heat pipe

Abstract

The present invention provides a heat pipe comprising: a. an elongated envelope surrounding an evaporator section at or toward a first end, a condenser section at or toward a second end, and an intermediate adiabatic section between the evaporator section and the condenser section; b. at least one first channel providing fluid communication of a working fluid evaporated from the evaporator section to the condenser section; c. at least one second channel providing effective wicking means for transferring a working fluid condensed from the condenser section to the evaporator section, wherein the first and second channels communicate with each other in the condenser section and the evaporator section of the first channel; and d. at least one coolant channel integrated within the envelope and adapted to transfer heat away from one or both of the first and second channels by means of a flowing coolant inside.

Description

Technology Field

[0001] The present invention relates to a 3-D printed heat pipe array, a method for designing and producing the same, and a method for using the same to remove heat from a high-tech device. Background Technology

[0002] In recent years, overheating of high-tech devices has become an increasingly significant barrier to achieving the highest possible level of operating performance.

[0003] High-tech devices thus present significant cooling challenges. Examples of high-tech devices requiring advanced cooling include semiconductors, IT hardware, EV power electronics, supercomputer CPUs, solid-state laser diodes, gyrotrons, radar transmitters, space propulsion rockets, chemical reactors, and nuclear fusion reactors.

[0004] The performance limiting factor for these high-tech devices is the amount of heat flux that can be dissipated without overheating. The ideal operating temperature depends on the device being cooled. For example, in the case of semiconductor devices such as power electronics, laser diodes, and CPUs, lower temperatures are required, whereas some other devices can withstand higher operating temperatures or even benefit from them.

[0005] The challenge of providing effective cooling is particularly critical for emerging technologies such as nuclear fusion. While nuclear fusion occurs naturally in stars, synthetic fusion processes are challenging due to the extreme conditions required. For fusion to occur, both fuel and a sealed environment with sufficiently high temperatures, pressures, and confinement times are required to generate plasma. Current engineering constraints make the practical applicability of nuclear fusion highly challenging, as achieving and stably maintaining the necessary conditions is difficult. For example, in a fusion reactor, the internal temperature would need to reach 150,000,000°C. Such high temperatures generate intense energy flows around the reactor walls, and without advanced cooling technology, the walls would be rapidly damaged.

[0006] Global demand for electricity is expected to surge by up to five times by 2050, and in an increasingly climate-conscious world, renewable energy sources alone cannot fully meet this increased energy demand. Nuclear fusion power has been increasingly advocated over the past few decades as a potential means to address global warming by meeting this demand. Fusion would also favorably overcome the challenges posed by nuclear waste generated by conventional fission methods. If a solution to critical cooling challenges is found, nuclear fusion could not only meet but exceed the world's energy needs.

[0007] In the field of technology, cooling devices are known for complex technological devices, such as nuclear fusion reactors, for example:

[0008] GB1525525 describes a method for removing heat from a fusion reactor, comprising blowing helium bubbles into the liquid coolant of the fusion reactor and thereby directly removing heat from the liquid coolant.

[0009] A heat pipe is an example of a passive heat transfer device that utilizes a phase transition to transfer heat between two interfaces. Heat pipes rely on two-phase cooling and capillary flow within a closed envelope and function effectively as thermal superconductors. A typical heat pipe consists of a sealed pipe or tube made of a material compatible with the working fluid contained within it. Due to high heat transfer coefficients for boiling and condensation, heat pipes are highly effective heat conductors.

[0010] In the technical field, heat pipes are known as heat transfer devices that utilize phase transitions:

[0011] US2007114008 describes a heat pipe comprising a casing for receiving a working fluid, a capillary wick arranged inside the casing, and a tube arranged inside the casing and in contact with the surface of the capillary wick. A vapor passage is formed inside the casing, a liquid channel is defined by the capillary wick, and the vapor passage is separated from the capillary wick by the tube. The working fluid in the vapor state and the liquid state flow along the vapor passage and the liquid channel in opposite directions from one end of the casing to the opposite end, respectively.

[0012] US2020064078 describes a flow boiling canopy wick that utilizes a perforated distribution layer to separate a liquid stream from a vapor space and membrane evaporation. The wick enables controlled evaporation of the liquid membrane at a point of critical heat flow rate by maintaining a constant supply of liquid to a heated surface.

[0013] Additive manufacturing, sometimes referred to as layered manufacturing due to the nature of the process, involves fabricating parts layer by layer from three-dimensional (3-D) data. Additive manufacturing systems can be used to create geometrically complex three-dimensional (3-D) objects by progressively stacking layers of material. Some additive manufacturing systems utilize inkjet or other similar printing technologies to apply parts of the material fabrication. Consequently, these methods are generally referred to as 3-D printing. Additive manufacturing devices can enable the direct conversion of computer-aided design (CAD) models or other digital representations of objects into physical objects using various different materials. Selective laser melting and selective laser sintering are examples of additive manufacturing technologies used to produce complex metal structures from loose metal powders by employing high-power lasers to selectively melt or sinter pre-placed powder materials. Selective laser technology enables the production of metal structures with high resolution, which is essential for the production of heat pipes.

[0014] In the field of technology, additive manufacturing technologies such as selective laser melting are known to produce technical objects:

[0015] WO2016113255 describes a method for producing 3-D components using selective laser melting, wherein successive layers of powder construction material are solidified by electromagnetic radiation such as a laser or an electron beam.

