Decrease In Effective Viscosity Research Articles

Rheological structure assessment of the plant alternative to yoghurt

The growth in the number of people suffering from milk components intolerance implies the creation of their plant alternatives, corresponding in organoleptic characteristics, nutritional and biological values, but not having milk allergens. Therefore, development and study of the rheological properties of plant analogues of dairy products is relevant. The article discusses the structural and mechanical parameters of fermented plant products, from oatmeal powder, sunflower protein and with the use of starter cultures Streptococcus salivarius subsp. termophilus and Lactobacillus delbrueckii subsp. bulgaricus, depending on the mass fraction of pectin structurant and its shelf life. It is shown that, by the nature of the flow, the curves obtained refer to pseudoplastic liquids. It has been established that the destruction of the structure of the fermented plant product, and hence the decrease in effective viscosity, occurs in two stages: avalanche-like - at a shear rate of 5 to 24 s-1; from 24 s-1 and further - with a damping speed relative to the beginning of destruction. The regression dependence of the effective viscosity change on the shear rate and pectin concentration has been calculated. It has been found that with an increase in the storage time of the samples, their hardness increases up to the seventh day. After that this indicator decreases, which characterizes gradual destruction of their structure. The hardness work, the adhesiveness, the adhesive force and the resilience of prototypes have been determined. The obtained research results correlate with the studies conducted in the field of rheological characteristics of fermented milk products.

Implicit Large-eddy Simulations of Global Solar Convection: Effects of Numerical Resolution in Nonrotating and Rotating Cases

Simulating deep solar convection and its coupled mean-field motions is a formidable challenge where few observational results constrain models that suffer from the nonphysical influence of the grid resolution. We present hydrodynamic global implicit large-eddy simulations of deep solar convection performed with the EULAG-MHD code, and we explore the effects of grid resolution on the properties of rotating and nonrotating convection. The results, based on low-order moments and turbulent spectra, reveal that convergence in nonrotating simulations may be achieved at resolutions not much higher than these considered here. The flow is highly anisotropic, with the energy contained in horizontal divergent motions exceeding their radial counterpart by more than three orders of magnitude. By contrast, in rotating simulations, the largest energy is in the toroidal part of the horizontal motions. As the grid resolution increases, the turbulent correlations change in such a way that a solar-like differential rotation, obtained in the simulation with the coarser grid, transitions to an antisolar differential rotation. The reason for this change is the contribution of the effective viscosity to the balance of the forces driving large-scale flows. As the effective viscosity decreases, the angular momentum balance improves, yet the force balance in the meridional direction lessens, favoring a strong meridional flow that advects angular momentum toward the poles. The results suggest that obtaining the correct distribution of angular momentum may not be a mere issue of numerical resolution. Accounting for additional physics, such as magnetism or the near-surface shear layer, may be necessary in simulating the solar interior.

The Cross model of liquid polymer- bitumen binder structure in a pipe with sudden expansion

The paper investigates the liquid polymer-bitumen binder in a pipe with a sudden expansion. At small values of the expansion parameter, the formation of a high-viscosity liquid zone occurs in the axial region, and the effective viscosity decreases at the periphery and nearwall zones. The destruction process of structural bonds, which intensively proceeds near the flow from the supply pipe, leads to a decrease in the effective viscosity. The formation of a corner area of reverse flows is accompanied by the increase in the effective viscosity.

Shear thinning effect on liquid foam distribution in heterogeneously constricted in vitro airway models

Treating diseased lung regions using inhalation therapy is often limited due to airway constrictions and obstructions that significantly reduce aerosol deposition efficiency. Intratracheal administration of liquid foams is a potential strategy to improve pulmonary drug delivery to these affected airway regions. Here, we use effective viscosity measurements and in vitro small-airway models to examine how shear thinning effects in the foam can be leveraged to achieve a more uniform distribution within heterogeneously constricted or partially obstructed airways. We find that a foamed solution based on the formulation of Tacholiquin® exhibited a 5.75-fold decrease in effective viscosity across a shear rate range spanning 970 to 14′500 s−1. As a result, the foam volume penetrating through the constricted airway models was up to 154% higher compared with air, depending on the cross-sectional area of the constrictions. This proof-of-concept study represents a first step towards understanding the transport mechanics of liquid foams towards future pulmonary delivery applications.

