Heat exchanger for strengthening flow boiling phase change based on alternating current electrowetting principle

Abstract

A heat exchanger for strengthening flowing boiling phase change based on the alternating current electrowetting principle sequentially comprises a base plate, a lower-layer high-temperature-resistant gasket, hydrophobic breathable carbon paper, an upper-layer high-temperature-resistant gasket and a cover plate from bottom to top, the upper surface of the hydrophobic breathable carbon paper is a breathable face, the lower surface of the hydrophobic breathable carbon paper is a hydrophobic face, and a carbon paper sealing ring is arranged on the periphery of the hydrophobic breathable carbon paper. The upper high-temperature-resistant gasket and the lower high-temperature-resistant gasket are provided with micro-channels and are partially overlapped, the carbon paper sealing ring, the upper high-temperature-resistant gasket and the cover plate are provided with a water inlet and a water outlet respectively, the water inlet and the water outlet are communicated with the micro-channel of the lower high-temperature-resistant gasket, and the cover plate is provided with an exhaust hole which is communicated with the micro-channel of the upper high-temperature-resistant gasket. The hydrophobic breathable carbon paper is connected with an alternating current cathode.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat dissipation, and particularly relates to a technology for enhancing flow boiling phase change heat transfer. Background Art

[0002] With the continuous increase in the power density of electronic devices, such as radar RF chips, lasers, high-computing power GPUs, etc., the heat dissipation demand shows an exponential growth. Microchannel heat exchangers have become a research and application hotspot due to their advantages such as compact volume and high specific surface area. Microchannel boiling phase change heat transfer can further improve the heat transfer performance by utilizing the large amount of heat absorbed during the phase change process of the working fluid.

[0003] The microchannel size is very small, usually less than 1 mm. Bubbles during the boiling process are easily retained on the heating surface due to the action of surface tension, forming a local vapor film coverage, resulting in a decrease in the critical heat flux (CHF) and a sudden increase in temperature. There are bottleneck problems of two-phase flow instability and CHF limitation in the boiling process in microchannels, posing safety hazards to heat exchange equipment and power systems.

[0004] Existing technologies reduce flow instability and increase the heat transfer limit through structural optimization design and externally applied electromagnetic field enhancement. For example: Patent CN116960084A uses a multi-manifold structure to enhance heat transfer, Patent CN107731767A uses a fin or groove flow-around structure, and Patent CN105263295A enhances heat transfer through the interaction between a magnetic field and a liquid metal working fluid. These related patents increase the overall flow resistance of the system. Patent CN111056525B utilizes the electro-wetting effect to reversibly change the wall hydrophilicity and hydrophobicity, enhancing the heat transfer at the bottom of the bubbles during boiling. However, due to the inability of the bubbles to be discharged in time during the boiling process, the CHF is relatively low.

[0005] The existing technologies separate the bubble dynamics control from the exhaust mechanism, lacking a collaborative design for boiling enhancement and flow instability. Summary of the Invention

[0006] In order to solve the technical problems of two-phase flow instability and reduced critical heat flux during the boiling process in microchannels, a technical solution is adopted that dynamically regulates the wall wettability using the electro-wetting principle and a hydrophobic and breathable porous membrane timely discharges the bubbles generated during the boiling phase change from the channel, resulting in the technical effects of inducing dynamic oscillation of the vapor-liquid interface during the boiling of the working fluid, suppressing the formation of vapor films, reducing bubble coverage, and increasing the critical heat flux.

[0007] The heat exchanger, from bottom to top, consists of a substrate, a lower high-temperature resistant gasket, a hydrophobic and breathable carbon paper, an upper high-temperature resistant gasket, and a cover plate. The upper surface of the hydrophobic and breathable carbon paper is the breathable surface, the lower surface is the hydrophobic surface, and a carbon paper sealing ring is set around it to prevent liquid leakage from the hydrophobic and breathable carbon paper. The upper and lower high-temperature resistant gaskets are provided with micro-channels and partially overlap. The carbon paper sealing ring, the upper high-temperature resistant gasket, and the cover plate are respectively provided with water inlets and outlets. The water inlets, outlets, and the micro-channels of the lower high-temperature resistant gasket are connected through. The cover plate is provided with exhaust holes and is connected through with the micro-channels of the upper high-temperature resistant gasket. The substrate is connected to the positive electrode of the alternating current, and the hydrophobic and breathable carbon paper is connected to the negative electrode of the alternating current.

[0008] Preferably, the substrate is made of silicon or germanium with high insulation and high thermal conductivity to conduct heat in time.

[0009] Furthermore, a hydrophobic dielectric electrode is provided on the surface of the substrate, which, from bottom to top, consists of an insulating layer, an electrode, a dielectric layer, and a hydrophobic layer. Each electrode is independently connected to a power supply.

[0010] Preferably, a 1 - 2 micron thick silicon dioxide insulating layer is prepared by plasma enhanced chemical vapor deposition method or thermal oxidation process.

