Microchannel pulsating heat pipe

Abstract

A microchannel pulsating heat pipe, preferably a closed loop, comprises a plate with microchannels having obstructions along the inner walls to increase surface area, increase nucleation sites for vaporization of the working fluid, and otherwise enhance fluid movement and heat transfer. Various shapes of obstructions are contemplated on one or more of the bottom, side, and top walls of the channels. A coating may be assembled on or around the plate to enhance strength and heat transfer. Ribs of thermally conductive material may be provided on the outer surfaces of the plate and / or coating to increase surface area and thereby promote heat transfer, and arranged to facilitate air movement across the outer surfaces.

Description

[0001] Priority claim

[0002] This application includes subject matter disclosed in and claims priority to U.S. Provisional Patent Application No. 62 / 953,435, filed by the present inventors on December 24, 2019, entitled “Pulsating HeatPipe,” which is hereby incorporated by reference. Background of the Invention 1. Technical Field

[0004] The present invention relates to heat removal and thermal management, and more particularly to passive microchannel pulsating heat pipe devices and related methods.

[0005] 2. Description of related prior art

[0006] Heat removal has become essential for the proper performance of high-density microelectronics, optical devices, instrumentation, and other electrical / electronic devices. Thermal control systems allow instruments, communications systems, power systems, and other electronic devices to operate within a specified temperature range. Simply put, cooling is achieved by conducting thermal energy from a heat source to a heat sink or heat exchanger, where it is then dissipated. This is particularly true in the field of portable electronics due to the small and lightweight nature of these devices.

[0007] Heat is dissipated using a heat sink and thermal diffusion shield formed from one or more of the following: a high thermal conductivity metal such as aluminum, copper, beryllium oxide, or a combination thereof; annealed pyrolytic graphite (APG) embedded in a metal; a capillary action heat pipe embedded in a metal; or a heat pipe in a metal. Metals with thermal conductivity greater than aluminum typically cause weight, cost, and / or manufacturing issues. Capillary action heat pipes typically require a minimum diameter that, even when flattened, can exceed the maximum required plate thickness. Many types of materials can be diffusion bonded, including: copper, Inconel, stainless steel, titanium, nickel, silver, and the like. In adapting PHP to electronic devices, US20180299206 suggests using a lightweight polymer-based PHP with high flexibility that produces heat transfer properties exceeding those of solid copper.

[0008] As is known in the art, a pulsating heat pipe (PHP) may comprise a microchannel embedded pulsating heat pipe incorporated into a substrate. When in a planar shape, the substrate takes the form of a plate. The use of embedded microchannels allows the thermal conductivity of conventional materials (such as aluminum and copper) to be increased by an order of magnitude or more via integral embedded heat pipes. PHP utilizes phase change and fluid motion to enhance heat transfer. A certain volume of working fluid, preferably in a vacuum, is introduced into the microchannel, which diffuses into liquid slugs separated by vapor wrap. Heating the contents of the microchannel in the evaporator region (heat source) will cause further vaporization in the microchannel, while cooling at the radiator will cause further condensation in the microchannel. Both heating and cooling serve to drive fluid flow or cause pulsation in the microchannel and effectively transfer heat.

[0009] A pulsating heat pipe is a passive heat control device that uses a heat source evaporating portion and a heat absorbing condensing portion of the pipe to effect a two-phase heat pipe. A pulsating heat pipe comprises one or more capillary-sized tubes bent into a curved structure to form a parallel or interwoven structure. Heat is applied to the evaporator region / zone of the tube, causing the vapor pressure to increase and disrupting the equilibrium of the system. As the vapor pressure increases, larger vapor bubbles are generated and pulsate from this high-pressure area. At the other end of the assembly is a condenser zone with a condenser. In the condenser zone, heat is removed through an external radiator or other means, and in doing so, the vapor decreases, thereby shrinking the bubbles and reducing the pressure.

[0010] Closed loop pulsating heat pipes (CLPHPs) can be constructed as serpentine channels (CLPHPs are designed to work without capillary wicks). The fluid in the CLPHP generates a highly unstable two-phase flow within the serpentine structure, moving back and forth or oscillating in one direction between the evaporator and condenser regions. PHPs can operate in many orientations (including vertical, inclined, horizontal, and inverted orientations), allowing innovative geometric layouts. Since the oscillatory motion does not depend (or depends very little) on gravity, PHPs also work in a vacuum. The pulsating fluid flow motion of elongated bubbles and liquid slugs within the serpentine structure is due to complex two-phase flow instabilities caused by the nucleation and growth of vapor bubbles in the evaporator region and their condensation and collapse in the condenser region. A well-designed pulsating heat pipe produces a higher "time-averaged" flow rate than conventional heat pipes or vapor chambers ("multi-finger" flat tube heat pipes) and transfers more latent heat from the evaporator to the condenser, while the back-and-forth flow suppresses the onset of dry-out.

