Patent Application
20240255229
This disclosure relates generally to the field of thermal management.
A cooling apparatus is an important component in modern engineering systems, such as electronic systems. Every electronic system ingests primary energy (e.g., either direct current or alternating current electricity) and converts this energy into some functional utility (e.g., communication, imaging, audio, computation, storage, control, navigation, etc.). However, due to fundamental thermodynamic constraints, not all of the primary energy may be successfully converted into useful form. That is, some of the primary energy is converted into thermal or heat energy (i.e., disordered energy) which raises the ambient temperature surrounding the electronic system. Since proper operation of any electronic system requires thermal management of the ambient temperature, a cooling apparatus is required to transport heat away from the electronic system to an external environment. Improvements in cooling apparatus design are strongly desired for efficient heat transfer in devices.
The following presents a simplified summary of one or more aspects of the present disclosure, in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated features of the disclosure, and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in a simplified form as a prelude to the more detailed description that is presented later.
In one aspect, the disclosure provides thermal management. Accordingly, an apparatus including a metal mesh layer; a porous metal powder layer coupled to the metal mesh layer; and a metal substrate coupled to the porous metal powder layer. In one example, the apparatus further includes a working fluid surrounding the metal mesh layer, the porous metal powder layer and the metal substrate.
In one example, heat flows through the metal substrate, the porous metal powder layer and the metal mesh layer to the working fluid. In one example, the metal mesh layer is a copper mesh layer, an aluminum mesh layer, a silver mesh layer or a metal alloy layer. In one example, the porous metal powder layer is a porous copper powder layer, a porous aluminum powder layer, a porous silver powder layer or a porous metal alloy powder layer. In one example, the porous metal powder layer is a porous copper powder layer, a porous aluminum powder layer, a porous silver powder layer or a porous metal alloy powder layer.
In one example, the metal substrate is a copper substrate, an aluminum substrate a silver substrate or a metal alloy substrate. In one example, the apparatus further includes a heat source coupled to the metal substrate, wherein heat generated from the heat source flows to the working fluid. In one example, the heat flows through one or more of the following: metal substrate, porous metal powder layer and metal mesh layer.
In one example, the apparatus further includes a first boiler structure; a condenser structure coupled to the first boiler structure; and one or more interconnect tubes linking the first boiler structure with the condenser structure. In one example, the condenser structure includes one or more metal foam condenser components.
In one example, the apparatus further includes a second boiler structure; and one or more boiler tubes linking the second boiler structure to the first boiler structure. In one example, the condenser structure includes one or more metal foam condenser components. In one example, one or more of the metal mesh layer, the porous metal powder layer or the metal substrate includes a plurality of micro cavities. In one example, the metal substrate includes a plurality of fins.
These and other aspects of the present disclosure will become more fully understood upon a review of the detailed description, which follows. Other aspects, features, and implementations of the present disclosure will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary implementations of the present invention in conjunction with the accompanying figures. While features of the present invention may be discussed relative to certain implementations and figures below, all implementations of the present invention can include one or more of the advantageous features discussed herein. In other words, while one or more implementations may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various implementations of the invention discussed herein. In similar fashion, while exemplary implementations may be discussed below as device, system, or method implementations it should be understood that such exemplary implementations can be implemented in various devices, systems, and methods.
The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.
While for purposes of simplicity of explanation, the methodologies are shown and described as a series of acts, it is to be understood and appreciated that the methodologies are not limited by the order of acts, as some acts may, in accordance with one or more aspects, occur in different orders and/or concurrently with other acts from that shown and described herein. For example, those skilled in the art will understand and appreciate that a methodology could alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all illustrated acts may be required to implement a methodology in accordance with one or more aspects.
Cooling of electronic systems has always been an important task in modern engineering systems. For example, transport of waste heat generated by integrated circuits is required for proper operation of the integrated circuits. For example, if the ambient temperature surrounding the integrated circuits is too high, adverse performance effects or device failure may occur.
