Phase behavior of oil-refrigerant mixtures – Modeling approaches

• Applicant: Dr.-Ing. Andreas Jäger
• Subject Area: Technical Thermodynamics ; Hydraulic and Turbo Engines and Piston Engines ; Fluid Mechanics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 510921053

Oil-injected rotary type positive displacement compressors are mainly used for the compression of refrigerants in various refrigeration applications. The efficiency of such machines depends on inevitable loss-mechanism, such as two-phase surge and gap flows. Modeling these flows is still a challenge today, on the one hand because of the complexity of simulating the two-phase flow in the narrow gaps with moving boundaries and on the other hand because of a lack of accurate models for the thermophysical properties of the highly asymmetric fluid mixtures of oil and refrigerant. This challenge is addressed with a multidisciplinary effort by DFG Research Unit FOR 5595.Within this Research Unit, the present subproject is concerned with the modeling of the phase behavior of oil-refrigerant mixtures and will investigate existing and develop new modeling approaches for strongly asymmetric mixtures. The aim is to provide a model that on the one hand is capable of describing the best available measurements within the experimental uncertainty and on the other hand can be flexibly and readily extended, e.g., for mixtures for which no experimental measurements or highly accurate reference equations of state are available. For modeling the thermodynamic properties of the oil-refrigerant mixtures, the multi-fluid mixture model will be used. This mixture model on the one hand allows the use of an arbitrary equation of state, such as highly accurate multiparameter equations of state formulated in the dimensionless Helmholtz energy, or simpler equations of state for which only few fluid-specific information are required, as for example cubic equations of state or the Lee-Kesler-Plöcker equation of state. On the other hand, the multi-fluid mixture model can also be combined with approaches for predictive calculations of thermodynamic properties of mixtures, such as the excess Gibbs energy models UNIFAC or COSMO-SAC. Besides the state-of-the-art corresponding-states based multi-fluid mixture model, which exhibits some certain shortcomings regarding the description of asymmetric mixtures, a non-corresponding-states based mixture model will be developed. This mixture model will likewise be combined with predictive excess Gibbs energy models in order to being able to transfer the developed models to other, less well investigated oil-refrigerant mixtures. The starting point for the model development will be relatively well-studied, non-asymmetric mixtures and the asymmetry of the mixtures will be increased during the course of this project with the final aim of understanding the thermodynamic behavior of strongly asymmetric oil-refrigerant mixtures.

• DFG Programme: Research Units
• Subproject of: FOR 5595: Oil-refrigerant multiphase flows in gaps with moving boundaries – Novel microscopic and macroscopic approaches for experiment, modeling, and simulation
• International Connection: USA
• Cooperation Partner: Ian H. Bell, Ph.D.