A study of the throughflow of nucleating steam in a turbine stage by a time-marching method

2013 ◽  
Vol 228 (5) ◽  
pp. 932-949 ◽  
Author(s):  
F Bakhtar ◽  
R Mohsin
Keyword(s):  
Nucleation And Growth ◽  
Steam Turbines ◽  
Turbine Stage ◽  
Two Phase ◽  
Droplet Nucleation ◽  
Direct Measurements ◽  
Time Marching ◽  
Phase Mixture ◽  
Marching Method ◽  
General Conservation

In the course of expansion in turbines, steam first supercools and then nucleates to become a two-phase mixture. The fluid then consists of a very large number of extremely small droplets which are carried by and interact with the parent vapour. The formation and subsequent behaviour of the liquid phase cause problems which lower the performance of the wet stages of steam turbines. To treat such flows the general conservation equations governing the whole field are combined with those describing droplet nucleation and growth and the set treated numerically. The article examines the solution of throughflows of nucleating steam in a turbine stage using a time-marching technique. The treatment which is the refinement of an earlier one has been applied to the flow in a turbine stage. Comparisons are presented between the results of theoretical solutions and direct measurements upstream and downstream of the nucleating stage and the agreement obtained is good.

An examination of the Throughflow of Nucleating Steam in a Turbine Stage by a Time-Marching Method

1989 ◽  
Vol 203 (4) ◽  
pp. 233-243 ◽  
Author(s):  
F Bakhtar ◽  
B O Bamkole
Keyword(s):  
Computer Program ◽  
Thermodynamic Equilibrium ◽  
Theoretical Treatment ◽  
Test Cases ◽  
Turbine Stage ◽  
Conservation Equations ◽  
Time Marching ◽  
Marching Method ◽  
Non Equilibrium

The paper describes a theoretical treatment for nucleating throughflow of steam in a turbine stage. The conservation equations governing the overall behaviour of the fluid are combined with those describing droplet behaviour and treated by a time-marching method. The computer program developed has been applied to some test cases and comparisons are presented between solutions allowing for non-equilibrium effects and those in which steam has been assumed to remain in thermodynamic equilibrium.

An Upwind Eulerian-Eulerian Model for Non-Equilibrium Condensation in Steam Turbines

2013 ◽  
Author(s):  
Xiaofeng Zhu ◽  
Xin Yuan ◽  
Zhirong Lin ◽  
Naoki Shibukawa ◽  
Tomohiko Tsukuda ◽  
...  
Keyword(s):  
Current Model ◽  
Finite Volume Scheme ◽  
Steam Turbines ◽  
Turbine Cascade ◽  
Wet Steam ◽  
Turbine Stage ◽  
Eulerian Model ◽  
Two Phase ◽  
Eigen Value ◽  
Non Equilibrium

The present paper proposes an Eulerian-Eulerian two-phase model for non-equilibrium condensing flow in steam turbines. This model is especially suitable for upwind finite volume scheme. An approximate Roe type flux using real water/vapor property is constructed to calculate the upwind wet-steam flux. This flux fully couples the wetness fraction with other conservative variables in the Jacobian Matrix whose eigen-vector and eigen-value are analitically derived. A novel treatment of real wet-steam property is developed by constructing a 3-DOFs TTSE table according to IAPWS97 formulas. The table is actually a cubic and uses the mixture’s density, the mixture’s internal energy and wetness as independent variables. Besides homogeneous condensation, heterogeneous condensing is also integrated into the model, which facilitates simulating the effect of salt impurities. The above methods are validated through two nozzle and one turbine cascade calculations and finally applied to a model LP steam turbine stage. Results show that the current model is very robust and is able to correctly capture the non-equilibrium condensation phenomena.

