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Rheometer
About: Rheometer is a research topic. Over the lifetime, 5759 publications have been published within this topic receiving 125849 citations.
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TL;DR: In this paper, the design of a device for rheological orthogonal superposition measurements on fluids is discussed, where a small amplitude oscillatory motion on a steady or transient shear flow provides a technique to probe flow-induced microstructural changes in situ by means of mechanical spectroscopy.
Abstract: The design of a device for rheological orthogonal superposition measurements on fluids is discussed. Superposing a small amplitude oscillatory motion on a steady or transient shear flow provides a technique to probe flow-induced microstructural changes in situ by means of mechanical spectroscopy. Oscillations perpendicular to the main shear flow possess intrinsic advantages over the parallel case. It is shown that the closed loop system of a force rebalanced transducer of an existing rheometer can be modified to drive an orthogonal oscillatory motion and to measure the material response. Nonhomogeneous flow, annular pumping or cavitation can occur and have to be avoided by means of a suitable flow cell. A double walled Couette cell, open at the bottom is suggested for that purpose. The device is evaluated with Newtonian fluids and with a viscoelastic polymer solution. The apparatus has two major advantages. First the forces associated with the main shear flow can be measured simultaneously with the orthog...
49 citations
TL;DR: In this paper, the normal force of concentrated carbonyl iron magnetorheological fluids (MRF) was measured using a plate-plate controlled-stress rheometer.
Abstract: The yield behavior of concentrated carbonyl iron magnetorheological fluids (MRF) is investigated measuring the normal force during shear flow in a plate–plate controlled-stress rheometer. For high enough external magnetic fields, a positive normal force is obtained below the yield point. This result is not explained using affine deformation chain models. However, the assumption of gapspanning particle chains and spheroidal aggregates of spheres predicts not only a positive normal force but also a maximum if we plot the normal force as a function of the strain, a result also found experimentally. The field dependence of the normal force suggests the existence of a threshold field, likely associated to the formation of gapspanning structures in the MRF. Another possible explanation for the maximum in the normal force lies on the phase transition from homogeneous to layered structures with cylindrical symmetry in the suspension. Steady-state and oscillometry studies show that the maximum in the normal force ...
49 citations
TL;DR: This paper used commercially available rheometers and well defined shear conditions, such effects due to shear rate and strain variation were studied, and the advantages of the new method used, particularly for research and process development, were discussed.
49 citations
TL;DR: In this article, a large series of hydrogels have been previously produced by polymerization of 1-vinyl-2-pyrrolidinone, with or without crosslinking.
Abstract: In order to develop an artificial vitreous, a large series of hydrogels have been previously produced by polymerization of 1-vinyl-2-pyrrolidinone, with or without crosslinking. Based on the assumption that a functional vitreous substitute should possess viscoelastic properties after its delivery, a number of selected gels were characterized rheologically by both oscillatory shear stress analysis and shear creep analysis, using a controlled stress rheometer in the cone/plate configuration. The experiments demonstrated a dramatic effect of injecting the gels through small-gauge needles, as many lost their viscoelasticity to become free-flowing fluids, probably because of the cleavage of chains and crosslinks. It was also found that the increase of comonomer content (2-hydroxyethyl methacrylate) and of crosslinking level generally had a strengthening effect. However, the effects of hydrophilic crosslinking agents (diallyl ether and divinyl glycol) were irregular. Eventually, only four hydrogels in this series showed viscoelastic characteristics after injection through a 30-gauge (0·13mm diameter) needle, maintaining behaviour typical of crosslinked networks and warranting further assessment as potential vitreous substitutes. © 1998 SCI.
49 citations
TL;DR: In this article, an experimental study of viscous heating in the flow of fluids with an exponential dependence of viscosity on temperature has shown that, for a given shear stress, two shear rates are possible.
Abstract: Theoretical investigations of viscous heating in the flow of fluids with an exponential dependence of viscosity on temperature have shown that, for a given shear stress, two shear rates are possible. Above a critical value, the stress decreases as the shear rate increases.
The present work is an experimental study of this phenomenon in plane and circular Couette flows and in cylindrical Poiseuille flow. ArochlorR 1260, a high viscosity Newtonian fluid with an extremely sensitive viscosity-temperature dependence is used as the test fluid. The results clearly show that two shear rates for Couette flow exist for one measured wall shear stress. Because of the viscosity-pressure dependence of the fluid, the Poiseuille flow results are inconclusive.
49 citations