Method for correcting surface tension calculation parameters of liquid drops in wet steam area of low-pressure cylinder of steam turbine

Abstract

The invention discloses a method for correcting surface tension calculation parameters of liquid drops in a wet steam area of a low-pressure cylinder of a steam turbine, and the method comprises the following steps: 1, introducing a surface tension correction coefficient a to correct the surface tension sigma of the liquid drops, and obtaining a new surface tension sigma '; 2, determining that the surface tension correction coefficient a ranges from 1 to 1.05 through experiments and numerical simulation; and 3, applying the corrected surface tension sigma'to the mathematical model of condensation nucleation in the wet steam area of the low-pressure cylinder of the steam turbine, and carrying out numerical calculation on the condensation nucleation in the wet steam area of the low-pressure cylinder of the steam turbine to obtain the distribution rule of the nucleation rate in the wet steam area of the steam turbine. On the basis of the classic nucleation model and the droplet growth model, the surface tension can be accurately corrected to predict the flow mechanism of non-equilibrium condensation of the wet steam area of the steam turbine, and reference is further provided for the problems such as the flow characteristics of the wet steam of the through-flow part of the real steam turbine.

Description

Technical Field

[0001] The invention belongs to the technical field of steam turbine power generation, and relates to a method for correcting calculation parameters of droplet surface tension in a wet steam region of a low-pressure cylinder of a steam turbine. Background Art

[0002] When water vapor expands and does work in a steam turbine, its temperature and pressure will continue to decrease. When the high-temperature and high-pressure superheated steam expands in the steam turbine and crosses the dry saturation line to a certain extent, the steam will spontaneously condense and produce liquid water droplets, and the working medium will become wet steam. The last two stages of the real steam turbine work in the wet steam area for a long time, and the spontaneous condensation of water vapor is common. Wet steam not only reduces the stage efficiency, but also seriously corrodes the moving blades, reducing the economy and safety of the steam turbine. The existence of non-equilibrium condensation in the low-pressure section of the steam turbine will lead to wet steam loss. The average humidity of about 1% caused by wet steam can reduce the stage efficiency by 1%. Therefore, in-depth research on the spontaneous condensation flow characteristics of water vapor is of great significance to improving the economy and safety of steam turbines.

[0003] Due to the complexity and rapidity of the phase change process, the non-equilibrium condensation phenomenon has not been fully resolved. Most scholars use numerical simulation methods to study the non-equilibrium condensation of wet steam. They use classical phase change theory to perform numerical calculations. Although reasonable results can be obtained, there are still errors compared with experimental data. Among them, surface tension σ is a very important parameter in the calculation process of classical nucleation and droplet growth. At present, the mathematical model of surface tension σ is not very suitable for studying the condensation process of wet steam in steam turbines. Summary of the invention

[0004] In view of the shortcomings mentioned in the background technology, the present invention provides a method for correcting the calculation parameters of the surface tension of the droplets in the wet steam area of ​​the low-pressure cylinder of the steam turbine. By correcting the surface tension σ of the droplets, the method can accurately obtain a new surface tension σ', making the calculation result of the condensation nucleation in the wet steam area of ​​the steam turbine more accurate.

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

[0006] A method for correcting calculation parameters of droplet surface tension in a wet steam region of a low-pressure cylinder of a steam turbine comprises the following steps:

[0007] Step 1: Introduce the surface tension correction coefficient a to correct the droplet surface tension σ and obtain the new surface tension σ':

[0008] σ'=a×σ

[0009] Step 2: Through experiments and numerical simulations, it is determined that the range of the surface tension correction coefficient a is between 1 and 1.05;

[0010] Step 3: Apply the corrected surface tension σ' to the mathematical model of condensation nucleation in the wet steam region of the low-pressure cylinder of the steam turbine, perform numerical calculations on the condensation nucleation in the wet steam region of the steam turbine, and obtain the distribution law of the nucleation rate in the wet steam region of the steam turbine.

[0011] Compared with the prior art, the present invention has the following advantages:

[0012] 1. The correction method proposed in the present invention can more accurately obtain the surface tension of the droplets in the wet steam area of ​​the low-pressure cylinder of the steam turbine, and thus can more accurately predict the condensation flow characteristics of the last-stage blades.

[0013] 2. Based on the classical nucleation model and droplet growth model, the present invention can accurately correct the surface tension to predict the flow mechanism of non-equilibrium condensation in the wet steam zone of the turbine, and further provide reference and reference for the flow characteristics of wet steam in the flow part of the real turbine. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a flow chart of the method for correcting the calculation parameters of the droplet surface tension in the wet steam area of ​​the low-pressure cylinder of the steam turbine. DETAILED DESCRIPTION

[0015] The technical solution of the present invention is further described below in conjunction with the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0016] The present invention provides a method for correcting the calculation parameters of the surface tension of droplets in the wet steam area of ​​a steam turbine low-pressure cylinder. The method proposes a new surface tension parameter by correcting the surface tension, verifies it, and finally applies it to the numerical simulation of the non-equilibrium condensation characteristics of the last-stage blades in the wet steam area of ​​the steam turbine low-pressure cylinder, so as to more accurately obtain the flow field of the last-stage blades in the wet steam area of ​​the steam turbine low-pressure cylinder, and provide reference and reference for the flow characteristics of wet steam in the flow part of the real steam turbine. Figure 1 As shown, the specific steps include:

[0017] Step 1: Introduce the surface tension correction coefficient a to correct the droplet surface tension σ and obtain the new surface tension σ':

[0018] σ'=a×σ

[0019] The expression of the droplet surface tension σ is as follows:

[0020]

[0021] Where T is the thermodynamic temperature.