Theoretical Treatments of Two-Dimensional Two-Phase Flows of Steam and Comparison with Cascade Measurements

2005 ◽  
Vol 219 (12) ◽  
pp. 1335-1355 ◽  
Author(s):  
F Bakhtar ◽  
A J White ◽  
H Mashmoushy
Keyword(s):  
Numerical Methods ◽  
Nucleation And Growth ◽  
Nucleation Theory ◽  
Two Dimensional ◽  
Wet Steam ◽  
Calculation Methods ◽  
Two Phase ◽  
Droplet Nucleation ◽  
Condensing Flows ◽  
State Path

During the course of expansion of steam in turbines, the state path crosses the saturation line and hence subsequent turbine stages operate with wet steam. These stages have lower thermodynamic efficiencies than those operating in the superheated region, and currently the phenomena contributing to the increased losses are not fully understood. The development of the nucleation theory has opened the way for the study of condensing flows in turbines. As, with the advances in numerical methods, the equations describing droplet nucleation and growth rates can be combined with the field conservation equations and the set treated numerically, which allows the behaviour of complex nucleating and wet steam flows in turbines to be analysed. This paper outlines and reviews wet steam calculation methods and discusses comparisons between numerical and experimental results. For the most part, the comparisons presented are based on work of the authors and their co-workers, but some more recent calculations by other investigators are also included.

On the performance of a cascade of turbine rotor tip section blading in nucleating steam Part 3: Theoretical treatment

1997 ◽  
Vol 211 (3) ◽  
pp. 195-210 ◽  
Author(s):  
F Bakhtar ◽  
M R Mahpeykar
Keyword(s):  
Integral Method ◽  
Turbine Rotor ◽  
Main Flow ◽  
Theoretical Treatment ◽  
Viscous Effects ◽  
Mixture Formation ◽  
Two Phase ◽  
Time Marching ◽  
Phase Mixture ◽  
Improved Design

During the course of expansion in turbines, steam first supercools and then nucleates to become a two-phase mixture. Formation and subsequent behaviour of the liquid lower the performance of turbine wet stages. This is an area where greater understanding can lead to improved design. This paper describes the theoretical part of an investigation into nucleating flows of steam in a cascade of turbine rotor tip section blading. The main flow field is regarded as inviscid and treated by the time-marching technique modified to allow for two-phase effects. The viscous effects are assumed to be concentrated in boundary layers which are treated by the integral method. Comparisons are carried out with the experimental measurements presented in the earlier parts of the paper and the agreement obtained is good.

Studies of phase transformation of Fe1-xS by in Situ TEM

1989 ◽  
Vol 47 ◽  
pp. 648-649
Author(s):  
Thao A. Nguyen ◽  
Linn W. Hobbs
Keyword(s):  
Phase Transformation ◽  
Single Phase ◽  
Nucleation And Growth ◽  
In Situ Tem ◽  
Two Phase ◽  
S Matrix ◽  
In Situ Heating ◽  
Phase Mixture ◽  
Lamellar Type

The transformation from Fe1-xS (IC) phase to a mixture of FeS (2C) and iron poor Fe1-xS (IC) phases has been investigated by a series of in-situ heating experiments. The purpose of this study is to resolve the controversy over the mechanism of phase transformation (spinodal decomposition versus nucleation and growth) and to explain the different microstructures observed in the two phase mixture of FeS and Fe1-xS (Figure 1).In-situ heating experiments were carried out using a JEOL JEM EM-SHTH double tilt heating holder. Synthetic “single” Fe0.97S crystals were cut into 3 mm disks, mechanically and ion thinned to electron transparency. In all cooling experiments, the sample was first held at 390 K, a temperature above the transition temperature in order to generate an initial single phase material; then, the temperature was quickly reduced to the temperature of interest.Figure 2a shows the development of a lamellar type microstructure after the sample's temperature was reduced from 390 K to 363 K and then held at this temperature for ten minutes. At 363 K, the undercooling is 27 K. The troilite FeS (2C) phase heterogeneously nucleates and grows along the edge of the sample. Diffraction analysis shows that the FeS (2C) phase is embedded in the iron-poor Fe1-x,S matrix with a rod-like structure.

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