Representing Polydispersed Droplet Behavior in Nucleating Steam Flow

2007 ◽  
Vol 129 (11) ◽  
pp. 1404-1414 ◽  
Author(s):  
A. G. Gerber ◽  
A. Mousavi
Keyword(s):  
Method Of Moments ◽  
Current Practice ◽  
Complex Geometry ◽  
Steam Flow ◽  
Steam Turbines ◽  
Two Phase ◽  
Cfd Models ◽  
Pressure Steam ◽  
Droplet Behavior ◽  
Computational Fluid Dynamics Cfd

The quadrature method of moments (QMOM) is applied to the particle size distribution (PSD) present in nucleating steam flow, with a particular emphasis on conditions relevant to low-pressure steam turbines. These machines exhibit heterogeneous and homogeneous phase transition in the presence of strong flow discontinuities due to shocks and complex geometry. They offer a particularly difficult two-phase modeling situation. The present work shows that QMOM is a robust and efficient method and, in comparison to current practice of using a monodispersed PSD in computational fluid dynamics (CFD) models, offers promise for dealing with the complex two-phase conditions present in real machines.

Representing Polydispersed Droplet Behavior in Nucleating Steam Flow With the Quadrature-Method-of-Moments

2006 ◽  
Author(s):  
A. Mousavi ◽  
A. G. Gerber ◽  
M. J. Kermani
Keyword(s):  
Phase Transition ◽  
Method Of Moments ◽  
Supersonic Nozzle ◽  
Droplet Size Distribution ◽  
Quadrature Method ◽  
Steam Turbines ◽  
Two Phase ◽  
Wide Range ◽  
Quadrature Method Of Moments ◽  
Droplet Behavior

This paper applies the Quadrature-Method-of-Moments (QMOM) to the polydispersed droplets spectrum typical in low pressure steam turbines. Various modes of nonequilibrium phase transition are present in steam turbines, starting with primary and secondary homogeneous nucleation as the main source of moisture followed by heterogeneous nucleation and surface entrainment sources. The range of phase transition possibilities leads to a wide range of droplet sizes, which are present under various combinations of inertial and thermal nonequilibrium. Given the extensive prevalence of CFD in turbomachinery design, it is of interest to develop an efficient modeling approach for polydispersed droplet flows that avoids solving an excessive number of equations to represent the droplet size distribution. Methods based on QMOM have shown promise in this regard in other applications areas of two-phase flow, and this paper attempts to quantify its potential for steam turbine applications by applying the method to supersonic nozzle studies with homogeneous and heterogeneous phase transitions.

On the Effects of Unsteadiness on the Condensation Process in Low-Pressure Steam Turbines

2009 ◽  
Author(s):  
Keramat Fakhari
Keyword(s):  
Large Scale ◽  
Flow Direction ◽  
Low Pressure ◽  
Droplet Growth ◽  
Condensation Process ◽  
Steam Turbines ◽  
Two Phase ◽  
Condensation Zone ◽  
Scale Temperature ◽  
Pressure Steam

The condensation process in a turbomachine is in reality an essentially random and unsteady phenomenon. On a time-averaged basis, the condensation zone is spread over a much greater distance in the flow direction than a simple steady-flow calculation would indicate. The droplet growth rate also shows different characteristics which are observed in experiments measured in real low-pressure steam turbines. These differences are mainly introduced by the large-scale temperature fluctuations which are caused by the segmentation of blade wakes by successive blade rows. Furthermore, the additional losses by condensation have to be reconsidered for an unsteady simulation. This paper describes a time-accurate Eulerian/Lagrangian two-phase model which is implemented within the DLR in-house code TRACE [1]. The phases are coupled through appropriately generated source terms for heat, mass and momentum. For the subcooled thermodynamic properties of steam the local formulation of IAPWS-IF97 [2, 3] is used. The implementation has been validated in a previous publication of the author [4] using one and two-dimensional experiments of Laval nozzles and a cascade blade from literature. The focus of this work is on the unsteady Phenomena which are investigated in a stage of an industrial low-pressure steam turbine.

Validation of Computational Fluid Dynamics Models for Industrial Applications

2021 ◽  
Author(s):  
Milorad B. Dzodzo
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Complex Geometry ◽  
Mesh Size ◽  
Industrial Applications ◽  
Cfd Models ◽  
Long Duration ◽  
Computational Fluid Dynamics Cfd ◽  
Accident Scenarios ◽  
Dynamics Models

Abstract Validation of Computational Fluid Dynamics (CFD) models for industrial applications is more challenging due to the complex geometry and long duration and complexity of various postulated accident scenarios, resulting in different and wide ranges of length and time scales. Thus, CFD models for industrial applications are restricted to the smaller subdomains and short periods of postulated accident scenarios. Validation is most often based on the comparisons with experimental results obtained with the scaled down test facilities. Thus, the effect of scaling needs to be considered and incorporated in the validation process. During validation, valuable experience is gained related to geometry simplifications, needed mesh size, turbulence and heat transfer modeling, effects of initial and boundary conditions, different fluid thermophysical properties and interaction with other phenomena and processes. Based on the gained experience the validated CFD models are adjusted and used to simulate prototypical domains and conditions. Several examples of validations of CFD models for industrial applications are presented.

