Papers by Keyword: Herschel-Bulkley Model

Abstract: Drilling fluid rheology is very important aspect for judging its suitability for the well-drilling operation. This study looked at how fly ash affected the rheological characteristics of drilling fluids that were based on water. Six different drilling fluid samples (combination of water-bentonite-fly ash) have been prepared: 4 samples without engine oil additives and 2 samples with engine oil additive. The shear stress between fluid layers vs. shear rate curves and the viscosity of fluid vs. shear rate curves have been plotted for the controlled shear rate application by rotational rheometer MCR 102 (Make: Anton-Paar Inc.). Curve fitting have been done successfully with the Herschel-Bulkley rheology model and various parameters have been obtained. It is found that addition of fly ash as well as additive oil imparts favorable rheology to water based drilling fluids.

Abstract: We propose a methodology for the rheological characterization of semisolid metal slurries using experimental squeeze flow data. The material is modelled as a structural thixotropic viscoplastic material, obeying the regularized Herschel-Bulkley constitutive equation. The yield stress and the power-law exponent are assumed to vary with the structural parameter that is governed by a first-order kinetics. The squeeze flow is simulated using finite elements in a Lagrangian framework. The evolution of the sample height has been studied for all the ranges of the Bingham and Reynolds numbers, the power-law exponent as well as the kinetics parameters of the structural parameter. Systematic comparisons have been carried out with experimental data on a semisolid aluminium alloy (A356) sample, compressed from its topside at a temperature of 582 °C under a specified load, which eventually becomes constant. Excellent agreement with the experimental data could be achieved provided that at the initial instances (up to 0.01s) of the experiment the applied load is much higher than the nominal experimental load and that the yield stress and the power-law exponent vary linearly with the structural parameter. The first requirement implies that a different model should be employed during the initial stages of the experiment. As for the second one, the evolution of the sample height can be reproduced allowing the yield stress to vary from 0 (no structure) to a maximum nominal value (full structure) and the power-law exponent from 0.2 to 1.4.

Abstract: In this paper, the steady-state flow of non-Newtonian fluid in a planar channel with sudden expansion is investigated. The rheological behavior of this media is described by the Herschel-Bulkley model. To determine both steady-state velocity and pressure fields, a numerical algorithm based on the relaxation method and SIMPLE procedure is used.The mathematical problem statement includes three non-dimensional parameters: the Reynolds number, the Bingham number (non-dimensional viscoplasticity parameter), and the power-law index. The results of numerical simulation are obtained in a range of the Reynolds number 1 ≤ Re ≤ 40, Bingham number 0 ≤ Se ≤ 2, and power-law index 0.4 ≤ k ≤ 2 (for shear thinning, Newtonian, and shear thickening fluids).The distribution of the main fluid flow characteristics and localization of the two-dimensional region in an expansion zone is presented. The impact of main parameters of the problem on a dead zone distribution in the fluid flow is shown.

Abstract: A crucial problem concerned with the semi-solid forming process is the liquid segregation phenomena during shape formation, especially for rheo-casting process. Liquid segregation occurs due to the separation phenomena of the solid grain and the liquid phase. In this work, using commercial finite element software, the liquid segregation during rheo-casting process was numerically investigated by Eulerian-granular multiphase model based on the comparable results of single phase model, Eulerian-granular two-phase and three-phase model, along with Eulerian-granular DDPM three-phase model. In the study, solid grains and liquid phases were regarded as rigid material and non-Newtonian fluid at microscale, separately. This validation was experimentally proved and also compared to the proposed relationship of power law, Herschel-Bulkley model with yield stress at macroscale.

Abstract: In this work we revisit the issue of obtaining true material constants for semisolid slurries. Therefore, we consider the circular Couette flow of Herschel-Bulkley fluids. We first show how true constants can be obtained using an iterative procedure from experimental data to theory and vice versa. The validity of the assumption that the rate-of-strain distributions across the gap share a common point is also investigated. It is demonstrated that this is true only for fully-yielded Bingham plastics. In other cases, e.g., for partially-yielded Bingham plastics or fully-yielded Herschel-Bulkley materials, the common point for the fully-yielded Bingham case provides a good approximation for determining the material constants only if the gap is sufficiently small. It can thus be used to simplify the iterative procedure in determining the material constants.

Abstract: Sodium metatungstate (SMT) solution is an inorganic heavy liquid which is widely used in density fractionation. However, rheological properties of aqueous SMT solutions have never been fully researched. The objective of the present work was to study the rheological properties of aqueous SMT solutions and effects of temperature and density on the apparent viscosity. The steady flow experimental data was fitted using Herschel-Bulkley model. The results show that aqueous SMT solutions of different density are pseudoplastic fluids and the flow curves of SMT solutions were described by the Hershel-Bulkley equation. The apparent viscosity decreases monotonically with increasing temperature under the same density and increases exponentially with increasing density at the fixed temperature. Rheological properties of aqueous SMT solutions can be applied in the calculation of density fractionation efficiency and provides a theoretical basis for flow simulation.

Abstract: In this paper, utilizing Herschel-Bulkley model, the equation of MR fluid pressure gradient is derived in order to predict MR damper’s force-velocity behavior. The equation, showing as a complicated nonlinear algebraic expression including various parameters, is then simplified to a nondimensional equation. This is followed by the analysis of the root of this nondimensional equation and an approximate root closely corresponding to numerical result is given.