Dynamic Viscosity Coefficient Research Articles

Generation of steady longitudinal vortices in hypersonic boundary layer

AbstractIn this paper we study the three-dimensional perturbations produced in a hypersonic boundary layer by a small wall roughness. The flow analysis is performed under the assumption that the Reynolds number, $R{e}_{0} = {\rho }_{\infty } {V}_{\infty } L/ {\mu }_{0} $, and Mach number, ${M}_{\infty } = {V}_{\infty } / {a}_{\infty } $, are large, but the hypersonic interaction parameter, $\chi = { M}_{\infty }^{2} R{ e}_{0}^{- 1/ 2} $, is small. Here ${V}_{\infty } $, ${\rho }_{\infty } $ and ${a}_{\infty } $ are the flow velocity, gas density and speed of sound in the free stream, ${\mu }_{0} $ is the dynamic viscosity coefficient at the ‘stagnation temperature’, and $L$ is the characteristic distance the boundary layer develops along the body surface before encountering a roughness. We choose the longitudinal and spanwise dimensions of the roughness to be $O({\chi }^{3/ 4} )$ quantities. In this case the flow field around the roughness may be described in the framework of the hypersonic viscous–inviscid interaction theory, also known as the triple-deck model. Our main interest in this paper is the nonlinear behaviour of the perturbations. We study these by means of numerical solution of the triple-deck equations, for which purpose a modification of the ‘skewed shear’ technique suggested by Smith (United Technologies Research Center Tech. Rep. 83-46, 1983) has been used. The technique requires global iterations to adjust the viscous and inviscid parts of the flow. Convergence of such iterations is known to be a major problem in viscous–inviscid calculations. In order to achieve improved stability of the method, both the momentum equation for the viscous part of the flow, and the equations describing the interaction with the flow outside the boundary layer, are treated implicitly in this study. The calculations confirm the fact that in this sort of flow the perturbations are capable of propagating upstream in the boundary layer, resulting in a perturbation field which surrounds the roughness on all sides. We found that the perturbations decay rather fast with the distance from the roughness everywhere except in the wake behind the roughness. We found that if the height of the roughness is small, then the perturbations also decay in the wake, though much more slowly than outside the wake. However, if the roughness height exceeds some critical value, then two symmetric counter-rotating vortices form in the wake. They appear to support themselves and grow as the distance from the roughness increases.

Rheology of Blast Furnace Slags Admitted High Concentration of Titanium Oxides

The applying of burden materials containing titanium compounds in the blast furnace process and the processes of forming titanium carbides and nitrides has a directly impact on the physical and chemical properties of slag and pig iron. Thereby affecting the course of the process, its efficiency and economy. It is known that the dynamic viscosity coefficient of slag – with an increased titanium compounds content in the reducing conditions of the blast furnace - may rapidly change. The products of the reduction reaction, precipitation and separation of titanium compounds are responsible for the thickening effect of the slag and the problems of permeability of blast furnace, causing anomalies in the functioning of the unit. The presence of solid components (particles) in the melts determines the rheological character of the entire system. Authors have performed a rheological study of synthetic furnace slag concentration of TiO2 in the range of 6% to 30%. The measurements were performed at temperatures in the range between 1310-1490oC. The obtained results made it possible to carry out the rheological characteristics of analyzed liquid and semi-solid slag systems and draw of flow curves. Identifying the rheological character of semi-solid slag systems provides opportunities for the development of mathematical modeling of liquid phase flows in a dripping zone of the blast furnace, allowing e.g to indentify the unstable parts of a metallurgical aggregate.

Optimization of fractional composition of the excipient in the elastomeric covering for asphalt highways

The computational method of optimum fractional composition of a dispersible filler of polymeric composite on the basis of three-dimensionally linked elastomer is developed according to non-linear programming. The coefficient of dynamic viscosity of polymeric suspension or the initial module of a viscoelasticity of the join solidification low-molecular rubbers with the final functional groups, filled by many fractional dioxide of silicon are considered as criteria of optimization. Influence of the limiting volume filling on energy of mechanical destruction was investigated. The elastomeric material is offered for use as a covering of asphalt highways in the form of a frost-proof waterproofing layer, which allowing multiply to increase operating properties.

