Viscosity-temperature Relation Research Articles

Yttria substitution effect of tantalate aluminosilicate glasses with ultra‐high Young's modulus

AbstractWe report novel oxide glasses that are compatible with ultra‐high Young's modulus (∼150 GPa) and a small coefficient of thermal expansion (∼5.0 ppm/K). These glasses were prepared using a conventional melt‐quenching technique. The viscosity–temperature relation provides the reshaping temperature for the stiff and less dilated oxide glasses. The origin of the ultra‐high Young's modulus is the inclusion of Y2O3 as well as five‐ and six‐coordinated alumina oxide and Ta2O5, which has a large ionic packing ratio due to higher oxygen coordination numbers. On the other hand, the small thermal expansion coefficient originates from including Ta2O5 and SiO2 with large dissociation energy due to strong bonds.

Shock Structures Using the OBurnett Equations in Combination with the Holian Conjecture

In the present work, we study the normal shock wave flow problem using a combination of the OBurnett equations and the Holian conjecture. The numerical results of the OBurnett equations for normal shocks established several fundamental aspects of the equations such as the thermodynamic consistency of the equations, and the existence of the heteroclinic trajectory and smooth shock structures at all Mach numbers. The shock profiles for the hydrodynamic field variables were found to be in quantitative agreement with the direct simulation Monte Carlo (DSMC) results in the upstream region, whereas further improvement was desirable in the downstream region of the shock. For the discrepancy in the downstream region, we conjecture that the viscosity–temperature relation (μ∝Tφ) needs to be modified in order to achieve increased dissipation and thereby achieve better agreement with the benchmark results in the downstream region. In this respect, we examine the Holian conjecture (HC), wherein transport coefficients (absolute viscosity and thermal conductivity) are evaluated using the temperature in the direction of shock propagation rather than the average temperature. The results of the modified theory (OBurnett + HC) are compared against the benchmark results and we find that the modified theory improves upon the OBurnett results, especially in the case of the heat flux shock profile. We find that the accuracy gain is marginal at lower Mach numbers, while the shock profiles are described better using the modified theory for the case of strong shocks.

Viscosity-temperature relation based on the evolution of medium-range structures of silica

The viscosity of glass is the most important technological property to glass manufactures and various applications. Practically, finding an accurate equation to express the glass viscosity behavior in the entire glass transition temperature range is tremendously challenge because it spans more than ten orders of magnitude. After a brief review of existing empirical viscosity equations, this work focuses on the correlating silica viscosity behavior with the evolution of glass medium-range structure, based on the recently proposed nanoflake model. From this new model, a new equation is constructed, which correctly describes the Arrhenius-type behavior of silica viscosity η above the melting temperature Tm, and non-Arrhenius-type behavior from Tm to a critical temperature Tc. At temperature lower than Tc, the equation predicts Arrhenius-type behavior again for the viscous flow with increased activation energy. The new equation agrees with experimental data in the entire temperature spanned from extremely high to extremely low. The application of the new equation is shown to extend to sodium silicate glasses as well.

Modelling Transitions in Regimes of Lubrication for Rough Surface Contact

Accurately predicting frictional performance of lubrication systems requires mathematical predictive tools with reliable lubricant shear-related input parameters, which might not be easily accessible. Therefore, the study proposes a semi-empirical framework to predict accurately the friction performance of lubricant systems operating across a wide range of lubricant regimes. The semi-analytical framework integrates laboratory-scale experimental measurements from a pin-on-disk tribometer with a unified numerical iterative scheme. The numerical scheme couples the effect of hydrodynamic pressure generated from the lubricant and interacting asperity pressure, essential along the mixed lubrication regime. The lubricant viscosity-pressure coefficient is determined using a free-volume approach, requiring only the lubricant viscosity-temperature relation as the input. The simulated rough surface contact shows transition in lubricant regimes, from the boundary to the elastohydrodynamic lubrication regime with increasing sliding velocity. Through correlation with pin-on-disk frictional measurements, the slope of the limiting shear stress-pressure relation γ and the pressure coefficient of boundary shear strength m for the studied engine lubricants are determined. Thus, the proposed approach presents an effective and robust semi-empirical framework to determine shear properties of fully-formulated engine lubricants. These parameters are essential for application in mathematical tools to predict more accurately the frictional performance of lubrication systems operating across a wide range of lubrication regimes.

