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Bioglass 45S5 is widely known for its ability to regenerate bone. However, this glass cannot be fully densified by viscous flow due to its very high tendency for crystallization. In this work, we evaluate the sintering and bioactivity of Bioglass 45S5-based compositions in which Na2O is incrementally replaced by K2O. Our sintering tests demonstrated that the densification of Bioglass 45S5 powders can be significantly enhanced due to a decreased crystallization tendency. The composition in which half of the original Na2O content was substituted by K2O exhibits the highest densification rate, evidencing the mixed alkali effect (MAE) in the viscous-flow-driven sintering process. The replacement of Na2O by K2O significantly improved both the densification rate and the in vitro performance. These results are very relevant for this particular glass and also for the design of new bioactive glasses with improved sinterability.

A two-dimensional viscous flow in a rough curved channel is investigated. The roughness are considered to be sinusoidal corrugations. The asymptotic solution is obtained using boundary perturbation technique for small amplitude of the corrugations. It is found that, for any radius of curvature, the flow rate is invariably decreased by the corrugations. The effect of corrugations on the flow rate increases with the corrugation wavenumber, as well as the phase difference between the corrugated curved walls. For sufficiently large corrugation wavenumbers, the phase difference between the corrugated walls becomes insignificant. The findings of this study indicate that a smooth curved channel with no corrugations, will give more flow rate than a corrugated curved channel, comparatively, for the same radius of curvature, as the flow resistance is relatively higher for the latter, due to the effects of the wall-surface roughness.

The effects of MgO/Al2O3 ratio on the viscous behaviors of MgO–Al2O3–TiO2–CaO–SiO2 systems were investigated by the rotating cylinder method. Raman spectroscopy was used to analyze the structural characteristics of slag and Factsage 7.0 was adopted to demonstrate the liquidus temperature of slag. The results show that the viscosity and activation energy for viscous flow decrease when the MgO/Al2O3 ratio increases from 0.82 to 1.36. The break point temperature and liquidus temperature of slag initially decrease and subsequently increase. The complex viscous structures are gradually depolymerized to simple structural units. In conclusion, with the increase of MgO/Al2O3 ratio, the degree of polymerization of slag decreases, which improves the fluidity of slag. The variations of liquidus temperature of slag lead to the same changes of break point temperature.

Cement emulsified asphalt composite binder (simplified as CEACB) is a type of composite binder existed in cement and asphalt mortar (simplified as CA mortar). The effects of freeze-thaw cycles on the dynamic mechanical properties of CEACB were analyzed based on viscoelastic mechanical model and dynamic frequency scanning test. The effects of freeze-thaw cycles, temperatures and mix proportions on the viscoelastic behavior of CEACB were analyzed. This study demonstrates that, as freeze-thaw cycles increasing, constitutive equation parameters E1 and η1 decrease, and r tends to increase. The ability of CEACB to resist elastic deformation and viscous flow is reduced, and CEACB shows a tendency of softening. With asphalt to cement ratio (A/C) increasing and temperature rising, both E1 and η1 decrease, while r increases, and CEACB tends to be like viscous material. As freeze-thaw cycles increasing, the pore content of CEACB increases. Freeze-thaw causes obvious structural damage and viscoelastic mechanical properties of CEACB were changed.

The densities, ρ, ultrasonic speeds, u and viscosities, η of the drug isoniazid in water and in aqueous– d -glucose/ d -sucrose (5 wt% and 10 wt% glucose/sucrose in water) solvents were measured at temperatures (293.15, 298.15, 303.15, 308.15, 313.15 and 318.15) K and at atmospheric pressure. The ρ, u and η data have been used to calculate apparent molar volumes, V ϕ , limiting apparent molar volumes, V ϕ ∘ , apparent molar compressibilities, K s , ϕ , limiting apparent molar compressibilities, K s , ϕ ∘ , transfer volumes, V ϕ , t r ∘ and transfer compressibilities, K s , ϕ , t r ∘ . The viscosity data have been used to determine Falkenhagen Coefficients, A and Jones-Dole coefficients, B. The calculated parameters have been discussed in terms of various solute-solute and solute-solvent interactions prevailing in these solutions. The structure making/breaking ability of isoniazid in these solutions has been examined by using the sign of dB/dT. Furthermore, the Gibbs energies of activation of viscous flow per mole of solvent, Δ μ 1 ∘ # and per mole of solute, Δ μ 2 ∘ # , enthalpies, Δ H ∘ and entropies, Δ S o of activation of viscous flow, were also calculated and discussed in terms of transition state theory.

The application of an unsteady viscous flow around a bluff body has covered a wide range of scientific fields. This paper reviews the wakes of different cross-sectional bluff bodies, including circular, square, triangular and rectangular cylinders. The two most prominent parameters (e.g., Reynolds number and cylinder geometry) that can significantly alter the wake are taken into account. The dependence on the two parameters of Strouhal number, vorticity, circulation, and efflux angle of vortices in the wake of bluff bodies is investigated. The detailed features of the wakes for different bluff-body shapes at different Reynolds are identified and summarized.

