Dynamical Viscosity Research Articles

Effects of the variation of viscosity on the stability of thin liquid film flows along a uniformly heated substrate under heat flux boundary condition

The effects of variable viscosity on the stability of gravity-driven, Newtonian, thin liquid film flowing down a uniformly heated substrate under heat flux (HF) boundary condition is investigated. HF boundary condition allow us to consider the heat loss from the system at the solid–air interface as well as the heat flux by the rigid wall to the surrounding liquid, both of which effects the temperature gradient on the solid–liquid interface. This model is more realistic in comparison with specified temperature (ST) boundary condition/Dirichlet condition. The underlying assumption of ST boundary condition is that the heat flux at the solid–liquid interface is equal to the heat loss at the solid–air interface. It results in vanishing temperature gradient on the top surface of the rigid wall. Consequently, both the heat flux at solid–liquid and solid–air interfaces have no influence on the thin liquid film flow over the rigid substrate. Considering exponential variation of viscosity, together with the linear variation of surface tension, an evolution equation is constructed, using long-wave expansion technique. This evolution equation captures the effect of the variation of viscosity, thermocapillarity, and heat flux at the solid–air interface, through the parameters, Kμ (coefficient of dynamical viscosity), MBs (products of film Marangoni and free surface Biot number), and Bw (wall film Biot number), respectively. Using normal mode approach, the linear stability analysis reveals the destabilizing behavior of Kμ, MBs, and stabilizing effect of Bw. Using multiple-scale analysis, the weakly nonlinear study demarcates the supercritical (subcritical) stable (unstable) zones and their dependence on Kμ and Bw. Finally, the numerical simulation of the evolution equation, by the spectral method over a periodic domain, confirms the results obtained by the linear and weakly nonlinear study.

Flow correlations from a hydrodynamics model with dynamical freeze-out and initial conditions based on perturbative QCD and saturation

We extend the applicability of the hydrodynamics, perturbative QCD and saturation -based EKRT (Eskola-Kajantie-Ruuskanen-Tuominen) framework for ultrarelativistic heavy-ion collisions to peripheral collisions by introducing dynamical freeze-out conditions. As a new ingredient compared to the previous EKRT computations we also introduce a nonzero bulk viscosity. We compute various hadronic observables and flow correlations, including normalized symmetric cumulants, mixed harmonic cumulants, and flow--transverse-momentum correlations, and compare them against measurements from the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC) . We demonstrate that the inclusion of the dynamical freeze-out and bulk viscosity allows a better description of the measured flow coefficients in peripheral collisions and enables the use of an extended centrality range when constraining the properties of QCD matter in the future.

Falling liquid films on a slippery substrate with variable fluid properties

We investigate the stability of a gravity-driven, thin, Newtonian liquid flowing on a uniformly heated slippery inclined plane. We construct a mathematical model of the flow that comprises the Navier–Stokes equation coupled with the equation of energy. While the rest of the boundary conditions are standard for thin-film problems, we apply a Navier slip boundary condition at the solid–liquid interface. We assume that the fluid thermophysical properties — density, dynamical viscosity, surface tension, and thermal diffusivity vary linearly with temperature as long as the change in temperature is small. In the analysis part, we follow the standard long-wave theory and construct a nonlinear evolution equation for the film thickness. This is followed by a linear and weakly nonlinear stability analysis. The linear analysis allows us to compute the critical Reynolds number of our problem and from this study, we conclude that the slippery substrate destabilizes the film flow. The weakly nonlinear stability analysis finds a finer description of various stable/unstable zones. Finally, we perform a numerical simulation of the evolution equation in a periodic domain using spectral methods. Our numerical results support the analytical predictions of the instability threshold using the linear and weakly nonlinear theories. The influence of the small Biot number is also investigated in presence of the slip length together with the variable fluid properties.