[0016] WO2022119559 describes an additive manufacturing system comprising an additive manufacturing device for forming a 3-D printed object having regions of different porousness, and a controller for forming the object. The system produces the object by controlling the discharge of a first binder onto the porous region and the non-porous region of the object, and controlling the discharge of a second binder onto the non-porous region of the object.

[0017] In the technology field, 3-D printing of heat transfer devices, such as heat pipes and other thermal management systems, is known:

[0018] US20170235349 describes a thermal management system for an electronic device, such as a microprocessor, produced by 3-D printing. The thermal management device is made of a single continuous component comprising two heat exchangers, wherein the first heat exchanger comprises a vapor chamber, a heat pipe, or a vapor chamber and a heat pipe, and the second heat exchanger comprises a heat sink, and the heat sink comprises fins extending away from the outer surface of the vapor chamber, the heat pipe, or the vapor chamber and the heat pipe.

[0019] CN111660062 describes a high-temperature heat pipe produced using 3-D printing and a method for producing the same. The heat pipe comprises a shell with channels in its inner wall, a silk screen fixed to a porous support, a tail cover, and an alkali metal working medium, wherein the shell with channels and the porous support are formed in situ simultaneously via 3-D printing. The shell and tail cover plates are made of a high-temperature alloy or a niobium alloy, the porous support and the silk screen are made of a molybdenum-based material, and the shell structure and the porous structure are printed synchronously.

[0020] However, to date, none of the conventional technologies have satisfactorily provided a system capable of dissipating the highest possible heat flux, let alone a system capable of providing advanced cooling that enables the long-term operation of high-tech devices such as electronic components, semiconductors, IT hardware, and fusion reactors, by combining both the reliability and efficiency of heat pipes with the versatility of additive manufacturing.

[0021] According to the present invention,

[0022] a. An elongated envelope surrounding an evaporator section at or toward the first end, a condenser section at or toward the second end, and an intermediate adiabatic section between the evaporator section and the condenser section;

[0023] b. At least one first channel providing fluid communication of the working fluid evaporated from the evaporator section to the condenser section;

[0024] c. At least one second channel providing an effective wicking means for transferring condensed working fluid from a condenser section to an evaporator section, wherein the first and second channels communicate with each other in the condenser section and the evaporator section of the first channel;

[0025] d. A heat pipe is provided comprising at least one coolant channel integrated within an envelope and adapted to transfer heat away from one or both of the first and second channels by means of a flowing coolant inside.

[0026] Preferably, the first and second channels do not communicate with each other in the adiabatic section of the first channel, and thus deny any limitation on effects caused by entrainment limits, such as between a counter-flowing evaporated fluid and a condensed working fluid.

[0027] Preferably, a plurality of second channels are provided, and preferably, in this case, the plurality of second channels communicate independently with the evaporator section of the first channel. This separation of the wicked flow avoids stagnation points in the evaporator region and, consequently, increases the boiling limit.

[0028] Also advantageously, the second channel wick means may be provided with a porous structure to increase the capillary limit and / or boiling limit of the system. Typically, the porous structure may be provided in the second channel in its communication area with the first channel in the evaporator section, and the second channel may not have a porous structure along at least a portion of its length including or extending from the evaporator section toward its communication area with the first channel in the condenser section.

[0029] A porous structure may be provided during or as a result of the manufacturing process. Through an additive manufacturing process, such as selective laser melting using fine powder that can be melted locally and selectively, the fine powder may be captured in the second channel. In a specific embodiment of the present invention, the porous structure of the second channel wick means may be created by precision sintering or melting metal build powder particles deposited in at least a portion of the interior of the second channel. Such precision sintered or melted porous structure may transport working fluid from the condenser section to the evaporator section by capillary action.

[0030] Preferably, the average pore size of the porous structure of the second channel wick means may be equal to or smaller than the diameter of the second channel in the condenser section and / or adiabatic section. Preferably, the average pore size of the porous structure of the second channel wick means is smaller than the diameter of the second channel in the evaporator section. In some embodiments, the average pore size of the porous structure of the second channel wick means may be larger in the condenser section than in the evaporator section. Advantageously, by having a smaller average pore size in the evaporator section than in the condenser section, capillary action draws the working fluid into the evaporator section, which prevents the heat pipe from drying out.

[0031] The heat pipes of the present invention can be produced by an additive manufacturing method (also known as 3-D printing), which is an important aspect of the preference to be described below. Essentially, additive manufacturing makes it possible to manufacture somewhat complex internal structures within each heat pipe (and in any array of such heat pipes) relatively easily, thereby enabling the production of structures of an optimized form as described herein.

[0032] One exemplary additive manufacturing technique suitable for the production of heat pipes of the present invention includes selective laser melting.

[0033] The heat pipe may be manufactured from any suitable material, for example, steel, Inconel, Hastelloy, Monel, Haynes, aluminum, copper, nickel, titanium, niobium, tantalum, molybdenum, zirconium, tungsten, or rhenium, or any compatible alloy or any compatible carbide of one or more of the above.

[0034] The working fluid may be selected from any of, for example, water, ammonia, sodium, lithium, helium, hydrogen, neon, nitrogen, oxygen, methane, ethane, propylene, 1,1,1,2-tetrafluoroethane (R134a), Freon compounds, acetone, methanol, toluene, naphthalene, aluminum bromide, mercury, cesium, potassium, process sodium-potassium, or silver. In a preferred embodiment, the working fluid may be selected from water, ammonia, sodium, or lithium.

