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.

Influence of surface properties on the flow of a yield stress fluid around spheres

Abstract: This experimental analysis addresses the non-inertial flow of a yield stress fluid around spheres. The analysis was conducted for two spheres with different surface conditions. Friction laws at their interface have been determined. For the bulk behaviour of the fluid, elastoviscoplasticity and viscoelasticity have also been characterised. The resulting parameters have been used to analyse the experimental results. The drag coefficient was determined with respect to hydrophobic properties and surface roughness. From this determination, a criterion enabling the prediction of a sphere’s stability in a yield stress fluid as a function of the fluid/sphere interfacial properties has been proposed. The kinematic fields have also been measured by PIV. These fields enable the quantification of the velocity fields around the spheres according to the adherence conditions of the fluid. This quantification has enabled the characterisation of the extent and the shape of sheared and static rigid zones. Moreover, the calculations of the drag force due to the shear stresses and the drag force due to the normal stresses have revealed the preponderance of the latter in the total drag force.

Agitation of Herschel–Bulkley fluids with the Scaba–anchor coaxial mixers

Abstract: The design of the coaxial mixers depends on many interrelated parameters including the geometry and dimensions of the mixing vessel, the location and type of the impellers, speed ratio, impeller diameter, rotation mode, and fluid rheology. No study has been reported in the literature regarding the mixing performance of the coaxial mixers in the agitation of yield-pseudoplastic fluids. Thus, the main objective of this study was to evaluate the performance of a Scaba–anchor coaxial mixer (a novel configuration) in the mixing of xanthan gum solutions (yield-pseudoplastic fluids). The Herschel–Bulkley model was used to describe the rheological behavior of the xanthan gum solutions. To develop new correlations for the generalized Reynolds and power numbers of the coaxial mixers employed in the agitation of this class of non-Newtonian fluids, we utilized numerous experimental and computational fluid dynamics (CFD) data. The new correlations were tested successfully at different operating conditions (e.g. speed ratio, fluid rheology, and operation mode).

Determination of the constitutive equations for a magnetic fluid

Abstract: The principal aim of this paper is to derive constitutive equations describing a magnetic fluid. The fluid is modelled as a dilute suspension of small spheroidal magnetic particles in a non-magnetic solute. The conditions for stability of fluid (against coagulation) are discussed and upper and lower bounds for particle sizes are determined. For a stationary fluid, the bulk magnetization is calculated with allowance for particle-particle interactions. The full stress tensor is determined for a flowing fluid that experiences an externally applied magnetic field. Both the flow and field may have arbitrary spatial and time dependences provided only that the lengthscale of spatial variations is large compared with particle dimensions, and that the timescale is long compared with the particle relaxation time due to Brownian motion. These results are applied to shear and pipe flows, where comparison with experiment is made, and to flow induced by rotating magnetic fields. Finally the damping of ultrasound having a characteristic period of the same order as the particle relaxation time is considered.