Simulation of Bulk Condensation during Expansion of a Vapor-Gas Mixture in the Flow Path of a Stage of a Turboexpander Unit

The working fluid entering a turboexpander under actual operating conditions may contain some impurities that affect the flow characteristics, the resulting temperature at the outlet of the turboexpander unit (TEU) stage, and the service life of its flow path. The presence of impurities often causes erosive damage to the TEU impeller blades due to their bombardment by droplets of the formed condensate. Modern standard methods for calculating the effects of cavitation and volume condensation either cannot take into account the presence of these effects and the extent of their influence on the flow characteristics and the TEU flow path at the design stage or they have a poor accuracy and are only a tool for probabilistic prediction of the effects of cavitation and volume condensation. Thus, modern refrigeration equipment and the overall turbomachine building industry require such a tool that would be free from these disadvantages. The problem of volume condensation during the expansion of a vapor-gas mixture in the flow path of a specific TEU stage was solved for the first time using a condensation model, which is based on the kinetic equation for the droplet size distribution function in a nonstationary 3D formulation. The model was implemented as a special module integrated into the CFD-package. Three-dimensional nonstationary predictions are used as the basis for a comparative analysis of the effect of condensation on the thermogasdynamics of the process of expansion of an incondensable gas carrier and a condensable impurity in the flow path of a stage in a specific TEU model. Regions where volume condensation may occur are localized. Their location is used as the basis for an analysis of the potential consequences (whether this will have any effect on thermogasdynamics and whether regions susceptible to erosive wear will appear). In this paper, we propose a method for calculating the expansion of multicomponent mixtures in the flow path of the TEU stage with or without condensation.