Method for simulating motion of discrete droplets in a reactor core under a loss-of-coolant accident

Abstract

The application discloses a simulation method for motion of discrete droplets in a reactor core under a reactor coolant loss condition and relates to the technical field of nuclear reactors.The simulation method for motion of discrete droplets in the reactor core under the reactor coolant loss condition comprehensively considers generation, motion, fragmentation, evaporation, deposition of the discrete droplets and collision phenomena between the discrete droplets and between the discrete droplets and a heated wall, performs prediction calculation on the phenomena, can predict various complex behaviors of the discrete droplets in a reactor channel, realizes simulation capability of a whole life cycle (generation-motion-disappearance) of the discrete droplets, provides an important research tool for a reactor system safety analysis program, and improves prediction accuracy of a film boiling droplet entrainment amount, a highest cladding temperature and a heat exchange condition of a heating rod surface.

Description

Technical Field

[0001] This invention relates to the field of nuclear reactor technology, and in particular to a method for simulating the motion of discrete droplets in the reactor core under reactor coolant loss conditions. Background Technology

[0002] Currently, in large breach accidents (LBLOCA) in pressurized water reactors (PWRs), sudden coolant leakage triggers a catastrophic heat transfer crisis, with fuel element surface temperatures rising sharply after coolant loss. To prevent element meltdown, Emergency Core Cooling Systems (ECCS) inject cooling water into the core. When this cooling water comes into contact with the high-temperature fuel surface, it triggers a violent flash boiling phenomenon, instantly generating a large number of discrete droplet clusters (0.1 mm to 3.0 mm in diameter). The dynamic behavior of these millimeter-sized discrete droplets directly determines the cooling efficiency of film boiling heat transfer during the quenching phase of an LBLOCA accident in the PWR core. Accurately characterizing the droplet size, distribution, trajectory, and interactions has become a core issue for improving the accuracy of film boiling heat transfer prediction during the quenching phase.

[0003] However, in current engineering practice, reactor transient analysis methods often simplify the simulation of discrete droplet phases to improve computational efficiency. They primarily rely on empirical relationships based on macroscopic parameters such as the two-phase volume fraction and the Sauter mean diameter of the droplets, lacking consideration for the multi-scale characteristics of discrete droplet motion. For example, the RELAP5 transient analysis program, by using the lumped parameter method to simulate the heat transfer enhancement of discrete droplets, ignores the simulation of the actual droplet motion behavior, resulting in problems such as underestimated entrainment, prediction errors in the peak cladding temperature (PCT), and inaccurate reflection of the actual heat transfer on the heater surface. Summary of the Invention

[0004] Therefore, it is necessary to provide a method, apparatus, medium, and equipment for simulating the motion of discrete droplets in the reactor core under reactor coolant loss conditions, in order to address the above-mentioned technical problems.

[0005] The present invention adopts the following technical solution: This invention provides a method for simulating the motion of discrete droplets in a reactor core under coolant loss conditions. First, the vapor phase velocity is determined based on the steam generation rate, continuous vapor phase fluid density, wetted perimeter of the cooling water flow channel, and critical gas film thickness during the flash boiling phenomenon. Then, the axial height of the downstream liquid film at the quenching front is determined based on the continuous liquid phase mass change within the cooling water flow channel, the liquid phase density at saturation temperature, and the flow area of ​​the cooling water flow channel. A momentum conservation equation for discrete droplets is established. Next, the number of discrete droplets generated on the liquid film due to the Helmholtz instability mechanism and the hot wall jet mechanism are determined. Finally, the droplet size, particle size, and other parameters are considered based on the axial height of the liquid film. Initial values ​​are assigned to velocity and spatial distribution. Then, based on the initial values ​​of each discrete droplet and the momentum conservation equation for the discrete droplets, collisions between discrete droplets and between discrete droplets and the heated wall are simulated. Furthermore, based on the vapor phase velocity and the velocity of each discrete droplet, airflow disturbance and breakup simulations are performed. Based on the diameter and equilibrium diameter of each discrete droplet, capillary breakup simulations are performed. The relative position of each discrete droplet within the cooling water flow channel to the continuous liquid phase is determined based on the axial height of the liquid film, and deposition simulations are performed. Finally, the evaporation rate of each discrete droplet in the vapor phase is determined to simulate evaporation.

