A device and method for impact test of single supercooled large droplets

Abstract

The application provides a single supercooled large water droplet impact test device and method, which comprises an environment control system, a supercooled water droplet generation system, a data acquisition system, a test substrate system and a shooting system. The environment control system comprises a low-temperature environment box system, a low-temperature constant-temperature tank system and a drying system; the supercooled water droplet generation system comprises a water droplet generation system and an air source system; the data acquisition system comprises a temperature acquisition system and a humidity acquisition system; the test substrate system comprises a substrate sample, an electric sliding table and a heat exchanger; and the shooting system comprises a high-speed camera, a calibration plate and a light source system. The application can realize the generation of single supercooled large water droplet, can record and measure the temperature of the supercooled water droplet, the air temperature and the substrate temperature at the same time, and can record the kinetic process of the supercooled large water droplet impacting the dry substrate.

Description

Technical Field

[0001] This application relates to an impact test device and method for a single supercooled large water droplet, belonging to the field of aircraft anti-icing. Background Technology

[0002] The impact freezing of supercooled water droplets is widespread in industries such as aviation, power, and telecommunications, posing a serious threat to flight safety and power grid security. Although supercooled water exists in a highly unstable metastable state in actual low-temperature environments, it is prevalent in the atmosphere. The freezing process of supercooled water droplets differs significantly from that of water droplets at room temperature. Therefore, studying the impact and freezing behavior of supercooled water droplets on low-temperature surfaces is beneficial for a deeper understanding of the supercooled water freezing phenomenon. The impact of supercooled water droplets on supercooled surfaces couples the droplet impact with the phase transition freezing process. Because supercooled water droplets are in a metastable state, although the phase transition process of water droplets frozen on a wall necessarily involves a supercooling stage, the generation and preparation of supercooled water droplets are relatively difficult. Considering that the significant spreading, retraction, and oscillation processes involved in droplet impact affect the morphology of water droplets in a stable state, experimental studies must consider the freezing process of supercooled water droplets under impact velocities.

[0003] Currently, the methods for preparing supercooled water droplets are mainly divided into two categories: natural convection heat transfer and forced convection heat transfer. Natural convection heat transfer involves the water droplet remaining stationary in a cold environment and undergoing continuous heat exchange; forced convection heat transfer involves the water droplet undergoing free fall within a cold environment. The methods for measuring the supercooling degree of supercooled water droplets are mainly divided into two categories: direct measurement and indirect measurement. Direct measurement uses a temperature acquisition system to directly measure the internal or surface temperature of the water droplet; indirect measurement measures the temperature of the air near the droplet or the medium in contact with the droplet, and then calculates the supercooling degree through theoretical calculations, or assumes that the indirectly measured temperature is approximately equal to the droplet's temperature. These methods provide effective means for experimentally generating supercooled water droplets and measuring their supercooling degree, but the following problems still exist:

[0004] Conventional subcooled water droplet generating devices and methods have low accuracy in measuring the subcooling degree of water droplets;

[0005] Conventional supercooled water droplet generating devices and methods cannot control ambient humidity;

[0006] Conventional subcooled water droplet generating devices and methods cannot obtain subcooled water droplets with high subcooling.

[0007] Conventional supercooled water droplet generating devices and methods are complex in structure and difficult to operate.

[0008] Although research on the impact freezing behavior of supercooled water droplets has been conducted, the design methods for supercooled water droplet generators can be further improved, and methods for measuring the supercooling of water droplets need to be supplemented. Furthermore, research considering the coupled dynamic and phase transition processes during supercooled water droplet impact is still relatively scarce. Therefore, to better study the impact mechanism of supercooled water droplets, it is essential to establish an integrated experimental device that combines supercooled water droplet generation, supercooling measurement, impact, and imaging. Summary of the Invention

[0009] The purpose of this invention is to address the above-mentioned problems by providing an impact testing device and method for a single supercooled large water droplet. By controlling the time when the supercooled water droplet is blown off, the supercooling degree of the water droplet can be precisely controlled, and the temperature of the water droplet, the ambient temperature / humidity, and the substrate temperature can be well controlled.

