Blood viscosity in tube flow: dependence on diameter and hematocrit.
Pries, A R; Neuhaus, D; Gaehtgens, P
1992-12-01
Since the original publications by Martini et al. (Dtsch. Arch. Klin. Med. 169: 212-222, 1930) and Fahraeus and Lindqvist (Am. J. Physiol. 96: 562-568, 1931), it has been known that the relative apparent viscosity of blood in tube flow depends on tube diameter. Quantitative descriptions of this effect and of the dependence of blood viscosity on hematocrit in the different diameter tubes are required for the development of hydrodynamic models of blood flow through the microcirculation. The present study provides a comprehensive data base for the description of relative apparent blood viscosity as a function of tube diameter and hematocrit. Data available from the literature are compiled, and new experimental data obtained in a capillary viscometer are presented. The combined data base comprises measurements at high shear rates (u > or = 50 s-1) in tubes with diameters ranging from 3.3 to 1,978 microns at hematocrits of up to 0.9. If corrected for differences in suspending medium viscosity and temperature, the data show remarkable agreement. Empirical fitting equations predicting relative apparent blood viscosity from tube diameter and hematocrit are presented. A pronounced change in the hematocrit dependence of relative viscosity is observed in a range of tube diameters in which viscosity is minimal. While a linear hematocrit-viscosity relationship is found in tubes of < or = 6 microns, an overproportional increase of viscosity with hematocrit prevails in tubes of > or = 9 microns. This is interpreted to reflect the hematocrit-dependent transition from single- to multifile arrangement of cells in flow. PMID:1481902
Calculated viscosity-distance dependence for some actively flowing lavas
NASA Technical Reports Server (NTRS)
Pieri, David
1987-01-01
The importance of viscosity as a gauge of the various energy and momentum dissipation regimes of lava flows has been realized for a long time. Nevertheless, despite its central role in lava dynamics and kinematics, it remains among the most difficult of flow physical properties to measure in situ during an eruption. Attempts at reconstructing the actual emplacement viscosities of lava flows from their solidified topographic form are difficult. Where data are available on the position of an advancing flow front as a function of time, it is possible to calculate the effective viscosity of the front as a function of distance from the vent, under the assumptions of a steady state regime. As an application and test of an equation given, relevant parameters from five recent flows on Mauna Loa and Kilauea were utilized to infer the dynamic structure of their aggregate flow front viscosity as they advanced, up to cessation. The observed form of the viscosity-distance relation for the five active Hawaiian flows examined appears to be exponential, with a rapid increase just before the flows stopped as one would expect.
Two-Phase Flow in Porous Media: Predicting Its Dependence on Capillary Number and Viscosity Ratio
Ferer, M.; Anna, Shelley L.; Tortora, Paul; Kadambi, J. R.; Oliver, M.; Bromhal, Grant S.; Smith, Duane H.
2011-01-01
Motivated by the need to determine the dependencies of two-phase flow in a wide range of applications from carbon dioxide sequestration to enhanced oil recovery, we have developed a standard two-dimensional, pore-level model of immiscible drainage, incorporating viscous and capillary effects. This model has been validated through comparison with several experiments. For a range of stable viscosity ratios (M=μ_{injected,nwf}/μ_{defending,wf} ≥ 1), we had increased the capillary number, N_{c} and studied the way in which the flows deviate from fractal capillary fingering at a characteristic time and become compact for realistic capillary numbers. This crossover has enabled predictions for the dependence of the flow behavior upon capillary number and viscosity ratio. Our results for the crossover agreed with earlier theoretical predictions, including the universality of the leading power-law indicating its independence of details of the porous medium structure. In this article, we have observed a similar crossover from initial fractal viscous fingering (FVF) to compact flow, for large capillary numbers and unstable viscosity ratios M < 1. In this case, we increased the viscosity ratio from infinitesimal values, and studied the way in which the flows deviate from FVF at a characteristic time and become compact for non-zero viscosity ratios. This crossover has been studied using both our pore-level model and micro-fluidic flow-cell experiments. The same characteristic time, τ = 1/M^{0.7}, satisfactorily describes both the pore-level results.
Time-dependent convective flows with high viscosity contrasts under micro gravity conditions.
NASA Astrophysics Data System (ADS)
Zaussinger, Florian; Egbers, Christoph; Krebs, Andreas; Schwarzbach, Felix; Kunze, Christian
2015-04-01
Thermal driven convection in spherical geometry is of main interest in geo- and astrophysical research. To capture certain aspects of temperature dependent viscosity we investigate the micro-gravity experiment GeoFlow-IIb, located on the ISS. This unique experimental setup consists of a bottom heated and top cooled spherical gap, filled with the silicon oil 1-Nonanol. However, rotation and varying temperature gradients can be applied, to spread the experimental parameter space. The main focus of the current mission is the investigation of time dependent convective flow structures. Since the ISS requirements makes it impossible to use tracer particles, the flow structures are captured by interferometry, whose outcome is analysed by an ground based adapted image processing technique. To guarantee valid results the experimental time of each parameter is in the order of the thermal time scale, which is about 40 min. We are presenting latest results of plume-like and sheet-like time-dependent convective patterns in the spherical shell, their evolution and temporal behaviour under high viscosity contrasts. Due to an unexpected nonlinear coupling between the temperature dependent viscosity of the working fluid and the applied dielectrophoretic force field, we are able to maintain a viscosity contrast of 50 and more. This gives the chance to compare cautiously our experimental results with theoretical assumptions of the mantle convection theory. Besides, numerical simulations in the same parameter regime are performed, which give the opportunity to deduce the internal structure of the experimental flow flied. The main focus of the presented results are the long time temporal evolution of convective plumes in the spherical gap, image capturing- and processing techniques and the deduction of the internal flow field based on planar interferometry pictures.
Thin film flow in MHD third grade fluid on a vertical belt with temperature dependent viscosity.
Gul, Taza; Islam, Saed; Shah, Rehan Ali; Khan, Ilyas; Shafie, Sharidan
2014-01-01
In this work, we have carried out the influence of temperature dependent viscosity on thin film flow of a magnetohydrodynamic (MHD) third grade fluid past a vertical belt. The governing coupled non-linear differential equations with appropriate boundary conditions are solved analytically by using Adomian Decomposition Method (ADM). In order to make comparison, the governing problem has also been solved by using Optimal Homotopy Asymptotic Method (OHAM). The physical characteristics of the problem have been well discussed in graphs for several parameter of interest. PMID:24949988
Thin Film Flow in MHD Third Grade Fluid on a Vertical Belt with Temperature Dependent Viscosity
Gul, Taza; Islam, Saed; Shah, Rehan Ali; Khan, Ilyas; Shafie, Sharidan
2014-01-01
In this work, we have carried out the influence of temperature dependent viscosity on thin film flow of a magnetohydrodynamic (MHD) third grade fluid past a vertical belt. The governing coupled non-linear differential equations with appropriate boundary conditions are solved analytically by using Adomian Decomposition Method (ADM). In order to make comparison, the governing problem has also been solved by using Optimal Homotopy Asymptotic Method (OHAM). The physical characteristics of the problem have been well discussed in graphs for several parameter of interest. PMID:24949988
VERTICAL STRUCTURE OF TIME-DEPENDENT FLOW FOR VISCOSITY THAT DEPENDS ON BOTH DEPTH AND TIME
A previously developed eigenfunction expansion, that describes horizontal current as a function of depth and time, is extended to include any eddy viscosity given as a product of a function of depth and a function of time. (Copyright (c) 1982 American Meteorological Society.)
NASA Astrophysics Data System (ADS)
Jang, Seok Pil; Lee, Ji-Hwan; Hwang, Kyo Sik; Choi, Stephen U. S.
2007-12-01
An experimental and theoretical investigation has been performed on the effective viscosity of Al2O3-water nanofluids flowing through micrometer- and millimeter-sized circular tubes in the fully developed laminar flow regime. We have discovered that the effective viscosity of Al2O3-water nanofluids increases nonlinearly with the volume concentration of nanoparticles even in the very low range of 0.02-0.3vol% and strongly depends on the ratio of the nanoparticle diameter to the tube diameter. We have developed a modified Einstein model that accounts for the slip mechanism in nanofluids. The new model captures these new rheological features of nanofluids.
Numerical study on the fluid flow pass a square cylinder: The temperature-viscosity dependence
NASA Astrophysics Data System (ADS)
Lu, Jianhua; Li, Sheng; Guo, Zhaoli; Shi, Baochang
2014-10-01
In this paper, the 2D fluid flow pass a heated/cooled square cylinder exposed to a constant free-stream upward velocity is simulated via a multiple relaxation time (MRT) lattice-Boltzmann (LB) method. The buoyancy effect on the drag and lift coefficients as well as Nusselt number related is compared with the results in the existing literatures to validate the code used. The effect of temperature-viscosity dependence is then investigated to test whether the effect can be neglected or not for the mixed convection case. It is shown that the effect cannot be ignored when |Ri| > 0.15. Fortunately, the effect can be captured by using an effective temperature formula [J. M. Shi, D. Ferlach, M. Breuer, G. Biswas and F. Durst, Phys. Fluids16, 4331 (2004)] in a rather large range of Ri. All the numerical results, from another angle, also demonstrate that the MRT method is an efficient tool in simulating the problems such as the present one.
NASA Astrophysics Data System (ADS)
Boufadel, Michel C.; Suidan, Makram T.; Venosa, Albert D.
1999-04-01
We present a formulation for water flow and solute transport in two-dimensional variably saturated media that accounts for the effects of the solute on water density and viscosity. The governing equations are cast in a dimensionless form that depends on six dimensionless groups of parameters. These equations are discretized in space using the Galerkin finite element formulation and integrated in time using the backward Euler scheme with mass lumping. The modified Picard method is used to linearize the water flow equation. The resulting numerical model, the MARUN model, is verified by comparison to published numerical results. It is then used to investigate beach hydraulics at seawater concentration (about 30 g l -1) in the context of nutrients delivery for bioremediation of oil spills on beaches. Numerical simulations that we conducted in a rectangular section of a hypothetical beach revealed that buoyancy in the unsaturated zone is significant in soils that are fine textured, with low anisotropy ratio, and/or exhibiting low physical dispersion. In such situations, application of dissolved nutrients to a contaminated beach in a freshwater solution is superior to their application in a seawater solution. Concentration-engendered viscosity effects were negligible with respect to concentration-engendered density effects for the cases that we considered.
Compositional dependence of lower crustal viscosity
NASA Astrophysics Data System (ADS)
Shinevar, William J.; Behn, Mark D.; Hirth, Greg
2015-10-01
We calculate the viscosity structure of the lower continental crust as a function of its bulk composition using multiphase mixing theory. We use the Gibbs free-energy minimization routine Perple_X to calculate mineral assemblages for different crustal compositions under pressure and temperature conditions appropriate for the lower continental crust. The effective aggregate viscosities are then calculated using a rheologic mixing model and flow laws for the major crust-forming minerals. We investigate the viscosity of two lower crustal compositions: (i) basaltic (53 wt % SiO2) and (ii) andesitic (64 wt % SiO2). The andesitic model predicts aggregate viscosities similar to feldspar and approximately 1 order of magnitude greater than that of wet quartz. The viscosity range calculated for the andesitic crustal composition (particularly when hydrous phases are stable) is most similar to independent estimates of lower crust viscosity in actively deforming regions based on postglacial isostatic rebound, postseismic relaxation, and paleolake shoreline deflection.
NASA Astrophysics Data System (ADS)
Attia, H. A.
2007-04-01
It has come to the attention of the Institute of Physics that this article should not have been submitted for publication owing to its plagiarism of an earlier paper (Hossain A, Hossain M A and Wilson M 2001 Unsteady flow of viscous incompressible fluid with temperature-dependent viscosity due to a rotating disc in presence of transverse magnetic field and heat transfer Int. J. Therm. Sci. 40 11-20). Therefore this article has been retracted by the Institute of Physics and by the author, Hazem Ali Attia.
On the similarity of variable viscosity flows
NASA Astrophysics Data System (ADS)
Voivenel, L.; Danaila, L.; Varea, E.; Renou, B.; Cazalens, M.
2016-08-01
Turbulent mixing is ubiquitous in both nature and industrial applications. Most of them concern different fluids, therefore with variable physical properties (density and/or viscosity). The focus here is on variable viscosity flows and mixing, involving density-matched fluids. The issue is whether or not these flows may be self-similar, or self-preserving. The importance of this question stands on the predictability of these flows; self-similar dynamical systems are easier tractable from an analytical viewpoint. More specifically, self-similar analysis is applied to the scale-by-scale energy transport equations, which represent the transport of energy at each scale and each point of the flow. Scale-by-scale energy budget equations are developed for inhomogeneous and anisotropic flows, in which the viscosity varies as a result of heterogeneous mixture or temperature variations. Additional terms are highlighted, accounting for the viscosity gradients, or fluctuations. These terms are present at both small and large scales, thus rectifying the common belief that viscosity is a small-scale quantity. Scale-by-scale energy budget equations are then adapted for the particular case of a round jet evolving in a more viscous host fluid. It is further shown that the condition of self-preservation is not necessarily satisfied in variable-viscosity jets. Indeed, the jet momentum conservation, as well as the constancy of the Reynolds number in the central region of the jet, cannot be satisfied simultaneously. This points to the necessity of considering less stringent conditions (with respect to classical, single-fluid jets) when analytically tackling these flows and reinforces the idea that viscosity variations must be accounted for when modelling these flows.
NASA Astrophysics Data System (ADS)
Elgazery, Nasser S.
2009-04-01
In this paper, the problem of magneto-micropolar fluid flow, heat and mass transfer with suction and blowing through a porous medium is analyzed numerically. This problem was studied under the effects of chemical reaction, Hall, ion-slip currents, variable viscosity and variable thermal diffusivity. The governing fundamental equations are approximated by a system of non-linear ordinary differential equation. This system is solved numerically by using the Chebyshev pseudospectral method. Details of the velocities, temperature and concentration fields as well as the local skin-friction, the local Nusselt number and the local Sherwood number for the various values of the parameters of the problem are presented. The numerical results indicate that, the concentration decreases as the permeability parameter, the chemical reaction parameter and Schmidt number increase and it increases as variable viscosity and variable thermal diffusivity increase. The local Nusselt number and the local Sherwood number decrease as the magnetic field and ion-slip current parameters increase, whereas they increase as Hall current parameter increases. Also, there is a (non-linear) strong dependency of the concentration gradient at the wall on both Schmidt number and the mass transfer parameter.
Ali, N; Javid, K; Sajid, M; Anwar Bég, O
2016-01-01
Peristaltic motion of a non-Newtonian Carreau fluid is analyzed in a curved channel under the long wavelength and low Reynolds number assumptions, as a simulation of digestive transport. The flow regime is shown to be governed by a dimensionless fourth-order, nonlinear, ordinary differential equation subject to no-slip wall boundary conditions. A well-tested finite difference method based on an iterative scheme is employed for the solution of the boundary value problem. The important phenomena of pumping and trapping associated with the peristaltic motion are investigated for various values of rheological parameters of Carreau fluid and curvature of the channel. An increase in Weissenberg number is found to generate a small eddy in the vicinity of the lower wall of the channel, which is enhanced with further increase in Weissenberg number. For shear-thinning bio-fluids (power-law rheological index, n < 1) greater Weissenberg number displaces the maximum velocity toward the upper wall. For shear-thickening bio-fluids, the velocity amplitude is enhanced markedly with increasing Weissenberg number. PMID:26158210
Solvent viscosity dependence for enzymatic reactions
NASA Astrophysics Data System (ADS)
Sitnitsky, A. E.
2008-09-01
A mechanism for relationship of solvent viscosity with reaction rate constant at enzyme action is suggested. It is based on fluctuations of electric field in enzyme active site produced by thermally equilibrium rocking (crankshaft motion) of the rigid plane (in which the dipole moment ≈3.6 D lies) of a favourably located and oriented peptide group (or may be a few of them). Thus the rocking of the plane leads to fluctuations of the electric field of the dipole moment. These fluctuations can interact with the reaction coordinate because the latter in its turn has transition dipole moment due to separation of charges at movement of the reacting system along it. The rocking of the plane of the peptide group is sensitive to the microviscosity of its environment in protein interior and the latter is a function of the solvent viscosity. Thus we obtain an additional factor of interrelationship for these characteristics with the reaction rate constant. We argue that due to the properties of the crankshaft motion the frequency spectrum of the electric field fluctuations has a sharp resonance peak at some frequency and the corresponding Fourier mode can be approximated as oscillations. We employ a known result from the theory of thermally activated escape with periodic driving to obtain the reaction rate constant and argue that it yields reliable description of the pre-exponent where the dependence on solvent viscosity manifests itself. The suggested mechanism is shown to grasp the main feature of this dependence known from the experiment and satisfactorily yields the upper limit of the fractional index of a power in it.
Empirical slip and viscosity model performance for microscale gas flows.
Gallis, Michail A.; Boyd, Iain D.; McNenly, Matthew J.
2004-07-01
For the simple geometries of Couette and Poiseuille flows, the velocity profile maintains a similar shape from continuum to free molecular flow. Therefore, modifications to the fluid viscosity and slip boundary conditions can improve the continuum based Navier-Stokes solution in the non-continuum non-equilibrium regime. In this investigation, the optimal modifications are found by a linear least-squares fit of the Navier-Stokes solution to the non-equilibrium solution obtained using the direct simulation Monte Carlo (DSMC) method. Models are then constructed for the Knudsen number dependence of the viscosity correction and the slip model from a database of DSMC solutions for Couette and Poiseuille flows of argon and nitrogen gas, with Knudsen numbers ranging from 0.01 to 10. Finally, the accuracy of the models is measured for non-equilibrium cases both in and outside the DSMC database. Flows outside the database include: combined Couette and Poiseuille flow, partial wall accommodation, helium gas, and non-zero convective acceleration. The models reproduce the velocity profiles in the DSMC database within an L{sub 2} error norm of 3% for Couette flows and 7% for Poiseuille flows. However, the errors in the model predictions outside the database are up to five times larger.
NASA Astrophysics Data System (ADS)
Kiefer, W. S.
1993-02-01
For a fixed heat flow, the surface flow velocity of a convecting layer is not strongly sensitive to the variation of viscosity as a function of depth. Thus, the inferred absence of a low viscosity asthenosphere on Venus can not account for the limited surface motions there. The surface velocity is dependent on the convective geometry. Cartesian geometry convection can produce large surface velocities if the high viscosity surface layer is broken in places by weak zones. On the other hand, a high viscosity surface layer may inhibit the development of large surface velocities in axisymmetric convection.
NASA Technical Reports Server (NTRS)
Kiefer, Walter S.
1993-01-01
For a fixed heat flow, the surface flow velocity of a convecting layer is not strongly sensitive to the variation of viscosity as a function of depth. Thus, the inferred absence of a low viscosity asthenosphere on Venus can not account for the limited surface motions there. The surface velocity is dependent on the convective geometry. Cartesian geometry convection can produce large surface velocities if the high viscosity surface layer is broken in places by weak zones. On the other hand, a high viscosity surface layer may inhibit the development of large surface velocities in axisymmetric convection.
Fiber optic sensor for flow and viscosity measurement
NASA Astrophysics Data System (ADS)
Wang, Wei-Chih; Leang, Jonathan
2016-04-01
A sensitive fluid viscosity and flow measurement device using optical intensity based sensing is presented. The sensing principle makes use of the damping characteristic of a vibrating optical fiber probe with approximate hinge-free end configuration. The viscosity and mass flow are determined by measuring the vibration of a sinusoidally excited tapered optical fiber under different flow conditions. By measuring the frequency response of the fiber probe, viscosity and mass flow can be deduced from the damping coefficient of the response. The concepts and experimental data presented demonstrate and refine the sensing process of the proposed system.
NASA Astrophysics Data System (ADS)
Khaleque, Tania S.; Fowler, A. C.; Howell, P. D.; Vynnycky, M.
2015-07-01
Motivated by convection of planetary mantles, we consider a mathematical model for Rayleigh-Bénard convection in a basally heated layer of a fluid whose viscosity depends strongly on temperature and pressure, defined in an Arrhenius form. The model is solved numerically for extremely large viscosity variations across a unit aspect ratio cell, and steady solutions for temperature, isotherms, and streamlines are obtained. To improve the efficiency of numerical computation, we introduce a modified viscosity law with a low temperature cutoff. We demonstrate that this simplification results in markedly improved numerical convergence without compromising accuracy. Continued numerical experiments suggest that narrow cells are preferred at extreme viscosity contrasts, and this conclusion is supported by a linear stability analysis.
Torque Transient of Magnetically Drive Flow for Viscosity Measurement
NASA Technical Reports Server (NTRS)
Ban, Heng; Li, Chao; Su, Ching-Hua; Lin, Bochuan; Scripa, Rosalia N.; Lehoczky, Sandor L.