Performance investigation of micro-pocketed textured pad thrust bearing

PurposeThe purpose of this paper is to conceive a new surface texture incorporating a tiny shape among the micro-pockets (with circular, rectangular, trapezoidal and triangular cross-sections) and dimples (cylindrical, hemispherical and ellipsoidal) for exploring to enhance the maximum possible performance behaviors of sector shape pad thrust bearing.Design/methodology/approachNumerical simulation of hydrodynamically lubricated sector shape textured pad thrust bearing has been presented incorporating thermal and cavitation effects. The coupled solution of governing equations (Reynolds equation, film thickness expression, viscosity–temperature relation, energy equation and Laplace equation) has been achieved using finite difference method and Gauss–Seidel iterative scheme.FindingsWith new textured pads, higher load-carrying capacity and lower coefficient of friction are obtained in comparison to plain sector shape pad. Texture pattern comprising square cross-sectional pockets yields higher load-carrying capacity and lower coefficient of friction in comparison to other cross-sectional shapes (circular, trapezoidal and triangular) of pockets considered herein.Originality/valueThis study reports a new texture, which involves micro-pockets of square cross-sectional shapes to improve the performance behavior of sector shape pad thrust bearing. About 75 per cent increase in load carrying capacity and 42 per cent reduction in coefficient of friction have been achieved with pad having new texture in comparison to conventional pad.

Revealing a structural transition in typical Fe-based glass-forming alloy melts

The viscosity-temperature relation of three typical Fe-based glass-forming alloys was investigated by rotational vibration-type high-temperature melt viscometry and ab initio molecular dynamics simulation. It was shown that during the first heating process until 1500 °C, the viscosity decreased suddenly at approximately 1400 °C, demonstrating a structural transition which was confirmed by the thermoanalysis. However, if the heating temperature was below 1400 °C or during the following second thermal cycle, such structural transition cannot be observed. The viscosity curves of all samples during cooling processes can be well described by the Arrhenius equation, in which the activation energy was inversely proportional to the Fe content. The Fe2B-like clusters have higher total energy, higher melting point and larger size than that of Fe3B-like clusters. Thus, we suggested that the structural transition may be related to the transformation from Fe2B-like clusters to Fe3B-like clusters. The structural transition in liquid was eliminated and a homogeneous Fe-based alloy melt was obtained after a rather long relaxation time at a temperature higher than the melting point of infusible clusters. This study could offer some helpful reference for understanding the nature of alloy melt and the quality control of Fe-based amorphous alloys.

Viscosity of TiO2-FeO-Ti2O3-SiO2-MgO-CaO-Al2O3 for High-Titania Slag Smelting Process

The present study demonstrates the dependence of viscosity on chemical composition and temperature of high-titania slag, a very important raw material for producing titanium dioxide. The results indicated that completely molten high-titania slag exhibits a viscosity of less than 1 dPa s with negligible dependence on temperature. However, it increases dramatically with decreasing temperature slightly below the critical temperature, i.e., the solidus temperature of the slag. Above the critical temperature, the slag samples displayed the same order of viscosity at 0.6 dPa s, regardless of their compositional variation. However, the FeO, CaO, and MgO were confirmed to decrease viscosity, while SiO2 and Ti2O3 increase it. The apparent activation energy for viscosity-temperature relation and liquidus temperature based on experiments and thermodynamic calculations are also presented. Conclusively, the critical temperatures of the slags are on average 15 K below their corresponding calculated liquidus temperatures. The increase in FeO content was found to considerably lower the critical temperature, while the increase in both Ti2O3 and TiO2 contents increases it. The main phases of the slag in solid state, as indicated by X-ray diffraction, are (Fe, Mg)xTiyO5 (x + y = 3, pseudobrookite) and rutile.