STRUCTURE AND RHEOLOGICAL PROPERTIES OF WATER SOLUTIONS OF SODIUM CARBOXYMETHYL STARCH OBTAINED IN SOLID PHASE

Synthesis of the sodium salt of carboxymethyl starch was carried out by modification of corn starch in the solid phase. It was determined that moistening of the reaction mixture by small quantities of water, alcohols, and their water solutions caused a considerable increase in the degree of substitution of obtained products. By varying the ratio of the initial reagents and nature of solvent for moistening of reaction mixture samples of the sodium salt of carboxymethyl starch with the degree of substitution from 0.12 to 0.95 have from obtained. It was shown that the degree of substitution in obtaining product depended not only on the ratio of initial reagents but also on the nature of the used solvent. The morphology and structure of samples of the sodium salt of carboxymethyl starch have been investigated. By method of rotational, viscometry rheological properties of water solutions of the sodium salt of carboxymethyl starch was investigated and it was determined that with increasing degree of substitution dynamical viscosity of their solutions has increased

“In Silico” Seawater

Many important processes affecting the earth’s climate are determined by the physical properties of seawater. In addition, desalination of seawater is a significant source of drinking water for the human population living in coastal areas. Since the physical properties of seawater governing these processes depend on the molecular interactions among its components, a deeper knowledge of seawater at the molecular level would contribute to a better understanding of these phenomena. However, in strong contrast with the situation in other areas such as biomolecules or materials science, molecular simulation studies reporting the physical properties of seawater are currently lacking. This is probably due to the usual perception of the seawater composition being too complex to approach. This point of view ignores the fact that physical properties of seawater are dependent on a single parameter representing the composition, namely the salinity. This is because the relative proportions of any two major constituents of seasalt are always the same. Another obstacle to performing molecular simulations of seawater could have been the unavailability of a satisfactory force field representing the interactions between water molecules and dissolved substances. However, this drawback has recently been overcome with the proposal of the Madrid-2019 force field. In this work we show for the first time that molecular simulation of seawater is feasible. We have performed molecular dynamics simulations of a system, the composition of which is close to the average composition of standard seawater and with the molecular interactions given by the Madrid-2019 force field. In this way we are able to provide quantitative or semiquantitative predictions for a number of relevant physical properties of seawater for temperatures and salinities from the oceanographic range to those relevant to desalination processes. The computed magnitudes include static (density), dynamical (viscosity and diffusion coefficients), structural (ionic hydration, ion–ion distribution functions), and interfacial (surface tension) properties.

Correlative Imaging of Motoneuronal Cell Elasticity by Pump and Probe Spectroscopy

Because of their role of information transmitter between the spinal cord and the muscle fibers, motor neurons are subject to physical stimulation and mechanical property modifications. We report on motoneuron elasticity investigated by time-resolved pump and probe spectroscopy. A dual picosecond geometry simultaneously probing the acoustic impedance mismatch at the cell-titanium transducer interface and acoustic wave propagation inside the motoneuron is presented. Such noncontact and nondestructive microscopy, correlated to standard atomic force microscopy or a fluorescent labels approach, has been carried out on a single cell to address some physical properties such as bulk modulus of elasticity, dynamical longitudinal viscosity, and adhesion.

Transport Coefficients of Air - PMMA Mixtures Thermal Plasmas

The transport coefficients of Air - PMMA mixtures thermal plasmas is important to estimate the performances of cutting of the electrical arc in this gas by a circuit breaker. In this paper, Air - PMMA mixtures thermal plasmas dynamical viscosity, thermal and electrical conductivities coefficients are calculated in a temperature range from 5000K to 30000K. The calculations are made by supposing thermodynamic equilibrium at pressure of 1 bar to 10 bar. The results of the calculations show the influence of the initial proportion of PMMA but also that of the pressure on the mixture plasma transport coefficients. As the efficiency of the breaking of the electric current by the circuit breaker depends closely on the thermal and electrical characteristics of the extinguishing medium, this extinguishing medium should have a high thermal conductivity and an electrical conductivity varying rapidly with temperature. The plasma of the mixture constituted by 80% of air and 20% of PMMA presents at first sight best characteristics for the breaking of electric current. It has the highest thermal conductivity peak among the plasmas of the mixtures studied.

Heating and flow computations of an amorphous polymer in the liquefier of a material extrusion 3D printer

The heating of a polymer in a liquefier of a material extrusion 3D printer is numerically studied. The problem is investigated by solving the mass, momentum, and energy conservation equations. The polymer is taken as a generalized Newtonian fluid with a dynamical viscosity function of shear rate and temperature. The system of equations is solved using a finite element method. The boundary conditions are adapted by comparison with the previous work of Peng et al. [5] showing that the thermal contact between the polymer and the liquefier is very well established. The limiting printing conditions are studied by determining the length over which the polymer temperature is below the glass transition temperature. This provides a simple relation for the inlet velocity as a function of the working parameters and the polymer properties.

