Controllable spray droplet efficient cooling and heat transfer experimental platform

Abstract

The present invention discloses a controllable spray droplet efficient cooling and heat exchange experimental platform, including a droplet generating device, multiple groups of piezoelectric droplet generators that can realize droplet string arrays; a thin film heater located at the downstream end of the piezoelectric droplet generator process, the thin film heater is prepared using a magnetron sputtering process, the thin film heater uses a 500μm double-polished silicon wafer as a substrate, and a metal platinum film is magnetron sputtered on the substrate using a magnetron sputtering process; and an optical imaging and temperature measurement system. The experimental platform of the present invention is designed based on multiple groups of piezoelectric droplet generators, and can capture and accurately measure both the temperature field and the flow field. The advanced droplet generator achieves a droplet flow rate that the existing single group of droplets does not have, while also taking into account accuracy and controllability. The designed microchip thin film heater reduces resistance error and experimental error, and the heat loss is less than 1%. This experimental platform has an important impact on the exploration of droplet physics and the field of efficient heat exchange of continuous droplets.

Description

Technical Field

[0001] The present invention relates to the multidisciplinary cross-technical field of microfluidics, high-efficiency heat exchange technology, and MEMS micro-electromechanical processing technology, and in particular to a controllable spray droplet high-efficiency cooling and heat exchange experimental platform based on a high-precision droplet generator, a high-precision thin film heater (microchip), optical high-speed shooting technology, and high-precision infrared temperature measurement technology. Background Art

[0002] In recent years, the performance of electronic devices such as supercomputers and the gradual miniaturization of chips have increased the difficulty of heat dissipation under high heat flux density. Continuous droplets have more efficient cooling than jets and are more controllable than sprays. After detailed research on the fluid dynamics and heat transfer process from a single group of droplets to an array of droplets impacting the heated surface under constant heat flux experimental conditions, due to the continuous miniaturization and performance of electronic devices, the heat load has increased so rapidly that the thermal management problem of electronic devices remains severe.

[0003] Higher heat flux will lead to challenges in the safety and life of electronic systems. At present, many cutting-edge researches rely on removing a large amount of heat in a small area. In the future, the high heat flux density will be on the order of 10 2 -10 3 W / cm 2 In some superconducting circuits, the heat flux density can reach 600w W / cm 2 Therefore, the demand for more innovative cooling technologies is more urgent.

[0004] Research on sprays and jets has matured over the past few decades, and both jet impingement cooling and spray cooling are widely used in the field of high-efficiency cooling. Both jets and sprays are produced by passing fluid through small orifices. The spray is broken into dispersed, smaller droplets before impacting the surface and coating the heat transfer surface. Compared to jets, spray cooling offers significant advantages in uniformity and heat transfer capacity, and is therefore considered the optimal cooling method for high heat flux applications in the future. While spray cooling offers many advantages, it also has its own drawbacks. For example, compared to jets, spray cooling has an uncertain coverage area; droplet size and quantity cannot be precisely controlled; and there is randomness associated with droplet collisions.

[0005] Although some studies have focused on the heat transfer performance of controllable continuous droplets, they are still based on single-group droplet string tests. Due to the limitations of droplet generator technology, they have not been extended to the effects of large numbers and regular arrays of continuous droplet strings on heat transfer.

[0006] Therefore, based on the integrated piezoelectric multi-group uniform droplet generator of the Chinese invention patent with authorization announcement number CN1147749219B in the prior art, technical personnel in this field urgently need to develop a controllable spray droplet efficient cooling and heat exchange experimental platform based on high-precision droplet generator, high-precision thin film heater (microchip), optical high-speed shooting technology and high-precision infrared temperature measurement technology. Summary of the Invention

[0007] The purpose of the present invention is to provide a controllable spray droplet efficient cooling and heat exchange experimental platform. The platform is based on a high-precision droplet generator, a high-precision thin film heater (microchip), optical high-speed photography technology and high-precision infrared temperature measurement technology. The precise microfluidics of multiple columns of droplet emitters provides technical guarantees for high-precision controllable spray cooling.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] The controllable spray droplet efficient cooling and heat exchange experimental platform of the present invention comprises:

