A method for detecting the spatial falling velocity of atomized droplets considering particle size variation

Abstract

A method for detecting the spatial falling velocity of atomized droplets taking into account the change in particle size is based on an experimental device for measuring the spatial particle size and velocity change of atomized droplets. The spatial droplet particle size and droplet velocity are collected during the experiment, the initial droplet velocity is calculated, and the axial distance of the initial droplet from the nozzle outlet is measured; the Sauter mean diameter (SMD) of the droplets at each measuring point in the space is calculated based on the droplet particle size information, a model of the droplet SMD changing with space is established, and the initial droplet particle size is obtained based on the axial distance of the initial droplet from the nozzle outlet; by performing a force analysis on the droplets during the falling process, a droplet falling acceleration change model in space is obtained based on the initial droplet particle size, and combined with the initial droplet velocity, a reference model for the change in droplet velocity in space is obtained, which is used to estimate the change in the atomized droplet velocity of the nozzle of a nuclear power plant at a spatial height. The present invention comprehensively considers the aerodynamic breakup caused by the relative motion of atomized droplets and gas during the falling process, as well as the collision and aggregation between droplets, and establishes a prediction model for the change of atomized droplet particle size and velocity with spatial height from the comprehensive effects, which can more quickly and accurately evaluate the spray cooling and pressure reduction performance in the containment under accident conditions.

Description

Technical Field

[0001] The present invention relates to a technology in the field of nuclear industry safety, in particular to a method for detecting the spatial falling speed of atomized droplets taking into account the change in particle size. Background Art

[0002] Existing nuclear power plants use the containment spray system to spray supercooled water to condense high-temperature steam, thereby reducing the temperature and pressure inside the containment after an accident. The changes in the droplet size and velocity of the atomized droplets formed during the spraying process at the spatial height will directly affect the efficiency of cooling and pressure reduction and the efficiency of controlling accident disasters.

[0003] The existing spray system evaluation technology does not consider the changes in droplet size and velocity at spatial height. However, the aerodynamic force generated by the relative motion of droplets with the ambient gas during the falling process can cause the droplets to break up, and the droplets can also collide and coalesce due to different velocities, which can cause the droplet size to change at spatial height. Therefore, the existing technology cannot accurately evaluate the actual condensation situation. Summary of the invention

[0004] The present invention aims to solve the shortcomings of the prior art in that the calculation of the spatial falling velocity of atomized droplets does not take into account the change in droplet particle size, the spatial falling velocity of atomized droplets cannot be accurately calculated, and the simulation software takes a long time to calculate the change in droplet velocity. A method for detecting the spatial falling velocity of atomized droplets taking into account the change in particle size is proposed. The method comprehensively considers the aerodynamic breakup caused by the relative motion of the atomized droplets and the gas during the falling process, as well as the collision and aggregation between the droplets, and establishes a prediction model for the change in the particle size and velocity of the atomized droplets with the spatial height from the comprehensive effect. The method can more quickly and accurately evaluate the spray cooling and depressurization performance in the containment under accident conditions.

[0005] The present invention is achieved through the following technical solutions:

[0006] The invention relates to a method for detecting the spatial falling speed of atomized droplets taking into account the change in particle size. The method comprises the following steps: based on an experimental device for measuring the spatial particle size and speed change of atomized droplets, collecting information on the spatial droplet particle size and droplet speed during the experiment, calculating the initial droplet speed, and measuring the axial distance between the initial droplet and a nozzle outlet; calculating the Sauter mean diameter (SMD) of the droplets at each measuring point in the space according to the droplet particle size information, establishing a model for the change of the droplet SMD with space, and obtaining the initial droplet particle size according to the axial distance between the initial droplet and the nozzle outlet; and performing force analysis on the droplets in the falling process, obtaining a droplet falling acceleration change model in the space based on the initial droplet particle size, and combining the initial droplet speed to obtain a reference model for the change in droplet speed in the space, which is used for estimating the change in the velocity of atomized droplets of a nozzle of a nuclear power plant at a spatial height.