In this paper we investigated the viscosity and density of melts Fe73.5Cu1M3Si13,5B9 where M = Nb, Mo, V, Cr. It is shown that the lowest viscosity and activation energy of viscous flow has a melt with Nb, whose atomic radius is the largest. It is shown that the free volume of the melt is higher during cooling compared to heating, and it indicates irreversible structural changes in the melt. The critical temperature Tk = 1770 K is found, above which the activation energy of the viscous flow changes.

Hemodialysis is a common treatment for end-stage renal-disease patients to manage their renal failure while awaiting kidney transplant. Arteriovenous graft (AVG) is a major vascular access for hemodialysis but often fails due to the thrombosis near the vein-graft anastomosis. Almost all of the existing computational studies involving AVG assume that the vein and graft are rigid. As a first step to include vein/graft flexibility, we consider an ideal vein-AVG anastomosis model and apply the lattice Boltzmann-immersed boundary (LB-IB) framework for fluid-structure-interaction. The framework is extended to the case of non-uniform Lagrangian mesh for complex structure. After verification and validation of the numerical method and its implementation, many simulations are performed to simulate a viscous incompressible flow past the anastomosis model under pulsatile flow condition using various levels of vein elasticity. Our simulation results indicate that vein compliance may lessen flow disturbance and a more compliant vein experiences less wall shear stress (WSS).

Shape memory polymer composites (SMPCs) can be used to improve the mechanical properties of the shape memory polymers (SMPs). They also have the potential to enhance or enable new stimulus approaches and novel shape memory effects (SMEs). In this paper, a thermoviscoelastic finite deformation constitutive model is developed for thermally activated unidirectional continuous elastic fiber reinforced SMPCs. Since the structural relaxation and viscous flow mainly exist in the SMP matrix, an internal state variable modeling approach is used to describe the thermomechanical behavior of the SMPCs. Recent works mainly focus on the thermomechanical behavior of carbon fiber reinforced SMPCs in the small strain range, for the tensile tolerant strain of carbon fiber is small. The model that is developed here shows that the unidirectional continuous carbon fiber reinforced SMPCs with proper fiber inclination angle and volume fraction can also be used in finite deformation range for the first time. The finite deformation thermomechanical response of unidirectional continuous carbon fiber reinforced SMPCs with different inclination angles and volume fractions is addressed here. Therefore, this study provides useful guidance for reasonable design of unidirectional continuous elastic fiber reinforced SMPCs.

Von Karman swirling viscous flow due to an infinite rotating disk with uniform suction is investigated analytically, when the fluid at infinity is in a state of rigid body rotation. Different from previous results by numerical techniques or an asymptotic expansion method which is dependent on small or big values of the suction parameter, the analytical solution is independent of the suction parameter and uniformly valid for various values of suction parameter a , which helps to enrich the solution family of von Karman swirling viscous flow.

Transport property prediction of fatty acid methyl esters (FAMEs) is essential to its utilisation as biodiesel and biolubricant which can work under high-pressure conditions. Equilibrium molecular simulation is performed to study the viscosity, diffusivity, density and molecular structure dynamics at conditions up to 300 MPa. Among the transport properties, convergence of the viscosity needs a sufficiently large number of independent replications of the simulation. The system size effect on diffusion coefficient should be taken into consideration in fitting the Stokes-Einstein relation. The capability of three different force fields on predicting transport properties is evaluated in terms of the united-atom molecular model and all-atom molecular model. The solidification of FAMEs under high pressure occurs with parallel molecular alignment. The spatial inhomogeneity results in the breakdown of Stokes-Einstein relation. A hybrid effective hydrodynamic radius is established on the linear relation between experimental viscosity and diffusion coefficient in molecular simulation. This provides a predictive method to estimate viscosity from molecular diffusion coefficient over a broad range of conditions provided that Stokes-Einstein relation applies.

This paper discusses the modelling of CO 2 absorption in water as an absorbent via a hollow fiber membrane contactor to predict the performance of the absorption process under various operational conditions. The governing equations are two dimensional. Since, the gas diffusion along the pores is responsible for the mass transfer across the membrane thickness, i.e. both the skin layer and the membrane bulk, how to estimate the effective gas diffusivity has a vital degree of importance. When small pores combined with low pressures are dealt with, a challenging issue appears, i.e. the effective gas diffusivity is a contributive phenomenon, in which, several mechanisms are cooperated. Selecting an inappropriate model, inevitably leads to unrealistic values for the tuning parameters. Conventionally, the Bosanquet equation has been widely used for modelling the gas diffusivity through the membrane pores. In the current paper, it is intended to prove that the Bosanquet model is a limiting form of Wakao et al. model, when we are far enough from the continuum region. The modelling results are compared with six sets of different membranes from the open literature including high and low pressures. The results show that, ignoring the viscous flow contribution in D g,eff (the Bosanquet gas diffusivity model) causes underestimation of the absorption flux. Based on the observations, there is a meaningful consistency between the model and the experimental data once the contribution of the viscous flow in D eff (the Wakao et al. gas diffusivity model) is considered.