[0010] A droplet generating device, comprising a constant temperature water bath and a piezoelectric droplet generator connected to the constant temperature water bath, wherein a plurality of the piezoelectric droplet generators are arranged in an array;

[0011] A thin film heater located at the downstream end of the piezoelectric droplet generator process, wherein the thin film heater is manufactured by a magnetron sputtering process, wherein the thin film heater uses a 500 μm double-polished silicon wafer as a substrate, and a metal platinum film is magnetron sputtered on the substrate by a magnetron sputtering process; and

[0012] Optical imaging and temperature measurement system;

[0013] The optical imaging and temperature measurement system collects temperature data of the thin film heater through an infrared camera, transmits the collected photos to a computer to obtain a time-averaged temperature field, and performs post-processing of the time-averaged temperature field through Matlab code to obtain a temperature field cloud map.

[0014] Furthermore, the constant temperature water bath is connected to the piezoelectric droplet generator via a peristaltic pump and a flow meter;

[0015] The cooling liquid transported by the constant temperature water bath to the piezoelectric droplet generator is pure fluid, and the pure fluid is deionized water.

[0016] Furthermore, the piezoelectric droplet generator is electrically connected to a signal generator, and the signal generator is electrically connected to the piezoelectric droplet generator via a power amplifier;

[0017] The signal generator sends a square wave signal, the square wave signal is amplified by the power amplifier, and drives the piezoelectric module on the wall of the piezoelectric droplet generator to vibrate at a high frequency to generate continuous droplets.

[0018] Furthermore, the height of the piezoelectric droplet generator relative to the thin film heater is adjusted by a vertical automatic lifting platform.

[0019] Furthermore, the process flow of the magnetron sputtering heating layer of the thin film heater mainly includes the following steps: Figure 7 :

[0020] S101, cut out a double-polished silicon wafer with a size of 14mm*14mm, and mask the upper and lower sides with brown film to form a metal sputtering area of ​​14mm*10mm;

[0021] S102, turn on the cooling water, turn the chamber door lock upside down, then open the vent valve to release air, turn the flow meter panel channel "ON", open the air valve and clean the air pipe, and wait for the vacuum to reach 5.0*10 1 After pa, open the solenoid valve, open the baffle controller, and wait until the vacuum reaches 1.9*10 1 After pa, run the molecular pump, close the roughing valve after the molecular pump panel displays the speed, open the high valve to the maximum position, and the vacuum is generally pumped to 5.0*10 -3 pa or 3.0*10 -3 pa started the coating experiment;

[0022] S103, turning on the turntable, first, plating a metal chromium film, turning on the thermal controller to set the substrate temperature to 80°C, the diameter of the chromium metal target to 10 cm, the sputtering gas pressure to 0.2 Pa, installing a magnetron sputtering power supply on the corresponding target, turning on the magnetron sputtering power supply, keeping the baffle closed, and adjusting the power value through the knob to perform pre-sputtering. The power value is set to 200-400W for high-power sputtering, and the sputtering time is 50-120s. A chromium film with a thickness of less than 50nm is obtained on the silicon wafer as a connecting layer;

[0023] S104, chromium film is the key bonding film connecting platinum and semiconductor silicon. After the chromium film deposition is completed, the sputtering pressure remains unchanged, the substrate temperature remains unchanged, the power is changed to 150-300w, and the sputtering time is 90s. After completion, the resistance is measured by the four-probe measurement method to be 7Ω / cm 2 , the error of the measured resistance value of the same batch is within 0.05Ω;

[0024] S105. Mask the double-polished silicon wafer again, cover the central platinum area of ​​10mm*10mm with the mask, and perform step S103 to magnetron sputter a gold film. The sputtering pressure is set to 0.3Pa, the power is set to 50-150W, the time is 10min, and the film thickness is 500nm.

