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The horizontal steam generator (SG) is one of specific features of Russian-type pressurized water reactors (VVERs). The main advantages of horizontal steam generator are connected with low steam loads on evaporation surface, simple separation scheme and high circulation ratio. The complex three-dimensional steam-water flows in the steam generator vessel influence significantly the processes of the steam separation, distribution, and deposition of the soluble and nonsoluble impurities and determine the efficiency and reliability of the steam generator operation. The 3D code for simulation of the three-dimensional steam-water flows in the steam generator could be effective tool for design and optimization of the horizontal steam generator. The results of the code calculations are determined mainly by the set of the correlations describing interaction of the steam-water mixture with the inner constructions of the SG and interfacial friction. The results obtained by 3D code STEG with the usage of the different interfacial friction correlations are presented and discussed in the paper. These results are compared with the experimental ones obtained at the experimental test facility PGV-1500 constructed for investigation of the processes in the horizontal steam generator.

The complex three-dimensional steam-water flows in the steam generator vessel influence significantly the processes of the steam separation, distribution, and deposition of the soluble and nonsoluble impurities and determine the efficiency and reliability of the steam generator operation [

Up to date, several computer codes were developed for simulation of the three-dimensional thermal hydraulic processes in the complex geometries [

The development, analysis, and systematization of the interfacial friction correlations were fulfilled during the development of the system thermal-hydraulic codes RELAP5, TRAC, CATHARE, and so on. In this activity, several typical flow patterns of the steam-water mixture were identified (bubble flow, dispersed flow, and so on), and for each pattern, the interfacial friction correlations were deriven. It was assumed that the flow pattern for each local point could be one of the patterns identified earlier depending on void fraction, mass flow rate of the steam-water mixture, or another parameter determined by a so-called map of the two-phase flow regimes. A large number of the tests devoted to the investigation of the steam-water flows were analyzed by these thermal-hydraulic codes. These codes demonstrate enough predictive capability of the two-velocity two-temperature models supplemented to the flow regime map. It should be mentioned that the majority of these tests were devoted to the investigation of the flows in the pipes, and the tests were simulated by the one-dimensional thermal-hydraulic codes.

The computer code STEG was developed for numerical simulation of the three-dimensional flows of the steam-water mixture and distribution of the soluble impurities in the steam generator [

The PGV-1500 is a horizontal SG developed for new VVER-1500 reactor. Previously STEG code was validated in relation to the horizontal SG PGV-1000 of the VVER-1000 reactor. The geometrical and thermal-hydraulic parameters of PGV-1500 significantly differ from the PGV-1000 parameters. In order to validate STEG in relation to the thermal-hydraulic phenomena listed above taking into account parameters of the PGV-1500, the experimental thermal-hydraulic model was constructed in OKB Gidropress (Russian Chief Designer of VVER reactors).

General view of the experimental model is presented in Figure

General view of experimental model. 1: heated tube bundle, 2: non-heated tube bundle, 3: SPS, and 4: SSPS.

The following thermal-hydraulic parameters were measured at the model:

average void fractions based on hydrostatic method;

collapsed levels above SPS;

pressure differences on SPS and heated tube bundle;

steam humidity;

flow rate of steam supply;

water temperature.

The accuracy of the pressure differences measurement was 0.5%, and the accuracy of the water temperature measurements was 2.4°C.

The general scheme of the void fraction measurements is presented in Figure

Positions of the void fraction measurements.

Nine tests were performed at the model. All of them are divided into three cases:

simultaneous steam supply and heating of heated tube bundle;

heating of heated tube bundle without steam supply;

steam supply without heating of heated tube bundle.

More thorough description of the experimental model is presented in [

The mathematical model of the STEG code is based on the methods of the multiphase flow dynamics [

The mass conservation equations are

Constitutive relations for interfacial friction and heat exchange are based on the map of the flow regimes. The heat flux from primary to secondary one is assigned as boundary condition. The simulation of the friction of the steam-water flow with the tube bundles was based on the correlations [

The paper contains analysis of experimental regime in which the steam-water flow was induced by the steam supply under the tube bundles of the model. The calculation grid 42 × 1 × 46 (number of control volumes along the length, width, and height of the model) was used. It should be mentioned that in fact 2D nodalization scheme was used for simulation, because thermal-hydraulic processes along the width of the narrow slice model of the PGV-1500 were negligible. This grid was chosen on the basis of the experience of the similar calculations. Nodalization of the SG model is presented in Figure

Nodalization of the SG model.