Безглютеновые масляные бисквиты для питания детей школьного возраста

The research in the field of technology of gluten-free butter biscuits of functional purpose for nutrition of schoolchildren of junior and middle age using rice, millet, corn flour and carrot puree is presented. The quality indicators of biscuit dough and biscuit were investigated, the nutritional value and caloric content of the product were calculated. Experimental studies have shown that with a complete replacement of wheat flour with gluten-free flour of various types, the quality of biscuit dough and biscuit improves: the density of the dough decreases, its effective viscosity decreases, the products have a pleasant pronounced taste and aroma, the correct shape, the porosity of products and their specific volume increase. The developed sample of gluten-free sponge cake in terms of the content of potassium, magnesium, vitamins of groups B, A and E can be attributed to functional foods for schoolchildren's nutrition.

Rheological Behavior of Nanocellulose Aqueous Suspensions

The rheological properties of aqueous suspensions of spherical and needle-shaped nanocellulose particles in the range of 25–70°C are compared. Nanocellulose samples are obtained by the acid hydrolysis of cotton cellulose fibers in H2SO4 (61–65%) at 25–45°C. The shape of nanocellulose particles affects the yield strength and non-Newtonian character of the suspension flow. In the shear stress region above 100 Pa, a decrease in effective viscosity occurs, depending on the shape of the particles and the temperature of the suspension. In the region of the shear rate close to the yield strength, the activation energy of the viscous flow of suspensions of spherical particles is 12 kJ/mol; needle-shaped particles, 18 kJ/mol. Features of the rheological behavior are due to the fact that spherical particles are involved mainly in rotational-translational motion, while the needle-like particles are oriented in the direction of flow.

SHVEDOV-BINGHAM MODEL OF STEADY FLOW OF VISCO-PLASTIC BITUMEN BINDER IN CYLINDRICAL TUBE

This paper studies the bitumen binder flow in terms of the Shvedov-Bingham model in a cylindrical tube. The dependence of the fluid flow rate on pressure drop is determined as well as the dependences between the radial velocity distribution and effective flow viscosity. Near the wall, the effective viscosity is low. However, in the vicinity of the rigid zone, a significant increase in the effective viscosity is observed. With increasing strain rates the effective viscosity decreases, which is explained by the destruction of the medium microstructure. With the pressure drop, the size of the hard zone decreases. With the increasing yield stress the fluid becomes less mobile, the rigid zone in the centre of the pipe increases in size. In this case, the velocity values decrease over the entire pipe section. Variation in the plastic viscosity does not affect the position of the rigid zone. It is shown that when the Bingam number Bn < 0.1, the non-Newtonian properties of the flow can be ignored. In this case, the Newtonian flow with viscosity mpl should be considered with an accuracy sufficient for engineering calculations.

Theory of microscopic electrodeposition under a uniform parallel magnetic field - 2. Suppression of 3D nucleation by micro-MHD flow

In electrodeposition under a uniform parallel magnetic field, the suppression of three-dimensional (3D) nucleation by microscopic magnetohydrodynamic flow (micro-MHD flow) and formation of stream pattern of macroscopic MHD flow by the multiple nucleation of 3D nuclei are theoretically clarified. The interference of micro-MHD flow with concentration fluctuation generally results in the suppression of 3D nucleation (1st micro-MHD effect). However, due to the small scale of length of 3D nucleus, the effective viscosity is too high for micro-MHD flow to sufficiently work on individual 3D nuclei, so that the suppression is not so obvious. On the other hand, for 3D nucleus groups after multiple nucleation, due to larger scale of length, effective viscosity decreases, so that micro-MHD flow easily interacts with the corresponding concentration fluctuation, which gives rise to a striped pattern reflecting macroscopic MHD flow.

Numerical Investigation of Air–Oil–Thermal Coupling Mechanism in Floating Ring Bearings

Floating ring bearings (FRBs) are widely used in automobile turbochargers. However, there is no satisfying explanation of phenomenon that ring rotation speed levels off when the shaft speed reaches a certain value under low oil-supplied pressure condition. The traditional opinion that effective viscosity decreases with increasing temperature cannot completely explain this phenomenon. In this study, the air entrainment effect is introduced and evaluated using computational fluid dynamics (CFD). CFD results considering air entrainment, viscous heating, and heat transfer are compared with experimental results to evaluate each effect. The decrease in effective viscosity as a result of air–oil–thermal coupling effect is the mechanism behind the abovementioned phenomenon. This study provides calculated data and visual results of the air entrainment in low oil-supplied pressure FRB.

