Method and device for determining critical fragmentation speed of impact of partially melted ice crystals

Abstract

The present invention belongs to the technical field of ice crystal particle impact experiments, and provides a method and device for determining the critical fragmentation velocity of partially melted ice crystal impacts. In view of the impact problem of partially melted ice crystals, the present invention conducts experimental research on partially melted ice crystals, combines experimental data with the impact dynamics model, and obtains a dimensionless model of the critical fragmentation velocity of partially melted ice crystals, which has important guiding significance for many fields involving ice crystals. For example, in the aviation field, it can help study the safety of aircraft engines and other components when they encounter impacts from partially melted ice crystals when the aircraft passes through clouds, and provide key parameters for the design and optimization of aircraft anti-icing and de-icing systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of ice crystal particle impact experiments, and particularly relates to a method and device for determining the critical fragmentation speed of partially melted ice crystal impacts. Background Art

[0002] After high-altitude ice crystals enter the engine interior, they will form ice accretion inside the engine, which may cause engine failures in severe cases. After the ice crystals enter the engine, they will form partially melted ice crystals under the engine's thermal environment. When the partially melted ice crystals impact the engine surface, behaviors such as cracking, rebounding, and adhesion will occur. Currently, there is no experimental research, impact dynamics model, or correlation formula for the impact behavior of partially melted ice crystals encountered in the flight environment in China.

[0003] To accurately simulate the fragmentation of partially melted ice crystals, the present invention conducts experimental research on the impact of partially melted ice crystals. By combining the experimental data with the impact dynamics model, a dimensionless model for the critical fragmentation speed of partially melted ice crystals is obtained. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a method and device for determining the critical fragmentation speed of partially melted ice crystal impacts to solve the problems in the prior art. The technical solution adopted by the present invention is as follows:

[0005] A method for determining the critical fragmentation speed of partially melted ice crystal impacts includes the following steps:

[0006] Step 1: Suspend distilled water droplets above a suspension device to form suspended particles, and freeze the suspended particles through a low-temperature gas stream.

[0007] Step 2: Measure the diameter and melting rate of the suspended particles in real time.

[0008] Step 3: Turn off the low-temperature gas stream, and the suspended particles gradually melt.

[0009] Step 4: When the melting rate of the suspended particles reaches a specified value, impact the suspended particles with a high-speed impact rod, and a high-speed camera records the impact process.

[0010] Step 5: Set different impact speeds of the high-speed impact rod, diameters of the suspended particles, and melting rates of the suspended particles, and repeat Steps 1 to 4 to conduct multiple impact experiments.

[0011] Step 5: Collect experimental data, including the melting rate of the suspended particles, the diameter of the suspended particles, the impact speed of the high-speed impact rod, and the fragmentation situation of the suspended particles.

[0012] Step 6: By integrating experimental data and based on the ice crystal fragmentation model of impact dynamics and fracture mechanics, obtain the expression for the critical fragmentation velocity of suspended particles:

[0013] ;

[0014] In the formula, is the critical fragmentation velocity, is the diameter of the suspended particle, k is the critical fragmentation coefficient;

[0015] For completely frozen suspended particles, the melting rate is 0, k is a determined constant;

[0016] For partially melted suspended particles, the melting rate is greater than 0, and the value of k is obtained by fitting experimental data, k The value of is positively correlated with the melting rate of the suspended particle.

[0017] Furthermore, in Step 2, the diameter of the suspended particle is obtained through a monitoring camera; for the melting rate of the suspended particle, the melting rate of the suspended particle is obtained by using the heat transfer method.

[0018] Furthermore, in Step 6, for completely frozen suspended particles:

[0019] Take the logarithm of both sides of formula (4) to obtain:

[0020] ;

[0021] Use the hinge loss function as the optimization criterion for fitting the experimental correlation:

[0022] ;

[0023] where i is the serial number and n is the total number of experimental groups; argmin f(x) represents the variable value when the objective function f(x) takes the minimum value, f sign is the sign function, e loss,i represents the loss function of the experimental point with serial number i, v i represents the impact velocity of the experimental point with serial number i, d ice,i represents the ice nucleus diameter of the experimental point with serial number i.