Two comparative calculations were carried out. In the first one, the interfacial friction was described by the TRAC correlations [

TRAC interfacial friction coefficient [

The interfacial friction coefficient

The profile slip factor is included to account for the migration of bubbles toward the higher-velocity region of the channel. The profile slip factor is defined as

In the annular-mist flow regime, the total interfacial drag force is assumed to be a superposition of the separate drag forces caused by the entrained droplets and the annular film

The interfacial friction force caused by the annular film is calculated as

The entrainment

The shear force

The interfacial friction force caused by the entrained droplet field is calculated as

In the transitions among the regimes, the interfacial drag coefficient is calculated as a weighted average of appropriate drag coefficients. Detailed description of the TRAC model is presented in [

A set of two gas-liquid interfacial friction correlations was proposed in [

Calculated void fraction in the upper part of the central downcomer (among points 1 and 2).

At first, let us consider the steam-water flow pattern observed in the experiment. In the area between tube bundles and submerged perforated sheet, the void fraction

In the upper and lower parts of the left downcomer, the void fraction was 0.25–0.3. In the central part of this downcomer this parameter was lower than 0.1. In the central and upper part of the right downcomer the void fraction was 0.15–0.2, and in the lower parts it was lower than 0.1.

In the area between the SPS bead and SG wall practically only water was observed (

The collapsed level above the SPS was 0.13 m above the left tube bundle, and 0.124 m above the right one.

Thus, large amount of water in the downcomers was observed in this experimental regime. In the area between the SPS bead and SG wall, only water was observed.

The comparison of the calculated and experimental void fractions in the central downcomer is presented in the Figure

Void fraction profile along height of the central downcomer in the experiment and in the calculations with the use of the models (

The comparison of the calculated and experimental void fractions in the left downcomer is presented in Figure

Void fraction profile along height of the left downcomer in the experiment and in the calculations with the use of the models (

The comparison of the calculated and experimental void fractions in the right downcomer is presented in Figure

Void fraction profile along height of the right downcomer in the experiment and in the calculations with the use of the models (

The comparison of the calculated and experimental void fractions in the area between the SPS bead and SG wall is presented in the Figure

Void fraction profile along height of the area between the SPS bead and SG wall in the experiment and in the calculations with the use of the models (

The comparison of the calculated and experimental void fractions under the SPS is presented in Figure

Void fraction profile along the width of the SG model in the area under the SPS in the experiment and in the calculations with the use of the models (

The comparison of the calculated and experimental collapsed level above SPS is presented in Table

Collapsed levels above SPS, m.

Bundle | Experiment | Calculation with ( | Calculation with ( |
---|---|---|---|

Left | 0.13 | 0.11 | 0.27 |

Right | 0.124 | 0.10 | 0.28 |

The results presented above are illustrated by two-dimensional distributions of the void fractions in Figure

(a) Void fraction distribution in the calculations with the use of the model (

The calculation results obtained with the use of the correlations (

The calculations of the experimental regime carried out at the model of the horizontal steam generator PGV-1500 [

The results obtained with the TRAC correlations (

[m^{−1}] Interfacial area per unit volume

[kg/m^{4}] Interfacial friction coefficient

[kg/m^{4}] Tubes wall friction coefficient

[m] Bubble diameter

[N/m^{3}] Interfacial friction force per unit volume

[N/m^{3}] Drag forces caused by the droplet field

[N/m^{3}] Drag forces caused by the annular film

[m/s^{2}] Gravitational constant

[J/kg] Enthalpy of the water source

[J/kg] Enthalpy of the steam source

[J/kg] Enthalpy

[J/kg] Water saturation enthalpy

[J/kg] Steam saturation enthalpy

[m/s] Water superficial velocity

[m/s] Steam superficial velocity

[m/s] Velocity

[Pa] Pressure

[kg/m^{3}s] Mass source term

[m/s] Velocity of the water source

[m/s] Velocity of the steam source

[J/m^{3}s] Wall heat-transfer rate

[J/m^{3}s] Interfacial heat transfer

[m] Droplet radius

[m] Sauter mean radius

[m/s] Droplet velocity

[m/s] Relative velocity

[kg/m^{3}s] Interfacial mass-transfer rate

[kg/m^{3}] Density

[kg/m^{3}] Density of the steam/droplet core

[N/m] Surface tension

[N/m^{2}] Interfacial shear

Liquid

Steam

Droplet.

Steam generator

3D thermal hydraulic code

Submerged perforated sheet

Steam separation perforated sheet

Water cooled water moderator energy reactor.

This research was supported in the frame of the Russian Federal Target Program “Scientific and scientific-pedagogical personnel of innovative Russia” in 2009–2013 by the State Contract no. Π491 of 13.05.2010, by the State Contract no. Π1091 of 31.05.2010, and by Russian Foundation for Basic Research, RFBR Projects 10-08-00373-a, 10-08-00086-a, and 09-08-00962-a, 09-08-00959-a.