Influence of water and oil clearance flow on the operational behavior of screw expanders

Abstract

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.

Keywords

Screw expander liquid flooded clearance flow incompressible flow frictional losses

Get full access to this article

View all access options for this article.

References

Janicki M. Modellierung und simulation von rotations – verdrängermaschinen. Dissertation, University Dortmund, Germany, 2007.

Hütker J and Brümmer A. Experimental and theoretical investigation of dry running high-speed screw motors. In: International rotating equipment conference – compressors users international forum 2012. Düsseldorf, Germany, 27–28 September, pp.75–86.

Kethidi

Kovačević

Stosic

. Modelling of turbulence in screw compressor flows. Turbul Heat Mass Transf 2007; 7.

Kovačević A and Rane S. 3D CFD analysis of a twin screw expander. In: 8th International conference on compressors and their systems, London, 2013, pp.417–429.

Spille-Kohoff A, Hesse J and El Shorbagy A. CFD simulation of a screw compressor including leakage flows and rotor heating. In: 9th International conference on compressors and their systems, London. IOP Conf. Ser: Mater Sci Eng 2015; 90:012009.

Harling B. Untersuchung zur Ölverteilung in Schraubenkompressoren mit Schmiermitteleinspritzung. Dissertation, University Dortmund, Germany, 1995.

Deipenwische R. Ein Beitrag zum Einsatz von Öl als Konstruktionselement in Schraubenmaschinen. Dissertation, University Dortmund, Germany, 2000.

Zellermann R. Optimierung von Schraubenmotoren mit Flüssigkeitseinspritzung. Dissertation, University Dortmund, Germany, 1996.

Kauder K and Deipenwisch R. Oil as a design parameter in screw-type compressors: oil distribution and power losses caused by oil in the working chamber of a screw-type compressor. Int Conf Compress Syst (IMechE Conf Trans), London, 1999;6:49–58.

10.

Nikolov A and Brümmer A. Influence of water injection on the operating behaviour of screw expanders. In: 9th International conference on screw machines, Dortmund, 2014, VDI Bericht Vol. 2228, pp.43–60.

11.

Kauder

. Energiewandlung in öleingespritzten Schraubenverdichtern. Technische Mitteilungen 1979; 72: 404–410.

12.

Gräßer M and Brümmer A. Influence of liquid in clearances on the operational behavior of twin screw expanders. In: 9th International conference on compressors and their systems, London, IOP Conf Ser: Mater Sci Eng 2015; 90: 012060.

13.

Gräßer M and Brümmer A. An analytic model of the incompressible one-phase clearance flow in liquid injected screw expanders. In: 9th International conference on screw machines, Dortmund, 2014, VDI Bericht Vol. 2228, pp.71–89.

14.

Rinder

Kuchler

Hackl

. Wassereinspritzung oder Öleinspritzung fr Schraubenkompressoren im Vergleich. Schraubenmaschinen 2004; 12: 65–74.

15.

Venu Madhav K and Kovačević A. Economics of water injected air screw compressor systems. In: 9th International conference on compressors and their systems, IOP Conf Ser: Mater Sci Eng 2015;90: 012012.

16.

Schlichting

Gersten

. Grenzschichttheorie 10th edn. Berlin: Springer-Verlag.

17.

Sauls J, Powell G and Weathers B. Transient thermal analysis of screw compressors, Part I: use of thermodynamic simulation to determine boundary conditions for finite element analyses. In: International compressor engineering conference 2006, Purdue, paper 1811.

18.

Sauls J, Powell G and Weathers B. Transient thermal analysis of screw compressors, Part II: transient thermal analysis of a screw compressor to determine rotor-to-housing clearance. International Compressor engineering conference 2006, Purdue, paper 1811.

19.

Dreißig B. Ein Beitrag zur Auslegung trockenlaufender Schraubenmotoren. Dissertation, University Dortmund, Germany, 1989.

20.

Hütker

Brümmer

. Inlet throttling loss and clearance flow during the filling process of screw-type engines. Dev Mech Eng 2010; 4: 105–121.

21.

Hütker J and Brümmer A. Physics of a dry running unsynchronized twin screw expander. In: 8th International conference on compressors and their systems, London, 2013, pp.407–416.