Wet Steam Flow Research Articles

F081001 渦流量計を用いた湿り蒸気の流量測定における湿り度の影響と実工場における渦流量計の適用([F08100]動力エネルギーシステム部門企画,湿り蒸気流量計測研究会)

Mainly steam is utilized as a means for thermal energy supply in industrial fields. It is important to be aware of the steam flow rate in the view point of energy management. However, steam becomes wet in many cases in the process to be sent through steam pipes to machinery using steam. It is well known that the wetness of steam sometimes causes measurement errors of the steam flow rate, and there has scarcely been the established method for estimating the influence caused by the wetness of steam flow. Accordingly, we conducted the experiments of wet steam flow rate measurement to clarify the measurement error caused by the wetness of steam. This paper reports the measurement using a vortex flow meter, following our previous paper using an orifice flow meter. As a result, the correlation between the measurement error and the flow condition was clarified. And a measurement example using vortex flow meters to heat consumption of drying process at a working factory is introduced

Research on wet steam spontaneous condensing flows considering phase transition and slip

A new dual-fluid model considering phase transition and velocity slip was proposed in this paper and the Cunningham correction was used in the droplet resistance calculation. This dual-fluid model was applied to the numerical simulations of wet steam flow in a 2D LAVAL nozzle and in the White cascade respectively. The results of two simulations demonstrate that the model is reliable. Meanwhile, the spontaneous condensing flow in White cascade was analyzed and it infers that the irreversible loss caused by condensation accounts for the largest share (about 8.78% of inlet total pressure) in total pressure loss while the loss caused by velocity slip takes the smallest share (nearly 0.42%), and another part of total pressure loss caused by pneumatic factors contributes a less share than condensation, i.e. almost 3.95% of inlet total pressure.

A Literature Review of Low Pressure Steam Turbine Exhaust Hood and Diffuser Studies

This paper summarizes the findings from research studies carried out over the last 30 years, to better understand the flows in steam turbine low pressure exhaust hoods and diffusers. The work aims to highlight the areas where further study is still required. A detailed description of the flow structure is outlined and the influence of the last turbine stage and the hood geometry on loss coefficient is explored. At present, the key challenge faced is numerically modeling the three-dimensional, unsteady, transonic, wet steam exhaust hood flow given the impractically high computational power requirement. Multiple calculation simplifications to reduce the computational demand have been successfully verified with experimental data, but at present there is no ‘best-practice’ approach to reduce the computational time for routine design exercises. This paper highlights the importance of coupling the exhaust hood to the last stage steam turbine blades to capture the interaction; ensuring the total pressure and swirl angle profiles, along with the tip leakage jet are accurately applied to the diffuser inlet. The nonaxial symmetry of the exhaust hood means it is also important to model the full blade annulus. More studies have emerged modeling the wet steam and unsteady flow effects, but more work is required in this area to fully understand the impact on the flow structure.

Experimental investigation of droplet size influence on low pressure steam turbine blade erosion

In the last stages of steam turbines, large droplets (so-called coarse water) are generated from the wet steam flow. These droplets collide with the following rotating blades with almost the peripheral speed of the rotor. This high speed impact is perceived in the form of erosion of low pressure steam turbine blades. Among others, impacting droplet size is a key parameter contributing to the erosion of low-pressure steam turbine blades. At the Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM) Stuttgart, the effect of droplet size on the erosion of steam turbine blade has been investigated with the help of an erosion test rig. The experiments confirm that the erosion increases with increasing droplet sizes. It is also found that volume loss per droplet impact increases with droplet size with a simple power law relation Erosion ~Ddropletn where value of n is found to be 3.2 up to 3.5 for common blade materials.

Two-fluid model for prediction of wet steam transonic flow

Summary The paper presents a description of a two-fluid slip velocity model dedicated to the steam condensing flow modeling. The model solves separate flow governing equations for the compressible, viscous and turbulent vapor phase, and for the compressible and inviscid liquid phase. The model is implemented into an in-house Computational Fluid Dynamics (CFD) code that has been successfully applied for the wet steam flow calculations for many years now. The homogeneous condensation model is used for modeling the liquid phase formation. Calculations of spontaneous condensing, transonic flows in the turbine blade-to-blade channel are presented. The comparison of the model predictions with the experimental data are discussed.

Numerical simulation of transonic flow of wet steam in nozzles and turbines

The paper presents several modifications of the flow model published in Stastný and Sejna (Proceedings of the 12th international conference of the properties of water and steam, Begel House, pp 711–719, 1995). Modifications related to the droplet growth model and the equation of state and their implementation into numerical code are described. The effect of droplet size spectra of incoming wet steam is also discussed. Numerical results of three-dimensional flow of wet steam in a turbine cascade show the effect of surface tension correction.