[0024] Furthermore, in Step 6, for partially melted suspended particles:

[0025] The diameter of the suspended particle in the mixed phase is , and its ice nucleus diameter , the water film thickness , the melting rate ;

[0026] Define the relative water film thickness coefficient to measure the influence of the water film thickness on the impact fragmentation of partially melted ice crystals, where the expression is:

[0027] ;

[0028] Through exponential fitting, the correlation formula between the relative water film thickness coefficient and the critical fragmentation coefficient k is obtained:

[0029] .

[0030] A device for determining the critical fragmentation velocity of the impact of partially melted ice crystals, the device includes: a nitrogen gas tank, a nitrogen bath, a low-temperature gas channel, an ultrasonic suspender, a high-speed impact rod, a high-speed camera, a monitoring camera, and two thermocouples;

[0031] The ultrasonic suspender is used to suspend distilled water droplets to form suspended particles;

[0032] The nitrogen gas tank is connected to the low-temperature gas channel through a gas pipeline, and a part of the gas pipeline is immersed in the nitrogen bath;

[0033] The exhaust end of the low-temperature gas channel faces the suspended particles and is used to eject low-temperature air flow to freeze the suspended particles;

[0034] The high-speed impact rod is located on one side of the suspended particles and is used to impact the suspended particles;

[0035] The high-speed camera is used to record the impact process;

[0036] The monitoring camera is used to obtain the diameter of the suspended particles;

[0037] Two thermocouples are respectively arranged on the front and rear sides of the suspended particles, and the two thermocouples are located on the flow path of the low-temperature gas. The temperatures of the low-temperature gas before and after passing through the suspended particles are measured by the two thermocouples to obtain the ambient temperature around the suspended particles.

[0038] The present invention has the following beneficial effects:

[0039] (1) By suspending and freezing distilled water droplets and then controlling their melting, the present invention can simulate the real state when ice crystals in the upper atmosphere enter the warm mainstream of the engine and partially melt. Measuring the diameter and melting rate of suspended particles in real time provides accurate initial conditions and process parameters for subsequent experiments, making the experimental data more accurate and reliable;

[0040] (2) By setting different impact speeds of the high-speed impact rod, diameters of suspended particles, and melting rates and repeating the experiments, various factors affecting ice crystal fragmentation are comprehensively considered. This multi-variable research method helps to deeply understand the relationship between various factors and the critical fragmentation speed, and reveals the internal law of the impact fragmentation of partially melted ice crystals;

[0041] (3) The present invention conducts experimental research and theoretical analysis on the problem of the impact of partially melted ice crystals, and finally obtains a model and correlation formula for the critical fragmentation speed of ice crystal impact, which has important guiding significance for many fields involving ice crystals; for example, in the aviation field, it can help study the safety of aircraft when engine and other components encounter the impact of partially melted ice crystals when passing through clouds, and provide key parameters for the design and optimization of aircraft anti-icing and de-icing systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is the structural diagram of the device of the present invention;

[0043] Figure 2 is the schematic diagram for checking the melting rate of ice crystals;

[0044] Figure 3 is the experimental data graph of the impact result at 0% melting rate;

[0045] Figure 4 is the experimental data graph of the impact result at 20% melting rate;

[0046] Figure 5 is the experimental data graph of the impact result at 40% melting rate;

[0047] Figure 6 is the experimental data graph of the impact result at 60% melting rate;

[0048] Figure 7 is the experimental data graph of the impact result at 80% melting rate;

[0049] Figure 8 is the schematic diagram of the structure of partially melted ice crystals;

[0050] Figure 9 is the schematic diagram for fitting the critical fragmentation coefficient;

[0051] Figure 10 is the ice crystal fragmentation model. DETAILED DESCRIPTION OF THE INVENTION

[0052] The following will combine with the Figures 1 - 10 in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. If not specifically specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0053] A method for determining the critical fragmentation velocity of partially melted ice crystal impacts includes the following steps:

[0054] Step 1: Suspend distilled water droplets above a suspension device to form suspended particles, and freeze the suspended particles through a low-temperature air flow;

