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ABSTRACT
SELECTEDPROBLEMSOFCFDMODELINGOFPOLYMER
EXTRUSION
Extrusionistheprimaryandmostmasspolymerprocessingtechniqueduetoitsextensiveapplica-
tionsintheproductionofprofileproducts,e.g.pipes,rods,platesandfilms,anditsapplicationsin
preparatoryprocessing,e.g.blending,granulation,chemicalandphysicalmodification,including
functionalization,insertionofadditives,reinforcementandfillingprocesses.Extrusioncanbecar-
riedoutinsinglescrewortwinscrew,co-rotatingorcounter-rotatingextruders.
Modelingthepolymerflowinanextruderisvitaltotheextrusionprocessdesign.Theflowinthe
extrusionprocessisacomplexfluidmechanicsproblem,usuallythree-dimensional,non-isothermal
andnon-Newtonian,oftenviscoelasticsometimesalsowithyieldstressandslipeffect.Itisrealized
ingeometricallycomplexsinglescrewortwinscrewsystems.Modelingsuchflowsis,inprinciple,
onlypossibleonthegroundofComputationalFluidDynamics(CFD),usuallybasedontheFinite
ElementsMethod(FEM).ModelingtheextrusionprocessbasedonFEMcalculationsiscomplex
andverytime-consuming.Therefore,itisreluctantlyusedinscientificandengineeringpractice.
Extrusionisaspecificpolymerprocessingprocessthatoccursasaresultofcontinuouscoop-
erationbetweenthemachine(extruder)andthetool(die).Inthisprocess,carriedoutclassically
withgravityfeed,theflowrateofthepolymerisnotknown“apriori”andisnotdeterminedbythe
operator.Itistheresultofinteractionbetweenthemachineandthetool,andisdeterminedduring
theprocessing.
Particularlychallengingistheso-calledglobalextrusionmodeling,whichrequiresthesearchfor
theflowrateinmultipleiterativeloops,inwhicheachtimethesolidpolymerflow,polymermelting
andtheflowofmoltenpolymerinthescrewandextrusiondie.Duetotheneedformultipleiterative
calculations,numericalFEMmethods,whicharefartootime-consuming,arenotusedhere.
ThisthesisproposestheconceptofCFDmodelingoftheextrusionprocessbasedonthedi-
mensionlesscharacteristicsofthepolymerflowintheextruder.Thesecharacteristicsareobtained
bydifficultandtime-consumingnumericalcalculations,buttheyareapproximatedbytheregres-
sionmodelsandareimplementedintoaglobalprocessmodel.Inmultiplecomputationaliterative
loops,theglobalmodelusesregressionmodels,whichprovidefastcalculationswithreasonable
accuracy.
Theproposedmodelingconceptispresentedforclassicalsinglescrewextrusionusingconven-
tionalandnon-conventional(specialized)screwelements.Thedevelopedmethodologyalsoapplies
tothemodelingoftwinscrewextrusion,co-rotatingandcounter-rotating,aswellassinglescrew
extrusionwithmetering.Thestudyalsopresentsoriginalsolutionstotheproblemofmodelingthe
flowwithslipeffectandtheflowwithyieldstress.Anovelattemptofcontinuousmodelingofpoly-
mermeltingintheextrusionprocesswasalsomade.
Inconclusion,thethesissolvestheissuesofCFDmodelingtheextrusionprocessofpolymers
asapartofglobalprocessmodeling,whichprovidesgoodaccuracyofmodelcalculations,with
areasonabletimeforthesecalculations.
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