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Research Papers

On Kinematic Relaxation and Deposition of Water Droplets in the Last Stages of Low Pressure Steam Turbines

[+] Author and Article Information
J. Starzmann

e-mail: starzmann@itsm.uni-stuttgart.de

M. V. Casey

Institute of Thermal Turbomachinery and Machinery Laboratory,
Pfaffenwaldring 6,
Stuttgart D-70569, Germany

F. Sieverding

Siemens AG,
Energy Sector,
Rheinstrasse 100,
Mülheim(Ruhr) D-45478, Germany

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 6, 2013; final manuscript received July 26, 2013; published online December 27, 2013. Editor: Ronald Bunker.

J. Turbomach 136(7), 071001 (Dec 27, 2013) (10 pages) Paper No: TURBO-13-1137; doi: 10.1115/1.4025584 History: Received July 06, 2013; Revised July 26, 2013

In the first part of the paper steady two-phase flow predictions have been performed for the last stage of a model steam turbine to examine the influence of drag between condensed fog droplets and the continuous vapor phase. In general, droplets due to homogeneous condensation are small and thus kinematic relaxation provides only a minor contribution to the wetness losses. Different droplet size distributions have been investigated to estimate at which size interphase friction becomes more important. The second part of the paper deals with the deposition of fog droplets on stator blades. Results from several references are repeated to introduce the two main deposition mechanisms which are inertia and turbulent diffusion. Extensive postprocessing routines have been programmed to calculate droplet deposition due to these effects for a last stage stator blade in three-dimensions. In principle the method to determine droplet deposition by turbulent diffusion equates to an approach for turbulent pipe flows and the advantages and disadvantages of this relatively simple method are discussed. The investigation includes the influence of different droplet sizes on droplet deposition rates and shows that for small fog droplets turbulent diffusion is the main deposition mechanism. If the droplets size is increased inertial effects become more and more important and for droplets around 1 μm inertial deposition dominates. Assuming realistic droplet sizes the overall deposition equates to about 1% to 3% of the incoming wetness for the investigated guide vane at normal operating conditions.

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References

Figures

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Fig. 1

Nucleation zones at design load conditions

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Fig. 2

Mean droplet size predicted by homogeneous nucleation (D×1), measured and studied droplet sizes in E30

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Fig. 3

Kinematic relaxation times of droplets

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Fig. 4

Streamlines of the vapor phase in black and the liquid phase in blue with arrows

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Fig. 5

Shadow regions shown by wetness contours in stator S3 at 50% span

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Fig. 6

Secondary nucleation in stator S3 at 50% span

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Fig. 7

Wetness fractions for D×4, upstream of stator S3 (E30), between stator S3 and rotor R3 (E31) and downstream of R3 (E32)

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Fig. 8

Wetness fractions for D×8 case, upstream of stator S3 (E30), between stator S3 and rotor R3 (E31) and downstream of R3 (E32)

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Fig. 9

Deposition regimes for turbulent pipe flows, taken from Young and Leeming [12]

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Fig. 10

Evaluation of inertial deposition on the blade surface

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Fig. 11

Relative deposition over span and profile length for different stator inlet droplet diameters

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Fig. 12

Fractional deposition rates with respect to the inlet liquid mass flow at last stage stator

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Fig. 13

Fractional deposition rates calculated for different streamtubes in the main flow region

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Fig. 14

Comparison of inertial fractional deposition rates

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