Thermoplastic polyimide (TPI) has a narrow processing temperature range, high viscosity, and high viscous flow temperature (Tf). These properties lead to difficulties in 3D printing and traditional forming with TPI owing to deformation caused by thermal stress, stratification, and other problems. The thermal stability of TPI raw materials and 3D printing filaments were analyzed in this study. Relationships between the Tf of the 3D printing filament and the starting printing temperature were studied. The influence of the 3D printing temperature on the interlayer bonding force of a 3D printed part was studied. The appropriate printing temperature range of TPI 3D printing was found to be 320–340 °C. When the printing temperature was 335 °C, the interlayer bonding force was 344.5 N. When the printing temperature was 340 °C, the interlayer bonding force decreased to 260.5 N. Within the appropriate 3D printing temperature range, complex TPI components with good interlayer bonding and high temperature resistance could be printed.

The deposition behavior of cold-sprayed metallic glass particles onto different metallic substrates was studied by numerical analysis and simulation using the ABAQUS/Explicit software. The mechanical response of a Vitreloy-1 particle was modeled accounting for the non-Newtonian and Newtonian regime of metallic glasses in the undercooled liquid state. The spreading, viscous dissipation and stress distribution of the metallic glass particle at impact showed a strong dependence on the substrate properties. By describing the rheological behavior of metallic glass particles according to the dynamics of viscous fluids, defining the impact Reynolds (Re) number, the Weissenberg (Wi) number and the Elasticity (El) number, the simulation results prove that shear thinning is the main deformation mechanism of metallic glass particles during impact, regardless of the substrate used. Specifically, a threshold value of Re exists, above which the MG particles undergo homogeneous flow, regardless of the substrate material. The generality of this finding is confirmed by its independence of the mathematical model used to describe substrate plasticity. However, the mechanical and thermal properties of the substrate have a strong influence on the shear thinning level experienced by particles impinging at Re values above the threshold. In this manner, the present study considers various aspects of relevant importance to build up metallic glass coatings by cold spray onto different metallic substrates.

In the lyophilization process for injections, the shelf temperature (Ts) and chamber pressure (Pc) have mainly been investigated to optimize the primary drying process. The objective of this study was to show that lyophilization of protein formulations can be achieved by adopting a fast ramp rate of Ts in the beginning of the primary drying process. Bovine serum albumin was used as the model protein, and seven different lyophilized formulations obtained were stored at elevated temperature. We found that although acceptable cake appearance was confirmed by the fast ramp cycle, all formulations of lyophilized cakes obtained by the slow ramp cycle severely collapsed (macrocollapse). It is thought that the collapse in the slow ramp cycle occurred during the shelf ramp in the beginning of primary drying and that insufficient removal of water from the dried matrix caused viscous flow (product collapse). Regarding storage stability, moisture-induced degradation was confirmed in some of the formulations prepared by the slow ramp cycle, whereas all lyophilized BSA formulations prepared by the fast ramp cycle were stable. Thus, the results indicate that the ramp rate appears to be one of the critical operational parameters required to establish a successful lyophilization cycle.

Densities, ρ, viscosities, η, and refractive indices, nD, were measured for the binary mixtures of tri-n-butyl phosphate (TBP) with toluene and ethylbenzene over the entire range of composition, and at different temperatures from T = (303.15 to 323.15) K. From experimental data of ρ, η, and nD, the excess molar volumes, VmE, partial molar volumes, V ¯ i , thermal expansivities, α, excess thermal expansivities, αE, deviations in viscosities, Δη, kinematic viscosities, ν, free energies, ∆G≠, excess free energies, ∆G≠E of viscous flow, deviations in refractive indices, ΔnD, and excess molar refractions, RmE, were calculated. To get the correlation coefficients and the relevant standard deviations, the values of ρ, η, and nD were correlated with concentration-dependent polynomial equations, whereas, those for the deviations/excess properties were fitted to the Redlich-Kister equation. Various laws of mixing for viscosities of liquid mixtures, such as, Grunberg-Nissan, Hind, Heric, Auslander, and McAllister, were investigated to check their correlating ability with these systems. Moreover, the temperature dependent Jouyban-Acree model was used to correlate the experimental values of ρ and η. For both systems, the signs of αE and ΔnD were found to be all negative and those of Δη were positive. Plots of VmE or RmE against the mole fraction of TBP were sigmoid and resembled with each other. These variation patterns were discussed in reference to the nature of molecular interactions taking place between the component liquids.

In this paper, a thermoviscoelastic constitutive model incorporating uncoupled structure and stress relaxation is proposed to capture the material behavior for thermally induced amorphous shape memory polymers. The leading particulars of this model is that the structure and stress relaxation mechanisms are not coupled but connected by the internal state variable which describes the degree of volume departure from equilibrium. Based on the internal variable, a simplified KAHR model is developed for the structure relaxation, and a new relaxation time model is proposed to describe the temperature and structure dependence of the characteristic stress relaxation. Moreover, the Eying model is modified by the new stress relaxation model to study the stress-activated viscous flow. Finally, the thermoviscoelastic constitutive model is applied to investigate the shape recovery behavior and the yielding and post-yielding behavior, and the simulation results show good agreement with the experimental data.

