Viscoelastic Properties Of Fluids Research Articles

The degeneration of turbulence in a liquid with internal rotation

Viscous fluids which possess even a small degree of elasticity behave in quite a different way from viscous fluids in non-steady-state flow which is fairly fast. The presence of elasticity leads to a change in the nature of the damping of small scale (high frequency) turbulent eddies when the turbulence becomes degenerate [1]. The difference in the specific properties of viscoelastic fluids manifests itself in the behavior of these eddies.

Velocity profiles in laminar oscillatory flow in tubes

The oscillatory laminar flow of a Newtonian fluid in a circular tube has been investigated when the fluid is subjected to a periodic pressure gradient. A technique has been developed which allows the velocity amplitude to be determined as a function of radius and the results agree closely with theoretical predictions. The work is being continued with a view to employing the technique for the determination of the rheological properties of viscoelastic fluids.

Turbulence phenomena in drag reducing systems

AbstractAn analysis based on the Townsend‐Bakewell model of the eddies in the wall regions of turbulent shear flows shows that viscoelastic fluid properties must lead to significant reductions in the rate of production of turbulent energy. This analysis in turn leads to the proper form of the similarity laws for drag reducing fluids, heretofore deduced empirically.Measurements of the axial and radial turbulence intensities for flow through smooth round tubes are reported, as are measurements of the time‐averaged velocity profiles and the drag coefficients. These indicate that for solutions exhibiting drag reduction at all Reynolds numbers the flow may be transitional to Reynolds numbers of the order of 105. This transitional flow consists of alternating patches of laminar and turbulent fluid, within each of which the flow characteristics are approximately similar to those of Newtonian fluids. At high Reynolds number conditions with the turbulent field fully developed the velocity profile in the core is flatter under drag‐reducing conditions than for turbulent Newtonian fluids, a change dependent on the increased isotropy of the turbulent field of the drag‐reducing fluid. These effects appear to be a result of increases in the time scales of the radial fluctuations caused by the fluid properties.Design calculations based upon the present results suggest that in large diameter pipelines, or in boundary layers on large objects, drag reduction may not be attainable under conditions of practical interest until fluids having relaxation times an order of magnitude larger than those presently available, but with comparable viscosity levels, are developed or, alternately, until fluids exhibiting Weissenberg numbers which do not change with deformation rate, can be found.

Tube flow of non‐Newtonian polymer solutions: Part II. Turbulent flow

AbstractA correlation of turbulent tube‐flow friction factors for non‐Newtonian polymer solutions, based upon the fluid property τ1/2 defined in Part I, has been found to represent data taken on seven solutions of Natrosol hydroxyethylcellulose in ½‐ and 1‐in, I.D. smooth tubes, with an average accuracy of 10.8%. Also, for these seven solutions, this correlation gives somewhat more accurate predictions of the point of transition into turbulent flow than are made by the Ryan‐Johnson stability theory.The correlation must be considered only provisional, however, because it does not simplify to the limiting case of extremely dilute solutions. Plausible extensions based on models of steady‐flow non‐Newtonian viscosity behavior, and other possible correlation schemes utilizing viscoelastic fluid properties, are briefly discussed.

Tube flow of non‐Newtonian polymer solutions: PART I. Laminar flow and rheological models

AbstractA correlation of turbulent tube‐flow friction factors for non‐Newtonian polymer solutions, based upon the fluid property τ1/2; defined in Part I, has been found to represent data taken on seven solutions of Natrosol hydroxyethylcellulose in ½‐ and 1‐in, I.D. smooth tubes, with an average accuracy of 10.8%. Also, for these seven solutions, this correlation gives somewhat more accurate predictions of the point of transition into turbulent flow than are made by the Ryan‐Johnson stability theory.The correlation must be considered only provisional, however, because it does not simplify to the limiting case of extremely dilute solutions. Plausible extensions based on models of steady‐flow non‐Newtonian viscosity behavior, and other possible correlation schemes utilizing viscoelastic fluid properties, are briefly discussed.

New Rheometer for Determining Rheological and Viscoelastic Properties of Fluids

A rising cylinder rheometer is described which can be used to study the flow properties of fluids in the low shear regions similar to those caused by a falling particle. The rheometer may also be used to study viscoelastic properties of fluids. The rheometer was used to obtain flow curves in the low shear region of several pharmaceutical suspending agents. Bingham yield values were obtained by extrapolating methods from these flow curves. Dynamic viscosities of these materials were obtained by analysis of their relaxation behavior. The dynamic viscosities are compared with the plastic viscosities of the materials in the low shear range.

Measurement of rheological properties of viscoelastic fluids in laminar shearing flow in tubes

Measurement of rheological properties of viscoelastic fluids in laminar shearing flow in tubes