摘要:

The slump test, initially developed to determine the flow properties of fresh concrete, has been adopted as a means of accurately measuring the yield stress of strongly flocculated suspensions. The slump test offers a quick and easy way of measuring yield stress without the need for sophisticated electronic equipment, thereby giving plant operators an effective tool for determining yield stress. The model used to predict the yield stress from the conical slump test was devised by Murata (1984) and corrected by Christensen (1991). In the present case the theory has been adapted for a cylindrical geometry. Yield stress measurements obtained with the vane for numerous mineral suspensions under known surface chemistry conditions are compared to the slump measurements and theoretical prediction. Good agreement is obtained.

ISSN:0148-6055    

DOI:10.1122/1.550780

出版商:The Society of Rheology    

年代:1996

数据来源: AIP

摘要:

The shear flow properties of aqueous silica suspensions at different solids loading in the presence of polyethylene oxide (PEO) and added salt (NaNO3) have been investigated. Particular attention is given to the evaluation of the role of electrolyte concentration,pH, and polymer concentration in viscosity reduction. The variation of the rheological properties with shear rate, solids loading, particle size,pH, electrolyte concentration, PEO concentration, and its molecular weight are discussed. The viscosity of the silica suspension was determined to be a decreasing function of the particle diameter and at 54% volume, the effect of particle size was scaled using Peclet number and relative viscosity of the suspension (hard sphere scaling). The flow properties of silica suspensions are highly affected by thepH of the suspending media and concentration of the added salt. At a fixed electrolyte concentration, the viscosity decreases by increasingpH, reaches a minimum, and then increases with further increase inpH. At a fixedpH level, the same behavior was observed for viscosity as a function of electrolyte concentration. The effect of the electrolyte concentration is more significant at lower shear rates. It is shown that the rheological properties of silica suspensions are strongly affected by the concentration of the added polymer and its molecular weight. For each sample, there is a critical amount of polymer that must be added before low viscosities result. There is a nearly linear relation between the critical polymer concentration and volume fraction of the particles. The results of this work provide useful information for selection of a properpH range, electrolyte concentration, and optimum polymer concentration to control the viscosity behavior of highly concentrated silica slurries.

ISSN:0148-6055    

DOI:10.1122/1.550781

出版商:The Society of Rheology    

年代:1996

数据来源: AIP

摘要:

The flow properties of dense kaolin suspensions are explored for volume fractions as large as 0.43. The particles were suspended in phosphate buffers at pHs of 7 and 10 where edge‐face interactions are negligible. These platey particles have an aspect ratio of approximately 12 and, thus, are likely to show alignment at volume fractions above a critical volume fraction φ*=0.10. As the concentration is increased from the dilute region of Newtonian behavior, the suspensions develop a yielding type of response near this critical volume fraction. The time dependence of the recoverable strain in some dense suspensions is found to scale on γ̇0twheretis the time after the stress is released and γ̇0is the steady shear rate prior to release of the stress. Over the same time period the elastic modulus remains constant. The magnitude of the modulus is, however, dependent on γ0decreasing from a low shear rate plateau value ofGmax′to a high shear rate plateau value ofGmin′. The shear rate halfway betweenGmax′andGmin′is independent of volume fraction and lies near 0.39D0rotwhereD0rotis the free solution rotational diffusion constant of the plates. This behavior is interpreted as indicating that the plates experience a tumbling/shear aligning transition as the shear rate is raised. Further evidence for alignment is found in shear induced changes in suspension conductivity.

ISSN:0148-6055    

DOI:10.1122/1.550798

出版商:The Society of Rheology    

年代:1996

数据来源: AIP

摘要:

Classical liquid crystal theories are used to develop a model to compute the normal forces and shear torques for liquid crystalline polymers. The model is applied to the parallel disk geometry and the normal forces from three representative average molecular orientations are computed. It is found that a positive normal force tending to separate the parallel disks will always be present whenever the orientation is subjected to a twisting deformation. For typical parameter values and geometries, the model predicts that normal forces are six orders of magnitude larger than shear torques. The model predictions are validated with the experimental data presented by Langelaan and Gotsis (1996).

ISSN:0148-6055    

DOI:10.1122/1.550795

出版商:The Society of Rheology    

年代:1996

数据来源: AIP

摘要:

A moving spectral element method is used to investigate the effects of non‐Newtonian lubricants on the dynamics of a journal bearing. It is well known that for a constant viscosity full‐film lubricant the journal eventually displays half‐speed whirl that is undesirable due to the accompanying fall in load bearing capacity and vibration. The inclusion of a cavitation model into the scheme stabilizes the motion of the journal in some situations. In this paper it is demonstrated that piezoviscous lubricants can stabilize the journal even without the incorporation of a cavitation model. The addition of a cavitation model is shown to stabilize the motion of the journal further in the sense that equilibrium points or limit cycles are reached more quickly. The effects of shear thinning and inertia on the motion of the journal are also considered.

ISSN:0148-6055    

DOI:10.1122/1.550782

出版商:The Society of Rheology    

年代:1996

数据来源: AIP