[0025] Furthermore, the thin film heater has a PCB circuit board;

[0026] The overall size of the PCB circuit board is 1.8cm*1.8cm, and the middle of the PCB circuit board is cut in a V-shape to form a cutting groove with a size of 1.3cm*1.3cm;

[0027] The PCB circuit board has four rectangular pads, two of the pads close to the outer side of the PCB circuit board have a width of 500 μm, and two of the pads close to the inner side of the PCB circuit board have a width of 200 μm. The copper coating thickness of the pads is more than 1 oz.

[0028] Furthermore, the welding and packaging process of the PCB circuit board and the silicon wafer prepared by the magnetron sputtering process is:

[0029] The PCB circuit board is first bonded to the silicon wafer produced by the magnetron sputtering process using conductive silver glue, and then the silicon wafer and PCB are packaged using a gold wire bonding process, with multiple 25μm gold wires used for packaging in both passes.

[0030] Furthermore, the experimental platform is also provided with a high-speed camera connected to the computer;

[0031] An LED light source and a diffuser are provided on one side of the high-speed camera. The high-speed camera is equipped with an AF Nikon zoom lens, and the magnification ratio of the high-speed camera is 1:1 to capture the flow field of the piezoelectric droplet generator, the continuous droplet breakup of the arranged droplet string, and the corresponding impact state under low heat flux density.

[0032] Furthermore, the optical imaging light path arrangement method of the experimental platform is:

[0033] S101. In order to capture a clear flow field, an optical right-angle prism with a surface coating that highly reflects visible light is used to obtain a higher reflectivity.

[0034] S102, use Leica double-head high-power gooseneck lamp with a 30-degree angle to the plane for bilateral lighting;

[0035] S103. In order to ensure that the process of droplets impacting the surface can be cleaned and captured, the high-speed camera is set to a frame rate of 5000 or more.

[0036] Furthermore, in the infrared temperature measurement system of the experimental platform, the infrared camera uses a zoom lens, and the resolution of the infrared camera is 512*512, and a right-angle reflecting prism coated with a highly reflective infrared film is used; by cropping the frame to obtain a larger viewing area and ensuring that the single pixel size is less than 500um, a series of photos are obtained when the entire cooling system is in a stable state, and then the temperature fields of multiple pictures are averaged using the Matlab image processing method to represent the average temperature under this working condition.

[0037] In the above technical solution, the controllable spray droplet efficient cooling and heat exchange experimental platform provided by the present invention has the following beneficial effects:

[0038] The experimental platform of the present invention is designed based on a piezoelectric droplet generator, which can capture and accurately measure both the temperature field and the flow field. The advanced droplet generator achieves precision and controllability that existing single-group droplets do not have. The designed microchip thin-film heater reduces resistance error and experimental error, and the heat loss is less than 1%. This experimental platform has an important impact on the exploration of droplet physics and the field of efficient heat exchange of continuous droplets. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments described in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0040] Figure 1 A system principle block diagram of a controllable spray droplet efficient cooling and heat exchange experimental platform provided by an embodiment of the present invention;

[0041] Figure 2 Schematic diagram of a 5*5 square-arranged droplet train for the controllable spray droplet efficient cooling and heat exchange experimental platform provided by an embodiment of the present invention;

[0042] Figure 3 Schematic diagram of a 7*7 square-arranged droplet train for a controllable spray droplet efficient cooling and heat exchange experimental platform provided by an embodiment of the present invention;

[0043] Figure 4 Schematic diagram of a 10*10 square-arranged droplet train for a controllable spray droplet efficient cooling and heat exchange experimental platform provided by an embodiment of the present invention;

[0044] Figure 5 A schematic diagram of the thin film heater structure of the controllable spray droplet efficient cooling and heat exchange experimental platform provided by an embodiment of the present invention;

[0045] Figure 6A schematic diagram of the structure of a PCB circuit board for a controllable spray droplet efficient cooling and heat exchange experimental platform provided by an embodiment of the present invention;

[0046] Figure 7 Schematic diagram of the process flow of the magnetron sputtering heating layer of the thin film heater of the controllable spray droplet efficient cooling and heat exchange experimental platform provided by an embodiment of the present invention.