2004-01-01
Viscosity is a good indicator of structural changes for complex liquids, such as semiconductor melts with chain or ring structures. This paper discusses the theoretical and experimental results of the transient torque technique for non-intrusive viscosity measurement. Such a technique is essential for the high temperature viscosity measurement of high pressure and toxic semiconductor melts. In this paper, our previous work on oscillating cup technique was expanded to the transient process of a magnetically driven melt flow in a damped oscillation system. Based on the analytical solution for the fluid flow and cup oscillation, a semi-empirical model was established to extract the fluid viscosity. The analytical and experimental results indicated that such a technique has the advantage of short measurement time and straight forward data analysis procedures
Temperature Dependence of Viscosities of Common Carrier Gases
ERIC Educational Resources Information Center
Sommers, Trent S.; Nahir, Tal M.
2005-01-01
Theoretical and experimental evidence for the dependence of viscosities of the real gases on temperature is described, suggesting that this dependence is greater than that predicted by the kinetic theory of gases. The experimental results were obtained using common modern instrumentation and could be reproduced by students in analytical or…
Probing equilibrium glass flow up to exapoise viscosities
Pogna, Eva Arianna Aurelia; Rodríguez-Tinoco, Cristian; Cerullo, Giulio; Ferrante, Carino; Rodríguez-Viejo, Javier; Scopigno, Tullio
2015-01-01
Glasses are out-of-equilibrium systems aging under the crystallization threat. During ordinary glass formation, the atomic diffusion slows down, rendering its experimental investigation impractically long, to the extent that a timescale divergence is taken for granted by many. We circumvent these limitations here, taking advantage of a wide family of glasses rapidly obtained by physical vapor deposition directly into the solid state, endowed with different “ages” rivaling those reached by standard cooling and waiting for millennia. Isothermally probing the mechanical response of each of these glasses, we infer a correspondence with viscosity along the equilibrium line, up to exapoise values. We find a dependence of the elastic modulus on the glass age, which, traced back to the temperature steepness index of the viscosity, tears down one of the cornerstones of several glass transition theories: the dynamical divergence. Critically, our results suggest that the conventional wisdom picture of a glass ceasing to flow at finite temperature could be wrong. PMID:25675511
Prediction of Anomalous Blood Viscosity in Confined Shear Flow
NASA Astrophysics Data System (ADS)
Thiébaud, Marine; Shen, Zaiyi; Harting, Jens; Misbah, Chaouqi
2014-06-01
Red blood cells play a major role in body metabolism by supplying oxygen from the microvasculature to different organs and tissues. Understanding blood flow properties in microcirculation is an essential step towards elucidating fundamental and practical issues. Numerical simulations of a blood model under a confined linear shear flow reveal that confinement markedly modifies the properties of blood flow. A nontrivial spatiotemporal organization of blood elements is shown to trigger hitherto unrevealed flow properties regarding the viscosity η, namely ample oscillations of its normalized value [η]=(η-η0)/(η0ϕ) as a function of hematocrit ϕ (η0=solvent viscosity). A scaling law for the viscosity as a function of hematocrit and confinement is proposed. This finding can contribute to the conception of new strategies to efficiently detect blood disorders, via in vitro diagnosis based on confined blood rheology. It also constitutes a contribution for a fundamental understanding of rheology of confined complex fluids.
Application of the Carreau viscosity model to the oscillatory flow in blood vessels
NASA Astrophysics Data System (ADS)
Tabakova, Sonia; Kutev, Nikolay; Radev, Stefan
2015-11-01
When studying the oscillatory flow in different types of blood vessels it is very important to know what type of the blood viscosity model has to be used. In general the blood viscosity is defined as a shear-thinning liquid, for which there exist different shear-dependent models, for example the Carreau model, which represents the viscosity as a non-linear function of the shear-rate. In some cases, however, the blood viscosity could be regarded as constant, i.e., the blood is treated as Newtonian fluid. The aim of the present work is to show theoretically and numerically some approximate limits of the Newtonian model application, when the blood vessel is assumed as a 2D straight tube. The obtained results are in agreement with other authors' numerical results based on similar blood viscosity models.
Viscosity dependence of the rates of diffusional processes
NASA Technical Reports Server (NTRS)
Weaver, D. L.
1982-01-01
It is shown that the rates of diffusion-controlled processes may have a solvent vicosity independent part as well as a viscosity dependent part. Some relevant experiments involving intramolecular polypeptide movements are discussed, and implications for some experiments on diffusion in membranes are outlined.
Viscosity parameter values in accretion flows around black holes.
NASA Astrophysics Data System (ADS)
Nagarkoti, Shreeram; Chakrabarti, Sandip Kumar
2016-07-01
Viscosity is responsible for the transport of angular momentum in accretion processes. Assuming mixed stress prescription suitable for flow discontinuities, we draw parameter space of specific angular momentum and specific energy of flow at the inner sonic point for all possible values of viscosity parameter. Then, we identify the region which is capable of producing standard Rankine-Hugoniot shocks. From this analysis, it is found that a large range of values of viscosity parameter (0.0-0.3) is capable of producing shocks. At values larger than this, the parameter space allowing shock formation is negligible. The shock formation causes piling up of matter in the post-shock region which Comptonizes soft X-ray photons coming from the Keplerian accretion disk, creating the hard X-Ray radiation. Since numerical simulations generally produce alpha parameters very smaller as compared to this upper limit, we conclude that the shocks remain essential component to model black hole spectral and timing properties.
NASA Astrophysics Data System (ADS)
Stemmer, K.; Harder, H.; Hansen, U.
2004-12-01
temperature dependent viscosity (Δ η =104-10^5) typically a few upwelling plume structures develop. The large scale structure of the plume stays intact over a long time while the plume geometry varies on a smaller scale. The downflows are generally organized in two-dimensional sheetlike flows. Additional pressure dependence strongly influences the dynamics even if the magnitude of pressure variation is relatively small. For an appropriate combination of pressure- and temperature-dependence we observe a well developed high-viscosity zone in the lower mantle.
Apparent Viscosity of Active Nematics in Poiseuille Flow
NASA Astrophysics Data System (ADS)
Cui, Zhenlu; Su, Jianbing; Zeng, Xiaoming
2015-09-01
A Leslie-Erickson continuum hydrodynamic for flowing active nematics has been used to characterize active particle systems such as bacterial suspensions. The behavior of such a system under a plane pressure-driven Poiseuille flow is analyzed. When plate anchoring is tangential and normal, we find the apparent viscosity formula indicating a significant difference between tangential anchoring and normal anchoring conditions for both active rodlike and discoid nematics.
Chauveteau, G.; Tirrell, M.; Omari, A.
1984-07-01
Polymer solutions are demonstrated to have apparent viscosities in small pores which depend on pore diameter (or the mean diameter of pore throats in irregular porous media) and which, therefore, can be considerably different from the viscosity of the same solution in an unbounded medium. The apparent viscosities in the pores can be greater or less than in bulk depending upon whether the pore wall is attractive or repulsive for the polymer. Specifically, if there is no adsorption (repulsive wall) we find that the solution viscosity is always less inside the pore than in bulk. On the other hand if the wall is attractive the apparent solution viscosity inside the pore may be greater or less, depending on the concentration of the flowing polymer solution. Data representing these effects are presented for aqueous solutions of hydrolyzed polyacrylamide and xanthan polysaccharide. The data are organized as suggested by a model recently proposed by Chauveteau for polymer solution flow in small pores. 47 references.
Temperature and pressure dependences of kimberlite melts viscosity (experimental-theoretical study)
NASA Astrophysics Data System (ADS)
Persikov, Eduard; Bykhtiyarov, Pavel; Cokol, Alexsander
2016-04-01
Experimental data on temperature and pressure dependences of viscosity of model kimberlite melts (silicate 82 + carbonate 18, wt. %, 100NBO/T = 313) have been obtained for the first time at 100 MPa of CO2 pressure and at the lithostatic pressures up to 7.5 GPa in the temperature range 1350 oC - 1950 oC using radiation high gas pressure apparatus and press free split-sphere multi - anvil apparatus (BARS). Experimental data obtained on temperature and pressure dependences of viscosity of model kimberlite melts at moderate and high pressures is compared with predicted data on these dependences of viscosity of basaltic melts (100NBO/T = 58) in the same T, P - range. Dependences of the viscosity of model kimberlite and basaltic melts on temperature are consistent to the exponential Arrenian equation in the T, P - range of experimental study. The correct values of activation energies of viscous flow of kimberlite melts have been obtained for the first time. The activation energies of viscous flow of model kimberlite melts exponentially increase with increasing pressure and are equal: E = 130 ± 1.3 kJ/mole at moderate pressure (P = 100 MPa) and E = 160 ± 1.6 kJ/mole at high pressure (P = 5.5 GPa). It has been established too that the viscosity of model kimberlite melts exponentially increases on about half order of magnitude with increasing pressures from 100 MPa to 7.5 GPa at the isothermal condition (1800 oC). It has been established that viscosity of model kimberlite melts at the moderate pressure (100 MPa) is lover on about one order of magnitude to compare with the viscosity of basaltic melts, but at high pressure range (5.5 - 7.5 GPa), on the contrary, is higher on about half order of magnitude at the same values of the temperatures. Here we use both a new experimental data on viscosity of kimberlite melts and our structural chemical model for calculation and prediction the viscosity of magmatic melts [1] to determine the fundamental features of viscosity of
NASA Astrophysics Data System (ADS)
González, M.; Jiang, W. G.; Zheng, P.; Barquist, C. S.; Chan, H. B.; Lee, Y.
2016-07-01
A microelectromechanical system vibrating in its shear mode was used to study the viscosity of normal liquid
NVP melt/magma viscosity: insight on Mercury lava flows
NASA Astrophysics Data System (ADS)
Rossi, Stefano; Morgavi, Daniele; Namur, Olivier; Vetere, Francesco; Perugini, Diego; Mancinelli, Paolo; Pauselli, Cristina
2016-04-01
After more than four years of orbiting Mercury, NASA's MESSENGER spacecraft came to an end in late April 2015. MESSENGER has provided many new and surprising results. This session will again highlight the latest results on Mercury based on MESSENGER observations or updated modelling. The session will further address instrument calibration and science performance both retrospective on MESSENGER and on the ESA/JAXA BepiColombo mission. Papers covering additional themes related to Mercury are also welcomed. Please be aware that this session will be held as a PICO session. This will allow an intensive exchange of expertise and experience between the individual instruments and mission. NVP melt/magma viscosity: insight on Mercury lava flows S. Rossi1, D. Morgavi1, O. Namur2, D. Perugini1, F.Vetere1, P. Mancinelli1 and C. Pauselli1 1 Dipartimento di Fisica e Geologia, Università di Perugia, piazza Università 1, 06123 Perugia, Italy 2 Uni Hannover Institut für Mineralogie, Leibniz Universität Hannover, Callinstraβe 3, 30167 Hannover, Germany In this contribution we report new measurements of viscosity of synthetic komatitic melts, used the behaviour of silicate melts erupted at the surface of Mercury. Composition of Mercurian surface magmas was calculated using the most recent maps produced from MESSENGER XRS data (Weider et al., 2015). We focused on the northern hemisphere (Northern Volcanic Province, NVP, the largest lava flow on Mercury and possibly in the Solar System) for which the spatial resolution of MESSENGER measurements is high and individual maps of Mg/Si, Ca/Si, Al/Si and S/Si were combined. The experimental starting material contains high Na2O content (≈7 wt.%) that strongly influences viscosity. High temperature viscosity measurements were carried out at 1 atm using a concentric cylinder apparatus equipped with an Anton Paar RheolabQC viscometer head at the Department of Physics and Geology (PVRG_lab) at the University of Perugia (Perugia, Italy
Raynaud's disease: reduced hand blood flows with normal blood viscosity.
McGrath, M A; Peek, R; Penny, R
1978-04-01
Hand blood flows and the blood and plasma viscosities were measured in patients with Raynaud's disease in an attempt to identify the mechanism of the episodic vascular insufficiency. Using venous occlusion plethysmography the following observations were made: (1) the hand blood flows were significantly less than in normals at 32 degrees, 27 degrees and 20 degrees C; (2) the percentage decrease in flow with cooling was greater in normals and (3) cooling of one hand from 32 degrees to 27 degrees C caused an abnormal decrease in flow through the contralateral hand. Using a rotational viscometer the blood and plasma viscosities were found to be normal at both high and low shear rates. The percentage increase in the blood viscosity with cooling from 35 degrees to 25 degrees was also normal. These studies demonstrate an increased constrictive response of the cutaneous vasculature of the hand to both local and reflex stimulation, and exclude a rheological abnormality, under conditions similar to those of the present study. PMID:277163
Coupled Marangoni-Benard/Rayleigh-Benard Instability with Temperature Dependent Viscosity
NASA Technical Reports Server (NTRS)
Skarda, J. Raymond Lee; Mccaughan, Frances E.
1994-01-01
The onset of convection induced by coupled surface tension gradient and buoyancy forces is investigated with temperature dependent viscosity. Both surface tension and viscosity are assumed to vary linearly with temperature. The limiting case, Ma=0, is the buoyancy driven convection problem typically referred to as the Rayleigh-Benard stability problem. The other limiting case, Ra=0, is the surface tension (gradient) driven flow problem referred to as the Marangoni-Benard problem. The equations and boundary conditions obtained from the linear analysis are solved numerically as a generalized eigenvalue problem. Neutral stability curves for different viscosity slopes have been generated for the Marangoni-Benard and Rayleigh-Benard problems. It is shown that the curves can be collapsed to a single curve by appropriately scaling the results for each of the limiting cases. The critical Marangoni number is determined as a function of the slope of the viscosity temperature variation, epsilon, for different values of the Rayleigh number. When the viscosity decreases linearly with temperature, the coupled buoyancy-surface tension problem, including the limiting cases of Ra=0 and Ma=0, is found to be more stable than the constant viscosity case.
NASA Astrophysics Data System (ADS)
Munekata, Mizue; Takaki, Hidefumi; Ohba, Hideki; Matsuzaki, Kazuyoshi
2005-12-01
Effects of non-Newtonian viscosity for surfactant solution on the vortex characteristics and drag-reducing rate in a swirling pipe flow are investigated by pressure drop measurements, velocity profile measurements and viscosity measurements. Non-Newtonian viscosity is represented by power-law model (τ=kD n). Surfactant solution used has shear-thinning viscosity with n<1.0. The swirling flow in this study has decay of swirl and vortex-type change from Rankin’s combined vortex to forced vortex. It is shown that the effect of shear-thinning viscosity on the decay of swirl intensity is different by vortex category and the critical swirl number with the vortex-type change depends on shear-thinning viscosity.
Temperature-Dependent Conformations of Model Viscosity Index Improvers
Ramasamy, Uma Shantini; Cosimbescu, Lelia; Martini, Ashlie
2015-05-01
Lubricants are comprised of base oils and additives where additives are chemicals that are deliberately added to the oil to enhance properties and inhibit degradation of the base oils. Viscosity index (VI) improvers are an important class of additives that reduce the decline of fluid viscosity with temperature [1], enabling optimum lubricant performance over a wider range of operating temperatures. These additives are typically high molecular weight polymers, such as, but not limited to, polyisobutylenes, olefin copolymer, and polyalkylmethacrylates, that are added in concentrations of 2-5% (w/w). Appropriate polymers, when dissolved in base oil, expand from a coiled to an uncoiled state with increasing temperature [2]. The ability of VI additives to increase their molar volume and improve the temperature-viscosity dependence of lubricants suggests there is a strong relationship between molecular structure and additive functionality [3]. In this work, we aim to quantify the changes in polymer size with temperature for four polyisobutylene (PIB) based molecular structures at the nano-scale using molecular simulation tools. As expected, the results show that the polymers adopt more conformations at higher temperatures, and there is a clear indication that the expandability of a polymer is strongly influenced by molecular structure.
From viscosity and surface tension to marangoni flow in melts
NASA Astrophysics Data System (ADS)
Sun, Shouyi; Zhang, Ling; Jahanshahi, Sharif
2003-10-01
This article covers some of our recent work on slag viscosity, the surface tension of liquid Cu-O alloys, and the relative role of Marangoni and bulk flow on refractory wear in iron-silicate slags. A viscosity model developed for slags containing SiO2, Al2O3, Fe2O3, CaO, MgO, MnO, FeO, PbO, NiO, Cu2O, ZnO, CoO, and TiO2 is capable of representing the effects of temperature, silica, and network-modifier cations within a wide range of temperatures and compositions. It forms a useful part of a computational package for multiphase-equilibrium (MPE) calculations and for predicting slag viscosities. The models are well applicable to a range of industrial slags (blast furnace, new iron making, base-metal and Platinum Group Metals (PGM) smelting, and coal-ash slags). The package has also some capability of predicting the viscosity of slags containing suspended solids. The surface tension of liquid copper-oxygen alloys has also been analyzed. The adsorption behavior of oxygen in liquid copper is well represented by the combined Langmuir-Gibbs isotherm. According to the rate data for silica-rod dissolution in liquid iron-silicate slags at 1573 K, the preferential attack at the slag line diminishes as the linear velocity of flow at the surface of the rotating silica rod reaches 9 to 16 cm/s. A tentative analysis gives the critical condition, that relates the critical Reynolds (Re) and Marangoni (Ma) number by the equation Re*2=0.13 Ma*.
A local eddy viscosity model for turbulent shear flow
NASA Technical Reports Server (NTRS)
Ortwerth, P. J.; Rabe, D. C.; Mcerlean, D. P.
1973-01-01
In the model described, the eddy viscosity is assumed to be a fluid property dependent on the state of the fluid locally, namely the local density, turbulent kinetic energy, turbulence scale, and Mach number. An empirical law was found which related eddy viscosity to these properties satisfactorily for free jets. This law is used without modification for a set of test cases in free shear layers, free-jet decay, coaxial mixing, and wakes. The scale of turbulence is taken as a constant at any axial location equal to the width of the shear layer. By utilizing the boundary-layer order-of-magnitude analysis, a coupled set of fluid dynamic equations is formulated, which of necessity includes the equation for the production of turbulent kinetic energy.
Effect of viscosity and shear flow on the nonlinear two fluid interfacial structures
Banerjee, Rahul
2012-12-15
A nonlinear formulation is presented to deal with the combined action of Rayleigh-Taylor and Kelvin-Helmholtz instabilities as well as combined Ricthmyer-Meshkov and Kelvin-Helmholtz instabilities at the two fluid interface under the influence of viscosity and consequent shear flow. Using Layzer's model, the development of the interfacial structures like bubbles is investigated analytically and numerically. It is found that the growth and normal velocity of the structures are dependent on the relative velocity shear and the kinematic coefficient of viscosity of both the fluids. Both the bubble growth and growth rate are reduced significantly for fluids of higher viscosity coefficient with small velocity shear difference. It is also observed that, for viscous fluids, the transverse velocity of the perturbed interface becomes slower under certain conditions.
Frequency-Dependent Viscosity of Xenon Near the Critical Point
NASA Technical Reports Server (NTRS)
Berg, Robert F.; Moldover, Michael R.; Zimmerli, Gregory A.
1999-01-01
We used a novel, overdamped oscillator aboard the Space Shuttle to measure the viscosity eta of xenon near its critical density rho(sub c), and temperature T(sub c). In microgravity, useful data were obtained within 0.1 mK of T(sub c), corresponding to a reduced temperature t = (T -T(sub c))/T(sub c) = 3 x 10(exp -7). The data extend two decades closer to T(sub c) than the best ground measurements, and they directly reveal the expected power-law behavior eta proportional to t(sup -(nu)z(sub eta)). Here nu is the correlation length exponent, and our result for the small viscosity exponent is z(sub eta) = 0.0690 +/- 0.0006. (All uncertainties are one standard uncertainty.) Our value for z(sub eta) depends only weakly on the form of the viscosity crossover function, and it agrees with the value 0.067 +/- 0.002 obtained from a recent two-loop perturbation expansion. The measurements spanned the frequency range 2 Hz less than or equal to f less than or equal to 12 Hz and revealed viscoelasticity when t less than or equal to 10(exp -1), further from T(sub c) than predicted. The viscoelasticity scales as Af(tau), where tau is the fluctuation-decay time. The fitted value of the viscoelastic time-scale parameter A is 2.0 +/- 0.3 times the result of a one-loop perturbation calculation. Near T(sub c), the xenon's calculated time constant for thermal diffusion exceeded days. Nevertheless, the viscosity results were independent of the xenon's temperature history, indicating that the density was kept near rho(sub c), by judicious choices of the temperature vs. time program. Deliberately bad choices led to large density inhomogeneities. At t greater than 10(exp -5), the xenon approached equilibrium much faster than expected, suggesting that convection driven by microgravity and by electric fields slowly stirred the sample.
Length-Scale Dependent Viscosity in Semidilute Polyelectrolyte Solutions
NASA Astrophysics Data System (ADS)
Poling-Skutvik, Ryan; Krishnamoorti, Ramanan; Conrad, Jacinta
2015-03-01
Using optical microscopy and particle tracking algorithms, we measured the mean-squared displacements (MSDs) of fluorescent polystyrene particles with diameters ranging from 300 nm to 2 μm suspended in semidilute solutions of high molecular weight partially hydrolyzed polyacrylamide. The solutions had polymer concentrations ranging from 0.67 to 67c*, where c* is the overlap concentration, and estimated correlation lengths of ~ 100 to 900 nm. At short times, the particles exhibited subdiffusive behavior characterized by MSD ~tα with α < 1 . On long time scales, the particles transitioned to Fickian diffusion (α = 1) and their diffusivity was calculated from the slope of the MSD. Whereas the large particles agreed with predictions using the Stokes-Einstein equation and bulk zero-shear viscosity, the smaller particles diffused much faster than predicted. The relative diffusivities do not collapse onto a single curve, but rather form a continuum that varies with particle size. This indicates that the particles experience a size-dependent effective viscosity mediated by the ratio of particle diameter to characteristic length scales in the polymer solution.
