A fast calculation method for cavitation fraction distribution of gas-liquid two-phase flow in rod bundle sub-channel

Abstract

The present invention discloses a method for quickly calculating the cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel, comprising the steps of: dividing the flow channel cross section into a grid, discretizing the flow channel cross section into a plurality of grid regions, and calculating the cavitation fraction distribution of the gas-liquid two-phase flow in a rod bundle sub-channel according to the average axial flow velocity of the flow channel. <j f >, preset cavitation fraction distribution α1 and total viscosity μ T , use the numerical solution method to obtain the axial velocity distribution u of the liquid phase: Step 2: Calculate the turbulent kinetic energy distribution TKE according to the axial velocity distribution u of the liquid phase and the preset cavitation fraction distribution α1; Step 3: Calculate the different radial interface forces of the bubble according to the liquid phase velocity distribution u and the turbulent kinetic energy distribution TKE; Step 4: Determine the cavitation fraction distribution α2 according to the mutual balance of different interface forces; Step 5: Determine whether the difference between α2 and α1 exceeds the threshold ε. If not, output α2 and complete the calculation; if exceeded, correct α1: and return to step 1 to recalculate until the iteration converges.

Description

Technical Field

[0001] The invention relates to the technical field of thermal hydraulic safety analysis of nuclear power systems, and in particular to a method for quickly calculating cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel. Background Art

[0002] Nuclear fuel is usually installed in the reactor core in the form of rod bundles. In gas-liquid two-phase flow, the cavitation fraction in the rod bundle subchannel presents a complex distribution pattern, which has a significant impact on the flow and heat transfer characteristics.

[0003] At present, nuclear thermal hydraulic analysis programs (such as subchannel analysis programs) use rod bundle subchannels as the smallest unit for modeling. It is assumed that the flow parameters are evenly distributed in a single subchannel, and it is difficult to consider the influence of fine cavitation fraction distribution in the subchannel on the flow. The cavitation fraction distribution of gas-liquid two-phase flow is dominated by the interface force, and will show a certain distribution pattern when the flow is fully developed. The size and geometric effects of different flow channels will affect the flow velocity distribution and turbulent kinetic energy distribution in the flow channel, affect the bubble interface force, and then affect the distribution pattern of the cavitation fraction.

[0004] Although the traditional computational fluid dynamics (CFD) method can predict the two-phase flow distribution in the rod bundle sub-channel based on the bubble interface force balance, this method has a large amount of calculation and a long calculation time, and cannot meet the requirements of fast calculation of nuclear power system safety analysis programs. Summary of the invention

[0005] In order to overcome the deficiencies in the prior art, the present invention provides a method for quickly calculating the cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel, which provides fine cavitation fraction distribution information in the sub-channel for a one-dimensional nuclear safety analysis program.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted to solve the technical problem is as follows:

[0007] A method for quickly calculating cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel comprises the following steps:

[0008] Step 1: Divide the flow channel cross section into a grid and discretize the flow channel cross section into several grid areas according to the average axial flow velocity of the flow channel. <j f >, preset cavitation fraction distribution α1 and total viscosity μ T , using the numerical solution method, solve the following differential equation to obtain the axial velocity distribution u of the liquid phase:

[0009]

[0010] The boundary conditions of the above formula are:

[0011] (1) The rod bundle surface is a no-slip wall boundary, u = 0 m / s;

[0012] (2) The non-bundle boundary is a symmetric boundary,

[0013] Where ρ is the liquid density, g is the gravitational acceleration, α1: is the cavitation fraction, and P is the pressure difference;

[0014] Adjust the pressure difference P until the calculated average liquid phase velocity is equal to the average axial velocity of the flow channel <j f >

[0015] Step 2: Calculate the turbulent kinetic energy distribution TKE according to the axial velocity distribution u of the liquid phase and the preset cavitation fraction distribution α1. The turbulent kinetic energy includes the turbulent kinetic energy caused by shear and the turbulent kinetic energy caused by bubbles.

