A method and system for analysis of a re-submersion cooling process

Abstract

The application discloses a re-submerged cooling process analysis method and system, comprising the following steps: step 1, obtaining re-submerged process data; step 2, obtaining liquid core shear stress relationship and constitutive relationship according to the re-submerged process data, and obtaining disturbance wave height; step 3, constructing liquid film dynamics balance relationship according to local quenching in the cooling process, and obtaining average vapor film thickness; step 4, obtaining axial distribution of minimum film boiling temperature according to the disturbance wave height and the average vapor film thickness; step 5, obtaining quenching time at different axial heights according to the axial distribution of the minimum film boiling temperature, obtaining the relationship among quenching speed, quenching time and height, and solving the quenching speed at all quenching times, that is, completing the re-submerged cooling process analysis; the application solves the strong correlation problem of time-physical behavior of two-phase evolution in the whole re-submerged process, and realizes accurate prediction of the whole strong transient re-submerged cooling process.

Description

Technical Field

[0001] This invention relates to the field of nuclear safety accident analysis methods, specifically to a method and system for analyzing reflooding cooling processes. Background Technology

[0002] Reflooding is a necessary means of accident control, and clarifying the key behaviors during reflooding is crucial for accident mitigation. However, the high-temperature reflooding cooling process is a complex thermodynamic, non-equilibrium, strongly transient two-phase flow heat transfer process, encompassing film boiling heat transfer in the precursor cooling stage and high-temperature quenching near the quenching front. Existing reflooding cooling analysis methods and models lack a process for analyzing the reflooding cooling process based on mechanistic behavior. Existing reflooding models address a single problem object, failing to fully elucidate the physical behavior of the entire reflooding process, and most models are empirical formulas, which, while showing accurate predictions within a certain range, lack physical meaning. Although reflooding calculation methods deconstruct the reflooding process temporally through two-phase governing equations, they also lack physical behavior and cannot explain local anomalies in actual results.

[0003] For example, existing patent 2022116081099 discloses a real-time monitoring device and terminal for the quenching front position of a reflooding experimental apparatus. It uses a large number of thermocouples arranged along the axial path to monitor the quenching front information, thus predicting the quenching propulsion behavior during reflooding. Although this method constructs an effective wall temperature-time change curve, it requires a large number of thermocouples for monitoring, making it difficult to effectively predict reflooding behavior under complex structures. Patent 202111424450X discloses a method for analyzing water loss accidents, achieving analysis of the entire water loss accident system through "hydraulic geometric modeling - sensitivity analysis - key model analysis - double 95% requirement analysis." However, in the "key model analysis" section of the post-water loss accident calculation program, empirical relationships are used for model closure, lacking guidance from the physical behavior of mechanistic models, making it difficult to explain local anomalies. Summary of the Invention

[0004] This invention provides a method and system for analyzing the reflooding cooling process, addressing the problems existing in the prior art.

[0005] The technical solution adopted in this invention is: a method for analyzing a re-flooding cooling process, comprising the following steps:

[0006] Step 1: Obtain re-flooding process data;

[0007] Step 2: Based on the resubmergence process data, obtain the shear stress relationship and constitutive relationship of the liquid core, and obtain the wave height of the disturbance wave;

[0008] Step 3: Based on the local quenching during the cooling process, construct the liquid film dynamic equilibrium relationship to obtain the average vapor film thickness;

[0009] Step 4: Obtain the axial distribution of the minimum film boiling temperature based on the disturbance wave height obtained in Step 2 and the average vapor film thickness obtained in Step 3;

[0010] Step 5: Based on the axial distribution of the minimum film boiling temperature, obtain the quenching time at different axial heights, obtain the relationship between quenching rate, quenching time and height, solve for the quenching rate at all quenching times, and thus complete the analysis of the re-submersion cooling process.

[0011] Furthermore, the reflooding process data includes pressure transient data and reflooding process image data;

[0012] After preprocessing, pressure transient data and image data are used to obtain liquid film peaks, disturbance wave velocities, and interfacial shear forces.