[0006] This invention provides a device for simulating the motion of discrete droplets in a reactor core under reactor coolant loss conditions, comprising: The initial condition construction module is used to determine the vapor phase velocity based on the steam generation rate, continuous vapor phase fluid density, wetted perimeter of the cooling water flow channel, and critical vapor film thickness in the flash boiling phenomenon of cooling water; to determine the axial height of the downstream liquid film at the quenching front based on the continuous liquid phase mass change in the cooling water flow channel, liquid phase density at saturation temperature, and flow area of ​​the cooling water flow channel; and to establish the discrete droplet phase momentum conservation equation. The initialization module is used to determine the number of discrete droplets generated on the liquid film due to the Helmholtz instability mechanism and the hot wall jet mechanism, respectively; and to assign initial values ​​to the particle size, velocity and spatial distribution of the discrete droplets according to the axial height of the liquid film. The collision simulation module is used to simulate the collisions between discrete droplets and between discrete droplets and the heated wall surface, based on the initial values ​​of each discrete droplet and the phase momentum conservation equation of the discrete droplets. The breakage simulation module is used to simulate the breakage of each discrete droplet by airflow disturbance based on the vapor phase velocity and the velocity of each discrete droplet, and to simulate the breakage of each discrete droplet by capillary breakage based on the diameter of each discrete droplet and the mechanical equilibrium diameter of the droplet. The deposition-evaporation simulation module is used to determine the relative position of each discrete droplet with the continuous liquid phase in the cooling water flow channel based on the axial height of the liquid film, and to perform deposition simulation for each discrete droplet; it also determines the evaporation rate of each discrete droplet in the vapor phase to perform evaporation simulation for the discrete droplets.

[0007] The present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-described method for simulating the motion of discrete droplets in the reactor core under reactor coolant loss conditions.

[0008] The present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the above-mentioned method for simulating the motion of discrete liquid droplets in the reactor core under reactor coolant loss conditions.

[0009] The above-mentioned at least one technical solution adopted in this invention can achieve the following beneficial effects: This invention provides a simulation method for the motion of discrete droplets in the reactor core under reactor coolant loss conditions. It comprehensively considers the generation, motion, fragmentation, evaporation, deposition, and collision phenomena between discrete droplets and between discrete droplets and heated walls. It performs predictive calculations on these phenomena and can predict various complex behaviors of discrete droplets in the reactor channel. It realizes the simulation capability of the entire life cycle of discrete droplets (generation-motion-disappearance), provides an important research tool for reactor system safety analysis programs, and improves the accuracy of predicting entrainment, maximum cladding temperature, and heat transfer on the surface of heated rods. Attached Figure Description

[0010] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0011] Figure 1 This is a schematic diagram of a method for simulating the motion of discrete droplets in a reactor core under reactor coolant loss conditions, provided by the present invention. Figure 2 This invention provides a schematic diagram of a simulation process for the movement of discrete droplets in the reactor core under reactor coolant loss conditions. Figure 3a This invention provides a schematic diagram of the spatial distribution and movement of droplets in a cooling water flow channel at time point 1. Figure 3b This invention provides a schematic diagram of the spatial distribution and movement of droplets in a cooling water flow channel at time point 2. Figure 3c This invention provides a schematic diagram of the spatial distribution and movement of droplets in a cooling water flow channel at time point 3. Figure 3d This invention provides a schematic diagram of the spatial distribution and movement of droplets in a cooling water flow channel at time point 4. Figure 4aA schematic diagram showing the comparison between the number of discrete droplets and the results of autonomous experiments under verification condition 1 provided by this invention; Figure 4b A schematic diagram showing the comparison between the number of discrete droplets and the results of autonomous experiments under verification condition 2 provided by this invention; Figure 4c A schematic diagram showing the comparison between the number of discrete droplets and the results of autonomous experiments under verification condition 3 provided by this invention; Figure 4d A schematic diagram showing the comparison between the number of discrete droplets and the results of autonomous experiments under different verification conditions provided by this invention; Figure 5a This is a schematic diagram illustrating the simulation verification of a single-bar quenching experimental system under quenching experimental condition 1 provided by the present invention. Figure 5b This is a schematic diagram illustrating the simulation verification of a single-bar quenching experimental system under quenching experimental condition 2 provided by the present invention. Figure 5c This is a schematic diagram of the simulation verification of a single-bar quenching experimental system under quenching experimental condition 3 provided by the present invention; Figure 5d This is a schematic diagram illustrating the simulation verification of three sets of quenching experimental conditions for a single-bar quenching experimental system provided by the present invention. Figure 6 This is a schematic diagram of a reactor core discrete droplet motion simulation device under reactor coolant loss conditions provided by the present invention. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0013] The technical solutions provided by the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0014] Figure 1 This is a schematic diagram of a method for simulating the motion of discrete droplets in a reactor core under reactor coolant loss conditions, as described in this invention. The method specifically includes the following steps: S101: Determine the vapor phase velocity based on the steam generation rate, continuous vapor phase fluid density, wetted perimeter length of the cooling water flow channel, and critical gas film thickness during the flash boiling phenomenon of core cooling water; determine the axial height of the liquid film downstream of the quenching front based on the continuous liquid phase mass change in the cooling water flow channel, liquid phase density at saturation temperature, and flow area of ​​the cooling water flow channel; establish the discrete droplet phase momentum conservation equation.

[0015] S102: Determine the number of discrete droplets generated on the liquid film caused by the Helmholtz instability mechanism and the hot wall jet mechanism, respectively; assign initial values ​​to the particle size, velocity and spatial distribution of the discrete droplets based on the axial height of the liquid film.