[0055] Step 2: Measure the diameter and melting rate of the suspended particles in real time;

[0056] Step 3: Turn off the low-temperature air flow, and the suspended particles gradually melt;

[0057] Step 4: When the melting rate of the suspended particles reaches a specified value, impact the suspended particles with a high-speed impact rod, and a high-speed camera records the impact process;

[0058] Step 5: Set different impact velocities of the high-speed impact rod, diameters of the suspended particles, and melting rates of the suspended particles, and repeat Steps 1 to 4 to conduct multiple impact experiments;

[0059] Step 5: Collect experimental data, including the melting rate of the suspended particles, the diameter of the suspended particles, the impact velocity of the high-speed impact rod, and the fragmentation situation of the suspended particles;

[0060] Step 6: By integrating the experimental data and based on the ice crystal fragmentation model of impact dynamics and fracture mechanics, obtain the expression of the critical fragmentation velocity of the suspended particles:

[0061] ;

[0062] In the formula, is the critical fragmentation velocity and also the normal velocity of the high-speed impact rod along the impact plane when the suspended particles fragment; is the diameter of the suspended particles; k is the critical fragmentation coefficient, which is used to represent the influence of material property parameters such as the yield strength and ice crystal particle density in the ice crystal material;

[0063] For completely frozen suspended particles, their melting rate is 0, k is a determined constant;

[0064] For partially melted suspended particles, their melting rate is greater than 0, and the value of k is obtained by fitting the experimental data, k and the value of is positively correlated with the melting rate of the suspended particles.

[0065] The following experimental data can be referred to. A total of 308 impact experiments were conducted. The parameters of the experiments are shown in Table 1. In addition to the dry ice crystal experimental group, 4 experimental groups with different melting rates were equally spaced.

[0066] Table 1 Experimental parameters

[0067]

[0068] In addition, in step six, based on the ice crystal fragmentation model of impact dynamics and fracture mechanics, consider the process of ice crystal particles with a radius of R0 hitting a dry surface at a relative velocity of v0. Since the impact surface is aluminum alloy, its strength and stiffness are much greater than those of the ice crystal particles, and the impact surface is considered a completely rigid flat plate. This impact process is similar to the impact problem of a long plastic Taylor bar, and the propagation of plastic waves causes the deformation of the bar. The ice crystal particles are regarded as semi-brittle materials. During the impact process, the deformed ice crystal particles can be divided into a crack zone, a plastic deformation zone, and a crushing zone, as Figure 10 shown.

[0069] The moving distance of the ice crystal particles along the normal direction of the impact plane is represented by the dimensionless distance , that is, the ratio of the normal moving distance to the radius. When the deformation of the ice crystal particles is small, the force on the particles during the impact process is approximately the contact area multiplied by the yield strength of the material, and the motion equation of the particles in the impact velocity direction is obtained:

[0070] ;

[0071] where t represents the contact time and V represents the volume of the ice crystal particles. Further, the maximum value of the indentation radius after the impact can be obtained :

[0072] ;

[0073] The indentation radius a and the material properties of the ice crystal particles determine the crack development of the particles. The crack length is estimated using the model of Ghadiri

[29] , and finally the expression of the critical fragmentation velocity of the particles is obtained:

[0074] .

[0075] Furthermore, in step two, with the positions of the camera and the suspender fixed, calibrate in advance the length corresponding to each pixel of the monitoring camera. For the two-dimensional particle image captured by the monitoring camera, obtain the diameter of the suspended particles through the inversion method; for the melting rate of the suspended particles, obtain the melting rate of the suspended particles using the heat transfer method.

[0076] Further, in step six, for the completely frozen suspended particles:

[0077] For the obtained ice crystal fragmentation data, it can be found that the experimental results of fragmentation and non-fragmentation are distributed alternately within a certain range. In most cases, there is no clear dividing line to distinguish between the fragmentation situation and the non-fragmentation situation. As Figures 3 - 7 shown, the impact cracking results of the particles are divided into fragmentation and non-fragmentation. However, according to the analysis of the experimental results, there is no clear dividing line, that is, there is no line that can completely separate them. Artificially dividing this dividing line has a great deal of subjectivity and lacks the rigor of scientific research. In order to find the corresponding k value in the empirical formula, we adopted this soft margin support vector machine method to determine k. With the experimental results, k is uniquely determined.