[0013] Furthermore, the shear stress relationship and constitutive relationship in step 2 are as follows:

[0014]

[0015] In the formula: τ i f is the shear force at the vapor-liquid interface. i ρ is the interfacial friction coefficient. l v is the density of the liquid phase. l Let be the liquid phase velocity, 'a' be the disturbance wave height, and 'C' be the liquid phase velocity. w To characterize the influence coefficient of surface tension on internal flow, μ l This represents the viscosity of the liquid phase.

[0016] Furthermore, the process for obtaining the average vapor film thickness in step 2 is as follows:

[0017] The dynamic equilibrium relationship of the liquid film is constructed based on the critical state of the KH boundary.

[0018] Furthermore, the calculation process for the average vapor film thickness is as follows:

[0019] The dynamic equilibrium relationship of the liquid film is as follows:

[0020] F p =F v +F σ-y (3)

[0021] In the formula: F p F is the vapor-liquid phase pressure difference. v For evaporation kinetic force, F σ-y The surface tension is in the Y direction;

[0022] in:

[0023]

[0024] F σ-y =2σWsinα (6)

[0025] In the formula: ρ g v is the density of the vapor phase. g Let δ be the vapor phase velocity. g Where W is the average vapor film thickness and h is the characteristic length. fg Let q' be the latent heat and q′ be the total heat flux density, where q′ = q + q T q is the wall heat flux density, q T The heat flux density resulting from sensible heat, λ c It is the critical wavelength;

[0026] Substituting equations (4), (5), and (6) into equation (3) yields the average vapor film thickness.

[0027] Furthermore, in step 4, a / δ g >1 is used as a criterion to construct an initial minimum film boiling temperature prediction model. The temperature change caused by local rapid cooling is substituted into the initial minimum film boiling temperature prediction model to obtain the required minimum film boiling temperature prediction model. The axial temperature distribution of the minimum film boiling temperature is obtained based on the minimum film boiling temperature prediction model.

[0028] Furthermore, the relationship between the quenching rate, quenching time, and height in step 5 is as follows:

[0029]

[0030] In the formula: v i Let L be the quenching rate of the i-th quenching. i Let t be the height of the i-th axis. i Let i be the i-th sudden cooling moment, where i is the sequence number.

[0031] A reflooding cooling process analysis system, comprising:

[0032] Transient fluctuation characteristics under high temperature phase transition, vapor film collapse quenching mechanism, and flood cooling process quenching module;

[0033] The transient wave characteristics module under high temperature phase transition constructs the liquid core shear stress relationship and constitutive relationship based on the resubmergence process data, and obtains the disturbance wave height;

[0034] The vapor film collapse quenching mechanism module obtains the average vapor film thickness based on the vapor film dynamics equilibrium relationship.

[0035] The quenching module in the submerged cooling process obtains the axial temperature distribution of the minimum film boiling temperature based on the disturbance wave height and the average vapor film thickness; based on the axial temperature distribution of the minimum film boiling temperature, it obtains a prediction model of the quenching front propulsion velocity distribution, thus completing the quenching process analysis.

[0036] A computer device includes a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the steps of the method.

[0037] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method.

[0038] The beneficial effects of this invention are:

[0039] This invention addresses the problem of strong time-physical correlation in the two-phase evolution of the entire resubmergence process by combining the transient fluctuation characteristics of anti-annular flow, the quenching mechanism of vapor film collapse, and the idea of ​​quenching caused by precursor cooling heat transfer under multiple factors. It also combines the axial distribution characteristics of initial wall temperature, minimum film boiling temperature, and decoupling of heat transfer behavior to obtain the advancement of the quenching front. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the analytical method of the present invention.

[0041] Figure 2 This is the analysis process of the entire re-flooding process in the embodiments of the present invention.

[0042] Figure 3 This describes the processing procedure of the transient fluctuation characteristic module under high-temperature phase transition in this embodiment of the invention.

[0043] Figure 4 This is a schematic diagram of the anti-annular flow core fluctuation in an embodiment of the present invention.

[0044] Figure 5 This is a schematic diagram of the kinetic equilibrium relationship of the vapor film in an embodiment of the present invention.