[0010] To achieve the above objectives, the present invention adopts the following solution:

[0011] An impact test apparatus for a single supercooled large water droplet, the apparatus comprising an environmental control system, a supercooled water droplet generation system, a data acquisition system, a test substrate system, and an imaging system;

[0012] The environmental control system includes a low-temperature environment chamber system, a low-temperature constant temperature bath subsystem, and a drying subsystem. The low-temperature environment chamber system is a coil type and uses compressor refrigeration to provide a sealed and dry low-temperature environment. The low-temperature constant temperature bath subsystem uses ethylene glycol as an external circulation medium to regulate the temperature of the test substrate. The drying subsystem uses dry nitrogen and color-changing silica gel to reduce the air humidity inside the low-temperature environment chamber.

[0013] The supercooled water droplet generation system includes a water droplet generation subsystem and an air source subsystem. The water droplet generation subsystem uses a capillary steel needle at the tip to generate a quantitative amount of water droplets. The air source subsystem uses cold air to blow the supercooled water droplets away from the thermocouple temperature sensor.

[0014] The data acquisition system includes a humidity sensor and a thermocouple sensor. The humidity sensor is used to detect the relative humidity inside the low-temperature environment chamber. The thermocouple sensor is used to monitor the temperature of water droplets, air temperature, and the surface temperature of the sample plate, respectively.

[0015] The test substrate system includes a sample substrate, an electric slide stage, and a heat exchanger, located within a low-temperature environment chamber system. The electric slide stage adjusts the position and angle of the sample substrate, and the heat exchanger adjusts the surface temperature of the sample substrate.

[0016] The imaging system includes a high-speed camera, a calibration plate, and a cold light source system. The high-speed camera is used to capture the dynamic process and phase transition process of supercooled large water droplets impacting the surface of a cold substrate. The calibration plate can be used to calculate the actual size of the water droplets.

[0017] The cold light source is used to illuminate the water droplets from behind to create a shadow pattern.

[0018] Furthermore, the low-temperature environment chamber system includes a low-temperature environment chamber, which uses a coil compressor for refrigeration. The right side of the low-temperature environment chamber has three through holes of different heights for inserting a water droplet generating subsystem.

[0019] The low-temperature constant temperature bath subsystem includes a low-temperature constant temperature bath and an aluminum heat exchanger. The low-temperature constant temperature bath is connected to the heat exchanger placed on an electric slide via a rubber tube. Ethylene glycol is used as the circulating cooling medium to cool the test substrate. The system drying subsystem uses dry nitrogen and color-changing silica gel to reduce the humidity of the air inside the low-temperature environment chamber. The nitrogen is introduced from the bottom and vented from the top. The color-changing silica gel is evenly spread on the bottom surface of the low-temperature environment chamber.

[0020] Furthermore, the water droplet generating subsystem includes a capillary steel needle, a hard aluminum rod, a syringe, a precision drive pump, and a rubber hose; the capillary steel needle is connected to the syringe via the rubber hose, the capillary steel needle and the rubber hose are embedded in the groove of the hard aluminum rod and fixed, and the drive end of the syringe is connected to the precision drive pump.

[0021] Furthermore, the air blowing subsystem includes a nozzle, a copper pipe, a cold air storage box, and a pulse air pump. The nozzle is positioned above a first thermocouple sensor and connected to the cold air storage box via a copper pipe, with the thermocouple sensor located below a stainless steel needle. The cold air storage box is located inside a low-temperature environment chamber and is connected to an externally positioned pulse air pump via a pipeline. The output end of the cold air storage box is connected to the nozzle.

[0022] Furthermore, the data acquisition system includes a humidity sensor and a thermocouple temperature sensor, wherein the humidity sensor is used to collect the relative humidity of the air inside the low-temperature environment chamber;

[0023] There are a total of four thermocouple temperature sensors used to measure the temperature of the water droplets, the air temperature, and the substrate temperature. The first thermocouple temperature sensor is located at the bottom of the water outlet of the water droplet generator and is used to measure the temperature of the suspended water droplets. The second thermocouple temperature sensor is at the same height as the first thermocouple temperature sensor and is used to measure the ambient air temperature. The third thermocouple temperature sensor is located at the substrate and is used to monitor the air temperature at the height of the sample substrate. The fourth thermocouple temperature sensor is located on the upper surface of the substrate and is used to monitor the temperature of the upper surface of the substrate.

