Quantitative evaluation of wetness losses in steam turbines based on three-dimensional simulations of non-equilibrium condensing flows

Abstract

Wet steam flow in steam turbines leads to degraded efficiency and blade erosion in the turbine stages. The Baumann rule, which has been used to predict wetness losses, is increasingly being questioned. More recently, the non-equilibrium condensation model is being increasingly applied to analyse wet steam flow. However, most of the influences caused by wetness losses on the aerodynamics of a wet steam turbine are excluded when this approach is used. Therefore, the efficiency of a wet steam turbine calculated by the non-equilibrium approach does not match the experimentally obtained values. To improve the accuracy of evaluating a wet steam turbine as well as the wetness losses, a quantitative evaluation program of wetness losses has been developed based on the calculation results of wet steam flow with non-equilibrium condensation using the FORTRAN language. Three-dimensional (3D) simulation of the wet steam flow with non-equilibrium condensation in turbine stages is first conducted. Then the 3D results are circumferentially averaged in the meridian plane, which are subsequently used to quantitatively evaluate the wetness losses. The wetness losses are divided into five categories: thermodynamic loss, droplet drag loss, braking loss, capturing loss and centrifuge loss. The wetness losses in the low pressure (LP) cylinder of a fossil steam turbine are calculated. The results show that the thermodynamic loss is mainly generated in the nucleation stage and the last stage of the turbine where non-equilibrium condensation occurs. The droplet drag loss is small in all wet steam stages. The braking loss is the most important component of the wetness losses, except in the nucleation stage. The capturing and centrifuge losses are moderate in the wet steam stages. The total wetness losses in the LP cylinder account for 3.65% of the total output power. This is less than the 5.14% losses predicted by the Baumann rule.

Keywords

Steam turbine wetness losses quantitative evaluation Baumann rule

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References

Moore

Siverding

. Two-phase steam flow in turbines and separators, Washington, DC: Hemisphere Publishing Corporation, 1976.

Baumann

. Recent developments in steam turbine practice. J Institution Electrical Eng 1912; 48: 768–842.

Hesketh

Walker

. Effects of wetness in steam turbines. Proc IMechE, Part C: J Mechanical Engineering Science 2005; 219: 1301–1314.

Kreitmeier

Greim

Congiu

. Experimental and numerical analyses of relaxation processes in LP steam turbines. Proc IMechE, Part C: J Mechanical Engineering Science 2005; 219: 1411–1436.

Guo T, Sumner WJ and Hofer DC. Development of highly efficient nuclear HP steam turbines using physics based moisture loss models. In: Proceedings of the ASME turbo expo, Montreal, Canada, 14–17 May 2007, pp.825–833.

Laali AR. A new approach for assessment of the wetness losses in steam turbines. PhD thesis, Electricité de France, 1991.

Kawagishi H, Onoda A, Shibukawa N, et al. Development of moisture loss models in steam turbines. Heat Transfer—Asian Res 2013; 42: 651–664.

Young

. Semi-analytical techniques for investigating thermal non-equilibrium effects in wet steam turbines. Int J Heat Fluid Flow 1984; 5: 81–91.

Liang

Zhenping

Guojun

. Numerical simulation of wet steam condensing flow with an Eulerian/Eulerian model. Chinese J Mech Eng 2003; 16: 156–159.

10.

Liang

Zhenping

Guojun

. Numerical study on the influence of stator-rotor interaction on condensing flow. J Eng Thermophys 2007; V28: 89–92.

11.

Liang L, Yu L, Lianwei W, et al. Numerical study on condensing flow in low pressure cylinder of a 300MW steam turbine. In: Proceedings of the ASME turbo expo, Glasgow, UK, 14–18 June 2010, pp.2289–2296.

12.

Gerber

Sigg

Völker

. Predictions of non-equilibrium phase transition in a model low-pressure steam turbine. Proc IMechE, Part A: J Power and Energy 2007; 221: 825–835.

13.

Young

Yau

. The inertial deposition of fog droplets on steam turbine blades. Transact ASME, J Turbomachine 1988; 110: 155–162.

14.

Yau

Young

. The deposition of fog droplets on steam turbine blades by turbulent diffusion. J Turbomachine 1987; 109: 429–435.

15.

Crane

. Droplet deposition in steam turbines. Proc IMechE, Part C: J Mechanical Engineering Science 2004; 218: 859–870.

16.

Young

Yau

Walters

. Fog droplet deposition and coarse water formation in low-pressure steam turbines: a combined experimental and theoretical analysis. J Turbomachine 1988; 110: 163–172.

17.

Morsi

Alexander

. An investigation of particle trajectories in two-phase flow systems. J Fluid Mech 1972; 55: 193–208.

18.

Chang

Wang

. Theoretical and experimental study on two-phase structure of planar mixing layer. AIAA J 1993; 31: 68–74.

19.

Gyarmathy G. Bases of a theory for wet steam turbines. Bull. 6, Inst. for Thermal Turbomachines, Federal Technical University, Zurich, 1962.

20.

Springer GS. Erosion by liquid impact. New York: John Wiley and Sons, 1976.

21.

Valha J. Liquid phase movement in the last stages of large condensing steam turbines. Proc. Inst. Mech. Eng. 1969; 184: 70–91.

22.

Williams

Lord

. Measurement of coarse water distribution in the LP cylinders of operating steam turbines. Proc IMechE 1976; 190: 59–69.

23.

Leyzerovich A. Wet-steam turbines for nuclear power plants. Tulsa: Penn Well Corporation, 2005.