[0035] In operation, at least one integrated cooling channel accommodates a coolant optionally selected from molten salt, liquid metal, inert gas, or molecular fluid. In some embodiments, the coolant may be the same as the working fluid.

[0036] Heat pipes can be used to provide cooling to flat or curved surfaces by being arranged as an array containing a number of heat pipes.

[0037] In an embodiment where the heated surface is flat, the heat pipes can be arranged substantially perpendicular to the surface.

[0038] In an embodiment where the heated surface is a curved surface, the heat pipes may be arranged substantially radially with respect to the surface.

[0039] In an embodiment where the heated surface is flat, the first channel of the heat pipe may be curved at least in its insulating region to provide optimal heat transfer, and the heat flux is radiated away from the flat surface in both planar and perpendicular directions. In this embodiment, the length of the insulating section of the heat pipe is directly proportional to the width of the heat pipe array.

[0040] Advantageously, when the length of the insulating section of the heat pipe is directly proportional to the width of the heat pipe array, this is directly related to the performance of the heat pipe, enabling the customization and optimization of the array for the application. An additional advantage is that the insulating sections themselves, as they are distributed from one another, provide space within the gaps between them for integrated coolant channels.

[0041] Importantly, the present invention provides a heat pipe array comprising a plurality of aligned heat pipes according to the above description.

[0042] Preferably, in this array, a single envelope surrounds a plurality of first, second, and integrated coolant channels.

[0043] At least one integrated coolant channel can run between adjacent heat pipes included within the heat pipe array.

[0044] Preferably, the envelope includes at least one inlet adapted to supply coolant to a plurality of coolant channels within the envelope, and at least one outlet adapted to recover coolant from the plurality of coolant channels.

[0045] Adjacent evaporator sections may be arranged in a plane so that the array adapts to remove heat from a flat surface, in which case the first channel may be curved at least in its adiabatic region to provide optimal heat transfer, and the heat flux is radiated away from the flat surface in both planar and perpendicular directions.

[0046] Alternatively, adjacent evaporator sections may be arranged in an arched shape to adapt the array to remove heat from a curved surface, in which case the first channel may be substantially straight at least in its adiabatic region.

[0047] The optimal geometry for heat pipes contained within a heat pipe array providing cooling on a flat surface is found to be such that the ratio of the average length of the insulating section of each heat pipe in the array to the collective width of the heat pipe array is as low as possible, as this provides space within the gaps between adjacent heat pipes for coolant channels. Preferably, this ratio is lower than about 1, optionally lower than about 0.9, optionally lower than about 0.8, and optionally lower than about 0.7. In some embodiments, the ratio may be about 0.5 to about 1, for example, about 0.6 to about 0.9 or about 0.6 to about 0.8.

[0048] Advantageously, this geometric structure provides space within the gap between the heat pipes for coolant channels, enabling effective heat removal. For example, by merging two adjacent rows of heat pipes into a single row and simultaneously rotating each second channel by 60°, space can be created between the heat pipes, and coolant channels can be positioned within the space.

[0049] Consequently, in one embodiment, the present invention provides a heat pipe array comprising a plurality of heat pipes, wherein each heat pipe is,

[0050] Integrated cooling channel;

[0051] Separation of liquid flow from vapor flow;

[0052] Separation of individual liquid flows; and

[0053] It additionally includes a free-form porous structure within the evaporator wick,

[0054] The heat pipe array is contained within a single component.

[0055] The inclusion of multiple heat pipes with integrated cooling channels as a single component is advantageous as it enables optimization of the capillary and / or boiling limit. Separation of the liquid flow from the vapor flow in the adiabatic section allows the heat pipe to bypass the accompanying limit. Separation of the liquid flows from each other is advantageous as it avoids stagnation points to delay the boiling limit. The inclusion of a free-form porous structure in the evaporator wick to trap and sinter powder is advantageous as it increases the capillary and / or boiling limit.

[0056] Heat pipes rely on two-phase cooling and capillary flow within a closed envelope, thereby effectively functioning as thermal superconductors. For example, by closely arranging (stacking) heat pipes near surfaces subjected to intense heat flux, such as the inner walls of a nuclear fusion reactor, semiconductor devices, microwave cavities of a gyrotron, trots of a rocket nozzle, leading edges of hypersonic aircraft, or targets / sources of high-energy beams, and by dispersing the heat pipes further away from these surfaces, the heat flux is reduced until it reaches a level where it can be transferred to and removed by conventional single-phase cooling channels, thereby cooling the device.

[0057] The heat pipe array of the present invention provides means for extremely high heat fluxes that are converted into more manageable heat fluxes, thereby enabling the single-phase coolant to absorb all residual heat with the same installation and operation effort as in conventional single-phase cooling systems.

[0058] As is true with respect to the heat pipe itself, it will be apparent that in certain embodiments of the present invention, the heat pipe array can be produced by an additive manufacturing method such as selective laser melting. The complex structure of the array of the present invention having integrated cooling channels is illustrated and described below, and its realization is facilitated particularly by an additive manufacturing method.

[0059] In a specific embodiment of the present invention, each heat pipe in the array comprises an evaporator, an adiabatic section, a condenser, a working fluid, and a coolant, all enclosed within a common envelope.