[0024] Furthermore, the test substrate system includes a sample substrate, an electric slide stage, and a heat exchanger. The sample substrate can be replaced according to test requirements and is attached to the heat exchanger with thermally conductive adhesive. The heat exchanger is fixed on the electric slide stage and connected to a low-temperature constant temperature bath via a rubber tube. The electric slide stage is connected to an external controller, which can adjust the position and angle of the test substrate.

[0025] Furthermore, the imaging system includes a high-speed camera, a calibration plate, and a cold light source system. The high-speed camera takes pictures through an imaging window with heated glass mounted on the side of the low-temperature environment chamber. The cold light source system is located inside the low-temperature environment chamber, opposite the lens of the high-speed camera, and creates a shadow pattern to illuminate the water droplets.

[0026] Based on the aforementioned impact test apparatus for a single supercooled large water droplet, this application also provides a test method, the method comprising the following:

[0027] Step 1: Connect the instruments and equipment, and test the entire experimental setup;

[0028] Step 2: Insert the water droplet generator, release water droplets onto the substrate, place the calibration board at the water droplet drop position, adjust the high-speed camera focus on the calibration board and record the number of pixels per millimeter for data analysis and conversion of actual size.

[0029] Step 3: Add color-changing silica gel to the low-temperature environment chamber, close the low-temperature environment chamber, open the side sealing plug and nitrogen valve in sequence, and introduce dry nitrogen until the air humidity inside the chamber drops to 20%, then close the nitrogen valve and seal the side opening.

[0030] Step 4: Run the low-temperature environment chamber and set the initial temperature; run the low-temperature constant temperature bath and set the circulating liquid temperature.

[0031] Step 5: Insert the water droplet generator through the small hole on the side of the low-temperature environment chamber, turn on the precision drive pump, and observe the water droplets falling onto the thermocouple sensor through the top observation window.

[0032] Step 6: Observe the temperature change of thermocouple sensor No. 1. When the target temperature T0 is reached, the high-speed camera starts shooting. At the same time, the pulse air pump is started to blow off the supercooled water droplets hanging on the thermocouple sensor using cold air.

[0033] Step 7: A high-speed camera records the dynamic process of supercooled water droplets impacting the surface of a low-temperature substrate at a high frame rate, or records the freezing process of supercooled water droplets impacting the substrate at a low frame rate.

[0034] Furthermore, the temperatures inside the low-temperature environment chamber and the low-temperature constant temperature bath are set based on feedback from the thermocouple sensor and the subcooling degree of the target water droplet and the temperature of the target substrate.

[0035] The present invention, by adopting the above technical solution, has the following technical effects:

[0036] By regulating the air temperature inside the chamber using a low-temperature environment chamber system, the supercooling of the water droplets is well controlled.

[0037] The supercooled water droplet generation system uses a method of suspending supercooled water droplets on thermocouple sensors, which can accurately measure the supercooling degree of the supercooled water droplets and obtain supercooled water droplets with a larger supercooling degree.

[0038] The dehumidification system uses dry nitrogen and color-changing silica gel for dehumidification, which can control the humidity of the low-temperature environment chamber to below 5%, effectively preventing frost formation on the overcooled substrate.

[0039] The low-temperature constant temperature bath heat exchange system enables stable control of the temperature on the upper surface of the substrate.

[0040] The single-axis electric slide moves the substrate position, allowing multiple substrates to be placed at once, avoiding the instability of temperature / humidity inside the low-temperature environment chamber caused by repeated opening and closing.

[0041] The data acquisition system uses a high-speed camera to record the falling process of water droplets, their dynamic behavior upon impacting the substrate surface, and the phase transition process. Attached Figure Description

[0042] Figure 1 This invention provides a schematic diagram of the overall structure of an impact testing device for a single supercooled large water droplet;

[0043] Figure 2 This is a schematic diagram of a heat exchanger;

[0044] Figure 3 This is a partially enlarged schematic diagram of the supercooled water droplet generation system;

[0045] Figure 4 A schematic diagram of a slotted hard aluminum rod;

[0046] Figure 1 In the middle, 1-low temperature environment chamber, 2-pulse air pump, 3-temperature / humidity acquisition device, 4-cold light source, 5-light source controller, 6-slide stage controller, 7-low temperature constant temperature bath, 8-DC power supply, 9-high speed camera, 10-computer workstation, 11-syringe, 12-precision drive pump, 13-hard aluminum rod, 14-capillary steel needle, 16-cold air nozzle, 17-cold air storage box, 18-K-type thermocouple sensor, 19-humidity sensor, 20-substrate, 21-heat exchanger, 22-single-axis electric slide stage, 23-lifting platform, 24-heated glass, 25-nitrogen cylinder, 26-rubber stopper;

[0047] Figure 2 2.1 Refrigerant imports, 2.2 Refrigerant exports;

[0048] Figure 3 3.1 - Cold air inlet, 3.2 - Cold air outlet, 3.3 - Distilled water inlet, 3.4 - Water droplet suspended on thermocouple sensor. Detailed Implementation

[0049] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0050] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art may make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific examples disclosed herein.

