Experimental investigations of the stability limit of the helical flow of pseudoplastic liquids

Abstract

The stability of the laminar helical flow of pseudoplastic liquids has been investigated with an indirect method consisting in the measurement of the rate of mass transfer at the surface of the inner rotating cylinder. The experiments have been carried out for different values of the geometric parameter rl = R 1 / R 2 (the radius ratio) in the range of small values of the Reynolds number, Re < 200. Water solutions of CMC and MC have been used as pseudoplastic liquids obeying the power law model. The results have been correlated with the Taylor and Reynolds numbers defined with the aid of the mean viscosity value. The stability limit of the Couette flow is described by a functional dependence of the modified critical Taylor number (including geometric factor) on the flow index n. This dependence, general for pseudoplastic liquids obeying the power law model, is close to the previous theoretical predictions and displays destabilizing influence of pseudoplasticity on the rotational motion. Beyond the initial range of the Reynolds numbers values (Re> 20), the stability of the helical flow is not affected considerably by the pseudoplastic properties of liquids. In the range of the monotonic stabilization of the helical flow the stability limit is described by a general dependence of the modified Taylor number on the Reynolds number. The dependence is general for pseudoplastic as well as Newtonian liquids. The m e t h o d applied to the experimental investigations is based on the m e a s u r e m e n t o f the rate of mass transfer at the surface o f the inner cylinder.

Linear stability of circular Couette flow of inelastic viscoplastic fluids

“…The theoretical results were always obtained for axisymetric modes ( [9][10][11]). The studies of [9] and [10] varied the radius ratio from 0.5 to 0.9 for relatively large fluid indexes (n > 0.5), whereas the study of [11] investigated the η → 1 limit and η = 0.5 for a wider range of fluid indexes. Even if their respective definitions of the Reynolds differ in some extent, all these studies conclude to a destabilizing influence of the shear thinning.…”

“…density stratification [3], radial temperature gradient [4], high corotation [5], elasticity [6], confinement [7]), have availed deeper understanding of the influence of those parameters on the generation of secondary flows. Likewise, some early studies have considered the stability of this flow for shear thinning or yield stress inelastic materials [8][9][10][11]. As those shear thinning or yield stress properties are very interesting from an industrial point of view, such materials are E-mail address: francois.caton@ensem.inpl-nancy.fr.…”

Heat transfer characteristics of Taylor vortex flow with shear-thinning fluids

“…They reported the original flow mode by the elastic instability. Wroński and Jastrzębski [23,24] investigated the effect of the shearthinning property on the stability experimentally and theoretically. Sinevic et al [25] measured power number and torque for shear-thinning fluids experimentally.…”