[0007] The experimental device includes: a water tank, a water pump, a spray head connected in sequence, and a laser particle size analyzer measurement system for measuring the droplet size and a particle image velocimetry system (PIV) for measuring the droplet velocity arranged on both sides of the droplet path below the spray head.

[0008] The particle image measurement system (PIV) includes: a laser sheet light source, a signal synchronization controller, a CCD high-speed camera and a PIV data processing unit, wherein: the laser sheet light source and the CCD high-speed camera are located in the same horizontal plane and are placed perpendicular to each other to measure the average velocity of droplets on a certain plane, the signal synchronization controller is connected to the laser sheet light source and the CCD high-speed camera respectively, and the PIV data processing unit is connected to the CCD high-speed camera.

[0009] The PIV data processing unit includes: an image preprocessing module, a feature matching module and a speed information generation module, wherein: the image preprocessing module performs denoising and contrast enhancement preprocessing according to the image information actually captured by the CCD high-speed camera; the feature matching module performs feature matching on the droplets in the preprocessed image to obtain the displacement of the droplets between two moments; the speed information generation module obtains the droplet speed at different positions and times according to the displacement information of the droplets.

[0010] Technical Effects

[0011] Compared with the prior art, the present invention constructs an experimental device for measuring the spatial particle size and velocity changes of atomized droplets, conducts an experiment to measure the spatial particle size and velocity changes of atomized droplets, comprehensively considers the breakup of aerodynamic forces generated by the relative velocity between the atomized droplets and the ambient gas during the falling process, and the collision and aggregation between the droplets, and establishes a model that can quickly and accurately calculate the droplet particle size and velocity changes in each section in the space, provides a method for detecting the spatial falling velocity of atomized droplets taking into account particle size changes, and provides technical support for nuclear power plants to mitigate the consequences of nuclear accidents.

[0012] This method can predict the diameter of the hollow cone nozzle with a diameter of 1-15 mm in a nuclear power plant within the range of 0.1-5 m. 3 The droplet size of atomized liquid changes greatly in space at a spray flow rate of 1 / h. At the same time, this method is also applicable to the speed prediction of the droplet size change process of other types of nozzles. This method is compared with the droplet speed value measured in the experiment of this embodiment to verify that it can more accurately predict the change of the droplet falling speed in space. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a flow chart of the present invention;

[0014] Figure 2 Schematic diagram of the experimental device for measuring the spatial particle size and velocity variation of atomized droplets;

[0015] Figure 3 This is the layout diagram of the laser particle size analyzer measurement system;

[0016] Figure 4 This is the layout diagram of the particle image measurement system (PIV);

[0017] Figure 5 It is a schematic diagram of the effect of the embodiment;

[0018] In the figure: 1 cooling water tank, 2 cooling water pump, 3 gate valve, 4 cooling water flow meter, 5 cooling water thermometer, 6 cooling spray head, 7 laser particle size analyzer measurement system, 8 particle image measurement system, 9 atomized droplet collector, 71 laser emission unit, 72 lens, 73 laser particle size analyzer receiver, 74 data acquisition system, 75 mobile measurement bracket, 81 laser sheet light source, 82 signal synchronization controller, 83 CCD high-speed camera, 84 PIV data processing unit. DETAILED DESCRIPTION

[0019] like Figure 1 As shown, a method for detecting the spatial falling speed of atomized droplets taking into account the change in particle size involved in this embodiment includes the following steps:

[0020] S1: Build an experimental device for measuring the spatial particle size and velocity change of atomized droplets, and obtain the droplet size and droplet velocity during the measurement experiment of the spatial particle size and velocity change of atomized droplets.

[0021] The experimental device includes: a cooling water tank 1, a cooling water pump 2, a gate valve 3, a cooling water flow meter 4, a cooling water thermometer 5 and a cooling spray head 6 connected in sequence, and a laser particle size analyzer measurement system 7 and a particle image velocimetry system 8 arranged on both sides of the droplet path below the cooling spray head 6.

