D.M. Binding

An approximate analysis for contraction and converging flows

Abstract An approximate analysis is presented for the flow of fluids through planar and axisymmetric contractions. Energy principles are employed to relate the entry pressure drop to flow rate and fundamental rheometric properties. One of the aims of the analysis is to investigate the influence of extensional viscosity on such flows, particularly with regard to the occurrence and enhancement of vortex motion in the entry corners. For the sake of mathematical simplicity, independent power-law models are used to represent the shear and extensional viscosity functions. The analysis indicates that, once significant vortex motion is present, enhancement occurs whenever the Trouton ratio is an increasing function of shearrate (or stretch-rate). It is readily seen how the occurrence of vortices serves as a stress relief mechanism. Indeed, for highly stretch-thickening materials, the entry pressure drop is seen to be dominated by shear properties. The power-law parameters of the extensional viscosity function may be obtained in a straight-forward way from entry pressure drop versus flow rate data. Finally, the extension and application of the analysis to other similar flows, such as through converging nozzles, is briefly discussed.

On the use of flow through a contraction in estimating the extensional viscosity of mobile polymer solutions

Abstract We consider the use of pressure measurements in contraction flows in the determination of the extensional viscosity behaviour of polymer solutions. The experimental data are interpreted on the basis of the recent theory of Binding. The resulting extensional viscosities are compared with those obtained from a commercial Spin Line Rheometer. We conclude that contraction flows provide a convenient means of determining the extensional viscosity of shear-thinning polymer solutions. The case is not so clear for constant viscosity Boger fluids. In the course of the experiments, it is shown that excess pressure losses in the contractions can be brought about by two distinct flow mechanisms in the case of Boger fluids. In the axisymmetric case, both vortex enhancement and excess pressure loss are observed, although there is not a strict one-to-one correlation between these phenomena. In the planar case, vortex enhancement is not conspicuously present, although there is still a substantial excess pressure loss at high flow rates. This excess must be associated with the ‘bulb’ flow field which essentially replaces the vortex-enhancement regime of the axisymmetric case.

The pressure dependence of the shear and elongational properties of polymer melts

A borderless printing easel comprised of a paper support base having a retaining border formed thereon, and a set of flat sectioned mask plates removably positionable on the base portion, the individual sections of said mask plate being hinged at their center by a pliable strip of adhesive material whereby the mask sections can be successively folded back onto the top of opposing mask sections to reproduce adjacent or nearly adjacent borderless prints on a single sheet of print paper.

The shear and extensional flow properties of M1

Abstract Steady shear, oscillatory shear and extensional flow experiments are carried out on the test liquid designated M1. The steady shear experiments cover a shear rate range up to 8 × 104 s−1 and the oscillatory shear experiments involve frequencies up to 40 Hz. Three different extensional flow experiments are involved, namely contraction flow, spinning and the open-syphon technique. A search is made for internal consistency between the various rheometrical tests and the continuum mechanics requirements in the limit of low shear rates and frequencies are confirmed.

On using the torsional balance rheometer to measure normal stresses in lubricating greases

SummaryA new instrument, a Torsional Balance rheometer, has been used to measure shear and normal stress functions of lubricating greases. The new rheometer is based on torsional flow between parallel plates, but differs from conventional torsional flow instruments in that the plate separation is not held constant but allowed to adjust until the normal force is balanced by the axial load. In dealing with materials that have a yield stress, such as greases, the Torsional Balance rheometer is superior to fixed-plate rheometers since the zero of the normal force measurement is not dependent on the yield stress. Results have been compared with those obtained on a capillary viscometer and a Weissenberg rheometer.ZusammenfassungEin neues Meßinstrument, das „Torsions-Balance-Rheometer“, wird zur Messung der Schub- und Normalspannungs-Funktionen von Schmierfetten verwendet. Das neue Rheometer realisiert die Torsionsströmung zwischen zwei parallelen Platten, unterscheidet sich aber von konventionellen Torsionsströmungs-Instrumenten dadurch, daß der Plattenabstand nicht fest vorgegeben wird, sondern sich auf einen Wert einstellen kann, bei dem die Normalkraft im Gleichgewicht mit der axialen Belastung ist. Bei Stoffen mit Fließgrenze, wie z. B. Fetten, ist das Torsions-Balance-Rheometer den Rheometern mit festem Plattenabstand überlegen, da der Nullpunkt der Normalspannungs-Messung nicht von der Fließspannung abhängt. Die Meßergebnisse werden mit entsprechenden Ergebnissen verglichen, die an einem Kapillarviskosimeter und einem Weissenberg-Rheogoniometer erhalten worden sind.

The rheometry of solutions of polyisobutylene in a mixed solvent

Abstract This paper is concerned with the rheometrical characterization of a family of liquids based on the S1 fluid which is currently the object of an international research programme. The programme has, as primary objective, the study of how a solvent influences the rheological properties of a polymer solution for as broad a range as possible of the solvent concentration. S1 is a specific solution of polyisobutylene (PIB) in a solvent which consists of a mixture of polybutene oil and Decalin. In this paper, a family of solutions having different concentrations of PIB is studied. Conventional rheometrical data is presented for the solutions and these are fitted to useful but relatively simple equations. Although the usual limiting relationships that are expected for continuous media are shown to be satisfied, the empirical Cox-Merz rule is found to be violated. The characterization was complicated by the occurrence of an apparent shear-thickening phenomenon which was studied in detail and explained. Also, the now familiar instability that often occurs in rotary shear flows was shown to occur, as expected, at the same Deborah number for each of the solutions studied.