Herschel–Bulkley fluid

About: Herschel–Bulkley fluid is a research topic. Over the lifetime, 1946 publications have been published within this topic receiving 49318 citations.

New measurements of the flow-curves for Carbopol dispersions without slip artefacts

Abstract: The thickening properties of many commercial thickeners are difficult to measure because of wall slip artefacts. Here we report a series of experiments on a typical thickener where these artefacts have been successfully eliminated. As a result, complete, steady-state flow-curves of aqueous Carbopol 980 (the toxicologically preferred version of the older and more well-known Carbopol 940) dispersions are reported for a range of concentrations of 0.045–1.0 wt%. The vane-and-basket flow geometry was used to avoid slip problems at low shear stress, with the geometry housed in a TA AR1000-N controlled-stress rheometer, whilst a Haake RV2 viscometer with an SV2P and MV2P concentric-cylinder geometries were used at higher shear rates. The flow-curves obtained show a smooth but steep transition from a very high Newtonian viscosity at low shear stress to a much lower viscosity at high shear stress. No real yield stresses were detected, but the higher shear rate results can be fitted to the Herschel-Bulkley model, which assumes an apparent yield stress. The various model parameters are displayed as a function of Carbopol concentration.

The Rayleigh-Stokes problem for a heated generalized second grade fluid with fractional derivative model

Abstract: The Rayleigh–Stokes problem for a generalized second grade fluid subject to a flow on a heated flat plate and within a heated edge was investigated. For description of such a viscoelastic fluid, fractional calculus approach in the constitutive relationship model was used. Exact solutions of the velocity and temperature fields were obtained using the Fourier sine transform and the fractional Laplace transform. The well-known solutions of the Stokes’ first problem for a viscous Newtonian fluid, as well as those corresponding to a second grade fluid, appear in limiting cases of our results.

Tip streaming from a liquid drop forming from a tube in a co-flowing outer fluid

Abstract: Dynamics of formation of a drop of an incompressible Newtonian fluid of viscosity μ1 and density ρ1 from the tip of a tube of radius R1 into a co-flowing immiscible, incompressible Newtonian fluid of viscosity μ2 and density ρ2 that is enclosed in a concentric cylindrical tube of radius R2 are investigated under creeping flow conditions. Transient drop shapes, and fluid velocities and pressures, are calculated numerically by solving the governing Stokes equations with the appropriate boundary and initial conditions using the Galerkin/finite element method for spatial discretization and an adaptive finite difference method for time integration. In accord with previous studies, the primary effect of increasing the ratio of the volumetric injection rate Q2 of the outer fluid to that of the inner fluid Q1, Qr≡Q2∕Q1, is shown to be a reduction in the volume of primary drops that are formed. When Qr is small, calculations show that drop formation occurs in a slug flow regime where the primary drops that are...

Stress overshoot in a simple yield stress fluid: An extensive study combining rheology and velocimetry

Abstract: We report a large amount of experimental data on the stress overshoot phenomenon which takes place during start-up shear flows in a simple yield stress fluid, namely a carbopol microgel. A combination of classical rheological measurements and ultrasonic velocimetry makes it possible to get physical insights on the transient dynamics of both the stress σ(t) and the velocity field across the gap of a rough cylindrical Couette cell during the start-up of shear under an applied shear rate . (i) At small strains (γ w. Finally, by changing the boundary conditions from rough to smooth, we show that there exists a critical shear rate s fixed by the wall surface roughness below which slip at both walls allows for faster stress relaxation and for stress fluctuations strongly reminiscent of stick-slip. Interestingly, the value of s is observed to coincide with the shear rate below which the flow curve displays a kink attributed to wall slip.

Flow analysis of field-controllable, electro- and magneto-rheological fluids using Herschel-Bulkley model

Abstract: The Bingham plastic constitutive model has been widely used to predict the post-yield behavior of electro- and magneto-rheological fluids (ER and MR fluids). However, if these fluids experience shear thinning or shear thickening, the Bingham plastic model may not be an accurate predictor of behavior, since the post-yield plastic viscosity is assumed to be constant. In a recent study, it was theoretically and experimentally demonstrated that the Herschel-Bulkley fluid model can be successfully employed when evaluating non-Newtonian post-yield behavior of ER and MR fluids. In this paper, we extend our previous work and adopt the Herschel-Bulkley model to include a detailed analysis of ER and MR fluid dynamics through pipes and parallel plates. Simplified explicit expressions for the exact formulation are also developed. It is shown that the proposed simplified model of the Herschel-Bulkley steady flow equations for pipes and parallel plates can be used as an accurate design tool while providing a convenient...