[0022] By correcting the droplet surface tension σ, the droplet critical radius can be calculated more accurately, and then the droplet nucleation rate can be accurately calculated. Therefore, the present invention introduces a surface tension correction coefficient a to correct the droplet surface tension σ to obtain a new surface tension σ'.

[0023] Step 2: Determine the value of the surface tension correction coefficient a and verify the selected surface tension correction coefficient a.

[0024] After a large number of experiments and numerical simulations, the present invention determines that the range of the surface tension correction coefficient a is between 1 and 1.05. For the wet steam stage of the steam turbine, different steam inlet parameters correspond to different surface tension correction coefficients a. Therefore, the present invention appropriately selects the value of the surface tension correction coefficient a based on a typical example, and takes a=1.03.

[0025] Step 3: Apply the corrected surface tension σ'.

[0026] The modified surface tension σ' is applied to the mathematical model of condensation nucleation in the wet steam region of the low-pressure cylinder of the steam turbine. The condensation nucleation in the wet steam region of the low-pressure cylinder of the steam turbine is numerically calculated, and the distribution law of the nucleation rate in the wet steam region of the steam turbine is obtained.

[0027] The following examples verify the beneficial effects of the present invention:

[0028] Embodiment 1:

[0029] The present invention takes the last-stage stationary blade of a steam turbine as an example to illustrate a method for correcting the calculation parameters of the droplet surface tension in the wet steam area of ​​the low-pressure cylinder of the steam turbine.

[0030] Step 1: Physically model the single-channel blades of the last-stage stator blades in the low-pressure cylinder of the turbine and perform meshing.

[0031] Step 2: Correct the surface tension by using the correction coefficient a=1.03, that is, σ'=1.03σ.

[0032] Step 3: Verify the corrected surface tension σ', respectively bring the corrected surface tension σ' and the uncorrected σ of the present invention into the mathematical model of condensation nucleation in the wet steam region of the low-pressure cylinder of the steam turbine, and perform numerical simulation prediction on the position of the Wilson point, and the comparison results are shown in Table 1. As can be seen from Table 1, when the mathematical model of the uncorrected surface tension is used to predict the position of the Wilson point, after comparison with the experimental data, it is found that the error is greatly different from the experimental value; when the mathematical model of the corrected surface tension is used to predict the position of the Wilson point, after comparison with the experimental data, it is found that the error is relatively small with the experimental value, all within 3%, indicating that the use of the corrected surface tension mathematical model can obtain more accurate calculation results.

[0033] Table 1 Prediction of Wilson point location by different models

[0034]

[0035]

[0036] Step 4: Import the corrected surface tension σ' into the nucleation model and droplet growth model, and solve the flow field of the last stator blade in the low-pressure cylinder of the steam turbine in OpenFOAM. -5 When the following is reached, the calculation ends and the calculation results are automatically generated.

[0037] Step 5: Import the result file into the fluid simulation post-processing open source software Paraview, and you can get the nucleation rate in the blade channel. The nucleation area is located near the throat of the flow channel, and the maximum value appears near the throat. This is because the speed in the throat is very high, which causes the thermal recovery of the steam to fail to keep up with the inertial recovery of the steam movement, which leads to the occurrence of non-equilibrium phenomenon, which is also the reason for the occurrence of non-equilibrium condensation phenomenon. This shows that the surface tension corrected by the surface tension correction coefficient proposed by the present invention can accurately calculate the nucleation rate of the wet steam area of ​​the turbine, and then effectively obtain the wet steam flow characteristics of the real turbine flow part.

Claims

1. A method for correcting the calculation parameters of the droplet surface tension in the wet steam region of a steam turbine low-pressure cylinder, characterized in that The method comprises the following steps: Step 1: Introduce the surface tension correction coefficient a to correct the droplet surface tension σ and obtain the new surface tension σ': σ'=a×σ Step 2: Through experiments and numerical simulations, it is determined that the range of the surface tension correction coefficient a is between 1 and 1.05; Step 3: Apply the corrected surface tension σ' to the mathematical model of condensation nucleation in the wet steam area of ​​the low-pressure cylinder of the steam turbine, perform numerical calculations on the condensation nucleation in the wet steam area of ​​the low-pressure cylinder of the steam turbine, and obtain the distribution law of the nucleation rate in the wet steam area of ​​the steam turbine.

2. The method for correcting the calculation parameters of the droplet surface tension in the wet steam region of the low-pressure cylinder of a steam turbine according to claim 1 is characterized in that The surface tension correction coefficient a=1.03.

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