Zeins of differing sub-class composition much more readily formed visco-elastic masses in water or acetic acid solutions than equivalent kafirin preparations. Visco-elastic masses could be formed from both zein and kafirin preparations by coacervation from glacial acetic acid. Dissolving the prolamins in glacial acetic acid apparently enabled protonation and complete solvation. Stress-relaxation analysis of coacervated zein and kafirin visco-elastic masses showed they were initially soft. With storage, they became much firmer. Zein masses exhibited predominantly viscous flow properties, whereas kafirin masses were more elastic. The γ-sub-class is apparently necessary for the retention of visco-elastic mass softness with kafirin and zein, and for elastic recovery of kafirin. Generally, regardless of water or acetic acid treatment, all the zein preparations had similar FTIR spectra, with greater α-helical conformation, than the kafirin preparations which were also similar to each other. Kafirin visco-elastic masses have a much higher elastic character than zein masses.

An optimization model is established for the reaction process of CO2 hydrogenation to light olefins in a fixed-bed tubular reactor based on finite time thermodynamics or entropy generation minimization theory. In the present study, the specific generation rate (entropy generation rate averaged by the production rate of the target product) is proposed as an optimization objective function and the optimal design parameters which minimize the objective function have been investigated. The model is developed based on the reversible kenetic models and their cooresponding kinetic parameters, which are obtained by fitting the experimental data. The irreversibilities due to heat transfer, chemical reactions and viscous flow are considered and the local entropy generation rate of each term is calculated according to the irreversible thermodynamics. The analyses of the performance characteristics are conducted as well. The results show that the CO2 hydrogenation to light olefins accords with a two-step reaction mechanism, and Fischer-Tropsch reaction is the rate-controlling step. The irreversibility mainly located in the front of the reactor, which most contributions are caused by chemical reactions. The reductions of the specific entropy generation up to 24.78% and 10.04% can be achieved for optimal reactor inner diameter and optimal catalyst bed density, respectively.

In this paper, the theoretical framework of viscous flow deformation is presented as a model to investigate the inherent role of applied pressure in the densification of Fe-based amorphous alloy powder during spark plasma sintering. The proposed model revealed that the evolution of the structural geometry of the powder compact resulted in an amplification of the applied pressure to a larger contact pressure. The resulting pressure controlled compressive viscous flow deformation of the particles exhibited the contribution of increased applied pressure towards enhancement of densification and thus confirmed the validity of the present model for analyzing pressure-assisted sintering of amorphous alloy powder. The application of this theoretical model correctly predicted the trend of increasing final density of the compacts with pressure while further improvement on its accuracy can be attained upon establishment of the relative contribution of mass flow and deformation of powder particles towards their consolidation.

In this study, model Ⅰ fracture toughness of three-dimensional random fibrous (3D RF) materials with a porosity of 83% is investigated from room temperature to 1273 K by performing experiments with compact tension (CT) specimens in the through-the-thickness (TTT) and in-plane (IP) directions. The experiments show that the fracture toughness in the TTT and IP directions increases from 0.0842 to 0.1162 MPa·m1/2 and 0.4292–0.6767 MPa·m1/2, respectively, with increasing temperature until a critical temperature (1073 K and 1223 K, respectively) is reached, following which the fracture toughness decreases from 0.1162 to 0.0819 MPa·m1/2 and from 0.6767 to 0.6170 MPa·m1/2, respectively. The significant changes at elevated temperatures are directly attributed to the viscous flow of the crack tip. In addition, a viscous flow contribution to the fracture surface energy of the 3D RF material is identified at high temperatures. The curves of the fracture surface energy versus temperature data for the TTT and IP directions can be partitioned into sections by fitting with experimental observations. Based on the two fitted curves, we calculate the activation energy of the viscous flow in the TTT and IP directions as 220.3 kJ/mol and 892.2 kJ/mol, respectively.

Depleted hydrocarbon reservoirs have been gradually recognized as the potential candidates for geological storage of carbon dioxide due to their wide geographical spread and large storage capacity. Reliably assess CO2 geosequestration capacity (CGC) of depleted hydrocarbon reservoirs lays the foundation of CO2 long-term geosequestration security. In this study, a model, considering CO2 viscous flow, diffusion, and adsorption in shale reservoirs, is established to determine bottom-hole pressure during CO2 injection through a hydraulic fractured multiwell-pad. The computational efficient semi-analytical solution is obtained by superposition principle and Laplace numerical inverse technique. Applying the developed model, a workflow is accordingly proposed to evaluate CGC of depleted shale reservoirs. As a case verification, the calculation on the CGC of a depleted shale reservoir from Barnett Shale in Texas is conducted, which illustrates that its CGC reaches up to 3.8 × 1012m3 when the constrained injection pressure (CIP) is high. Moreover, sensitivity analyses suggest that most reservoir parameters exhibit ignorable impacts on CGC when CIP is low whereas their effects on CGC are significant at high CIP. For instance, for the low-CIP, CGC just increases by approximately 6.7% when adsorption index increases from 2.5 to 250. As for the high-CIP scenario, CGC significantly increases 164 times for the same adsorption index range. In contrast to reservoir parameters, engineering parameters generally show great impacts on CGC at low CIP whereas their effects on CGC are negligible when CIP is high. To be more specific, CGC increases by 2.42 times when injection rate ratio of two wells ranges from 8 to 0.5 under low-CIP condition whereas CGC increases just by 0.47 times when CIP is high. The findings obtained in this study pave the way for the long-term CO2 geosequestration in depleted hydrocarbon reservoirs with much less efforts.