Effect of slag viscosity model on transient simulations of wall slag flow in an entrained coal gasifier

The viscosity-temperature relation of slag determines its behavior inside an entrained flow coal gasifier. However, existing prediction models give results with large variations among them. We investigated the influence of different viscosity models in the prediction of the steady and transient behaviors of slag flow on the wall of a gasifier undergoing gas temperature changes. Five viscosity models adopted showed differences in the temperature (T250) at 25 Pa∙s as large as 97 K for the selected slag composition, which was used as the interface temperature between the solid and liquid slag. When the predicted viscosity and corresponding T250 increased, the solid slag became thicker and the dynamic response of the slag became slower. In contrast, the differences in the liquid slag thickness were small. The influence of T250 predicted was dominant, compared to that of different viscosity curves of the liquid slag.

Kelvin–Helmholz instability in thermoviscous free shear flow

This paper is focused on the entrainment and mixing in the nonisothermal shear flow, wherein the velocity profile discontinuity arises due to viscosity–temperature relation, i.e. thermoviscosity. Kelvin–Helmholz instability generated at the interface paves the way to large-scale entrainment which is analysed in terms of perturbation growth rate and momentum thickness. The flow is simulated in the plane domain with periodic boundary conditions using second-order accuracy explicit CABARET numerical scheme in weakly compressible formulation. Initial instability evolution is fully governed by a universal scaling parameter kt, composed of Reynolds number Re and kinematic viscosity ratio Rν. There are seven flow configurations determined by nonlinear mode interaction, vorticity convection and diffusion and cascade vortex merger. The problem at issue appears to be analogues to the classical boundary layer theory that totally fortifies its remarkable features.

Simulation of phase separation with temperature-dependent viscosity using lattice Boltzmann method.

This paper presents an exploration of the phase separation behavior and pattern formation in a binary fluid with temperature-dependent viscosity via a coupled lattice Boltzmann method (LBM). By introducing a viscosity-temperature relation into the LBM, the coupling effects of the viscosity-temperature coefficient [Formula: see text] , initial viscosity [Formula: see text] and thermal diffusion coefficient [Formula: see text] , on the phase separation were successfully described. The calculated results indicated that an increase in initial viscosity and viscosity-temperature coefficient, or a decrease in the thermal diffusion coefficient, can lead to the orientation of isotropic growth fronts over a wide range of viscosity. The results showed that droplet-type phase structures and lamellar phase structures with domain orientation parallel or perpendicular to the walls can be obtained in equilibrium by controlling the initial viscosity, thermal diffusivity, and the viscosity-temperature coefficient. Furthermore, the dataset was rearranged for growth kinetics of domain growth and thermal diffusion fronts in a plot by the spherically averaged structure factor and the ratio of separated and continuous phases. The analysis revealed two different temporal regimes: spinodal decomposition and domain growth stages, which further quantified the coupled effects of temperature and viscosity on the evolution of temperature-dependent phase separation. These numerical results provide guidance for setting optimum temperature ranges to obtain expected phase separation structures for systems with temperature-dependent viscosity.

Poor glass-forming ability of Fe-based alloys: Its origin in high-temperature melt dynamics

The relatively poor glass-forming ability (GFA) of Fe-based alloys has limited the mass production of Fe-based bulk metallic glasses (MGs), and hence their applications. To clarify the origin of the low GFA of the Fe-based alloys, we investigate the dynamic behaviors of these alloy systems well above their respective liquidus temperatures. By using a torsional oscillating viscometer we have observed a dynamic transition, where the slope of the viscosity-temperature relation of the Fe-based metallic liquid increases upon cooling, and a viscosity hysteresis occurs between the heating and cooling processes. By using the concept of fluid cluster and supercooled liquid fragility in metallic liquids, it has been found that this dynamic transition makes the Fe-based supercooled liquids become more unstable, which leads to the poor GFA of Fe-based alloys. Further, it has been found that the degree of the dynamic transition relates to the different GFA among Fe-based alloys. By taking into account the thermodynamic effect accompanied with the dynamic transition in Fe-based melts, a possible scenario has been proposed from the aspect of the underlying structural evolution during cooling above the liquidus temperature.