Keska, Jerry K.; Hincapie, Juan; Jones, Richard
2011-02-15
In the steady-state flow of a heterogeneous mixture such as an air-liquid mixture, the velocity and void fraction are space- and time-dependent parameters. These parameters are the most fundamental in the analysis and description of a multiphase flow. The determination of flow patterns in an objective way is extremely critical, since this is directly related to sudden changes in spatial and temporal changes of the random like characteristic of concentration. Flow patterns can be described by concentration signals in time, amplitude, and frequency domains. Despite the vital importance and countless attempts to solve or incorporate the flow pattern phenomena into multiphase models, it has still been a very challenging topic in the scientific community since the 1940's and has not yet reached a satisfactory solution. This paper reports the experimental results of the impact of fluid viscosity on flow patterns for two-phase flow. Two-phase flow was created in laboratory equipment using air and liquid as phase medium. The liquid properties were changed by using variable concentrations of glycerol in water mixture which generated a wide-range of dynamic viscosities ranging from 1 to 1060 MPa s. The in situ spatial concentration vs. liquid viscosity and airflow velocity of two-phase flow in a vertical ID=50.8 mm pipe were measured using two concomitant computer-aided measurement systems. After acquiring data, the in situ special concentration signals were analyzed in time (spatial concentration and RMS of spatial concentration vs. time), amplitude (PDF and CPDF), and frequency (PSD and CPSD) domains that documented broad flow pattern changes caused by the fluid viscosity and air velocity changes. (author)
NASA Astrophysics Data System (ADS)
Lee, Wook; Lee, Jungchul; Kang, Seongwon
2013-11-01
In this study, we analyzed the flow characteristics and performance of a viscosity sensor based on a suspended microchannel resonator (SMR). First, we verified the assumptions of Sader et al. (2010) for their analytic solution using the approach of direction numerical simulation. Second, the relationship between monotonicity of the quality factor and the changes of integrated energy variables was investigated. It was found that the monotonicity to the Reynolds number is strongly dependent on a source term of the kinetic energy equation. Based on this, a change in the quality factor was related to specific patterns of the velocity and vorticity fields. Third, the effects of geometrical parameters of the SMR on performance as a viscosity sensor were investigated. The variations in the measurable viscosity range as well as the viscosity resolution were investigated in terms of the flow characteristics affected by the design parameters. It was found that the off-axis displacement shows a significant but consistent effect on performance of the SMR viscometer regardless of the flow condition. In contrast, the other geometric parameters show more complicated effects, as they are also related to the resonant frequency of the SMR and affected by the compressibility of a fluid.
Dependence of red edge on eddy viscosity model parameters
NASA Technical Reports Server (NTRS)
Deupree, R. G.; Cole, P. W.
1980-01-01
The dependence of the red edge location on the two fundamental free parameters in the eddy viscosity treatment was extensively studied. It is found that the convective flux is rather insensitive to any reasonable or allowed value of the two free parameters of the treatment. This must be due in part to the fact that the convective flux is determined more by the properties of the hydrogen ionization region than by differences in convective structure. The changes in the effective temperature of the red edge of the RR Lyrae gap resulting from these parameter variations is quite small (approximately 150 K). This is true both because the parameter variation causes only small changes and because large changes in the convective flux are required to produce any significant change in red edge location. The possible changes found are substantially less than the approximately 600 K required to change the predicted helium abundance mass fraction from 0.3 to 0.2.
Formation of Hrad Vallis (Mars) by low viscosity lava flows
NASA Astrophysics Data System (ADS)
Hopper, Joshua P.; Leverington, David W.
2014-02-01
Hrad Vallis is a Martian outflow channel previously interpreted as a product of aqueous outbursts from the subsurface, possibly involving mudflows associated with lahar-like events. However, an alternative volcanic hypothesis for the development of the system is worthy of consideration on the basis of (1) the nature of landforms preserved along component channels and adjacent uplands and (2) similarities between the basic properties of this system and large volcanic channels of the inner solar system. Hrad Vallis commences on the distal flanks of the Elysium Mons shield volcano, terminates within extensive volcanic plains, is associated with landforms typical of large volcanic channels, and shows evidence for having been a conduit for large volumes of lava. The properties of this system are consistent with incision by low viscosity lava. Crude thermal estimates suggest that this system could have formed through effusion of as little as ~ 10,900 km3 of magma to the surface, or ~ 6% of the volume of the terrestrial Columbia River Basalt Group. Incision rates of up to several meters per day are estimated for mechanical and thermal processes involving lava flows with depths of 5-20 m and dynamic viscosities of ~ 1 Pa s. Flow of lava within the Hrad Vallis system is predicted to have been fully turbulent and characterized by discharges as great as ~ 865,000 m3/s. Predicted flow conditions are consistent with those previously determined for Athabasca Valles, which also formed as a result of the expulsion of flows from structures associated with Elysium Mons.
Effect of bulk viscosity in low density, hypersonic blunt body flows
Rutledge, W.H. ); Hoffmann, K.A. )
1991-01-01
A computational fluids dynamics scheme is presented to solve the unsteady Thin-Layer Navier-Stokes (TLNS) equations over a blunt body at high altitude, high Mach number atmospheric reentry flow conditions. This continuum approach is directed to low density hypersonic flows by accounting for non-zero bulk viscosity effects in near frozen flow conditions. The TLNS equations are solved over an axisymmetric body at zero incidence relative to the free stream. The time dependent axisymmetric governing equations are transformed into a computational plane, then cast into weak conservative form and solved using a first-order fully implicit scheme in time with second-order flux vector splitting for spatial derivatives. The physical domain is defined over representative sphere and sphere/cone geometries using a body-fitted clustered algebraic grid within a fixed domain (i.e., shock capturing). At the present time, nonequilibrium thermo-chemistry effects are not modeled. Catalytic wall, ionization and radiation effects are also excluded from the current analysis. However, the significant difference from previous studies is the inclusion of the capability to model non-zero bulk viscosity effects. The importance of bulk viscosity is reviewed and blunt body flow field solutions are presented to illustrate the potential contribution of this phenomena at high altitude hypersonic conditions. The current technique is compared with experimental data and other approximate continuum solutions. A variety of test cases are also presented for a wide range of free stream Mach conditions. 18 refs., 42 figs.
NASA Astrophysics Data System (ADS)
Shit, G. C.; Majee, Sreeparna
2015-08-01
Unsteady flow of blood and heat transfer characteristics in the neighborhood of an overlapping constricted artery have been investigated in the presence of magnetic field and whole body vibration. The laminar flow of blood is taken to be incompressible and Newtonian fluid with variable viscosity depending upon temperature with an aim to provide resemblance to the real situation in the physiological system. The unsteady flow mechanism in the constricted artery is subjected to a pulsatile pressure gradient arising from systematic functioning of the heart and from the periodic body acceleration. The numerical computation has been performed using finite difference method by developing Crank-Nicolson scheme. The results show that the volumetric flow rate, skin-friction and the rate of heat transfer at the wall are significantly altered in the downstream of the constricted region. The axial velocity profile, temperature and flow rate increases with increase in temperature dependent viscosity, while the opposite trend is observed in the case of skin-friction and flow impedance.
Flow fields in soap films: Relating viscosity and film thickness
NASA Astrophysics Data System (ADS)
Prasad, V.; Weeks, Eric R.
2009-08-01
We follow the diffusive motion of colloidal particles in soap films with varying h/d , where h is the thickness of the film and d is the diameter of the particles. The hydrodynamics of these films are determined by looking at the correlated motion of pairs of particles as a function of separation R . The Trapeznikov approximation [A. A. Trapeznikov, Proceedings of the 2nd International Congress on Surface Activity (Butterworths, London, 1957), p. 242] is used to model soap films as an effective two-dimensional (2D) fluid in contact with bulk air phases. The flow fields determined from correlated particle motions show excellent agreement with what is expected for the theory of 2D fluids for all our films where 0.6≤h/d≤14.3 , with the 2D shear viscosity matching that predicted by Trapeznikov. However, the parameters of these flow fields change markedly for thick films (h/d>7±3) . Our results indicate that three-dimensional effects become important for these thicker films, despite the flow fields still having a 2D character.
NASA Astrophysics Data System (ADS)
Grayson, J. W.; Song, M.; Sellier, M.; Bertram, A. K.
2015-01-01
Viscosity in particles consisting of secondary organic material (SOM) have recently become an area of research focus, since information on viscosity is needed to predict the environmental impacts of SOM particles. Recently Renbaum-Wolff et al. (2013a) developed a poke-flow technique that was combined with simulations of fluid flow to constrain the viscosities of SOM samples of 1-5 mg mass, roughly the maximum that may be collected from environmental chambers or flow tubes on a reasonable time scale. The current manuscript expands on the initial validation experiments carried out by Renbaum-Wolff et al. (2013a). First, the poke-flow technique combined with simulations of fluid flow was used to determine the viscosity of sucrose-water particles over a relatively wide range of relatively humidities (RH). The lower and upper limits of viscosity at 59% RH were 1.0 ×101 Pa s and 1.6 × 104 Pa s, whilst at 45% RH the corresponding values were 9.1 × 102 and 4.1 × 105 Pa s, respectively. The results are in good agreement with recent measurements by Quintas et al. (2006) and Power et al. (2013). Second, the approach was used to determine the viscosity of two polybutene standards. The simulated lower and upper limits of viscosity for standard #1 was 2.0 × 102 and 1.2 × 104 Pa s, whilst for standard #2 the corresponding values were 3.1 × 102 and 2.4 × 104 Pa s. These values are in good agreement with values reported by the manufacturer. The results for both the sucrose-water particles and the polybutene standards show that the poke-flow technique combined with simulations of fluid flow is capable of providing both lower and upper limits of viscosity that are consistent with literature or measured values when the viscosity of the particles are in the range of 103-105 Pa s.
Asymptotic behavior of a viscous liquid-gas model with mass-dependent viscosity and vacuum
NASA Astrophysics Data System (ADS)
Liu, Qingqing; Zhu, Changjiang
In this paper, we consider two classes of free boundary value problems of a viscous two-phase liquid-gas model relevant to the flow in wells and pipelines with mass-dependent viscosity coefficient. The liquid is treated as an incompressible fluid whereas the gas is assumed to be polytropic. We obtain the asymptotic behavior and decay rates of the mass functions n(x,t), m(x,t) when the initial masses are assumed to be connected to vacuum both discontinuously and continuously, which improves the corresponding result about Navier-Stokes equations in Zhu (2010) [23].
NASA Astrophysics Data System (ADS)
Horiuchi, Shun-suke; Iwamori, Hikaru
2016-05-01
Water plays crucial roles in the subduction zone dynamics affecting the thermal-flow structure through the fluid processes. We aim to understand what controls the dynamics and construct a model to solve consistently fluid generation, fluid transport, its reaction with the solid and resultant viscosity, and thermal-flow structure. We highlight the effect of mechanical weakening of rocks associated with hydration. The viscosity of serpentinite (ηserp) in subduction zones critically controls the flow-thermal structure via extent of mechanical coupling between the subducting slab and overlying mantle wedge. When ηserp is greater than 1021 Pa s, the thermal-flow structure reaches a steady state beneath the volcanic zone, and the melting region expands until Cin (initial water content in the subducting oceanic crust) reaches 3 wt %, and it does not expand from 3 wt %. On the other hand, when ηserp is less than 1019 Pa s, the greater water dependence of viscosity (expressed by a larger fv) confines a hot material to a narrower channel intruding into the wedge corner from a deeper part of the back-arc region. Consequently, the overall heat flux becomes less for a larger fv. When ageba (age of back-arc basin as a rifted lithosphere) = 7.5 Ma, the increase in fv weakens but shifts the melting region toward the trench side because of the narrow channel flow intruding into the wedge corner, where as it shuts down melting when ageba=20 Ma. Several model cases (particularly those with ηserp=1020 to 1021 Pa s and a relatively large fv for Cin=2 to 3 wt %) broadly account for the observations in the Northeast Japan arc (i.e., location and width of volcanic chain, extent of serpentinite, surface heat flow, and seismic tomography), although the large variability of surface heat flow and seismic tomographic images does not allow us to constrain the parameter range tightly.
Malik, M; Dey, J; Alam, Meheboob
2008-03-01
Linear stability and the nonmodal transient energy growth in compressible plane Couette flow are investigated for two prototype mean flows: (a) the uniform shear flow with constant viscosity, and (b) the nonuniform shear flow with stratified viscosity. Both mean flows are linearly unstable for a range of supersonic Mach numbers (M). For a given M , the critical Reynolds number (Re) is significantly smaller for the uniform shear flow than its nonuniform shear counterpart; for a given Re, the dominant instability (over all streamwise wave numbers, alpha ) of each mean flow belongs to different modes for a range of supersonic M . An analysis of perturbation energy reveals that the instability is primarily caused by an excess transfer of energy from mean flow to perturbations. It is shown that the energy transfer from mean flow occurs close to the moving top wall for "mode I" instability, whereas it occurs in the bulk of the flow domain for "mode II." For the nonmodal transient growth analysis, it is shown that the maximum temporal amplification of perturbation energy, G(max), and the corresponding time scale are significantly larger for the uniform shear case compared to those for its nonuniform counterpart. For alpha=0 , the linear stability operator can be partitioned into L ~ L+Re(2) L(p), and the Re-dependent operator L(p) is shown to have a negligibly small contribution to perturbation energy which is responsible for the validity of the well-known quadratic-scaling law in uniform shear flow: G(t/Re) ~ Re(2). In contrast, the dominance of L(p) is responsible for the invalidity of this scaling law in nonuniform shear flow. An inviscid reduced model, based on Ellingsen-Palm-type solution, has been shown to capture all salient features of transient energy growth of full viscous problem. For both modal and nonmodal instability, it is shown that the viscosity stratification of the underlying mean flow would lead to a delayed transition in compressible Couette flow
The viscosity of gaseous propane and its initial density dependence
NASA Astrophysics Data System (ADS)
Vogel, E.
1995-11-01
Results of five series of high-precision viscosity measurements on gaseous propane, each differing in density, are reported. The measurements were performed in a quartz oscillating-disk viscometer with small gaps from room temperature up to about 625 K and for densities between 0.01 and 0.05 mol · L-1. The experimental data were evaluated with a first-order expansion, in terms of density, for the viscosity. Reduced values of the second viscosity virial coefficients deduced from the zero-density and initial-density viscosity coefficients for propane and for further n-alkanes are in close agreement with the theoretical representation of the Rainwater-Friend theory for the potential parameter ratios by Bich and Vogel. A new representation of the viscosity of propane in the limit of zero density is provided using the new experimental data and some data sets from literature. The universal correlation based on the extended principle of corresponding states extends over the temperature range 293 to 625 K with an uncertainty of ±0.5 % and deviates from earlier representations by about 1 % at the upper temperature limit.
The viscosity of gaseous propane and its initial density dependence
Vogel, E.
1995-11-01
Results of five series of high-precision viscosity measurements on gaseous propane, each differing in density, are reported. The measurements were performed in a quartz oscillating-disk viscometer with small gaps from room temperature up to about 625 K and for densities between 0.01 and 0.05 mol {center_dot} L{sup -1}. The experimental data were evaluated with a first-order expansion, in terms of density, for the viscosity. Reduced values of the second viscosity virial coefficients deduced from the zero-density and initial-density viscosity coefficients for propane and for further n-alkanes are in close agreement with the theoretical representation of the Rainwater-Friend theory for the potential parameter ratios by Bich and Vogel. A new representation of the viscosity of propane in the limit of zero density is provided using the new experimental data and some data sets from literature. The universal correlation based on the extended principle of corresponding states extends over the temperature range 293 to 625 K with an uncertainty of {plus_minus}0.5% and deviates from earlier representations by about 1% at the upper temperature limit.
Prediction of Transonic Vortex Flows Using Linear and Nonlinear Turbulent Eddy Viscosity Models
NASA Technical Reports Server (NTRS)
Bartels, Robert E.; Gatski, Thomas B.
2000-01-01
Three-dimensional transonic flow over a delta wing is investigated with a focus on the effect of transition and influence of turbulence stress anisotropies. The performance of linear eddy viscosity models and an explicit algebraic stress model is assessed at the start of vortex flow, and the results compared with experimental data. To assess the effect of transition location, computations that either fix transition or are fully turbulent are performed. To assess the effect of the turbulent stress anisotropy, comparisons are made between predictions from the algebraic stress model and the linear eddy viscosity models. Both transition location and turbulent stress anisotropy significantly affect the 3D flow field. The most significant effect is found to be the modeling of transition location. At a Mach number of 0.90, the computed solution changes character from steady to unsteady depending on transition onset. Accounting for the anisotropies in the turbulent stresses also considerably impacts the flow, most notably in the outboard region of flow separation.
Evaluation of the viscosities of a liquid crystal model system by shear flow simulation
NASA Astrophysics Data System (ADS)
Sarman, Sten; Laaksonen, Aatto
2009-09-01
The three Miesowicz viscosities of a liquid crystal model system consisting of the Gay-Berne fluid have been obtained by shear flow simulations. The viscosities along an isochore have been followed starting in the nematic phase at high temperatures across the nematic-smectic A phase transition down to low temperatures in the smectic A phase. The relative magnitudes of the viscosities as a function of the structure of the liquid crystal are discussed. The viscosities obtained by the shear flow simulations agree very well with those obtained by Green-Kubo relations in a previous work.
Mass dependence of shear viscosity in a binary fluid mixture: mode-coupling theory.
Ali, Sk Musharaf; Samanta, Alok; Choudhury, Niharendu; Ghosh, Swapan K
2006-11-01
An expression for the shear viscosity of a binary fluid mixture is derived using mode-coupling theory in order to study the mass dependence. The calculated results on shear viscosity for a binary isotopic Lennard-Jones fluid mixture show good agreement with results from molecular dynamics simulation carried out over a wide range of mass ratio at different composition. Also proposed is a new generalized Stokes-Einstein relation connecting the individual diffusivities to shear viscosity. PMID:17279895
NASA Astrophysics Data System (ADS)
Astanina, M. S.; Sheremet, M. A.
2016-04-01
Unsteady natural convection inside of a differentially-heated square enclosure filled with a fluid of temperature-dependent viscosity has been numerically studied. A mathematical model formulated in the dimensionless stream function and vorticity has been solved by a finite difference method of the second order accuracy. The effect of dimensionless time and Prandtl number on streamlines and isotherms has been investigated for Ra = 105. The results clearly demonstrate an evolution of fluid flow and heat transfer in the case of variable viscosity fluid.
On the role of anisotropic viscosity for plate-scale flow
NASA Astrophysics Data System (ADS)
Becker, T. W.; Kawakatsu, H.
2011-09-01
We study the role of partial melt- or lattice fabric-induced, viscous anisotropy for lithosphere-asthenosphere interactions using mantle flow models. Mechanical anisotropy has only a moderate influence on plate-scale flow and global geoid predictions for the cases considered, and anisotropic weakening effects are similar to those due to effective, isotropic viscosity reduction. While anisotropy modifies details of mantle flow and may be relevant for time-dependent scenarios, it may be safely ignored for a range of other studies. These findings increase our confidence in previous isotropic modeling. They also imply that melt-rich layers may be a dynamically valid explanation for the lithosphere-asthenosphere boundary, as far as our anisotropic models are applicable.
Effects of activation energy and activation volume on the temperature-dependent viscosity of water.
Kwang-Hua, Chu Rainer
2016-08-01
Water transport in a leaf is vulnerable to viscosity-induced changes. Recent research has suggested that these changes may be partially due to variation at the molecular scale, e.g., regulations via aquaporins, that induce reductions in leaf hydraulic conductance. What are the quantitative as well as qualitative changes in temperature-dependent viscosity due to the role of aquaporins in tuning activation energy and activation volume? Using the transition-state approach as well as the boundary perturbation method, we investigate temperature-dependent viscosity tuned by activation energy and activation volume. To validate our approach, we compare our numerical results with previous temperature-dependent viscosity measurements. The rather good fit between our calculations and measurements confirms our present approach. We have obtained critical parameters for the temperature-dependent (shear) viscosity of water that might be relevant to the increasing and reducing of leaf hydraulic conductance. These parameters are sensitive to temperature, activation energy, and activation volume. Once the activation energy increases, the (shear) viscosity of water increases. Our results also show that as the activation volume increases (say, 10^{-23}m^{3}), the (shear) viscosity of water decreases significantly and the latter induces the enhancing of leaf hydraulic conductance. Within the room-temperature regime, a small increase in the activation energy will increase the water viscosity or reduce the leaf hydraulic conductance. Our approach and results can be applied to diverse plant or leaf attributes. PMID:27627349
Rotating disk flow stability in electrochemical cells: Effect of viscosity stratification
NASA Astrophysics Data System (ADS)
Pontes, J.; Mangiavacchi, N.; Conceição, A. R.; Barcia, O. E.; Mattos, O. R.; Tribollet, B.