The Effects of Water Injections in Wet Steam Flow in Different Regions of a Mini Laval Nozzle

2008 ◽  
Author(s):  
M. R. Mahpeykar ◽  
E. Amirirad ◽  
E. Lakzian
Keyword(s):  
Nucleation Rate ◽  
Laval Nozzle ◽  
Pressure Rise ◽  
Steam Flow ◽  
Steam Turbines ◽  
Wet Steam ◽  
Water Droplets ◽  
Two Phase ◽  
Condensation Shock ◽  
Wet Steam Flow

Progress in the development of the steam turbines brings about a renewal of interest in wetness associated problems. In turbine steam expansion, the vapour first supercools and then condenses spontaneously to become a two phase mixture. The flow initially is single phase but after Wilson point water droplets are developed and there is a non equilibrium two phase flow. The formation and behavior of the liquid create problems that lower the performance of the turbine wet stage and the mechanisms underlying this are insufficiently understood. This growing droplets release their latent heat to the flow and this heat addition to the supersonic flow cause a pressure rise called condensation shock. Because of irreversible heat transfer in this region the entropy will increase tremendously. Removal of condensates from wet steam flow in the last stage of steam turbines significantly promotes stage efficiency and prevents erosion of rotors. The following study investigates the spraying water droplets at inlet and at throat of mini Laval nozzle and their effects on nucleation rate and condensation shock. According to the results, the nucleation rate is considerably suppressed and therefore the condensation shock nearly disappeared. In other words the injecting droplets would decrease the thermodynamic losses or improve the turbine efficiency.

Three-Dimensional Blade Stacking Strategies and Understanding of Flow Physics in Low-Pressure Steam Turbines—Part II: Stacking Equivalence and Differentiators

2015 ◽  
Vol 138 (6) ◽  
Author(s):  
Said Havakechian ◽  
John Denton
Keyword(s):  
Guide Vane ◽  
Three Dimensional ◽  
Low Pressure ◽  
Cfd Modeling ◽  
Steam Turbines ◽  
Flow Parameters ◽  
Pressure Steam ◽  
Computational Fluid Dynamics Cfd ◽  
Last Stage ◽  
Two Stages

Optimization of blade stacking in low-pressure (LP) steam turbine development constitutes one of the most delicate and time-consuming parts of the design process. This is the second part of two papers focusing on stacking strategies applied to the last stage guide vane and represents an attempt to discern the aerodynamic targets that can be achieved by each of the well-known and most often used basic stacking schemes. The effects of lean and twist have been investigated through an iterative process, involving comprehensive 3D computational fluid dynamics (CFD) modeling of the last two stages of a standard LP, where the basic lean and twist stacking schemes were applied on the last stage guide vanes while keeping the throat area (TA) unchanged. It has been found that it is possible to achieve the same target value and pattern of stage reaction by applying either tangential lean or an equivalent value of twist. Moreover, the significance of axial sweep on hub reaction has been found to become pronounced when the blade sweep is carried out at constant TA. The importance of hub-profiling has also been demonstrated and assessed. Detailed analysis of the flow fields has provided an overall picture, revealing the differences in the main flow parameters as produced by each of the alternative basic stacking schemes.

Three-Dimensional Blade-Stacking Strategies and Understanding of Flow Physics in Low-Pressure Steam Turbines—Part I: Three-Dimensional Stacking Mechanisms

2015 ◽  
Vol 138 (5) ◽  
Author(s):  
Said Havakechian ◽  
John Denton
Keyword(s):  
Guide Vane ◽  
Three Dimensional ◽  
Low Pressure ◽  
Stagnation Pressure ◽  
Steam Turbines ◽  
Wet Steam ◽  
Pressure Steam ◽  
Computational Fluid Dynamics Cfd ◽  
Last Stage ◽  
3D Stacking

Optimization of blade stacking in the last stage of low-pressure (LP) steam turbines constitutes one of the most delicate and time-consuming parts of the design process. This is the first of two papers focusing on the stacking strategies applied to the last stage guide vane (G0). Following a comprehensive review of the main features that characterize the LP last stage aerodynamics, the three-dimensional (3D) computational fluid dynamics (CFD) code used for the investigation and options related to the modeling of wet steam are described. Aerodynamic problems related to the LP last stage and the principles of 3D stacking are reviewed in detail. In this first paper, the results of a systematic study on an isolated LP stator row are used to elucidate the effects of stacking schemes, such as lean, twist, sweep, and hub profiling. These results show that stator twist not only has the most powerful influence on the reaction variation but it also produces undesirable spanwise variations in angular momentum at stator exit. These may be compensated by introducing a positive stagnation pressure gradient at entry to the last stage.