[0051] Example 1

[0052] like Figures 1 to 4 As shown, this invention provides an impact testing apparatus for a single supercooled large water droplet. The invention includes an environmental control system, a supercooled water droplet generation system, a data acquisition system, a test substrate system, and an imaging system.

[0053] This application discloses a supercooled water droplet generating device with controllable supercooling, which can control the supercooling and impact velocity of the water droplets. It includes an environmental control system, a supercooled water droplet generating system, a data acquisition system, a test substrate system, and an imaging system.

[0054] The environmental control system includes a low-temperature environment chamber system, a low-temperature constant-temperature bath subsystem, and a drying subsystem. The low-temperature environment chamber system uses a coil-type compressor for refrigeration and has three 10mm diameter holes at different heights on its side for inserting a water droplet generator. The initial velocity of the water droplets can be controlled by inserting them into the holes at different heights. The top surface and sides of the low-temperature environment chamber each have 50mm diameter holes fitted with heated glass to prevent frost formation. The top surface hole is an observation hole for observing the internal conditions of the chamber during the experiment, while the side hole is for photography. The low-temperature constant-temperature bath subsystem includes a low-temperature constant-temperature bath and an aluminum heat exchanger. The low-temperature constant-temperature bath is connected to the heat exchanger, which is placed on an electric slide, via rubber tubing. Ethylene glycol is used as the circulating cooling medium to cool the test substrate. The system's drying subsystem uses dry nitrogen and color-changing silica gel to reduce the humidity of the air inside the low-temperature environment chamber. The dry nitrogen stored in the cylinder is connected to an opening on the side of the low-temperature environment chamber through a rubber tube, and the exhaust port is the insertion hole for the water droplet generator. After the test pieces are installed and debugged inside the low-temperature environment chamber, the color-changing silica gel is evenly spread on the floor of the low-temperature environment chamber, and the top cover of the low-temperature environment chamber is closed.

[0055] The supercooled water droplet generation system includes a water droplet generation subsystem and an air source subsystem. The water droplet generation subsystem includes a thermocouple sensor, a capillary needle, a rigid aluminum rod, a syringe, and a precision drive pump. The air blowing subsystem includes a nozzle, a metal tube, a cold air storage tank, and a pulse-type air pump. The precision drive pump drives the syringe, which is connected to the capillary needle via a rubber tube. The thermocouple sensor is positioned 2mm below the water outlet of the capillary needle. To prevent experimental errors caused by capillary needle wobbling, a rigid aluminum rod with a diameter of 9mm and a length of 700mm has a groove with a depth and width of 2mm cut on its side. The capillary needle is embedded in the groove and reinforced with glue. The nozzle is positioned directly above the thermocouple sensor and is connected to the cold air storage tank via a metal tube. The cold air storage tank is placed in the cold environment of a low-temperature chamber at the same height as the thermocouple sensor below the water droplet generator. The cold air storage tank is connected to the pulse-type air pump, which is located outside the low-temperature chamber, via a metal tube.

[0056] The data acquisition system includes a humidity sensor and a type K thermocouple sensor. The temperature sensor is used to collect the relative humidity of the air inside the low-temperature environment chamber. A total of four thermocouple sensors are arranged inside the chamber: the first is placed at the outlet of the water droplet generator to suspend the water droplet and measure the air / water droplet temperature; the second thermocouple sensor is positioned at the same height as the first to measure the horizontal temperature gradient of the air inside the chamber; the third thermocouple sensor is placed near the substrate to monitor the air temperature at the substrate's height; and the fourth thermocouple sensor is placed on the upper surface of the substrate to detect the substrate temperature.