[0078] Therefore, a new method needs to be considered to complete the fitting of the critical fragmentation speed:

[0079] Taking the logarithm of both sides of formula (4), we get:

[0080] ;

[0081] Since then, the original problem has been transformed into a binary classification problem in a two-dimensional plane. However, considering that only the critical fragmentation coefficient k is to be determined and the soft margin support vector machine cannot be used to obtain the critical fragmentation coefficient k . Therefore, this paper uses the hinge loss function as the optimization criterion for fitting the experimental correlation formula:

[0082] ;

[0083] where i is the serial number and n is the total number of experimental groups; argmin f(x) represents the variable value when the objective function f(x) takes the minimum value, f sign is the sign function, e loss,i represents the loss function of the experimental point with serial number i, v i represents the impact velocity of the experimental point with serial number i, d ice,i represents the ice nucleus diameter of the experimental point with serial number i.

[0084] Further, in step six, for the partially melted suspended particles:

[0085] To investigate the effect of the melting rate on the critical fragmentation velocity, the impact fragmentation of partially melted ice crystals at different melting rates was sorted out based on the experimental results. The experimental results can be divided into two cases, namely rebound and fragmentation. Further, these experimental data were statistically analyzed, and the impact fragmentation of the ice nucleus diameter and impact velocity at different melting rates is as shown in Figures 3 - 7 shown, and the experimental correlation formula of the critical fragmentation velocity at different melting rates was obtained by fitting method.

[0086] According to the experimental results, it can be preliminarily concluded that as the melting rate increases, the critical fragmentation velocity required for the ice nucleus is also higher. When the average melting rate is 20%, the critical fragmentation velocity coefficient increases by 114.3%. When the melting rate is 60%, the critical fragmentation velocity coefficient increases by 173.5%. As the melting rate further increases, the velocity required for fragmentation also further increases.

[0087] To further reveal the influence of liquid water on the impact results during the impact of partially melted ice crystals and enhance the applicability of the critical fragmentation velocity correlation formula of ice crystal impact in the presence of liquid water, the ice crystal impact model under partial melting as shown in Figure 8 was proposed.

[0088] The model assumptions are as follows: the melting process of the ice crystal is simplified to a regular uniform melting process, that is, there is no eccentric melting problem during the melting process, and the ice nucleus is a uniform sphere. The diameter of the suspended particles in the mixed phase is , its ice nucleus diameter , the water film thickness , the melting rate ; considering that the changes in the melting rate and the ice nucleus diameter are non-linear. When the melting rate is high, the ice nucleus diameter will become very small and the water film will be very thick.

[0089] Therefore, the relative water film thickness coefficient is defined to measure the influence of the water film thickness on the impact fragmentation of partially melted ice crystals, where the expression is:

[0090] ;

[0091] Among them, the relationship between the melting rate and the relative water film thickness coefficient is non-linear. When is close to 100%, will increase sharply. Therefore, considering using the relative water film thickness coefficient to fit the experimental correlation formula with the critical fragmentation coefficient k is a more reasonable choice. Fitting the critical fragmentation coefficient k obtained from the previous experimental results, as shown inFigure 9 as shown Figure 9 In it, the red experimental points correspond to the relative water film thickness coefficient and the critical fragmentation coefficient k The relationship is that when the melting rate is higher, the water film is thicker, the ice nucleus diameter is smaller, the corresponding relative water film thickness coefficient is higher, and the critical fragmentation coefficient is also larger, resulting in a higher impact velocity required for fragmentation.

[0092] Through exponential fitting, the correlation formula between the relative water film thickness coefficient and the critical fragmentation coefficient k is obtained as follows:

[0093] .

[0094] In view of the problem of partially melted ice crystal impact, the present invention conducts experimental research and theoretical analysis, and finally obtains a model and a correlation formula for the critical fragmentation velocity of ice crystal impact.