Von Karman swirling viscous flow produced by an infinite rotating disk is investigated, both analytically and numerically, when the fluid at infinity is in a state of rigid body rotation. The analytical solution branch of the problem considered are shown conveniently when the fluid at infinity is rotating with a different ratio, 0 ≤ s ≤ 1, of the angular velocity to that of the disk. As for − 0.1575 ≤ s

Numerical model is a powerful tool in the solid oxide fuel cell (SOFC) study, but its application is seriously restricted by the tremendous demand of computational resources and time due to the high aspect ratio of functional layers. In this paper, the wall-function method widely used in turbulent flow model is introduced to simplify the SOFC model. By analyzing the similarity in SOFC functional layers to the viscous flow nearby wall, a set of wall functions is developed to calculate the generating current in functional layers instead of the traditional complex partial differential equations. Compared with traditional full 3D model, the simplified model based on wall-function method shows similar accuracy but uses only about one third mesh elements and spends less than a half of solution time. Numerical results show that there are two important advantages for the wall-function method: 1) it allows a coarse mesh which can significantly reduce the computational storage and time; 2) it allows the introduction of other information in wall-functions and uses denser points in thickness direction which can considerably improve the accuracy of model.

In this paper, the local behavior of the jet induced by the fluid impact is studied by a new viscous-inviscid interaction (VII) method. This method is based on the inviscid Eulerian-Langrangian (IEL) scheme implemented by the boundary element method (BEM), but it places additional sources on the wetted walls to model the viscous flow within the thin boundary layer. The volume of fluid (VOF) method is also carried out to compare the numerical boundary-layer patterns. The present method not only shows good agreement with the experimental results but also remains very efficient.

The effect of MnO and CaO substitution for BaO on the viscosity and structure of CaO-SiO2-MgO-Al2O3-BaO-MnO slag was investigated using the rotating cylinder method and the structure was analyzed by employing FT-IR and XPS. The results showed that the viscosity at various temperatures decreased gradually when MnO content increased from 0wt% to 3wt%, and increased with BaO content rising from 0wt% to 5wt%, which was consistent with the corrected optical basicity (Λcorr). The activation energy for viscous flow (Eη) showed the similar trend. FT-IR and XPS spectra analysis indicated that both [SiO4]-tetrahedral and [AlO4]-tetrahedral were influenced by MnO and BaO content. The [SiO4]-tetrahedral and [AlO4]-tetrahedral network structures were depolymerized due to an increase in the relative fraction of free oxygen (O2−) and decrease of bridging oxygen (O0) with the increasing MnO content. As a larger amount of CaO was substituted by BaO, the trough depth of [SiO4]-tetrahedral and [AlO4]-tetrahedral bands became deeper, indicating the complexity of network structure and polymerization degree of slag increased, which led to an increase in viscosity.

Source-rock permeability is a key parameter that controls the gas production rate from unconventional reservoirs. Measured source-rock permeability in the laboratory, however, is not an intrinsic property of a rock sample, but depends on pore pressure and temperature as a result of the relative importance of slip flow and diffusion in gas flow in low-permeability media. To estimate the intrinsic permeability which is required to determine effective permeability values for the reservoir conditions, this study presents a simple approach to correct the laboratory permeability measurements based on the theory of gas flow in a micro/nano-tube that includes effects of viscous flow, slip flow and Knudsen diffusion under different pore pressure and temperature conditions. The approach has been verified using published shale laboratory data. The “corrected” (or intrinsic) permeability is considerably smaller than the measured permeability. A larger measured permeability generally corresponds to a smaller relative difference between measured and corrected permeability values. A plot based on our approach is presented to describe the relationships between measured and corrected permeability for typical Gas Research Institute permeability test conditions. The developed approach also allows estimating the effective permeability in reservoir conditions from a laboratory permeability measurement.

We report on the formulation of a factor, f , that when applied together with the activation energy for viscous flow ( Q ), can be used to provide important insight into the densification mechanism that are active during powder sintering. We ascertain the validity of this formulation by comparing the densification behaviour of atomized and milled powders for Ti-6Al-4V alloy and pure Ti during spark plasma sintering, and identifying the underlying mechanisms.

The self-healing behavior of MoSi 2 /borosilicate glass composite was investigated by comparing the flexure strength of pre-scratched specimens before and after healing treatment. The post-healing strength partially recovered when healing temperature was higher than 800 °C, and the healing of the scratch was observed after healing treatment at 900 °C and 1400 °C. Two kinds of possible mechanisms were proposed on the basis of morphology and elemental analyses of healing areas. The specimen treated at 900 °C showed a porous healing area and the strength recovered 28.6% resulted from the oxidation of MoSi 2 into MoO 3 and SiO 2 . By contrast, the specimen treated at 1400 °C had a dense healing area and the strength recovered 86.9% due to the viscous flow of borosilicate glass.

