Miniature capillary heat pipe for smart wearables

Abstract

This invention discloses a microcapillary heat pipe for smart wearable devices. The microcapillary heat pipe includes a tube body, a capillary core inserted inside the tube body, and a phase change working fluid filled within it. The surface of the capillary core has several microgrooves and several nanopores. Non-metallic fibers are also implanted on the surface of the capillary core, forming a fiber bridging layer. This invention does not require high-temperature sintering. For the same diameter of 1.0mm to 2.0mm, compared to the existing ordinary sintered core with a capillary force rise height of 60-70mm, the capillary force rise height of this invention is ≥110mm. Compared to the existing ordinary sintered core with an effective thermal conductivity of 4500-5000 W / (m·K), the effective thermal conductivity Keff of this invention is ≥5500 W / (m·K). Compared to the existing ordinary sintered core, the three-point bending stiffness of this invention is increased by ≥10%.

Description

Technical Field

[0001] This utility model relates to the field of heat dissipation technology, and in particular to a micro capillary heat pipe for smart wearable devices. Background Technology

[0002] Smartwatches, smart bracelets, and other devices have extremely limited internal space, with highly integrated components such as processors and batteries. During operation, the processor generates concentrated heat, forming "hot spots." If this heat isn't dissipated promptly, the processor will automatically reduce its frequency due to overheating, causing the device to lag and become unresponsive. If the device overheats in a localized area, such as the back of a watch, it can feel hot to the touch or cause discomfort, affecting the wearing experience. Microcapillary heat pipes can quickly spread the heat from the CPU, preventing localized overheating and ensuring the chip continues to operate at high performance. These microcapillary heat pipes also rapidly conduct concentrated heat to the entire back of the watch case, increasing the heat dissipation area and resulting in a more uniform and gentler overall temperature, avoiding a burning sensation and improving comfort.

[0003] Existing wearable smart devices generally use wire mesh as the capillary core for heat pipes, with a process temperature of 700-950 ℃. This has the following drawbacks: high-temperature sintering leads to coarsening of the shell grains, reduced rigidity, and easy cracking during repeated bending; the thickness of the sintered core of the micro capillary heat pipe is difficult to be less than 0.3 mm, the steam cavity is limited, the wire mesh has poor stability, and conventional fixtures cannot be reused; the sintering process has high energy consumption and low yield, which cannot meet the needs of mass production.

[0004] The capillary pressure of existing wire mesh sintered cores is Pc≈2σ / r (σ is the surface tension of the liquid, and r is the effective aperture radius of the wire mesh). Limited by the wire mesh weaving process, r is typically ≥40 μm, resulting in Pc<6 kPa. Furthermore, sintering temperatures ≥700 ℃ cause the Cu grain size to grow from 10 μm to over 50 μm, weakening the Hall-Petch effect, reducing yield strength by approximately 30%, and making it prone to microcracks during repeated bending. Utility Model Content

[0005] The technical problem to be solved by this utility model embodiment is to provide a micro capillary heat pipe for smart wearable devices, so as to improve the rigidity and thermal conductivity of the heat pipe, avoid high-temperature sintering, reduce production costs, and improve production yield.

[0006] To address the aforementioned technical problems, this utility model proposes a micro capillary heat pipe for smart wearable devices, comprising a tube body, a capillary core inserted inside the tube body and filled with a phase change working fluid, the surface of the capillary core having several microgrooves and several nanopores, and non-metallic fibers implanted on the surface of the capillary core, the non-metallic fibers forming a fiber bridging layer on the surface of the capillary core.

[0007] Furthermore, the microgrooves of the capillary core are obtained by cold rolling, hot rolling, etching, or laser engraving.

[0008] Furthermore, the microgrooves of the capillary wick are inverted trapezoidal, inverted triangular, or omega-shaped.

[0009] Furthermore, the nanopores of the capillary core have a porosity of 10% to 60% and a pore size of 10 nm to 150 nm.