[0016] Step 3: Calculate different radial interface forces of the bubble, including the bubble lift F, based on the liquid phase velocity distribution u and turbulent kinetic energy distribution TKE L , wall lubrication force F W and turbulent dispersion force F T ;

[0017] Step 4: According to the bubble lift F L , wall lubrication force F W and turbulent dispersion force F T Balance each other and determine the cavitation share distribution α2;

[0018] Step 5: Determine whether the difference between the cavitation fraction distribution α2 calculated in step 4 and the cavitation fraction distribution α1 preset in step 1 exceeds the threshold ε. If not, output α2 as the cavitation fraction distribution under the working condition and complete the calculation; if exceeded, correct α1:

[0019] α3=α1+k(α2-α1)

[0020] α1=α3

[0021] And return to step 1 to recalculate until the iteration converges.

[0022] Furthermore, in step 1, the cavitation fraction distribution α1 is preset to be uniform distribution.

[0023] Furthermore, the total viscosity in step 1 can be divided into the physical viscosity of the liquid phase μ l , eddy viscosity μ caused by liquid shear turbulence t and eddy viscosity μ caused by bubble turbulence b .

[0024] Furthermore, in step 4, for the two-phase flow in the fully developed state, the radial interfacial force remains balanced, that is, F L +F W +FT =0, the interface force remains balanced and the unique radial cavitation fraction distribution α2 can be determined.

[0025] Furthermore, in step 5, the threshold ε<0.005.

[0026] Furthermore, in step 5, the coefficient k<1.

[0027] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art:

[0028] The invention discloses a method for quickly calculating the cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel, which provides fine cavitation fraction distribution information in the sub-channel for a one-dimensional nuclear energy safety analysis program. The method has small calculation amount and short calculation time, and can meet the requirements of fast calculation of the nuclear power system safety analysis program. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0030] Figure 1 It is a schematic flow chart of a method for quickly calculating cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel of the present invention;

[0031] Figure 2 It is a schematic diagram of rod bundle sub-channel boundary setting and grid division in a method for fast calculation of cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel of the present invention;

[0032] Figure 3 It is a schematic diagram of cavitation fraction distribution calculated in a fast calculation method for cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel of the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] like Figure 1 As shown, this embodiment discloses a method for quickly calculating the cavitation fraction distribution of a gas-liquid two-phase flow in a rod bundle sub-channel, comprising the following steps:

[0035] Step 1: Divide the flow channel cross section into grids and discretize the flow channel cross section into several grid areas, such as Figure 2 As shown. According to the average axial flow velocity of the flow channel <j f >, preset cavitation fraction distribution α1 and total viscosity μ T , using the numerical solution method, solve the following differential equation to obtain the axial velocity distribution u of the liquid phase:

[0036]

[0037] The boundary conditions of the above equation are: (1) the rod bundle surface is a no-slip wall boundary, u = 0 m / s; (2) the non-rod bundle boundary is a symmetric boundary, The cavitation fraction distribution α1 is preset to be uniform distribution.

[0038] Where ρ is the liquid density, g is the gravitational acceleration, α1: is the cavitation fraction, and P is the pressure difference;

[0039] Adjust the pressure difference P until the calculated average liquid phase velocity is equal to the average axial velocity of the flow channel <j f >

[0040] Furthermore, the total viscosity in step 1 can be divided into the physical viscosity of the liquid phase μ l , eddy viscosity μ caused by liquid shear turbulence t and eddy viscosity μ caused by bubble turbulence b , μ t and μ b Calculated using the corresponding model.

[0041] Step 2: Calculate the turbulent kinetic energy distribution TKE according to the axial velocity distribution u of the liquid phase and the preset cavitation fraction distribution α1. The turbulent kinetic energy includes the turbulent kinetic energy caused by shear and the turbulent kinetic energy caused by bubbles.

