Vortex breakdown in swirling pipe flow of fluids with shear-dependent viscosity

The rheology of saliva affects the coating and lubrication of oral surfaces and the consistency of ingested foods. Salivary gland dysfunction can cause tissue damage and dysphagia. Therefore, we have considered the problem of designing a synthetic saliva for medical management. Also, we have measured certain rheological properties [shear-dependent viscosity η (k)] and the frequency-dependent moduli [G′(f) and η′(f)] of normal stimulated whole saliva. Analysis of the rheological data and consideration of requirements for using artificial saliva have resulted in a better understanding of the rheological functions of natural saliva and the desirable characteristics of synthetic saliva. In addition, we have measured rheological properties of two commercial saliva substitutes for comparison.

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Stability of Shear-Thickening Liquids Between Rotating Cylinders

Volume 8: Dynamic Systems and Control, Parts A and B ◽

10.1115/imece2010-39854 ◽

2010 ◽

Author(s):

Nariman Ashrafi ◽

Habib Karimi Haghighi

Keyword(s):

Couette Flow ◽

Dynamical Behavior ◽

Shear Thickening ◽

Shear Thinning ◽

Taylor Vortex ◽

Shear Dependent Viscosity ◽

Shear Thinning Fluids ◽

Shear Thickening Fluids ◽

The Stability ◽

Dependent Viscosity

The effects of nonlinearities on the stability are explored for shear thickening fluids in the narrow-gap limit of the Taylor-Couette flow. It is assumed that shear-thickening fluids behave exactly as opposite of shear thinning ones. A dynamical system is obtained from the conservation of mass and momentum equations which include nonlinear terms in velocity components due to the shear-dependent viscosity. It is found that the critical Taylor number, corresponding to the loss of stability of Couette flow becomes higher as the shear-thickening effects increases. Similar to the shear thinning case, the Taylor vortex structure emerges in the shear thickening flow, however they quickly disappear thus bringing the flow back to the purely azimuthal flow. Naturally, one expects shear thickening fluids to result in inverse dynamical behavior of shear thinning fluids. This study proves that this is not the case for every point on the bifurcation diagram.

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Heat Transfer in Turbulent Pipe Flow for Liquids Having a Temperature-Dependent Viscosity

Journal of Heat Transfer ◽

10.1115/1.3450785 ◽

1978 ◽

Vol 100 (2) ◽

pp. 224-229 ◽

Cited By ~ 2

Author(s):

O. T. Hanna ◽

O. C. Sandall

Keyword(s):

Heat Transfer ◽

Friction Factor ◽

Pipe Flow ◽

Turbulent Pipe Flow ◽

Fluid Viscosity ◽

Temperature Dependent ◽

Temperature Dependent Viscosity ◽

Analytical Approximations ◽

Constant Viscosity ◽

Dependent Viscosity

Analytical approximations are developed to predict the effect of a temperature-dependent viscosity on convective heat transfer through liquids in fully developed turbulent pipe flow. The analysis expresses the heat transfer coefficient ratio for variable to constant viscosity in terms of the friction factor ratio for variable to constant viscosity, Tw, Tb, and a fluid viscosity-temperature parameter β. The results are independent of any particular eddy diffusivity distribution. The formulas developed here represent an analytical approximation to the model developed by Goldmann. These approximations are in good agreement with numerical solutions of the model nonlinear differential equation. To compare the results of these calculations with experimental data, a knowledge of the effect of variable viscosity on the friction factor is required. When available correlations for the friction factor are used, the results given here are seen to agree well with experimental heat transfer coefficients over a considerable range of μw/μb.

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A note on steady flow of fluids with shear dependent viscosity

Nonlinear Analysis ◽

10.1016/s0362-546x(97)00391-x ◽

1997 ◽

Vol 30 (5) ◽

pp. 3029-3039 ◽

Cited By ~ 33

Author(s):

Michael Ržička

Keyword(s):

Steady Flow ◽

Shear Dependent Viscosity ◽

Dependent Viscosity

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Annular Frictional Pressure Losses During Drilling—Predicting the Effect of Drillstring Rotation

Journal of Energy Resources Technology ◽

10.1115/1.4026205 ◽

2014 ◽

Vol 136 (3) ◽

Cited By ~ 19

Author(s):

Arild Saasen

Keyword(s):

Rheological Properties ◽

Pressure Loss ◽

Drilling Fluid ◽

Axial Flow ◽

Drilling Fluids ◽

Unstable Flow ◽

Pressure Losses ◽

Shear Dependent Viscosity ◽

Water Based ◽

Dependent Viscosity

Controlling the annular frictional pressure losses is important in order to drill safely with overpressure without fracturing the formation. To predict these pressure losses, however, is not straightforward. First of all, the pressure losses depend on the annulus eccentricity. Moving the drillstring to the wall generates a wider flow channel in part of the annulus which reduces the frictional pressure losses significantly. The drillstring motion itself also affects the pressure loss significantly. The drillstring rotation, even for fairly small rotation rates, creates unstable flow and sometimes turbulence in the annulus even without axial flow. Transversal motion of the drillstring creates vortices that destabilize the flow. Consequently, the annular frictional pressure loss is increased even though the drilling fluid becomes thinner because of added shear rate. Naturally, the rheological properties of the drilling fluid play an important role. These rheological properties include more properties than the viscosity as measured by API procedures. It is impossible to use the same frictional pressure loss model for water based and oil based drilling fluids even if their viscosity profile is equal because of the different ways these fluids build viscosity. Water based drilling fluids are normally constructed as a polymer solution while the oil based are combinations of emulsions and dispersions. Furthermore, within both water based and oil based drilling fluids there are functional differences. These differences may be sufficiently large to require different models for two water based drilling fluids built with different types of polymers. In addition to these phenomena washouts and tool joints will create localised pressure losses. These localised pressure losses will again be coupled with the rheological properties of the drilling fluids. In this paper, all the above mentioned phenomena and their consequences for annular pressure losses will be discussed in detail. North Sea field data is used as an example. It is not straightforward to build general annular pressure loss models. This argument is based on flow stability analysis and the consequences of using drilling fluids with different rheological properties. These different rheological properties include shear dependent viscosity, elongational viscosity and other viscoelastic properties.

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