[0045] Figure 6 This is the re-flooding decoupling process in an embodiment of the present invention. Detailed Implementation

[0046] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0047] A method for analyzing a reflooding cooling process includes the following steps:

[0048] Step 1: Obtain re-flooding process data;

[0049] Step 2: Based on the resubmergence process data, obtain the shear stress relationship and constitutive relationship of the liquid core, and obtain the wave height of the disturbance wave;

[0050] Step 3: Based on the local quenching during the cooling process, construct the liquid film dynamic equilibrium relationship to obtain the average vapor film thickness;

[0051] Step 4: Obtain the axial distribution of the minimum film boiling temperature based on the disturbance wave height obtained in Step 2 and the average vapor film thickness obtained in Step 3;

[0052] Step 5: Based on the axial distribution of the minimum film boiling temperature, obtain the quenching time at different axial heights, obtain the relationship between quenching rate, quenching time and height, solve for the quenching rate at all quenching times, and thus complete the analysis of the re-submersion cooling process.

[0053] A reflooding cooling process analysis system, comprising:

[0054] Transient fluctuation characteristics under high temperature phase transition, vapor film collapse quenching mechanism, and flood cooling process quenching module;

[0055] The transient wave characteristics module under high temperature phase transition constructs the liquid core shear stress relationship and constitutive relationship based on the resubmergence process data, and obtains the disturbance wave height;

[0056] The vapor film collapse quenching mechanism module obtains the average vapor film thickness based on the vapor film dynamics equilibrium relationship.

[0057] The quenching module in the submerged cooling process obtains the axial temperature distribution of the minimum film boiling temperature based on the disturbance wave height and the average vapor film thickness; based on the axial temperature distribution of the minimum film boiling temperature, it obtains a prediction model of the quenching front propulsion velocity distribution, thus completing the quenching process analysis.

[0058] like Figure 1 and Figure 2 As shown, a method for analyzing a reflooding cooling process includes the following steps:

[0059] Step 1: Obtain re-flooding process data;

[0060] Conduct reflooding cooling experiments under different thermal parameters to obtain the required data, including visualization results, experimental data such as temperature and pressure.

[0061] Step 2: Based on the resubmergence process data, obtain the shear stress relationship and constitutive relationship of the liquid core, and obtain the wave height of the disturbance wave;

[0062] The study process of transient fluctuation characteristics of anti-annular flow liquid film under high temperature phase change is as follows: Figure 3 As shown, a multi-parameter visualization study of submersion cooling was conducted based on a visualization resubmersion experimental rig. The obtained images were processed to obtain the liquid film peaks and liquid film wave propagation velocities under reverse annular flow; the evolution characteristics of liquid film amplitude and frequency were revealed using the multi-scale entropy method and wavelet method.

[0063] In reverse annular flow, the liquid struggles to break through the vapor film and wet the high-temperature wall surface; therefore, the vapor-liquid positions differ from those in annular flow. The liquid core is located at the center of the channel, and the vapor film covers the surface of the high-temperature wall. A schematic diagram of reverse annular flow is shown below. Figure 4 As shown. The height 'a' from the baseline to the peak of the liquid film is the disturbance wave height. The disturbance wave height can be obtained from the shear stress relationship and constitutive relationship constructed from the liquid core.

[0064]

[0065]

[0066] In the formula: τ i f is the shear force at the vapor-liquid interface. i ρ is the interfacial friction coefficient. l v is the density of the liquid phase. l Let be the liquid phase velocity, 'a' be the disturbance wave height, and 'C' be the liquid phase velocity. w To characterize the influence coefficient of surface tension on internal flow, N μ To decide C w The parameter, μ l ρ is the liquid phase viscosity, Δρ is the density difference between the vapor and liquid phases, and g is the gravitational constant.

[0067] Step 3: Based on the local quenching during the cooling process, construct the liquid film dynamic equilibrium relationship to obtain the average vapor film thickness;

[0068] Because the vapor generated by the evaporation of coolant in the narrow channel flows rapidly, the two-phase flow behavior in the channel is complex and the turbulence is intense. Before the quenching, there is not only a time-cumulative precursor cooling heat transfer process, but also a local quenching phenomenon caused by the instability of the KH interface.