Evolution of the Coefficient of Dynamic Viscosity with Growing Damage in Metals

Coefficient of dynamic viscosity (η) for uniaxial rectangular bar of steel is calculated using creep simulation in Ansys. Norton Secondary creep law with coefficients at 600 ᵒC is used. Steel bar is then inflicted with some damage elements in order to investigate the evolution of dynamic viscosity for varying degree of fatigued specimen at constant rate and temperature. Isotropic damage parameter (D) based on the volume fraction of damaged elements is used to formulate a linear relation between the coefficient of viscosity and D. It is found that with 0.001 increase is damage parameter (D), almost 0.6% decrease on the value of Coefficient of dynamic viscosity (η) is observed.

Computation and Comparison of Dynamic Viscosity Based on Quasi-Static and Dynamic FEM Analysis for AL7050-T7451

Coefficients of dynamic viscosity for AL7050-T7451 at room temperature is extracted by creep and stress relaxation simulations in Ansys. An analogy has been established for both creep and stress relaxation, with simple Maxwell Model. The stress relaxation curve thus obtained is then used to generate the Prony series coefficients which are then used to run some dynamic analysis in Ansys to see the effect of loading at different frequencies on the value of η (i.e dynamic viscosity). This will be verified with the simple analytical dynamic formulation based on the Maxwell Model. A good agreement has been found for both quasi-static and dynamic tests with Maxwell model.

On the temperature and pressure dependence of the dynamic viscosity of n-alkanes

Isotherms of the coefficient of dynamic viscosity and isobars of n-alkanes are considered. One-parameter correlations for the isobars are constructed based on the literature data. A linear correlation is revealed between the boiling and melting temperatures and the found parameter of the baric dependence of viscosity for a homological series of alkanes.

On calculation of the transport coefficients and thermodynamic properties of a helium-xenon gas mixture

Calculation and experimental investigations of the transport coefficients and thermodynamic properties of a helium-xenonmixture are reviewed. It seems that a combination of approaches of the Chapman-Enskog kinetic theory and the theory of corresponding states of dense gas is most promising. This combined approach results in semiempirical relationships for calculating the density, coefficient of dynamic viscosity, thermal conductivity coefficient, specific heat capacity at constant pressure, and specific heat capacity at constant volume. These relationships consider the influence of the temperature and pressure, and also the ratio of mixture components. For a fixed ratio of mixture components, the calculation algorithms constructed by the authors with the use of such semiempirical relationships are in good agreement with the engineering calculation procedure in which the influence of mixture components is not considered, whereas the influence of temperature and pressure is considered by simple formulas in a form of polynomials.

The Relative Viscosity of Concentrated Rubber Suspensions and Viscoelastic Modulus of 3D Сross-Linked Elastomers Filled with Solid Particles

For the first time, this paper describes the concentration dependence of the relative dynamic viscosity coefficient of rubber suspensions and the initial viscoelastic modulus of 3D cross-linked elastomers on the maximum volume filling with solid polydisperse particles. It allows to predict the rheological and mechanical properties of the polymer compositions being developed now. In this paper, we present the first experimental study of the pole of the concurrent lines of the concentration dependence in the coordinates of the linear form. The pole validates the invariant value of the constant of the developed equation and allows the experimental determination of the maximum volume filling of polymer binders filled with separate fractions or polydisperse mixtures. The results of the study are recommended for use in developing new polymer composite materials.

Correlation between diffraction and viscosity data for Bi–Ga molten alloys

Structure of Bi $_{\boldsymbol{100-x}}$ Ga $_{\boldsymbol{x}}$ molten alloys containing 38·5, 50, 70 and 91·5 at. % Ga has been studied by means of X-ray diffraction method and compared with viscosity measurements data. Significant changes in the structure factor profile were observed in vicinity of the concentration 70 at. % Ga. The dynamic viscosity coefficient was calculated by use of a statistical atomic distribution model and a Born–Green kinetic theory. The concentration dependence of viscosity is in agreement with change of structure parameters obtained from diffraction data.