Research of rheological properties of egg sponge with extruded corn flour

Addition of extruded corn flour affects the egg sponge stability. The dependence of the effective viscosity of egg sponge samples with different concentrations of extruded corn flour on the shear rate and stress is investigated. Viscosity index is closely associated with the water-retaining capacity of the egg sponge. So, there is a need to study the state of free and bound water in the egg sponge depending on the content of extruded corn flour. The aim of the research was to identify the impact of extruded corn flour on the rheological properties of the egg sponge under mechanical impact, and study of the effect of extruded corn flour addition on the ratio of the state of free and bound water in it. The most intensive decrease in viscosity with increasing shear rate is observed in the sponge based on the mixture with the content of extruded corn flour of 50 % at a shear rate of 2.4 s -1 . Further decrease in effective viscosity with increasing shear rate is less intense, and all the samples tend to approach a constant viscosity of 2.4 Pa•s for the control sample and the viscosity of 4.2 Pa•s in the sample with the content of extruded corn flour of 50 % at a shear rate of γ 11.65 s -1 . Increased amount of extruded corn flour raises the spin-spin relaxation time, indicating a decrease in the mobility of water molecules in solution. This suggests that increased amount of extruded corn flour in the egg sponge increases the amount of bound water, which contributes to retaining more moisture in the finished product. The research shows the feasibility of extruded corn flour in the technology of semi-finished sponge cake that will improve the quality indicators of the finished product and extend its life.

Efficiency of application of electroactivated aqueous solution in the production of bread low acidity

In diseases of the gastrointestinal tract, it is recommended to refrain from food oxidation. Therefore, the inclusion in the diet of bakery products with low acidity is important in the diet for such patients. One way to reduce the acidity of bread is the use of electric aqueous solution (EAS). Studied the effect of EAS with different values of рН (7.42; 9.34; 11.12) on the properties of dough and quality of bread from wheat flour first grade. The dough is kneaded straight dough method. In the fermentation process investigated the change in effective viscosity and titratable acidity. After fermentation the dough is molded, the test workpiece is subjected to proofing and baking. In ready from deliah determined the acidity, moisture content, porosity and specific volume. It is established that all samples of the test there was a decrease of effective viscosity in the fermentation process due to the occurrence of physico-chemical processes. The maximum value of effective viscosity is characterized by the semi-finished product, obtained using EAS рН of which 11.12 (3474 PA⋅s). It is revealed that the least value of ultimate рН (1.7 deg) also had a sample on EAS with a рН = 11.12. The use of catholyte fraction of HRES with the given value of рН allowed to decrease the acidity in the finished product (45.5%) compared with the control in the pilot study value was 1.2 degrees, while in the control to 2.2. The research concluded that the use of electroactivated aqueous solution suitable for the production of bakery products of low acidity.

Вплив інгредієнтного складу на структурно-механічні властивості драглеподібних продуктів для спортсменів

Gel-like products are the prospective tendency in new products for special dietetic purposes research. An important characteristic of gel-like products’ quality that defines their suitability for usage according to intended purpose is structural and mechanical properties. They must be stable to the influence of temperature and certain ingredients, especially organic acids. The expediency of combining gelling agents pectin and xanthan gum to stabilize the structural and mechanical properties of gel-like products for athletes was investigated. It was established that addition of 0.05-0.2 % of xanthan gum increases the effective viscosity and limiting shear stress of gel-like products on 38-62 % and 13.7-25 % respectively. The structure of gel-like products only with pectin collapses with addition of organic acid, it is accompanied with a sharp decrease of effective viscosity on 30-37% and strength of the system on 33 – 47 %. Gel-like products with addition of xanthan gum maintain the structure; their rheological properties stay practically unchanged. Dependence between xanthan gum concentration and system strength change in the time of heating was established: increase of the xanthan gum concentration in the system causes decrease of the temperature influence on its strength. The results of the undertaken study can be used to develop formulations of gel-like food products for athletes.