[0047] Description of reference numerals:

[0048] 1. Constant temperature water bath; 2. Peristaltic pump; 3. Flow meter; 4. Piezoelectric droplet generator; 5. Vertical automatic lift platform; 6. LED light source; 7. Diffuser; 8. DC power supply; 9. Thin film heater; 10. Infrared reflective prism; 11. Infrared camera; 12. Power amplifier; 13. Signal generator; 14. High-speed camera; 15. Computer; 16. PCB circuit board;

[0049] 1601, pad. DETAILED DESCRIPTION

[0050] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0051] See also Figures 1 to 7 As shown;

[0052] This embodiment discloses a controllable spray droplet efficient cooling and heat exchange experimental platform, which includes:

[0053] A droplet generating device, the droplet generating device includes a constant temperature water bath 1 and a piezoelectric droplet generator 4 connected to the constant temperature water bath 1, wherein a plurality of piezoelectric droplet generators 4 are arranged in an array;

[0054] Thin-film heater 9, located downstream of piezoelectric droplet generator 4, is fabricated using a magnetron sputtering process. Using a 500μm double-polished silicon wafer as its substrate, platinum film is magnetron sputtered onto the substrate. This results in significantly higher heating uniformity than conventional resistance-wire distributed heaters, with a uniformity error of only ±0.2°C across the entire heating surface.

[0055] Optical imaging and temperature measurement system;

[0056] The optical imaging and temperature measurement system collects temperature data of the thin film heater 9 through the infrared camera 11, and transmits the collected photos to the computer 15 to obtain the time-averaged temperature field. The time-averaged temperature field is post-processed by Matlab code to obtain a temperature field cloud map.

[0057] This application is based on the applicant's previously applied and authorized patent, with the authorization announcement number CN114749219B, and the Chinese invention patent named "Integrated Piezoelectric Uniform Droplet Generator". It uses a multi-column droplet generator to achieve precise microfluidics, and can generate multiple groups of droplet strings of any size to provide technical guarantees for high-precision controllable spray cooling. At the same time, the experimental platform of this embodiment is designed with a high-precision thin film heater. It is designed and manufactured using advanced MEMS technology to produce a high current and high heat flux density thin film heater that can strictly control the heating area. It is of great significance for high-precision experiments and is conducive to thermal analysis. Finally, a high-precision and stable fluid transportation system, an optical acquisition system, and an infrared temperature measurement system are configured to achieve the design purpose of efficient cooling of controllable spray droplets.

[0058] The specific structure and principle of the piezoelectric droplet generator 4 can be found in the Chinese invention patent with authorization announcement number CN114749219B, entitled "Integrated Piezoelectric Uniform Droplet Generator", and its structure and principle will not be described here in detail.

[0059] Preferably, for the liquid transport and droplet generation system, the liquid transport system of this embodiment mainly includes a Hengwei water bath 1, specifically: the constant temperature water bath 1 is connected to the piezoelectric droplet generator 4 through a peristaltic pump 2 and a flow meter 3;

[0060] The cooling liquid transported by the constant temperature water bath 1 to the piezoelectric droplet generator 4 is pure fluid, and the pure fluid is deionized water.