MODELING OF THE THERMO-PHYSICAL PROPERTIES OF LIQUIDS INVOLVED IN FOOD PROCESSING

Food processing industries are among the fewest industries that probably will last as long as humanity will survive. Unlike the other process industries, the food industries raw materials and products are easily degradable by external and internal factors, and most of them exhibit non-Newtonian behavior. Technologies and equipment for food processing have to be designed as a consequence of these facts. Rationally designed equipment needs a thoroughly knowledge of physical and thermo-dynamical properties (density, viscosity, thermal conductivity, thermal capacity and so on) of materials involved in food processing: raw materials, additives, intermediates, by-products and finished products. Most of the data concerning the properties of fluids involved in food industry are presented in tabular or graphical form. In this form, experimental data are difficult to use in calculus where properties values are often and repeatedly necessary at different temperatures: fluids flow, thermal balances and heat and mass transfer coefficients. Our study aims to correlate experimental data previously published by different authors as tables and/or charts in order to obtain mathematical equations with the general form: . = f(T,x), where . denotes the studied property (density, viscosity, thermal conductivity, etc.), T the temperature and x the concentration of the solution. Using literature data concerning the variation of thermo-physical properties of sugar solutions in water with the temperature and sugar concentration, two to five equations for density, dynamic viscosity coefficient, thermal conductivity coefficient and thermal capacity have been established. The obtained equations meet two essential requirements: simplicity and sufficient accuracy for engineering calculations.

Forced and natural convection in aggregate-laden nanofluids

A number of experimental and theoretical studies of convective heat transfer in nanofluids (liquid suspensions of nanoparticles, typically with features below 100 nm in size) reveal contrasting results; nanoparticles can either enhance or reduce the convective heat transfer coefficient. These disparate conclusions regarding the influence of nanoparticles on convective heat transfer may arise due to the aggregation of nanoparticles, which is often not considered in studies of nanofluids. Here, we examine theoretically forced and natural convective heat transfer of aggregate-laden nanofluids using Monte Carlo-based models to determine how the aggregate morphology influences the convective heat transfer coefficient. Specifically, in this study, it is first shown that standard heat transfer correlations should apply to nanofluids, and the main influence of the nanoparticles is to alter suspension thermal conductivity, dynamic viscosity, density, specific heat, and thermal expansion coefficient. Aggregated particles in suspension are modeled as quasi-fractal aggregates composed of individual primary particles described by the primary particle radius, number of primary particles, fractal (Hausdorff) dimension, pre-exponential factor, and degree of coalescence between primary particles. A sequential algorithm is used to computationally generate aggregates with prescribed morphological descriptors. Four types of aggregates are considered; spanning the range of aggregate morphologies observed in nanofluids. For each morphological type, the influences of aggregates on nanofluid dynamic viscosity and thermal conductivity are determined via first passage-based Brownian dynamics calculations. It is found that depending on both the material properties of the nanoparticles as well as the nanoparticle morphology, the addition of nanoparticles to a suspension can either increase or decrease both the forced and natural convective heat transfer coefficients, with both a 51% increase and a 32% decrease in the heat transfer coefficient achievable at particle volume fractions of 0.05. This study shows clearly that the influence of particle morphology needs to be accounted for in all studies of heat transfer in nanofluids.

Microfluidic separation process by the Soret effect in biological fluids

In this article the thermophysical and transport properties of mixtures composed of glucose and sucrose in dimethylsulfoxide (DMSO) are determined. The studied mass concentrations are 5%, 10%, 15%, 20% and 25% of glucose or sucrose in DMSO at an average temperature of 25 °C. The properties studied experimentally are the dynamic viscosity, density, mass and thermal expansion coefficient and thermodiffusion coefficient. The thermogravitational technique in flat configuration is used in order to obtain the thermodiffusion coefficients. Once these properties are known, the work is focused on the numerical study of applying a temperature gradient in microdevices in order to optimize the extraction of DMSO using the CFD Ansys Fluent software. The results show an improvement even of 35% on microfluidic separation techniques that are based on a purely diffusive regime.

