Modelling of Two-Phase Flows with Modelica

Sammanfattning: Modelica-TM is an object-oriented language for modeling physical systems that was designed in the last years with the goal to become a standardized multi-domain modeling language. This paper describes a robust model for homogenous and inhomogenous two phase flows with dynamic or static slip correlation. It was developed in the context of developing a Modelica base library for thermo-hydraulic applications. The model describes the transient behaviour of a fluid moving through a pipe during a phase change caused by heat transfer or pressure changes. Measurements from a refrigeration cycle were used to validate the model. Physical approaches were taken to model friction and momentum exchange between the phases. Specialized thermodynamic equations of state were developed in order to improve the simulation speed. The model also includes the one-phase flow of liquid or vapor as limiting cases in order to make the simulation of a complete phase-transition possible. The model is numerically robust in all flow regions. Modelica's language features are used to structure the code for reusability in different context. These features make the model well suited for a reusable model library.