[0042] Step 3: Calculate different radial interface forces of the bubble, including the bubble lift F, based on the liquid phase velocity distribution u and turbulent kinetic energy distribution TKE L , wall lubrication force F W and turbulent dispersion force F T ;

[0043] Step 4: According to the bubble lift F L , wall lubrication force F W and turbulent dispersion force F T Balance each other and determine the cavitation share distribution α2;

[0044] Step 5: Determine whether the difference between the cavitation fraction distribution α2 calculated in step 4 and the cavitation fraction distribution α1 preset in step 1 is less than the threshold value ε=0.005. If not, output α2 as the cavitation fraction distribution under the working condition and complete the calculation; if exceeded, correct α1:

[0045] α3=α1+k(α2-α1)

[0046] α1=α3

[0047] And return to step 1 to recalculate until the iteration converges.

[0048] Furthermore, in step 4, for the two-phase flow in the fully developed state, the radial interfacial force remains balanced, that is, F L +F W +F T =0, the interface force remains balanced and the unique radial cavitation fraction distribution α2 can be determined.

[0049] Furthermore, in step 5, the coefficient k<1. In this embodiment, the relaxation factor k in the correction process is 0.5.

[0050] Figure 3 The calculated cavitation fraction distribution results are given, and a significant cavitation fraction wall peak distribution is calculated.

[0051] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for quickly calculating the cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel, characterized in that: The following steps are involved: Step 1: Divide the flow channel cross section into a grid and discretize the flow channel cross section into several grid areas according to the average axial flow velocity of the flow channel. <j f >, preset cavitation fraction distribution α1 and total viscosity μ T , using the numerical solution method, solve the following differential equation to obtain the axial velocity distribution u of the liquid phase: The boundary conditions of the above formula are: (1) The rod bundle surface is a no-slip wall boundary, u = 0 m / s; (2) The non-bundle boundary is a symmetric boundary, Where ρ is the liquid density, g is the gravitational acceleration, α1: is the cavitation fraction, and P is the pressure difference; Adjust the pressure difference P until the calculated average liquid phase velocity is equal to the average axial velocity of the flow channel <j f > Step 2: Calculate the turbulent kinetic energy distribution TKE according to the axial velocity distribution u of the liquid phase and the preset cavitation fraction distribution α1. The turbulent kinetic energy includes the turbulent kinetic energy caused by shear and the turbulent kinetic energy caused by bubbles. Step 3: Calculate different radial interface forces of the bubble, including the bubble lift F, based on the liquid phase velocity distribution u and turbulent kinetic energy distribution TKE L , wall lubrication force F W and turbulent dispersion force F T ; Step 4: According to the bubble lift F L , wall lubrication force F W and turbulent dispersion force F T Balance each other and determine the cavitation share distribution α2; Step 5: Determine whether the difference between the cavitation fraction distribution α2 calculated in step 4 and the cavitation fraction distribution α1 preset in step 1 exceeds the threshold ε. If not, output α2 as the cavitation fraction distribution under the working condition and complete the calculation; if exceeded, correct α1: α3＝α1+k(α2-α1) α1＝α3 And return to step 1 to recalculate until the iteration converges.

2. A fast calculation method for cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel according to claim 1, characterized in that: In step 1, the cavitation fraction distribution α1 is preset to be uniform distribution.

3. The method for rapidly calculating cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel according to claim 1, characterized in that: The total viscosity in step 1 is divided into the physical viscosity of the liquid phase μ l , eddy viscosity μ caused by liquid shear turbulence t and eddy viscosity μ caused by bubble turbulence b .

4. The method for rapidly calculating cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel according to claim 1, characterized in that: In step 4, for the two-phase flow in the fully developed state, the radial interfacial force remains balanced, that is, F L +F W +F T =0, the interface force remains balanced and the unique radial cavitation fraction distribution α2 can be determined.

5. The method for rapidly calculating cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel according to claim 1, characterized in that: In step 5, the threshold ε<0.

005.

6. The method for rapidly calculating cavitation fraction distribution of gas-liquid two-phase flow in a rod bundle sub-channel according to claim 1, characterized in that: In step 5, the coefficient k<1.

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