[0016] S103: Based on the initial values ​​of each discrete droplet and the phase momentum conservation equation of the discrete droplets, the collisions between discrete droplets and between discrete droplets and the heated wall are simulated.

[0017] S104: Based on the vapor phase velocity and the velocity of each discrete droplet, perform airflow disturbance and breakup simulation on each discrete droplet, and perform capillary breakup simulation on each discrete droplet based on the diameter of each discrete droplet and the droplet mechanical equilibrium diameter.

[0018] S105: Determine the relative position of each discrete droplet with the continuous liquid phase in the cooling water flow channel based on the axial height of the liquid film, and perform deposition simulation for each discrete droplet; determine the evaporation rate of each discrete droplet in the vapor phase, and perform evaporation simulation for the discrete droplets.

[0019] For ease of explanation, the following description focuses solely on the server as the executing entity. The server mentioned in this invention can be a server set up on a business platform, or a device such as a desktop computer or laptop computer capable of executing the solution of this invention.

[0020] Figure 2 This is a schematic diagram of the simulation process of discrete droplet motion in the reactor core under reactor coolant loss conditions according to the present invention. The first step is to set the initial conditions of the continuous phase flow field, including the calculation of vapor phase velocity and the calculation of the axial height of the liquid film downstream of the quenching front.

[0021] Vapor phase velocity The calculation formula is: .

[0022] In the formula, The fluid density of the continuous vapor phase is given in kg·m³. -3 , Steam generation rate / kg·m -2 ·s -1 ; The wetted perimeter of the flow channel is measured in meters (m). The critical air film thickness is given in m.

[0023] The formula for calculating the critical air model thickness is as follows: .

[0024] In the formula, The viscosity of the vapor phase is expressed in Pa·s. It is the acceleration due to gravity. The fluid density of the continuous liquid phase is expressed in kg·m³. -3 ; The critical Reynolds number for the air film is set to 100 here.

[0025] The formula for calculating the steam generation rate is as follows: .

[0026] In the formula, Steam generation rate / kg·m -2 ·s -1 , Heat received by the liquid phase (J); Initial wall temperature / °C; The saturation temperature of the continuous liquid phase is given in °C. Thermal conductivity of the vapor phase / W·m -1 ·℃ -1 , Heat flux density input to the rod / kW·m -2 , Heating area / m 2 , Heating length / m Latent heat of vaporization of fluid / J·kg -1 .

[0027] When calculating the axial height of the liquid film downstream of the quenching front, it is assumed that the anti-annular flow liquid film is triangularly distributed along the longitudinal section of the flow channel, and the axial height of the liquid film is... The calculation formula is: .

[0028] In the formula, The flow area of ​​the passage / m 2 , The change in mass of the continuous liquid phase within the channel is expressed in kg. Liquid phase density at saturation temperature / kg·m -3 , The inlet velocity of the channel. Liquid phase density at the channel inlet (kg·m³) -3 , To calculate the time step / s, Precession velocity of the quenching front / ms-1 ; The total mass of the generated droplets is expressed in kg.

[0029] The second step is to calculate the new discrete droplets generated by Helmholtz instability and the hot wall jet mechanism.

[0030] (1) The number of discrete droplets generated on the liquid film due to the Helmholtz instability mechanism The calculation formula is: .

[0031] In the formula, The characteristic length is given in meters. For diffused film boiling, the characteristic length is taken as the heating rod circumference. For reverse annular flow, the characteristic length is taken as the reverse annular flow liquid film length. Characteristic droplet diameter / m; The critical wavelength is 1 / m.

[0032] The diameter of the characteristic droplet is determined by the following formula: , .

[0033] In the formula Hydraulic diameter / m; Vapor phase velocity / m / s -1 , Fluid surface tension / N·m -1 ; The coefficient of friction for a smooth interface.

[0034] The formula for calculating the critical wavelength is as follows: .

[0035] In the formula, gravitational acceleration / m·s -2 , The fluid density of the continuous vapor phase is given in kg·m³. -3 .

[0036] (2) The number of droplets generated on the liquid film due to the hot wall jet mechanism The calculation formula is: .

[0037] In the formula, The thickness of the reverse annular flow liquid film is superimposed on the length of the liquid film in meters where the fluctuation amplitude is greater than the width of the flow channel.

[0038] Among them, the amplitude of the anti-annular flow film fluctuation The calculation formula is: ; In the formula, The viscosity of the vapor phase is expressed in Pa·s. The experimental coefficient is set to 0.53. The interfacial shear force of the liquid film is expressed in N. denoted as the interfacial friction coefficient of the liquid film.

[0039] The formula for calculating the shear force at the liquid film interface is: ; In the formula, The velocity of the continuous liquid phase is expressed in m·s. -1 .

[0040] The formula for calculating the interfacial friction coefficient is: ; is the relative Reynolds number in the liquid phase.