[0011] Preferably, gold or aluminum electrodes with a thickness of 50 - 200 nanometers are prepared by photolithography and lift-off processes, and the arrangement pattern is an array arrangement with the same size or an alternating arrangement with different sizes.

[0012] Preferably, an alumina dielectric layer with high dielectric constant and high thermal conductivity is deposited by atomic deposition technology to prevent electrolysis reaction caused by direct contact between the electrode and the liquid.

[0013] Preferably, a 100 - 300 nanometer thick Teflon hydrophobic layer is spin-coated.

[0014] The dielectric layer is designed by electro-wetting effect. A certain voltage is applied to the substrate to change the surface tension between the substrate and the gas-liquid interface, and the contact angle is changed to adjust the wettability of the liquid on the solid surface. The initial surface state is a hydrophobic surface. A certain voltage is applied to change the contact angle and adjust the surface to a hydrophilic surface to maintain the liquid film at the interface.

[0015] The alternating current is used to make the contact angle between each electrode and the gas-liquid interface change periodically, and the liquid film at the interface oscillates to strengthen the effect of boiling phase change heat transfer.

[0016] Preferably, the upper and lower high-temperature resistant gaskets and the carbon paper sealing ring are made of silica gel or polydimethylsiloxane. The thickness of the upper and lower high-temperature resistant gaskets is the same as the depth of their micro-channels and less than 1 mm.

[0017] Preferably, PTFE is sprayed on the hydrophobic surface of the hydrophobic and breathable carbon paper, or Teflon dispersed in an ethanol solution is sprayed and calcined at 360 °C for 1 hour.

[0018] Spray a hydrophobic material on a porous conductive material carbon paper at the scale of hundreds of micrometers. It can be used as an electrowetting electrode, block liquids, allow gases to pass through, inhibit bubble formation, and prevent the gas film from covering the gas-liquid surface.

[0019] Preferably, the cover plate is made of semiconductor silicon, germanium, or high-temperature resistant polyether ether ketone, polycarbonate, or polymethyl methacrylate. Description of the Drawings

[0020] Figure 1 It is a deconstructed view of the microchannel.

[0021] Figure 2 It is a side view of the microchannel.

[0022] Figure 3 It is a side view of the hydrophobic dielectric electrode.

[0023] Figure 4 It is an array layout diagram of the electrodes.

[0024] Figure 5 It is an alternating layout diagram of the electrodes.

[0025] Figure 6 It is a side view of the hydrophobic breathable carbon paper.

[0026] Figure 7 It is a structural diagram of the lower high-temperature resistant gasket.

[0027] Figure 8 It is a structural diagram of the upper high-temperature resistant gasket.

[0028] Figure 9 It is a structural diagram of the carbon paper sealing ring.

[0029] Figure 10 It is a structural diagram of the cover plate. Detailed Embodiments

[0030] The technical solution of the present invention will be specifically described below with reference to the drawings.

[0031] The deconstruction of the microchannel is as Figure 1 shown. From bottom to top, there are a substrate 1, a lower high-temperature resistant gasket 2, a hydrophobic breathable carbon paper 3, an upper high-temperature resistant gasket 5, and a cover plate 6 in sequence. A carbon paper sealing ring 4 is arranged around the hydrophobic breathable carbon paper 3.

[0032] The side view of the microchannel is as Figure 2 shown. A hydrophobic dielectric electrode 10 is arranged on the surface of the substrate 1 and connected to the positive pole of the power supply, and the hydrophobic breathable carbon paper 3 is connected to the negative pole of the power supply.

[0033] The side view of the hydrophobic dielectric electrode 10 is as Figure 3As shown in the figure, from bottom to top, there is a 1-2 μm thick silica insulating layer 11 prepared by plasma enhanced chemical vapor deposition and thermal oxidation processes, a 50-200 nm thick gold and aluminum electrode 12 prepared by photolithography and lift-off processes, an alumina dielectric layer 13 with a high dielectric constant and a high thermal conductivity deposited by atomic deposition technology, a 100-300 nm thick Teflon hydrophobic layer 14 spin-coated, and different thicknesses are flexibly designed according to specific electrowetting driving conditions and heat dissipation requirements.

[0034] Each electrode 12 is individually connected to a power supply, and the arrangement is an array layout with the same size, such as Figure 4 shown, or an alternating layout with different sizes, such as Figure 5 shown.

[0035] The side view of the hydrophobic and breathable carbon paper 3 is as Figure 6 shown. The upper surface is the breathable surface, and the lower surface is the hydrophobic surface 30. PTFE is sprayed, or Teflon dispersed in an ethanol solution is sprayed and calcined at 360 °C for 1 hour.

[0036] The structure of the lower high-temperature resistant gasket 2 is as Figure 7 shown, with microchannels set. The structure of the upper high-temperature resistant gasket 5 is as Figure 7 shown, with microchannels, a water inlet 51, and a water outlet 52 set. The microchannel parts of the upper and lower high-temperature resistant gaskets overlap, and the thickness is consistent with the depth of its microchannel and less than 1 mm, and high-temperature resistant silicone and polydimethylsiloxane are used.