Picosecond ultrasounds as elasticity probes in neuron-like cells models

We report on elasticity measurements in neuronlike cells using picosecond acoustics pump and probe spectroscopy. The stimulated Brillouin oscillations were mapped in PC12 cells to reveal their internal elastic structure. Thanks to a Pearson correlation coefficient mapping, different areas could be distinguished. The nucleus material shows a bulk modulus equal to 12.9 GPa in the case of a dry cell. Attenuation of the Brillouin signature gives access to dynamical longitudinal viscosity equal to 10.6 mPa ⋅ s, one order of magnitude higher than that of water. The modulus considerably drops to 2.6 GPa in the most physiologically relevant case of a hydrated cell.

Bulk Viscosity and Contact Correlations in Attractive Fermi Gases.

The bulk viscosity determines dissipation during hydrodynamic expansion. It vanishes in scale invariant fluids, while a nonzero value quantifies the deviation from scale invariance. For the dilute Fermi gas the bulk viscosity is given exactly by the correlation function of the contact density of local pairs. As a consequence, scale invariance is broken purely by pair fluctuations. These fluctuations give rise also to logarithmic terms in the bulk viscosity of the high-temperature nondegenerate gas. For the quantum degenerate regime I report numerical Luttinger-Ward results for the contact correlator and the dynamical bulk viscosity throughout the BEC-BCS crossover. The ratio of bulk to shear viscosity ζ/η is found to exceed the kinetic theory prediction in the quantum degenerate regime. Near the superfluid phase transition the bulk viscosity is enhanced by critical fluctuations and has observable effects on dissipative heating, expansion dynamics, and sound attenuation.

A note on dissipative particle dynamics (DPD) modelling of simple fluids

In this paper, we show that a dissipative particle dynamics (DPD) model of a viscous Newtonian fluid may actually produce a linear viscoelastic fluid. We demonstrate that a single set of DPD particles can be used to model a linear viscoelastic fluid with its physical parameters, namely the dynamical viscosity and the relaxation time in its memory kernel, determined from the DPD system at equilibrium. The emphasis of this study is placed on (i) the estimation of the linear viscoelastic effect from the standard parameter choice; and (ii) the investigation of the dependence of the DPD transport properties on the length and time scales, which are introduced from the physical phenomenon under examination. Transverse-current auto-correlation functions (TCAF) in Fourier space are employed to study the effects of the length scale, while analytic expressions of the shear stress in a simple small amplitude oscillatory shear flow are utilised to study the effects of the time scale. A direct mechanism for imposing the particle diffusion time and fluid viscosity in the hydrodynamic limit on the DPD system is also proposed.

EPR study of spectra transformations of the intrinsic vanadyl-porphyrin complexes in heavy crude oils with temperature to probe the asphaltenes' aggregation

Temperature dependencies of electron paramagnetic resonance spectra of intrinsic paramagnetic vanadyl complexes and dynamical viscosity for two heavy crude oils and asphalt samples are measured. Transitions between the different motional conditions (from the rigid to the fast motion regimes) are observed. The rotational correlation times (in the model of the isotropic diffusion) are extracted. It is shown that the characteristic temperatures for the motional regime transitions are mainly defined by the asphaltenes’ content. From our analysis it follows that the thermal treatment leads to the destruction of the asphaltene complexes onto the 4–5 small pieces. The results indicate that paramagnetic vanadyl complexes are the sensitive intrinsic probes to study qualitatively and quantitatively structural transformations of aspahltenes of heavy crude oils in-situ.

