Method and system for analyzing reflooding cooling process

Abstract

The invention discloses a reflooding cooling process analysis method and system. The method comprises the following steps: step 1, obtaining reflooding process data; 2, according to the re-submerging process data, obtaining a liquid core shear stress relation and a constitutive relation, and obtaining a disturbance wave height; 3, according to local shock cooling in the cooling process, a liquid film dynamic equilibrium relation is constructed, and the average vapor film thickness is obtained; 4, axial distribution of the minimum film state boiling temperature is obtained according to the disturbance wave height and the average steam film thickness; 5, shock cooling moments at different axial heights are obtained according to the axial distribution of the minimum film state boiling temperature, the relationship among the shock cooling speed, the shock cooling moments and the heights is obtained, the shock cooling speed of all the shock cooling moments is solved, and then analysis of the re-submerging cooling process is completed; according to the method, the problem of strong correlation of time-physical behaviors of two-phase evolution in the whole re-submerging process is solved, and accurate prediction of the whole strong transient re-submerging cooling process is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear safety accident analysis methods, and in particular to a reflooding cooling process analysis method and system. Background Art

[0002] The reflooding process is a necessary means of accident control, and clarifying the key behaviors in reflooding is of great significance for accident mitigation. However, the high-temperature submergence cooling process is a complex thermodynamic non-equilibrium, highly transient two-phase flow heat transfer process, which includes 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. The existing reflooding models face a single problem object and fail to fully explain the physical behavior of the entire reflooding process. In addition, most models are empirical relationships. Although they show accurate predictions within a certain range, they lack physical meaning. Although the reflooding calculation method deconstructs the reflooding process in a temporal manner through the two-phase control equation, it is also unable to explain the local anomalies in the actual results due to the lack of physical behavior.

[0003] For example, the existing patent 2022116081099 discloses a real-time monitoring device, device and terminal for the position of the quenching front of a re-flooding experimental device. By arranging a large number of thermocouples along the axial direction to monitor the quenching front information, the prediction of the re-flooding quenching advancement behavior can be achieved. Although this method constructs an effective wall temperature-time change curve, it requires the arrangement of a large number of thermocouples for monitoring, and it is difficult to effectively predict the re-flooding behavior under complex structures. Patent 202111424450X discloses a method for analyzing a loss of water accident, which realizes the analysis of the entire system of the loss of water accident through "hydraulic geometric modeling-sensitivity analysis-key model analysis-double 95% requirement analysis". However, in the "key model analysis" in the calculation program after the loss of water accident, the empirical relationship is used to close the model, lacking the physical behavior guidance of the mechanism model, and it is difficult to explain local abnormal phenomena. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a re-flooding cooling process analysis method and system.

[0005] The technical solution adopted by the present invention is: a re-flooding cooling process analysis method, comprising the following steps:

[0006] Step 1: Obtain reflooding process data;

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

[0008] Step 3: Based on the local quenching during the cooling process, the liquid film dynamics equilibrium relationship is constructed 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: According to the axial distribution of the minimum film boiling temperature, the quenching moment at different axial heights is obtained, and the relationship between the quenching speed, quenching time and height is obtained. The quenching speed at all quenching moments is solved, and the analysis of the re-submergence cooling process is completed.

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

[0012] The pressure transient data and image data are preprocessed to obtain the liquid film peak, disturbance wave velocity and interface shear force.

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

[0014]

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

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

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

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

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

[0020] F p =F v +F σ-y (3)

[0021] Where: F p is the vapor-liquid pressure difference, F v is the evaporation kinetic force, F σ-y is the surface tension in the Y direction;

[0022] in:

[0023]

[0024] F σ-y =2σWsinα (6)

[0025] Where: ρ g is the vapor phase density, v g is the vapor phase velocity, δ g is the average film thickness, W is the characteristic length, h fg is the latent heat, q′ is the total heat flux, where q′=q+q T , q is the wall heat flux density, q T is the heat flux density brought by sensible heat, λ c is the critical wavelength;

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

[0027] Furthermore, in step 4, a / δ g >1 is used as the criterion to construct an initial minimum film boiling temperature prediction model. The temperature change caused by local sudden 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 according to the minimum film boiling temperature prediction model.