Investigation of Gas Local Effective Viscosity in Nano-scale Channels

The non-equilibrium molecular dynamics method is used in this paper to simulate the nano-scale shear-driven gas flows. The velocity gradients and shear stress profiles across the channel are first sampled according to molecular positions and thermal velocities. The Newton viscosity law is then adopted to obtain the local effective viscosity. By using this method, the distribution of effective viscosity across the channel is achieved for the first time. The effective viscosity in the bulk region of the channel agrees very well with the experimental data at different gas density and wall velocity. However, the local effective viscosity decreases when the fluid approaches the wall, because of the interactions between wall and gas molecules. The wall influence depth is independent of the wall velocity in Couette flow. However, this depth decreases with the increase of gas density due to more inter-molecule collisions.

Effective viscosity of magnetic nanofluids through capillaries

The simultaneous effect of magnetic field and temperature on the capillary viscosity of magnetic nanofluid is an important parameter for a new class of applications such as nanoduct flow, nanomotors, micro- and nanofluidic devices, for transformer cooling, magnetic targeted drug delivery, etc. The effective viscosity of a nanofluid is explained based on the rotation of the particles and the effect of torque on it due to an externally applied magnetic field. Two types of fluids are used here, temperature-sensitive and non-temperature-sensitive magnetic nanofluids. In both types of fluids, decrease in effective viscosity with temperature is observed, but in both cases the mechanism for the decrement is quite different. One is due to temperature dependence of the magnetic moment and the other is due to removal of the secondary surfactant. For temperature-sensitive magnetic nanofluids, a Curie temperature of ~80 °C is extracted from this study. For non-temperature-sensitive magnetic nanofluids ~65% of the secondary surfactant is removed for a change in temperature, ΔT = 40 °C. This is analogous with removal of a drug from magnetic particles for targeted drug delivery. Further, a linear dependence of effective viscosity with different capillary size and ξ (angle between magnetic field and flow direction, ξε[0,π/2]) is also observed. This linear dependence can also be a good approximation for the study of magnetic drug targeting, as in the human body the capillaries are of different sizes, and the externally applied magnetic field is not always parallel or perpendicular to the drug flow direction.

Mathematical simulation of a twisted pseudoplastic fluid flow in a cylindrical channel

The results of investigations of a pseudoplastic fluid twisted flow in a cylindrical channel are presented. With increase in the shear stresses caused by the flow twisting, the effective viscosity decreases. As a result, in the axial part of the channel a zone of lower pressure is formed which, at smaller flow twisting, leads to the formation of the zone of backward flows.

Hydrodynamic interaction of two colloids in nonadsorbing polymer solutions

The hydrodynamic interaction between two colloids mediated by non-adsorbing polymer chains is considered for spherical colloids moving along the symmetric line. We present a resistance analysis and determine the mobility function that incorporates the polymer depletion effect. The hydrodynamic friction is calculated by solving the Stokes equation with non-uniform viscosity using the vorticity-stream function method and a bispherical coordinate transformation. The numerical results show the effective viscosity asymptotically approaches the single sphere limit of Fan et al. (T.-H. Fan, B. Xie and R. Tuinier, Phys. Rev. E., 2007, 76, 051405) for a large interparticle distance. As the particles get closer the effective viscosity decreases and finally approaches the lubrication limit, where the friction equals that of two close-approached spheres in a pure solvent. The flow analysis shows that the circulation pattern, a characteristic for the presence of the depletion layer, expands upon approach of the particles. The pressure contribution to the total drag force is determined by a competition between the lubrication force and the apparent slip effect caused by overlap of the depletion layers. The friction of the single sphere limit is only attained in the limit of an extremely small colloid volume fractions. Our results help rationalize the long-time relative diffusivity of Brownian particles in polymer solutions and this is important for a better understanding of the depletion-induced demixing kinetics.

Effective viscosity of dilute bacterial suspensions: a two-dimensional model

Suspensions of self-propelled particles are studied in the framework of two-dimensional (2D) Stokesean hydrodynamics. A formula is obtained for the effective viscosity of such suspensions in the limit of small concentrations. This formula includes the two terms that are found in the 2D version of Einstein's classical result for passive suspensions. To this, the main result of the paper is added, an additional term due to self-propulsion which depends on the physical and geometric properties of the active suspension. This term explains the experimental observation of a decrease in effective viscosity in active suspensions.