Density (ρ) and kinematic viscosity (μ) are important physical properties of biodiesel. They are directly affected by both temperature and pressure. Accordingly, models which correlate density and kinematic viscosity of fatty acid methyl ester (FAME) and biodiesel to their carbon numbers, number of double bonds of fatty acid are proposed. Gibbs free energy additivity is used as an alternative approach to quantitative structure-property relationship (QSPR) in estimating density and kinematic viscosity at high temperature and pressure of FAME and biodiesel. It is one of the best models for estimating density of FAME, mixtures of FAMEs or biodiesels and biodiesel blends at different temperatures (283.15–333.15 K) and pressures (0.2–40 MPa). For kinematic viscosity, the model is simply derived from the sum (or subtraction) of the Gibbs energies of dynamic viscous flow and volumetric expansion. Thus, this is the first model proposed for prediction of kinematic viscosity of FAME and biodiesel ay different temperatures and pressures. Because there is no experimental value in the literature, the accuracy of the model is tested against the experimental density and experimental dynamic viscosity (η) via the classical equation (μ = η/ρ).

Fast and accurate airfoil design under uncertainty using non-intrusive polynomial chaos (NIPC) expansions and utility functions is proposed. The NIPC expansions provide a means to efficiently and accurately compute statistical information for a given set of input variables with associated probability distribution. Utility functions provide a way to rigorously formulate the design problem. In this work, these two methods are integrated for the design of airfoil shapes under uncertainty. The proposed approach is illustrated on a numerical example of lift-constrained airfoil drag minimization in transonic viscous flow using the Mach number as an uncertain variable. The results show that compared with the standard problem formulation the proposed approach yields more robust designs. In other words, the designs obtained by the proposed approach are less sensitive to variations in the uncertain variables than those obtained with the standard problem formulation.

The densification mechanism of amorphous Fe 48 Cr 15 Mo 14 Y 2 C 15 B 6 alloy powder during isochronal spark plasma sintering was analyzed to determine the innate function of high heating rates. Densification ensued and concluded at gradually lower temperatures while attaining higher maximum rates with increasing heating rates in the first stage. The shrinkage behavior analyzed under the theoretical framework of viscous flow revealed a steady reduction in the activation energy leading to a resultant enhancement of densification rate in the initial stage.

The Helvetic nappe system exhibits three-dimensional (3-D) features such as the lateral variation in geometry between the Morcles and Doldenhorn fold nappes or the Rawil depression. We perform 3-D finite element simulations of linear and power-law viscous flow to investigate fold nappe formation during shortening of a half graben with laterally varying thickness. 3-D ellipsoids and corresponding 2-D intersection ellipses are used to quantify finite strain. Fold nappes which formed above a thicker graben have (i) larger amplitudes, (ii) a less sheared and thinned overturned limb, and (iii) a larger thickness than fold nappes formed above a thinner graben. These results agree with observations for the Morcles and Doldenhorn nappes. We also perform 3-D simulations for a tectonic scenario suggested for the evolution of the Rawil depression. The basement is shortened and extended laterally and includes a graben which is oblique to the shortening direction and acts as mechanical weak zone. The graben causes laterally varying basement uplift generating a depression whose amplitude depends on the graben orientation and the stress exponent of basement and sediments. The axial plunge of the depression is smaller (approximately 10°) than the observed plunge (approximately 30°) indicating that additional processes are required to explain the geometry of the Rawil depression.

The sinterability of fumed silica composites used for thermal insulation is strongly activated by TiB 2 additions. Shrinkage kinetics measured by dilatometry are in good agreement with viscous flow model predictions. In these materials, mass transport is accelerated after TiB 2 oxidation, which starts around 450 °C. This is due to the formation of small liquid pockets by reaction between boron containing oxides and the surrounding fumed silica particles. At temperatures below 1000 °C, activation energies calculated from shrinkage data are close to those reported for silica gels. At higher temperatures, activation energies are much higher due to the rapid loss of surface area. TiB 2 additions also induce a hardening effect that can be used to improve the material consistency after sintering.

Dense mullite–Mo (45 vol%) composites with homogeneous microstructure have been obtained by plasma activated sintering of a mixture of Mo and mullite precursors at a relatively low temperature (1350 °C) and a pressure of 30 MPa. The mullite precursor was synthesized by a sol–gel process followed by a heat-treatment at 1000 °C. The influence of different mullite precursors on the densification behavior and the microstructure of mullite–Mo composites has been studied. The precursor powder heat-treated at 1000 °C with only Si–Al spinel but no mullite phase shows an excellent sintering activity. Following the sintering shrinkage curves, a two-stage sintering process is designed to enhance the composite densification for further reducing the sintering temperature. The study reveals that viscous flow sintering of amorphous SiO2 at low temperatures effectively enhances the densification. Moreover, microstructure of these composites can be controlled by selecting different precursors and sintering temperatures.

Hydrogen bonding as a commonly used dynamic crosslink in elastomers suffered from inefficient stability against elevated temperature or low tensile rate. Herein, a bioinspired strategy was developed to retard the dissociation process, therefore resulting in mechanically strong and stable thermoplastic polyisoprene. Specifically, penta-alanine groups pendant on polyisoprene assemble into β-sheets and serve as crosslinkers, which usually are unstable and disassemble at moderate temperature or low tensile rate. In this work the addition of Ca2+ ions will destroy partial β-sheet structures, but at the same time coordinate with peptide aggregates and retard the dissociative process of hydrogen bonding against either the increase of temperature or stretching speed in a controlled manner. Stress relaxation test showed that the activation energies for viscous flow and relaxation time below 127 °C are obviously increased after the addition of Ca2+ ions. The mechanism study showed that the well mixing of calcium salt and peptide phase in polyisoprene matrix is critical for the formation of coordination interactions, which manipulate the dissociation of peptide aggregates. This strategy represents a feasible approach to tune the viscoelastic response of elastomers in a wide range.