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

[0029]

[0030] Where: v i is the ith quenching rate, L i is the ith axial height, t i is the i-th sudden cooling moment, and i is the sequence number.

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

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

[0033] The transient wave characteristics module under high-temperature phase change constructs the liquid core shear stress relationship and constitutive relationship based on the reflooding process data to obtain 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 of 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, the quenching front advancement velocity distribution prediction model is obtained to complete the quenching process analysis.

[0036] A computer device includes a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the method when executing the computer program.

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

[0038] The beneficial effects of the present invention are:

[0039] The present invention decouples the transient fluctuation characteristics of the anti-annular flow, the vapor film collapse quenching mechanism, and the idea of quenching caused by pioneer cooling and heat transfer under multiple factors, and obtains the advancement of the quenching front by combining the initial wall temperature, the axial distribution characteristics of the minimum film boiling temperature, and the heat transfer behavior, thereby solving the problem of strong correlation between the time and physical behavior of the two-phase evolution in the entire reflooding process. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the analytical method of the present invention.

[0041] Figure 2 This is an analysis of the entire reflooding process in an embodiment of the present invention.

[0042] Figure 3 This is the processing process of the transient fluctuation characteristic module under high temperature phase change in an embodiment of the present invention.

[0043] Figure 4 Schematic diagram of the reverse annular flow core fluctuation in an embodiment of the present invention.

[0044] Figure 5 Schematic diagram of the dynamic equilibrium relationship of the steam film in an embodiment of the present invention.

[0045] Figure 6 This is the reflooding decoupling process in an embodiment of the present invention. DETAILED DESCRIPTION

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

[0047] A reflooding cooling process analysis method comprises the following steps:

[0048] Step 1: Obtain reflooding process data;

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

[0050] Step 3: Based on the local quenching during the cooling process, the liquid film dynamics equilibrium relationship is constructed 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: According to the axial distribution of the minimum film boiling temperature, the quenching moment at different axial heights is obtained, and the relationship between the quenching speed, quenching time and height is obtained. The quenching speed at all quenching moments is solved, and the analysis of the re-submergence cooling process is completed.

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

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

[0055] The transient wave characteristics module under high-temperature phase change constructs the liquid core shear stress relationship and constitutive relationship based on the reflooding process data to obtain 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 of 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, the quenching front advancement velocity distribution prediction model is obtained to complete the quenching process analysis.

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

[0059] Step 1: Obtain reflooding process data;

[0060] Conduct re-flooding cooling experiments under different thermal parameters to obtain the required data, including visualization results, temperature, pressure and other experimental data.

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

[0062] The research process of transient fluctuation characteristics of anti-annular flow liquid film under high temperature phase change is as follows Figure 3 As shown in Figure 2, a multi-parameter visualization study of submerged cooling was conducted based on a visual re-submergence experimental rig. The resulting images were processed to reveal the liquid film wave crests and wave propagation velocities under anti-annular flow. Multiscale entropy and wavelet methods were used to reveal the evolution characteristics of the liquid film wave amplitude and frequency.

[0063] Under the anti-annular flow, it is difficult for the liquid to break through the vapor film and wet the high-temperature wall. Therefore, the vapor-liquid position is different from the annular flow condition. The liquid core is located in the center of the channel, and the vapor film covers the surface of the high-temperature wall. The flow diagram of the anti-annular flow is shown in the figure below. Figure 4 The height a from the baseline to the liquid film peak is the perturbation wave height. The perturbation wave height can be obtained from the shear stress relationship and constitutive relationship of the liquid core.