[0060] In a preferred embodiment, the heat pipe array may include ammonia-aluminum, ammonia-stainless steel, water-titanium, water-copper, water-Inconel, sodium-stainless steel, sodium-Inconel, sodium-molybdenum, sodium-tungsten, lithium-molybdenum, or lithium-tungsten heat pipes. In a most preferred embodiment, the heat pipe array may include lithium-tungsten heat pipes.

[0061] According to a second aspect of the present invention, a method for producing a heat pipe array according to the claim is provided, wherein the heat pipe is produced using additive manufacturing.

[0062] Advantageously, additive manufacturing methods such as selective laser melting or 3-D printing enable an array of complex, optimized heat pipes to be integrated into a single component made of high-performance materials. Additive manufacturing methods produce reliable and more consistent results.

[0063] According to a third aspect of the present invention, a heat pipe array is provided, comprising a plurality of heat pipes, wherein the heat pipes follow an arc and the cooling channels follow a semi-ellipse.

[0064] In a specific embodiment, the heat pipe array comprises a heat pipe further comprising an integrated cooling channel, separation of liquid flow and vapor flow, separation of individual liquid flow, and a free-form porous structure within an evaporator, and the heat pipe array is accommodated within a single component.

[0065] In an additional embodiment of the heat pipe array, the width of the heat pipe is proportional to the length of the insulating section of the heat pipe.

[0066] Advantageously, when the width is proportional to the height (L) of the insulation section, this is directly related to the performance of the heat pipe. Therefore, the invention according to the third aspect of the present invention provides a means to customize the performance of the heat pipe for an application.

[0067] In a specific embodiment, the heat pipe array is oriented downwards.

[0068] Advantageously, it has been found that when the heat pipe array is oriented downward, a higher level of performance can be achieved, and in this orientation, when the heat pipes receive gravity assistance, the heat pipes can exhibit significantly superior performance compared to other conventional cooling technologies.

[0069] According to a third aspect of the present invention, a method of using a heat pipe array to provide cooling to a device is provided.

[0070] In a specific embodiment of the present invention, the device may be a nuclear fusion reactor, an electrical component, a semiconductor, IT hardware, a solid-state laser, a radar transmitter, a 5G / 6G emitter antenna, a supercomputer, a hypersonic aircraft or missile, a gyrotron, a particle accelerator, a power electronic device, or a rocket system. Brief explanation of the drawing

[0071] The present invention will now be described in more detail with reference to the following examples and drawings; FIG. 1 illustrates a single heat pipe (without a surrounding envelope) according to an embodiment of the present invention. FIG. 2 illustrates an array of heat pipes and coolant channels (without an surrounding envelope) according to an embodiment of the present invention. FIG. 3 illustrates a simplified cross-sectional view of an evaporator section of a heat pipe according to an embodiment of the present invention. Specific details for implementing the invention

[0072] A heat pipe is a closed, passive system that relies on a gas-liquid phase transition combined with the capillary pressure of a working fluid, capable of handling very high heat fluxes. Heat pipes function as heat flux converters that transform high heat fluxes from a heated surface into lower heat fluxes over a wider surface area, and cooling channels can efficiently absorb and remove heat from the large surface area.

[0073] Additive manufacturing methods such as selective laser melting and 3-D printing make it possible to produce heat pipe arrays with integrated cooling channels as a single component.

[0074] The section of the heat pipe in contact with the heated surface is called the evaporator section, the section in contact with the cooling channel is called the condenser section, and the section where the heat pipe is distributed between them is called the adiabatic section.

[0075] The performance of heat pipes depends strongly on their geometric structure. Preferably, heat pipes can be positioned perpendicular to the heated surface, enabling the maximum number of heat pipes to be utilized to cool the surface. Furthermore, while cooling channels can be positioned as close as possible to the heated surface for maximum efficiency, the heat pipes must be dispersed as they move away from the heated surface to create space for this. In the case of a curved heated surface, such as a cylinder, straight heat pipes are naturally dispersed; however, in the case of a flat heated surface, the heat pipes themselves need to be curved to be dispersed. This constrains the width of the heat pipe array, but the length can be arbitrarily extended, enabling the heated surface to be effectively cooled in a strip shape.

[0076] The size of the heat pipe can be independent of the size of the cooling system, which allows the heat pipe to be optimized for different purposes.

[0077] In a heat pipe, liquid flow and vapor flow can be separated to bypass the concomitance limit, and their respective channels are called arteries and vapor cores, and both can be optimized independently of each other. The concomitance limit is reached when the vapor velocity in the heat pipe is high enough to shear the liquid from the wick.

[0078] The heat pipe is filled with a working fluid. In the heat pipe, the liquid flow and vapor flow can be separated to bypass the concomitant limit, and their respective channels can be known as the artery and vapor core. Each of these sections can be optimized independently.

[0079] The evaporator is the most critical section of a heat pipe array because it is the first to be affected when drying occurs. For structural integrity, the vapor core can be designed with spherical end caps to withstand the internal pressure of the heat pipe. Evaporation takes place at the interface between the liquid and vapor phases, where the wick is exposed to the vapor core. The wick connects arteries to these pores through a branching network of channels with progressively decreasing diameters from the arteries to the vapor core. The interface between the liquid and vapor phases in the evaporator can contain countless pores to generate or control capillary pressure.

[0080] The incoming heat flux can be conducted by a matrix consisting of a solid wick and a liquid phase before reaching the liquid-vapor interface. If the heat flux is too high, superheating can cause the liquid phase to boil. The boiling limit can be increased by reducing the thermal resistance of the matrix, which can be achieved by minimizing the thickness of the wick and selecting an envelope material and working fluid with high thermal conductivity. When the heat flux reaches the interface, the heat flux is absorbed by the phase transition from liquid to vapor accompanied by the corresponding mass flow from the evaporator to the condenser.