[0022] The laser particle size analyzer measuring system comprises: a laser emitting unit 71, a lens 72, a laser particle size analyzer receiver 73, a data acquisition system 74 and a mobile measuring bracket 75 for positioning, wherein: the laser emitting unit, the lens and the laser particle size analyzer receiver are placed on the same horizontal line to measure the droplet particle size on a laser path.

[0023] The particle image measurement system 8 includes: a laser sheet light source 81, a signal synchronization controller 82, a CCD high-speed camera 83 and a PIV data processing unit 84, wherein: the laser sheet light source system and the CCD high-speed camera are located in the same horizontal plane and are placed perpendicular to each other to measure the average velocity of droplets on a certain plane.

[0024] The PIV data processing unit 84 includes: an image preprocessing module, a feature matching module and a speed information generation module, wherein: the image preprocessing module performs denoising and contrast enhancement preprocessing according to the image information actually captured by the CCD high-speed camera; the feature matching module performs feature matching on the droplets in the preprocessed image to obtain the displacement of the droplets between two moments; the speed information generation module obtains the droplet speed at different positions and times according to the displacement information of the droplets.

[0025] The experimental process of measuring the spatial particle size and velocity change of atomized droplets is as follows: the cooling spray system is turned on with a constant working fluid flow rate, and the spatial height L of the entire experimental device is divided into n equal parts, that is, the height dL of the i-th section through which the droplets pass and the time dt taken to pass the i-th section i The laser particle size analyzer measurement system in the parameter measurement system is used to measure the droplet particle size of each segment dL in the space, and the particle image measurement system (PIV) is used to measure the droplet velocity of each segment dL in the space.

[0026] The droplet size and droplet velocity are obtained by the following method:

[0027] 1) The droplets formed near the spray nozzle are taken as the initial droplets in the space. The spray liquid will form droplets with the Weber number falling below the critical value in the cascade secondary breakup area near the spray nozzle. The formed droplets move downward with a certain particle size and speed, and the particle size and speed are used as the initial information of the droplets in the space.

[0028] 2) Obtaining the initial droplet size based on the established intra-space droplet SMD variation model: Obtain the axial distance Z0 of the initial droplet from the nozzle outlet through experiments, and substitute it into the subsequently established intra-space droplet SMD variation model to obtain the initial particle size.

[0029] In this embodiment, the axial distance Z0=10 cm.

[0030] 3) Calculate the initial droplet velocity Where: ΔP is the pressure difference between inside and outside of the spray outlet, ρ l is the density of the spray liquid, and k is the correction coefficient obtained from the experiment.

[0031] In this embodiment, the correction coefficient k is 0.6.

[0032] S2: Count the droplet diameters and numbers of each measuring point in the space by the laser particle size analyzer measuring system 7 in step S1, and calculate the droplet SMD variation model of each measuring point in the space Then we get the model of droplet SMD changing with spatial height. Substitute the axial distance Z0 of the initial droplet from the nozzle outlet obtained in step S1 into the initial droplet diameter D 32,0, where: D is the droplet size, N is the number of droplets counted, D 32 is the droplet SMD, D0 is the nozzle outlet aperture, Z is the axial height of the droplet from the nozzle outlet, and the Reynolds number at the nozzle outlet Weber number at the nozzle outlet is the mass flow rate of the spray liquid, μ l is the spray liquid viscosity, ρ l is the density of the spray liquid, v l is the flow rate of the spray liquid at the spray outlet, and δ is the surface tension coefficient of the liquid.

[0033] In this embodiment, the intermediate parameters are a=1.93, b=-0.04, c=-0.25, and d=-0.13.

[0034] S3: Force analysis of atomized droplets is performed to establish a model of the acceleration change of droplets falling in space. Specifically, the volume of the droplets is small, so the friction resistance is small and can be ignored. The resistance of the droplets during the falling process is The falling acceleration of the droplet in space: The acceleration of the droplet in the i-th segment of space The droplet acceleration variation model in space is established: Where: g is the gas density of the experimental device, C D is the drag coefficient, according to the droplet Reynolds number Calculated, v is the droplet falling velocity in space, m and V are the droplet mass and volume in space, g is the gravitational acceleration, C D,i is the resistance coefficient of the i-th space height, C D,i The droplet Reynolds number at the height of the i-th space is Get, v i-1 is the droplet falling speed in the i-th space height, D 32,i is the droplet size corresponding to the i-th spatial height.