2004-03-01
This work is about the effect of viscosity stratification on the hydrodynamic instability of rotating disk flow, and whether or not it can take into account experimental observations of the lowering of critical Reynolds numbers in electrochemical systems, where a viscosity stratification is assumed to result from the gradients of chemical species existing in the convective boundary layer near the disk electrode. The analysis is for temporal stability of a class of von Kármán solutions: fully three-dimensional modes are considered and the neutral curves are therefore functions of not only the Reynolds number but also the wave frequency and the two wave numbers. Global minimization over wave numbers and also over the frequency gives the critical Reynolds number. The neutral curves exhibit a two-mode structure and the dependence of both modes on parameters is studied. It is shown that viscosity stratification leads to an increase in the range of parameters where perturbations are amplified and to a reduction of the critical Reynolds number, in a wide range of perturbation frequencies. The results support the hypothesis that the current oscillations may originate from a hydrodynamic instability.
NASA Astrophysics Data System (ADS)
Grayson, J. W.; Song, M.; Sellier, M.; Bertram, A. K.
2015-06-01
Viscosity in particles consisting of secondary organic material (SOM) has recently become an area of research focus, since information on viscosity is needed to predict the environmental impacts of SOM particles. Recently Renbaum-Wolff et al. (2013a) developed a poke-flow technique that was combined with simulations of fluid flow to constrain the viscosities of SOM samples of 1-5 mg mass, roughly the maximum that may be collected from environmental chambers or flow tubes on a reasonable timescale. The current manuscript expands on the initial validation experiments carried out by Renbaum-Wolff et al. First, the poke-flow technique combined with simulations of fluid flow was used to determine the viscosity of sucrose-water particles over a relatively wide range of relative humidities (RHs). The lower and upper limits of viscosity at 59% RH were 1.0 × 101 and 1.6 × 104 Pa s, whilst at 37% RH the corresponding values were 7.2 × 104 and 4.7 × 106 Pa s, respectively. The results are in good agreement with recent measurements by Quintas et al. (2006) and Power et al. (2013). Second, the approach was used to determine the viscosity of two polybutene standards. The simulated lower and upper limits of viscosity for standard #1 was 2.0 × 102 and 1.2 × 104 Pa s, whilst for standard #2 the corresponding values were 3.1 × 102 and 2.4 × 104 Pa s. These values are in good agreement with values reported by the manufacturer. The results for both the sucrose-water particles and the polybutene standards show that the poke-flow technique combined with simulations of fluid flow is capable of providing both lower and upper limits of viscosity that are consistent with literature or measured values when the viscosity of the particles are in the range of ≈ 5 × 102 to ≈ 3 × 106 Pa s.
NASA Astrophysics Data System (ADS)
Parmentier, E. M.
2015-12-01
Release of a volatile phase, usually considered to be water, from the downgoing plate and the upward migration of volatile saturated melt toward higher temperatures in the interior of the wedge is one mechanism for generation of melt at a convergent plate boundary (Gill, 1981; Grove et al. 2012). However, other volatiles, including CO2, may be released. Adding CO2 reduces the water mole fraction in melt that is stable at a given temperature. Dissolved water has a large effect on melt viscosity; but, CO2 has practically none, leading to the possibility of significant viscosity variations in melt rising through the mantle wedge. This may have important implications for the heterogeneity of erupted melts as discussed below."Saffman-Taylor" instability occurs as a low viscosity fluid flowing in porous media displaces another of higher viscosity. The low viscosity fluid forms fingers that extend progressively into the high viscosity fluid. For miscible fluids (no surface tension effects) in a non-compacting matrix (Chouke, 1982), the development of fingers is controlled by interdiffusion of the fluids.Numerical experiments to be reported examine viscous fingering in a compacting permeable matrix at conditions appropriate for melt generation in a mantle wedge. Mixing of melts with different CO2/water by diffusion in silicate melts alone is generally slow; however, fingering reduces the scale of CO2/water heterogeneity making diffusion more effective. We explore the persistence of a CO2/water heterogeneity of a given scale rising through the mantle wedge at a rate fast enough to preserve 230Th disequilibrium. The rise height over which heterogeneity can persist as fingers develop depends on the viscosity, i.e. CO2/water, variation initially present; viscosity variations on the order of 10% allow km-scale heterogeneity to persist over vertical scales comparable to the height of the wedge.
Effects of Red Blood Cell Aggregation on the Apparent Viscosity of Blood Flow in Tubes.
NASA Astrophysics Data System (ADS)
Hitt, Darren L.; Lowe, Mary L.
1996-11-01
In arterioles and venules (20-200μ diameter), the low shear rates enable red blood cells to form aggregate structures of varying sizes and morphology. The size and distribution of the aggregates affect the flow impedance within a microvascular network; this effect may be characterized by an "apparent viscosity". In this study, we measure the apparent viscosity of blood flow in 50μ glass tubes as a function of shear rate and red blood cell volume fraction (hematocrit); for a fixed tube geometry and an imposed flow rate, the viscosity is determined by measuring the pressure drop across the tube. To correlate the apparent viscosity with the size and spatial distribution of the aggregates in the flow, video images of the flow are recorded and analyzed using power spectral techniques. Pig blood and sheep blood are used as the models for aggregating and non-aggregating blood, respectively. Supported by NSF PFF Award CTS-9253633
Dependence of the viscosity on the chain end dynamics in polymer melts
NASA Astrophysics Data System (ADS)
Paeßens, Matthias
2003-06-01
We compare the Rubinstein-Duke model for reptation to a model where the boundary dynamics are modified by calculating the viscosity of polymer melts. The question is investigated whether the viscosity is determined by details of the dynamics of the polymer ends or by the stretching of the polymer. Toward this end, the dependence of the viscosity on the particle density of the lattice gas models which can be identified by the stretching is determined. We show that the influence of the stretching of the polymer on the absolute value of the viscosity in the scaling limit of very long chains is much bigger than the influence of the boundary dynamics, whereas the corrections of the scaling of the viscosity depends significantly on the details of the boundary dynamics.
Effects of a temperature-dependent viscosity on thermal convection in binary mixtures
NASA Astrophysics Data System (ADS)
Hilt, Markus; Glässl, Martin; Zimmermann, Walter
2014-05-01
We investigate the effect of a temperature-dependent viscosity on the onset of thermal convection in a horizontal layer of a binary fluid mixture that is heated from below. For an exponential temperature dependence of the viscosity, we find, in binary mixtures as a function of a positive separation ratio ψ and beyond a certain viscosity contrast, a discontinuous transition between two stationary convection modes having different wavelengths. In the range of negative values of the separation ratio ψ, a (continuous or discontinuous) transition from an oscillatory to a stationary onset of convection occurs beyond a certain viscosity contrast, and for large values of the viscosity ratio, the oscillatory onset of convection is suppressed.
Effects of a temperature-dependent viscosity on thermal convection in binary mixtures.
Hilt, Markus; Glässl, Martin; Zimmermann, Walter
2014-05-01
We investigate the effect of a temperature-dependent viscosity on the onset of thermal convection in a horizontal layer of a binary fluid mixture that is heated from below. For an exponential temperature dependence of the viscosity, we find, in binary mixtures as a function of a positive separation ratio ψ and beyond a certain viscosity contrast, a discontinuous transition between two stationary convection modes having different wavelengths. In the range of negative values of the separation ratio ψ, a (continuous or discontinuous) transition from an oscillatory to a stationary onset of convection occurs beyond a certain viscosity contrast, and for large values of the viscosity ratio, the oscillatory onset of convection is suppressed. PMID:25353805
Torczynski, J.R.; Henderson, J.A.; O`Hern, T.J.; Chu, T.Y.; Blanchat, T.K.
1994-01-01
Three-dimensional natural convection of a fluid in an enclosure is examined. The geometry is motivated by a possible magmaenergy extraction system, and the fluid is a magma simulant and has a highly temperature-dependent viscosity. Flow simulations are performed for enclosures with and without a cylinder, which represents the extractor, using the finite-element code FIDAP (Fluid Dynamics International). The presence of the cylinder completely alters the flow pattern. Flow-visualization and PIV experiments are in qualitative agreement wit the simulations.
Yang, Xiaogang; Wang, Qi
2016-01-28
We study channel flows of active polar liquid crystals (APLCs) focusing on the role played by the active viscosity (β) and the self-propelling speed (ω) on the formation and long time evolution of spontaneous flows using a continuum model. First, we study the onset of spontaneous flows by carrying out a linear stability analysis on two special steady states subject to various physical boundary conditions. We identify a single parameter b1, proportional to a linear combination of the active viscosity and the self-propelling speed, and inversely proportional to a Frank elastic constant, the solvent viscosity, and the liquid crystal relaxation time. We show that the active viscosity and the self-propelling speed influence the onset of spontaneous flows through b1 in that for any fixed value of the bulk activity parameter ζ, large enough |b1| can suppress the spontaneous flow. We then follow spontaneous flows in long time to further investigate the role of β and ω on spatial-temporal structures in the nonlinear regime numerically. The numerical study demonstrates a strong correlation between the most unstable eigenfunction obtained from the linear analysis and the terminal steady state or the persistent, traveling wave structure, revealing the genesis of flow and orientational structures in the active matter system. In the nonlinear regime, a nonzero b1 facilitates the formation of traveling waves in the case of boundary anchoring (the Dirichlet boundary condition) so long as the linear stability analysis predicts an onset of spontaneous flows; in the case of the free boundary condition (the Neumann boundary condition), a stable, spatially homogeneous tilted state always emerges in the presence of two active effects. Finally, we note that various fully out-of-plane spatio-temporal structures can emerge in long time dynamics depending on the boundary condition as well as the initial state of the polarity vector field. PMID:26583506
Jun Kang, Yang; Ryu, Jeongeun; Lee, Sang-Joon
2013-01-01
The accurate viscosity measurement of complex fluids is essential for characterizing fluidic behaviors in blood vessels and in microfluidic channels of lab-on-a-chip devices. A microfluidic platform that accurately identifies biophysical properties of blood can be used as a promising tool for the early detections of cardiovascular and microcirculation diseases. In this study, a flow-switching phenomenon depending on hydrodynamic balancing in a microfluidic channel was adopted to conduct viscosity measurement of complex fluids with label-free operation. A microfluidic device for demonstrating this proposed method was designed to have two inlets for supplying the test and reference fluids, two side channels in parallel, and a junction channel connected to the midpoint of the two side channels. According to this proposed method, viscosities of various fluids with different phases (aqueous, oil, and blood) in relation to that of reference fluid were accurately determined by measuring the switching flow-rate ratio between the test and reference fluids, when a reverse flow of the test or reference fluid occurs in the junction channel. An analytical viscosity formula was derived to measure the viscosity of a test fluid in relation to that of the corresponding reference fluid using a discrete circuit model for the microfluidic device. The experimental analysis for evaluating the effects of various parameters on the performance of the proposed method revealed that the fluidic resistance ratio (RJL/RL, fluidic resistance in the junction channel (RJL) to fluidic resistance in the side channel (RL)) strongly affects the measurement accuracy. The microfluidic device with smaller RJL/RL values is helpful to measure accurately the viscosity of the test fluid. The proposed method accurately measured the viscosities of various fluids, including single-phase (Glycerin and plasma) and oil-water phase (oil vs. deionized water) fluids, compared with conventional methods. The proposed
NASA Astrophysics Data System (ADS)
Koo, Hyearn-Maw
2016-07-01
The shear-rate-dependent viscosity coefficients of hard ellipsoids are derived for arbitrary relative orientations to the shear flow geometry. Each of the nine components of the coefficients scaled by the Newtonian shear viscosity agrees with the previous result for the viscosity in the zero-shear-rate limit. Among the components, the shear viscosity is graphically displayed for nematic ellipsoids with an axis ratio greater than 1 and for disc-like ellipsoids with an axis ratio less than 1 over the whole range of relative orientations of the axis of ellipsoid to the plane shear layer. As the primary axis of the ellipsoid rotates from the x-axis to the y-axis in the x-y plane, the shear viscosity increases or decreases for nematic or disc-like ellipsolids, respectively.
Shear time dependent viscosity of polystyrene-ethylacrylate based shear thickening fluid
NASA Astrophysics Data System (ADS)
Chen, Qian; Xuan, Shouhu; Jiang, Wanquan; Cao, Saisai; Gong, Xinglong
2016-04-01
In this study, the influence of the shear rate and shear time on the transient viscosity of polystyrene-ethylacrylate based shear thickening fluid (STF) is investigated. If the shear rate is stepwise changed, it is found that both the viscosity and critical shear rate are affected by the shear time. Above the critical shear rate, the viscosity of the STF with larger power law exponent (n) increases faster. However, the viscosity tends to decrease when the shear time is long enough. This phenomenon can be responsible for the reversible structure buildup and the break-down process. An effective volume fraction (EVF) mechanism is proposed to analyze the shear time dependent viscosity and it is found that viscosity changes in proportion to EVF. To further clarify the structure evolution, a structural kinetic model is studied because the structural kinetic parameter (λ) could describe the variation in the effective volume fraction. The theoretical results of the structural kinetic model agree well with the experimental results. With this model, the change in viscosity and EVF can be speculated from the variation of λ and then the structure evolution can be better illustrated.
Photodirecting Marangoni Flow to Pattern Thin Polymer Films: Decoupling Viscosity and Diffusivity
NASA Astrophysics Data System (ADS)
Kim, Chae Bin; Jones, Amanda; Janes, Dustin; Arshad, Talha; Bonnecaze, Roger; Ellison, Christopher
The Marangoni effect causes liquids to flow towards localized regions of higher surface tension. In thin polymer films, this effect could offer a practically useful route to manufacture topographically patterned surfaces. In this presentation, we report a photochemical strategy to harness Marangoni flow as a versatile patterning method along with comparisons to a theoretical model that reveals the underlying physics of this process. The model agrees well with experiments with no adjustable parameters. It further indicates that higher aspect ratio features are favored by large surface tension gradients, low diffusivities and low viscosities. However, as described by the Rouse model, low viscosities are generally correlated with high diffusivities; diffusivity is also an important factor in the timescale by which the spatial surface tension patterns decay. This coupling between diffusivity and viscosity could critically limit feature aspect ratio for any given surface tension pattern. A potential strategy that decouples diffusivity and viscosity of the film components will be presented.
Fluid friction and wall viscosity of the 1D blood flow model.
Wang, Xiao-Fei; Nishi, Shohei; Matsukawa, Mami; Ghigo, Arthur; Lagrée, Pierre-Yves; Fullana, Jose-Maria
2016-02-29
We study the behavior of the pulse waves of water into a flexible tube for application to blood flow simulations. In pulse waves both fluid friction and wall viscosity are damping factors, and difficult to evaluate separately. In this paper, the coefficients of fluid friction and wall viscosity are estimated by fitting a nonlinear 1D flow model to experimental data. In the experimental setup, a distensible tube is connected to a piston pump at one end and closed at another end. The pressure and wall displacements are measured simultaneously. A good agreement between model predictions and experiments was achieved. For amplitude decrease, the effect of wall viscosity on the pulse wave has been shown as important as that of fluid viscosity. PMID:26862041
Effect of Large Bulk Viscosity on Two-Dimensional Transonic Flow
NASA Astrophysics Data System (ADS)
Cramer, Mark
2012-11-01
We examine steady two-dimensional transonic flows over a thin airfoil or turbine blade. The wing Reynolds number is taken to be large and the fluid is described by the classical Navier-Stokes equations. The bulk viscosity is taken to be large compared to the shear viscosity. We use the Method of Matched Asymptotic Expansions to give the conditions under which the effects of large bulk viscosity are no longer negligible. We show that longitudinal viscous effects must be considered at lowest order when the ratio of bulk to shear viscosity is on the order of the product of the conventional Reynolds number times the two-thirds power of the non-dimensional airfoil thickness. Under these conditions the flow is shown to be frictional, irrotational, and governed by the viscous form of the transonic small disturbance equation. This work was supported by NSF Grant CBET-0625015.
NASA Technical Reports Server (NTRS)
Lin, T C; Street, R E
1954-01-01
Schamberg was the first to solve the differential equations of slip flow, including the Burnett terms, for concentric circular cylinders assuming constant coefficients of viscosity and thermal conductivity. The problem is solved for variable coefficients of viscosity and thermal conductivity in this paper by applying a transformation which leads to an iteration method. Starting with the solution for constant coefficients, this method enables one to approximate the solution for variable coefficients very closely after one or two steps. Satisfactory results are shown to follow from Schamberg's solution by using his values of constant coefficients multiplied by a constant factor, leading to what are denoted as the effective coefficients of viscosity and thermal conductivity.
NASA Technical Reports Server (NTRS)
Lin, T C; Street, R E
1953-01-01
The differential equations of slip flow, including the Burnett terms, were first solved by Schamberg assuming that the coefficients of viscosity and heat conduction of the gas were constants. The problem is solved herein for variable coefficients of viscosity and thermal conductivity by applying a transformation leading to an iteration method. The method, starting with the solution for constant coefficients, enables one to approximate the solution for variable coefficients very closely after one or two steps. Satisfactory results are shown to follow from Schamberg's solution by using his values of the constant coefficients multiplied by a constant factor 'N', leading to what are denoted as the effective coefficients of viscosity and thermal conductivity.
Parallel Plate Flow of a Third-Grade Fluid and a Newtonian Fluid With Variable Viscosity
NASA Astrophysics Data System (ADS)
Yıldız, Volkan; Pakdemirli, Mehmet; Aksoy, Yiğit
2016-07-01
Steady-state parallel plate flow of a third-grade fluid and a Newtonian fluid with temperature-dependent viscosity is considered. Approximate analytical solutions are constructed using the newly developed perturbation-iteration algorithms. Two different perturbation-iteration algorithms are used. The velocity and temperature profiles obtained by the iteration algorithms are contrasted with the numerical solutions as well as with the regular perturbation solutions. It is found that the perturbation-iteration solutions converge better to the numerical solutions than the regular perturbation solutions, in particular when the validity criteria of the regular perturbation solution are not satisfied. The new analytical approach produces promising results in solving complex fluid problems.
Effect of bulk viscosity on elliptic flow near the QCD phase transition
Denicol, G. S.; Kodama, T.; Mota, Ph.; Koide, T.
2009-12-15
In this work, we examine the effect of bulk viscosity on elliptic flow, taking into account the critical behavior of the equation of state and transport coefficients near the QCD phase transition. We found that the p{sub T} dependence of v{sub 2} is quantitatively changed by the presence of the QCD phase transition. Within reasonable values of the transport coefficients, v{sub 2} decreases by a factor of 15% at small p{sub T} values (<1 GeV). However, for larger values of p{sub T} (>2 GeV), the interplay between the velocity of sound and transport coefficient near the QCD phase transition enhances v{sub 2}. We point out that Grad's 14-moment approximation cannot be applied for the calculation of the one-particle distribution function at the freeze-out.
Temperature and density dependence of the shear viscosity of liquid sodium
NASA Astrophysics Data System (ADS)
Meyer, N.; Xu, H.; Wax, J.-F.
2016-06-01
The density and temperature dependence of the shear viscosity of liquid sodium is studied. The stress autocorrelation function is calculated by equilibrium molecular dynamics simulations, which allow us to obtain the value of shear viscosity using the Green-Kubo formula. The Fiolhais potential is used to calculate the interionic interactions, which are validated by comparison between simulation and experimental data along the liquid-gas coexistence curve. The behavior of viscosity over a wide range of the liquid phase of the phase diagram is studied. Along isochoric lines, it presents a minimum, while it monotonically increases along isotherms. An expression is proposed for the viscosity as a function of temperature and density which reproduces our data for liquid sodium at any density in the range [1000-2000 kg m-3 ] and any temperature in the range [700-7000 K]. The validity of the Stokes-Einstein relation over the investigated state points is discussed.
Viscosity Dependence of Some Protein and Enzyme Reaction Rates: Seventy-Five Years after Kramers.