[0095] The present invention also relates to a device for determining the critical fragmentation velocity of partially melted ice crystal impact, and the device includes: a nitrogen gas tank, a nitrogen bath, a low-temperature gas channel, an ultrasonic levitator, a high-speed impact rod, a high-speed camera, a monitoring camera, and two thermocouples;

[0096] The ultrasonic levitator is used to levitate distilled water droplets to form suspended particles;

[0097] The nitrogen gas tank is connected to the low-temperature gas channel through a gas pipeline, and a part of the gas pipeline is immersed in the nitrogen bath;

[0098] The exhaust end of the low-temperature gas channel faces the suspended particles and is used to eject low-temperature air flow to freeze the suspended particles;

[0099] The high-speed impact rod is located on one side of the suspended particles and is used to impact the suspended particles;

[0100] The high-speed camera is used to record the impact process;

[0101] The monitoring camera is used to obtain the diameter of the suspended particles;

[0102] Two thermocouples are respectively arranged on the front and back sides of the suspended particles, and the two thermocouples are located on the flow path of the low-temperature gas. The temperatures of the low-temperature gas before and after passing through the suspended particles are measured by the two thermocouples to obtain the ambient temperature around the suspended particles.

[0103] In order to realize the preparation and melting rate measurement of partially melted ice crystals and carry out impact experiments, this paper designs and builds a high-speed impact experimental platform for partially melted ice crystals. The schematic diagram of the experimental platform is as Figure 1As shown. The experimental platform mainly includes: an ice crystal suspension freezing system, an ice crystal melting rate measurement system, and a high-speed impact system.

[0104] The low-temperature suspension freezing system mainly consists of a nitrogen cylinder, a copper coil heat exchanger, and a flow meter, which is used to provide a low-temperature gas flow for freezing suspended droplets. The outlet gas flow speed and temperature are controlled by adjusting the pressure reducing valve and the needle valve. The gas flow speed can be calculated in real time according to the indication of the gas flow meter. A T-type thermocouple is set at the outlet of the gas flow to measure the outlet gas flow temperature. The ultrasonic levitator provides stable suspension conditions for the particles.

[0105] The ice crystal melting rate measurement system mainly includes a monitoring camera, a thermocouple thermometer, and several T-type thermocouples. The average temperature around the suspended particles is measured by several T-type thermocouples. Using the image information captured by the monitoring camera, the volume of the particles can be further calculated. After closing the low-temperature gas flow, the particles melt in the natural convection environment, and the real-time measurement of the ice crystal melting rate is realized by means of heat transfer.

[0106] The high-speed impact system includes a self-developed high-speed impact rod, a high-brightness programmable light source, a digital delay pulse generator, and a high-speed camera. The digital delay pulse generator is used as a signal generator to realize the synchronous control of the high-brightness programmable light source, the high-speed camera, and the high-speed impact rod. The melting rate of the suspended particles is measured in real time using a melting rate measurement method based on heat transfer. When the ice crystal melting reaches the specified melting rate, a signal is sent to synchronously turn on the light source, start the high-speed camera, and start the high-speed impact rod. After the solenoid valve of the high-speed impact rod is activated, the impact rod is pushed out by high-pressure gas and impacts the suspended ice crystal. The impact rod speed can be changed by adjusting the pressure of the high-pressure gas storage tank. The light source is placed in the backlight position, and the high-speed camera is used to capture the impact process of the partially melted ice crystal.

[0107] In addition, in the present invention, a heat transfer method is adopted to realize the real-time measurement of the ice crystal melting rate. Along the direction of the cold air flow, thermocouples are respectively installed in front of and behind the suspended particles. The thermocouple thermometer accurately measures the air flow temperature at a frequency of 10 Hz, and the weighted processing of the temperature is carried out to obtain the ambient temperature around the suspended particles .

