3245

3016

كارشناسي ارشد

﴿ شيمي فيزيك ﴾

اصفهان : دانشگاه صنعتي اصفهان ، دانشكده شيمي

1384

[ شش ] ، 96 ، [I] ص : مصور ، جدول ، نمودار

يوسف غايب ، بيژن نجفي

عزت كشاورزي ، غلامعباس پارسافر

شيمي

ID3016

به فارسي : قابل رويت در نسخه ديجيتالي

AbstractIn this thesis a new method for the viscosity calculation of pure and binary mixtures ofsupercritical gases is presented in which pressure is appeared explicitly rather than density The fundamental difference between the friction theory and other available theories is thefact that the viscosity of dense fluids which characterizes pure shear flow is approached asa mechanical rather than a transport property and it is not until the approaching of thedilute gas limit that the kinetic principles of the theory of gases become important Thus since this new theory is applicable to dense fluids in most cases it should be used togetherwith a dilute gas model the Chapman Enskog theory in order to cover the low to high pressure rangeAccording to the van der Waals theory of fluids in the case of a fluid at rest the totalpressure p is given by p p r pawhere p r and p a are the contribution to the pressure coming from the short rangerepulsive and the long range intermolecular forces respectively In turn the shear stress i e dragging force acting between the moving fluid layers can be written as the additionof a dilute gas collision term which becomes important at the ideal gas limit and a residualfriction term Consequently the total fluid viscosity must have the form 0 fwhere 0 is the zero limit density viscosity and f is the friction contribution viscosity andgiven by f f r f a f rrwhere f r k r pr f a k a pa f rr k rr pr2 andThe combining and mixing laws are used in determining the attractive and repulsivepressure of mixture and this equation of the pure fluid is extended for the mixture bymixing laws With the comparison of the empirical and the calculated viscosity of gasesand refrigerants the high precision of this calculating method is expressed The predicted viscosity values of some binary typical gases are compared withexperimental values As shown the accuracy of the predicted viscosities is withinexperimental uncertainties about0 4 The main advantage of this method is that theviscosity of binary mixtures can be calculated directly by inserting the pressure valuesrather than density

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