[0035] In this embodiment, the resistance coefficient C of the i-th space height is D,i C D,i =24 / Re d,i , Re d,i <0.2; 0.2≤Re d,i ≤500; C D,i =0.44,500≤Re d,i ≤10 5 .

[0036] S4: Based on the models obtained in step S1 and step S3, a reference model of droplet velocity variation in space is established Among them: the relationship between each height and speed is dL = vi-1 t i ; The droplet falls to the height Z of the i-th space i =Z0+idL; the speed of the drop after passing through the height of the i-th space

[0037] S5: After specific actual experiments, based on the reference model of droplet velocity variation in space, for a nozzle with an aperture of 9 mm in a nuclear power plant, the predicted droplet spatial falling velocity variation curve considering particle size variation is compared with the droplet spatial falling velocity variation curve without considering particle size variation and the measured experimental value of droplet height falling velocity variation under the setting of nozzle outlet pressure difference of 0.9 bar, as shown in Figure 5. Figure 5 And as shown in Table 1.

[0038] Table 1

[0039]

[0040] As can be seen from the table above, the calculation of the velocity of the atomized droplets by this method is closer to the measured value of the actual experiment, and the change of the falling velocity of the droplets in space is more accurately estimated.

[0041] In summary, the present invention establishes a model for the change in particle size and velocity of cold-state atomized droplets, comprehensively considering the aerodynamic forces generated by the relative velocity between the atomized droplets and the ambient gas during the falling process, and the collision and aggregation between the droplets, and truly establishes a spatial variation model of the droplet particle size; comprehensively considering the effects of gravity, pressure difference resistance and buoyancy on the droplets during the falling process, and combining the spatial variation model of the droplet particle size, a spatial variation model of the atomized droplet velocity is obtained. This method provides a reference for the rapid calculation of the spatial falling velocity of atomized droplets under accident conditions, which is closer to the actual situation.

[0042] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. Each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. A method for detecting the spatial falling velocity of atomized droplets taking into account the change in particle size, characterized in that: Based on the experimental device for measuring the spatial particle size and velocity change of atomized droplets, the spatial droplet particle size and droplet velocity are collected during the experiment, the initial droplet velocity is calculated, and the axial distance of the initial droplet from the nozzle outlet is measured; the Sauter mean diameter (SMD) of the droplets at each measuring point in the space is calculated based on the droplet particle size information, a model of the droplet SMD changing with space is established, and the initial droplet particle size is obtained based on the axial distance of the initial droplet from the nozzle outlet; by analyzing the force on the droplets during the falling process, a droplet falling acceleration change model in space is obtained based on the initial droplet particle size and combined with the initial droplet velocity, a reference model for the droplet velocity change in space is obtained, which is used to estimate the change in the atomized droplet velocity of the nuclear power plant nozzle at the spatial height; The droplet size and droplet velocity are obtained by the following method: 1) The droplets formed near the spray port are taken as the initial droplets in the space. The spray liquid forms droplets whose Weber number drops below the critical value in the cascade secondary breakup area near the spray port. The formed droplets move downward with a certain particle size and speed, and the particle size and speed are taken as the initial information of the droplets in the space; 2) Obtaining the initial droplet size according to the established droplet SMD variation model in space: Obtain the axial distance Z0 of the initial droplet from the nozzle outlet through experiments, and substitute it into the droplet SMD variation model in space established later to obtain the initial particle size; The initial droplet particle size is used to calculate the droplet particle size and number at each measuring point in the space by the laser particle size analyzer measurement system, and the droplet SMD change model at each measuring point in the space is calculated. Then we get the model of droplet SMD changing with spatial height. Substitute the axial distance Z0 between the initial droplet and the nozzle outlet to obtain the initial droplet size D 32,0 , where: D is the droplet size, N is the number of droplets counted, D 32 is the droplet SMD, D0 is the nozzle outlet aperture, Z is the axial height of the droplet from the nozzle outlet, and the Reynolds number at the nozzle outlet Weber number at the nozzle outlet is the mass flow rate of the spray liquid, μ l is the spray liquid viscosity, ρ l is the density of the spray liquid, v l is the flow rate of the spray liquid at the spray outlet, and δ is the surface tension coefficient of the liquid.

