Papers by Keyword: Shear Viscosity

Abstract: Stokes-Einstein relation is a convenient way to evaluate diffusion properties in liquids from viscosity results (and vice-versa). However, the accuracy of this relation in the case of atomic fluids is often debated as it was initially established in the case of a big Brownian particle immersed in a fluid. Especially, the question is raised to properly define the hydrodynamic radius entering the formula, as well as the constant depending on the boundary conditions at the surface of the particle. In this study, we use our results of viscosity and self-diffusion coefficient obtained by molecular dynamics simulations in the case of alkali metals and their alloys to evaluate the applicability of Stokes-Einstein relation in the case of these liquids. In the case of pure metals, its validity is discussed over a wide range of thermodynamic states, from ambient pressure up to several gigapascals. In the case of alloys, the evolution of its accuracy as a function of temperature and composition is considered. Both definitions of hydrodynamic radius and boundary conditions constant are examined.

Abstract: In tyre industries, rheological and processability properties of rubber and polymer are great of importance since there are alot extrusion processes involved in the tyre manufacturing other than calendaring and moulding processes. Uniformity and consistency in the flow behaviour and processability of rubber are essential in providing the solution to the rubber industries in order to improve productivity, products quality and energy conservation. In this works, effects of silane coupling agent on rheological behaviour and extrusion performance of silica filled ENR tread compounds were studied and compared to NR/BR tread compound. The compounds were prepared by melt mixing in tangential internal mixer, while the rheological properties of compounds were determined by Capillary Rheometer, Cure Rheometer and Mooney viscometer. The compound were further examined for its extrudability performance evaluation by extruded the rubber through 30mm cold feed extruder machine using ASTM Extrusion Die, ‘Garvey’ type. Results showed that, ENR/silica compounds exhibit higher shear viscosity curves as compared to NR/BR compound at low shear rate regime. However an opposite trend was observed towards high shear rate regime tested which ENR/silica compounds gave slightly lower shear viscosity curve compared to NR/BR compound. As for extrudability performance evaluation, NR/BR compound gave better extrusion characteristics and appearance as compared to ENR/silica compounds.

Abstract: Atomic transport properties like self diffusion coefficient (D), viscosity coefficient (η) of 3d liquid transition metals are studied. Here we have applied our own model potential to describe electron ion interaction with different reference system like Percus - Yevick Hard Sphere (PYHS), One Component Plasma (OCP) and Charge Hard Sphere (CHS) systems. We have investigated the effect of different correction function like Hartree (H), Vashishta-Singwi (VS), Hubbard-Sham (HS), Sarkar et al (S), Ichimaru-Utsumi(IU), Taylor (T) and Farid et al (F) on atomic transport properties. The proper choice of the model potential alongwith the local field correction function and reference system plays a vital role in the study of the atomic transport properties of 3d liquid transition metals.

Abstract: Present article deals with atomic transport properties like self-diffusion coefficient (D) and viscosity coefficient (η) of 4d transition metals in liquid state. To describe structural information we have used different reference systems like Percus - Yevick Hard Sphere (PYHS), One Component Plasma (OCP) and Charge Hard Sphere (CHS) systems alongwith our newly constructed parameter free model potential. To see the effect of different correction functions on atomic transport properties, we have used different local field correction functions like Hartree (H), Vashishta-Singwi (VS), Hubbard-Sham (HS), Sarkar et al (S), Ichimaru-Utsumi (IU), Taylor (T) and Farid et al (F). From the present results we conclude that our newly constructed model potential successfully calculated atomic transport properties of 4d transition metals in liquid phase.