In one example, several thermal management systems, such as heat pipes, immersion cooling, forced water cooling, etc., may be employed but may incur design challenges with high temperatures and concentrated heat in a small area (i.e., high heat flux density). For example, microprocessors have an increasingly greater circuit density (i.e., transistors per area) to provide improved computational power and processing speed. However, this increased circuit density results in increasingly smaller device sizes with higher heat flux density. That is, continual product development may result in increased primary energy consumption and increased thermal energy generation in integrated circuits such as a central processing unit (CPU) and a graphic processing unit (GPU).
In one example, cooling systems, such as heat pipes and forced water cooling, may have limitations in handling increased heat flux density. For example, a heat pipe is a passive heat transfer apparatus which contains a working fluid, such as a liquid, as a heat carrier and a porous metal powder layer (e.g., a copper powder layer) sintered uniformly around an inner wall to provide a capillary force (e.g., a narrow fluid flow). Ideally, the heat pipe removes heat from a heat input area by vaporizing the liquid in an evaporation or boiling area, then the vapor travels along the pipe, releases its latent heat, becomes liquid again in a condensation area and returns to the heat input area for another circulation sequence by capillary force. The condensed working fluid returns to the evaporation area for proper operation. The working fluid relies solely on the capillary force to return the working fluid to the evaporation area, but the liquid supply may not be efficient at high demand due to limited copper powder thickness and restricted direction. The idealized heat cycle may be maintainable at low heat input, but may be difficult with high heat input and rapid liquid loss. An insufficient liquid flow may cause a dry-out in the evaporation area which may cause an undesired sudden performance degradation.
For example, as an alternative thermal management system, a forced water cooling system uses a circulating working fluid inside a closed loop with a pump. The water cooling system includes a heat exchange interface which has contact with a heat input where the heat from the processing unit may be dispensed. The heat exchange interface may have fins or pins forming a network of channels along the inner surface to increase contact area and duration between the working fluid and the heated area. When the heated liquid is cooled down, the system is capable of dispensing heat from a thermal source. In one example, fins or pins may be used to optimize the liquid contact with the heated area to allow greater heat flux. In practice, the fins or pins may have a linear dimension of about less than 0.1 mm. In one example, smaller dimensions may incur undesired additional cost and design complexity. For example, the speed of the pump is crucial for system performance, and with aging, the pump may require frequent maintenance over its life cycle. For example, due to the flow direction, the outlet portion of the forced water cooling system may be hotter than the inlet portion which may affect performance.
In one example, a thermosyphon is another cooling system or thermal management system. For example, a thermosyphon may be compact, require low maintenance and have high heat transport efficiency. For example, the thermosyphon may outperform other thermal management systems with lower cost.
For example, boiling is the predominant heat transfer process in a thermosyphon. The heat transfer may transport thermal energy from a thermal source to a condenser structure using a phase change of a working fluid. In one example, a boiling method for the working fluid is a key thermal management issue. For example, increasing a nucleate site density in the active heat transfer area is an effective means of increasing heat transfer efficiency. In one example, nucleate site density is a measure of number of nucleate sites per surface area. For example, sintering (e.g., heating without melting) metal (e.g., copper) powder onto a substrate may be useful in increasing nucleate site density. However, in one example, when transferring heat from high heat flux resources, the required thickness for such a porous metal powder layer may increase accordingly to avoid dry-out to sustain a virtuous cycle of effective nucleate boiling. Although increasing porous layer thickness helps prevent dry-out, it may lead to two issues: increased thermal resistance of the porous layer and increased flow resistance for formed bubbles to escape the porous layer. In one example, these two issues may have impacts on thermal transfer efficiency and may result in decreased system performance.
In one example, a hybrid wick structure 105 is introduced into the thermosyphon to increase thermal transfer efficiency and/or increase system performance.