[0108] After the freezing is stable, the low-temperature gas flow is closed, and the ice crystal melts in the natural convection environment. The diameter of the melting ice crystal is obtained through the monitoring camera , in the case of knowing the ambient temperature around , the melting rate of the ice crystal can be calculated by using the heat transfer method . Specifically, the real-time measurement of the ice crystal melting rate by using the heat transfer method includes the following methods:

[0109] The phase change process of the ice crystal particles is divided into three stages. (1) Solid state stage: The particle temperature Less than the melting temperature , that is , the particles are pure solid ice crystals, and the ice crystal particles conduct convective heat transfer with the external environment until the temperature reaches the melting temperature . (2) Melting stage: The particle temperature equals the melting temperature , that is , under the further heat transfer effect, the ice crystals start to melt from the outside, and the temperature remains unchanged. (3) Liquid stage: The particle temperature is greater than the melting temperature , that is , and the ice crystal particles completely melt into a droplet state. This study only focuses on the solid state and the melting stage

[0110] The heat and mass transfer equations in the solid state are as follows:

[0111] ;

[0112] In the formula, is the mass of the ice crystal, is the specific heat capacity of the ice crystal, is the particle diameter, is the Nusselt number, is the air thermal conductivity, is the air temperature is the sublimation mass flow rate, and are the latent heat of fusion and the latent heat of evaporation respectively is the Sherwood number, is the air density, is the vapor diffusion rate in the air and represent the mass fractions of the vapor in the particle surface and the free surface respectively

[0113] The heat and mass transfer equations in the melting stage are as follows:

[0114] ;

[0115] In the formula, is the evaporation mass flow rate, is the melting mass flow rate and are the mass and diameter of the ice nuclei during the melting process respectively

[0116] Input the measured data such as temperature, humidity, and ambient atmospheric pressure into the program, and through the heat transfer model, the heat transfer situation of the ice crystals can be calculated, so as to calculate the melting rate of the ice crystals in real time

[0117] Considering it is a natural convection problem, an empirical correlation for natural convection heat transfer of a spherical object is adopted:

[0118] ;

[0119] where Nu is the Nusselt number, Pr is the Prandtl number of air, Gr is the Grashof number.

[0120] To verify the accuracy of this measurement method, we adopted two different measurement methods for the ice crystal melting rate for cross-validation. These two methods are the direct measurement method based on impacting ice nuclei and the indirect measurement method based on heat transfer. The melting rate obtained by the direct measurement method based on impacting ice nuclei is denoted as "melting rate measured by the impact method" , and the melting rate obtained by the indirect measurement method based on heat transfer is denoted as "melting rate measured by the heat transfer method" .

[0121] The principle of the direct measurement method based on impacting ice nuclei is as follows: Under the natural convection environment, the ice crystal has a melting process from the outside to the inside. It is in a mixed phase state during the melting process. By controlling the impact speed and adopting an appropriate speed, let the impact rod impact a partially melted ice crystal to separate the unmelted ice nucleus from the outer water film. After calculating the volume of the ice nucleus , the melting rate of the partially melted ice crystal can be further obtained. In the experiments of this study, considering the possible eccentric melting and the flow of the surface melting water film, the ice nuclei often present irregular shapes.

[0122] Therefore, for the "melting rate measured by the impact method" , this invention uses the stereology method to calculate the volume of the ice nucleus.

[0123] Assume the diameter of the mixture before impact , and the volume of the ice nucleus is . According to the law of conservation of mass, we can get:

[0124] ;

[0125] where is the melting rate measured by the impact method, and represent the densities of water and ice respectively, is the equivalent diameter of the ice nucleus, expressed as:

[0126] ;

[0127] 54 groups of ice crystal melting rate calibration experiments were carried out. Compare and , as Figure 2As shown. Most of the experimental points fall near the consistency line. To obtain the accurate volume of ice nuclei, a lower impact velocity of 3 m / s to 6 m / s is used to ensure that the ice nuclei inside the partially melted ice crystals do not break after being impacted. Affected by the liquid viscous force, some liquid water in the form of a water film will adhere to the surface of the ice nuclei after impact, which amplifies the measurement error of the direct measurement method based on the impacted ice nuclei at low melting rates, resulting in the measurement of the melting rate by the impact method deviates from the true melting rate to a greater extent. It can be seen from the linear fitting results and the verification results at higher melting rates (greater than 40%) that and The absolute error is within 17%. In summary, using the heat transfer method to measure the melting rate to estimate the true melting rate has a certain feasibility, and it is considered that this melting rate measurement method can be used to measure the melting rate of partially melted ice crystals in suspension.