Long wave instability of thin film flowing down an inclined plane with linear variation of thermophysical properties for very small Biot number

We investigated interfacial instability of a thin liquid film flowing down an inclined plane, considering the linear variation of fluid properties such as density, dynamical viscosity, surface tension and thermal diffusivity, for the small variation of temperature. Using long wave expansion method and considering order analysis specially for very small Biot number (Bi) we obtained a single surface equation in terms of the free surface h(x,t). Considering sinusoidal perturbation method we carried out linear stability analysis and obtained the critical Reynolds number (Rec) and linear phase speed (cr), both of which depend on Kμ,Kρ but independent of Kσ,Kκ. Using the method of multiple scales, weakly nonlinear stability analysis is carried out. We demarcated subcritical, supercritical, unconditional and explosive zones and their variations for the variation of Kμ,Kρ and Kσ. Also we discussed the variations of threshold amplitude in the subcritical as well as in the supercritical zones for the variation of Kμ,Kρ and Kσ. Finally we discussed the variation of nonlinear wave speed Ncr for the variation of Kμ,Kρ and Kσ.

РОЛЬ НАРУШЕНИЙ РЕОЛОГИЧЕСКИХ СВОЙСТВ ЭРИТРОЦИТОВ В ПАТОГЕНЕЗЕ ВОСПАЛИТЕЛЬНЫХ ЗАБОЛЕВАНИЙ КИШЕЧНИКА У ДЕТЕЙ

Цель исследования: изучение роли нарушений реологических свойств эритроцитов в патогенезе воспалительных заболеваний кишечника у детей. Материалы и методы. Обследовано 37 детей с воспалительными заболеваниями кишечника (ВЗК): 17 детей с болезнью Крона (БК) и 20 — с язвенным колитом (ЯК). Исследовали деформируемость эритроцитов, спонтанную агрегацию тромбоцитов в искусственном сдвиговом потоке, динамическую вязкость крови, морфологию агрегатов эритроцитов, состояние цитоскелета эритроцитов методом термоиндукции, состояние гемостаза на тромбоэластографе, среднемолекулярные пептиды, сорбционную емкость эритроцитов, связывающую способность альбумина. Результаты. Выявлено, что ВЗК сопровождаются значительным ухудшением гемореологических свойств крови, что является важным фактором патогенеза этих заболеваний и лежит в основе нарушений микроциркуляции при ВЗК. Установлено, что при БК нарушения большинства исследованных показателей не только существеннее, чем при ЯК, но и стабильнее — они сохраняются даже после проведенного лечения. Также как и реологические нарушения, эндогенная интоксикация сохраняется при БК и после проведенного лечения. Заключение. Нарушения реологических свойств крови являются важным фактором, обуславливающим ишемические повреждения кишечника. Это дает основание рекомендовать использование при ВЗК адъювантных методов борьбы с гипоксией и нарушениями микроциркуляции. Aim: to study the role of disturbances in erythrocytes rheological properties in pathogenesis of inflammatory bowel diseases (IBD) in children. Materials and methods. The study included 37 patients with IBD: 17 with Crohn’s disease (CD) and 20 with ulcerative colitis (UC). Erythrocyte deformability, spontaneous platelet aggregation, dynamical blood viscosity, morphology of erythrocyte aggregates, the state of erythrocyte cytoskeleton by thermoinduction method, hemostasis state by thromboelastograph, medium molecular peptides, erythrocyte sorption capacity, binding ability of albumin were researched. Results. We revealed that IBD accompanied by a significant degradation of blood hemorheological properties. It is an important factor in the pathogenesis of these diseases and is at the core of microcirculation disorders at IBD. It was found that at CD disorders the majority of studied parameters were not only more significant than in UC, but they also remained much more stable even after the treatment. At CD endogenous intoxication as well as rheological disorders persisted after treatment. Conclusion. Disorders of blood rheological properties are an important factor causing ischemic damage of the intestine. This gives reason for recommending the use of adjuvant methods to reduce hypoxia and microcirculatory disturbances at IBD.