In one example, the metal mesh layer 410 may serve as an assisting structure for working fluid 470 to flow back to the nucleate boiling porous region effectively. For example, usage of the hybrid wick structure may solve several issues simultaneously. For example, high thermal resistance may be solved since with a hybrid wick structure, even a thin boiling layer may sustain a high heat flux without drying out. In one example, high thermal resistance may be solved since the metal mesh layer 410 may be made of metal wires with high porosity. In one example, porosity is measured as a fraction of the volume of voids divided by the total volume. In one example, high porosity is greater than 20%.
In one example, the hybrid wick structure 105 may be further improved by chemical and plasma etching to increase surface roughness. In one example, increased surface roughness may result in overall capillary pressure increase in the hybrid wick structure 105 which makes working fluid 470 reflow more effective. In one example, improved replenishing mechanisms of the working fluid 470 may increase heat transfer coefficient and critical heat flux.
As illustrated in
As illustrated in
In one example, the relatively high overall thickness of the hybrid wick structure 105 provides low flow resistance for the working fluid to replenish the heated regions. The metal mesh layer provides high permeability for working fluid to reflow efficiently, thus a higher critical heat flux may be reached. In one example, the porous metal powder layer may serve two main purposes: 1) it provides a high capillary pressure and 2) it provides nucleation sites. For example, some methods avoid using small radius metal powder because of the restriction of nucleation site density, capillary pressure and/or permeability. Although smaller porous metal powder layers may provide desirable higher nucleation sites density and capillary pressure, the permeability becomes much lower such that critical heat flux reduces substantially. For example, in a design, a metal powder of larger radius (e.g., >100 μm) may be used in a porous structure to avoid early dry-out even if heat transfer efficiency is sacrificed.
In one example, the hybrid wick structure 105 allows smaller radius metal powder to be used without sacrificing the critical heat flux. The high capillary pressure provided by the porous metal powder layer and the high permeability provided by the metal mesh layer work together to achieve a very high overall replenishment rate of the working fluid. Due to the high permeability of the hybrid wick structure 105, metal powder with very low radius (e.g., 1 μm to 10 μm) may provide an extremely large number of nucleate sites in the given working volume. For example, if the radius of metal powder used is lowered by half, the number of metal powder in the same volume is 8 times higher compared to the original configuration. That is, in one example, nucleation site density is inversely proportional to radius cubed. The hybrid wick structure 105 may utilize metal mesh layers to assist in delivery of the working fluid. Thus, a lower radius metal powder may be used in porous metal powder layers to achieve higher heat transfer efficiency and critical heat flux through the extremely high nucleation sites density and replenishment rate of working fluid provided by the hybrid wick structure 105.
In one example, vertical grid units formed within the metal mesh layer may facilitate transport of bubbles out of the porous metal powder boiling layer. In one example, in a porous metal powder boiling layer, after bubbles are formed within the porous metal powder boiling layer, the bubbles may escape to the working fluid and gather to form a bubble that may be larger at a contact surface between a working fluid and a porous metal powder boiling layer. For example, the formed bubble is undesired since a partial dry-out region is formed under the formed bubble and the formed bubble itself interferes with working fluid reflow The formed bubble lowers both heat transfer efficiency and critical heat flux.
In one example, however, using metal mesh layers which facilitate working fluid reflow may improve the regional dry-out problem because of the high permeability provided. The vertical grid units formed within the metal mesh layer separate a vapor flow direction and a working fluid reflow direction. When small bubbles form within the porous metal powder layer, the vertical grid units not only prevent the formation of a large bubble, but also provide a vapor channel for venting the vapors. As the formation of a large bubble only occurs on top of the metal mesh layers, the metal mesh layers 400 also provide good channels for working fluid to be delivered to a boiling region more efficiently.