Sashi, Pulikallu; Bhuyan, Abani K
2015-07-28
Kramers rate theory is a milestone in chemical reaction research, but concerns regarding the basic understanding of condensed phase reaction rates of large molecules in viscous milieu persist. Experimental studies of Kramers theory rely on scaling reaction rates with inverse solvent viscosity, which is often equated with the bulk friction coefficient based on simple hydrodynamic relations. Apart from the difficulty of abstraction of the prefactor details from experimental data, it is not clear why the linearity of rate versus inverse viscosity, k ∝ η(-1), deviates widely for many reactions studied. In most cases, the deviation simulates a power law k ∝ η(-n), where the exponent n assumes fractional values. In rate-viscosity studies presented here, results for two reactions, unfolding of cytochrome c and cysteine protease activity of human ribosomal protein S4, show an exceedingly overdamped rate over a wide viscosity range, registering n values up to 2.4. Although the origin of this extraordinary reaction friction is not known at present, the results indicate that the viscosity exponent need not be bound by the 0-1 limit as generally suggested. For the third reaction studied here, thermal dissociation of CO from nativelike cytochrome c, the rate-viscosity behavior can be explained using Grote-Hynes theory of time-dependent friction in conjunction with correlated motions intrinsic to the protein. Analysis of the glycerol viscosity-dependent rate for the CO dissociation reaction in the presence of urea as the second variable shows that the protein stabilizing effect of subdenaturing amounts of urea is not affected by the bulk viscosity. It appears that a myriad of factors as diverse as parameter uncertainty due to the difficulty of knowing the exact reaction friction and both mode and consequences of protein-solvent interaction work in a complex manner to convey as though Kramers rate equation is not absolute. PMID:26135219
Yahya, S M; Anwer, S F; Sanghi, S
2013-10-01
In this work, Thermal Large Eddy Simulation (TLES) is performed to study the behavior of weakly compressible Newtonian fluids with anisotropic temperature-dependent viscosity in forced convection turbulent flow. A systematic analysis of variable-viscosity effects, isolated from gravity, with relevance to industrial cooling/heating applications is being carried out. A LES of a planar channel flow with significant heat transfer at a low Mach number was performed to study effects of fluid property variation on the near-wall turbulence structure. In this flow configuration the top wall is maintained at a higher temperature (T hot ) than the bottom wall (T cold ). The temperature ratio (R θ = T hot /T cold ) is fixed at 1.01, 2 and 3 to study the effects of property variations at low Mach number. Results indicate that average and turbulent fields undergo significant changes. Compared with isothermal flow with constant viscosity, we observe that turbulence is enhanced in the cold side of the channel, characterized by locally lower viscosity whereas a decrease of turbulent kinetic energy is found at the hot wall. The turbulent structures near the cold wall are very short and densely populated vortices but near the hot wall there seems to be a long streaky structure or large elongated vortices. Spectral study reveals that turbulence is completely suppressed at the hot side of the channel at a large temperature ratio because no inertial zone is obtained (i.e. index of Kolmogorov scaling law is zero) from the spectra in these region. PMID:24158263
The role of crystallinity and viscosity in the formation of submarine lava flow morphology
NASA Astrophysics Data System (ADS)
McClinton, J. Timothy; White, Scott M.; Colman, Alice; Rubin, Kenneth H.; Sinton, John M.
2014-09-01
Submarine lava flow morphology is commonly used to estimate relative flow velocity, but the effects of crystallinity and viscosity are rarely considered. We use digital petrography and quantitative textural analysis techniques to determine the crystallinity of submarine basaltic lava flows, using a set of samples from previously mapped lava flow fields at the hotspot-affected Galápagos Spreading Center. Crystallinity measurements were incorporated into predictive models of suspension rheology to characterize lava flow consistency and rheology. Petrologic data were integrated to estimate bulk lava viscosity. We compared the crystallinity and viscosity of each sample with its flow morphology to determine their respective roles in submarine lava emplacement dynamics. We find no correlation between crystallinity, bulk viscosity, and lava morphology, implying that flow advance rate is the primary control on submarine lava morphology. However, we show systematic variations in crystal size and shape distribution among pillows, lobates, and sheets, suggesting that these parameters are important indicators of eruption processes. Finally, we compared the characteristics of lavas from two different sampling sites with contrasting long-term magma supply rates. Differences between lavas from each study site illustrate the significant effect of magma supply on the physical properties of the oceanic upper crust.
NASA Astrophysics Data System (ADS)
Tartakovsky, Alexandre M.; Meakin, Paul; Huang, Hai
2004-12-01
Stochastic analysis is commonly used to address uncertainty in the modeling of flow and transport in porous media. In the stochastic approach, the properties of porous media are treated as random functions with statistics obtained from field measurements. Several studies indicate that hydrological properties depend on the scale of measurements or support scales, but most stochastic analysis does not address the effects of support scale on stochastic predictions of subsurface processes. In this work we propose a new approach to study the scale dependence of stochastic predictions. We present a stochastic analysis of immiscible fluid-fluid displacement in randomly heterogeneous porous media. While existing solutions are applicable only to systems in which the viscosity of one phase is negligible compare with the viscosity of the other (water-air systems for example), our solutions can be applied to the immiscible displacement of fluids having arbitrarily viscosities such as NAPL-water and water-oil. Treating intrinsic permeability as a random field with statistics dependant on the permeability support scale (scale of measurements) we obtained, for one-dimensional systems, analytical solutions for the first moments characterizing unbiased predictions (estimates) of system variables, such as the pressure and fluid-fluid interface position, and we also obtained second moments, which characterize the uncertainties associated with such predictions. Next we obtained empirically scale dependent exponential correlation function of the intrinsic permeability that allowed us to study solutions of stochastic equations as a function of the support scale. We found that the first and second moments converge to asymptotic values as the support scale decreases. In our examples, the statistical moments reached asymptotic values for support scale that were approximately 1/10000 of the flow domain size. We show that analytical moment solutions compare well with the results of Monte
One-, two- and three-phase viscosity treatments for basaltic lava flows.
Harris, Andrew J L; Allen, John S
2008-01-01
Lava flows comprise three-phase mixtures of melt, crystals, and bubbles. While existing one-phase treatments allow melt phase viscosity to be assessed on the basis of composition, water content, and/or temperature, two-phase treatments constrain the effects of crystallinity or vesicularity on mixture viscosity. However, three-phase treatments, allowing for the effects of coexisting crystallinity and vesicularity, are not well understood. We investigate existing one- and two-phase treatments using lava flow case studies from Mauna Loa (Hawaii) and Mount Etna (Italy) and compare these with a three-phase treatment that has not been applied previously to basaltic mixtures. At Etna, melt viscosities of 425 ± 30 Pa s are expected for well-degassed (0.1 w. % H(2)O), and 135 ± 10 Pa s for less well-degassed (0.4 wt % H(2)O), melt at 1080°C. Application of a three-phase model yields mixture viscosities (45% crystals, 25-35% vesicles) in the range 5600-12,500 Pa s. This compares with a measured value for Etnean lava of 9400 ± 1500 Pa s. At Mauna Loa, the three-phase treatment provides a fit with the full range of field measured viscosities, giving three-phase mixture viscosities, upon eruption, of 110-140 Pa s (5% crystals, no bubble effect due to sheared vesicles) to 850-1400 Pa s (25-30% crystals, 40-60% spherical vesicles). The ability of the three-phase treatment to characterize the full range of melt-crystal-bubble mixture viscosities in both settings indicates the potential of this method in characterizing basaltic lava mixture viscosity. PMID:21691456
Time dependent parallel viscosity and relaxation rate of poloidal rotation in the banana regime
Hsu, C.T.; Shaing, K.C.; Gormley, R. )
1994-01-01
Time dependent ion parallel viscous force in the banana regime with arbitrary inverse aspect ratio [epsilon] is calculated using the eigenfunction approach. The flux surface averaged viscosity is then used to study the relaxation process of the poloidal rotation which leads to oscillatory relaxation behavior. The relaxation rate [nu][sub [ital p
A new non-eddy viscosity subgrid-scale model and its application to channel flow
NASA Technical Reports Server (NTRS)
Shah, K. B.; Ferziger, J. H.
1995-01-01
To date, most large-eddy simulations (LES) have been carried out with eddy viscosity subgrid scale (SGS) models, with only a few exceptions that used the mixed model. Even though the assumptions behind Smagorinsky's model are rather stringent, it has been applied successfully to a variety of turbulent flows. This success is attributed to the ability of eddy viscosity models to drain energy from large scales, thus simulating the dissipative nature of turbulence. Most SGS models are absolutely dissipative, i.e. they remove energy from the large scales at every instant. However, SGS stresses may transfer energy back to the large scales intermittently; this reverse transfer or backscatter is especially important in geophysical flows and in transition. In a fully developed channel flow, there is reverse flow of energy from small to large scales near the walls, but eddy viscosity models are unable to account for this important feature. The dynamic localization eddy viscosity model of Ghosal et al. (1995) allows backscatter by co-evolving an auxiliary equation for the SGS energy; however, the computational cost is considerably larger than for conventional SGS models (Cabot 1994). In this report, a new non-eddy viscosity model based on local approximation of total quantities in terms of filtered ones is introduced; the scale similarity model of Bardina (1983) is a special case of this model. This procedure does not require the assumption of homogeneity, permits backscatter of energy from small to large scales, and is readily implemented in finite difference codes. The results of applying the proposed model to second order finite volume simulation of plane channel flow at high Reynolds numbers (Re(sub b) = 38,000) is described in this report. Greater emphasis is placed on the high Reynolds number flow since it provides a more rigorous test of the SGS model and its potential application. The results are compared to ones produced by the conventional and dynamic Smagorinsky
Oral glucose retention, saliva viscosity and flow rate in 5-year-old children.
Negoro, M; Nakagaki, H; Tsuboi, S; Adachi, K; Hanaki, M; Tanaka, D; Takami, Y; Nakano, T; Kuwahara, M; Thuy, T T
2000-11-01
There are significant differences of glucose retention in site-specificity and individuals. Sixty-two 5-year-old nursery schoolchildren participated in this study on the relation between the viscosity of saliva and flow rate and glucose retention. Each child was instructed to rinse his/her mouth with a glucose solution (0.5 M, 5 ml) and then to spit out. Three minutes after rinsing, glucose retention was determined. Resting saliva was collected by a natural outflow method, then the flow rate was determined. A rotational viscometer was used to determine the viscosity. Glucose retention and flow rate were correlated at the left maxillary primary molars, and glucose retention and viscosity were correlated at the maxillary central primary incisors. It was concluded that glucose retention after glucose mouth rinsing was site-specific, and that glucose retention and the index of decayed, missing and filled primary teeth (dmft) were slightly correlated with the salivary viscosity and flow rate. PMID:11000387
CONSTRAINTS ON THE VISCOSITY AND MAGNETIC FIELD IN HOT ACCRETION FLOWS AROUND BLACK HOLES
Liu, B. F.; Taam, Ronald E. E-mail: r-taam@northwestern.edu
2013-07-15
The magnitude of the viscosity and magnetic field parameters in hot accretion flows is investigated in low luminosity active galactic nuclei (LLAGNs). Theoretical studies show that a geometrically thin, optically thick disk is truncated at mass accretion rates less than a critical value by mass evaporated vertically from the disk to the corona, with the truncated region replaced by an advection dominated accretion flow (ADAF). The critical accretion rate for such a truncation is a function of the viscosity and magnetic field. Observations of X-ray photon indices and spectral fits of a number of LLAGNs published in the literature provide an estimate of the critical rate of mass accretion and the truncation radius, respectively. By comparing the observational results with theoretical predictions, the viscosity and magnetic field parameters in the hot accretion flow region are estimated. Specifically, the mass accretion rates inferred in different sources constrain the viscosity parameter, whereas the truncation radii of the disk, as inferred from spectral fits, further constrain the magnetic field parameter. It is found that the value of the viscosity parameter in the corona/ADAF ranges from 0.17 to 0.5, with values clustered about 0.2-0.3. Magnetic pressure is required by the relatively small truncation radii for some LLAGNs and is found to be as high as its equipartition value with the gas pressure. The inferred values of the viscosity parameter are in agreement with those obtained from the observations of non-stationary accretion in stellar mass black hole X-ray transients. This consistency provides support for the paradigm that a geometrically thin disk is truncated by means of a mass evaporation process from the disk to the corona at low mass accretion rates.
Thin Film Flow of a Third Grade Fluid with Variable Viscosity
NASA Astrophysics Data System (ADS)
Nadeem, Sohail
2009-10-01
The effects of variable viscosity on the flow and heat transfer in a thin film flow for a third grade fluid has been discussed. The thin film is considered on the outer side of an infinitely long vertical cylinder. The governing nonlinear differential equations of momentum and energy are solved analytically by using homotopy analysis method. The expression for the viscous dissipation and entropy generation are also defined. The graphical results are presented for various physical parameters appearing in the problem
Indirect on-line determination of Newtonian fluid viscosity based on numerical flow simulations
NASA Astrophysics Data System (ADS)
Bachelet, C.; Dantan, Ph.; Flaud, P.
2003-01-01
A new indirect method of determining the viscosity of a Newtonian fluid flowing in a tube with a geometrical singularity is proposed. Due to this singularity, the shape of the dimensionless velocity profiles is closely correlated with the Reynolds number of the flow. Newtonian fluid flows were simulated numerically with various Reynolds numbers. Based on the results of these calculations, an abacus was plotted showing the relationship between the dimensionless velocity and the dimensionless viscosity. On the other hand, dimensionless velocities were also obtained by measuring velocity profiles on a hydrodynamic bench with an ultrasonic Doppler velocimeter. These experimental values were plotted on the abacus and the viscosity of the actual fluid was thus determined. Comparisons were made with viscometer measurements in order to assess the accuracy of the method and its range of validity. This method is of great potential interest for application to industrial plans when it is necessary to know the viscosity of a fluid undergoing a transformation without interrupting the process by taking fluid samples.
The effects of depth-dependent viscosity in the lithosphere on post-seismic viscous relaxation
NASA Astrophysics Data System (ADS)
Yamasaki, T.; Houseman, G. A.
2010-12-01
Following an earthquake elastic strain is relaxed by several mechanisms, including aseismic slip, poroelastic relaxation and viscous relaxation. The observed surface deformation reflects the integrated effect of these mechanisms, and it is therefore essential to evaluate the behaviour of each deformation process in order to advance our understanding of the co-and post-seismic deformations in the earthquake cycle. This evaluation requires mathematical models of the deformation, ground-truthed where possible using geodetic data (GPS and/or InSAR) to measure the surface deformation that accompanies and follows the earthquake. In this study, the effects of depth-dependent viscosity (DDV) variation in the lithosphere on the signature of post-seismic viscous relaxation are compared with the predictions of a uniform viscosity (UNV) model. For this purpose, we use a new parallelized 3-D finite element code, oregano_ve, to solve the linear Maxwell visco-elastic response following an applied internal fault displacement in a rectangular block. The model consists of a visco-elastic layer overlain by an elastic layer; the visco-elastic layer has a depth-dependent viscosity: η = η0exp[c(z0-z)], where η0 is the viscosity at the bottom of the layer, c is a constant (c = 0 for UNV model), z is the depth and z0 is the depth at the bottom of the layer. The fault displacement is implemented using the split node method developed by Melosh and Raefsky (BSSA, 71,1391,1981). We compare the relaxation of displacement that occurs on the surface after an instantaneous strike-slip faulting event for UNV and DDV models. For any given DDV model, we can choose a UNV model which approximately mimics the behaviour of the DDV model, but the required UNV viscosity depends on the distance from the fault; a smaller UNV viscosity is implied for a surface point that is further from the fault. The quality with which a UNV model can match a DDV simulation also depends on distance from the fault. In the
Steady flow on to a conveyor belt - Causal viscosity and shear shocks
NASA Technical Reports Server (NTRS)
Syer, D.; Narayan, Ramesh
1993-01-01
Some hydrodynamical consequences of the adoption of a causal theory of viscosity are explored. Causality is introduced into the theory by letting the coefficient of viscosity go to zero as the flow velocity approaches a designated propagation speed for viscous signals. Consideration is given to a model of viscosity which has a finite propagation speed of shear information, and it is shown that it produces two kinds of shear shock. A 'pure shear shock' corresponds to a transition from a superviscous to a subviscous state with no discontinuity in the velocity. A 'mixed shear shock' has a shear transition occurring at the same location as a normal adiabatic or radiative shock. A generalized version of the Rankine-Hugoniot conditions for mixed shear shocks is derived, and self-consistent numerical solutions to a model 2D problem in which an axisymmetric radially infalling stream encounters a spinning star are presented.
Effect of liquid viscosity on wave behavior in gas-liquid two-phase flow
Kondo, Yoshiyuki; Mori, Koji; Yagishita, Takuya; Nakabo, Akinobu
1999-07-01
Measurements of time-spatial distributions of liquid holdups for the vertical upward gas-liquid two-phase flow were carried out by using the supermultiple cross-sectional mean liquid holdup probes (S-CHOP) and the semi-supermultiple point-electrode probes (SS-PEP) in the wide range of superficial gas and liquid velocity, j{sub g} and j{sub {ell}}, and the liquid kinematic viscosities were {nu}{sub {ell}} = 1 x 10{sup {minus}6}, 10 x 10{sup {minus}6} and 20 x 10{sup {minus}6} m{sup 1}/s. The time-spatial maps of wave behavior and the interfacial profiles were presented. Close inspection of these results reveals that there also exist huge waves and disturbance waves in the higher liquid viscosity conditions. To clarify the characteristics of these waves, the wave-vein analysis and the cluster analysis by K-mean algorithm were applied. These methods distinguished huge wave and disturbance wave objectively. The appearance regions of liquid slug, huge wave, and disturbance wave for each liquid viscosity condition were presented and the effects of liquid viscosity on them were discussed. Furthermore, velocity, width and height of these waves were determined, and the effects of liquid viscosity on them were clarified.
THE INFLUENCE OF PRESSURE-DEPENDENT VISCOSITY ON THE THERMAL EVOLUTION OF SUPER-EARTHS
Stamenkovic, Vlada; Noack, Lena; Spohn, Tilman; Breuer, Doris E-mail: Lena.Noack@dlr.de E-mail: Tilman.Spohn@dlr.de
2012-03-20
We study the thermal evolution of super-Earths with a one-dimensional (1D) parameterized convection model that has been adopted to account for a strong pressure dependence of the viscosity. A comparison with a 2D spherical convection model shows that the derived parameterization satisfactorily represents the main characteristics of the thermal evolution of massive rocky planets. We find that the pressure dependence of the viscosity strongly influences the thermal evolution of super-Earths-resulting in a highly sluggish convection regime in the lower mantles of those planets. Depending on the effective activation volume and for cooler initial conditions, we observe with growing planetary mass even the formation of a conductive lid above the core-mantle boundary (CMB), a so-called CMB-lid. For initially molten planets our results suggest no CMB-lids but instead a hot lower mantle and core as well as sluggish lower mantle convection. This implies that the initial interior temperatures, especially in the lower mantle, become crucial for the thermal evolution-the thermostat effect suggested to regulate the interior temperatures in terrestrial planets does not work for massive planets if the viscosity is strongly pressure dependent. The sluggish convection and the potential formation of the CMB-lid reduce the convective vigor throughout the mantle, thereby affecting convective stresses, lithospheric thicknesses, and heat fluxes. The pressure dependence of the viscosity may therefore also strongly affect the propensity of plate tectonics, volcanic activity, and the generation of a magnetic field of super-Earths.
Endre, Z H; Kuchel, P W
1986-08-01
Metabolically active human erythrocytes were incubated with [alpha-13C]glycine which led to the specific enrichment of intracellular glutathione. The cells were then studied using 13C-NMR in which the longitudinal relaxation times (T1) and nuclear Overhauser enhancements of the free glycine and glutathione were measured. The T1 values of labelled glycine were also determined in various-concentration solutions of bovine serum albumin and glycerol and also of the natural abundance 13C of glycerol in glycerol solutions. From the T1 estimates the rotational correlation time (tau r) was calculated using a formula based on a model of an isotropic spherical rotor or that of a symmetrical ellipsoidal rotor; for glycine the differences in estimates of tau r obtained using the two models were not significant. From the correlation times and by use of the Stokes-Einstein equations viscosity and translational diffusion coefficients were calculated; thus comment can be made on the likelihood of diffusion control of certain enzyme-catalysed reactions in the erythrocyte. Bulk viscosities of the erythrocyte cytoplasm and the above-mentioned solutions were measured using Ostwald capillary viscometry. Large differences existed between the latter viscosity estimates and those based upon NMR-T1 measurements. We derived an equation from the theory of the viscosity of concentrated solutions which contains two phenomenological interaction parameters, a 'shape' factor and a 'volume' factor; it was fitted to data relating to the concentration dependence of viscosity measured by both methods. We showed, by using the equation and interaction-parameter estimates for a particular probe molecule in a particular solution, that it was possible to correlate NMR viscosity and bulk viscosity; in other words, given an estimate of the bulk viscosity, it was possible to calculate the NMR 'micro' viscosity or vice versa. However, the values of the interaction parameters depend upon the relative sizes of
NASA Astrophysics Data System (ADS)
Song, M.; Liu, P. F.; Hanna, S. J.; Li, Y. J.; Martin, S. T.; Bertram, A. K.
2015-05-01
Oxidation of isoprene is an important source of secondary organic material (SOM) in atmospheric particles, especially in areas such as the Amazon Basin. Information on the viscosities, diffusion rates, and mixing times within isoprene-derived SOM is needed for accurate predictions of air quality, visibility, and climate. Currently, however, this information is not available. Using a bead-mobility technique and a poke-flow technique combined with fluid simulations, the relative humidity (RH)-dependent viscosities of SOM produced from isoprene photo-oxidation were quantified for 20-60 μm particles at 295 ± 1 K. From 84.5 to 0% RH, the viscosities for isoprene-derived SOM varied from ~ 2 × 10-1 to ~ 3 × 105 Pa s, implying that isoprene-derived SOM ranges from a liquid to a semisolid over this RH range. These viscosities correspond to diffusion coefficients of ~ 2 × 10-8 to ~ 2 × 10-14 cm2 s-1 for large organic molecules that follow the Stokes-Einstein relation. Based on the diffusion coefficients, the mixing time of large organic molecules within 200 nm isoprene-derived SOM particles ranges from approximately 0.1 h to less than 1 s. To illustrate the atmospheric implications of this study's results, the Amazon Basin is used as a case study for an isoprene-dominant forest. Considering the RH and temperature range observed in the Amazon Basin and with some assumptions about the dominant chemical compositions of SOM particles in the region, it is likely that SOM particles in this area are liquid and reach equilibrium with large gas-phase organic molecules on short time scales, less than or equal to approximately 0.1 h.