VISCOSITY END ELECTRICAL CONDUCTIVITY OF LIQUID HYPEREUTECTIC ALLOYS Al-Si

The kinematic viscosity of AlSi20 liquid alloy was measured by using the crucible rotating oscillation damping method, and the viscosity-temperature relation curve ν(T) in the temperature range of 850∼1200K was obtained. The viscosity changed abnormally with temperature in the heating process, i.e., the viscosity turned from rapid increase to gradual decrease when the temperature increased to 1000∼1100 K, while the viscosity diminishes exponentially with temperature in the subsequent cooling process. The microscopic mechanism of the evolution of viscosity was analyzed from the viewpoint of the micro-inhomogeneity theory of metallic melts, and it was found that the destruction of the β-Si phase was the basic reason of the head-turning change of viscosity. The paper discussed the correlation of the viscosity and atomic density, which is thought that the viscosity corresponds to the atomic density to some extent. The abstract should be written in the past tense, because it refers to work which was already done. Any equations and references are not allowed. It must state the main object, scope, findings, describe the methodology, summarize the results and state the principal conclusions.

Viscosity correlations for jojoba oil blends with biodiesel and petroleum diesel

ABSTRACTIn this study, the effect of temperature and mixture composition on viscosity of Jojoba oil-Biodiesel (JO-BD) and Jojoba oil-Diesel (JO-PD) blends are investigated. Moreover, the relationship between the viscosity and the specific gravity of the blends is studied. Experimental viscosity data for the temperature range between 20°C and 80°C are used. The results show that the viscosity–temperature dependency can be well correlated by Vogel model for the viscosity–temperature relation. Also, a method that could estimate the blends viscosity from the specific gravity data is established.

Combined effect of variable viscosity and thermal conductivity on free convection flow of a viscous fluid in a vertical channel

Purpose – The purpose of this paper is to investigate the effect of exponential viscosity-temperature relation, exponential thermal conductivity-temperature relation and the combined effects of variable viscosity and variable thermal conductivity on steady free convection flow of viscous incompressible fluid in a vertical channel. Design/methodology/approach – The governing equations are solved analytically using regular perturbation method. The analytical solutions are valid for small variations of buoyancy parameter and the solutions are found up to first order for variable viscosity. Since the analytical solutions have a restriction on the values of perturbation parameter and also on the higher order solutions, the authors resort to numerical method which is Runge-Kutta fourth order method. Findings – The skin friction coefficient and the Nusselt number at both the plates are derived, discussed and their numerical values for various values of physical parameters are presented in tables. It is found that an increase in the variable viscosity enhances the flow and heat transfer, whereas an increase in the variable thermal conductivity suppresses the flow and heat transfer for variable viscosity, variable thermal conductivity and their combined effect. Originality/value – This research is relatively original as, to the best of the authors’ knowledge, not much work is done on the considered problem with variable properties.

Numerical research of influence of viscosity–temperature relation on structure of Couette flow

In work results of a numerical research of influence of viscosity-temperature relation on structure of a convective Couette flow of thermoviscous liquid are presented in ring area between two coaxial cylinders under a condition when one of them has more high temperature. Comparison of a convective Couette flow of model liquid with non-monotone temperature dependence of viscosity and liquid with constant viscosity is carried out. Depending on parameters of viscosity anomaly the steady and oscillation flow regimes both with periodic and with not repeating fluctuations of vortex structures are found. The number of time-constant vortex structures also depends on parameters of viscosity anomaly.