F082003 各種蒸気流量計による湿り蒸気流量計測(【F08200】湿り蒸気流量計測,動力エネルギーシステム部門企画,先端技術フォーラム)

It is well known that the wetness of steam flow sometimes causes measurement errors of the steam flow meter. However, it is difficult to clarify a particular error quantitatively in actual plants and factories, and thus far, there has been no established method for estimating the error caused by the wetness of steam flow. Therefore, wet steam flow rate measurement experiments were conducted to clarify the measurement error caused by the wetness of steam flow in a plant and a factory. We have conducted 3 types of the steam flow meter, orifice flow meter, vortex flow meter and ultrasonic flow meter. In this paper, we introduce the correlation between the measurement error and the flow condition and correction methods.

F082002 湿り蒸気流量計測における標準化の現状とトレーサビリティについて(【F08200】湿り蒸気流量計測,動力エネルギーシステム部門企画,先端技術フォーラム)

F082002 湿り蒸気流量計測における標準化の現状とトレーサビリティについて(【F08200】湿り蒸気流量計測,動力エネルギーシステム部門企画,先端技術フォーラム)

Influence of the Wetness on Flow Rate Measurement of Wet Steam Using a Vortex Flow Meter

Mainly steam is utilized as a means for thermal energy supply in industrial fields. It is important to be aware of the steam flow rate in the view point of energy management. However, steam becomes wet in many cases in the process to be sent through steam pipes to machinery using steam. It is well known that the wetness of steam sometimes causes measurement errors of the steam flow rate, and there has scarcely been the established method for estimating the error caused by the wetness of steam flow. Accordingly, we conducted the experiments of wet steam flow rate measurement to clarify the measurement error caused by the wetness of steam. This paper reports the measurement using a vortex flow meter, following our previous paper using an orifice flow meter(1). The experiments were conducted with the conditions in changing the flow rate, pressure and wetness. As a result, the correlation between the measurement error and the flow condition was clarified.

Numerical assessment of steam nucleation on thermodynamic performance of steam ejectors

Steam nucleation is a prevalent phenomenon in supersonic steam flows. It seems to occur to the high-speed flow in steam ejectors. The fundamental approach in evaluating the performance parameters of ejectors is to consider steam as an ideal gas. However, in a supersonic flow of vapor under specific circumstances, nucleation phenomenon occurs and consequently vapor condensation is observed. Therefore, it is necessary to consider the effects of moisture content on the performance of such devices. In the present study, the numerical simulation of a steam ejector under the assumption of homogenous nucleation is undertaken. The novelty of this research is the analytical modeling of the effects of wet steam on the aerodynamics and thermodynamic performance of steam ejectors. The numerical results are validated in a Laval nozzle with a set of experimental data reported in the literature. The performance parameters emerge numerically from the analysis, and information concerning the deviation of wet steam flow properties from the dry steam is revealed. It is shown that steam condensation in supersonic regions reduces the maximum value of flow Mach number in the ejector and increases the ejector’s performance parameters in comparison to those of assuming steam as a dry gas.

Numerical investigation on wet steam non-equilibrium condensation flow in turbine cascade

Based on the two-phase wet steam flow with spontaneous condensation, experimental verification and flow analysis on nozzle and 2D cascade are carried out. The 3D Reynolds-Averaged gas-liquid two-phase flow control equation solver is explored with k-ɛ-kp turbulence model. Furthermore, 3D flow numerical simulation on the last stage stator of the steam turbine is carried out. The results show that a sudden pressure rise on blade suction surface is mainly caused by the droplet growth in condensation flow. The more backward the condensation position is in cascade passage, the less the sudden pressure rise from condensation is, and the larger the nucleation rate is, the maximum under-cooling and the number of droplets per unit volume are. Interaction of condensation wave and shock wave has imposed greater influence on the parameters of the blade cascade outlet.

Wet steam flow energy analysis within thermo-compressors

Thermo-compressors are widely used in industries for steam compression through a thermal process. Common methods of thermo-compressors analysis are based on the hypothesis of considering steam as a perfect gas. In this study, the deviation of thermo-compressor performance at wet steam conditions from the performance under the ideal gas assumption has been investigated. Firstly, a numerical method has been implemented to evaluate the formation of droplets due to condensation in a convergent–divergent nozzle. The results have been validated using existing experimental data for single nozzles. Afterwards, the verified numerical scheme has been applied to internal flow of the thermo-compressor. The formation of droplets due to condensation effect and the resulting supersonic core in the thermo-compressor have been deeply investigated. Finally, the effect of wet steam assumption on the performance characteristics of thermo-compressors has been presented.

Models for water steam condensing flows

Models for water steam condensing flows The paper presents a description of selected models dedicated to steam condensing flow modelling. The models are implemented into an in-house computational fluid dynamics code that has been successfully applied to wet steam flow calculation for many years now. All models use the same condensation model that has been validated against the majority of available experimental data. The state equations for vapour and liquid water, the physical model as well as the numerical techniques of solution to flow governing equations have been presented. For the single-fluid model, the Reynolds-averaged Navier-Stokes equations for vapour/liquid mixture are solved, whereas the two-fluid model solves separate flow governing equations for the compressible, viscous and turbulent vapour phase and for the compressible and inviscid liquid phase. All described models have been compared with relation to the flow through the Laval nozzle.

