Effects of Wake Chopping on Droplet Sizes in Steam Turbines

Bakhtar, F.; Heaton, Alan

doi:10.1243/095440605x69291

Cited by 10 publications

(9 citation statements)

References 30 publications

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“…Steady codes are generally not able to predict the poly-dispersed droplet spectra and the average radius typically measured in the rear stages of steam turbines, and therefore, they cannot provide a good assessment of the losses in these stages. References [40][41][42][43] showed that the effect of unsteadiness due to the interaction of blade wakes with downstream blade rows is to broaden significantly the droplet-size distribution giving a shape and a mean diameter closer to the experimental measurements in real turbines. The authors use a statistical approach to account for the temperature fluctuations produced by the flow unsteadiness and showed very good agreements with measurements.…”

Section: Numerical Analyses Of Relaxation Processes In Lp Flowsmentioning

confidence: 99%

Experimental and Numerical Analyses of Relaxation Processes in LP Steam Turbines

Kreitmeier

Greim

Congiu

et al. 2005

Proceedings of the Institution of Mechanical Engineers, Part C:

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Flow fields in low-pressure (LP) steam turbines, starting expansion well above the saturation line, show four pronounced non-equilibrium processes (called relaxation processes). The first one above the saturation line is centred around heterogeneous nucleation/ condensation, the second one around subcooling and the subsequent homogeneous nucleation/ condensation ('Wilson point'), and the third and the fourth ones are characterized by thermodynamic and mechanical effects in the established droplet-loaded part of the flow field.All these relaxation processes are interacting downwards in the progressive expansion in the turbine. In a multistage LP turbine, the most important ones are the second -because it is mainly responsible for the number of droplets (sizes) -and the third -because it creates most of the dissipation. In addition, the first and the fourth ones can damage the flow guiding geometry by corrosion and erosion, respectively.More than 40 years ago, Gyarmathy formulated the first strictly physical basis for these processes. Subsequently, many researchers have contributed to increase the physical understanding using both experimental and numerical methods. The intuition that the one-dimensional treatment of the flow field in multistage turbines cannot explain the measured droplet sizes behind the blading has been particularly relevant. It became clear that especially the temperature fluctuation within the blading has to be included in homogeneous nucleation/condensation considerations. Also of some importance has been the improved understanding of the first relaxation process, which was initially underestimated.This article highlights the current situation seen by a turbomachinery company that has been contributing to and supporting this discipline for many decades. A wide literature survey and a critical appraisal of published Baumann factors are included. High quality experimental tools and procedures are introduced on the basis of two generations of split-shaft model LP turbines and Damköhler numbers. Further, an overview of the in-house numerical tools and processes developed for wet steam applications is given.More recent experimental results on the influence of impurities and conditioning agents in the relaxation processes and newer numerical results on the influence of phase transition in the flow field around a blade row are presented.

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Section: Numerical Analyses Of Relaxation Processes In Lp Flowsmentioning

confidence: 99%

Experimental and Numerical Analyses of Relaxation Processes in LP Steam Turbines

Kreitmeier

Greim

Congiu

et al. 2005

Proceedings of the Institution of Mechanical Engineers, Part C:

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“…As indicated by Bakhtar [29], the wake chopping effects due to the inherent unsteadiness in turbine may have impact on the nucleation process and droplet sizes. It is the ambition of the authors to consider the unsteadiness effect when estimating moisture losses in the future.…”

Section: Discussionmentioning

confidence: 99%

A 3D method to evaluate moisture losses in a low pressure steam turbine: Application to a last stage

Zhang

Xie

et al. 2015

International Journal of Heat and Mass Transfer

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“…The method accounts for the effect of wake chopping on the droplet size. 23 It is based on the random character of dissipation experienced by fluid particles passing through a multistage turbine, depending on a randomly chosen streamline (2D approach) within each blade row with a given pitch-wise distribution of polytropic efficiency. Different fluid particles thus undergo different nucleation conditions resulting in a broader droplet size distribution.…”

Section: Wet Steam Energy Lossmentioning

confidence: 99%

“…7,22 A statistical 2D evaluation method has been employed for the computational simulation of the losses. 23–25 It models the random character of dissipation undertaken by a fluid particle passing through a multi-stage LP steam turbine. Different particles undergo different nucleation conditions resulting in a broader distribution of the droplet sizes.…”

Section: Introductionmentioning

confidence: 99%

Wet steam energy loss and related Baumann rule in low pressure steam turbines

Petr

Kolovratník

2013

Proceedings of the Institution of Mechanical Engineers, Part A:

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This paper presents the results of a computational analysis of the wet steam energy loss occurring in a 210 MW fossilfired and a 1000 MW nuclear LP steam turbine. The turbines operate under considerably different conditions as regards pressure level in the droplet nucleation zone, exit moisture level and droplet size spectra determined from optical extinction measurements. An evaluation of the basic wetness energy losses has been carried out including the thermodynamic loss, drag loss of the fine and coarse droplets, impact loss, collected water loss, centrifuging loss and exit loss. A statistical 2D evaluation method has been employed for the computational simulation of the loss. The objective of the analysis was to determine whether an equilibrium based Baumann factor of order 0.6 can be used for predicting the wet steam loss.

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Effects of Wake Chopping on Droplet Sizes in Steam Turbines

Cited by 10 publications

References 30 publications

Experimental and Numerical Analyses of Relaxation Processes in LP Steam Turbines

Experimental and Numerical Analyses of Relaxation Processes in LP Steam Turbines

A 3D method to evaluate moisture losses in a low pressure steam turbine: Application to a last stage

Wet steam energy loss and related Baumann rule in low pressure steam turbines

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