A Comparison of Modelling Techniques for Polydispersed Droplet Spectra in Steam Turbines

2015 ◽  
Author(s):  
Fiona R. Hughes ◽  
Jörg Starzmann ◽  
Alexander J. White ◽  
John B. Young
Keyword(s):  
Method Of Moments ◽  
Vapour Phase ◽  
Phase Behaviour ◽  
Droplet Growth ◽  
Quadrature Method ◽  
Steam Turbines ◽  
Two Phase ◽  
Quadrature Method Of Moments ◽  
The Moment ◽  
Speed Accuracy

Within steam turbine flows, condensation phenomena give rise to complex droplet spectra that can span more than two orders of magnitude in size. To predict the behaviour of the two-phase flow and the resulting losses, the interactions between the vapour phase and droplets of all sizes must be accurately calculated. The estimation of thermodynamic losses and droplet deposition rates, in particular, depend on the size range and shape of the droplet spectrum. These calculations become computationally burdensome when a large number of droplet groups are present, and it is therefore advantageous to capture the complete droplet spectrum in a compressed form. This paper compares several methods for reducing the complexity of the droplet spectrum: a single representative droplet size (equivalent monodispersion), the moment method (including various growth rate approximations), the quadrature method of moments, and spectrum pruning. In spectrum pruning, droplet groups are individually nucleated, but their number is subsequently reduced by combining groups together in a manner that preserves droplet number, wetness fraction, and the shape of the initial spectrum. The various techniques are compared within a Lagrangian framework by tracking the two-phase behaviour along predefined pressure-time trajectories. Primary and secondary nucleation, droplet evaporation, and a representative turbomachinery case are modelled. The calculations are compared in terms of speed, accuracy, and robustness. It is shown that both the moment methods and spectrum pruning provide an appreciable improvement in accuracy over the use of an ‘equivalent’ monodispersion without compromising calculation speed. Although all the examined methods are adequate for primary nucleation and droplet growth calculations, spectrum pruning and the quadrature method of moments are most accurate over the range of conditions considered.

Evaluation of flow hydrodynamics in a pilot-scale dissolved air flotation tank: a comparison between CFD and experimental measurements

2015 ◽  
Vol 72 (7) ◽  
pp. 1111-1118 ◽  
Author(s):  
B. Lakghomi ◽  
Y. Lawryshyn ◽  
R. Hofmann
Keyword(s):  
Pilot Scale ◽  
Solid Particles ◽  
Cfd Model ◽  
Two Phase ◽  
Dissolved Air Flotation ◽  
Cfd Models ◽  
Three Phase ◽  
Computational Fluid Dynamics Cfd ◽  
Air Flotation ◽  
Dissolved Air

Computational fluid dynamics (CFD) models of dissolved air flotation (DAF) have shown formation of stratified flow (back and forth horizontal flow layers at the top of the separation zone) and its impact on improved DAF efficiency. However, there has been a lack of experimental validation of CFD predictions, especially in the presence of solid particles. In this work, for the first time, both two-phase (air–water) and three-phase (air–water–solid particles) CFD models were evaluated at pilot scale using measurements of residence time distribution, bubble layer position and bubble–particle contact efficiency. The pilot-scale results confirmed the accuracy of the CFD model for both two-phase and three-phase flows, but showed that the accuracy of the three-phase CFD model would partly depend on the estimation of bubble–particle attachment efficiency.

Two-Phase Eulerian/Lagrangian Model for Nucleating Steam Flow

2002 ◽  
Vol 124 (2) ◽  
pp. 465-475 ◽  
Author(s):  
A. G. Gerber
Keyword(s):  
Three Dimensional ◽  
Low Pressure ◽  
Steam Flow ◽  
Nucleation Theory ◽  
Lagrangian Model ◽  
Classical Nucleation Theory ◽  
Navier Stokes ◽  
Steam Turbines ◽  
Complex Flow ◽  
Two Phase

This paper describes an Eulerian/Lagrangian two-phase model for nucleating steam based on classical nucleation theory. The model provides an approach for including spontaneous homogeneous nucleation within a full Navier-Stokes solution scheme where the interaction between the liquid and gas phases for a pure fluid is through appropriately modeled source terms. The method allows for the straightforward inclusion of droplet heat, mass, and momentum transfer models along with nucleation within complex flow systems as found, for example, in low pressure steam turbines. The present paper describes the solution method, emphasizing that the important features of nucleating steam flow are retained through comparison with well-established 1-D solutions for Laval nozzle flows. Results for a two-dimensional cascade blade and three-dimensional low pressure turbine stage are also described.

Modeling Steam Dryers

2010 ◽  
Author(s):  
Dani Fadda ◽  
David Taylor ◽  
Jason Burr ◽  
Michael Sredzienski ◽  
Jeff Gardner
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Steam Generator ◽  
Computational Models ◽  
Steam Flow ◽  
High Quality ◽  
Cfd Models ◽  
Full Capacity ◽  
Computational Fluid Dynamics Cfd ◽  
Very High

Nuclear steam dryers are used to reduce the moisture carryover (MCO) to levels often well below 0.1%, by weight, water in the steam. The dryers are designed to provide very high quality steam at the full capacity of the steam generator. The purpose of this paper is to present computational fluid dynamics (CFD) models of the steam flow in a generator and the decisions that are required to evaluate different designs. These computational models are successful and proven in field operations.

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