[0037] The carbon paper seal ring 4 is made of high-temperature resistant silicone and polydimethylsiloxane, and the structure is as Figure 9 shown, with a water inlet 41 and a water outlet 42 set. The cover plate 6 is made of semiconductor silicon, germanium, or high-temperature resistant polyether ether ketone, polycarbonate, polymethyl methacrylate, and the structure is as Figure 10 shown, with a water inlet 61, a water outlet 62, and an exhaust hole 63 set.

[0038] The water inlets and outlets of the cover plate 6, the upper high-temperature resistant gasket 5, and the carbon paper seal ring 4 are respectively communicated with the microchannels of the lower high-temperature resistant gasket 2, and the exhaust hole of the cover plate 6 is communicated with the microchannels of the upper high-temperature resistant gasket 5, as Figure 1 shown.

[0039] The liquid flows into the microchannels of the lower high-temperature resistant gasket 2 from the water inlet, absorbs heat and undergoes boiling phase change to generate bubbles and a gas-liquid interface. By using the electrowetting effect, adjusting the alternating current, dynamically changing the contact angle of the gas-liquid interface and performing periodic oscillation, the generated bubbles pass through the hydrophobic and breathable carbon paper 3 and enter the microchannels of the upper high-temperature resistant gasket 5, and are discharged from the exhaust hole of the cover plate 6, achieving the effects of enhancing boiling phase change heat transfer and suppressing flow instability.

[0040] The above embodiments of the present invention do not limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention are all included within the protection scope of the present invention.

Claims

1. A heat exchanger for enhancing flow boiling phase change based on the principle of alternating current electrowetting, characterized in that: include: From bottom to top, they are substrate, lower high temperature resistant gasket, hydrophobic breathable carbon paper, upper high temperature resistant gasket, and cover plate. The upper surface of the hydrophobic breathable carbon paper is a breathable surface, the lower surface is a hydrophobic surface, and a carbon paper sealing ring is arranged around it. The upper and lower high temperature resistant gaskets are provided with microchannels and partially overlap. The carbon paper sealing ring, the upper high temperature resistant gasket, and the cover plate are respectively provided with a water inlet and a water outlet. The water inlet, the water outlet and the microchannel of the lower high temperature resistant gasket are connected. The cover plate is provided with an exhaust hole and is connected with the microchannel of the upper high temperature resistant gasket. The substrate is connected to the positive pole of AC power, and the hydrophobic breathable carbon paper is connected to the negative pole of AC power.

2. The heat exchanger for enhanced flow boiling phase change based on the alternating current electrowetting principle according to claim 1 is characterized in that: The substrate is made of insulating silicon or germanium with high thermal conductivity.

3. The heat exchanger for enhanced flow boiling phase change based on the alternating current electrowetting principle according to claim 1 is characterized in that: A hydrophobic dielectric electrode is arranged on the surface of the substrate, including: an insulating layer, an electrode, a dielectric layer, and a hydrophobic layer from bottom to top, and each electrode is individually connected to a power source.

4. The heat exchanger for enhanced flow boiling phase change based on the alternating current electrowetting principle according to claim 3 is characterized in that: The insulating layer comprises: a silicon dioxide insulating layer with a thickness of 1 to 2 microns prepared by plasma enhanced chemical vapor deposition and thermal oxidation processes.

5. The heat exchanger for enhanced flow boiling phase change based on the alternating current electrowetting principle according to claim 3 is characterized in that: The electrodes include: gold and aluminum electrodes with a thickness of 50 to 200 nanometers prepared by photolithography and stripping processes, and arranged in an array arrangement of the same size or an alternating arrangement of different sizes.

6. The heat exchanger for enhanced flow boiling phase change based on the alternating current electrowetting principle according to claim 3 is characterized in that: The dielectric layer comprises: an aluminum oxide dielectric layer with high dielectric constant and high thermal conductivity deposited by atomic deposition technology.

7. The heat exchanger for enhanced flow boiling phase change based on the alternating current electrowetting principle according to claim 1 is characterized in that: The hydrophobic layer comprises: a Teflon hydrophobic layer with a thickness of 100 to 300 nanometers which is spin-coated.

8. The heat exchanger for enhanced flow boiling phase change based on the alternating current electrowetting principle according to claim 1 is characterized in that: The upper and lower high temperature resistant gaskets and the carbon paper sealing ring are made of silicone and polydimethylsiloxane. The thickness of the upper and lower high temperature resistant gaskets is consistent with the depth of the microchannels and is less than 1 mm.

9. The heat exchanger for enhanced flow boiling phase change based on the alternating current electrowetting principle according to claim 1 is characterized in that: The hydrophobic and breathable carbon paper comprises: a hydrophobic surface sprayed with PTFE or Teflon dispersed in an ethanol solution, and calcined at 360° C. for 1 hour.

10. The heat exchanger for enhanced flow boiling phase change based on the alternating current electrowetting principle according to claim 1, characterized in that: The cover plate comprises: semiconductor silicon, germanium or high temperature resistant polyetheretherketone, polycarbonate, polymethyl methacrylate.

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