Abstract: Criticality of rheology for heavy oil recovery is the main purpose of this paper supported by different results. The Bingham Plastic, Power Law and Herschel Bulkley rheological models have been adopted for the purpose of this paper. Rheological characterisation was carried out for different temperatures. Rheological behaviour of non-Newtonian heavy oil for different shear rates is analysed in this paper. Effective shear and bulk viscosities for different flow rates are compared for all rheological models. Using the horizontal well productivity model, the drawdown values for all rheological models are determined. Similarly for the sand management purpose the critical rates of Newtonian and these three non-Newtonian fluids are plotted to determine the critical drawdown values for each type of fluid. Impact of drainage profile on the effective viscosities is also compared for different drainage profiles. Shear rate models are proposed in this paper for Bingham Plastic, Power Law and Herschel Bulkley rheological models. The new Micro-PVT equipment is also introduced for determining the PVT properties and rheological behaviour of heavy oil. Nomenclature

Abstract: Viscoelasticity is an inherent property of the soft biological tissue and is increasingly used as a diagnostic parameter, e.g. in characterizing Brain disease, liver fibrosis and breast tumors or tissue-mimicking phantoms preparation. MR elastography (MRE) enables the noninvasive determination of the viscoelastic behavior of human internal organs. In this study, multifrequency magnetic resonance elastography was used to investigate and validate the numerical simulation of human brain viscoelasticity generated by ABAQUS. The dynamic behavior of storage modulus (G') and loss modulus (G") obtained by MRE at different frequency ranges were used to generate viscoelastic FE model of brain tissue. Then, shear modulus (µ) and shear viscosity (η) were compared to experimental data. MRE validate the finite element as an effective technique for measurement of rheological material properties. Results indicate the capability of FEM to simulation and comparison of experimental results.

Abstract: In the present work, there are presented the results of experimental studies on the basis of regression analysis and FEM-based modeling of the processes of aluminum alloys preforms and semi-finished products manufacture including such widely known processes as cutting rolled products by shear and thixotropic stamping (stamping of metal during crystallization). It is investigated the influence of technological heredity created by variation of cant angles of end surfaces and mono- and poly-directional pulling-down by shear in cutting rolled blanks on stability of the process of subsequent longitudinal upsetting while producing preforms for bulk stamping. As a result of studying the ways of eliminating such negative consequences of technological heredity and increasing high-strength aluminum alloys technological plasticity, there is revealed the possibility of using phase transitions (from solid to liquid state and back) while manufacturing semifinished products in thixotropic conditions close to superplastic deformation.

Abstract: Rheological properties of water films nanoconfined in two parallel Au plates are investigated with the aid of molecular dynamics simulations. The density distribution, velocity profile, and diffusion coefficients of the water film in a Couette flow are studied. Shear viscosity and its dependence on the shear rate of the water film are also examined in the present research. It is found that the density of the water molecules near the plates is much higher than that in the other regions. This indicates that many water molecules are adsorbed by the plates and adsorbed layers are formed in the vicinity of the plates. The diffusion of the whole film increases dramatically as the shear rate becomes greater than 1010 s-1. The shear viscosity decreases as the shear rate increases, especially for the water film with a small thickness, which indicates the shear-thinning behavior for viscosity of the nanoconfined film. Moreover, an increase in shear viscosity with a decrease in the film thickness can also be found in the present study.

Abstract: The rheological properties and phase orientation of liquid crystalline polymer (LCP) melts flowing in a nanochannel with different surface roughness are investigated by molecular dynamics (MD) simulations. Simulation results show the surface roughness has great impact on the rheological properties and phase orientation of LCP melts in the nanochannel (cross section is 12nm). As the amplitude of serrations increases, the shear viscosity increases nonlinearly and the value of orientational order parameter decreases. When the serration amplitude is larger than 1.1nm, a phase transition (from nematic to isotropic phase) of LCP melt happens, which makes flowing in nanochannels more difficult. On the other hand, the influence of serration period on the shear viscosity and orientational order parameter are found not so obvious. Findings in this study will be helpful for injection molding plastic products with nanofeatures.

Abstract: The paper presents the results of detailed measurements of the isothermal tensile stress relaxation in Pd40Cu30Ni10P20 bulk and ribbon samples, which differ by ∼ 104 times in their production quenching rates. The relaxation law is derived. It is shown that the relaxation kinetics is not much affected by the quenching rate.