Wet Steam Flow Research Articles

Deposition of fog drops on low pressure steam turbine blades

Mechanisms for depositing drops from two-phase flow and methods for predicting deposition rates are discussed in the context of wet steam flow in low pressure turbines. Representative calculations are presented confirming that direct inertial impaction on blade leading edges and concave surfaces cannot account for observed water quantities if the fog drops are of order 0·1 μm dia. A similar conclusion is reached by application of a recent method for calculating deposition from turbulent boundary layers but it is shown how variation of blade boundary layer properties could reduce the discrepancy. A major source of uncertainty in computing turbulent deposition rates arises from the lack of a boundary layer prediction method which will adequately handle compressible, two-phase flow over rough, curved surfaces. Laboratory experiments are described which indicate that concentrated deposition can occur in the reattachment region of a separation bubble, but this process also appears to require drop diameter to be of order 1 μm in order to cause significant deposition, by an inertial mechanism, on a turbine blade.

Wellbore Heat Losses and Pressure Drop In Steam Injection

This mathematical model of the mechanics of flow of wet and saturated steam down the wellbore during steam injection takes into account the variation of steam temperature and pressure due to friction, as well as heat losses by radiation, conduction, and convection. It consists of two coupled nonlinear equations that are solved iteratively. Introduction Chekalyuk et al., Moss and White, and Fokeev and Kepyrin, investigated wellbore heat losses during injection of a hot or cold fluid down the casing. Ramey made a comprehensive study of the injection of liquids and gases down casing or tubing. Squier et al. presented a complete analytical treatment of hot water injection down the wellbore. Satter extended Ramey's treatment to the case of steam injection. Huygen and Huitt, presented results of a theoretical and experimental treatment of wellbore heat losses during steam injection, and pointed out the importance of the radiation heat loss. Holst and Flock as well as Earlougher extended the above treatments by including, steam pressure calculations. Eickmeier et al. considered the early transient performance, using a finite-difference model. performance, using a finite-difference model. Apart from these studies, Leutwyler gave a comprehensive treatment of casing temperature behavior, and Willhite presented a complete calculation of the over-all heat presented a complete calculation of the over-all heat transfer coefficients. The chief objective of our work was to formulate a comprehensive mathematical model of steam injection into a reservoir to include simultaneous calculation of steam pressure and quality. The model took into account the variation of steam temperature and pressure due to friction, as well as heat losses by pressure due to friction, as well as heat losses by radiation, conduction, and convection, and consisted of two coupled nonlinear differential equations that were solved iteratively. The model results were compared with those predicted by several of the above-mentioned approaches. Formulation of the Model Steam at a constant injection pressure, constant mass flow rate, and constant quality (at the surface) is injected through the tubing into the wellbore. The complete system consists of the fluid, the tubing, the annular space containing low-pressure air, the casing, the cement, and the formation. We propose to compute the pressure and the quality of steam as functions of depth and time. An energy balance and a momentum balance can be written for the flowing fluid as follows: Energy balance ..........(1) Momentum balance ..............................(2) The term dQ is given by,...................(3) where the rate of heat transfer to the formation is (4) dq = , JPT P. 139

The definition and measurement of wet steam properties

Possible states of thermal equilibrium and disequilibrium within a wet steam flow are examined. Proceeding from simplified models of the flow, a “general composite” property is proposed which is related to the respective mass concentrations, property magnitudes and velocities of the constituents. Examination of the physical processes which the mixture would undergo in order to exhibit such properties enables appraisal of the feasibility of practical measuring instruments. It is concluded that there is little scope for devising instruments on principles not already known or exploited. The feasibility of the stagnation temperature probe is analysed in detail.

Disintegration of moisture films running of the edges of steam turbine nozzle blades

The dimensions of the droplets and moisture “tongues” running off the edges of the nozzle blades of wet-steam stages have been determined experimentally and as a result of calculations based on the formulas of various authors. A physical picture of runoff and disintegration in the edge wake has been obtained for subsonic, near-sonic, and supersonic wet-steam flows.

Paper 39: The Flow of Wet Steam in a Turbine

This article considers methods of calculating condensation processes in wet steam turbines. Equations are given for determining the rate of nucleation, the growth of droplets, and the wet steam parameters. The condensation processes within the blade ring of a steam turbine are used by way of example. It is made clear that the condensation process is continuous at large enthalpy gradients. Under these conditions the theory of discontinuous condensation will not represent the actual process. Calculations based on the kinetic theory of phase change agree well with experimental findings. The constructional features of the blading which operates within the Wilson zone can have a considerable effect on the extent of the undercooling and on the size of the droplets. The trajectories of the droplets in the space between blade rings can be determined using standard approximate equations. The Coriolis force has a considerable influence on the motion of the entrained liquid within the moving blades. Under the influence of this force the liquid may move either with the flow or against it.

Paper 26: The Concurrent Measurement of Momentum and Stagnation Enthalpy in a High-Quality Wet Steam Flow

This paper describes the problems encountered in the design, operation, and calibration of a small momentum balance fitted within an isokinetic sampling probe located in the test section of a wet steam ‘wind’ tunnel. The probe is suitable for use in air, dry steam, or wet steam. It has an opening of ½ in diameter, a maximum diameter of 1¼ in, and a length of 4½ in, and will detect momentum forces greater than 0·001 lbf. The signal is transmitted by causing the impulse cage to compress a bellows. Turpentine enclosed therein raises the level of its meniscus in a capillary tube and the change in level is observed with a micrometer microscope. An electrical superheating calorimeter is employed in series with the impulse-measuring probe to determine the stagnation enthalpy of the sample. Results are reported for air and steam. For steam the ranges of the respective variables are: pressure, 20–25 inHg vacuum; velocity, 200–500 ft/s; and wetness, 0–10 per cent by weight. Owing to the small size of the momentum cage it was not possible to isolate the contribution to the total momentum made by the entrained liquid.