[0081] Heat pipes can be densely packed in a geometric (e.g., hexagonal) arrangement, where a vapor core occupies the center of a regular geometric shape (e.g., a hexagon) and arteries occupy the gaps between them (e.g., corners). In this arrangement, each heat pipe consists of two arteries connected to a single vapor core. The arteries and the vapor core can be separated by a minimum wall thickness limited by the additive manufacturing process. Each heat pipe can occupy an area covered by a single hexagon.

[0082] The insulating section of a curved heated surface can be straight as the heat pipes are naturally distributed by extending directly perpendicularly to the heated surface. However, for a flat heated surface, the geometry can be more complex and may be curved as the pipes extend away from the surface. The heat pipe array can be of any length, but its width (W) may be limited due to the distribution of the heat pipes in the insulating section. The insulating sections of multiple heat pipes in the array are distributed as the distance from the heated surface increases, advantageously providing space for coolant channels to pass between the individual heat pipes contained within the array.

[0083] In some embodiments of the present invention, the width of the heat pipe array may be proportional to the height of the insulating section of the heat pipe, and this is directly related to the performance of the heat pipe.

[0084] For a flat heated surface, a heat pipe array comprising a plurality of heat pipes may include heat pipes following a circular arc and cooling channels following a semi-ellipse. In this embodiment, the heat pipes may follow a circular arc, and the cooling channels follow a semi-ellipse with a constant length-to-width ratio.

[0085] In this embodiment, the first channel of the heat pipe may be curved in at least its insulating region to provide optimal heat transfer, and the heat flux is radiated away from the flat surface in both planar and perpendicular directions. In this embodiment, the length of the insulating section of the heat pipe is directly proportional to the width of the heat pipe array.

[0086] Preferably, the ratio of the length of the insulating section of the heat pipe to the width of the heat pipe array is as low as possible. Most preferably, the ratio of the length of the insulating section of the heat pipe to the width of the heat pipe array may be lower than about 1, optionally lower than about 0.9, optionally lower than about 0.8, and optionally lower than about 0.7.

[0087] In a specific embodiment, the ratio of the length of the insulating section of the heat pipe to the width of the heat pipe array may be about 0.778.

[0088] Each heat pipe can be somewhat flattened at least in its condenser section to maximize heat transfer. In this case, the heat pipes can be arranged axially with respect to the heated surface, so that the flattened sections provide additional space between the flattened sections for the insertion of cooling channels.

[0089] The condenser section begins where the first cooling channel is inserted. The condenser is not as critical as the evaporator section, as the heat pipes continue to spread outward to increase the contact area with the cooling channel as needed. The heat pipes can widen further inward into the condenser section to create the maximum contact area with the cooling channel, resulting in a circular sector pattern. Vapor condenses on the cooled surface, and the wick draws the vapor from the liquid phase and transports it through the branch network to the artery with minimal resistance, from where the vapor is transported to the evaporator section.

[0090] In the condenser section, the heat pipe may not be cylindrical, and the heat pipe may be flattened to increase the surface area for cooling. Two cooled surfaces in contact with the cooling channel may be connected by struts to provide structural integrity.

[0091] To ensure permanent priming of the evaporator wick, the average pore size of the wick means may be equal to or smaller than the artery diameter in the condenser section and / or adiabatic section. The average pore size of the wick means is preferentially smaller than the artery diameter in the evaporator section.

[0092] The heat pipes of a heat pipe array are mainly composed of three materials: the working fluid, the envelope, and the coolant.

[0093] The working fluid determines the critical heat flux of the heat pipe. The working fluid can be operated at any temperature between the triple point and the critical point. However, the vapor pressure near the triple point of the working fluid will be insufficient to transfer a significant heat flux, and the distinction between the liquid and vapor phases disappears near the critical point. The relevant physical properties of the working fluid are a function of temperature and therefore depend on the desired operating temperature. These properties are surface tension, latent heat, viscosity, density, vapor pressure, and thermal conductivity.

[0094] The working fluid may be selected from, for example, helium, hydrogen, neon, nitrogen, oxygen, methane, ethane, propylene, 1,1,1,2-tetrafluoroethane (R134a), Freon compounds, acetone, methanol, toluene, naphthalene, aluminum bromide, mercury, cesium, potassium, process sodium-potassium, or silver. In a preferred embodiment of the present invention, the working fluid may be selected from water, ammonia, sodium, or lithium.

[0095] Liquid metals such as lithium have the highest performance among any heat pipe working fluids. However, only refractory metals such as molybdenum can withstand liquid lithium at an operating temperature of 1300°C, and these are difficult to manufacture and have limited design freedom for optimization.

[0096] The amount of heat flux that can be processed by a heat pipe is limited by capillary and boiling limits. These limits are critical, as exceeding them means the heat pipe will dry out locally and cease functioning. Determining boiling limits theoretically is difficult due to their dependence on micro-surface characteristics unique to the manufacturing process.

[0097] Two design concepts can be implemented to change the critical heat flow rate.

