Abstract
Massive droplets can be generated to form two-phase flow in steam turbines, leading to erosion issues to the blades and reduces the reliability of the components. A condensing two-phase flow model was developed to assess the flow structure and loss considering the nonequilibrium condensation phenomenon due to the high expansion behaviour in the transonic flow in linear blade cascades. A novel dehumidification strategy was proposed by introducing turbulent disturbances on the suction side. The results show that the Wilson point of the nonequilibrium condensation process was delayed by increasing the inlet superheated level at the entrance of the blade cascade. With an increase in the inlet superheated level of 25 K, the liquid fraction and condensation loss significantly reduced by 79% and 73%, respectively. The newly designed turbine blades not only remarkably kept the liquid phase region away from the blade walls but also significantly reduced 28.1% averaged liquid fraction and 47.5% condensation loss compared to the original geometry. The results provide an insight to understand the formation and evaporation of the condensed droplets inside steam turbines.
Highlights
A steam turbine is one of essential components to achieve energy conversion and utilisation for industrial applications [1,2,3,4,5]
The dehumidification characteristics were achieved by optimising the structures [15] and operating conditions [16], which were based on the nonequilibrium condensation in transonic flows
The droplet number and liquid fraction are solved by two additional scalar equations by User-Defined Scalar (UDS), while the source terms are employed to describe the mass generation during nonequilibrium condensations in transonic flows by User-Defined Functions (UDF)
Summary
A steam turbine is one of essential components to achieve energy conversion and utilisation for industrial applications [1,2,3,4,5]. The polydispersed droplet distribution was studied using numerical modelling in blade cascades in steam turbines. Gerber and Mousavi [22] investigated the accuracy and robustness of the quadrature method of moment in modelling the distribution of the droplet sizes in the two-phase flow in low-pressure turbines. Furst et al [23] developed a pressure-based solver to model the wet steam flow in OpenFOAM and successfully predicted the nonequilibrium condensation in turbine blades. Han et al [26] developed a numerical model to evaluate the effect of surface heating on the condensation behaviour in steam turbines and subsequently optimised the blade performance. The purpose of this study was to develop a condensing two-phase flow model to predict the transient nucleation and condensation processes because of high expansion characteristics in steam turbines.
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