Geijselaers, H.J.M.

Huetink, J.

Owczarek, P.

English

University of Twente Research Information

Oil-free piston compressorsP. Owczarek, H.J.M. Geijselaers and J. HuétinkInstitute of Mechanics, Processes and Control - TwenteUniversity of TwenteP.O. Box 217, 7500 AE Enschede, The Netherlandsphone +31-(0)53-4894175, email p.owczarek@ctw.utwente.nlIntroductionMaterial wear and working gas deterioration limit lifetime and reliability of Stirling compressors. The aimof the project is to design a high performance oil-freepiston compressor for application in cooling systems.The proper material selection regarding sliding, anti-wear properties and the piston cylinder assemblydesign is considered for improved efficiency.MethodsExperiments A home developed vacuum tribo-tester is used for friction and wear measurementsin vacuum and inert gas atmospheres on the pre-selected materials. The new design concepts and theselected materials performance will be demonstratedand validated on the gas spring test rig.headcooling inletcooling outletpistonvacuumchamberdrivertribo-metercylinderGas springBasecompressorFigure 1 : The vacuum tribo-tester and gas springCalculations 1) The FE code DiekA is used forthermo - mechanical simulations of the piston -cylinder assembly under transient thermal loads (fromboth compressed gas and friction). The thermo-elastic instability leading to seizure can be analyzed,see preliminary results in Figure 2.2) A new model for piston - gas film interaction isdeveloped considering piston shape, dynamics andoperating conditions. Simulations of the pistonssecondary motion were performed. Figure 3 showsthe trajectory of point ’a’. The influence of designparameters is investigated to find an optimum pistonshape that reduces the radial motion and tiltingcreating a stable, uniform gas film.Uy(t)T(t)contact thermal elements, axi-symsolid thermal elements, axi-symTemperatureTmaxTrefa) b)UyTBDCTDCtimeFigure 2 : a)Half cross-section of the piston-cylinder fitb) Deformed shape and temperature field after seizureRPxPrPgxeanominal0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4-0.500.511.522.5timenormalized clearance, x/ctapered pistonnominal pistoncontacttaperedd.p.Figure 3 : Schematic drawing of piston and results ofsecondary piston motion simulationsDiscussionThe integrated approach of structural mechanics,thermal engineering and tribology aims to design anadvanced piston compressor. Based on numericalresults design concepts will be proposed. Thefollowing companies joined the project Stirling BV,Grasso BV, Bekaert BV,Thales C-N, NPT BV, PhilipsDAPC,ANSYS Europe Ltd.Tenth Engineering Mechanics Symposium P-45

Oil-free piston compressors

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