[0064]

[0065]

[0066] Where: τ i is the shear force at the vapor-liquid interface, f i is the interfacial friction coefficient, ρ l is the liquid density, v l is the liquid phase velocity, a is the disturbance wave height, C w To characterize the influence coefficient of surface tension on internal flow, N μ To decide C w Parameters, μ l is the liquid viscosity, Δρ is the difference in vapor and liquid density, and g is the gravity constant.

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

[0068] Due to the rapid flow of steam generated by the evaporation of coolant in the narrow channel, the two-phase flow behavior in the flow channel is complex and the turbulence is severe. Before the sudden cooling, there is not only a pioneer cooling heat exchange process with time accumulation, but also a local sudden cooling phenomenon caused by the instability of the KH interface.

[0069] According to the force conditions, the dynamic equilibrium of the liquid film (vertical to the wall) is established. Figure 5 As shown, the average vapor film thickness δ is calculated by combining the following formula g :

[0070] F p =F v +F σ-y (3)

[0071] Where: F p is the vapor-liquid pressure difference, F v is the evaporation kinetic force, F σ-y is the surface tension in the Y direction;

[0072]

[0073] F σ-y =2σWsinα (6)

[0074] Where: ρ g is the vapor phase density, v g is the vapor phase velocity, δ g is the average film thickness, W is the characteristic length, hfg is the latent heat, q′ is the total heat flux, where q′=q+q T , q is the wall heat flux density, q T is the heat flux density brought by sensible heat, λ c is the critical wavelength of KH interface instability;

[0075] Substituting equations (4), (5) and (6) into equation (3) can obtain 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 as the criterion to construct the initial minimum film boiling temperature prediction model T min , the temperature change caused by local quenching is substituted into the initial minimum film boiling temperature prediction model T min , the required minimum film boiling temperature prediction model is obtained; according to the minimum film boiling temperature prediction model, the minimum film boiling temperature axial temperature distribution is obtained.

[0078] The specific process is as follows: The local sudden cooling phenomenon is discovered through the phenomenon and wall temperature curve, and the local sudden cooling characteristics are extracted. Finally, based on the local sudden cooling hypothesis, the temperature drop effect caused by the local sudden cooling is obtained and brought back into the T min model, and then reconstruct the strong transient phenomenological minimum film boiling temperature prediction model.

[0079]

[0080] Where: Re in is the inlet Reynolds number, Ja sub is the Jacobi distribution of the supercooled coolant, μ f is the liquid phase dynamic viscosity, ρ f is the liquid density, v f is the liquid phase velocity, σ is the surface tension coefficient, α is the disturbance wave angle, q is the wall heat flux density, T sat is the saturation temperature at the current pressure, h IAFB is the anti-annular flow heat transfer coefficient.

[0081] Step 5: According to the axial distribution of the minimum film boiling temperature, the quenching moment at different axial heights is obtained, and the relationship between the quenching speed, quenching time and height is obtained. The quenching speed at all quenching moments is solved, and the analysis of the re-submergence cooling process is completed.

[0082] The quenching rate is a quantitative criterion for determining whether the superheated wall can be cooled quickly. However, the complex submergence process corresponds to the unknown axial distribution of the quenching temperature and the heat transfer process. Therefore, it is necessary to explore the temporal distribution of the quenching behavior in the axial direction and establish a quenching rate prediction model. Figure 6 shown.

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

[0084]

[0085] Where: 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 formula (9), according to the axial height of the measuring point {L1, L2..., L n}Construct the “speed-time-distance” relationship and obtain the quenching front advancing velocity distribution model {v1, v2…, v n}.

[0087]

[0088] Where: v i is the ith quenching rate, L i is the ith axial height, t i is the i-th sudden cooling moment, and i is the sequence number.