[0011] A microchannel embedded pulsating heat pipe (ME-PHP) consists simply of a microchannel in a serpentine configuration placed in the middle of a plate. The phase change from liquid to vapor and back, combined with the pulsation of vapor bubbles / liquid slugs through the wickless flow channel between the condenser and evaporator, facilitates heat transfer and cooling. The flow channel diameter is smaller than the plate diameter (or cross-sectional area), and the central path of the flow channel lies essentially within a two-dimensional planar region. CLPHP is one possible ME-PHP concept.

[0012] The pulsating heat pipe has different regions, including the evaporator region, the condenser region, and possibly an adiabatic region. When the pulsating heat pipe is stationary, with no heat introduced and no heat removed, the system is in equilibrium. When heat is applied to the evaporator, the system becomes unbalanced. The heat then converts more of the working fluid into vapor, and the vapor bubbles become larger within that portion of the pulsating heat pipe. Similarly, at the condenser, heat is removed from the PHP, and the bubble size decreases. The volume expansion due to vaporization and the contraction due to condensation cause oscillatory motion within the channel. The net effect of the temperature gradient between the evaporator and condenser and the disturbances introduced from the serpentine pattern of the microchannels is to create non-equilibrium pressure conditions. Combining this with the vapor / liquid filling distributed throughout the PHP, a self-sustaining oscillatory driving force is obtained to provide thermal fluid transfer. Since these pressure pulsations are completely thermally driven and due to the solid-state structure of the PHP, no external power or energy is required to operate the PHP, other than heat input from a heat source.

[0013] The concept of pulsating heat pipes is well known in the art. For example, US 6,672,373 describes improvements in the geometry of the tube to improve heat transfer in pulsating heat pipes. For example, changing the diameter of the tube is considered to be a method of providing a hydrothermal difference in the heat / mass transfer coefficient to promote heat transfer. US 8,919,426 considers the concept of a fine channel PHP that can be combined with a bearing cross-section having different diameters, such as a circle and / or a rectangle, to promote annular flow in a wider portion along the side wall, thereby allowing heat transfer via vaporization. CN102691999B also envisions a triangular cross-section. CN104792200A adds a lyophilic coating to the inner wall of the PHP to enhance heat exchange into the PHP channel wall.

[0014] PHP has also been considered for larger scale implementations, such as in air conditioning units, as shown in CN 102944052. Inadequate heat transfer power of PHP when adapted for handheld electronic devices led to US 9,750,160 describing multiple stages of oscillating heat pipes in and around electronic modules.

[0015] Thermal dissipation is a limiting factor for high-end chips powering mobile devices. Overheating of various processor / modem chips and packages leads to performance degradation or even failure of these devices. Next-generation high-power density electronics and communications technologies (5G and beyond) require superior cooling solutions compared to today's existing solutions (Al / Cu heat sinks and heat spreaders, wick-driven heat pipes, and vapor chambers).

[0016] A new two-phase closed-loop pulsating heat pipe (CLPHP) technology and geometry was developed / optimized / built to enhance cooling of high-density electronics and reduce the energy dissipated by microprocessors.

[0017] At this time, passive PHPs are not widely used for thermal management of electronic devices using heat sinks or heat transfer mechanisms, nor are they highly used to maintain temperature gradients in electronic products. Improvements in the design and functionality of PHPs can promote growth in their adoption and applications.

[0018] It is therefore an object of the present invention to improve the heat transfer capabilities of a pulsating heat pipe.

[0019] Another object of the present invention is to provide a portable heat pipe that is lightweight.

[0020] Another object of the present invention is to provide a pulsating heat pipe system that can be used in electronic devices and electronic equipment. Summary of the Invention

[0021] The heat transfer coefficient of PHP can be improved by promoting the flow of fluid slugs, vapor parcels, and further promoting the vaporization of the working fluid within the pipe. To overcome the disadvantage of PHP's slugs being inactive except along the edges, additional nucleation sites can be used to increase the potential for vaporization and decomposition of the slugs. Tubes of various geometries can be used, and the geometry of the tubes can be improved by including regular or random obstructions within the tubes to promote nucleation. By controlling vapor pressure and surface tension, nucleation can occur at sharp boundaries. By stretching the slug containing the working fluid in liquid form, the thin liquid layer is subjected to greater vapor pressure, increased surface area, and is more likely to vaporize. Nucleation sites can be achieved by adding structures that act as obstacles within the channel. Obstacles can be regularly arranged on one or more sides and have various shapes. With these microchannel sizes, obstacles can also be introduced without changing the shape of the channel exterior.