[0041] The third step is to initialize and assign values ​​to the new discrete droplets, including their size, velocity, and spatial distribution.

[0042] The initial spatial distribution of the discrete droplets is set to be uniformly distributed radially along the cooling water flow channel. The initial axial velocity of the droplets is set to be the same as the velocity of the liquid film at the droplet generation point, and the initial velocity direction is a random value within the range of (-90°, +90°) perpendicular to the liquid film. The particle size distribution of the newly generated discrete droplets adopts the classical log-normal distribution form.

[0043] The fourth step involves performing collision simulations between discrete droplets and between discrete droplets and the heated wall. In one or more embodiments of this invention, the server can simulate complete rebound, collision aggregation, stretching separation, and splash separation between discrete droplets based on the initial values ​​of each discrete droplet and the discrete droplet phase momentum conservation equation; and simulate heat transfer during complete rebound between discrete droplets and the heated wall based on the initial values ​​of each discrete droplet, the discrete droplet phase momentum conservation equation, the longest contact time between the discrete droplet and the wall, the temperature of the heated wall, and the temperature of the discrete droplets.

[0044] Specifically, the calculation process for discrete droplet collisions is as follows: (1) Collision calculation between droplets.

[0045] The B-We droplet collision diagram, composed of dimensionless eccentricity B and Weber number We, is used to determine the results of binary droplet collisions under different collision conditions: a. Complete rebound.

[0046] After a complete rebound, the velocity relationship of the binary droplet is: , , .

[0047] In the formula, Velocity after large droplet collision / ms -1 ; Velocity of the small droplet after collision / ms -1 ; Velocity of the large droplet before collision / ms -1 ; Velocity of the droplet before collision / ms -1 ; The diameter of the large droplet before collision (in meters); The diameter of the droplet before collision is given in meters. The collision recovery factor is set to 0.85.

[0048] b. Collision and aggregation.

[0049] The formulas for calculating the radius and velocity of the polymer droplet are as follows: , .

[0050] In the formula, Let be the radius of the polymer droplet. The velocity of the polymer droplets.

[0051] c. Stretch separation.

[0052] Define separation volume efficiency The ratio of energy consumed during the coalescence collision of two discrete droplets to the initial energy is used to characterize the energy dissipated during the coalescence collision. The calculation formula is as follows: , , , .

[0053] In the formula, The total surface energy of the droplet is expressed in J. The total tensile energy of the droplet is expressed in J. The total energy dissipated by the droplet is expressed in J. The experimental coefficient is set to 0.3. The fluid density of the droplet is given by kg·m³. -3 ; for and speed difference / ms -1 ; The collision time is expressed in seconds.

[0054] in and The formula for calculating the proportion of satellite droplets obtained from large and small droplets to their original volume is as follows: when hour .

[0055] when hour .

[0056] Assuming that the satellite droplets generated after the separation of the binary droplets have the same particle size and velocity, then the radius of the satellite droplets after the stretching separation of the droplets is... The calculation formula is: , , .

[0057] in, The characteristic radius of the satellite droplet is given in meters (dimensionless). Solving the equation, we get: , .

[0058] In the formula: and The experimental coefficients are 11.5 and 0.45, respectively.

[0059] After the droplets undergo stretching separation, the satellite droplet velocity The calculation formula is: .

[0060] Number of satellite droplets after droplet stretching separation Main droplet radius and Main droplet velocity and The calculation formula is: when hour: , .

[0061] when hour: , .

[0062] when hour: , .

[0063] in, The characteristic time is calculated using the following formula: .

[0064] This is a dimensionless coefficient, and its value is determined by the following formula: ， .

[0065] In the formula: This is the efficiency coefficient for merging.

[0066] d. Splash separation Assuming that the satellite droplets generated after the separation of the binary droplets have the same particle size and velocity, then the radius of the satellite droplets after the backsplash separation is... The calculation formula is: , .

[0067] Among them, dimensionless number Solving the equation, we get: , .

[0068] In the formula, and The experimental coefficients are 11.5 and 0.45, respectively.

[0069] After the discrete droplets separate by splashing, the satellite droplet velocity The calculation formula is: .

[0070] After the discrete droplets separate by backsplash, the velocity of the main droplet... and The calculation formula is: .

[0071] In the formula, For fluid fraction.

[0072] (2) Collisions between discrete droplets and the wall surface.

[0073] The collision behavior between the discrete droplet and the wall is set as a complete bounce, with the size of the discrete droplet remaining unchanged and only its velocity direction changing. The longest contact time between the discrete droplet and the wall is... The calculation formula is:

[0074] .

[0075] In the formula: The experimental constant is taken as 3.92; denoted as the diameter of the discrete droplet.

[0076] Heat transfer from collision and rebound of a single discrete droplet against a wall The calculation formula is: .

[0077] In the formula: The wall temperature; This is the saturation temperature.