[0098] The first design concept addresses the boiling limit by recognizing that boiling always begins because superheating is highest at the point where the liquid is in contact with the evaporator envelope for the longest time. Therefore, since the superheating of the liquid at this point is removed only through conduction, stagnation points must be avoided. In a specific embodiment of the present invention, the heat pipe may be symmetrical in the evaporator section. In this embodiment, the liquid flows from two arteries toward the plane of symmetry. Since any liquid in this plane will form a stagnation point, the envelope may be extended to the vapor core to separate the liquid flow and avoid the undesirable stagnation point.

[0099] The second design concept addresses the capillary and / or boiling limit by recognizing that the capillary and / or boiling limit is directly related to the average pore size of the evaporator. A finer average pore size implies higher capillary pressure, but there is a minimum channel diameter that can be reliably achieved by additive manufacturing via selective laser melting. Any smaller diameter and powder cannot always be extracted. However, if the powder can be controlled, it can be advantageous because once these trapped powders are sintered together, they form a porous structure with a very fine average pore size that is much smaller than what can be achieved through the determined channels. According to the present invention, a free-form porous structure is introduced into the evaporator wick to trap the powder so that it is subsequently sintered to form a fine porous structure.

[0100] The envelope provides direct thermal contact between the heated surface and the evaporator, and between the condenser and the cooling channel, while preventing the rupture of the heat pipe. The envelope can be made of a material with high thermal conductivity or yield stress. Materials with high yield stress can have thin walls, in which case thermal conductivity is less relevant; conversely, materials with high thermal conductivity may not require high yield stress because they can have thick walls. In addition to these characteristics, the envelope material must also be compatible with the working fluid and the additive manufacturing process.

[0101] In a specific embodiment of the present invention, the envelope may be made of any suitable material, for example, steel, Inconel, Hastelloy, Monel, Hyness, aluminum, copper, nickel, titanium, niobium, tantalum, molybdenum, zirconium, tungsten, or rhenium, or any compatible alloy or any compatible carbide of one or more of the above.

[0102] The optimal envelope material depends on the working fluid used, as some envelope materials are incompatible with one another. Suitable envelope materials for ammonia working fluids are (stainless) steel, aluminum, and nickel. For water working fluids, nickel, copper, Inconel, and titanium are suitable; for sodium working fluids, stainless steel, nickel, Inconel, Hastelloy, or refractory metals are suitable, whereas for lithium working fluids, only refractory metals such as niobium, tantalum, molybdenum, tungsten, and rhenium are suitable.

[0103] In a preferred embodiment, the working fluid-envelope combination may include ammonia-aluminum, ammonia-stainless steel, water-titanium, water-copper, water-Inconel, sodium-stainless steel, sodium-Inconel, sodium-molybdenum, sodium-tungsten, lithium-molybdenum, or lithium-tungsten.

[0104] The coolant flows through cooling channels to absorb heat released by the condenser and transport it away from the heat pipe array. To maintain the heat pipe array at a uniform temperature while avoiding excessive pressure drop, the coolant must have a high specific heat capacity and low viscosity. The coolant also needs to be compatible with the envelope material. In the presence of a magnetic field, magnetic field magnetohydrodynamic drag must also be considered for electrically conductive fluids, such as liquid metals.

[0105] If a heat pipe filled with an electrically conductive working fluid, such as liquid metal, is maintained in the presence of a magnetic field, the liquid phase can be pumped by using the Lorentz force to drive an electric current through the heat pipe. This effect can help the performance of the heat pipe.

[0106] In a specific embodiment of the present invention, the coolant may be the same as the working fluid.

[0107] In a further embodiment of the present invention, the coolant may be selected from molten salt, liquid metal, inert gas, or molecular fluid such as water, glycol, or silicone oil.

[0108] Heat pipes can be used for a series of cooling applications. Semiconductor dies are typically square and smaller than the width of a 3-D printed heat pipe array, which makes them fit very well into rows of semiconductor dies to be cooled, for example, by a combination of ammonia or water. Liquid metal heat pipe arrays can be used in vacuum or low-pressure plasma environments receiving intense beams, such as lasers, electrons, or particle beams. Heat pipe arrays can also be intended for cooling nuclear fission or fusion reactors.

[0109] 3-D printed heat pipe arrays can be fabricated from various material combinations, ranging from molecular liquids to liquid metals, to provide solutions for different temperature range requirements. Advantageously, 3-D printed heat pipe arrays also do not accommodate moving parts, thereby minimizing the risk of sudden failure and providing enhanced reliability.

[0110] Referring to FIG. 1, a single heat pipe (without an enveloping envelope) is illustrated. The evaporator section (101) is connected to the condenser section (102) by an adiabatic section (103). The working fluid evaporates from liquid to gas in the evaporator section (101), and the evaporated working fluid passes through the adiabatic section (103) to the condenser section (102), where the gas is condensed into liquid. The liquid is returned to the evaporator (101) by an artery (104) separated from the other liquid flow.

[0111] Referring to FIG. 2, an array of heat pipes and coolant channels (without an enveloping envelope) for removing heat flux from a flat surface is illustrated. The array consists of a plurality of heat pipes (201). The heat pipes (201) include evaporator sections (203), and the evaporators of the array form a flat surface (204) from which heat flux is removed. The heat pipes (201) additionally include arteries (205) that transport condensed working fluid from the condenser sections to the evaporator sections (203). The arteries (205) are located outside the individual heat pipes (201). The array of heat pipes (201) removes heat flux from the flat surface, and heat is transferred from the condenser sections to the coolant channels (202). The coolant channels (202) are integrated into the heat pipe array to provide optimal heat removal.