[0128] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations, variations, modifications, and substitutions made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for determining the critical fragmentation speed of partially melted ice crystals impacted, characterized in that, It includes the following steps: Step 1: Suspend distilled water droplets above the suspender to form suspended particles, and freeze the suspended particles through a low-temperature gas flow; Step 2: Measure the diameter and melting rate of the suspended particles in real time; Step 3: Turn off the low-temperature gas flow, and the suspended particles gradually melt; Step 4: When the melting rate of the suspended particles reaches the specified value, impact the suspended particles with a high-speed impact rod, and a high-speed camera records the impact process; Step 5: Set different impact speeds of the high-speed impact rod, diameters of the suspended particles, and melting rates of the suspended particles, and repeat Steps 1 to 4 to conduct multiple impact experiments; collect experimental data, including the melting rate of the suspended particles, the diameter of the suspended particles, the impact speed of the high-speed impact rod, and the fragmentation situation of the suspended particles; Step 6: By integrating the experimental data and based on the ice crystal fragmentation model of impact dynamics and fracture mechanics, obtain the expression of the critical fragmentation speed of the suspended particles: ； In the formula, is the critical fragmentation velocity, is the diameter of the suspended particles, k is the critical fragmentation coefficient; For completely frozen suspended particles, the melting rate is 0, k which is a constant; For partially melted suspended particles, whose melting rate is greater than 0, the k value is obtained by fitting the experimental data, and k the value size is positively correlated with the melting rate of the suspended particles. In Step 6, for partially melted suspended particles: The suspension particle diameter of the mixed phase is , its ice nucleus diameter , the water film thickness , the melting rate m r ; Define the relative water film thickness coefficient to measure the influence of the water film thickness on the impact fragmentation of partially melted ice crystals, where the expression is: ； The relative water film thickness coefficient is obtained by exponential fitting and the correlation formula of the critical breakup coefficient k is as follows: 。 2. The method for determining the critical fragmentation speed of partially melted ice crystal impacts according to claim 1, wherein In Step 2, obtain the diameter of the suspended particles through a monitoring camera; for the melting rate of the suspended particles, use the heat transfer method to obtain the melting rate of the suspended particles.

3. The method for determining the critical fragmentation speed of partially melted ice crystals impacting as claimed in claim 1, wherein In Step 6, for completely frozen suspended particles: Take the logarithm of both sides of formula (4) to obtain: ； Use the hinge loss function as the optimization criterion for fitting the experimental correlation: ； where i is the serial number and n is the total number of experimental groups; argmin f(x) represents the variable value when the objective function f(x) takes the minimum value, f sign is the sign function, e loss,i represents the loss function of the experimental point with serial number i, v i represents the impact velocity of the experimental point with serial number i, d ice,i represents the ice nucleus diameter of the experimental point with serial number i.

4. An apparatus for determining the critical fragmentation velocity of impact of partially melted ice crystals, which adopts the method for determining the critical fragmentation velocity of impact of partially melted ice crystals according to any one of claims 1-3, characterized in that, The device includes: a nitrogen gas tank, a nitrogen bath, a low-temperature gas channel, an ultrasonic suspender, a high-speed impact rod, a high-speed camera, a monitoring camera, and two thermocouples; The ultrasonic suspender is used to suspend distilled water droplets to form suspended particles; The nitrogen gas tank is connected to the low-temperature gas channel through a gas pipeline, and a part of the gas pipeline is immersed in the nitrogen bath; The exhaust end of the low-temperature gas channel faces the suspended particles and is used to eject a low-temperature gas flow to freeze the suspended particles; The high-speed impact rod is located on one side of the suspended particles and is used to impact the suspended particles; The high-speed camera is used to record the impact process; The monitoring camera is used to obtain the diameter of the suspended particles; Two thermocouples are respectively arranged on the front and back sides of the suspended particles. The two thermocouples are located on the flow path of the low-temperature gas. Measure the temperatures of the low-temperature gas before and after passing through the suspended particles through the two thermocouples to obtain the ambient temperature around the suspended particles.

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