Influence of water and oil clearance flow on the operational behavior of screw expanders
Gräßer, M. and Brümmer, A.
PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS, PART E: JOURNAL OF PROCESS MECHANICAL ENGINEERING
Volume: 23 Pages: 38-46
Currently, the simulation of multi-phase rotary displacement machines in reasonable accordance with the experimental results is not possible. Clearance sealing, additional frictional losses, heat transfer and lubrication are among the various effects caused by the presence of a liquid, which would all have to be modelled. Moreover, complex processes, such as condensation and evaporation affecting the thermodynamic equilibrium, as well as expansion of the multi-phase gas-liquid-mixture would have to be included. With the purpose of achieving a better understanding of liquid-flooded screw expanders, this paper describes a theoretical evaluation of clearance sealing by means of a liquid, and the resulting frictional losses. The influence of different auxiliary liquids, namely water and oil, is examined. Thus, after introducing the expander geometry and the auxiliary liquids, the results of a thermodynamic analysis are presented. The multi-chamber model-based simulation tool KaSim, that has been developed at the Chair of Fluidics, is applied to analyze the maximum potential of clearance sealing. Subsequently, dry running and liquid-flooded screw expanders are compared, taking clearance sealing as well as frictional losses into account. On the one hand, the study demonstrates that the influence of liquid water on temperature is negligible. On the other hand, the results show that reasonable modelling of oil requires a consideration of temperature-dependent dynamic viscosity for this auxiliary liquid. Finally, an extension of the presented simulation approach is introduced. © IMechE 2016.