[0078] The collision calculation between discrete droplets only considers the interaction between binary droplets. When multiple droplets at a certain position meet the collision conditions, the process is simplified, and the two discrete droplets with the closest relative positions are directly selected for collision calculation.

[0079] The fifth step is to perform calculations on discrete droplet airflow disturbance and breakup and capillary breakup.

[0080] The calculation formulas for discrete droplet airflow disturbance breakup and capillary breakup are as follows: (1) The airflow disturbance is broken.

[0081] A critical value of 22 is set for the discrete droplet breakup time. When the droplet breakup time reaches this critical value, the droplet undergoes gas flow disturbance and breakup. After the gas flow disturbance and breakup, the average volume diameter of the sub-droplets becomes 1 / 5 of the original diameter. The discrete droplet breakup time is determined by the following formula based on the vapor phase velocity and the velocity of each discrete droplet. :

[0082] .

[0083] In the formula: The time per second during which the droplet Weber number exceeds the critical Weber number (set to 6.5). The time for aerodynamic droplet fragmentation is given in seconds.

[0084] (2) Capillary breakage.

[0085] When the droplet diameter is set within ±20% of the droplet's equilibrium diameter, capillary breakup occurs in the discrete droplet, and the volume-average diameter of the broken satellite droplets becomes half of its original diameter. (Droplet equilibrium diameter) The calculation formula is:

[0086] .

[0087] In the formula, This represents the total number of discrete droplets.

[0088] The sixth step is to perform calculations for discrete droplet deposition.

[0089] The deposition of discrete droplets is calculated. Based on the axial height of the liquid film, the relative position of the discrete droplets with the continuous liquid phase in the cooling water flow channel is compared to determine whether droplet deposition has occurred. Deposition simulation is performed on each discrete droplet.

[0090] The seventh step is to perform calculations for the evaporation of discrete droplets.

[0091] The evaporation rate is used to characterize the evaporation process of discrete droplets. The formula for calculating the evaporation rate of discrete droplets in the vapor phase is as follows: .

[0092] In the formula, The specific heat capacity at constant pressure in the vapor phase. For ambient temperature, It is the latent heat of vaporization of the fluid.

[0093] The formula for calculating the interphase heat transfer between discrete droplets and vapor during evaporation is as follows: .

[0094] In the formula, The Nusselt number represents the heat transfer between discrete droplets and vapor phases. The vapor phase Reynolds number; For the vapor phase Prandtl number.

[0095] based on Figure 1 The simulation method for discrete droplet motion in reactor core under reactor coolant loss conditions comprehensively considers the generation, motion, fragmentation, evaporation, deposition, and collision phenomena between discrete droplets and between discrete droplets and heated walls. It performs predictive calculations on these phenomena and can predict various complex behaviors of discrete droplets in reactor channels. It realizes the simulation capability of the entire life cycle of discrete droplets (generation-motion-disappearance), provides an important research tool for reactor system safety analysis programs, and improves the accuracy of predicting entrainment, maximum cladding temperature, and heat transfer on the surface of heated rods.

[0096] When applying the reactor core discrete droplet motion simulation method under reactor coolant loss conditions provided by this invention, it is not necessary to rely on... Figure 1 The steps shown are executed in sequence. The specific execution order of each step can be determined as needed, and this invention does not impose any restrictions on it.

[0097] Furthermore, the present invention also provides application examples of the method of the present invention. Figures 3a-3d This diagram illustrates the spatial distribution and movement of droplets within the cooling water flow channel at different time points in this invention. The simulated operating parameters are: initial temperature 450℃, fluid temperature 54.2℃, and inlet velocity 5.37 cms. -1 Power density 0.70 kWm -1 . Figures 3a-3d The spatial distribution and motion of droplets in the flow channel at four time points: 0.5, 2.0, 3.0, and 5.5. Figures 3a-3d The data points clearly illustrate the spatial position of discrete droplets within the flow channel. The direction vector of each data point indicates the direction of droplet motion, and the vector length proportionally reflects the magnitude of the droplet's net velocity. Comparative analysis of the data at four time points demonstrates that this invention successfully simulates the generation process of discrete droplets and their migration path within the channel. Furthermore, this invention can capture collisions between droplets (as shown in Figure 3a). Figure 3b and Figure 3c As shown), the collision of droplets with the heated wall surface (e.g.) Figure 3a and Figure 3d As shown), the droplet breakup process (such as...) Figure 3b As shown in the figure), and the phenomena of droplet evaporation and deposition (such as...). Figure 3c and Figure 3d (As shown). The results show that the present invention has the ability to simulate the entire life cycle (generation-movement-disappearance) of discrete droplets.

[0098] Figures 4a-4d This is a schematic diagram comparing the number of discrete droplets with the results of autonomous experiments under different verification conditions in this invention. The three sets of experimental conditions are shown in Table 1: Table 1 Parameter Settings The formula for the discrete droplet size distribution probability density function in Experimental Condition 1 of Table 1 is as follows: .