[0089] The present invention takes into account the transient fluctuation characteristics of the anti-annular flow, the mechanism of sudden cooling due to vapor film collapse, and the method of sudden cooling caused by pioneer cooling heat transfer under multiple factors. It combines the initial conditions (initial wall temperature), the end conditions (axial distribution characteristics of the minimum film boiling temperature) and the decoupling of heat transfer behavior to obtain the advancement of the sudden cooling front, solves the problem of the strong correlation between the time and physical behavior of the two-phase evolution of the entire reflooding process, and realizes the accurate prediction of the entire process of strong transient reflooding cooling. A prediction and solution method for the time series relationship of the complex flow and heat transfer behavior of coupled reflooding cooling is constructed. It is applicable to the complete reflooding process flow and heat transfer behavior in different structures and a wide temperature range from the initial stage of core exposure to the core melt collapse.

Claims

1. A reflooding cooling process analysis method, characterized in that: The following steps are involved: Step 1: Obtain reflooding process data; Step 2: Based on the reflooding process data, the liquid core shear stress relationship and constitutive relationship are obtained to obtain the disturbance wave height; Step 3: Based on the local quenching during the cooling process, the liquid film dynamics equilibrium relationship is constructed to obtain the average vapor film thickness; 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; Step 5: According to the axial distribution of the minimum film boiling temperature, the quenching moment at different axial heights is obtained, and the relationship between the quenching speed, quenching time and height is obtained. The quenching speed at all quenching moments is solved, and the analysis of the re-submergence cooling process is completed.

2. A reflooding cooling process analysis method according to claim 1, characterized in that: The reflooding process data includes pressure transient data and reflooding process image data; The pressure transient data and image data are preprocessed to obtain the liquid film peak, disturbance wave velocity and interface shear force.

3. A reflooding cooling process analysis method according to claim 2, characterized in that: The shear stress relationship and constitutive relationship in step 2 are as follows: Where: τ i is the shear force at the vapor-liquid interface, f i is the interfacial friction coefficient, ρ l is the liquid density, v l is the liquid phase velocity, a is the disturbance wave height, C w To characterize the influence coefficient of surface tension on internal flow, μ l is the liquid phase viscosity.

4. A reflooding cooling process analysis method according to claim 3, characterized in that: The process of obtaining the average vapor film thickness in step 2 is as follows: The liquid film dynamic equilibrium relationship is constructed based on the critical state of the KH boundary.

5. A reflooding cooling process analysis method according to claim 4, characterized in that: The calculation process of the average vapor film thickness is as follows: The liquid film dynamic equilibrium relationship is as follows: F p =F v +F σ-y (3) Where: F p is the vapor-liquid pressure difference, F v is the evaporation kinetic force, F σ-y is the surface tension in the Y direction; in: F σ-y =2σWsinα (6) Where: ρ g is the vapor phase density, v g is the vapor phase velocity, δ g is the average film thickness, W is the characteristic length, h fg is the latent heat, q′ is the total heat flux, where q′=q+q T , q is the wall heat flux density, q T is the heat flux density brought by sensible heat, λ c is the critical wavelength; Substituting equations (4), (5) and (6) into equation (3) can obtain the average vapor film thickness.

6. A reflooding cooling process analysis method according to claim 5, characterized in that: In step 4, a / δ g >1 is used as the criterion to construct an initial minimum film boiling temperature prediction model. The temperature change caused by local sudden 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 according to the minimum film boiling temperature prediction model.

7. A reflooding cooling process analysis method according to claim 6, characterized in that: The relationship among the quenching speed, quenching time and height in step 5 is as follows: Where: v i is the ith quenching rate, L i is the ith axial height, t i is the i-th sudden cooling moment, and i is the sequence number.

8. An analysis system using the re-flooding cooling process analysis method according to any one of claims 1 to 7, characterized in that: include: Transient fluctuation characteristics module under high temperature phase change, vapor film collapse quenching mechanism module and submerged cooling process quenching module; The transient wave characteristics module under high-temperature phase change constructs the liquid core shear stress relationship and constitutive relationship based on the reflooding process data to obtain 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 of 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, the quenching front advancement velocity distribution prediction model is obtained to complete the quenching process analysis.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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