Berteau, Cecile; Filipe-Santos, Orchidée; Wang, Tao; Rojas, Humberto E; Granger, Corinne; Schwarzenbach, Florence
2015-01-01
Aim The primary objective of this study was to evaluate the impact of fluid injection viscosity in combination with different injection volumes and flow rates on subcutaneous (SC) injection pain tolerance. Methods The study was a single-center, comparative, randomized, crossover, Phase I study in 24 healthy adults. Each participant received six injections in the abdomen area of either a 2 or 3 mL placebo solution, with three different fluid viscosities (1, 8–10, and 15–20 cP) combined with two different injection flow rates (0.02 and 0.3 mL/s). All injections were performed with 50 mL syringes and 27G, 6 mm needles. Perceived injection pain was assessed using a 100 mm visual analog scale (VAS) (0 mm/no pain, 100 mm/extreme pain). The location and depth of the injected fluid was assessed through 2D ultrasound echography images. Results Viscosity levels had significant impact on perceived injection pain (P=0.0003). Specifically, less pain was associated with high viscosity (VAS =12.6 mm) than medium (VAS =16.6 mm) or low (VAS =22.1 mm) viscosities, with a significant difference between high and low viscosities (P=0.0002). Target injection volume of 2 or 3 mL was demonstrated to have no significant impact on perceived injection pain (P=0.89). Slow (0.02 mL/s) or fast (0.30 mL/s) injection rates also showed no significant impact on perceived pain during SC injection (P=0.79). In 92% of injections, the injected fluid was located exclusively in SC tissue whereas the remaining injected fluids were found located in SC and/or intradermal layers. Conclusion The results of this study suggest that solutions of up to 3 mL and up to 15–20 cP injected into the abdomen within 10 seconds are well tolerated without pain. High viscosity injections were shown to be the most tolerated, whereas injection volume and flow rates did not impact perceived pain. PMID:26635489
Vertical two-phase flow regimes and pressure gradients: Effect of viscosity
Da Hlaing, Nan; Sirivat, Anuvat; Siemanond, Kitipat; Wilkes, James O.
2007-05-15
The effect of liquid viscosity on the flow regimes and the corresponding pressure gradients along the vertical two-phase flow was investigated. Experiment was carried out in a vertical transparent tube of 0.019 m in diameter and 3 m in length and the pressure gradients were measured by a U-tube manometer. Water and a 50 vol.% glycerol solution were used as the working fluids whose kinematic viscosities were 0.85 x 10{sup -6} and 4.0 x 10{sup -6} m{sup 2}/s, respectively. In our air-liquid annular two-phase flow, the liquid film of various thicknesses flowed adjacent to the wall and the gas phase flowed at the center of the tube. The superficial air velocity, j{sub air}, was varied between 0.0021 and 58.7 m/s and the superficial liquid velocity, j{sub liquid}, was varied between 0 and 0.1053 m/s. In the bubble, the slug and the slug-churn flow regimes, the pressure gradients decreased with increasing Reynolds number. But in the annular and the mist flow regimes, pressure gradients increased with increasing Reynolds number. Finally, the experimentally measured pressure gradient values were compared and are in good agreement with the theoretical values. (author)
Membrane Viscosity Determined from Shear-Driven Flow in Giant Vesicles
NASA Astrophysics Data System (ADS)
Honerkamp-Smith, Aurelia R.; Woodhouse, Francis G.; Kantsler, Vasily; Goldstein, Raymond E.
2013-07-01
The viscosity of lipid bilayer membranes plays an important role in determining the diffusion constant of embedded proteins and the dynamics of membrane deformations, yet it has historically proven very difficult to measure. Here we introduce a new method based on quantification of the large-scale circulation patterns induced inside vesicles adhered to a solid surface and subjected to simple shear flow in a microfluidic device. Particle image velocimetry based on spinning disk confocal imaging of tracer particles inside and outside of the vesicle and tracking of phase-separated membrane domains are used to reconstruct the full three-dimensional flow pattern induced by the shear. These measurements show excellent agreement with the predictions of a recent theoretical analysis, and allow direct determination of the membrane viscosity.
The effect of viscosity on steady transonic flow with a nodal solution topology
NASA Technical Reports Server (NTRS)
Owocki, Stanley P.; Zank, Gary P.
1991-01-01
The effect of viscosity on a steady, transonic flow for which the inviscid limit has a nodal solution topology near the critical point is investigated. For the accelerating case, viscous solutions tend to repel each other, so that a very delicate choice of initial conditions is required to prevent them from diverging. Only the two critical solutions extend to arbitrarily large distances into both the subsonic and supersonic flows. For the decelerating case, the solutions tend to attract, and so an entire two-parameter family of solutions now extends over large distances. The general effect of viscosity on the solution degeneracy of a nodal topology is thus to reduce or limit it for the accelerating case and to enhance it for the decelerating case. The astrophysical implications of these findings are addressed.
The effects of viscosity on the stability of a trailing-line vortex in compressible flow
NASA Technical Reports Server (NTRS)
Stott, Jillian A. K.; Duck, Peter W.
1994-01-01
We consider the effects of viscosity on the inviscid stability of the Batchelor vortex in a compressible flow. The problem is tackled asymptotically, in the limit of large (streamwise and azimuthal) wavenumbers, together with large Mach numbers. Previous studies, with viscous effects neglected, found that the nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumber. This structure persists when viscous effects are included in the analysis. In the present study the mode present in the incompressible case ceases to be unstable at high Mach numbers and a center mode forms, whose stability characteristics are determined primarily by conditions close to the vortex axis. We find generally that viscosity has a stabilizing influence on the flow, while in the case of center modes, viscous effects become important at much larger Reynolds numbers than for the first class of disturbance.
Membrane viscosity determined from shear-driven flow in giant vesicles.
Honerkamp-Smith, Aurelia R; Woodhouse, Francis G; Kantsler, Vasily; Goldstein, Raymond E
2013-07-19
The viscosity of lipid bilayer membranes plays an important role in determining the diffusion constant of embedded proteins and the dynamics of membrane deformations, yet it has historically proven very difficult to measure. Here we introduce a new method based on quantification of the large-scale circulation patterns induced inside vesicles adhered to a solid surface and subjected to simple shear flow in a microfluidic device. Particle image velocimetry based on spinning disk confocal imaging of tracer particles inside and outside of the vesicle and tracking of phase-separated membrane domains are used to reconstruct the full three-dimensional flow pattern induced by the shear. These measurements show excellent agreement with the predictions of a recent theoretical analysis, and allow direct determination of the membrane viscosity. PMID:23909365
NASA Technical Reports Server (NTRS)
Izmailov, Alexander F.; Myerson, Allan S.
1995-01-01
The physical properties of a supersaturated binary solution such as its density rho, shear viscosity eta, and solute mass diffusivity D are dependent on the solute concentration c: rho = rho(c), eta = eta(c), and D = D(c). The diffusion boundary layer equations related to crystal growth from solution are derived for the case of natural convection with a solution density, a shear viscosity, and a solute diffusivity that are all depen- dent on solute concentration. The solution of these equations has demonstrated the following. (1) At the vicinity of the saturation concentration c(sub s) the solution shear viscosity eta depends on rho as eta(sub s) = eta(rho(sub s))varies as square root of rho(c(sub s)). This theoretically derived result has been verified in experiments with several aqueous solutions of inorganic and organic salts. (2) The maximum solute mass transfer towards the growing crystal surface can be achieved for values of c where the ratio of d ln(D(c)/dc) to d ln(eta(c)/dc) is a maximum.
NASA Astrophysics Data System (ADS)
Cook, Richard L.; King, H. E., Jr.; Herbst, Chris A.; Herschbach, Dudley R.
1994-04-01
The pressure and temperature dependent viscosities of two glass forming liquids, glycerol and dibutyl phthalate (DBP), have been studied in the range P=0-3 GPa, T=0-125 °C, and η=101-1010 cP. These studies were made using a combination of a rolling-ball and a centrifugal-force diamond anvil cell viscometer. The majority of the results extend up to viscosities of 107 cP, with those at 22.5 °C going to 1010 cP. The overall precision of the data are approximately 10% or better throughout. This level of precision allows us to define a viscosity surface which can then be extrapolated to the glass transition along both temperature and pressure cuts. The T-dependence of viscosity is larger for glycerol than DBP but the P-dependence smaller for glycerol than for DBP, whereas the T-dependence is much more pressure sensitive for DBP. These data provide an assessment of the T-dependence of an isothermal model (free volume), the P-dependence of an isobaric model (Vogel-Tammann-Fulcher) and by extension that for isochoric conditions. Fragility parameters are evaluated for these three isometric conditions. For glycerol and (less conclusively) DBP under isobaric conditions, the fragility increases markedly at high pressure. Under isochoric conditions, the fragility for both glycerol and DBP increases with increasing density. This is dramatic for DBP, which goes from a strong to an intermediate-strength liquid. For the isothermal model, we derive a new measure of fragility. Using this, DBP shows a trend common to several liquids, a decrease in fragility with increasing temperature. Glycerol, however, becomes more fragile over the same temperature range. For glycerol, the trends towards increased fragility at elevated pressure and temperature are consistent with diminished hydrogen bonding under those conditions. The P-dependence of the glass transition is also determined over a wide range of T. The slope, dTg/dP, is positive with the pressure dependence for glycerol being
Meng, Xuhui; Guo, Zhaoli
2015-10-01
A lattice Boltzmann model with a multiple-relaxation-time (MRT) collision operator is proposed for incompressible miscible flow with a large viscosity ratio as well as a high Péclet number in this paper. The equilibria in the present model are motivated by the lattice kinetic scheme previously developed by Inamuro et al. [Philos. Trans. R. Soc. London, Ser. A 360, 477 (2002)]. The fluid viscosity and diffusion coefficient depend on both the corresponding relaxation times and additional adjustable parameters in this model. As a result, the corresponding relaxation times can be adjusted in proper ranges to enhance the performance of the model. Numerical validations of the Poiseuille flow and a diffusion-reaction problem demonstrate that the proposed model has second-order accuracy in space. Thereafter, the model is used to simulate flow through a porous medium, and the results show that the proposed model has the advantage to obtain a viscosity-independent permeability, which makes it a robust method for simulating flow in porous media. Finally, a set of simulations are conducted on the viscous miscible displacement between two parallel plates. The results reveal that the present model can be used to simulate, to a high level of accuracy, flows with large viscosity ratios and/or high Péclet numbers. Moreover, the present model is shown to provide superior stability in the limit of high kinematic viscosity. In summary, the numerical results indicate that the present lattice Boltzmann model is an ideal numerical tool for simulating flow with a large viscosity ratio and/or a high Péclet number. PMID:26565362
Viscosity controls humidity dependence of N2O5 uptake to citric acid aerosol
NASA Astrophysics Data System (ADS)
Gržinić, G.; Bartels-Rausch, T.; Berkemeier, T.; Türler, A.; Ammann, M.
2015-12-01
The heterogeneous loss of dinitrogen pentoxide (N2O5) to aerosol particles has a significant impact on the night-time nitrogen oxide cycle and therefore the oxidative capacity in the troposphere. Using a 13N short-lived radioactive tracer method, we studied the uptake kinetics of N2O5 on citric acid aerosol particles as a function of relative humidity (RH). The results show that citric acid exhibits lower reactivity than similar dicarboxylic and polycarboxylic acids, with uptake coefficients between ∼ 3 × 10-4-∼ 3 × 10-3 depending on humidity (17-70 % RH). At RH above 50 %, the magnitude and the humidity dependence can be best explained by the viscosity of citric acid as compared to aqueous solutions of simpler organic and inorganic solutes and the variation of viscosity with RH and, hence, diffusivity in the organic matrix. Since the diffusion rates of N2O5 in highly concentrated citric acid solutions are not well established, we present four different parameterizations of N2O5 diffusivity based on the available literature data or estimates for viscosity and diffusivity of H2O. Above 50 % RH, uptake is consistent with the reacto-diffusive kinetic regime whereas below 50 % RH, the uptake coefficient is higher than expected from hydrolysis of N2O5 within the bulk of the particles, and the uptake kinetics is most likely limited by loss on the surface only. This study demonstrates the impact of viscosity in highly oxidized and highly functionalized secondary organic aerosol material on the heterogeneous chemistry of N2O5 and may explain some of the unexpectedly low loss rates to aerosol derived from field studies.
Upper Limit of the Viscosity Parameter in Accretion Flows around a Black Hole with Shock Waves
NASA Astrophysics Data System (ADS)
Nagarkoti, Shreeram; Chakrabarti, Sandip K.
2016-01-01
Black hole accretion is necessarily transonic; thus, flows must become supersonic and, therefore, sub-Keplerian before they enter into the black hole. The viscous timescale is much longer than the infall timescale close to a black hole. Hence, the angular momentum remains almost constant and the centrifugal force ˜ {l}2/{r}3 becomes increasingly dominant over the gravitational force ˜ 1/{r}2. The slowed down matter piles creating an accretion shock. The flow between shock and inner sonic point is puffed up and behaves like a boundary layer. This so-called Comptonizing cloud/corona produces hard X-rays and jets/outflows and, therefore, is an important component of black hole astrophysics. In this paper, we study steady state viscous, axisymmetric, transonic accretion flows around a Schwarzschild black hole. We adopt a viscosity parameter α and compute the highest possible value of α (namely, {α }{cr}) for each pair of two inner boundary parameters (namely, specific angular momentum carried to horizon, lin and specific energy at inner sonic point, E({x}{in})) which is still capable of producing a standing or oscillating shock. We find that while such possibilities exist for α as high as {α }{cr}=0.3 in very small regions of the flow parameter space, typical {α }{cr} appears to be about ˜0.05-0.1. Coincidentally, this also happens to be the typical viscosity parameter achieved by simulations of magnetorotational instabilities in accretion flows. We therefore believe that all realistic accretion flows are likely to have centrifugal pressure supported shocks unless the viscosity parameter everywhere is higher than {α }{cr}.
Vertex dynamics simulations of viscosity-dependent deformation during tissue morphogenesis.
Okuda, Satoru; Inoue, Yasuhiro; Eiraku, Mototsugu; Adachi, Taiji; Sasai, Yoshiki
2015-04-01
In biological development, multiple cells cooperate to form tissue morphologies based on their mechanical interactions; namely active force generation and passive viscoelastic response. In particular, the dynamic processes of tissue deformations are governed by the viscous properties of the tissues. These properties are spatially inhomogeneous because they depend on the tissue constituents, such as cytoplasm, cytoskeleton, basement membrane and extracellular matrix. The multicellular mechanics of tissue morphogenesis have been investigated in vertex dynamics models. However, conventional models are applicable only to quasi-static deformation processes, which do not account for tissue viscosities. We propose a vertex dynamics model that simulates the viscosity-dependent dynamic deformation processes during tissue morphogenesis. By incorporating local velocity fields into the governing equation of vertex movements, the model turns Galilean invariant. In addition, the viscous properties of tissue components are newly expressed by formulating friction forces on vertices as functions of the relative velocities among the vertices. The advantages of the proposed model are examined by epithelial growth simulations under the employed condition for quasi-static processes. As a result, the epithelial vesicle simulated by the proposed model is linearly elongated with nearly free stress, while that simulated by the conventional model is undulated with compressive residual stress. Therefore, the proposed model is able to reflect the timescale of deformations by satisfying Galilean invariance. Next, the applicability of the proposed model is assessed in epithelial growth simulations of viscous extracellular materials. In this test, the epithelial vesicles are deformed into tubular shapes by oriented cell divisions, and their morphologies are extremely sensitive to extracellular viscosity. Therefore, the dynamic deformations in the proposed model depend on the viscous properties
Effects of viscosity in a partially ionized channel flow with thermionic emission
Mikellides, Ioannis G.
2009-01-15
The flow of the partially ionized gas inside thermionic hollow cathodes spans a diverse range of theoretical disciplines in plasma physics and fluid mechanics. Understanding and predicting the evolution of such flows has many practical implications because hollow cathodes are critical components of electric propulsion systems used onboard scientific and commercial spacecraft presently in space or in the mission planning stages. As space missions become more demanding of the propulsion system in terms of throughput, understanding and predicting failure mechanisms of the system becomes imperative. Two-dimensional numerical simulations of the partially ionized gas generated by a thermionic hollow cathode have been performed to quantify the effects of viscosity inside the cylindrical channel of the device. A comparison of the inviscid and fully viscous flow fields shows that viscosity has a significant impact on the atomic species and a lesser effect on the ions. The internal pressure is determined to be more than 40% higher compared to the inviscid solution and the Reynolds number for the flow of atoms is found to be less than 20 inside the channel. Although the Mach number is computed to be <0.1 for approximately 95% of the channel, the solution for the velocity flow field begins to deviate from the Poiseuille (parabolic) solution at about 50% of the channel due mainly to collisional drag with ions.
Viscous shock anomaly in a variable-viscosity Burgers flow with an active scalar
NASA Astrophysics Data System (ADS)
Talbot, B.; Mammeri, Y.; Bedjaoui, N.
2015-12-01
This paper examines the effect of viscosity variability on the formation of shocklets (small transient shocks) through the inhomogeneity in composition of the propagating medium. For this purpose, both analytical estimates and numerical spectral method are applied to a Burgers’ equation—where viscosity is a space-time function depending on a coupled advection-diffusion equation for the local mass fraction. The coefficient of viscosity thus behaves as an active scalar. The inhomogeneous shocklet is modeled by a fixed sine wave for the initial velocity profile while different sine waves of higher frequency are used for the initial embedded distribution of scalar. The initial kinematic viscosity ratio {R}ν ={ν }{max}/{ν }{min} ranges from 1 to 4. It is found that, surprisingly, for all conditions at Rν > 1, i.e., for waves becoming more and more viscous on average, there was (1) a steeper maximum gradient in the shock transition zone, and consequently (2) velocity spectra extended toward the finest small scales, and (3) an enhanced energy dissipation rate is observed at the time of peak energy dissipation. These results will be useful to the understanding of small-scale dynamics for one-dimensional shocklets propagating in multi-component gas mixtures where noticeable active scalar effects are present.
Barenblatt, G I; Chorin, A J
1996-06-25
The small viscosity asymptotics of the inertial range of local structure and of the wall region in wallbounded turbulent shear flow are compared. The comparison leads to a sharpening of the dichotomy between Reynolds number dependent scaling (power-type) laws and the universal Reynolds number independent logarithmic law in wall turbulence. It further leads to a quantitative prediction of an essential difference between them, which is confirmed by the results of a recent experimental investigation. These results lend support to recent work on the zero viscosity limit of the inertial range in turbulence. PMID:11607688
NASA Technical Reports Server (NTRS)
Macaraeg, M. G.; Streett, C. L.; Hussaini, M. Y.
1987-01-01
Standard techniques used to model chemically-reacting flows require an artificial viscosity for stability in the presence of strong shocks. The resulting shock is smeared over at least three computational cells, so that the thickness of the shock is dictated by the structure of the overall mesh and not the shock physics. A gas passing through a strong shock is thrown into a nonequilibrium state and subsequently relaxes down over some finite distance to an equilibrium end state. The artificial smearing of the shock envelops this relaxation zone which causes the chemical kinetics of the flow to be altered. A method is presented which can investigate these issues by following the chemical kinetics and flow kinetics of a gas passing through a fully resolved shock wave at hypersonic Mach numbers. A nonequilibrium chemistry model for air is incorporated into a spectral multidomain Navier-Stokes solution method. Since no artificial viscosity is needed for stability of the multidomain technique, the precise effect of this artifice on the chemical kinetics and relevant flow features can be determined.
Concentration and temperature dependence of the viscosity of polyol aqueous solutions.