[0061] The above-mentioned piezoelectric droplet generator 4 is used to prepare dispersed droplets arranged in a multi-structure. According to the above definition, the cooling liquid transported by the constant temperature water bath 1 to the piezoelectric droplet generator 4 is a pure fluid such as deionized water; secondly, the piezoelectric droplet generator 4 of this embodiment is electrically connected to a signal generator 13, and the signal generator 13 is electrically connected to the piezoelectric droplet generator 4 through a power amplifier 12; the signal generator 13 emits a square wave signal, which is amplified by the power amplifier 12 and drives the piezoelectric module on the wall of the piezoelectric droplet generator 4 to vibrate at a high frequency to generate continuous droplets. Due to the Plateau-Rayleigh instability mechanism, the jet will break into continuous droplets, and the outlet orifice plate can be designed from 1 to 100 holes by itself. This application only uses array forms of 25, 49, and 100 as examples for further explanation and illustration. The holes in this embodiment are first drilled using a micro-drill, followed by a plasma polishing and cleaning process. Compared to traditional processes, this method has been repeatedly verified to avoid the tapered hole problem associated with laser drilling and achieve a high dimensional accuracy (aperture ±0.1%). The entire hole is burr-free and high-quality.

[0062] To ensure the quality and quantity of droplets and the stability of droplet generation, the height of the droplet generator 4 in the array of 25, 49, and 100 groups is controlled at 20-100mm from the thin film heater 9. Through actual testing, the error between the number of continuous droplets generated and the set frequency is within ±0.03%. Figures 2 to 4 The droplet generator produces real pictures of droplets, with the maximum number of droplets exceeding one million per second.

[0063] This embodiment uses multiple columns of droplet generators, and a single droplet generator can achieve an array effect. In addition, each column of jet droplets operates more stably and has a better breakup effect. Compared with pneumatic droplet generators, it has a wider range of applications and better effects. The droplet generator of this embodiment is inexpensive and has a wide range of applications. By using jet sheets instead of nozzles, there is no need to replace fixed nozzles multiple times, which makes operation simple and cost-effective.

[0064] In order to facilitate height adjustment, the piezoelectric droplet generator 4 of this embodiment is adjusted in height relative to the thin film heater 9 via a vertical automatic lifting platform 5 .

[0065] See also Figure 5 As shown, the thin film heater 9 of this embodiment has an overall size of 1.8cm*1.8cm*2mm. Through the PCB circuit board and corresponding processing, the thin film heater 9 can achieve a maximum current of 35A, thus achieving high power. The magnetic current flux is not common in general electronic components. Furthermore, the PCB and the magnetron sputtering thin film gold layer are bonded using gold wire, which allows for precise control of the heating area. The target heating area of ​​the thin film heater 9 of this embodiment is 10mm*10mm, with a left and right side length error within ±25μm.

[0066] Preferably, the process flow of the magnetron sputtering heating layer of the thin film heater 9 of this embodiment mainly includes the following steps:

[0067] S101, cut out a double-polished silicon wafer with a size of 14mm*14mm, and mask the upper and lower sides with brown film to form a metal sputtering area of ​​14mm*10mm;

[0068] S102, turn on the cooling water, turn the chamber door lock upside down, then open the vent valve to release air, turn the flow meter panel channel "ON", open the air valve and clean the air pipe, and wait for the vacuum to reach 5.0*10 1 After pa, open the solenoid valve, open the baffle controller, and wait until the vacuum reaches 1.9*10 1 After pa, run the molecular pump, close the roughing valve after the molecular pump panel displays the speed, open the high valve to the maximum position, and the vacuum is generally pumped to 5.0*10 -3 pa or 3.0*10 -3 pa started the coating experiment;

[0069] S103, turning on the turntable, first, plating a metal chromium film, turning on the thermal controller to set the substrate temperature to 80°C, the diameter of the chromium metal target to 10 cm, the sputtering gas pressure to 0.2 Pa, installing a magnetron sputtering power supply on the corresponding target, turning on the magnetron sputtering power supply, keeping the baffle closed, and adjusting the power value through the knob to perform pre-sputtering. The power value is set to 200-400W for high-power sputtering, and the sputtering time is 50-120s. A chromium film with a thickness of less than 50nm is obtained on the silicon wafer as a connecting layer;