[0069] Establish the dynamic equilibrium relationship of the liquid film (perpendicular to the wall) based on the force conditions, as follows: Figure 5 As shown, the average vapor film thickness δ is calculated using the following formula. g :

[0070] F p =F v +F σ-y (3)

[0071] In the formula: F p F is the vapor-liquid phase pressure difference. v For evaporation kinetic force, F σ-y The surface tension is in the Y direction;

[0072]

[0073] F σ-y =2σWsinα (6)

[0074] In the formula: ρ g v is the density of the vapor phase. g Let δ be the vapor phase velocity. g Where W is the average vapor film thickness and h is the characteristic length.fg Let q' be the latent heat and q′ be the total heat flux density, where q′ = q + q T q is the wall heat flux density, q T The heat flux density resulting from sensible heat, λ c This is the critical wavelength for instability at the KH interface;

[0075] Substituting equations (4), (5), and (6) into equation (3) yields the average vapor film thickness.

[0076] Step 4: Obtain the axial distribution of the minimum film boiling temperature based on the disturbance wave height obtained in Step 2 and the average vapor film thickness obtained in Step 3;

[0077] a / δ g >1 was used as the criterion to construct the initial minimum film boiling temperature prediction model T. min Substituting the temperature change caused by localized rapid cooling into the initial minimum film boiling temperature prediction model T min The minimum film boiling temperature prediction model is obtained; the axial temperature distribution of the minimum film boiling temperature is obtained based on the minimum film boiling temperature prediction model.

[0078] The specific process is as follows: Localized rapid cooling phenomena are observed through observations and wall temperature curves, and the characteristics of localized rapid cooling are extracted. Finally, based on the hypothesis of localized rapid cooling, the temperature drop effect caused by localized rapid cooling is obtained and substituted back into T. min The model was then used to reconstruct a strong transient phenomenological minimum film boiling temperature prediction model.

[0079]

[0080] In the formula: Re in For the inlet Reynolds number, Ja sub Jacobs, μ, is a supercooled coolant. f For the dynamic viscosity of the liquid phase, ρ f v is the density of the liquid phase. f Let T be the liquid phase velocity, σ be the surface tension coefficient, α be the disturbance wave angle, q be the wall heat flux density, and T be the total liquid phase velocity. sat h is the saturation temperature under the current pressure. IAFB The heat transfer coefficient for reverse annular flow is given.

[0081] Step 5: Based on the axial distribution of the minimum film boiling temperature, obtain the quenching time at different axial heights, obtain the relationship between quenching rate, quenching time and height, solve for the quenching rate at all quenching times, and thus complete the analysis of the re-submersion cooling process.

[0082] The quenching rate is a quantitative standard for determining whether a superheated wall can be cooled rapidly. However, the complex flooding process corresponds to the unknown axial distribution of quenching temperature and heat transfer process. Therefore, it is necessary to explore the temporal distribution of quenching behavior along the axial direction and establish a quenching rate prediction model. The process is as follows: Figure 6 As shown.

[0083] The minimum film boiling temperature prediction model is used to obtain the axial temperature distribution {T} of the minimum film boiling temperature. min-1 T min-2 …, T min-n}, taking this result as the focus of the evolution process, with the peak cladding temperature {T1, T2, ..., T} as the key point. n As the starting point of the evolution process, the coupling of droplet-like film boiling heat transfer, anti-annular film boiling heat transfer, and axial heat conduction (the total heat transfer coefficient of the three types of heat transfer is h) is considered. 先驱冷却 The quenching time L at different axial heights is obtained according to the following formula.

[0084]

[0085] In the formula: δ is the thickness of the heating plate, ρ is the density of the heating plate, c is the specific heat capacity, and ΔT(t) is the temperature change at time t.

[0086] According to equation (9), based on the axial height of the measuring point {L1, L2, ..., L...} n By constructing the "velocity-time-distance" relationship, we obtain the propulsion velocity distribution model {v1, v2, ..., v} of the quenching front. n}

[0087]

[0088] In the formula: v i Let L be the quenching rate of the i-th quenching. i Let t be the height of the i-th axis. i Let i be the i-th sudden cooling moment, where i is the sequence number.