[0010] Furthermore, the non-metallic fiber is one or more of polyimide, aramid, glass fiber, and basalt fiber, and its diameter is 1 μm to 10 μm.

[0011] Furthermore, the microgrooves of the capillary core satisfy the following: w ranges from 0.05 mm to 0.10 mm, h ranges from 0.05 mm to 0.10 mm, and p ranges from 0.10 mm to 0.15 mm; where w is the groove width of the microgroove, h is the depth of the microgroove, and p is the center distance between adjacent microgrooves.

[0012] The beneficial effects of this invention are as follows: The microgrooves of this invention provide millimeter-level liquid channels, and the groove depth h and groove width w satisfy h / w≈1, which allows the liquid to form Corner flow in the groove, with a pressure difference ΔPcorner=σ(1 / R1+1 / R2), where R1 and R2 are the radii of curvature of the liquid surface, and ΔPcorner≈4.8 kPa is calculated; The nanopores of this invention form a secondary capillary structure on the surface of the groove, with a pore size ≤150 nm, and an additional capillary pressure Pnano≈2σ / nano≈7 kPa; The non-metallic fiber bridging layer of this invention establishes a three-dimensional liquid film network between the groove and the nanopore, with a fiber spacing Df≈2 μm, generating a fiber capillary pressure Pfiber≈2σ / Df≈72 kPa. This invention connects the three components in series, resulting in a total capillary pressure Ptotal≈Pc+Pnano+Pfiber≥83 kPa, which is 13 times that of traditional wire mesh cores, thereby increasing the vertical climbing height from 65 mm to ≥110 mm. This invention does not require high-temperature sintering. For the same specifications with a diameter of 1.0 mm to 2.0 mm, compared to the existing ordinary sintered core with a capillary climbing height of 60-70 mm, this invention achieves a capillary climbing height of ≥110 mm. Compared to the existing ordinary sintered core with an effective thermal conductivity of 4500-5000 W / (m·K), this invention achieves an effective thermal conductivity Keff ≥5500 W / (m·K). Compared to the existing ordinary sintered core, this invention increases the three-point bending stiffness by ≥10%. Attached Figure Description

[0013] Figure 1(a) is a cross-sectional view of the micro capillary heat pipe for smart wearable devices according to Embodiment 1 of the present invention, Figure 1(b) is a cross-sectional view of the micro capillary heat pipe for smart wearable devices according to Embodiment 2 of the present invention, Figure 1(c) is a cross-sectional view of the micro capillary heat pipe for smart wearable devices according to Embodiment 3 of the present invention, and Figure 1(d) is a cross-sectional view of the micro capillary heat pipe for smart wearable devices according to Embodiment 4 of the present invention.

[0014] Figure 2(a) is a cross-sectional view of the micro capillary heat pipe for smart wearable devices according to Embodiment 5 of the present invention, Figure 2(b) is a cross-sectional view of the micro capillary heat pipe for smart wearable devices according to Embodiment 6 of the present invention, Figure 2(c) is a cross-sectional view of the micro capillary heat pipe for smart wearable devices according to Embodiment 7 of the present invention, and Figure 2(d) is a cross-sectional view of the micro capillary heat pipe for smart wearable devices according to Embodiment 8 of the present invention.

[0015] Figure 3(a) is a cross-sectional view of the micro capillary heat pipe for smart wearable devices according to Embodiment 9 of the present invention, Figure 3(b) is a cross-sectional view of the micro capillary heat pipe for smart wearable devices according to Embodiment 10 of the present invention, Figure 3(c) is a cross-sectional view of the micro capillary heat pipe for smart wearable devices according to Embodiment 11 of the present invention, and Figure 3(d) is a cross-sectional view of the micro capillary heat pipe for smart wearable devices according to Embodiment 12 of the present invention.