[0057] The test substrate system includes a sample substrate, an electric slide stage, and a heat exchanger. The sample substrate can be replaced according to test requirements. The substrate is attached to the heat exchanger with thermally conductive adhesive, and the heat exchanger is connected to the low-temperature constant temperature chamber via rubber tubing. The electric slide stage is connected to a slide stage controller outside the low-temperature environment chamber, which allows adjustment of the position and angle of the test substrate.

[0058] The data acquisition system is a high-speed camera placed on the side of the low-temperature chamber, which takes pictures through a shooting window with heated glass on the side of the low-temperature chamber; the lighting system is a cold light source and a brightness adjuster, with the cold light source located on the opposite side of the high-speed camera lens; the data processing system is a computer workstation.

[0059] The shooting system includes a high-speed camera calibration plate and a cold light source system. The high-speed camera takes pictures through a small hole in the side of the low-temperature environment chamber with heated glass. The calibration plate is a scale with a unit graduation of 0.025mm. The cold light source system includes a cold light source and a brightness adjustment device. The cold light source is placed on the opposite side of the high-speed camera lens, and the brightness of the cold light source is adjusted according to actual needs.

[0060] The environmental control system includes a low-temperature environmental chamber 1, a heat exchanger 21, a low-temperature constant temperature bath 7, and a nitrogen cylinder 25.

[0061] The supercooled water droplet generating system includes a type K thermocouple sensor 18, a capillary steel needle 14, a hard aluminum rod 13, a syringe 11, a precision drive pump 12, a cold air nozzle 16, a cold air storage tank 17, and a pulse air pump 2.

[0062] The data acquisition system includes a type K thermocouple sensor 18, a humidity sensor 19, and a temperature / humidity data logger 3;

[0063] The test substrate system includes an electric slide table 22, a heat exchanger 21, and a test substrate 20;

[0064] The shooting system includes a high-speed camera 9, a cold light source 4, a light source controller 5, and a computer workstation 9;

[0065] Where a: length, b: width, h: height, c: wall thickness, φ: diameter, d: outer diameter

[0066] Furthermore, in the aforementioned supercooled water droplet generating system, the outer diameter of 14 is d = 1.5 mm, the diameter of 13 is φ = 9 mm, the groove width is b = 2 mm, the groove depth is h = 2 mm, the length * width * height of 17 is a * b * h = 100 mm * 50 mm * 20, and the wall thickness is c = 0.5 mm.

[0067] Furthermore, the aforementioned 21 length * width * height = a * b * h = 120mm * 35mm * 10mm.

[0068] Example 2

[0069] This invention also provides a test method based on the above-mentioned integrated test device for measuring fuel water distribution and pipeline icing amount, the method comprising the following steps:

[0070] (1) Connect the instruments and equipment, and test the entire experimental setup;

[0071] (2) Insert the water droplet generator, drop a water droplet on the test substrate, adjust the high-speed camera's focal length, aperture and cold light intensity, place the calibration board at the position of the water droplet, and take a picture of the calibration board.

[0072] (3) Add color-changing silica gel to the low-temperature environment chamber, close the top cover of the low-temperature environment chamber, open the three sealing plugs on the side of the low-temperature environment chamber, open the nitrogen valve, introduce dry nitrogen, and close the nitrogen valve after the humidity drops to 20%, and seal the three small holes on the side.

[0073] (4) Turn on the low-temperature environment chamber switch and set the initial temperature; turn on the low-temperature thermostat switch and set the circulating liquid temperature. Adjust the air temperature and substrate temperature inside the low-temperature environment chamber based on the feedback from the thermocouple sensor.

[0074] (5) Insert the water droplet generator through the small hole on the side of the low temperature environment chamber, turn on the precision drive pump, and observe through the observation window on the upper surface of the low temperature environment chamber until the water droplet falls onto the thermocouple sensor.

[0075] (6) Observe the water droplet temperature on the monitor to reach the target temperature T0, click the shutter of the high-speed camera, and at the same time start the pulse air pump to blow the supercooled water droplet suspended on the thermocouple sensor.

[0076] (7) After the experiment, turn off all the switches of the electrical system, clean the experimental device, and remove the condensate adsorbed on the walls of the low temperature environment chamber and the surfaces of all the test devices inside the low temperature environment chamber.