Structure parameters and structure sensitive properties of Sn0.739Pb0.261 melt

Structure, interdiffusion, and dynamic viscosity of eutectic Sn-Pb melt have been experimentally investigated in a wide temperature range. On the basis of the obtained data on the position and form of the first maximum of the structure factor in the framework of the hard sphere model, values of sphere packing index and sphere diameter have been determined for the melt at 470 and 570 K. Correlations resulting from the model of hard spheres served to calculate coefficients of dynamic viscosity and interdiffusion of liquid alloy. Besides, temperature dependence of dynamic viscosity has been calculated with the use of thermodynamic approximation of Kozlov — Romanov — Petrov. Calculated values of the properties have been compared with experimental data.

Influence of Dynamic Viscosity on Automatic Dynamic Balance

The paper deals with analysis of dynamic stability and behavior of automatic dynamic balance (ADB) by applying theoretical approach. Differential equations of the considered system were established using Lagrange equation. Numerical analysis of the dynamic equations was performed and influence of dynamic viscosity coefficient on self-balancing process was estimated. It is demonstrated that the balancing time decreases in non-linear character. The optimal value of dynamic viscosity for achieving minimal balancing time can be determined for the analyzed system.

Thermodynamic model of viscosity of hydrocarbons and their mixtures

Activation hypothesis suggested by Eyring for modeling viscosity of liquids is generalized for calculation coefficient of dynamic viscosity of pure hydrocarbons and their mixtures in wide region of temperature, pressure and concentrations. Energy of vacancy activation is modeled as difference between enthalpy of ideal gas and enthalpy of real substance. Enthalpy and other thermodynamic parameters for pure substances and mixtures are calculated on the base of well-known Lee–Kesler equation of state. Thermodynamics of mixture calculated in the frame of pseudofluid hypothesis with pseudocritical thermodynamic constants. Pseudocritical thermodynamic constants are estimated with the help of mixing rules offered also by Lee–Kesler. Two additional constants are including in the suggested model of viscosity. For normal paraffin these constant have universal value. For other substances, for example, oxygen containing hydrocarbons values of the constant are installed in accordance to the experimental data. The model with sufficiently accuracy reproduces viscosity experimental data as pure substances in vapor and liquid phases and also solutions in the wide regions of thermodynamical parameters and concentrations. Calculation results are compared with the literature experimental data.

Air–Water Two-Phase Frictional Pressure Drop in Minichannels

This article presents the results of experiential investigations of frictional pressure drop in horizontal minichannels. An air–water mixture was used as the working fluid. The test section was made from stainless-steel pipes with internal diameters of 1.05, 1.35, 1.68, and 2.30 mm. Investigations were carried out at mass flux of 170–7350 kg/m2-s and gas quality from 0.001 to 0.22. Superficial velocity ranges of water and air were 0.2–7.4 m/s and 1.7–41.8 m/s, respectively. The results of experimental investigations were compared with theoretical values obtained from a homogeneous equilibrium model. The dynamic viscosity coefficient was calculated using dependences proposed by Owens, McAdams, Ackers, Cicchitti, Dukler, Beattie and Whalley, and Lin. It is found that none of the tested correlations can predict the two-phase pressure drop gradient satisfactorily. The homogeneous model with a correction factor proposed by Chen to use in minichannels was also used. In this case, the results of calculations were worst without consideration of which correlation was used to determine the dynamic viscosity coefficient.