[0112] Referring to FIG. 3, a simplified cross-sectional view of the evaporator section of the heat pipe (301) is shown. The evaporator is where evaporation occurs at the interface between the liquid phase and the vapor phase, where the wick (302) is exposed to the vapor core (303). The liquid-vapor interface (304) consists of a number of pores to generate capillary pressure. The wick (302) further comprises a matrix of a free-form porous structure (305). The wick (302) connects the artery (306) to the liquid-vapor interface (304) through a branching network of channels, and the diameter of the channel gradually decreases from the artery (306) to the vapor core (303). The heat flux of the heated surface (307) is conducted to the liquid-vapor interface by the envelope (308), and then by the matrix (305) consisting of the solid wick and the liquid phase. When the heat flux reaches the liquid-vapor interface (304) within the evaporator wick (302), the heat flux is absorbed by the phase change of the working fluid from liquid to vapor, accompanied by a corresponding mass flow from the evaporator wick (302) toward the condenser. The heat pipes (301) are densely packed in a hexagonal arrangement, and the evaporator includes two arteries (306) connected to a single vapor core (303). The arteries (306) and the vapor core (303) are separated, and thus the liquid flow and vapor flow are separated by a thin wall (309). The individual arteries (306) are not joined at the center (310) and are separated by the walls of the matrix.

[0113] yes

[0114] Example 1

[0115] A prototype water-titanium heat pipe was designed with optimal parameters, and several additional prototypes with variations from the theoretical optimal were manufactured and tested for critical heat flow rates.

[0116] Using an experimental design approach, critical heat flux was calculated for multiple variations of arterial and vapor core diameters for a 20 mm wide heat pipe array. Theoretical optimal and suboptimal parameter combinations were identified, and 13 single heat pipes of various dimensions were fabricated. The envelopes were made of titanium, and the working fluid was water. Single heat pipes were selected for the experiment because all heat pipes in the 3-D printed heat pipe array are identical, and therefore a single heat pipe can represent the entire array.

[0117] Thirteen heat pipes were analyzed by CT scanning, which identified that all heat pipes were completely filled with residual powder left from the manufacturing process, with the exception of heat pipes 2 and 6, which were only partially filled with powder from the evaporator. These two heat pipes were selected for further testing.

[0118] The heat pipe was tested using a calorimeter. AlNiCo magnets were attached to the sides of the heat pipe into which the heat flux enters, and the magnets were placed on an induction heater to simulate the heat flux. The heat flux was conducted into the heat pipe, which then dissipates heat along its length.

[0119] A constant flow rate of ethylene glycol, a coolant, was sent along the back of the heat pipe to absorb and remove heat. The coolant was supplied from a temperature-controlled reservoir using an adjustable pump. Pressure was monitored and maintained constant to maintain a constant flow rate. A flow meter was attached to the heat pipe, where the coolant leaves the pipe to return to the reservoir. The flow meter [records] a known amount of heat ( P fm = 6.765 W) was injected into the coolant, and the temperature difference (Δ) between the inlet and outlet of both the heat pipe and the flow meter was T hp wa ΔT fm ) was measured. The following mathematical formula I related to internal energy was used to calculate the temperature difference:

[0120] [Mathematical Formula I]

[0121] E = mcΔT

[0122] The mathematical expression was differentiated with respect to time and rewritten to yield mathematical expression II.

[0123] [Mathematical Formula II]

[0124]

[0125] This is mass flow ( ) and specific heat capacity( c This is possible because both are the same in the heat pipe and flow meter.

[0126] Heat flux ( Q ) is the cross-section occupied by a single heat pipe in a 3D-printed heat pipe array according to mathematical formula III ( A Heat pipe power with ) P hp It was determined by dividing ), and heat loss to the environment was considered:

[0127] [Mathematical Formula III]

[0128]

[0129] In the experiment, the induction heater power is first increased until drying occurs in the heat pipe, which is detected by a rapid rise in the magnet's temperature. Subsequently, both the induction heater and the flow meter are switched on, and the induction heater operates directly below the point where drying occurs. Once a steady state is reached, Δ T hp,on wa Δ T fm,on This is recorded. Then, both the induction heater and the flow meter are turned off, and when a steady state is reached again, Δ T hp,off wa Δ T fm,off was measured.

[0130] Two functional single heat pipes were measured vertically with gravity assisting or hindering the flow, resulting in a total of four measurements. The results of these measurements are summarized in the table below.

[0131] Critical heat flux at 130℃ Heat pipe 2 Heat pipe 6 cross-sectional area 3.2 ㎟ 4.63 ㎟ Gravity Assist 3.9 W / ㎟ 8.9 W / ㎟ Gravity resistance 1.1 W / ㎟ 1.6 W㎟

[0132] Experiments identified that gravity plays a significant role in the performance of heat pipes. Therefore, whenever possible, 3-D printed heat pipe arrays should be oriented downwards for maximum performance. Experiments also identified a significant discrepancy between theoretical and experimental results, attributed to powders affecting the internal flow of the heat pipes. Nevertheless, under gravity resistance conditions, the 3-D printed heat pipe arrays were comparable to other conventional cooling technologies such as direct water and jet collision cooling, and the heat pipe arrays exhibited significantly superior performance when assisted by gravity.