[0022] Various obstacle geometries and arrangements are included, such as the use of hemispherical attachments to the side walls and / or top and bottom walls, semi-cylindrical attachments, rising cylindrical or rectangular posts through the entire channel (preferably through the center), semi-cylindrical attachments through the channel, or semi-cylindrical posts on each wall and top / bottom, etc.

[0023] Additionally, PHP boards can incorporate external structures or coatings. For example, a thin copper film or coating can be applied to part or all of the board. Coatings can be provided on the evaporator and / or condenser regions. Similarly, ribs can be incorporated into the coating to provide additional surface area. Ribs can be placed along longitudinal channels, diagonally, or transversely. The rib width can correspond to the channel width or the spacing between channels. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be described more particularly and clearly with reference to the following drawings, in which:

[0025] Figure 1 A side cross-sectional view of a conventional standard portable electronic device is shown.

[0026] Figure 2 A top cross-sectional plan view of a conventional PHP is shown.

[0027] Figure 3 A top cross-sectional plan view of a PHP is shown, in accordance with an embodiment of the present invention.

[0028] Figure 4 A top cross-sectional view of a PHP is shown, in accordance with an embodiment of the present invention.

[0029] Figure 5 Four cross-sectional views of four existing heat pipe types are shown.

[0030] Figure 5 A and Figure 5 B shows Figure 5 Enlarged views of Section A and Section B.

[0031] Figure 6 A plan view of a serpentine passageway is shown in accordance with an embodiment of the present invention.

[0032] Figure 7 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0033] Figure 8 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0034] Figure 9 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0035] Figure 10 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0036] Figure 11 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0037] Figure 12A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0038] Figure 13 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0039] Figure 14 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0040] Figure 15 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0041] Figure 16 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0042] Figure 17 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0043] Figure 18 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0044] Figure 19 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0045] Figure 20 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0046] Figure 21 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0047] Figure 22 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0048] Figure 23 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0049] Figure 24 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0050] Figure 25 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0051] Figure 26 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0052] Figure 27 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0053] Figure 28A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0054] Figure 29 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0055] Figure 30 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0056] Figure 31 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0057] Figure 32 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0058] Figure 33 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0059] Figure 34 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0060] Figure 35 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0061] Figure 36 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0062] Figure 37 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0063] Figure 38 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0064] Figure 39 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0065] Figure 40 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0066] Figure 41 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0067] Figure 42 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0068] Figure 43 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0069] Figure 44A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0070] Figure 45 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0071] Figure 46 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0072] Figure 47 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0073] Figure 48 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0074] Figure 49 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0075] Figure 50 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0076] Figure 51 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0077] Figure 52 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0078] Figure 53 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0079] Figure 54 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0080] Figure 55 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0081] Figure 56 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0082] Figure 57 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0083] Figure 58 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0084] Figure 59 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0085] Figure 60A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0086] Figure 61 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0087] Figure 62 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0088] Figure 63 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0089] Figure 64 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0090] Figure 65 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0091] Figure 66 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0092] Figure 67 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0093] Figure 68 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0094] Figure 69 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0095] Figure 70 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0096] Figure 71 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0097] Figure 72 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0098] Figure 73 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0099] Figure 74 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0100] Figure 75 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0101] Figure 76A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0102] Figure 77 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0103] Figure 78 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0104] Figure 79 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0105] Figure 80 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0106] Figure 81 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0107] Figure 82 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0108] Figure 83 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0109] Figure 84 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0110] Figure 85 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0111] Figure 86 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0112] Figure 87 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0113] Figure 88 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0114] Figure 89 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0115] Figure 90 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0116] Figure 91 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0117] Figure 92A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0118] Figure 93 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0119] Figure 94 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0120] Figure 95 A top cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0121] Figure 96 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0122] Figure 97 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0123] Figure 98 A side cross-sectional view of a PHP channel is shown according to an embodiment of the present invention.

[0124] Figure 99 A cross-sectional view of a PHP channel according to an embodiment of the present invention is shown.

[0125] Figure 100 Shown is a perspective cross-sectional view of a PHP channel in a plate according to an embodiment of the present invention.

[0126] Figure 101 A top perspective view of a PHP board is shown, in accordance with an embodiment of the present invention.

[0127] Figure 102 A top view of a PHP board is shown, in accordance with an embodiment of the present invention.

[0128] Figure 102A Shown Figure 92 A cross-sectional view of the PHP board.

[0129] Figure 103 A top view of a PHP board is shown, in accordance with an embodiment of the present invention.

[0130] Figure 103A Shown Figure 92 A cross-sectional view of the PHP board.

[0131] Figure 104 A top view of a PHP board is shown, in accordance with an embodiment of the present invention.

[0132] Figure 104A Shown Figure 92 A cross-sectional view of the PHP board.

[0133] Figure 105A cross-sectional view of a PHP board according to an embodiment of the present invention is shown.

[0134] Figure 106 A top view of a PHP board is shown, in accordance with an embodiment of the present invention.