[0099] The formula for the discrete droplet size distribution probability density function in experimental condition 2 in Table 1 is as follows: .

[0100] The formula for the discrete droplet size distribution probability density function in experimental condition 3 in Table 1 is as follows: .

[0101] like Figures 4a-4dAs shown, the droplet number variation trend over time simulated in the three verification conditions of this invention is consistent with the data from independent experiments. In the initial stage of the quenching process, droplets are continuously generated from the continuous liquid surface, causing the droplet density in the flow channel to gradually increase over time. With the continuous increase in the number of droplets, collisions and breakup between droplets lead to a peak in the number of droplets within a short period. However, the sub-droplets generated after droplet breakup have a larger specific surface area, making them more easily evaporated and disappear in vapor convection. Furthermore, as the anti-annular flow film continues to advance within the flow channel, droplet deposition leads to a decreasing trend in the number of discrete droplets within the flow channel. Meanwhile, as... Figure 4d As shown, the cumulative number of droplets simulated by this invention has a relative error of ±10% compared to the experimental value. Therefore, it can be seen that this invention can accurately reflect the change law of the number of droplets in the flow channel over time, and can accurately simulate the number of discrete droplets in the experimental flow channel, demonstrating its effectiveness in simulating the motion of discrete droplets.

[0102] Figures 5a-5d This is a schematic diagram illustrating the simulation verification of the single-bar quenching experimental system under different quenching experimental conditions in this invention. The operating parameter settings for the embodiment are shown in Table 2:

[0103] Table 2 Parameter Settings The droplet size distribution probability density function formulas for experimental conditions 1, 2, and 3 in Table 2 are as follows: .

[0104] like Figures 5a-5d As shown, the simulated droplet number variation over time in the three verification conditions is consistent with the data from the single-bar quenching experiment at Chongqing University. The root mean square errors of the simulated and experimental droplet number values ​​in the three experimental conditions were 3.7937, 3.3024, and 4.5205, respectively. Meanwhile, as... Figure 5d As shown, the relative error between the simulated and experimental values ​​during the quenching process is within ±13%. This also demonstrates that the present invention can accurately reflect the change in the number of droplets in the flow channel over time, as well as the number of discrete droplets in the flow channel.

[0105] In summary, the results of the embodiments demonstrate that the present invention achieves the simulation function of the entire life cycle (generation-movement-disappearance) of discrete droplets. Although the standard deviation of the number of discrete droplets changing over time was larger in the autonomous experiment due to the large flow area and long visualization segment, the deviation between the simulated total number of discrete droplets and the experimental value could be kept within ±13%, which still verifies the reliability of the present invention.

[0106] The above describes a method for simulating the motion of discrete droplets in the reactor core under reactor coolant loss conditions, provided by one or more embodiments of the present invention. Based on the same idea, the present invention also provides a corresponding device for simulating the motion of discrete droplets in the reactor core under reactor coolant loss conditions, such as... Figure 6 As shown.

[0107] Figure 6 A schematic diagram of a reactor core discrete droplet motion simulation device under reactor coolant loss conditions provided by the present invention includes: The initial condition construction module 201 is used to determine the vapor phase velocity based on the steam generation rate, continuous vapor phase fluid density, wetted perimeter of the flow channel, and critical gas film thickness in the flash boiling phenomenon of cooling water; to determine the axial height of the downstream liquid film at the quenching front based on the continuous liquid phase mass change in the flow channel, liquid phase density at saturation temperature, and flow area of ​​the flow channel; and to establish the discrete droplet phase momentum conservation equation. Initialization module 202 is used to determine the number of droplets generated on the liquid film due to the Helmholtz instability mechanism and the number of discrete droplets generated on the liquid film due to the hot wall jet mechanism; and to assign initial values ​​to the particle size, velocity and spatial distribution of the generated discrete droplets. The collision simulation module 203 is used to simulate the collisions between discrete droplets and between discrete droplets and the heated wall surface based on the initial values ​​of each discrete droplet and the phase momentum conservation equation of the discrete droplets. The breakage simulation module 204 is used to simulate the breakage of each discrete droplet by airflow disturbance based on the vapor phase velocity and the velocity of each discrete droplet, and to simulate the breakage of each discrete droplet by capillary breakage based on the diameter of each discrete droplet and the mechanical equilibrium diameter of the droplet. The deposition-evaporation simulation module 205 is used to perform deposition simulation on each discrete droplet based on its relative position to the continuous liquid phase in the flow channel; and to determine the evaporation rate of each discrete droplet in the vapor phase in order to perform evaporation simulation on the discrete droplets.

[0108] Specific limitations regarding the reactor core discrete droplet motion simulation device under reactor coolant loss conditions can be found in the limitations of the reactor core discrete droplet motion simulation method under reactor coolant loss conditions described above, and will not be repeated here. Each module in the aforementioned reactor core discrete droplet motion simulation device under reactor coolant loss conditions can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the corresponding operations of each module.