[0070] S104, chromium film is the key bonding film connecting platinum and semiconductor silicon. After the chromium film deposition is completed, the sputtering pressure remains unchanged, the substrate temperature remains unchanged, the power is changed to 150-300w, and the sputtering time is about 90s. After completion, the resistance is measured by the four-probe measurement method to be 7Ω / cm 2 , the error of the measured resistance value of the same batch is within 0.05Ω;

[0071] S105. Mask the double-polished silicon wafer again, cover the central platinum area of ​​10mm*10mm with the mask, and perform step S103 to magnetron sputter a gold film. The sputtering pressure is set to 0.3Pa, the power is set to 50-150W, the time is 10min, and the film thickness is about 500nm.

[0072] See also Figure 6 As shown, preferably, the film heater of this embodiment has a PCB circuit board;

[0073] The overall size of the PCB circuit board 16 is 1.8 cm*1.8 cm, and the middle of the PCB circuit board 16 is cut in a V-shape to form a cutting groove with a size of 1.3 cm*1.3 cm;

[0074] The PCB circuit board 16 has four rectangular pads 1601 , two pads 1601 close to the outside of the PCB circuit board 16 have a width of 500 μm, and two pads 1601 close to the inside of the PCB circuit board 16 have a width of 200 μm. The copper thickness of the pads 1601 is 3 oz.

[0075] The welding and packaging process of the PCB circuit board 16 and the silicon wafer prepared by the magnetron sputtering process is as follows:

[0076] The PCB circuit board 16 is first bonded to the silicon wafer produced by the magnetron sputtering process using conductive silver glue, and then the silicon wafer and the PCB are packaged using a gold wire bonding process, with several 25μm gold wires used for packaging in both passes.

[0077] Through testing, it was found that under steady-state conditions, the temperature distribution was extremely uniform, and the temperature difference across the entire test surface was less than 0.2 degrees, providing reliable support for a uniform temperature field. The preparation of this chip thin film heater strictly controlled the resistance, making it easy to measure. Compared with existing similar thin film heaters 9, it had higher accuracy, and the heat loss was less than 1% through testing.

[0078] In addition, the experimental platform of this embodiment is also provided with a high-speed camera 14 connected to a computer 15;

[0079] An LED light source 6 and diffuser 7 are positioned to one side of a high-speed camera 14. The camera, equipped with an AF Nikon zoom lens and boasting a 1:1 magnification, captures the flow field of the piezoelectric droplet generator 4, including the continuous droplet breakup and impact conditions under low heat flux. Images are also captured of continuous droplet arrays of 5*5, 7*7, and 10*10, as well as the flow field morphology of the impact surface.

[0080] The temperature of this system is collected by a side-mounted infrared camera 11 (FLIR SC7000) through a reflective prism 10. The reflective prism 10 is gold-coated and held by optical components, providing excellent infrared reflection, with a reflection efficiency exceeding 0.95. The infrared wavelength of the heater falls within the post-infrared spectral range (2-5.1μm). The infrared camera 11 has a resolution of 640*512, and a single bin size of 16μm. For the tested temperature range, an integration time of 1143μs, a collection frequency of 115Hz, and a collection time of 4s allow for the acquisition of 460 images. The resulting images are then used to calculate the time-averaged temperature field using software functions. Matlab code is then used to perform temperature field post-processing to produce a temperature field cloud map.

[0081] Secondly, the optical imaging light path arrangement method of the experimental platform is:

[0082] S101. In order to capture a clear flow field, an optical right-angle prism with a surface coating that highly reflects visible light is used to obtain a higher reflectivity.

[0083] S102, use Leica double-head high-power gooseneck lamp with a 30-degree angle to the plane for bilateral lighting;

[0084] S103 , in order to ensure that the process of droplets impacting the surface can be cleaned and captured, the high-speed camera 14 is set to a frequency of 5000 frames or more.