[0089] This invention considers the transient fluctuation characteristics of anti-annular flow, the quenching mechanism of film collapse, and the method of quenching caused by precursor cooling heat transfer under multiple factors. By combining initial conditions (initial wall temperature), endpoint conditions (axial distribution characteristics of minimum film boiling temperature), and decoupling heat transfer behavior to obtain the advancement of the quenching front, it solves the problem of strong time-physical correlation in the two-phase evolution of the entire reflooding process, achieving accurate prediction of the entire strong transient reflooding cooling process. A predictive solution method is constructed to couple the time-series relationships of complex flow and heat transfer behaviors in reflooding cooling. It is applicable to the complete flow and heat transfer behavior of the reflooding process across a wide temperature range from the initial stage of core exposure to before core melting and collapse, regardless of different structures.

Claims

1. A method for analyzing a reflooding cooling process, characterized in that, Includes the following steps: Step 1: Obtain data on the re-flooding process; Step 2: Based on the resubmergence process data, obtain the shear stress relationship and constitutive relationship of the liquid core, and obtain the disturbance wave height; the shear stress relationship and constitutive relationship are as follows: （1） （2） In the formula: τ i This refers to the shear force at the vapor-liquid interface. The coefficient of interfacial friction, The density of the liquid phase is... For liquid phase velocity, a For the height of the disturbance wave, To characterize the influence coefficient of surface tension on internal flow, The viscosity is the liquid phase viscosity. Step 3: Based on the localized rapid cooling during the cooling process, establish the liquid film dynamic equilibrium relationship to obtain the average vapor film thickness; the calculation process for the average vapor film thickness is as follows: The dynamic equilibrium relationship of the liquid film is as follows: （3） In the formula: This refers to the vapor-liquid phase pressure difference. For evaporation kinetic force, The surface tension is in the Y direction; in: （4） （5） （6） In the formula: Where is the density of the vapor phase. For vapor phase velocity, The average vapor film thickness, For characteristic length, Latent heat, Let be the total heat flux density, where , The wall heat flux density, The heat flux density resulting from sensible heat. It is the critical wavelength; The surface tension coefficient, The angle between the disturbance waves; Substituting equations (4), (5), and (6) into equation (3) yields the average vapor film thickness. Step 4: Based on the disturbance wave height obtained in Step 2 and the average film thickness obtained in Step 3, obtain the axial distribution of the minimum film boiling temperature; As a criterion, an initial minimum film boiling temperature prediction model is constructed. The temperature change caused by local rapid cooling is substituted into the initial minimum film boiling temperature prediction model to obtain the required minimum film boiling temperature prediction model. The axial temperature distribution of the minimum film boiling temperature is obtained based on the minimum film boiling temperature prediction model. Step 5: Based on the axial distribution of the minimum film boiling temperature, obtain the quenching time at different axial heights, and determine the relationship between quenching rate, quenching time, and height. Solve for the quenching rate at all quenching times to complete the re-submersion cooling process analysis; the relationship between quenching rate, quenching time, and height is as follows: In the formula: For the first i A rapid cooling rate, For the first i One axial height, For the first i A sudden cold moment, i For serial numbers.

2. The method for analyzing a re-flooding cooling process according to claim 1, characterized in that, The reflooding process data includes pressure transient data and reflooding process image data; After preprocessing, pressure transient data and image data are used to obtain liquid film peaks, disturbance wave velocities, and interfacial shear forces.

3. The method for analyzing a re-flooding cooling process according to claim 1, characterized in that, The process for obtaining the average vapor film thickness in step 2 is as follows: The dynamic equilibrium relationship of the liquid film is constructed based on the critical state of the KH boundary.

4. An analysis system employing the re-flooding cooling process analysis method as described in any one of claims 1 to 3, characterized in that, include: Transient fluctuation characteristics under high temperature phase transition, vapor film collapse quenching mechanism, and flood cooling process quenching module; The transient wave characteristics module under high temperature phase transition constructs the liquid core shear stress relationship and constitutive relationship based on the resubmergence process data, and obtains the disturbance wave height; The vapor film collapse quenching mechanism module obtains the average vapor film thickness based on the vapor film dynamics equilibrium relationship. The quenching module in the submerged cooling process obtains the axial temperature distribution of the minimum film boiling temperature based on the disturbance wave height and the average vapor film thickness; based on the axial temperature distribution of the minimum film boiling temperature, it obtains a prediction model of the quenching front propulsion velocity distribution, thus completing the quenching process analysis.

5. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 3.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 3.

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