Although in some examples, the metal mesh layer is a copper mesh layer, one skilled in the art would understand that other types of metals may be used within the scope and spirit of the present disclosure. Although in some examples, the porous metal powder layer is a copper powder layer, one skilled in the art would understand that other types of metals may be used within the scope and spirit of the present disclosure.
Moreover, in one example, multiple steps of chemical etching may be used to raise the efficiency higher. After the main step of chemical etching, a secondary plasma etching may be applied to the hybrid wick structure to create nanoscale structures on the previously formed microscale structures. Heavy particles such as argon may be used to bombard microscale structures to create surface roughness of much higher precision. In one example, one or more etching processes (e.g., chemical etching, plasma etching, etc.) may create micro cavities in the hybrid wick structure, for example, in one or more of the metal mesh layer, metal powder layer and/or metal substrate.
In one example, modified macroscopic surface geometry, other than flat surfaces, to increase active surface area for boiling heat transfer is effective to increase heat transfer efficiency and postpone dry-out heat flux simultaneously. For example, macroscopic surfaces with fins 108 (shown in
In one example, a hybrid wick structure with fins may have at least two advantages. A first advantage is a lowered temperature gradient required to accomplish phase change heat transfer due to lowered heat flux on macroscopic wick structure. A second advantage is an increased input heat flux to trigger dry-out phenomenon.
In one example, the hybrid wick structure with fins may be fabricated by machining. In one example, the machining may be governed by graphic molding to generate macroscopic fins. In one example, the hybrid wick structure with fins may be fabricated by sintering a porous metal powder layer with desired thickness and then sintering a desired number of metal mesh layers onto a porous structure. In one example, etching methods (such as, but not limited to those described herein) may also be used to increase overall heat transfer efficiency.
In one example, a fin attached to a condenser structure may improve heat transfer to the surrounding environment by forced convection with air. For example, generation of turbulent air flow may enhance forced convection heat transfer efficiency. Increased fin surface roughness may initiate chaotic changes in pressure and flow velocity of air blown through fans attached to the condenser structure. Thus, air flow with higher turbulence may be generated. For example, methods such as sand blasting, etching and sintering metal powder may be effective ways to increase surface roughness. On the other hand, increasing fin surface roughness through methods described herein may also increase effective heat exchange surface area of forced convection with air. In one example, the fin surface roughness may be at least 100 μm root mean square (rms) deviation from a reference surface (e.g., a flat surface). Although the present disclosure may state a single fin, a plural quantity of fins or one or more fins, one skilled in the art would understand that in any of the exampled disclosure, any quantity of fins (i.e., one or more) is within the scope and spirit of the present disclosure.
In one example, a metal foam condenser component may be composed of condenser tubes and attached metal foam. For example, porous structures with metal foam may be excellent turbulent flow generators. For example, a high specific surface area of metal foam may also enhance thermal energy transfer efficiency by reducing heat flux on the active surface area where forced convection heat exchange occurs. However, obtaining good contact between condenser tubes and metal foam may be challenging. Certain methods such as stacking fins to condenser tubes may result in insufficient contact between metal foam and condenser tubes due to virtual contract points formed by irregular branches inside metal foam. An effective way to overcome this problem is pasting relatively thick solder material to fill voids or small gaps among irregular metal foam branches and condenser tubes. After melting, the solder material may make solid connections with improved thermal conductivity. In one example, a condenser structure may include one or more metal foam condenser components.
In one example, a hybrid wick structure 905 is coupled directly to the boiler structure 910 where the heat is received. As illustrated in
In one example, the boiler structure 910 includes an upper portion and a lower portion. For example, a heat receiving portion may be at the center of the lower portion. Since the lower portion has a direct contact to the thermal source, it may be preferably made of high thermal conductive materials, such as copper, aluminum, silver, etc. One skilled in the art would understand that the example high thermal conductive materials mentioned herein are not exclusive and that other conductive materials may be used within the scope and spirit of the present disclosure.