[0109] The present invention also provides a computer-readable storage medium storing a computer program that can be used to execute the above-described... Figure 1A method for simulating the motion of discrete droplets in the reactor core under reactor coolant loss conditions is provided.

[0110] This invention also provides a computer device. At the hardware level, the computer device includes a processor, an internal bus, a network interface, memory, and non-volatile memory, and may also include other hardware required for various operations. The processor reads the corresponding computer program from the non-volatile memory into memory and then executes it to achieve the above-mentioned functions. Figure 1 A method for simulating the motion of discrete droplets in the reactor core under reactor coolant loss conditions is provided.

[0111] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. Any references to memory, storage, databases, or other media used in the embodiments provided by this invention can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, or optical storage, etc. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0112] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this invention.

Claims

1. A method for simulating the motion of discrete droplets in a reactor core under reactor coolant loss conditions, characterized in that, include: The vapor phase velocity is determined based on the steam generation rate, continuous vapor phase fluid density, wetted perimeter length of the cooling water flow channel, and critical gas film thickness during the flash boiling phenomenon of the reactor core cooling water; the axial height of the downstream liquid film at the quenching front is determined based on the continuous liquid phase mass change in the cooling water flow channel, the liquid phase density at saturation temperature, and the flow area of ​​the cooling water flow channel. Establish the momentum conservation equation for discrete droplets; The number of discrete droplets generated on the liquid film caused by the Helmholtz instability mechanism and the hot wall jet mechanism were determined respectively; initial values ​​were assigned to the particle size, velocity and spatial distribution of the discrete droplets based on the axial height of the liquid film. Based on the initial values ​​of each discrete droplet and the phase momentum conservation equation of the discrete droplets, the collisions between discrete droplets and between discrete droplets and the heated wall are simulated. Based on the vapor phase velocity and the velocity of each discrete droplet, airflow disturbance and breakup simulation is performed on each discrete droplet. Based on the diameter of each discrete droplet and the droplet mechanical equilibrium diameter, capillary breakup simulation is performed on each discrete droplet. The relative positions of each discrete droplet to the continuous liquid phase in the cooling water flow channel are determined based on the axial height of the liquid film, and deposition simulation is performed on each discrete droplet; the evaporation rate of each discrete droplet in the vapor phase is determined to perform evaporation simulation on the discrete droplets.

2. The method for simulating the motion of discrete droplets in the reactor core under reactor coolant loss conditions as described in claim 1, characterized in that, The establishment of the discrete droplet phase momentum conservation equation specifically includes: Assuming that the discrete droplet is a standard sphere, there is no temperature gradient inside the discrete droplet, the discrete droplet has no rotation, there is no pressure gradient inside or outside the discrete droplet, the relative velocity between the discrete droplet and the load gas phase remains constant within the same time step, and the diffusion force caused by the concentration gradient of the discrete droplet is ignored, the momentum conservation equation of the discrete droplet is discretized in time to obtain the axial momentum equation and the radial momentum equation of the discrete droplet.

3. The method for simulating the motion of discrete droplets in the reactor core under reactor coolant loss conditions as described in claim 1, characterized in that, The determination of the number of discrete droplets generated on the liquid film due to the Helmholtz instability mechanism and the hot-wall jet mechanism specifically includes: The number of discrete droplets generated on the liquid film due to the Helmholtz instability mechanism is determined by the following formula: ； ， ， ； The number of discrete droplets generated on the liquid film due to the hot-wall jetting mechanism is determined by the following formula: ； ， ， ； in, The number of discrete droplets generated on the liquid film due to the Helmholtz instability mechanism. The characteristic length is the heating rod thermal perimeter during diffuse flow film boiling and the reverse annular flow liquid film length during reverse annular flow. The characteristic droplet diameter, This is the critical wavelength. The hydraulic diameter, The fluid density of the continuous vapor phase. For vapor phase velocity, For smooth interfaces, the coefficient of friction is... The relative Reynolds number of the vapor phase. For fluid surface tension, It is the acceleration due to gravity. The number of discrete droplets generated on the liquid film due to the hot-wall jet mechanism. The thickness of the reverse annular flow liquid film is superimposed on the length of the liquid film in the portion where the fluctuation amplitude is greater than the width of the cooling water flow channel; This refers to the amplitude of the anti-annular flow film fluctuation. Let be the viscosity of the vapor phase fluid. For experimental coefficients, This represents the interfacial shear force of the liquid film. Let be the interfacial friction coefficient of the liquid film. For the velocity of the continuous liquid phase, The relative Reynolds number of the liquid phase. The density of the continuous liquid phase.