[0135] Figure 107 A top view of a PHP board is shown, in accordance with an embodiment of the present invention.

[0136] Figure 108 A top view of a PHP board is shown, in accordance with an embodiment of the present invention.

[0137] Figure 109 A top view of a PHP board is shown, in accordance with an embodiment of the present invention.

[0138] Figure 110 A top view of a PHP board is shown, in accordance with an embodiment of the present invention.

[0139] Figure 111 A top view of a PHP board is shown, in accordance with an embodiment of the present invention.

[0140] Figure 112 A top view of a PHP board is shown, in accordance with an embodiment of the present invention.

[0141] Figure 113 A top view of a PHP board is shown, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION

[0142] In the field of electronic device cooling, radiators and thermal energy dissipation devices have been used to absorb and discharge thermal energy from components. Pulsating heat pipes (PHP) have been designed by others to utilize a serpentine path of alternating bubbles and slugs to move energy from a heat source (evaporator) to a cooling (condensation) area, and to diffuse and dissipate heat in other ways. Serpentine paths have been developed in a variety of shapes, orientations, sizes, repetitions, etc. So far, serpentine paths have utilized simple cross-sections to allow working fluids to move / alternate through the system. Working fluids are known in the art and are preferably low global warming potential fluids, preferably acting with low vapor pressures. Conventional cross-sections are circular, semi-cylindrical, rectangular, square, etc. Preferably, the plate is composed of a substrate (having sidewalls and a bottom wall) having a pipe formed by machining, laser processing or other means, and a top plate forming a top wall to complete the plate. The features on the top plate can be consistent with the arrangement and shape of the pipe, and the top wall formed by the top plate forms a channel. Preferably, the plate is made of materials known in the art, or can be developed in other ways. Current technology suggests ceramics such as Al-Ni, Al-Cu, Cu, C (e.g., graphite), etc. The plate is preferably sized for mobile technology such as tablets, mobile phones, or servers. The microchannel size is preferably on the order of 500 microns for plates with a size of 10 microns to 1 mm. For example, for a phone embodiment, the plate can be 400 to 800 microns high, with channels 250 to 500 microns in size.

[0143] No current solution suggests placing obstacles in the path or modifying the shape of the path to achieve advanced cooling. The present invention relates to alternative path cross-sections, including multiple obstacle geometries and arrangements. One or more obstacles can be constrained to the left, right, top and / or bottom of the channel to force the fluid to move around the obstacles. Various path and obstacle corners, as well as junctions and lines, are created in the pathway. Repeating and random patterns can be used in coordinated, parallel and / or staggered patterns. Posts can be used to traverse the pathway, or longitudinal protrusions, or obstacles can be used alone or in combination with alternative obstacle arrangements. The size of the obstacles can be varied to provide the appropriate balance between heat flux and forcing the fluid to engage with the surface in order to reduce flow resistance and enhance heat transfer. These obstacles increase the surface area within the channel and can create additional nucleation sites to enhance heat transfer between the working fluid and the plate.

[0144] The system introduces the idea of ​​an obstacle, multiple obstacles or otherwise non-standard pathway for the pulsating heat pump serpentine path. The system can be extended for a variety of embodiments, ranging from portable electronic devices (mobile phones, tablets or laptops, approximately 180×80 mm) to small devices and components, and larger systems such as server blades, data centers, etc., approximately 1 m×0.5 m. The serpentine or straight forward pathway can be modified with an electric current system. The channel can be of any size, and preferred embodiments include channels that are 200 microns to 1 mm high and 200 microns to 700 microns wide. When used on a portable electronic device, it is envisioned that the board holding the PHP can be the size of a printed circuit board, or more preferably a large portion of one side of the inner case of the mobile device, as is known in the art for other heat sinks and dissipation technologies.

[0145] For illustrative purposes, in mobile applications, the PHP device thickness can range from 0.3 mm to 2 mm. The microchannel height can range from 0.2 mm to 1.5 mm, in this case for mobile devices. For larger-scale applications, such as data centers and base stations, the device thickness can range from 1.5 mm to 5 cm.

[0146] The heat transfer coefficient of PHP can be improved by promoting the flow of fluid slugs and vapor parcels, and further promoting the vaporization of the working fluid within the pipe. To overcome the disadvantage of PHP slugs being immobile except along the edges, additional nucleation can be used to increase the potential for slug vaporization and decomposition. With these microchannel sizes, obstructions can also be introduced without changing the external shape of the channel.

[0147] Utilizing embodiments of the present invention, a PHP can be designed wherein the evaporator is located in the center of the PHP and multiple condensers are located at the ends, and / or the evaporator is located at the end of the PHP and the condenser is located at the opposite end. An adiabatic zone can be provided between the condenser zone and the evaporator zone.