Numerical modelling of steam condensing flow in low and high-pressure nozzles

The paper presents the computational results of the wet steam flow through the Laval nozzles for low and high inlet pressures. The results of the numerical modelling are compared with experimental data. The comparisons constitute validation tests of the condensation model implemented into an in-house CFD code solving the RANS equations for the real gas equation of state. The steam condensing flow is modelled by means of the single-fluid model, which means that the conservation equations are formulated for the vapour/liquid mixture. The water vapour properties are described by means of the local equation of state. An effective method of determination of water vapour properties are presented in the cases of expansion in the nozzle at high pressures. The presented results are compared with published experimental values. The validation of the in-house CFD code proves its usefulness for modelling the steam condensing flow for both low and high inlet pressures.

0319 数値タービンとDDMのカップリングに関する研究(OS3 流体機械の研究開発とそれに関連した複雑流動現象,オーガナイズドセッション)

This paper presents the numerical simulation of steam-droplet flows through a three stage steam turbine. The fundamental equations of compressible wet-steam flow in this study consist of conservation laws of the density of water vapor, the momentums, the total energy, the density of water liquid, and the number density of water droplets and they are coupled with SST turbulence model with relative velocities in general curvilinear coordinates. Compressible Navier-Stokes equations and mathematical models for equilibrium condensation are solved using the high-order high-resolution finite-difference method based on the fourth-order compact MUSCL TVD scheme, Roe's approximate Riemann solver, and the LU-SGS scheme. On the other hand, as the equation of motion of the droplets, the drag force, the unsteady drag force, the centrifugal force and the Coriolis force are calculated.

Flow accelerated corrosion: Experience from examination of components from nuclear power plants

Flow accelerated corrosion (FAC) has affected a large number of components made from carbon steel in the secondary as well as primary circuits of light water reactors worldwide. This is primarily a corrosion process enhanced by (electro) chemical dissolution and mass transfer, rather than a mechanical process. It has caused rupture of all sizes of pipelines as well as other components carrying either single phase water or two phase (wet steam) flow. It is reported to be the only mechanism that has significant potential for large leaks in the secondary circuit. This paper describes the observations from examination of a number of components that were affected by FAC in Pressurized Heavy Water Reactors in the past 5 years. Failure analysis done on the 10% feed water line, non-return valve (NRV) in the auxiliary feed water system and on the affected pipeline components from the secondary water system of various reactors has been described in this paper. The surface features observed (the signature pattern of FAC) on the inner surfaces of the pipelines affected by FAC in the primary and the secondary circuits of nuclear reactors have been described. Signature patterns of FAC, on components severely affected by single phase FAC (scallops) and on components affected by dual phase FAC (tiger striping) are recorded and reported. Components where FAC degradation had just initiated showed that the patterns were not well defined. The signature patterns became evident only after the degradation had occurred to a large extent. FAC like features were not seen in stainless steel components in the secondary side. Case studies showing that thinning of carbon steel components is not always attributable to FAC in the secondary circuit of the reactors are also described and reasons of these thinning illustrated to show the importance of establishing the cause of each thinning case. The paper also discusses if the size of the scallops is possible to be correlated to the FAC rate.

Single- and two-fluid models for steam condensing flow modeling

The paper presents a description of two models dedicated to steam condensing flow modeling. The models are implemented into an in-house computational fluid dynamics (CFD) code that has been successfully applied to a wet steam flow calculation for many years now. Both models use the same condensation model that has been validated against the majority of available experimental data. The state equations for vapor and liquid water, the physical model as well as the numerical techniques of solution to flow governing equations have been presented. For the single-fluid model (SFM), the Reynolds-averaged Navier–Stokes (RANS) equations for vapor/liquid mixture are solved, whereas the two-fluid model solves separate flow governing equations for the compressible, viscous and turbulent vapor phase and for the compressible and inviscid liquid phase. Both described models have been compared with relation to the flow through the Laval nozzle.

S081013 湿り蒸気流量計測におけるオリフィス流量計の測定精度([S08101]高効率ヒートポンプの要素技術とその応用)

S081013 湿り蒸気流量計測におけるオリフィス流量計の測定精度([S08101]高効率ヒートポンプの要素技術とその応用)

1604 湿り蒸気中の非定常現象評価のための数値計算コードMATIS-SCの開発(OS16.エネルギー機器システムの設計・保守へのCFD適用,OS・一般セッション講演)

1604 湿り蒸気中の非定常現象評価のための数値計算コードMATIS-SCの開発(OS16.エネルギー機器システムの設計・保守へのCFD適用,OS・一般セッション講演)

J051011 タービン多段翼列を通る三次元湿り蒸気流れの非定常計算([J05101]流体機械の研究開発におけるEFD/CFD(1))

J051011 タービン多段翼列を通る三次元湿り蒸気流れの非定常計算([J05101]流体機械の研究開発におけるEFD/CFD(1))