The amino acid-drug interactions have been examined by using measurements of physical properties, such as densities, ρ, ultrasonic speeds, u and viscosities, η of glycine, l-alanine, l-valine and l-isoleucine in aqueous-gentamicin sulphate solvents at the temperatures from 293.15 to 318.15 K with intervals of 5 K. The ρ data are used to calculate the apparent molar properties, Vϕ, Vϕ° and the transfer volumes, Vϕ,tr°. From the u data, the apparent molar isentropic compressibilities, Ks,ϕ, Ks,ϕ° and the transfer compressibilities, Ks,ϕ,tr° have been evaluated. The η data were used to evaluate Falkenhagen coefficient, A, Jones-Dole coefficient, B. The enthalpies, ΔH°# and entropies, ΔS°# and activation parameters, Δμ1°# and Δμ2°# of viscous flow were also calculated. The effect of concentration, temperature and solute structure were discussed in terms of solute-solvent and solute-solute interactions prevailing in these systems. The structure making/breaking ability of amino acids has also been examined using temperature derivative of B-coefficient, dB/dT. In addition, the values of Vϕ°, Ks,ϕ°, B and Δμ2°# have also been split into groups’ contributions of the amino acids.

Owing to the micrometric size of the probed volume and the minute duration of a test, microindentation provides a unique tool to characterize the non-aging creep properties of a cement paste in hygral equilibrium. Microindentation techniques have been emerging as rapid technique to characterize the logarithmic creep rate of cement pastes. The objective of this study is to develop the analytical microindentation solutions of modern creep models, such as Microprestress-Solidification theory (MPS), Generalized Kelvin-Voigt model (GKV), and a recent microindentation two-fold creep model (M2C), which considers viscoelastic strain in series with a viscous flow strain of which viscosity is exponentially dependent on the viscous flow deformation, to provide a rapid calibration method. To minimize the effect of residual clinker, a cement paste with a water-to-cement ratio of 0.42 was cured for one year before testing. Subsequently, a microindentation grid of both creep and relaxation tests was carried out by employing a spherical tip at low penetration depth to reduce inelastic deformation. The microindentation analytical solutions of the aforementioned creep models were developed and its dual relaxation response was numerically developed. Microindentation creep and relaxation tests were employed to calibrate and validate the creep parameters, respectively. While microindentation allowed identifying the parameters of the considered creep models in a satisfactory manner, the implemented M2C creep model permitted to gain insight into the two-fold basic creep mechanism from a microindentation perspective.

The activation parameters of viscous flow can be used to probe the molecular interactions in fluids from viscosity experimental data. They are assessed by mathematical derivations of the Eyring equation, but differences in these derivations can generate parameters that lead to conflicting interpretations. In this work, a new method for the estimation of the activation parameters of viscous flow is proposed and compared with two other methods previously reported in the literature. It is shown that the new method is the only presenting theoretically consistent trends, as confirmed by its application to alkanes and ionic liquids.

Metamaterials have allowed unprecedented control of physical fields by harnessing material tensors derived from coordinate-transformation of governing equations. Among them, hydrodynamic metamaterials have recently received immense interests, showing the possibility of viscous flow control. However, the extant metamaterials cannot work for laminar flow which accompanies inertia force as well as viscous force. Herein, we propose a novel methodology for manipulating laminar flow to use the material tensors derived from the coordinate-transformed Navier–Stokes equations. The laminar flow manipulators for cloaking, concentrating, and rotating hydrodynamic flows are implemented numerically by applying both tensoric viscosity and density. The tensors give a direction for designing and fabricating metamaterials to control laminar flow.

The present paper derives a simple analytical approximation for hydrodynamic permeability of a membrane. Numerical results of the hydrodynamic permeability calculation in the framework of the cell model technique are used. The membranes considered include spherical cells of various structure: a simple solid–liquid, a porous-liquid, and a solid-porous-liquid cell in a viscous flow. The paper provides maximally brief and simple dependences of hydrodynamic permeability on the cell structure and liquid characteristics which are validated via the least-squares method.

The forces and moments on slender axisymetric bodies are studied using a hydrodynamic impulse formulation for viscous flow in non-inertial body frames of reference. The problems of steady translation and steady turning are specifically addressed. A computational fluid dynamics data base is used to evaluate the hydrodynamic impulse for 3 submarine shaped bodies with slenderness ratios of 7.35, 8.38, and 8.75. It was found that the forces and moments calculated using the hydrodynamic impulse formulation give equivalent forces and moment to the traditional method of integrating pressure and shear stress on the body. In addition, it is shown that the lateral force distribution can be calculated directly from the Lamb vector distribution over cross sectional planes. Linearized forms of the hydrodynamic impulse equations are derived for both translation and steady rotation.