4. The method for simulating the motion of discrete droplets in the reactor core under reactor coolant loss conditions as described in claim 1, characterized in that, The simulation of collisions between discrete droplets and between discrete droplets and the heated wall surface is based on the initial values ​​of each discrete droplet and the phase momentum conservation equation of the discrete droplets. Specifically, this includes: Based on the initial values ​​of each discrete droplet and the phase momentum conservation equation of the discrete droplets, the complete rebound, collision aggregation, stretching separation and splash separation between discrete droplets are simulated. Based on the initial values ​​of each discrete droplet, the phase momentum conservation equation of the discrete droplet, the longest contact time between the discrete droplet and the wall, the temperature of the heated wall and the temperature of the discrete droplet, the heat transfer during the complete rebound between the discrete droplet and the heated wall is simulated.

5. The method for simulating the motion of discrete droplets in the reactor core under reactor coolant loss conditions as described in claim 1, characterized in that, The simulation of airflow disturbance and breakup of each discrete droplet, based on the vapor phase velocity and the velocity of each discrete droplet, specifically includes: When the discrete droplet breakup time reaches the preset critical value, the discrete droplet undergoes airflow disturbance breakup. After the airflow disturbance breakup, the average volumetric diameter of the sub-droplets is 1 / 5 of the original discrete droplet diameter. During airflow disturbance breakup, the discrete droplet breakup time is determined by the following formula based on the vapor phase velocity and the velocity of each discrete droplet: ； in, For discrete droplet breakup time. The fluid density of the continuous vapor phase. The fluid density of the continuous liquid phase. For discrete droplet aerodynamic breakup time. The time when the Weber number of the discrete droplet exceeds the critical Weber number. For vapor phase velocity, For the velocity of discrete droplets, For time.

6. The method for simulating the motion of discrete droplets in the reactor core under reactor coolant loss conditions as described in claim 1, characterized in that, The capillary breakup simulation of each discrete droplet based on its diameter and equilibrium diameter includes: When the diameter of the discrete droplet falls within ±20% of the droplet's equilibrium diameter, capillary breakup occurs, and the volume-average diameter of the broken satellite droplets becomes half the original discrete droplet diameter. During capillary breakup, the droplet's equilibrium diameter is determined using the following formula: ； in, The droplet's equilibrium diameter is... The total number of discrete droplets. denoted as the diameter of the discrete droplet.

7. The method for simulating the motion of discrete droplets in the reactor core under reactor coolant loss conditions as described in claim 1, characterized in that, The determination of the evaporation rate of each discrete droplet in the vapor phase, in order to simulate the evaporation of the discrete droplets, specifically includes: The evaporation rate of each discrete droplet in the vapor phase is determined by the following formula: ； The interphase heat transfer between discrete droplets and vapor during the evaporation process is determined by the following formula: ； in, Let be the evaporation rate of discrete droplets in the vapor phase. Let be the radius of the discrete droplet. The vapor phase thermal conductivity is The specific heat capacity at constant pressure in the vapor phase. For ambient temperature, For discrete droplet temperatures, The latent heat of vaporization of the fluid, The Nusselt number represents the heat transfer rate between discrete droplets and vapor phases. The relative Reynolds number of the vapor phase. For the vapor phase Prandtl number.

8. A device for simulating the motion of discrete droplets in a reactor core under reactor coolant loss conditions, characterized in that, include: The initial condition construction module is used to determine the vapor phase velocity based on the steam generation rate, continuous vapor phase fluid density, wetted perimeter of the cooling water flow channel, and critical vapor film thickness in the flash boiling phenomenon of cooling water; and to determine the axial height of the downstream liquid film at the quenching front based on the continuous liquid phase mass change in the cooling water flow channel, liquid phase density at saturation temperature, and flow area of ​​the cooling water flow channel. Establish the momentum conservation equation for discrete droplets; The initialization module is used to determine the number of discrete droplets generated on the liquid film due to the Helmholtz instability mechanism and the hot wall jet mechanism, respectively; and to assign initial values ​​to the particle size, velocity and spatial distribution of the discrete droplets according to the axial height of the liquid film. The collision simulation module is used to simulate the collisions between discrete droplets and between discrete droplets and the heated wall surface, based on the initial values ​​of each discrete droplet and the phase momentum conservation equation of the discrete droplets. The breakage simulation module is used to simulate the breakage of each discrete droplet by airflow disturbance based on the vapor phase velocity and the velocity of each discrete droplet, and to simulate the breakage of each discrete droplet by capillary breakage based on the diameter of each discrete droplet and the mechanical equilibrium diameter of the droplet. The deposition-evaporation simulation module is used to determine the relative position of each discrete droplet with the continuous liquid phase in the cooling water flow channel based on the axial height of the liquid film, and to perform deposition simulation for each discrete droplet; it also determines the evaporation rate of each discrete droplet in the vapor phase to perform evaporation simulation for the discrete droplets.

9. A computer-readable storage medium, characterized in that, The storage medium stores a computer program that, when executed by a processor, implements the method as described in any one of claims 1 to 7.

10. A computer device, characterized in that, It includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the method as described in any one of claims 1 to 7.

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