[0085] In the infrared temperature measurement system of this experimental platform, the infrared camera 11 uses a zoom lens, and the resolution of the infrared camera 11 is 512*512. In order to obtain a clear infrared temperature field at the bottom, a right-angle reflection prism coated with a highly reflective infrared film is used; by cropping the frame to obtain a higher viewing area and ensuring that the single pixel size is less than 500um, a series of photos are obtained when the entire cooling system is in a stable state, and then the temperature fields of multiple pictures are averaged using the Matlab image processing method to represent the average temperature under this working condition.

[0086] In the above technical solution, the controllable spray droplet efficient cooling and heat exchange experimental platform provided by the present invention has the following beneficial effects:

[0087] The experimental platform of the present invention is designed based on a piezoelectric droplet generator 4, which can capture and accurately measure both the temperature field and the flow field. The advanced droplet generator achieves precision and controllability that existing single-group droplets do not have. The designed microchip thin-film heater reduces resistance error and experimental error, and the heat loss is less than 1%. This experimental platform has an important impact on the exploration of droplet physics and the field of efficient heat exchange of continuous droplets.

[0088] The above description is merely illustrative of certain exemplary embodiments of the present invention. It goes without saying that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims.

Claims

1. Controllable spray droplet efficient cooling and heat exchange experimental platform, characterized by: The experimental platform includes: A droplet generating device, comprising a constant temperature water bath (1) and a piezoelectric droplet generator (4) connected to the constant temperature water bath (1), wherein a plurality of the piezoelectric droplet generators (4) are arranged in an array; a thin film heater (9) located at the downstream end of the piezoelectric droplet generator (4), wherein the thin film heater (9) is prepared by a magnetron sputtering process, wherein the thin film heater (9) uses a 500 μm thick double-polished silicon wafer as a substrate, and a metal platinum film is magnetron sputtered on the substrate by a magnetron sputtering process; and Optical imaging and temperature measurement system; The optical imaging and temperature measurement system collects temperature data of the thin film heater (9) through an infrared camera (11), transmits the collected photos to a computer (15) to obtain a time-averaged temperature field, and performs post-processing of the time-averaged temperature field through Matlab code to obtain a temperature field cloud map; The process flow of the magnetron sputtering heating layer of the thin film heater (9) mainly includes the following steps: S101, cut out a double-polished silicon wafer with a size of 14mm*14mm, and mask the upper and lower sides with brown film to form a metal sputtering area of ​​14mm*10mm; S102, turn on the cooling water, turn the chamber door lock upside down, then open the vent valve to release air, turn the flow meter panel channel "ON", open the air valve and clean the air pipe, and wait for the vacuum to reach 5.0*10 1 After pa, open the solenoid valve, open the baffle controller, and wait until the vacuum reaches 1.9*10 1 After pa, run the molecular pump, close the roughing valve after the molecular pump panel displays the speed, open the high valve to the maximum position, and the vacuum is generally pumped to 5.0*10 -3 pa or 3.0*10 -3 pa started the coating experiment; S103, turning on the turntable, first, plating a metal chromium film, turning on the thermal controller to set the substrate temperature to 80°C, the diameter of the chromium metal target to 10 cm, the sputtering gas pressure to 0.2 Pa, installing a magnetron sputtering power supply on the corresponding target, turning on the magnetron sputtering power supply, keeping the baffle closed, and adjusting the power value through the knob to perform pre-sputtering. The power value is set to 200-400W for high-power sputtering, and the sputtering time is 50-120s. A chromium film with a thickness of less than 50nm is obtained on the silicon wafer as a connecting layer; S104, chromium film is the key bonding film connecting the platinum layer and semiconductor silicon. After the chromium film deposition is completed, the sputtering pressure remains unchanged, the substrate temperature remains unchanged, the power is changed to 150-300w, and the platinum layer sputtering time is 90s. After completion, the resistance is measured by the four-probe measurement method to be 7Ω / cm 2 , the error of the measured resistance value of the same batch is within 0.05Ω; S105, masking the double-polished silicon wafer again, with the mask covering a 10 mm*10 mm area of ​​the central platinum layer, and performing step S103 to magnetron sputter a gold film, with the sputtering pressure set to 0.3 Pa, the power set to 50-150 W, the time set to 10 min, and the film thickness set to 500 nm; The thin film heater (9) has a PCB circuit board (16); The overall size of the PCB circuit board (16) is 1.8 cm*1.8 cm, and a V-shaped cut is adopted in the middle of the PCB circuit board (16) to form a cutting groove with a size of 1.3 cm*1.3 cm; The PCB circuit board (16) has four rectangular pads (1601), two of the pads (1601) close to the outside of the PCB circuit board (16) have a width of 500 μm, and two of the pads (1601) close to the inside of the PCB circuit board (16) have a width of 200 μm, and the copper coating thickness of the pads (1601) is more than 1 oz; The welding packaging process of the PCB circuit board (16) and the magnetron sputtering heating layer is as follows: The PCB circuit board (16) is first bonded to the magnetron sputtering heating layer using conductive silver glue, and then the magnetron sputtering heating layer and the PCB are packaged using a gold wire bonding process, with multiple 25μm gold wires on each side for packaging.