Thermal convection of micropolar fluid in the presence of suspended particles in rotation

A study has been made of the convection of micropolar fluids heated from below in the presence of suspended particles (fine dust) and uniform vertical rotation Ω ­(0; 0;­ Ω ). The effect of Coriolis forces on the stability is chosen along the direction of the gravitational field. It is found that the presence of coupling between thermal and micropolar effects, rotation parameter and suspended particles may introduce overstability in the system. Using the Boussinesq approximation, the linearized stability theory and normal mode analysis, the exact solutions are obtained for the case of two free boundaries. Graphs have been plotted by giving numerical values to the parameters accounting for rotation Ω­ (0; 0;­ Ω ­) and the dynamic microrotation viscosity kappa and coefficient of angular viscosity γ' to depict the stability characteristics, for both the cases of stationary convection and overstability. It is found that Rayleigh number for the case of overstability and stationary convection increases with increase in rotation parameters and decreases with increase in micropolar coefficients, for a fixed wave number, showing thereby the stabilizing effect of rotation parameters and destabilizing effect of micropolar coefficients on the thermal convection of micropolar fluids. Thus there is a competition between the stabilizing effect of rotation parameters and destabilizing effect of micropolar coeffcients and the suspended particles. It is also found from the graphs that the Rayleigh number for the case of overstability is always smaller than the Rayleigh number for the case of stationary convection, for a fixed wave number.

Modeling of aluminum alloy profile extrusion process using finite volume method

The most popular numerical method used for simulating aluminum alloy extrusion process is finite element method (FEM). But aluminum alloy profile extrusion process is a metal forming process with severe and large plastic deformation. If finite element method is used to simulate aluminum profile extrusion process, mesh always distorts quickly and frequent remeshing is needed. In addition, the checks for node-separation-from or node-contact-to die surfaces are also frequently needed. The continuous remeshing and node-separation-contact checks usually decrease the accuracy of FEM-based simulation results and increase the CPU time. In this paper, finite volume method (FVM) based on Euler mesh is used to simulate three-dimensional steady or transient aluminum alloy profile hot extrusion process. Semi-implicit method for pressure-linked equations (SIMPLE) algorithm is used to calculate the velocity field and the pressure field of the extrusion process. The dynamic viscosity coefficient of the material mostly dependent on temperature and the effective strain-rate is updated in every SIMPLE inner iteration. At every exterior time step, the method of volume of fluid (VOF) is applied to catch the transient free surface of the material. “Moving grids system” is also used to deal with the moving problem of the boundaries of the calculated domain caused by the moving of the extrusion ram. To ensure the stability and efficiency of the simulation, automatic adjustment of the time increment is realized. Two typical extrusion processes are simulated by the FVM model of this paper. Some results are compared with those simulated by FEM. The material flow characteristics from transient state of extrusion process to steady state of extrusion process are also discussed.

Effect of vacuum-microwave drying on selected mechanical and rheological properties of carrot

Carrots were dried using the vacuum-microwave method and strength tested using an Instron 5566 with measuring heads of class 0.5. The values of the cutting and the compression forces were calculated. The testing was performed on materials that were initially blanched, osmotically dehydrated, and untreated before drying. As a result of the vacuum-microwave drying, dried carrots with a moisture content within the range (3.2–3.8)% were obtained. The blanching operation resulted in an almost two-fold increase in the dry matter resistance to compression compared to that of the dry matter obtained from initially untreated carrot. Osmotic dehydration reduced the product resistance to compression more than two-fold. A five-element Maxwell model adequately described the reduction in stresses with time. The values of the modulus of elasticity and the coefficients of dynamic viscosity for the rheological model were calculated. The highest values of the modulus of elasticity were obtained for the raw material subjected to blanching.

Tidal-Scale Hydrodynamics within Mangrove Swamps

Both the drag force and the horizontal eddy viscosity play a dominant role in the tidal-scale hydrodynamics in mangrove wetlands. Using field observations and basic fluid mechanics laws, the drag coefficient and the coefficient of dynamic eddy viscosity are found to be predictable as a function of the Reynolds Number based on the characteristic length scale of the vegetation. The characteristic length scale of the vegetation varies greatly with vegetation species, vegetation density and tidal elevation. Both these coefficients decrease with increasing values of the Reynolds Number. At the low range of the Reynolds Number both these coefficients reach much higher values than those typical of vegetation-poor estuaries and rivers. Consequently, the tidal flow within mangrove areas depends to a large degree upon the submerged vegetation density that varies with the tidal stage. These findings may be applied also in other vegetated tidal wetlands, including salt marshes.