In one example, one or more fins are part of the metal substrate (e.g., 430, 530, 630, 730) to enlarge the heat exchanging area. Fins may be formed with a triangular cross-sectional shape or trapezoid cross-sectional shape (see
In one example, the hybrid wick structure 905 may be sintered upon the surface of the fins to become part of the boiler structure 910. Although the thickness of the porous metal powder layer may be less than 1 mm, multiple metal mesh layers may be used. In one example, a copper powder layer with a thickness less than 50 μm may be used to form the porous metal powder layer with an overall thickness ranging between 100 μm and 500 μm. For example, after the fins and the hybrid wick structure are coupled together, the metal substrate may be etched to improve the boiling efficiency further.
In one example, the upper portion of the boiler structure 910 may include a plurality of ports that connect either directly or via the interconnect tube 914 to the condenser structure 920 and other boiler structures. The upper portion may be constructed using materials such as stainless steel, titanium, copper, aluminum, etc. In one example, if the upper portion is not to serve as a heat exchanger, its thermal conductivity property would not be significant. However, in the example where the upper portion is to aid in serving as a heat exchanger, its thermal conductivity property would be significant and should be accounted for in the material used on the upper portion. In one example, the upper portion may be bound to the lower portion after the hybrid wick structure 905 is installed.
In one example, the working fluid 970 for the thermosyphon 900 may be water, refrigerant or dielectric fluids. Although some examples of the working fluid 970 are disclosed herein, one skilled in the art would understand that these examples are not exclusive and that other example fluids may be used within the scope and spirit of the present disclosure. In one example, the working fluid 970 submerges boiling regions. An evacuation port for the working fluid may be sealed subsequent to liquid charging and deaeration. The evacuation port may be provided in the form of a tube and may be located in the body of the condenser structure 920.
In one example, the condenser structure 920 may include a plurality of channels which may be interconnected. At external surfaces of the condenser structure 920, there may be fins spreading heat from tubes of the condenser structure 920 where water vapor condenses into liquid water. For example, when water vapor condenses, the condensed water may flow back to the boiler structure 910 by gravity.
In one example, an electronic system generates heat during its operation. In one example, the electronic system is coupled to a metal substrate (e.g., 430, 530, 630, 730). For example, the heat may be transferred by the metal substrate and spread to a hybrid wick structure (e.g., 100) when nucleate boiling occurs. For example, the working fluid 970 may vaporize, refill and repel formed bubbles (e.g., bubble 450, 550). For example, the high pressure vapor of the working fluid 970 may condense at the colder and lower pressure side in the condenser structure 920.
Within the present disclosure, the word “exemplary” is used to mean “serving as an example, instance, or illustration.” Any implementation or aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term “aspects” does not require that all aspects of the disclosure include the discussed feature, advantage or mode of operation. The term “coupled” is used herein to refer to the direct or indirect coupling between two objects. For example, if object A physically touches object B, and object B touches object C, then objects A and C may still be considered coupled to one another-even if they do not directly physically touch each other. The terms “circuit” and “circuitry” are used broadly, and intended to include both hardware implementations of electrical devices and conductors that, when connected and configured, enable the performance of the functions described in the present disclosure, without limitation as to the type of electronic circuits, as well as software implementations of information and instructions that, when executed by a processor, enable the performance of the functions described in the present disclosure.
One or more of the components, steps, features and/or functions illustrated in the figures may be rearranged and/or combined into a single component, step, feature or function or embodied in several components, steps, or functions. Additional elements, components, steps, and/or functions may also be added without departing from novel features disclosed herein. The apparatus, devices, and/or components illustrated in the figures may be configured to perform one or more of the methods, features, or steps described herein. The novel algorithms described herein may also be efficiently implemented in software and/or embedded in hardware.
The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a; b; c; a and b; a and c; b and c; and a, b and c. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”
One skilled in the art would understand that various features of different embodiments may be combined or modified and still be within the spirit and scope of the present disclosure.