[0077] Specific examples:

[0078] Watson's brand distilled water was selected as the test water, with a water droplet supercooling of 4°C and a substrate temperature of -5°C. The test procedures were conducted according to the above test conditions:

[0079] (1) Connect the instruments and equipment, and test the entire experimental setup;

[0080] (2) Insert the water droplet generator, drop a water droplet on the test substrate, adjust the high-speed camera's focal length, aperture, and cold light source intensity until the image is clear, place the calibration plate at the position of the water droplet, and take a picture of the calibration plate. Remove the calibration plate and wipe the surface of the test substrate dry with a non-woven cloth.

[0081] (3) Add 1kg of color-changing silica gel to the low temperature environment chamber, close the top cover of the low temperature environment chamber, open the dry nitrogen valve, pull out the rubber plug on the side of the low temperature chamber until the humidity inside the low temperature environment chamber drops below 20%; close the nitrogen valve and plug the small hole on the side of the low temperature environment chamber with the rubber plug.

[0082] (4) Turn on the cooling switch of the low temperature environment chamber, connect the low temperature constant temperature bath, and adjust according to the temperature feedback of the thermocouple sensor until the substrate temperature reaches -5℃ and the air temperature at the water outlet of the water droplet generator reaches -4℃.

[0083] (5) Insert the hard aluminum rod with embedded capillary steel needles into the small hole on the side of the low temperature environment chamber until the water outlet of the water drop generator reaches the thermocouple sensor. Place a water drop on the thermocouple sensor. According to the temperature feedback of the thermocouple sensor, when the temperature of the water drop reaches the required level, start the pulse air pump. The water drop suspended on the thermocouple sensor will be blown off. At the same time, the high-speed camera will capture the impact process of the supercooled water drop.

[0084] (6) After the experiment, turn off all the switches of the powered systems, clean the experimental apparatus, and remove the condensate adsorbed on the walls of the low temperature environment chamber and the surfaces of all systems inside the low temperature environment chamber.

[0085] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art can make various modifications and adjustments within the technical scope disclosed in the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An impact testing device for a single supercooled large water droplet, characterized in that, The device includes an environmental control system, a supercooled water droplet generation system, a data acquisition system, a test substrate system, and an imaging system; The test substrate system includes a sample substrate, an electric slide stage, and a heat exchanger, located within a low-temperature environment chamber system. The electric slide stage adjusts the position and angle of the sample substrate, and the heat exchanger adjusts the surface temperature of the sample substrate. The environmental control system includes a low-temperature environment chamber system, a low-temperature constant temperature bath subsystem, and a drying subsystem. The low-temperature environment chamber system includes a low-temperature environment chamber, which is refrigerated using a coil compressor. The right side of the low-temperature environment chamber has three through holes of different heights for inserting a water droplet generating subsystem. The low-temperature environment chamber system is a coil type, using compressor refrigeration to provide a sealed, dry low-temperature environment; the low-temperature constant temperature bath subsystem uses ethylene glycol as an external circulation medium to regulate the temperature of the sample substrate; the drying subsystem uses dry nitrogen and color-changing silica gel to reduce the air humidity inside the low-temperature environment chamber. The supercooled water droplet generation system includes a water droplet generation subsystem and an air source subsystem. The water droplet generation subsystem uses a capillary steel needle at the tip to generate a quantitative amount of water droplets. The air source subsystem uses cold air to blow the supercooled water droplets away from the thermocouple temperature sensor. The data acquisition system includes a humidity sensor and a thermocouple sensor. The humidity sensor is used to detect the relative humidity inside the low-temperature environment chamber. The thermocouple sensor is used to monitor the temperature of water droplets, air temperature, and the surface temperature of the sample substrate, respectively. The imaging system includes a high-speed camera, a calibration plate, and a cold light source system. The high-speed camera is used to capture the dynamic process and phase transition process of supercooled large water droplets impacting the surface of the sample substrate. The calibration plate can be used to calculate the actual size of the water droplets. The cold light source is used to illuminate the water droplets from behind to create a shadow pattern.

2. The impact testing device for a single supercooled large water droplet according to claim 1, characterized in that: The low-temperature constant temperature bath subsystem includes a low-temperature constant temperature bath and an aluminum heat exchanger. The low-temperature constant temperature bath is connected to the heat exchanger placed on an electric slide via a rubber tube. Ethylene glycol is used as the circulating cooling medium to cool the sample substrate. The drying subsystem uses dry nitrogen and color-changing silica gel to reduce the humidity of the air inside the low-temperature environment chamber. The nitrogen is introduced from the bottom and vented from the top. The color-changing silica gel is evenly spread on the bottom surface of the low-temperature environment chamber.