Longinotti, M Paula; Trejo González, José A; Corti, Horacio R
2014-08-01
The concentration and temperature dependence of the viscosity of supercooled polyol (sucrose, trehalose, glucose and glycerol) aqueous solutions was analyzed with the aim of finding simple and accurate correlation equations for the description of this transport property. Three different equations were examined and compared, two empirical equations and an equation derived from the Avramov-Milchev (AM) model. If a description of the viscosity temperature dependence is intended, the AM model gives the best representation of the experimental data with only two adjustable parameters, which have a clear physical meaning. However, if we focus on both, temperature and concentration dependence, the empirical equations are found to be superior to the AM model, except for the glycerol aqueous system. The AM model includes a parameter related to the system fragility, which was obtained for all the aqueous polyol mixtures previously mentioned as a function of concentration, and also for water-trehalose-sodium tetraborate mixtures as a function of the electrolyte content. The results show that the fragility parameter increases with polyol concentration in the series glycerol
Plate-like convection in fluids with temperature-dependent viscosity
NASA Astrophysics Data System (ADS)
Mancho, Ana M.; Curbelo, Jezabel
2013-11-01
The study of instabilities in fluids in which viscosity experiences a transition at a certain temperature range is of great interest for the understanding of planetary interiors, since this phenomena models the melting and solidification of a magma ocean and thus is suitable for representing a lithosphere over a convecting mantle. To this end, we study a 2D convection problem in which viscosity depends on temperature by abruptly changing its value by a factor 400 within a narrow temperature gap at which magma melts. We perform a study which combines bifurcation analysis and time dependent simulations. Solutions such as limit cycles are found that are fundamentally related to the presence of the O(2) symmetry. Sporadically during these cycles, through abrupt bursts, spontaneous plate-like behaviors that rapidly evolve towards a stagnant lid regime emerge. The plate-like evolution alternates motions towards either right or left, introducing temporary asymmetries on the convecting styles. Further time dependent regimes are described for different transition laws which are greatly influenced by the presence of the symmetry. We thank CESGA for computing facilities. This research is supported by the Spanish Ministry of Science under grant MTM2011-26696 and MINECO: ICMAT Severo Ochoa project SEV-2011-0087.
NASA Astrophysics Data System (ADS)
Garai, S.; Janaki, M. S.; Chakrabarti, N.
2016-09-01
The nonlinear propagation of low frequency waves, in a collisionless, strongly coupled dusty plasma (SCDP) with a density dependent viscosity, has been studied with a proper Galilean invariant generalized hydrodynamic (GH) model. The well known reductive perturbation technique (RPT) has been employed in obtaining the solutions of the longitudinal and transverse perturbations. It has been found that the nonlinear propagation of the acoustic perturbations govern with the modified Korteweg-de Vries (KdV) equation and are decoupled from the sheared fluctuations. In the regions, where transversal gradients of the flow exists, coupling between the longitudinal and transverse perturbations occurs due to convective nonlinearity which is true for the homogeneous case also. The results, obtained here, can have relative significance to astrophysical context as well as in laboratory plasmas.
Kanatharana, J.; Sukpisan, J.; Wang, S.Q.
1995-12-01
The dependences on the polyion concentration through the scaling relations in {eta} {alpha} c{sup {alpha}} and {Tau}{sub q} {alpha} c{sup {beta}}, where {eta} and {Tau}{sub q} are the solution viscosity and the relaxation time obtained from the dynamic light scattering respectively, are investigated for the partially hydrolyzed polyacrylamides at different degrees of hydrolysis. The scaling exponents a and {beta}, as determined in the semidilute regime, depend critically on the amount of salt added or the ionic strength. Both exponents, however, are independent of the amount of glycerol added which suggests that the excluded volume effect is relatively small in comparison with the effect of electrostatic repulsion. The salt-concentration dependence of the solution is also investigated: the corresponding scaling exponents for the 70% HPAM are insensitive to the solvent quality. The present experiment results are compared with recent scaling theories.
NASA Astrophysics Data System (ADS)
Sawko, Robert; Thompson, Chris P.
2010-09-01
This paper presents a series of numerical simulations of non-Newtonian fluids in high Reynolds number flows in circular pipes. The fluids studied in the computations have shear-thinning and yield stress properties. Turbulence is described using the Reynolds-Averaged Navier-Stokes (RANS) equations with the Boussinesq eddy viscosity hypothesis. The evaluation of standard, two-equation models led to some observations regarding the order of magnitude as well as probabilistic information about the rate of strain. We argue that an accurate estimate of the rate of strain tensor is essential in capturing important flow features. It is first recognised that an apparent viscosity comprises two flow dependant components: one originating from rheology and the other from the turbulence model. To establish the relative significance of the terms involved, an order of magnitude analysis has been performed. The main observation supporting further discussion is that in high Reynolds number regimes the magnitudes of fluctuating rates of strain and fluctuating vorticity dominate the magnitudes of their respective averages. Since these quantities are included in the rheological law, the values of viscosity obtained from the fluctuating and mean velocity fields are different. Validation against Direct Numerical Simulation data shows at least an order of magnitude discrepancy in some regions of the flow. Moreover, the predictions of the probabilistic analysis show a favourable agreement with statistics computed from DNS data. A variety of experimental, as well as computational data has been collected. Data come from the latest experiments by Escudier et al. [1], DNS from Rudman et al. [2] and zeroth-order turbulence models of Pinho [3]. The fluid rheologies are described by standard power-law and Herschel-Bulkley models which make them suitable for steady state calculations of shear flows. Suitable regularisations are utilised to secure numerical stability. Two new models have been
Better Strategies for Finite Element Solutions of Variable Viscosity Stokes Flow
NASA Astrophysics Data System (ADS)
Hasenclever, Jörg; Phipps Morgan, Jason; Shi, Chao
2010-05-01
Accurate numerical solution of variable viscosity Stokes Flow is one of the most important issues for better geodynamic understanding of mantle convection and mantle melting. While a good Stokes solver is usually an integral part of a good Navier-Stokes solver, typically Navier-Stokes equations are solved for flow of a fluid with uniform viscosity. The lumped-mass-matrix is an excellent and cheap preconditioner for uniform viscosity Stokes flow (cf. Maday and Patera, 1989), therefore for most applications to Navier-Stokes flow the ‘Stokes' part of the problem is viewed as well-resolved. Unfortunately, the inverse-viscosity-scaled lumped mass matrix does not work nearly as well to precondition Stokes flow in a fluid with strongly varying viscosity. This issue is already central to accurate numerical studies of convection in Earth's silicate-fluid mantle (May and Moresi, 2008; van Geenen et al., 2009; Burstedde et al., 2009) and may become central for researchers investigating Navier-Stokes problems with lateral variations in viscosity. Here we discuss several known computational hurdles to progress, and suggest strategies that offer promise in overcoming them. The choices for solving the discrete pressure equation arising from Stokes flow typically involve several tradeoffs between speed and storage requirements. In exact math, the discrete pressure matrix S is symmetric, so that it should be possible to use a symmetric preconditioned conjugate gradient (CG) Krylov algorithm instead of needing an asymmetric GMRES (cf. Saad, 2003) or GCR (Generalized Conjugate Residual, cf. Van der Vorst, 2003) that would require ~10-50 times more storage of past search directions. However, a CG-like method requires that the action of both S and any pressure preconditioner must be almost perfectly symmetric. This means that we must be very careful about the effects of roundoff in any iterative solver-based pressure preconditioner that may introduce numerically asymmetric operators
NASA Astrophysics Data System (ADS)
Lin, Jaw-Ren; Chu, Li-Ming; Hung, Chi-Ren; Lu, Rong-Fang
2011-09-01
According to the experimental work of C. Barus in Am. J. Sci. 45, 87 (1893) [1], the dependency of liquid viscosity on pressure is exponential. Therefore, we extend the study of squeeze film problems of long partial journal bearings for Stokes non-Newtonian couple stress fluids by considering the pressure-dependent viscosity in the present paper. Through a small perturbation technique, we derive a first-order closed-form solution for the film pressure, the load capacity, and the response time of partial-bearing squeeze films. It is also found that the non-Newtonian couple-stress partial bearings with pressure-dependent viscosity provide better squeeze-film characteristics than those of the bearing with constant-viscosity situation.
NASA Astrophysics Data System (ADS)
Moore, James D. P.; Parsons, Barry
2015-07-01
One of the unresolved questions concerning fault deformation is the degree and cause of localization of shear at depth beneath a fault. Geologic observations of exhumed shear zones indicate that while the motion is no longer planar, it can still be localized near the down-dip extension of the fault; however, the degree of localization is uncertain. We employ simple analytic and numerical models to investigate the structural form of distributed shear beneath a strike-slip fault, and the relative importance of the physical mechanisms that have the potential to localize a shear zone. For a purely depth dependent viscosity, η = η0 exp (-z/z0), we find that a shear zone develops with a half-width δ _w˜ √{z_0} for small z0 at the base of the layer, where lengths are non-dimensionalized by the layer thickness (d km). Including a non-linear stress-strain-rate relation (dot{ɛ }∝ σ ^n) scales δw by 1/√{n}, comparable to deformation length scales in thin viscous sheet calculations. We find that the primary control on the shear-zone width is the depth dependence of viscosity that arises from the temperature dependence of viscosity and the increase in temperature with depth. As this relationship is exponential, scaling relations give a dimensional half-width that scales approximately as tilde{δ}_w≈ T_{1/2}√{Rd/nQβ } km, where T_{1/2} (K) is the temperature at the midpoint of the layer, R (J mol-1 K-1) the gas constant, Q (J mol-1) the activation energy and β (K km-1) the geothermal gradient. This relation predicts the numerical results for the parameter range consistent with continental rheologies to within 2-5 per cent and shear-zone half-widths from 2 to 6 km. The inclusion of shear-stress heating reduces δw by only an additional 5-25 per cent, depending on the initial width of the shear zone. While the width of the shear zone may not decrease significantly, local temperature increases from shear-stress heating range from 50 to 300 °C resulting in a
NASA Technical Reports Server (NTRS)
Hyer, Robert W.; Trapaga, G.; Flemings, M. C.
1999-01-01
The viscosity of a liquid metal was successfully measured for the first time by a containerless method, the oscillating drop technique. This method also provides a means to obtain a precise, non-contact measurement of the surface tension of the droplet. This technique involves exciting the surface of the molten sample and then measuring the resulting oscillations; the natural frequency of the oscillating sample is determined by its surface tension, and the damping of the oscillations by the viscosity. These measurements were performed in TEMPUS, a microgravity electromagnetic levitator (EML), on the Space Shuttle as a part of the First Microgravity Science Laboratory (MSL-1), which flew in April and July 1997 (STS-83 and STS-94). Some results of the surface tension and viscosity measurements are presented for Pd82Si18. Some observations of the fluid dynamic characteristics (dominant flow patterns, turbulent transition, cavitation, etc.) of levitated droplets are presented and discussed together with magnetohydrodynamic calculations, which were performed to justify these findings.
Arora, Simran Kaur; Patel, A A; Kumar, Naveen; Chauhan, O P
2016-04-01
The shear-thinning low, medium and high-viscosity fiber preparations (0.15-1.05 % psyllium husk, 0.07-0.6 % guar gum, 0.15-1.20 % gum tragacanth, 0.1-0.8 % gum karaya, 0.15-1.05 % high-viscosity Carboxy Methyl Cellulose and 0.1-0.7 % xanthan gum) showed that the consistency coefficient (k) was a function of concentration, the relationship being exponential (R(2), 0.87-0.96; P < 0.01). The flow behaviour index (n) (except for gum karaya and CMC) was exponentially related to concentration (R(2), 0.61-0.98). The relationship between k and sensory viscosity rating (SVR) was essentially linear in nearly all cases. The SVR could be predicted from the consistency coefficient using the regression equations developed. Also, the relationship of k with fiber concentration would make it possible to identify the concentration of a particular gum required to have desired consistency in terms of SVR. PMID:27413236
Viscosity-dependent structural fluctuation of the M80-containing Ω-loop of horse ferrocytochrome c
NASA Astrophysics Data System (ADS)
Kumar, Rajesh; Jain, Rishu; Kumar, Rajesh
2013-06-01
To determine the effect of solvent viscosity on low-frequency local motions that control the slow changes in structural dynamics of proteins, we have studied the effects of solvent viscosity on the structural fluctuation of presumably the M80-containing Ω-loop by measuring the rate of thermally-driven CO-dissociation from a natively-folded carbonmonoxycytochrome c (NCO-state) in the 0.65-92.5 cP range of viscosity at pH 7.0. At low viscosities (⩽8 cP), the rate coefficient, kdiss for dissociation of CO from the NCO-state varies inversely with the viscosity, but saturates at high viscosities, suggesting that CO-dissociation reaction involves sequential stages that depend differently on solvent friction, i.e., solvent coupled and nonsolvent-coupled stages of the process. In the low viscosity regime (0.65 ⩽ ηs ⩽ 8.0 cP), the rate-viscosity data were fitted to modified Kramers model, kdiss = [A'/(σ + ηs)n]exp(-ΔG/RT), which produced internal friction, σ = 1.35 cP (±0.88), which suggests that the speed of CO-dissociation from NCO at ηs ⩽ 8.0 cP is controlled by internal friction.
A Study of Effects of Viscosity on Flow over Slender Inclined Bodies of Revolution
NASA Technical Reports Server (NTRS)
Allen, H Julian; Perkins, Edward W
1951-01-01
The observed flow field about slender inclined bodies of revolution is compared with the calculated characteristics based upon potential theory. The comparison is instructive in indicating the manner in which the effects of viscosity are manifest. Based on this and other studies, a method is developed to allow for viscous effects on the force and moment characteristics of bodies. The calculated force and moment characteristics of two bodies of high fineness ratio are shown to be in good agreement, for most engineering purposes, with experiment. (author)
Triamine-Modified Polyimides Having Improved Processability and Low Melt Flow Viscosity
NASA Technical Reports Server (NTRS)
Meador, Michael A. (Inventor); Nguyen, Baochan N. (Inventor); Eby, Ronald K. (Inventor)
2001-01-01
Addition-cured polyimides that contain the reaction product of an aromatic triamine or trianhydride analogue thereof, a reactive end group such as 5-norbornene-2, 3-dicarboxylic acid, ester derivatives of 5-norbornene-2, 3-dicarboxylic acid, anhydride derivatives of 5-norbornene-2, 3-dicarboxylic acid, or 4-phenylethynylphthalic anhydride, an aromatic diamine, and a dialkyl ester of an aromatic tetracarboxylic acid. The resultant starlike polyimides; exhibit lower melt flow viscosity than its linear counterparts, providing for improved processability of the polyimide. Also disclosed are methods for the synthesis of these polyimides as well as composite structures formed using these polyimides.
Beadles, J.R.; Spellman, G.P.
1992-03-01
This report is an evaluation of sensor technology for continuously determining pressure, flow, viscosity, and moisture content of the resin in fiber composite laminates that are being cured in an autoclave. An effort has been made to identify the individuals and firms active in research and manufacture of such sensors. Monitoring technologies of interest include dielectric, fiber optic, strain gage, capacitive, ultrasonic, piezoelectric, nuclear magnetic resonance, resistance change, vibration, tracer/fluorescent particle analysis, and anemometer. The focus is on sensors that produce real-time data; techniques that rely on indirect correlations and modeling for estimates of effects are discussed only briefly.
Jun Kang, Yang; Yeom, Eunseop; Lee, Sang-Joon
2013-01-01
Blood viscosity has been considered as one of important biophysical parameters for effectively monitoring variations in physiological and pathological conditions of circulatory disorders. Standard previous methods make it difficult to evaluate variations of blood viscosity under cardiopulmonary bypass procedures or hemodialysis. In this study, we proposed a unique microfluidic device for simultaneously measuring viscosity and flow rate of whole blood circulating in a complex fluidic network including a rat, a reservoir, a pinch valve, and a peristaltic pump. To demonstrate the proposed method, a twin-shaped microfluidic device, which is composed of two half-circular chambers, two side channels with multiple indicating channels, and one bridge channel, was carefully designed. Based on the microfluidic device, three sequential flow controls were applied to identify viscosity and flow rate of blood, with label-free and sensorless detection. The half-circular chamber was employed to achieve mechanical membrane compliance for flow stabilization in the microfluidic device. To quantify the effect of flow stabilization on flow fluctuations, a formula of pulsation index (PI) was analytically derived using a discrete fluidic circuit model. Using the PI formula, the time constant contributed by the half-circular chamber is estimated to be 8 s. Furthermore, flow fluctuations resulting from the peristaltic pumps are completely removed, especially under periodic flow conditions within short periods (T < 10 s). For performance demonstrations, the proposed method was applied to evaluate blood viscosity with respect to varying flow rate conditions [(a) known blood flow rate via a syringe pump, (b) unknown blood flow rate via a peristaltic pump]. As a result, the flow rate and viscosity of blood can be simultaneously measured with satisfactory accuracy. In addition, the proposed method was successfully applied to identify the viscosity of rat blood, which circulates in a
NASA Astrophysics Data System (ADS)
Logan, N. C.; Park, J.-K.; Paz-Soldan, C.; Lanctot, M. J.; Smith, S. P.; Burrell, K. H.
2016-03-01
This paper presents a single mode model that accurately predicts the coupling of applied nonaxisymmetric fields to the plasma response that induces neoclassical toroidal viscosity (NTV) torque in DIII-D H-mode plasmas. The torque is measured and modeled to have a sinusoidal dependence on the relative phase of multiple nonaxisymmetric field sources, including a minimum in which large amounts of nonaxisymmetric drive is decoupled from the NTV torque. This corresponds to the coupling and decoupling of the applied field to a NTV-driving mode spectrum. Modeling using the perturbed equilibrium nonambipolar transport (PENT) code confirms an effective single mode coupling between the applied field and the resultant torque, despite its inherent nonlinearity. The coupling to the NTV mode is shown to have a similar dependence on the relative phasing as that of the IPEC dominant mode, providing a physical basis for the efficacy of this linear metric in predicting error field correction optima in NTV dominated regimes.
NASA Astrophysics Data System (ADS)
Whittington, A. G.; Romine, W. L.
2014-12-01
Understanding the dynamics of rhyolitic conduits and lava flows, requires precise knowledge of how viscosity (η) varies with temperature (T), pressure (P) and volatile content (X). In order to address the paucity of viscosity data for high-silica rhyolite at low water contents, which represent water saturation at near-surface conditions, we made 245 viscosity measurements on Mono Craters (California) rhyolites containing between 0.01 and 1.1 wt.% H2O, at temperatures between 796 and 1774 K using parallel plate and concentric cylinder methods at atmospheric pressure. We then developed and calibrated a new empirical model for the log of the viscosity of rhyolitic melts, where non-linear variations due to temperature and water content are nested within a linear dependence of log η on P. The model was fitted to a total of 563 data points: our 245 new data, 255 published data from rhyolites across a wide P-T-X space, and 63 data on haplogranitic and granitic melts under high P-T conditions. Statistically insignificant parameters were eliminated from the model in an effort to increase parsimony and the final model is simple enough for use in numerical models of conduit or lava flow dynamics: log η = -5.142+(13080-2982log(w+0.229))/(T-(98.9-175.9 log(w+0.229)))- P(0.0007-0.76/T ) where η is in Pa s, w is water content in wt.%, P is in MPa and T is in K. The root mean square deviation (rmsd) between the model predictions and the 563 data points used in calibration is 0.39 log units. Experimental constraints have led previously to spurious correlations between P, T, X and η in viscosity data sets, so that predictive models may struggle to correctly resolve the individual effects of P, T and X, and especially their cross-correlations. The increasing water solubility with depth inside a simple isothermal sheet of obsidian suggests that viscosity should decrease by ~1 order of magnitude at ~20m depth and by ~2 orders of magnitude at ~100m depth. If equilibrium water
Elliptic flow and shear viscosity of the shattered color glass condensate
NASA Astrophysics Data System (ADS)
Ruggieri, Marco; Scardina, Francesco; Plumari, Salvatore; Greco, Vincenzo
2014-07-01
In this contribution, we report on our results about the computation of the elliptic flow of the quark-gluon-plasma produced in relativistic heavy ion collisions, simulating the expansion of the fireball by solving the relativistic Boltzmann equation for the parton distribution function tuned at a fixed shear viscosity to entropy density ratio η/s. We emphasize the role of saturation in the initial gluon spectrum modelling the shattering of the color glass condensate, causing the initial distribution to be out of equilibrium. We find that the saturation reduces the efficiency in building-up the elliptic flow, even if the thermalization process is quite fast τtherm ≈ 0.8fm/c. and the pressure isotropization even faster τisotr ≈ 0.3fm/c. The impact of the initial non-equilibrium manifests for non-central collisions and can modify the estimate of the viscosity respect to the assumption of full thermalization in pT-space.
The effects of rotational flow, viscosity, thickness, and shape on transonic flutter dip phenomena
NASA Technical Reports Server (NTRS)
Reddy, T. S. R.; Srivastava, Rakesh; Kaza, Krishna Rao V.
1988-01-01
The transonic flutter dip phenomena on thin airfoils, which are employed for propfan blades, is investigated using an integrated Euler/Navier-Stokes code and a two degrees of freedom typical section structural model. As a part of the code validation, the flutter characteristics of the NACA 64A010 airfoil are also investigated. In addition, the effects of artificial dissipation models, rotational flow, initial conditions, mean angle of attack, viscosity, airfoil thickness and shape on flutter are investigated. The results obtained with a Euler code for the NACA 64A010 airfoil are in reasonable agreement with published results obtained by using transonic small disturbance and Euler codes. The two artificial dissipation models, one based on the local pressure gradient scaled by a common factor and the other based on the local pressure gradient scaled by a spectral radius, predicted the same flutter speeds except in the recovery region for the case studied. The effects of rotational flow, initial conditions, mean angle of attack, and viscosity for the Reynold's number studied seem to be negligible or small on the minima of the flutter dip.
Assessing the numerical dissipation rate and viscosity in CFD simulations of fluid flows
NASA Astrophysics Data System (ADS)
Schranner, F. S.; Domaradzki, J. A.; Hickel, S.; Adams, N. A.
