, features described with respect to certain configurations may be combined in various other configurations. Different aspects and elements of the configurations may be combined in a similar manner. Also, technology evolves and, thus, many of the elements are examples and do not limit the scope of the disclosure or claims.

[0114] Embodiments of the present disclosure, for example, are described above with reference to block diagrams and / or operational illustrations of methods, systems, and computer program products according to embodiments of the present disclosure. The functions / acts noted in the blocks may occur out of the order as shown in any flowchart. For example, two blocks shown in succession may in fact be executed substantially concurrent or the blocks may sometimes be executed in the reverse order, depending upon the functionality / acts involved. Additionally, or alternatively, not all of the blocks shown in any flowchart need to be performed and / or executed. For example, if a given flowchart has five blocks containing functions / acts, it may be the case that only three of the five blocks are performed and / or executed. In this example, any of the three of the five blocks may be performed and / or executed.

[0115] A statement that a value exceeds (or is more than) a first threshold value is equivalent to a statement that the value meets or exceeds a second threshold value that is slightly greater than the first threshold value, e.g., the second threshold value being one value higher than the first threshold value in the resolution of a relevant system. A statement that a value is less than (or is within) a first threshold value is equivalent to a statement that the value is less than or equal to a second threshold value that is slightly lower than the first threshold value, e.g., the second threshold value being one value lower than the first threshold value in the resolution of the relevant system.

[0116] Specific details are given in the description to provide a thorough understanding of example configurations (including implementations). However, configurations may be practiced without these specific details. This description provides example configurations only, and doesALY-016PC not limit the scope, applicability, or configurations of the claims. Rather, the preceding description of the configurations will provide those skilled in the art with an enabling description for implementing described techniques. Various changes may be made in the function and arrangement of elements without departing from the spirit or scope of the disclosure.

[0117] Having described several example configurations, various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosure. For example, the above elements may be components of a larger system, wherein other rules may take precedence over or otherwise modify the application of various implementations or techniques of the present disclosure. Also, a number of steps may be undertaken before, during, or after the above elements are considered.

Claims

ALY-016PCCLAIMSWhat is claimed is:

1. A part for use in two-phase cooling, comprising: a flow path configured for two-phase fluid flow; and a lattice structure defining at least a portion of the flow path within the part, wherein the lattice structure is configured to have a hydraulic diameter that varies dynamically along the flow path to increase internal volume for vapor phase transport.

2. The part of claim 1, wherein the lattice structure comprises at least one of a gyroid, Schwarz-diamond, other triply periodic minimal surface (TPMS), or tessellated pattern.

3. The part of claim 1, wherein the wetted surface of the part along the flow path is microscopically textured or patterned to selectively promote and distribute nucleation boiling within the part.

4. The part of claim 3, wherein the surface texture or patterns have features on the order of tens of nanometers to hundreds of microns.

5. The part of claim 3, wherein the surface texture or patterns are configured to prevent overboiling in a region of the part.

6. The part of claim 1, wherein the part is configured such that during its use the fraction of vapor flow to liquid flow is less than 20%.

7. The part of claim 1, wherein the hydraulic diameter increases along the flow path.

8. The part of claim 1, wherein the lattice structure has a minimal surface.

9. The part of claim 1, wherein the part is a cold plate or a heat exchanger.

10. The part of claim 1, wherein the lattice structure comprises a dense network of small hydraulic diameter pores and channels.

11. A method of manufacturing a part for two-phase cooling, the method comprising: providing a plurality of patterned sheets; and bonding the plurality of patterned sheets together via a laminated object manufacturing (LOM) technique to form a part comprising a lattice structure defining at least a portion of a flow path,ALY-016PC wherein the lattice structure is configured to have a hydraulic diameter that varies dynamically along the flow path to increase internal volume for vapor phase transport.

12. The method of claim 11, wherein bonding is accomplished via at least one of solid-state diffusion bonding, semi-solid state diffusion bonding, or transient liquid-phase bonding.

13. The method of claim 11, wherein the patterned sheets comprise metal sheets of different thicknesses layered into the part to create surface features on the same length scale as the thickness of the metal sheet.

14. The method of claim 11, further comprising cutting features into at least one of the patterned sheets with a cutting tool prior to bonding to form at least part of the lattice structure.

15. The method of claim 14, wherein the cutting tool is a laser cutter.

16. The method of claim 15, further comprising roughening at least part of a surface of at least one patterned sheet using the laser cutter.

17. The method of claim 11, wherein the lattice structure comprises at least one of a gyroid, Schwarz-diamond, other triply periodic minimal surface (TPMS), or tessellated pattern.

18. The method of claim 11, further comprising microscopically texturing or patterning a wetted surface of the part.

19. The method of claim 17, wherein the texturing or patterning is performed as part of the LOM manufacturing process or in a post-production step.

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