[0148] A new two-phase closed-loop pulsating heat pipe (CLPHP) introduces a disruptive design to enhance cooling of high-power dissipating electronic devices and saves over 40% to 50% of microprocessor energy dissipation compared to today's leading cooling solutions for mobile computing and power microelectronics (capillary wick-driven heat pipes and vapor chambers). Flow instabilities are generated in a custom CLPHP system featuring disruptive nucleation sites (pits, rods, pillars, and columns) in the evaporator, an innovative condenser and serpentine microchannel geometry, and a selective refrigerant option. The system "pumps" the two-phase liquid back and forth at a higher frequency to very efficiently carry latent heat from the device hotspot to the condenser without the need for pumps, wiring, or controllers. This cooling technology can be scaled to benefit a wide range of applications, from the mobile industry (millions of mobile phones, tablets, and laptops) to the Internet of Things, large processor and data center cabinets and aisles, automotive, and aerospace applications, among others. For high-power mobile microelectronics and PCs, the system operates effectively without forced convection.

[0149] Compared to the prior art, the innovation of the proposed PHP enhances flow pulsation to increase the total cooling capacity by 50% or more. Adding hemispherical (hemispherical) or semi-cylindrical ribs will increase the wetted surface area per unit area of ​​​​occupancy and reduce the heat flux on the wetted surface area, thereby increasing the input heat flux that can be cooled; and is expected to contribute 15% to 20% of the cooling enhancement.

[0150] The heat transfer mechanism is that elongated bubbles in the film provide cooling of the wetted surface area through evaporation (or condensation) of the liquid film. By increasing the wetted surface area per unit occupied area, the liquid film thickness can be reduced and the local heat transfer coefficient increased because the heat transfer coefficient is generated per unit thermal conductivity / film thickness; this can contribute 30% cooling enhancement.

[0151] Pits, rods, posts, and other obstructions will increase the heat transfer coefficient in a liquid slug by disrupting and restarting the thermal boundary layer; contributing ~20% to 30% cooling enhancement. Obstructions will create nucleation sites or "corners" that act as preferred nucleation sites; this can increase heat transfer by approximately 15% to 20%.

[0152] Figure 1 The cross section of a standard portable electronic device 1 is shown. The device 1 comprises a housing 2 with an electronic device 3. A pulsating heat pipe 4 (PHP) may be provided close to or near the electronic device 3, and a heat sink is provided near a condensing portion (not shown), preferably opposite the electronic device. When viewed from a planar surface, as shown in FIG. Figure 2 As shown, the PHP 4 may have a filling valve or charging port 9. Figures 2 to 4As shown, the PHP 4 may include a closed loop 10 as is known in the art, whereby the working fluid is contained within the closed loop 10. A channel 17 forms a serpentine passage 12 through the PHP plate. The passage 12 forms a serpentine design with various bends 20 and straight sections 18 to increase the total channel length in a single plane. The length of the straight sections 18 can be maximized in the channel 17 to facilitate the functionality of the present invention. Each end has a bend 20, including a radiating rod 19 at the condenser 22. A heat source is placed near the evaporator 25. The fluid forms a liquid slug 26, with vapor parcels 28 forming bubbles therebetween. The condenser 22 is positioned near the heat sink 11, typically out of plane, but possibly in a plane parallel to the channel 17. Heat enters the PHP at the evaporator 25 and is released at the condenser 22. The condenser 22 can be positioned on either side or on one side, while the evaporator 25 can be positioned in the middle or at one end, or as required by the particular electronic device.

[0153] To distinguish standard capillary heat pipes, such as Figure 5 and Figure 5 A and Figure 5 As shown in FIG. 2B , the channel 17 may include a capillary wick 29 as a feature or texture along the sidewall surface. A liquid slug 26 is disposed within the capillary wick and allows a vapor parcel 28 to pass through the center. In contrast to PHP, the vapor parcel is confined by the liquid slug. Compared to existing heat pipes, Figure 6 In the figure the passage and condensation zone of a standard closed loop PHP are introduced, with the condenser 22 being arranged at one end with the radiant rod 19 and the evaporator zone being arranged opposite thereto.

[0154] like Figures 7 to 99 As shown, focusing on the channel facilitates viewing the top, side, and cross-sectional views. While existing PHP circuits are quite smooth, the present invention introduces the concept of obstacles 50, which differ from the capillary action in existing heat pipes. The obstacles allow for nucleation sites 55 along the outer surface of the obstacles 50 within the channel 17. It is contemplated that a slug of working fluid liquid may pass through part or all of one or more obstacles 50 in the channel 17. The obstacles are generally referred to as obstacles 50, but various shapes are included, such as hemisphere 52, hemicylinder 56, post 58, etc. In practice, the specific shape of the obstacle may not easily conform to the geometrically described shape. In this document, the term "hemispherical" can refer to a hemispherical object, a spherical cross-section, a generally circular shape, a spike, or a dimple, typically as a feature extending from a wall. A semi-cylindrical portion can refer to a semi-cylinder, a portion of a cylinder, or a rod extending from at least a portion of a wall, preferably spanning to an opposing wall. A post can be cylindrical, but refers to any shape that spans opposing walls without contacting adjacent walls. Similar concepts apply to all obstacles described herein. Preferably, the obstruction is confined to the evaporator region, but may also be included in the insulation and / or condenser regions.