[0133] Further experiments were conducted with copies of heat pipes 2 and 6 from which the powder had been completely removed. These powder-removed heat pipes showed somewhat poorer performance than the original heat pipes 2 and 6, indicating that the presence of some powder in the evaporator wick increases the critical heat flux that can be removed by the heat pipe.

[0134] Example 2

[0135] A 3-D printed lithium-molybdenum heat pipe capable of handling heat flux requirements for high-temperature devices was designed and tested.

[0136] To investigate whether molybdenum could be 3-D printed and sealed without leakage, 13 cylinders with wall thicknesses of 1 to 2 mm were produced with different orientations. The cylinders were vacuum brazed to stainless steel tubes using pure copper. Standard Swagelok compression fittings were attached to these tubes, allowing them to be connected to a helium leak tester.

[0137] The helium leak test is all cylinders 2.5 to 10 -12 It was identified that it is perfectly sealed up to the detector limit of mbarL / s. This corresponds to a maximum hole size of 1 angstrom, which is smaller than the helium atom, the smallest single atom, and demonstrates that 3D-printed molybdenum is suitable as an envelope for liquid lithium in heat pipes.

Claims

Claim 1 A heat pipe comprising: a. an elongated envelope surrounding an evaporator section at or toward a first end, a condenser section at or toward a second end, and an intermediate insulating section between said evaporator section and said condenser section; b. at least one first channel providing fluid communication of a working fluid evaporated from said evaporator section to said condenser section; c. at least one second channel providing effective wicking means for transferring the working fluid condensed from said condenser section to said evaporator section, wherein said first and second channels communicate with each other in said condenser section and said evaporator section of said first channel; d. at least one coolant channel integrated within said envelope and adapted to transfer heat away from one or both of said first and second channels by means of a flowing coolant inside. Claim 2 In claim 1, the heat pipe, wherein the first and second channels do not communicate with each other in the insulating section of the first channel. Claim 3 A heat pipe having a plurality of second channels in paragraph 2. Claim 4 In paragraph 3, the plurality of second channels are heat pipes that communicate independently with the evaporator section of the first channel. Claim 5 In any one of claims 1 to 4, the second channel wick means is provided with a porous structure, a heat pipe. Claim 6 In paragraph 5, the porous structure is provided to the second channel in the communication area with the first channel in the evaporator section, a heat pipe. Claim 7 In claim 6, the second channel is a heat pipe without a porous structure along at least a portion of its length, extending from the evaporator section toward the communication area with the first channel in the condenser section or including the same. Claim 8 A heat pipe according to any one of claims 5 to 7, wherein the average pore size of the porous structure of the second channel wick means may be equal to or smaller than the diameter of the second channel in the condenser section and / or insulation section. Claim 9 A heat pipe according to any one of claims 5 to 8, wherein the average pore size of the porous structure of the second channel wick means is smaller than the diameter of the second channel in the evaporator section. Claim 10 A heat pipe produced by additive manufacturing in any one of claims 1 to 9. Claim 11 In item 10, a heat pipe produced using selective laser melting. Claim 12 A heat pipe according to any one of claims 1 to 11, manufactured from steel, Inconel, Hastelloy, Monel, Hyness, aluminum, copper, nickel, titanium, niobium, tantalum, molybdenum, zirconium, tungsten, or rhenium, or any one or more of the aforementioned compatible alloys or any compatible carbides. Claim 13 A heat pipe according to any one of claims 1 to 12, comprising a working fluid optionally selected from water, ammonia, sodium, lithium, helium, hydrogen, neon, nitrogen, oxygen, methane, ethane, propylene, 1,1,1,2-tetrafluoroethane (R134a), Freon compounds, acetone, methanol, toluene, naphthalene, aluminum bromide, mercury, cesium, potassium, process sodium-potassium, or silver. Claim 14 A heat pipe according to any one of claims 1 to 13, wherein the at least one integrated cooling channel accommodates a coolant optionally selected from molten salt, liquid metal, inert gas, or molecular fluid. Claim 15 A heat pipe according to any one of claims 1 to 14, wherein the ratio of the length of the insulating section of the heat pipe to the width of the heat pipe is about 0.5 to about 1, optionally about 0.6 to about 0.9, and optionally about 0.7 to about 0.

8. Claim 16 A heat pipe array comprising a plurality of aligned heat pipes according to any one of claims 1 to 15. Claim 17 In paragraph 16, a heat pipe array in which a single envelope surrounds a plurality of first, second, and integrated coolant channels. Claim 18 In claim 17, the heat pipe array comprises an envelope having at least one inlet adapted to supply coolant to a plurality of coolant channels within the envelope, and at least one outlet adapted to recover coolant from the plurality of coolant channels. Claim 19 A heat pipe array according to any one of claims 16 to 18, wherein at least one integrated coolant channel extends between adjacent first and / or second channels. Claim 20 A heat pipe array according to any one of claims 16 through 19, wherein adjacent evaporator sections are arranged in a plane such that the array is adapted to remove heat from a flat surface. Claim 21 In paragraph 20, the heat pipe array, wherein the first channel is curved in at least its insulating region. Claim 22 A heat pipe array according to any one of claims 16 through 19, wherein adjacent evaporator sections are arranged in an arched shape so as to adapt the array to remove heat from a curved surface. Claim 23 In paragraph 22, the heat pipe array, wherein the first channel is substantially straight in at least its insulating region. Claim 24 A method of using a heat pipe array according to any one of claims 16 to 23 for providing cooling for a device, wherein the device is optionally a nuclear fusion reactor or an electronic device.

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