Modeling of Random Relaxation Paths of Amorphous Material

This study aims to understand the viscosity variation of amorphous materials, and hence establish a theoretical model for reliable applications. The investigation was carried out by simplifying an amorphous system to a mixture of many subsystems which switch their energy states and relaxation processes stochastically. The response of the macroscopic system is then treated as an ensemble average of relaxations of individual subsystems. Our derivation illuminates the transition from exponential to nonexponential relaxation and that the sudden increase of fragility in the viscosity–temperature relation with reducing temperature could be attributed to the bifurcation from the harmonic mean of the subsystems towards the arithmetic mean. The successful application of our model to the amorphous selenium indicates that the model captures the fundamental mechanism of viscosity variation.

Viscosity-temperature Relation of Aggregation Energies in Glass Forming Process

Based on the dynamics of vitrification process driven by the configurational entropy, a novel expression of viscosity- temperature relation with the form of Fermi-type function is deduced below melting temperature by supposed an exponential function of average aggregation energy with temperature. The ‘molecular rearrangement’ to form aggregated regions at temperatures below the melting temperature is major contribution to the aggregation energies for describing vitrification process. The expression of relaxation time or viscosity is confirmed with several super-cooled liquids in broad temperature region. The expression contains the Vogel-Fulcher relation in limited temperature region and can avoid Kauzmenn paradox. The derived fragility shows that a reduced temperature may be a common structural variable in comparing various glassy liquids.

A comparison of the value of viscosity for several water models using Poiseuille flow in a nano-channel

The viscosity-temperature relation is determined for the water models SPC/E, TIP4P, TIP4P/Ew, and TIP4P/2005 by considering Poiseuille flow inside a nano-channel using molecular dynamics. The viscosity is determined by fitting the resulting velocity profile (away from the walls) to the continuum solution for a Newtonian fluid and then compared to experimental values. The results show that the TIP4P/2005 model gives the best prediction of the viscosity for the complete range of temperatures for liquid water, and thus it is the preferred water model of these considered here for simulations where the magnitude of viscosity is crucial. On the other hand, with the TIP4P model, the viscosity is severely underpredicted, and overall the model performed worst, whereas the SPC/E and TIP4P/Ew models perform moderately.

Micro-mechanism for the evolution of viscosity versus temperature in magnesium-aluminum alloy melts

The kinematic viscosity of magnesium-aluminum alloy melts was measured by using the crucible rotating oscillation damping method, and the viscosity-temperature relation curve v(T) in the temperature range of 850∼1200K was obtained. The viscosity changed abnormally with temperature in the heating process, i.e., the viscosity turned from rapid increase to gradual decrease when the temperature increased to 1000∼1100K, while the viscosity decreased exponentially with temperature in the subsequent cooling process. The microscopic mechanism of the evolution of viscosity was analyzed from the viewpoint of the micro-inhomogeneity theory of metallic melts, and it was found that the destruction of the structure of the β-like metastable phase (Mg17Al12) was the basic reason of the head-turning change of viscosity.

Study on glassy characteristics of dispersion transition in relaxor ferroelectrics

Based on the common behavior of the Vogel-Fulcher relation followed by both dielectric dispersion of relaxor ferroelectrics in transition region and the viscosity-temperature relation for glassy liquids in supercooled state, vacancy compensation principles of donor doped barium titanate systematic ceramics are analyzed. By the introduction of the concept of configurational entropy, the temperature dependent Ti cation vacancy reaction potential is investigated, and the results show that the increase in donor content gives rise to the increase in disorder degree, the increase in Ti cation vacancy content, and the decrease in size of average polar region; on condition that configurational entropy satisfies the Vogel-Fulcher relation, Ti cation vacancy reaction regime and therefore the polar region will both increase with temperature lowing, and the variation of the regime causes dielectric dispersion of relaxor ferroelectrics. Frozen effect happens and dispersion disappears for the Ti cation vacancy reaction at a certain lower temperature.