Response of an emulsion of leaky dielectric drops immersed in a simple shear flow: Drops less conductive than the suspending fluid

Direct numerical simulations of the effects of an electric field on an emulsion of drops are presented. A simple shear flow configuration is adopted where the electric field is applied perpendicular to the sliding plates. Both the drops and the suspending fluid are assumed to behave as leaky dielectric fluids. Here, drops less conductive than the suspending fluid with an electrical conductivity ratio smaller than the dielectric permittivity ratio are considered. This combination of electrical properties leads to a viscous fluid motion from the poles to the equator. The response of an emulsion is governed by the competition between the electrical forces, the fluid shear, and the capillary forces. The Mason number [Mn=(3λ+2)μγ̇∕6(λ+1)ε0β2E∞2] and the electric capillary number [Ce=ε0β2E∞2a∕γ] are used to describe the response of the systems. As previously observed in experiments at low shear rates, Mn<0.2, the drops aggregate in chains that tilt under a shear. The competition between the electrical forces and the fluid shear results in shorter chains at intermediate shear rates, 0.2<Mn<2.0. As the fluid shear becomes stronger than the electrical attraction, Mn>2.0, the chains of drops break up. The rheological properties mainly depend on the emulsion microstructure. The effective viscosity exhibits a strong shear-thinning response because the chains of drops, which appear at low shear rates, increase the resistance of the system to shear. As the chains shorten and break up, the effective viscosity decreases. The elastic properties of the emulsion are also affected by the presence of the electric field. Normal stress differences arise as a consequence of the deformation of the drops and the surface tension acting on the interface between the fluids. The shape of the drops is determined by the deformation caused by the viscous forces and the deformation due to the electric stresses. At low shear rates, the electric effects are predominant and the application of an electric field leads the drops to deform into oblate shapes. The oblate deformation results in higher stresses in the direction parallel to the shearing motion than perpendicular to it, which results in a significant increase in the first normal stress difference. As the shear rate is increased, the oblate deformation is supplemented by the deformation due to the fluid shear. The deformation caused by the electric field is also responsible for the negative magnitude of the second normal stress difference in three-dimensional emulsions.

Finite amplitude folding of single layers: elastica, bifurcation and structural softening

The amplification of viscous single-layer folds, from infinitesimal amplitudes up to finite amplitudes and large strains, is investigated analytically. Analytical solutions for finite amplitude folding of viscous layers valid for large viscosity contrasts and for post-buckling of elastic columns are shown to be identical. The failure of the classical, exponential amplification solution for folding is quantified using a nonlinear amplification equation similar to the Landau equation. The evolution of fold amplitude–strain for single layers with different initial amplitudes and viscosity contrasts essentially depends on a single parameter rather than three parameters as commonly assumed (strain, initial amplitude and viscosity contrast). This single parameter is constructed by scaling the strain with the crossover strain, which is the specific value of strain at which the linear solutions fail. Scaling the strain with the crossover strain yields a collapse of all amplitude evolution paths for different initial amplitudes and viscosity contrasts onto a single amplification path. Analytical solutions for the evolution of the layer-parallel deviatoric stress within the layer during folding are presented showing a decrease of the layer-parallel deviatoric stress with increasing fold amplitude. All stress–amplitude evolution paths for different initial amplitudes and viscosity contrasts can be collapsed onto a single stress–amplitude evolution path, if the amplitude is scaled by the crossover amplitude. The decrease in stress is proportional to a decrease in effective viscosity of the layer during folding. This decrease in effective viscosity represents structural softening, because the true, Newtonian viscosity of the layer remains constant. †Now at: Geological Insitute, ETH Zentrum, CH-8092 Zurich.

Structural softening of the lithosphere

AbstractStructural softening is a decrease in the amount of stress needed to deform the lithosphere at a particular rate because of its structural reorganization while all true rheological properties remain constant. Structural softening is fundamentally different than material softening, where the decrease in stress is generated by a change in rheological properties with progressive deformation, such as grain size reduction resulting from large shearing strain. We study structural softening generated by folding of the crust‐mantle boundary, which is a structural instability that inevitably develops during compression of the mechanically layered lithosphere. For ductile rheologies, the stress decrease represents a decrease of the effective lithospheric viscosity, which is proportional to the ratio of stress to lithospheric shortening strain rate. We present analytical and numerical results quantifying the decrease in stress and effective viscosity that occur during shortening at a constant rate. The decrease in effective viscosity can be up to 10‐fold.