On the uses of classical or improved heat transfer correlations for the predictions of convective thermal performances of water-[formula omitted] nanofluids

This paper reports calculations aimed at predicting the convective heat transfer enhancement evaluated in terms of the ratio of the nanofluid and base fluid heat transfer coefficients. Either usual single-phase heat transfer correlations or improved correlations involving slip velocity due to inertia, Brownian and thermophoretic diffusions are considered. In this regard, eight classical flow configurations, both for laminar and turbulent forced or natural convection, are first examined. In each case, five to six commonly used models for the effective thermal conductivity and viscosity are compared for water-Al2O3 nanofluids, with nanoparticle volume fractions ranging from 1% to 5%. In order to recover anomalous convective heat transfer enhancements, we examine mainly the influences of simultaneous augmentations of thermal conductivity and dynamical viscosity. The opposite influences of these two fluid properties on the heat transfer coefficient are clearly established. In the second part of the Result section, we attempt to give a critical interpretation of the previous results by using new published improved correlations derived with the objective to show that the usual correlations are not relevant for predicting nanofluid convective heat transfer. However, most of the present results reveal that the increase in the particle volume fraction tends to deteriorate the heat transfer in comparison with the base fluid.

Fluid/gravity correspondence for massive gravity

In this paper, we investigate the fluid/gravity correspondence in the framework of massive Einstein gravity. Treating the gravitational mass terms as an effective energy-momentum tensor and utilizing the Petrov-like boundary condition on a timelike hypersurface, we find that the perturbation effects of massive gravity in bulk can be completely governed by the incompressible Navier-Stokes equation living on the cutoff surface under the near horizon and nonrelativistic limits. Furthermore, we have concisely computed the ratio of dynamical viscosity to entropy density for two massive Einstein gravity theories, and found that they still saturate the Kovtun-Son-Starinets (KSS) bound.

Measurements of fluid viscosity using a miniature ball drop device.

This paper describes measurement of fluid viscosity using a small ball drop device. It requires as little as 100 μl of fluid. Each measurement can be performed in seconds. The experiment is designed to yield reliable viscosity values by operating at properly chosen tilt angles and with calibration using well-characterized Newtonian fluids such as mixtures of glycerol and water. It also yields dynamical viscosity of non-Newtonian fluids at moderate shear rates. The device is easy to assemble and it allows for the measurement of viscosity even when the fluid samples are too small to measure using most commercial viscometers or rheometers. Therefore, the technique is particularly useful in characterizing biological fluids such as solutions of proteins, DNA, and polymers frequently used in biomaterial applications.

From Petrov–Einstein–Dilaton–Axion to Navier–Stokes equation in anisotropic model

In this paper we generalize the previous works to the case that the near-horizon dynamics of the Einstein–Dilaton–Axion theory can be governed by the incompressible Navier–Stokes equation via imposing the Petrov-like boundary condition on hypersurfaces in the non-relativistic and near-horizon limit. The dynamical shear viscosity η of such dual horizon fluid in our scenario, which isotropically saturates the Kovtun–Son–Starinet (KSS) bound, is independent of both the dilaton field and axion field in that limit.

Foaming behavior of water-soluble cellulose derivatives: hydroxypropyl methylcellulose and ethyl hydroxyethyl cellulose

Hydroxypropyl methylcellulose and ethyl hydroxyethyl cellulose could be interesting candidates for production of lightweight, foamed packaging material originating from non-fossil, renewable resources. The foaming ability of nine different grades of the two cellulose derivatives, using water as the blowing agent, was investigated using a hot-mold process. The foaming process was studied by evaluating the water loss during the heating, both in a real-time experiment and by thermal gravimetric analysis. Further, the development of the rheological properties of the derivative-water mixtures during a simulated foaming process was assessed using dynamical mechanical thermal analysis and viscosity measurements. Five of the studied derivatives showed promising properties for hot-mold foaming and the final foams were characterized with regard to their apparent density. It was concluded that the foamability of these systems seems to require a rather careful tailoring of the viscoelastic properties in relation to the water content in order to ensure that a network structure is built up and expanded during the water evaporation.

Constraining quantum critical dynamics: (2+1)D Ising model and beyond.

Quantum critical (QC) phase transitions generally lead to the absence of quasiparticles. The resulting correlated quantum fluid, when thermally excited, displays rich universal dynamics. We establish nonperturbative constraints on the linear-response dynamics of conformal QC systems at finite temperature, in spatial dimensions above 1. Specifically, we analyze the large frequency or momentum asymptotics of observables, which we use to derive powerful sum rules and inequalities. The general results are applied to the O(N) Wilson-Fisher fixed point, describing the QC Ising model when N=1. We focus on the order parameter and scalar susceptibilities, and the dynamical shear viscosity. Connections to simulations, experiments, and gauge theories are made.