The Deposition of Fog Droplets on Steam Turbine Blades by Turbulent Diffusion

Abstract

A theoretical approach for calculating the rate of deposition of fog droplets on steam turbine blades by turbulent diffusion is described. The theory is similar to that which has proved successful for predicting deposition of small particles in pipe flow and includes a recent correlation for the inertia-moderated regime. A reliable estimate of the blade surface shear stress distribution is required and is obtained by a quasi-three-dimensional inviscid flow calculation to give the blade surface velocity distribution, followed by a two-dimensional boundary layer calculation. The theory has been applied to two representative case studies. The first involves deposition on the final stage blading of the low-pressure cylinder of an operating 500 MW turbine, and the second concerns deposition in a high-pressure, wet steam turbine. Results are presented showing the effect of fog droplet size, surface roughness, and other flow parameters on the deposition rate. A comparison is made between the rates of deposition by diffusional and purely inertial mechanisms. In low-pressure turbines these are of comparable magnitude, but in high-pressure machines diffusional deposition may dominate.

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

“…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.…”

“…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.…”

“…In this work, the deposition of liquid droplets by the turbulent diffusion and inertial impact on the stationary and moving blades of the last stage of a 1000 MW fossil-fired steam turbine are calculated by the method of Yau and Young [10] and a number of full-3D Euler-Lagrangian computations. Based on the results of droplets deposition and the 3D multi-phase flow solutions, a physically consistent 3D method to evaluate the moisture losses is presented and six categories of the moisture losses are determined for the last stage.…”

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 .…”