2. The controllable spray droplet efficient cooling and heat exchange experimental platform according to claim 1 is characterized in that: The constant temperature water bath (1) is connected to the piezoelectric droplet generator (4) via a peristaltic pump (2) and a flow meter (3); The cooling liquid transported by the constant temperature water bath (1) to the piezoelectric droplet generator (4) is a pure fluid, and the pure fluid is deionized water.

3. The controllable spray droplet efficient cooling and heat exchange experimental platform according to claim 2 is characterized in that: The piezoelectric droplet generator (4) is electrically connected to a signal generator (13), and the signal generator (13) is electrically connected to the piezoelectric droplet generator (4) via a power amplifier (12); The signal generator (13) emits a square wave signal, the square wave signal is amplified by the power amplifier (12), and drives the piezoelectric module on the wall of the piezoelectric droplet generator (4) to vibrate at a high frequency to generate continuous droplets.

4. The controllable spray droplet efficient cooling and heat exchange experimental platform according to any one of claims 1 to 3, characterized in that: The height of the piezoelectric droplet generator (4) relative to the thin film heater (9) is adjusted by a vertical automatic lifting platform (5).

5. The controllable spray droplet efficient cooling and heat exchange experimental platform according to claim 1 is characterized in that: The experimental platform is also provided with a high-speed camera (14) connected to the computer (15); An LED light source (6) and a diffuser (7) are provided on one side of the high-speed camera (14). The high-speed camera (14) is equipped with an AF nikon zoom lens, and the magnification of the high-speed camera (14) is 1:1 to photograph the flow field of the piezoelectric droplet generator (4), the continuous droplet breakup of the arranged droplet string, and the corresponding impact state under low heat flux density.

6. The controllable spray droplet efficient cooling and heat exchange experimental platform according to claim 1 is characterized in that: The optical imaging light path arrangement method of the experimental platform is as follows: S101. In order to capture a clear flow field, an optical right-angle prism with a surface coating that highly reflects visible light is used to obtain a higher reflectivity. S102, use Leica double-head high-power gooseneck lamp with a 30-degree angle to the plane for bilateral lighting; S103. In order to ensure that the process of droplets impacting the surface can be cleaned and captured, the high-speed camera is set to a frame rate of 5000 or more.

7. The controllable spray droplet efficient cooling and heat exchange experimental platform according to claim 1 is characterized in that: In the infrared temperature measurement system of the experimental platform, the infrared camera (11) adopts a zoom lens, and the resolution of the infrared camera (11) is 512*512, and a right-angle reflection prism coated with a high-reflection infrared film is used; by cropping the frame to obtain a higher viewing area and ensuring that the single pixel size is less than 500um, a series of photos are obtained when the entire cooling system is in a stable state, and then the temperature fields of multiple pictures are averaged by Matlab image processing method to represent the average temperature under this working condition.

Images