[0016] Explanation of icon numbers 1. Tube body, 2. Capillary core, 3. Micro grooves. Detailed Implementation

[0017] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other. The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] In this embodiment of the invention, directional indicators (such as up, down, left, right, front, back, etc.) are only used to explain the relative positional relationship and movement of the components in a specific posture (as shown in the attached figure). If the specific posture changes, the directional indicators will also change accordingly.

[0019] Furthermore, in this utility model, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features.

[0020] Referring to Figures 1-3, the microcapillary heat pipe for smart wearable devices according to this embodiment of the invention includes a tube body. A capillary wick is inserted into the tube body and filled with a phase change working fluid. The length and outer diameter of the capillary wick match the length and inner diameter of the tube body. The microcapillary heat pipe of this invention can be integrated into the heat dissipation path of smart wearable devices (head / neck / foot / wrist wear, AR / VR glasses, smart wearables, etc.).

[0021] The capillary wick surface has several microgrooves along the axial direction. The microgrooves of the capillary wick are obtained by cold rolling, hot rolling, etching, or laser engraving. The microgrooves of the capillary wick are inverted trapezoidal, inverted triangular, or omega-shaped. Examples 1-4, please refer to Figures 1(a)-1(d). In Example 1, the microgrooves of the microcapillary heat pipe for smart wearable devices are inverted triangular, and the capillary wick is semi-circular rod-shaped; in Example 2, the microgrooves of the microcapillary heat pipe for smart wearable devices are inverted triangular, and the capillary wick is semi-circular tubular; in Example 3, the microgrooves of the microcapillary heat pipe for smart wearable devices are inverted triangular, and the capillary wick is circular tubular; in Example 4, the microgrooves of the microcapillary heat pipe for smart wearable devices are inverted triangular, and the capillary wick is circular rod-shaped. Examples 5-8, please refer to Figures 2(a)-2(d). In Example 5, the microgroove of the microcapillary heat pipe for smart wearable devices is an inverted trapezoid, and the capillary core is a semi-circular rod. In Example 6, the microgroove of the microcapillary heat pipe for smart wearable devices is an inverted trapezoid, and the capillary core is a semi-circular tube. In Example 7, the microgroove of the microcapillary heat pipe for smart wearable devices is an inverted trapezoid, and the capillary core is a circular tube. In Example 8, the microgroove of the microcapillary heat pipe for smart wearable devices is an inverted trapezoid, and the capillary core is a circular rod. Examples 9-12, please refer to Figures 3(a)-3(d). In Example 9, the microgrooves of the microcapillary heat pipe for smart wearable devices are omega-shaped, and the capillary core is semi-circular rod-shaped. In Example 10, the microgrooves of the microcapillary heat pipe for smart wearable devices are omega-shaped, and the capillary core is semi-circular tube-shaped. In Example 11, the microgrooves of the microcapillary heat pipe for smart wearable devices are omega-shaped, and the capillary core is circular tube-shaped. In Example 12, the microgrooves of the microcapillary heat pipe for smart wearable devices are omega-shaped, and the capillary core is circular rod-shaped.

[0022] This invention utilizes inverted trapezoidal microgrooves / triangular grooves / omega-shaped grooves formed simultaneously by cold rolling / hot rolling / etching / laser microgrooving, followed by high penetration and work hardening, to maintain high rigidity even with a thickness of 0.25mm-1.7mm.

[0023] The capillary wick surface has several nanopores formed through oxidation / corrosion. The porosity of the nanopores in the capillary wick is 10%~60%, and the pore size is 10 nm~150 nm. This invention can improve capillary pressure and avoid high-temperature sintering.

[0024] Non-metallic fibers are also implanted on the surface of the capillary core, forming a fiber bridging layer. This fiber bridging layer provides additional toughening. The non-metallic fibers are one or more of polyimide, aramid, glass fiber, and basalt fiber. The diameter of the non-metallic fibers ranges from 1 μm to 10 μm. The fiber bridging layer establishes three-dimensional liquid film channels between the grooves, enhancing liquid-vapor coupling and resulting in an overall Keff ≥ 5500 W / (m·K).