An improved bubble breakup model has been developed by adequately describing the internal flow inside the deformed bubble, to account for the significant effect of pressure on the bubble breakup behaviors and hydrodynamics in a bubble column. In this new model, several significant conditions and experimental findings, such as static stress analysis, interfacial stress of bubble neck, viscous flow resistance, were taken into account. These issues were not considered and led to under-predictions of the bubble breakup rate in our previous model. The bubble breakup rate and daughter bubble size distribution predicted by this improved model were consistent with available experimental data. Moreover, this bubble breakup model was directly used in the CFD-PBM model to numerically simulate a bubble column operated at different pressures. A good agreement between the simulated and experimental results was obtained under complex operating conditions.

An investigation has been made into the nonlinear aeroelastic behavior of an airfoil system with free-play nonlinear stiffness in transonic flow. Computational Fluid Dynamics (CFD) and Reduced Order Model (ROM) based on Euler and Navier-Stokes equations are implemented to calculate unsteady aerodynamic forces. Results show that the nonlinear aeroelastic system experiences various bifurcations with increasing Mach number. Regular subcritical bifurcations are observed in low Mach number region. Subsequently, complex Limit Cycle Oscillations (LCOs) and even non-periodic motions appear at specific airspeed regions. When the Mach number is increased above the freeze Mach number, regular subcritical bifurcations occur again. Comparisons with inviscid solutions are used to identify and elaborate the effect of viscosity with the help of aeroelastic analysis techniques, including root locus, Single Degree of Freedom (SDOF) flutter and aerodynamic influence coefficient (AIC). For low Mach numbers in the transonic regime, the viscosity has little effect on the linear flutter characteristic because of limited influence on AIC, but a remarkable impact on the nonlinear dynamic behavior due to the sensitivity of the nonlinear structure. As the Mach number increases, the viscosity becomes significantly important due to the existence of shock-boundary layer interaction. It affects the unstable mechanism of linear flutter, impacts the aerodynamic center and hence the snap-through phenomenon, influences the AIC and consequently the nonlinear aeroelastic response. When the Mach number is increased further, the shock wave dominates the air flow and the viscosity is of minor importance.

The no-slip condition of the viscous flow theory on the contact line is violated, where an interface between two fluids reaches the solid surface. Despite over a century of the scientific research, slip on the contact line is an issue that is still being debated. In this paper we present a theoretical discussion of the slip origin. The basic assumption is that the mechanism of slippage for liquid and gas on the wall is same. The idea is that, on the contact line, the tangential velocity of liquid molecules after collision with the surface by liquid and gas molecules is not diminished sufficiently, and this provides a way for liquid molecules to slip on the surface. In addition, from contact line toward liquid phase, with the increase in the number of liquid molecules and the collisions, the tangential velocity of the molecules decrease gradually and the no-slip state is dominated.

An efficient compatibility criterion is proposed to solve the nonlinear boundary problem arising in the study of the classical problem of viscous fluid flow due to a stretching sheet due to Crane (Crane, 1970). The compatibility and generalized group analysis make it simple to obtain the exact solution of the classical boundary layer problem.

In this paper, the liquid structure of Zn 100 − x Bi x ( x = 5, 20, 40, 63, 80, 95) alloys were studied with resistivity and viscosity (for Zn 20 Bi 80 and Zn 80 Bi 20 alloys). The resistivity descends linearly and clusters size and viscous flow activation energy increase exponentially with the decreasing temperature for Zn 20 Bi 80 alloy. For Zn 80 Bi 20 alloy, viscous flow activation energy increases like parabola at temperatures 711 to 861 K and exponentially at temperatures from 886 to 1086 K and descends at temperature between 861 and 886 K. The resistivity curve is linear and parabolic at temperatures from 838 to 1085 K and 690 to 838 K respectively during cooling process, which is in accord with clusters size. There are differences of isothermal resistivity tendency between heating and cooling process. It has been found that the size of the fluid clusters is in negative correlation with resistivity and positive correlation with viscous flow activation energy. Resistivity is commonly controlled by the size of the fluid clusters and interface. The composition dependence of resistivity shows that the clusters are mainly composed of Bi–Bi coordination and the contribution of clusters to resistivity is related with the volume percentage of clusters in Zn–Bi alloy.

In microfluidic applications, the beating behaviors of artificial cilia determine the efficacy of artificial cilia-based micromixers. The same is especially true when the rapid mixing of two fluids with artificial cilia actuation is highly demanded in many biomedical and analytical chemistry contexts. The transient hydrodynamics induced by the diversely dynamic motions of artificial cilia and the associated interactions with surrounding flow fields engender speculation for identifying an ideal trajectory of artificial cilia in an effective micromixing process. Intrigued by this motive, we selected four distinct beating behaviors for comparing micromixing performance. The tangled interactions between the induced flow by artificial cilia and the imposing flow through syringe pump actuation were also documented. A parametric study was performed via a micro-particle image velocimetry technique to elucidate the synergic effects contributed by dominant parameters, such as the beating speed and patterns of artificial cilia. Depth-resolved induced flow patterns through artificial cilia actuation were provided using a computational fluid dynamic method to elucidate how micromixing was achieved in a whole-field point of view. A new microscale flow mixing concept was therefore initiated and demonstrated in this work to extend the current practices related to artificial cilia-based micromixers for highly viscous flow manipulation applications.

The present analysis is based upon the numerical solution of the full Navier-Stokes equations for laminar viscous flow. The convection-diffusion model is used for the determination of the flow particle concentration and the formation of typical sedimentation zones. The results are compared with available experimental data.