2. The method for detecting the spatial falling velocity of atomized droplets taking into account the change in particle size according to claim 1 is characterized in that: The experimental device comprises: a water tank, a water pump, a spray head connected in sequence, and a laser particle size analyzer measuring system for measuring the droplet diameter and a particle image velocimetry system for measuring the droplet velocity arranged on both sides of the droplet path below the spray head.

3. The method for detecting the spatial falling velocity of atomized droplets taking into account the change in particle size according to claim 2 is characterized in that: The particle image velocimetry system comprises: a laser sheet light source and a CCD high-speed camera located on the same horizontal plane and placed perpendicular to each other to measure the average velocity of droplets on a certain plane, a signal synchronization controller connected to the laser sheet light source and the CCD high-speed camera respectively, and a PIV data processing unit connected to the CCD high-speed camera.

4. The method for detecting the spatial falling velocity of atomized droplets taking into account the change in particle size according to claim 3 is characterized in that: The PIV data processing unit includes: an image preprocessing module, a feature matching module and a speed information generation module, wherein: the image preprocessing module performs denoising and contrast enhancement preprocessing according to the image information actually captured by the CCD high-speed camera; the feature matching module performs feature matching on the droplets in the preprocessed image to obtain the displacement of the droplets between two moments; the speed information generation module obtains the droplet speed at different positions and times according to the displacement information of the droplets.

5. The method for detecting the spatial falling velocity of atomized droplets taking into account the change in particle size according to claim 2, characterized in that: The laser particle size analyzer measuring system comprises: a laser emitting unit, a lens, a laser particle size analyzer receiver, a data acquisition system and a mobile measuring bracket for positioning, wherein: the laser emitting unit, the lens and the laser particle size analyzer receiver are placed on the same horizontal line to measure the droplet particle size on a laser path.

6. The method for detecting the spatial falling velocity of atomized droplets taking into account the change in particle size according to any one of claims 1 to 5, characterized in that: The experimental process of measuring the spatial particle size and velocity change of atomized droplets is as follows: the cooling spray system is turned on with a constant working fluid flow rate, and the spatial height L of the entire experimental device is divided into n equal parts, that is, the height dL of the i-th section through which the droplets pass and the time dt taken to pass the i-th section i The laser particle size analyzer measurement system in the parameter measurement system is used to measure the droplet particle size of each segment dL in the space, and the particle image velocimetry system is used to measure the droplet velocity of each segment dL in the space.

7. The method for detecting the spatial falling velocity of atomized droplets taking into account the change in particle size according to claim 1, characterized in that: The droplet acceleration variation model in space is established by analyzing the force on the atomized droplets to establish the droplet falling acceleration variation model in space. Specifically, the droplet volume is small, so the friction resistance is small and can be ignored. The resistance of the droplet in the falling process is The falling acceleration of the droplet in space: The acceleration of the droplet in the i-th segment of space The droplet acceleration variation model in space is established: Where: g is the gas density of the experimental device, C D is the drag coefficient, according to the droplet Reynolds number Calculated, v is the droplet falling velocity in space, m and V are the droplet mass and volume in space, g is the gravitational acceleration, C D,i is the resistance coefficient of the i-th space height, C D,i The droplet Reynolds number at the height of the i-th space is Get, v i-1 is the droplet falling speed in the i-th space height, D 32,i is the droplet size corresponding to the i-th spatial height.

8. The method for detecting the spatial falling velocity of atomized droplets taking into account the change in particle size according to claim 1, characterized in that: The reference model of droplet velocity variation in space is specifically: Among them: the relationship between each height and speed is dL = v i-1 t i ; The droplet falls to the height Z of the i-th space i =Z0+idL; the velocity of the droplet after passing through the height of the i-th space

Images