[0025] This invention employs a composite capillary core consisting of "cold rolling / hot rolling / etching / laser microgrooving + chemically etched nanopores + directional fiber bridging," eliminating the sintering process. During the cold rolling / hot rolling / etching / laser microgrooving process, the microgrooving simultaneously introduces a work-hardened substrate metallurgical bond and a chemical coating / micro-etching, while the fiber layer provides additional toughening. The three elements work together to enhance stiffness.

[0026] This invention can efficiently and quickly diffuse the heat from hot spots (such as chips) inside smart wearable devices evenly to a larger surface area of ​​the entire device, thereby achieving passive heat dissipation.

[0027] This invention utilizes a three-tiered structure of 'microgrooves + nanopores + fiber bridging' to reduce the equivalent pore radius to ≤150 nm and increase Pc to ≥12 kPa; simultaneously, the entire process temperature is ≤450 ℃ to avoid grain growth and maintain the yield strength at ≥550 MPa.

[0028] In one implementation, the microgrooves of the capillary wick satisfy the following conditions: w ranges from 0.05 mm to 0.10 mm, h ranges from 0.05 mm to 0.10 mm, and p ranges from 0.10 mm to 0.15 mm. For example, w = 0.08 mm, h = 0.08 mm, and p = 0.12 mm. w is the groove opening width of the microgroove, h is the depth of the microgroove, and p is the center-to-center distance between adjacent microgrooves.

[0029] The numerical ranges in the embodiments of this utility model can be proportionally enlarged or reduced by ±20% while maintaining capillary performance. For example, when w=0.10 mm, h=0.10 mm, and p=0.15 mm, the measured vertical climbing height is 108 mm, Keff=5520 W / (m·K), and the three-point bending stiffness is 0.36 N·mm².

[0030] The tube body is made of Cu-Ni-Si reinforced alloy (of which, by mass percentage, Cu is 91%, Ni is 8%, and Si is 1%). After rolling, σ0.2≥550 MPa is ≥0.5 times higher than that of pure copper. Both the oxide layer and the fiber layer are processed at medium and low temperatures to avoid recrystallization and softening.

[0031] This novel microcapillary heat pipe requires only one low-temperature (≤400℃) operation. The capillary is formed into microgrooves in a single process via cold rolling / hot rolling / etching / laser forming, followed by online chemical etching of nanopores and electrostatic flocking. Subsequent micro-fusion welding sealing significantly shortens the manufacturing cycle compared to conventional heat pipes. The combination of the tube body and capillary core enhances the overall strength of the microcapillary heat pipe by at least 1 time.

[0032] The preparation method of the microcapillary heat pipe for smart wearable devices in this embodiment of the invention includes steps S1 to S5.

[0033] Step S1: Prepare the tube body and capillary core. The tube body is made of Cu-Ni-Si alloy and is obtained by sequentially melting and casting, rolling, annealing, straightening, flaw detection, cleaning, and cutting.

[0034] In one implementation method, in step S1, a capillary wick is prepared according to the following steps: Step S11: Take a copper rod of a preset size and form several micro-grooves on the surface of the copper rod by cold rolling, hot rolling, etching, or laser engraving. Step S12: Oxidize / corrode the copper rod using an acidic chemical etching liquid to create several nanopores on the surface of the copper rod. Step S13: Non-metallic fibers are electrostatically transferred onto the surface of the copper rod to form a fiber bridging layer, resulting in a capillary core. Finally, the capillary force is tested to ensure it is up to standard. If it is up to standard, it can be used in smart wearable devices.

[0035] Example: Take 0.4~0.8mm Cu rod → cold rolling / hot rolling / etching / laser microgrooving (w=0.08 mm, h=0.08 mm, p=0.12 mm) → acid corrosion for 5 min or less → flocking 1~10 μm non-metallic fibers → test capillary force (the dimensions can be adjusted by capillary force and thermal properties).

