Rheometer

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

Transient filament stretching rheometer II: Numerical simulation

Abstract: The Lagrangian specification is used to simulate the transient filament stretching rheometer. Simulations are performed for a dilute PIB-solution modeled as a four mode Oldroyd-B fluid and a semidilute PIB-solution modeled as a non-linear single integral equation. The simulations are used to investigate a sequence of filament stretching rheometers. The questions of special and temporal homogeneity of the experiment are investigated. The simulations are compared with data from a specific rheometer by Tirtaadmadja and Sridhar.

Characterization of yield stress fluids with concentric cylinder viscometers

Abstract: The methods normally employed for shear rate calculations from concentric cylinder viscometer data generally are not applicable for fluids with a yield stress. In cylindrical systems with large radius ratios, as usually is the case with suspensions, the yield stress induces two possible flow regimes in the annulus. Unless the yield value is exceeded everywhere in the gap only part of the fluid can be sheared while the remaining region behaves like a solid plug. A correct calculation of the shear rate must take into account the presence of a variable effective gap width determined by the extent of the sheared layer. For time-independent yield stress fluids, a two-step procedure, which does not require any specific flow model, is proposed for analysing the experimental torque-speed data. Under the partially sheared condition, the shear rate can be computed exactly, whereas for the fully sheared flow the Krieger and Elrod approximation is satisfactory. The method is assessed by examining both semi-ideal data generated with a Casson fluid with known properties, and experimental data with an industrial suspension. A more complicated problem associated with characterization of time-dependent yield stress fluids is also identified and discussed. An approximate procedure is used to illustrate the dependence of the shear rate on time of shear in constant-speed experiments.

Transition to shear banding in pipe and Couette flow of wormlike micellar solutions

Abstract: We used both conventional rheometry and nuclear magnetic resonance (NMR) velocimetry to study shear banding in a solution of 200 mM cetylpyridinium chloride and 120 mM sodium salicylate in 0.5 M sodium chloride. The solution behaved as a Maxwell fluid up to frequencies of 10 Hz. Theoretical predictions of critical strain rate and shear stress were in good agreement with measurements obtained using controlled strain rate rheometry. Using NMR velocimetry, we observed convincing evidence of shear banding in capillary flow with a band of very high, approximately constant, shear rate next to the wall that grew in thickness with increasing apparent shear rate. We believe that the shear rate in this band (∼600 s−1) marks the beginning of the hypothesized high shear rate limb of the flow curve. We also observed shear banding in both the cylindrical Couette and cone-and-plate geometries. Shear banding started at shear rates that were approximately the same as the critical shear rate measured with the mechanical rh...

Study of magnetorheological fluids at high shear rates

Abstract: The tunable rheological properties of magnetorheological (MR) materials at high shear rates are studied using a piston-driven flow-mode-type rheometer. The proposed method provides measurement of the apparent viscosity and yield stress of MR fluids for a shear rate range of 50 to 40,000 s−1. The rheological properties of a commercial MR fluid, as well as a newly developed MR polymeric gel, and a ferrofluid-based MR fluid are investigated. The results for apparent viscosity and dynamic and static shear stresses under different applied magnetic fields are reported.