[0155] The channel 17 comprises a side wall 41, a bottom wall 42 and a top wall 43. Due to current technological limitations, during the construction of the PHP, the top wall is preferably placed on the bottom and side walls. As shown in the first embodiment, Figures 7 to 9 A half cylinder 56 is shown as an obstruction 50 in the passage. Here, the half cylinder 56 is fixed to the side wall 41. The half cylinder can be fixed to one or both side walls and can extend from the bottom wall to the top wall or a large part thereof on the side wall. The half cylinders can be arranged opposite each other or offset. A regular pattern can be used, or the obstacles can be randomly combined. Figures 10 to 12 As shown, hemispherical shapes 52 can be used to create nucleation sites 55 on the outer surface of the obstacle 50 and can be provided along the sidewalls. Preferably, the hemispherical shapes 52 are provided at the mid-wall between the top and bottom, but quarter-spheres can be provided along the bottom and sides, and / or at the intersection of the top and sidewalls.

[0156] like Figures 13 to 17 As shown, an offset pattern is shown, and obstacles 50 can be arranged on the side wall in an offset pattern. The obstacles can be staggered or offset and can be hemispherical 52 and / or semi-cylinder 56 on the side wall 41.

[0157] In some embodiments, obstacles 50 are formed on the side walls 41 and the bottom wall 42. Figures 18 to 22 As shown, the bottom wall 42 may include a hemispherical shape 52, and the side walls may include a hemispherical shape 52 and / or a semi-cylinder 56. Figures 23 to 27 In the alternative embodiment shown, a semi-cylindrical body 56 may traverse the channel 17 to join the two side walls 41. The side walls may also have a hemispherical shape 52 and / or a semi-cylindrical body 56. Figures 33 to 37 As shown, it is preferred to stagger the semi-cylinders 56 on the bottom wall 42 with the features of the side wall 41. Figures 28 to 32 As shown, objects may be staggered.

[0158] Other configurations include the combination of a semi-cylinder 56 and a semi-cylindrical obstacle. Figures 38 to 42 As shown, the semi-cylindrical portion can be provided on all four side walls 41, the bottom wall 42 and the top wall 43. Figures 38 to 39 When arranged in unison as shown, they severely restrict passage 17. Figures 41 to 42 As shown, when arranged in a staggered or offset pattern, they require the fluid to pass through in a manner that requires alternating lateral restrictions (when the side walls are obstructed) and vertical restrictions (when the bottom and / or top are restricted). When using a semi-cylindrical rod connecting the top wall 43 and the bottom wall 42 along the side wall 41, as shown Figures 43 to 47 As shown, the hemispherical shape 52 can be provided on the top wall 43 and the bottom wall 42. The obstacle can be as Figures 43 to 44 Align as shown, or as Figures 46 to 47 The array is shown offset in a staggered arrangement.

[0159] like Figures 48 to 55 As shown, the obstructions may be provided on three of the four walls of the passageway, with the semi-cylinders 56 provided along the walls, which may or may not extend the entire length of the walls and the hemispheres 52. All four walls may include hemispheres 52 or other similar features extending from each wall, such as Figures 56 to 60 As shown, aligned or staggered. Figures 61 to 65 As shown, the rods as semi-cylinders 56 can be connected to the side walls 41, wherein the hemispherical shapes 52 are arranged on the other walls in an aligned or staggered manner, such as Figures 61 to 65 shown.

[0160] like Figures 66 to 68 As shown, when channel 17 is disturbed by longitudinal rods 53, nucleation can extend along the length of the channel. Hemispherical shapes 52 can optionally be added to one, two, or three sidewalls, or as shown, longitudinal rods can pass through bottom wall 42 and top wall 43, while sidewall 41 has extended features. Alternatively, the sidewalls can have rods, while the top and bottom can optionally have hemispherical shapes or not.

[0161] like Figures 69 to 71 As shown, the corners 45 of the channel 17 may include obstruction features such as longitudinal bars 53. The longitudinal bars 53 may extend the length of the straight portion, being disposed only within the evaporator region, or may be short members more akin to quarter-spheres or spikes extending along the corners 45 of the channel 17 to the center 51 of the channel.

[0162] In the case where column 58 is required, as Figures 72 to 74 As shown, the entire post can extend from sidewall to sidewall, or from top 43 to bottom wall 42, as shown. It is feasible that post 58 can be cylindrical or rectangular, or have a continuous diameter or width from top to bottom.