[0036] Step S2: Insert the capillary core into the tube.

[0037] Step S3: Seal the pipe opening at one end of the pipe body using laser or argon arc welding.

[0038] Step S4: Inject the working fluid into the tube.

[0039] Step S5: Remove residual air from the tube and then seal the other end of the tube with micro-fusion welding to obtain a micro capillary heat pipe for smart wearable devices.

[0040] In one implementation method, in step S3, low-temperature annealing is performed after the pipe opening is sealed.

[0041] All steps of this invention can be carried out at room temperature (≤450 ℃) (cold rolling, medium and low temperature oxidation, fiber curing, micro-fusion welding), reducing energy consumption by ≥25% and yield by ≥78%.

[0042] The structure of this invention, consisting of a Cu-Ni-Si tube body, cold-rolled hardened capillary, and a non-metallic fiber layer for toughening, increases its three-point bending stiffness by ≥13% compared to micro capillary heat pipes of the same specifications.

[0043] With a specification of 0.8 mm × 0.15 mm × ~20 teeth, this utility model has a vertical capillary climb height of ≥100 mm and improved bending resistance.

[0044] To verify the above mechanism, the following test conditions and results were obtained: Sample specifications: Cu-Ni-Si tube with an outer diameter of 1.0 mm, a wall thickness of 0.15 mm, and a length of 40 mm; the capillary core is a cold-rolled grooved copper rod with a diameter of 0.8 mm, w=0.08 mm, h=0.08 mm, p=0.12 mm, a nanopore porosity of 45%, a pore size of 100 nm, a fiber with a diameter of 5 μm polyimide fiber, and deionized water as the working fluid with a filling rate of 20%.

[0045] Test methods: Vertical climbing height was measured according to ASTM C1275-15, with an ambient temperature of 25 ℃; effective thermal conductivity Keff was measured using the steady-state axial heat flow method with an input power of 1 W, yielding ΔT = 0.18 ℃; three-point bending stiffness was measured according to GB / T 1449, with a span of 20 mm and a loading rate of 2 mm / min.

[0046] Measured results: Vertical climbing height 112 mm; Keff = 5680 W / (m·K); Three-point bending stiffness 0.38 N·mm². Compared with ordinary sintered cores, the improvement is consistent with the mechanism analysis.

[0047] Compared with ordinary sintered cores, the improvement of this invention is shown in Table 1.

[0048] Table 1

[0049] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A microcapillary heat pipe for smart wearable devices, comprising a tube body, characterized in that, The tube contains a capillary core and a phase change working medium. The surface of the capillary core has several microgrooves and several nanopores. Non-metallic fibers are also implanted on the surface of the capillary core, forming a fiber bridging layer on the surface of the capillary core.

2. The microcapillary heat pipe for smart wearable devices as described in claim 1, characterized in that, The microgrooves of the capillary core are obtained by cold rolling, hot rolling, etching, or laser engraving.

3. The microcapillary heat pipe for smart wearable devices as described in claim 1, characterized in that, The microgrooves of the capillary core are inverted trapezoidal, inverted triangular, or omega-shaped.

4. The microcapillary heat pipe for smart wearable devices as described in claim 1, characterized in that, The nanopores of the capillary core have a porosity of 10% to 60% and a pore size of 10 nm to 150 nm.

5. The microcapillary heat pipe for smart wearable devices as described in claim 1, characterized in that, The non-metallic fiber is one or more of polyimide, aramid, glass fiber, and basalt fiber, and its diameter is 1 μm to 10 μm.

6. The microcapillary heat pipe for smart wearable devices as described in claim 1, characterized in that, The microgrooves of the capillary core satisfy the following conditions: w ranges from 0.05 mm to 0.10 mm, h ranges from 0.05 mm to 0.10 mm, and p ranges from 0.10 mm to 0.15 mm; where w is the groove width of the microgroove, h is the depth of the microgroove, and p is the center distance between adjacent microgrooves.

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