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

Author:

Starzmann J.1,Kaluza P.,Casey M. V.2,Sieverding F.3

Affiliation:

1. e-mail:

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

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

Abstract

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.

Publisher

ASME International

Subject

Mechanical Engineering

Reference27 articles.

1. Predictions of Nonequilibrium Phase Transition in a Model Low-Pressure Steam Turbine;Proc. IMechE, J. Power Energy,2007

2. Numerical and Experimental Investigation of Steam Condensation in LP Part of a Large Power Turbine;ASME J. Fluids Eng.,2009

3. Chandler, K., White, A., and Young, J. B., 2012, “Comparison of Unsteady Non-Equilibrium Wet-Steam Calculations With Model Turbine Data,” Baumann Centenary Wet Steam Conference, Cambridge, UK, September 10–11, Paper No. BCC-2012-10.

4. Starzmann, J., Casey, M., Mayer, J. F., and Sieverding, F., 2012, “Wetness Loss Prediction for a Low Pressure Steam Turbine Using CFD,” Baumann Centenary Wet Steam Conference, Cambridge, UK, September 10–11, Paper No. BCC-2012-14.

5. The Spontaneous Condensation of Steam in Supersonic Nozzles,1982

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