3. The impact testing device for a single supercooled large water droplet according to claim 2, characterized in that: The water droplet generating subsystem includes a capillary steel needle, a hard aluminum rod, a syringe, a precision drive pump, and a rubber hose; the capillary steel needle is connected to the syringe via the rubber hose, the capillary steel needle and the rubber hose are embedded in the groove of the hard aluminum rod and fixed, and the drive end of the syringe is connected to the precision drive pump.

4. The impact testing apparatus for a single supercooled large water droplet according to claim 3, characterized in that: The gas source subsystem includes a nozzle, a copper pipe, a cold air storage box, and a pulse-type air pump. The nozzle is positioned above a first thermocouple sensor and connected to the cold air storage box via a copper pipe. The thermocouple sensor is located below a stainless steel needle. The cold air storage box is located inside a low-temperature environment chamber and is connected to an externally positioned pulse-type air pump via a pipeline. The output end of the cold air storage box is connected to the nozzle.

5. The impact testing apparatus for a single supercooled large water droplet according to claim 4, characterized in that: There are a total of four thermocouple temperature sensors used to measure the temperature of the water droplet, the air temperature, and the sample substrate temperature. The first thermocouple temperature sensor is located at the bottom of the water outlet of the water droplet generation subsystem and is used to measure the temperature of the suspended water droplet. The second thermocouple temperature sensor is at the same height as the first thermocouple temperature sensor and is used to measure the ambient air temperature. The third thermocouple temperature sensor is located at the sample substrate and is used to monitor the air temperature at the height of the sample substrate. The fourth thermocouple temperature sensor is located on the upper surface of the sample substrate and is used to monitor the upper surface temperature of the sample substrate.

6. The impact testing apparatus for a single supercooled large water droplet according to claim 1, characterized in that: The sample substrate can be replaced according to experimental requirements and is attached to the heat exchanger with thermally conductive adhesive; the heat exchanger is fixed on the electric slide and connected to the low-temperature constant temperature bath through a rubber tube; the electric slide is connected to an external controller, which can adjust the position and angle of the sample substrate.

7. The impact testing apparatus for a single supercooled large water droplet according to claim 1, characterized in that: The high-speed camera takes pictures through a shooting window with heated glass on the side of the low-temperature environment chamber; the cold light source system is located inside the low-temperature environment chamber, opposite to the high-speed camera lens, to create a shadow pattern to illuminate the water droplets.

8. The test method based on the impact test device for a single supercooled large water droplet as described in claim 5, characterized in that, The method includes the following: Step 1: Connect the instruments and equipment, and test the entire experimental setup; Step 2: Insert the water droplet generation subsystem, release water droplets onto the sample substrate, place the calibration plate at the water droplet drop position, adjust the high-speed camera focus on the calibration plate and record the number of pixels per millimeter for data analysis and conversion to actual size. Step 3: Add color-changing silica gel to the low-temperature environment chamber, close the chamber, and then open the side sealing plug and nitrogen valve in sequence to introduce dry nitrogen gas until the humidity inside the chamber decreases to [value missing]. Then close the nitrogen valve and seal the side through hole; Step 4: Run the low-temperature environment chamber and set the initial temperature; run the low-temperature constant temperature bath and set the circulating liquid temperature. Step 5: Insert the water droplet generation subsystem through the small hole on the side of the low-temperature environment chamber, turn on the precision drive pump, and observe the water droplets falling onto the thermocouple sensor through the top observation window. Step six: Observe the temperature change of the first thermocouple sensor until the target temperature is reached. The high-speed camera begins to take pictures, and at the same time, the pulse air pump is activated to use cold air to blow off the supercooled water droplets suspended on the thermocouple sensor. Step 7: The high-speed camera records the dynamic process of supercooled water droplets impacting the sample substrate surface at a high frame rate, or records the freezing process of supercooled water droplets impacting the substrate at a low frame rate.

9. The test method based on claim 8, characterized in that, The temperatures inside the low-temperature environment chamber and the low-temperature constant temperature bath are set based on feedback from the thermocouple sensor, the supercooling of the target water droplet, and the temperature of the sample substrate.

Images