[0163] refer to Figures 75 to 86 , posts 58 may be used to connect the top wall 43 and the bottom wall 42. Additional features including hemispherical shapes 52 and semi-cylinders 56 may be used in combination, either aligned or staggered on the side wall 41, or as shown. Figures 87 to 89As shown, when referring to hemispheres 52 and semi-cylinders 56 or posts 58, the exact geometry is not necessarily required, but is suggested. At these small scales, only an approximation of these features may be required, and the exact shapes are discussed and illustrated in the figures to convey this idea. Any protrusion along a wall is discussed as a hemisphere, while any feature extending between opposing walls, whether or not of uniform diameter, is referred to as a cylinder or semi-cylinder. Furthermore, it is contemplated that a feature extending between two opposing walls may not actually contact one or both of the walls, but rather be viewed as an approximation of a shape that can be used to introduce nucleation sites 55 along the exterior surface.

[0164] exist Figures 90 to 99 , which shows a central riser or longitudinal ridge similar in shape to the semi-cylindrical ridge on the bottom wall 42 in the channel. The ridges can be used on any wall. Figure 91 The offset hemispherical shape 52 shown, or may be aligned with the sidewall 41 feature (more similar to Figure 92 sidewall features as shown). May be on opposing surfaces, such as Figures 92 to 94 As shown, longitudinal ridges may be employed, for example, on the bottom wall 42 and the top wall 43. The side wall features may be aligned, as shown. Figures 92 to 94 As shown, or more preferably staggered. Figures 95 to 99 As shown, a single protuberance may be provided with features such as a half cylinder 56 that reaches between two opposing sides, adjacent sides, and opposing sides, as shown. Figures 96 to 97 As shown, or with hemispherical features on adjacent (possibly opposing) sides, as Figures 98 to 99 shown.

[0165] Now refer to the overall shape, outline and composition of PHP. Figure 100 , the plate 15 is shown in a cross-sectional perspective view. The channels 17 form a serpentine structure through the plate 15, with the side walls 41 exposed, and the bottom wall 42 and top wall 43 as shown. The side wall thickness can form a uniform span width between the channels. The plate 15 includes a plate surface 30 and a bottom surface 32. Preferably, the channels 17 are regularly arranged through the structure to form a serpentine structure, and the passages 12 are arranged parallel to each other at the straight portion 18. Each channel 17 includes a channel width 44 (between the side walls within the channel) and a channel height 47 (between the top wall and the bottom wall within the channel), preferably consistent with the approximate manufacturing technology. The outer wall thickness of the top wall 43 and the bottom wall 42 can be similar or dissimilar to each other. Each channel 17 includes a height 49 that may or may not be reduced by an obstacle (not shown). As Figures 100 to 101As shown, the PHP 4 includes a flat plate 15 which may be rigid or flexible. A heat sink 11 may take the form of an electronic component positioned along, adjacent to, or in contact with the board surfaces 30 and / or 32. The PHP has an overall width 14 and a length 13.

[0166] Various deployments of thin conductive sheets, such as the plating 34, serve as heat sinks and physical reinforcement for the PHP to prevent unwanted bending of the board and possible cracking or deformation that could interfere with the function of the PHP. The plating (or foil) may be 10 microns to 500 microns thick, more preferably 20 microns to 150 microns, and most preferably 20 microns to 25 microns. Figures 102 to 104 As shown, the coating 34 may be provided on the plate surface 30 of the plate 15 in a partially smooth layer on the condenser portion, as shown. Figure 102 As shown, Figure 103 Shown across the entire width, across both sides (not shown).

[0167] Alternatively, a portion of the plate surface 30 may be equipped with external ribs as spreader elements to distribute heat at the condenser. Micro-ribs 36 may extend parallel to the straight portion 18, while a smooth coating 34 may be provided on the remainder of the plate surface 30. It is envisaged that the preferred embodiment shows micro-ribs 36, and that the top and bottom surfaces of the plate are plated in a similar manner, with the condenser being provided by micro-ribs on both sides. Figure 105 As shown in the cross-sectional view of , the micro-ribs 36 can be used with valleys 38 disposed between each rib, and there can be more ribs than channels 17 in the plate 15, with the minimum base 37 disposed directly above the plate surface 30. It is contemplated that the number of ribs can be equal to the number of channels, or positioned above each channel. The width of each rib can be sized based on the channel width and / or sidewall width. The external ribs and valleys can have equal widths, but preferably, the valleys are wider than the external ribs. The external ribs provide additional surface area for heat dissipation from the condenser to the radiator. For example, for a coating thickness of 20 to 25 microns, the external ribs can have a pitch (defined as the distance between microchannels) that is less than the distance between the channels. Alternatively, the external ribs can be aligned with the internal channel spacing, or larger. When the PHP is disposed vertically or aligned vertically with the external ribs, air plumes can form and move through the valleys to enhance heat dissipation.

