Rheometer

About: Rheometer is a research topic. Over the lifetime, 5759 publications have been published within this topic receiving 125849 citations.

Yield Stress and Time‐dependent Rheological Properties of Mango Pulp

Abstract: Mango pulp was tested for time-independent and time-dependent flow properties using a coaxial cylinder rheometer. Mango pulp is a pseudoplastic liquid with yield stress, and exhibits thixotropic properties. The yield stress calculated using the Casson or Bingham plastic models, had markedly higher values than those determined by stress relaxation, controlled stress experiments, or from stress-strain plots. The yield stress of mango pulp tested in this experiment was sensitive to temperature and decreased rapidly as temperature increased. The time-dependent model of Weltman was found to be most applicable (|r| ≥ 0.991, p ≤ 0.01) for mango pulp.

A rheometrical study of boger fluids

Abstract: A rheometrical study is reported on a series of Boger fluids (solutions of polyacrylamide in a water/maltose syrup base). Steady-shear and oscillatory-shear experiments lead to the now-accepted conclusion that Boger fluids appear to be more “elastic” in steady shear than they do in oscillatory shear. At the same time, the limiting continuum relations for the material functions at low shear rates and low frequencies are not violated. It is concluded that it is more appropriate to use an Oldroyd B model in the interpretation of the results than the upper-convected Maxwell model, in line with the suggestion of Prilutski et al. [9]. At relatively high shear rates, shear thickening is observed in steady-shear flow, associated with a time-dependent anti-thixotropic behaviour. The new Sangamo Spin-Line Rheometer is used to obtain an estimate of the Boger fluids' resistance to an extensional flow. Trouton ratios as high as 104 are obtained for one of the Boger fluids.

Investigation of the microscopic reason for the magnetoviscous effect in ferrofluids studied by small angle neutron scattering

Abstract: Experimental studies made on different ferrofluid samples under shear flow have shown that an increase of magnetic field strength yields an increase of the fluid's viscosity, the so-called magnetoviscous effect, while increasing shear rate leads to a decrease of the viscosity. The change of the viscosity with magnetic field strength can be theoretically explained as an effect of chain-like structure formation and therefore can be related to the modification of the microstructure of ferrofluids. Using a specially designed rheometer, ferrofluids having different magnitude of the magnetoviscous effect were investigated by small angle neutron scattering (SANS). Correlated to the structure formation in the fluid, the scattered intensity shows a variation with magnetic field and shear rate only for fluids with a high magnetoviscous effect. The results obtained show a good agreement with the qualitative model elaborated to explain the magnetoviscous effect, indicating a strong connection between the rheological behaviour of ferrofluids and their microstructure.

Elastic turbulence in shear banding wormlike micelles.

Abstract: We study the dynamics of the Taylor-Couette flow of shear banding wormlike micelles. We focus on the high shear rate branch of the flow curve and show that for sufficiently high Weissenberg numbers, this branch becomes unstable. This instability is strongly subcritical and is associated with a shear stress jump. We find that this increase of the flow resistance is related to the nucleation of turbulence. The flow pattern shows similarities with the elastic turbulence, so far only observed for polymer solutions. The unstable character of this branch led us to propose a scenario that could account for the recent observations of Taylor-like vortices during the shear banding flow of wormlike micelles.