The Inertial Deposition of Fog Droplets on Steam Turbine Blades

Abstract

A theoretical approach for calculating the rate of deposition of fog droplets on steam turbine blades by inertial impaction is described. Deposition rates are computed by tracking a number of droplet path lines through a specified blade-to-blade vapor flowfield and identifying the limiting trajectories that just intersect the blade surface. A new technique for performing the calculations efficiently has been developed whereby the mathematical stiffness of the governing equations is removed, thus allowing the numerical integration to proceed stably with comparatively large time increments. For high accuracy, the vapor flowfield is specified by a quasi-three-dimensional flow calculation involving both meridional and blade-to-blade plane calculations. Results are presented for two representative “test cases,” namely the final stage blading of the low-pressure cylinder of a 500 MW turbine and a typical stage in a high-pressure wet steam turbine. The effect on the deposition rate of fog droplet size and blade profile geometry is investigated for both on- and off-design flowfields. Comparisons are made with the predictions of a simplified theory for inertial deposition and the effect of blade rotation in flows with high pitch angles is discussed.

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

“…One may observe that the trends and magnitudes of the fractional diffusional deposition rate of the three results are roughly similar as expected since the method used to calculate the diffusional deposition is same. The similar trends and magnitudes of the total deposition rate for the three results indicate that the Lagrangian particle track model employed in the current work and in the work of Young and Yau [11] to calculate the inertial deposition can obtain equivalent results as the method based on the inhomogeneous multi-fluid model utilized by Starzmann. The three results show that, when the droplet size is small, the diffusional deposition dominates.…”

“…Since the liquid density is much larger than the vapor density, non-drag forces, i.e. virtual mass force and pressure gradient force, which are significant when the density of disperse phase is less than the continuous phase's density, are neglected and only the viscous drag force on droplets is considered [11]. The viscous drag force is calculated by Schiller and Naumann model having the form of Eq.…”

“…In general, the mechanisms of fog droplet deposition onto the turbine blades can be divided into the inertial impaction and turbulent diffusion. The deposition of small particles in turbulent pipe flow has been the subject of a large number of investigations but a few papers focused on fog droplets deposition in steam turbine, for example the work by Gyarmathy [4], Crane [9], Yau [10], Young [11,12] and Starzmann [13]. Yau and Young [10,11] extended the theories of diffusional deposition proposed by Wood [14] to predict the diffusional deposition of fog droplets on the steam turbine blades and employed a quasi-3D Lagrangian particle track method to determine the inertial deposition.…”

“…The deposition of small particles in turbulent pipe flow has been the subject of a large number of investigations but a few papers focused on fog droplets deposition in steam turbine, for example the work by Gyarmathy [4], Crane [9], Yau [10], Young [11,12] and Starzmann [13]. Yau and Young [10,11] extended the theories of diffusional deposition proposed by Wood [14] to predict the diffusional deposition of fog droplets on the steam turbine blades and employed a quasi-3D Lagrangian particle track method to determine the inertial deposition. Starzmann [13] implemented the diffusional theory of Yau and Young [10] into a full 3D multi-momentum two phase model to calculate the diffusional deposition of fog droplets on the stationary blades of the last stage of a model low-pressure steam turbine.…”

Study on water extraction of hollow stationary blade under wet steam flow conditions

“…Especially, the water extraction via the suction slots on hollow stationary blade is one of the most efficient methods 18 . The deposition of submicron particles on turbine blades was experimentally studied 19 , and the inertial deposition of droplets was numerically investigated [20][21][22] , where the turbulence effect is considered. It indicates that due to the weak effect of turbulence on the trajectories of coarse droplets, the numerical prediction of deposition rates is relatively accurate 23 .…”