[0168] exist Figures 106 to 109 An alternative arrangement of ribs is shown in FIG. The coating 34 remains on the plate surface 30 (and preferably also on the bottom surface (not shown)) of the plate 15. The ribs may be as follows Figure 106 As shown, it is arranged along the straight line of the serpentine structure, as shown Figure 107 Traverse as shown, such as Figure 108 As shown, they are arranged diagonally (such as 45 degrees), or as Figure 109It is shown crisscrossed in a square grid array with extra valleys at the intersections.

[0169] exist Figures 110 to 113 An alternative positioning of the plates and ribs is shown in FIG. Figure 110 As shown, both the top and bottom surfaces may be left uncovered or unplated. Figures 111 to 112 1 shows the top and bottom of the plate 15, with the plate surface 30 of the plate 15 at the condenser region being provided with a smooth coating 34 and the remaining portion being provided with micro-ribs 36, while the bottom surface 32 of the plate 15 includes all the micro-ribs 36. Figure 113 The open window embodiment shown in FIG. 3 can be used with a smooth coating 34 on the evaporator surface and micro-ribs 36 at the condenser area with an open window 39 disposed therebetween.

Claims

1. A two-phase microchannel embedded closed-loop pulsating heat pipe, comprising: a first sheet material having a serpentine trace pattern, the serpentine trace pattern comprising a trace pattern; a second sheet bonded to the first sheet such that, when the first and second sheets are bonded together to form a bonded sheet, a continuous serpentine microchannel is defined in the bonded sheet, the channel comprising a rectangular cross-sectional shape, a bottom wall, a top wall opposite the bottom wall, and two opposing side walls; wherein the serpentine microchannel defines a closed loop adapted to contain a fluid within the serpentine microchannel; and a working fluid in liquid and / or vapor form partially filling the passage; wherein the microchannel comprises one or more obstacles, at least one obstacle being selected from the group consisting of: a semi-cylindrical obstruction spanning two opposing walls, a cylindrical strut disposed between the top wall and the bottom wall, a hemispherical obstacle disposed on at least one of the top wall and the bottom wall, a transverse semi-cylindrical obstacle; The barrier is mounted on at least one of the top wall, bottom wall and / or side wall; Wherein the bonding plate includes a first region defining a condenser region coupled to a heat sink and a second region including an evaporator region coupled to or near at least one heat source.

2. The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 1, wherein the one or more obstacles include semi-cylindrical obstructions spanning two opposite walls among the bottom wall, the top wall, and the two opposite side walls.

3. The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 1, wherein the one or more obstacles include cylindrical pillars arranged between the top wall and the bottom wall in the microchannel, and the pillars do not contact any of the side walls. 4 . The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 1 , wherein the one or more obstacles include a hemispherical obstacle provided on at least one of the top wall and the bottom wall.

5. The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 4, wherein the hemispherical obstacle is arranged on the bottom wall and is in a straight line with at least one obstacle arranged along at least one of the side walls.

6. The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 4, wherein the hemispherical obstacles are arranged on the bottom wall and are staggered relative to at least one obstacle arranged along at least one of the side walls.

7. The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 4, wherein the hemispherical obstacle is arranged on the top wall and is in a straight line with at least one obstacle arranged along at least one of the side walls.

8. The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 4, wherein the hemispherical obstacles are arranged on the top wall and are staggered relative to at least one obstacle arranged along at least one of the side walls.

9. The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 1, wherein the one or more obstacles include a semi-cylindrical obstacle provided on at least one of the top wall and the bottom wall, and the semi-cylindrical obstacle spans between the side walls.

10. The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 9, wherein the hemispherical obstacle is arranged on the bottom wall and is in a straight line with at least one obstacle arranged along at least one of the side walls.

11. The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 9, wherein the semi-cylindrical obstacles are arranged on the bottom wall and are staggered relative to at least one obstacle arranged along at least one of the side walls.

12. The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 9, wherein the hemispherical obstacle is arranged on the top wall and is in a straight line with at least one obstacle arranged along at least one of the side walls.

13. The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 9, wherein the semi-cylindrical obstacles are arranged on the top wall and are staggered relative to at least one obstacle arranged along at least one of the side walls.

14. The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 1, wherein The channel forms a plurality of bends.

15. The two-phase microchannel embedded closed-loop pulsating heat pipe according to claim 1, further comprising: a conductive plating extending over at least a portion of the exterior of the bonding sheet, and The channel comprises a continuous serpentine microchannel having a well-defined extending straight line, the channel including a rectangular cross-sectional shape, a bottom wall, a top wall opposite the bottom wall, and two opposite side walls.

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