2014-11-01
We describe a method for quantifying the effective numerical dissipation rate and the effective numerical viscosity in Computational Fluid Dynamics simulations. Differently from the previous approach that was formulated in spectral space, the proposed method is developed in a physical-space representation and allows for determining numerical dissipation rates and viscosities locally, i.e., at the individual cell level or for arbitrary subdomains of the computational domain. The method is self-contained using only results produced by the Navier-Stokes solver being investigated. Since no extraneous information is required, the method is suitable for a straightforward quantification of the numerical dissipation as a post-processing step. We demonstrate the method's capabilities on the example of implicit large-eddy simulations of three-dimensional Taylor-Green vortex flows that exhibit laminar, transitional, and turbulent flow behavior at different stages of time evolution. For validation, we compare the numerical dissipation rate obtained using this method with exact reference data obtained with an accurate, spectral-space approach. Supported by Deutsche Forschungsgemeinschaft and Alexander von Humboldt Foundation.
NASA Technical Reports Server (NTRS)
Shih, T.-H.; Liou, W. W.; Shabbir, A.; Yang, Z.; Zhu, J.
1994-01-01
A new k-epsilon eddy viscosity model, which consists of a new model dissipation rate equation and a new realizable eddy viscosity formulation, is proposed. The new model dissipation rate equation is based on the dynamic equation of the mean-square vorticity fluctuation at large turbulent Reynolds number. The new eddy viscosity formulation is based on the realizability constraints: the positivity of normal Reynolds stresses and Schwarz' inequality for turbulent shear stresses. We find that the present model with a set of unified model coefficients can perform well for a variety of flows. The flows that are examined include: (1) rotating homogeneous shear flows; (2) boundary-free shear flows including a mixing layer, planar and round jets; (3) a channel flow, and flat plate boundary layers with and without a pressure gradient; and (4) backward facing step separated flows. The model predictions are compared with available experimental data. The results from the standard k-epsilon eddy viscosity model are also included for comparison. It is shown that the present model is a significant improvement over the standard k-epsilon eddy viscosity model.
NASA Astrophysics Data System (ADS)
Shih, T.-H.; Liou, W. W.; Shabbir, A.; Yang, Z.; Zhu, J.
1994-08-01
A new k-epsilon eddy viscosity model, which consists of a new model dissipation rate equation and a new realizable eddy viscosity formulation, is proposed. The new model dissipation rate equation is based on the dynamic equation of the mean-square vorticity fluctuation at large turbulent Reynolds number. The new eddy viscosity formulation is based on the realizability constraints: the positivity of normal Reynolds stresses and Schwarz' inequality for turbulent shear stresses. We find that the present model with a set of unified model coefficients can perform well for a variety of flows. The flows that are examined include: (1) rotating homogeneous shear flows; (2) boundary-free shear flows including a mixing layer, planar and round jets; (3) a channel flow, and flat plate boundary layers with and without a pressure gradient; and (4) backward facing step separated flows. The model predictions are compared with available experimental data. The results from the standard k-epsilon eddy viscosity model are also included for comparison. It is shown that the present model is a significant improvement over the standard k-epsilon eddy viscosity model.
Lv, Chunmei; Zou, Dawei; Qin, Meng; Meng, Wei; Cao, Yi; Wang, Wei
2013-08-27
Many cellular processes, such as the diffusion of biomacromolecules, the movement of molecular motors, and the conformational dynamics of proteins, are subjected to hydrodynamic forces because of the high viscosities of cellular environments. However, it is still unknown how hydrodynamic forces are related to the physical properties of different viscogens. Here, using the atomic force microscope-based force spectroscopy technique, we directly measured the hydrodynamic forces acting on a moving cantilever in various viscogen solutions. We found that the hydrodynamic force is not only dependent on the viscosity but also related to the molecular weight of viscogens. Counterintuitively, at the same macroscopic viscosity, the hydrodynamic force rises with the increasing molecular weight of viscogens, although the local microscopic viscosity of the solution decreases. This finding provides insights into the origin of hydrodynamic forces in biomolecule solutions and could inspire many force-spectroscopy-based techniques to measure the molecular weight and conformational changes of biomacromolecules in biological settings directly. PMID:23944228
NASA Astrophysics Data System (ADS)
Bunge, Hans-Peter; Richards, Mark A.; Baumgardner, John R.
1997-06-01
Mantle convection is influenced simultaneously by a number of physical effects: brittle failure in the surface plates, strongly variable viscosity, mineral phase changes, and both internal heating (radioactivity) and bottom heating from the core. Here we present a systematic study of three potentially important effects: depth-dependent viscosity, an endothermic phase change, and bottom versus internal heating. We model three-dimensional spherical convection at Rayleigh Ra=108 thus approaching the dynamical regime of the mantle. An isoviscous, internally heated reference model displays point-like downwellings from the cold upper boundary layer, a blue spectrum of thermal heterogeneity, and small but rapid time variations in flow diagnostics. A modest factor 30 increase in lower mantle viscosity results in a planform dominated by long, linear downwellings, a red spectrum, and great temporal stability. Bottom heating has the predictable effect of adding a thermal boundary layer at the base of the mantle. We use a Clapeyron slope of γ=-4 MPa °K-1 for the 670 km phase transition, resulting in a phase buoyancy parameter of P=-0.112. This phase change causes upwellings and downwellings to pause in the transition zone but has little influence on the inherent time dependence of flow and only a modest reddening effect on the heterogeneity spectrum. Larger values of P result in stronger effects, but our choice of P is likely already too large to be representative of the mantle transition zone. Combinations of all three effects are remarkably predictable in terms of the single-effect models, and the effect of depth-dependent viscosity is found to be dominant.
Energy Dissipating Structures Produced by Walls in Two-Dimensional Flows at Vanishing Viscosity
NASA Astrophysics Data System (ADS)
Nguyen van Yen, Romain; Farge, Marie; Schneider, Kai
2011-05-01
We perform numerical experiments of a dipole crashing into a wall, a generic event in two-dimensional incompressible flows with solid boundaries. The Reynolds number (Re) is varied from 985 to 7880, and no-slip boundary conditions are approximated by Navier boundary conditions with a slip length proportional to Re-1. Energy dissipation is shown to first set up within a vorticity sheet of thickness proportional to Re-1 in the neighborhood of the wall, and to continue as this sheet rolls up into a spiral and detaches from the wall. The energy dissipation rate integrated over these regions appears to converge towards Re-independent values, indicating the existence of energy dissipating structures that persist in the vanishing viscosity limit.
Logan, Nikolas C.; Park, Jong -Kyu; Paz-Soldan, Carloa; Lanctot, Matthew J.; Smith, Sterling P.; Burrell, K. H.
2016-02-05
This paper presents a single mode model that accurately predicts the coupling of applied nonaxisymmetric fields to the plasma response that induces neoclassical toroidal viscosity (NTV) torque in DIII-D H-mode plasmas. The torque is measured and modeled to have a sinusoidal dependence on the relative phase of multiple nonaxisymmetric field sources, including a minimum in which large amounts of nonaxisymmetric drive is decoupled from the NTV torque. This corresponds to the coupling and decoupling of the applied field to a NTV-driving mode spectrum. Modeling using the perturbed equilibrium nonambipolar transport (PENT) code confirms an effective single mode coupling between themore » applied field and the resultant torque, despite its inherent nonlinearity. Lastly, the coupling to the NTV mode is shown to have a similar dependence on the relative phasing as that of the IPEC dominant mode, providing a physical basis for the efficacy of this linear metric in predicting error field correction optima in NTV dominated regimes.« less
Design of a High Viscosity Couette Flow Facility for Patterned Surface Drag Measurements
NASA Astrophysics Data System (ADS)
Johnson, Tyler; Lang, Amy
2009-11-01
Direct drag measurements can be difficult to obtain with low viscosity fluids such as air or water. In this facility, mineral oil is used as the working fluid to increase the shear stress across the surface of experimental models. A mounted conveyor creates a flow within a plexiglass tank. The experimental model of a flat or patterned surface is suspended above a moving belt. Within the gap between the model and moving belt a Couette flow with a linear velocity profile is created. PIV measurements are used to determine the exact velocities and the Reynolds numbers for each experiment. The model is suspended by bars that connect to the pillow block housing of each bearing. Drag is measured by a force gauge connected to linear roller bearings that slide along steel rods. The patterned surfaces, initially consisting of 2-D cavities, are embedded in a plexiglass plate so as to keep the total surface area constant for each experiment. First, the drag across a flat plate is measured and compared to theoretical values for laminar Couette flow. The drag for patterned surfaces is then measured and compared to a flat plate.
Kuss, N; Bauknecht, E; Felbinger, C; Gehm, J; Gehm, L; Pöschl, J; Ruef, P
2015-10-01
Determination of shear stresses at given shear rates allow approximation of flow curves by mathematical models and to calculate viscosities of non-Newtonian fluids. In term neonates, the mean arterial blood pressure (MAP) is markedly below that of adults, therefore rheological properties of blood play an important role in maintaining perfusion. Whole blood viscosity was measured in umbilical cord blood taken from 62 term neonates using the LS 300 viscometer. Individual parameters that influence the viscosity of whole blood were measured: red blood cell (RBC) aggregation, plasma viscosity, hematocrit, and RBC deformability. The flow curve of whole blood of neonates was approximated by the method of Ostwald with the highest quality whereas in adults the best approximation was found by the method of Casson. With hematocrits of 0.40, the viscosity of whole blood in newborns approximated by Ostwald (9.84 ± 5.12 mPa·s) was significantly lower than that of adults (15.34 ± 3.01 mPa·s). The aggregation index of the blood of newborns was markedly lower (2.98 ± 2.12) than in adults (14.63 ± 3.50) whereas RBC deformability was higher in neonates. The viscosity of plasma determined by Ostwald revealed a lower exponent (n) in neonates (0.94 ± 022) compared to adults (1.01 ± 0.12) and the viscosity determined by Newton was lower in neonates (1.04 ± 0.16 mPa·s) than in adults (1.19 ± 0.07 mPa·s). The flow curve of neonatal blood which is best approximated by the model of Ostwald emphasizes its important viscous properties necessary for conditions with physiologically low blood pressure. PMID:26444620
Sarman, Sten; Laaksonen, Aatto
2012-09-14
We have calculated the twist viscosity and the alignment angle between the director and the stream lines in shear flow of a liquid crystal model system, which forms biaxial nematic liquid crystals, as functions of the density, from the Green-Kubo relations by equilibrium molecular dynamics simulation and by a nonequilibrium molecular dynamics algorithm, where a torque conjugate to the director angular velocity is applied to rotate the director. The model system consists of a soft ellipsoid-string fluid where the ellipsoids interact according a repulsive version of the Gay-Berne potential. Four different length-to-width-to-breadth ratios have been studied. On compression, this system forms discotic or calamitic uniaxial nematic phases depending on the dimensions of the molecules, and on further compression a biaxial nematic phase is formed. In the uniaxial nematic phase there is one twist viscosity and one alignment angle. In the biaxial nematic phase there are three twist viscosities and three alignment angles corresponding to the rotation around the various directors and the different alignments of the directors relative to the stream lines, respectively. It is found that the smallest twist viscosity arises by rotation around the director formed by the long axes, the second smallest one arises by rotation around the director formed by the normals of the broadsides, and the largest one by rotation around the remaining director. The first twist viscosity is rather independent of the density whereas the last two ones increase strongly with density. One finds that there is one stable director alignment relative to the streamlines, namely where the director formed by the long axes is almost parallel to the stream lines and where the director formed by the normals of the broadsides is almost parallel to the shear plane. The relative magnitudes of the components of the twist viscosities span a fairly wide interval so this model should be useful for parameterisation
NASA Astrophysics Data System (ADS)
Moore, J. D. P.; Parsons, B.
2014-12-01
One of the unresolved questions concerning fault deformation is the degree and cause of localisation of shear at depth beneath a fault. Geologic observations of exhumed shear zones indicate that whilst the motion is no longer planar, it can still be localised near the down-dip extension of the fault; however, the degree of localisation is uncertain. We employ simple analytic and numerical models to investigate the structural form of distributed shear beneath a strike-slip fault, and the relative importance of the physical mechanisms that have the potential to localise a shear zone. As we are concerned with long-term structure the model is time-averaged across the earthquake cycle, consisting of an idealised strike-slip fault within a rigid lid over a viscous layer. For a depth dependent viscosity, η = η0 exp (-z/z0), we find a shear zone develops with a half-width δw √z0 for small z0, where lengths are non-dimensionalised by the layer thickness (d km). Including a non-linear stress-strain rate relation (ɛ ˙ ∝ σn) scales δw by 1/√n, comparable to deformation length scales in thin viscous sheet calculations. We find that the primary control on δw is the depth dependence of viscosity arising from the increase in temperature with depth. As this relationship is exponential, scaling relations give a half-width that scales approximately as δw≈T(z=1/2)RdnQβ-----√km,delta_wapprox T(z=1/2){sqrtfrac{Rd}{nQbeta}} km, with T (K), gas constant R (J/mol K), activation energy Q (J/mol), and geotherm β (K/km). Figure illustrates shear zones for a dry olivine composition. For n = 1 the shear zone half-width is δw = 4 km, which reduces to δw = 2.3 km when n = 3; other parameter choices consistent with laboratory-derived rheological properties give δwfrom 2-6 km. The inclusion of shear-stress heating only reduces δw by an additional 5-25%, depending on the initial width of the shear zone; in the case of dry olivine with n = 3 we get δw = 1.8 km. This
Anisotropic eddy viscosity models
NASA Technical Reports Server (NTRS)
Carati, D.; Cabot, W.
1996-01-01
A general discussion on the structure of the eddy viscosity tensor in anisotropic flows is presented. The systematic use of tensor symmetries and flow symmetries is shown to reduce drastically the number of independent parameters needed to describe the rank 4 eddy viscosity tensor. The possibility of using Onsager symmetries for simplifying further the eddy viscosity is discussed explicitly for the axisymmetric geometry.
Shear-thinning and constant viscosity predictions for rotating sphere flows
NASA Astrophysics Data System (ADS)
Garduño, Isaías E.; Tamaddon-Jahromi, Hamid R.; Webster, Michael F.
2016-02-01
The steady motion of a rotating sphere is analysed through two contrasting viscoelastic models, a constant viscosity (FENE-CR) model and a shear-thinning (LPTT) model. Giesekus (Rheol. Acta 9:30-38, 1970) presented an intriguing rotating viscoelastic flow, which to date has not been completely explained. In order to investigate this flow, sets of parameters have been explored to analyse the significant differences introduced with the proposed models, while the momentum-continuity-stress equations are solved through a hybrid finite-element/finite volume numerical scheme. Solutions are discussed for first, sphere angular velocity increase (\\varOmega), and second, through material velocity-scale increase (α). Numerical predictions for different solvent-ratios (β) show significant differences as the sphere angular velocity increases. It is demonstrated that an emerging equatorial anticlockwise vortex emerges in a specific range of \\varOmega. As such, this solution matches closely with the Giesekus experimental findings. Additionally, inside the emerging inertial vortex, a contrasting positive second normal stress-difference (N2 ( dot{γ} ) = τ_{rr} - τ_{θθ}) region is found compared against the negative N2-enveloping layer.
Roar Skartlien; Espen Sollum; Andreas Akselsen; Paul Meakin
2012-07-01
A 3D lattice Boltzmann model for two-phase flow with amphiphilic surfactant was used to investigate the evolution of emulsion morphology and shear stress in starting shear flow. The interfacial contributions were analyzed for low and high volume fractions and varying surfactant activity. A transient viscoelastic contribution to the emulsion rheology under constant strain rate conditions was attributed to the interfacial stress. For droplet volume fractions below 0.3 and an average capillary number of about 0.25, highly elliptical droplets formed. Consistent with affine deformation models, gradual elongation of the droplets increased the shear stress at early times and reduced it at later times. Lower interfacial tension with increased surfactant activity counterbalanced the effect of increased interfacial area, and the net shear stress did not change significantly. For higher volume fractions, co-continuous phases with a complex topology were formed. The surfactant decreased the interfacial shear stress due mainly to advection of surfactant to higher curvature areas. Our results are in qualitative agreement with experimental data for polymer blends in terms of transient interfacial stresses and limited enhancement of the emulsion viscosity at larger volume fractions where the phases are co-continuous.
NASA Astrophysics Data System (ADS)
Kim, Yongsam; Lai, Ming-Chih
2012-12-01
An inextensible vesicle under shear flow experiences a tank-treading motion on its membrane if the viscosity contrast between the interior and exterior fluids is small. Above a critical threshold of viscosity contrast, the vesicle undergoes a tumbling bifurcation. In this paper, we extend our previous work [Kim and Lai, J. Comput. Phys.JCTPAH0021-999110.1016/j.jcp.2010.03.020 229, 4840 (2010)] to the case of different viscosity and investigate the transition between the tank-treading and tumbling motions in detail. The present numerical results are in a good agreement with other numerical and theoretical studies qualitatively. In addition, we study the inertial effect on this transition and find that the inertial effect might inhibit the tumbling motion in favor of the tank-treading motion, which is observed recently in the literature. The critical viscosity contrast for the transition to the tumbling motion usually increases as the reduced area increases in the Stokes regime. However, we surprisingly observe that the critical viscosity contrast decreases as the reduced area increases to some point in the flow of slightly higher Reynolds number. Our numerical result also shows that the inertial effect has stronger inhibition to tumbling motion when the reduced area is small.
Fang, J. Y.; Hsu, C. P.; Kang, Y. W.; Fang, K. C.; Kao, W. L.; Yao, D. J.; Chen, C. C.; Li, S. S.; Yeh, J. A.; Wang, Y. L.; Lee, G. Y.; Chyi, J. I.; Hsu, C. H.; Huang, Y. F.; Ren, F.
2013-11-28
The drain current fluctuation of ungated AlGaN/GaN high electron mobility transistors (HEMTs) measured in different fluids at a drain-source voltage of 0.5 V was investigated. The HEMTs with metal on the gate region showed good current stability in deionized water, while a large fluctuation in drain current was observed for HEMTs without gate metal. The fluctuation in drain current for the HEMTs without gate metal was observed and calculated as standard deviation from a real-time measurement in air, deionized water, ethanol, dimethyl sulfoxide, ethylene glycol, 1,2-butanediol, and glycerol. At room temperature, the fluctuation in drain current for the HEMTs without gate metal was found to be relevant to the dipole moment and the viscosity of the liquids. A liquid with a larger viscosity showed a smaller fluctuation in drain current. The viscosity-dependent fluctuation of the drain current was ascribed to the Brownian motions of the liquid molecules, which induced a variation in the surface dipole of the gate region. This study uncovers the causes of the fluctuation in drain current of HEMTs in fluids. The results show that the AlGaN/GaN HEMTs may be used as sensors to measure the viscosity of liquids within a certain range of viscosity.
NASA Astrophysics Data System (ADS)
Curbelo, J.; Mancho, A. M.
2013-10-01
We focus on the study of a convection problem in a two-dimensional setup in the presence of the O(2) symmetry. The viscosity in the fluid depends on the temperature as it changes its value abruptly in an interval around a temperature of transition. The influence of the viscosity law on the morphology of the plumes is examined for several parameter settings, and a variety of shapes ranging from spout- to mushroom-shaped are found. We explore the impact of the symmetry on the time evolution of this type of fluid, and we find solutions which are greatly influenced by its presence: at a large aspect ratio and high Rayleigh numbers, traveling waves, heteroclinic connections, and chaotic regimes are found. These solutions, which are due to the presence of symmetry, have not been previously described in the context of temperature-dependent viscosities. However, similarities are found with solutions described in other contexts such as flame propagation problems or convection problems with constant viscosity also in the presence of the O(2) symmetry, thus confirming the determining role of the symmetry in the dynamics.
NASA Technical Reports Server (NTRS)
Li, C.; Ban, H.; Lin, B.; Scripa, R. N.; Su, C.-H.; Lehoczky, S. L.
2004-01-01
The relaxation phenomenon of semiconductor melts, or the change of melt structure with time, impacts the crystal growth process and the eventual quality of the crystal. The thermophysical properties of the melt are good indicators of such changes in melt structure. Also, thermophysical properties are essential to the accurate predication of the crystal growth process by computational modeling. Currently, the temperature dependent thermophysical property data for the Hg-based II-VI semiconductor melts are scarce. This paper reports the results on the temperature dependence of melt density, viscosity and electrical conductivity of Hg-based II-VI compounds. The melt density was measured using a pycnometric method, and the viscosity and electrical conductivity were measured by a transient torque method. Results were compared with available published data and showed good agreement. The implication of the structural changes at different temperature ranges was also studied and discussed.
Oulaid, Othmane; Saad, Abdul-Khalik W; Aires, Pedro S; Zhang, Junfeng
2016-01-01
The tank-treading rotation of red blood cells (RBCs) in shear flows has been studied extensively with experimental, analytical, and numerical methods. Even for this relatively simple system, complicated motion and deformation behaviors have been observed, and some of the underlying mechanisms are still not well understood. In this study, we attempt to advance our knowledge of the relationship among cell motion, deformation, and flow situations with a numerical model. Our simulation results agree well with experimental data, and confirm the experimental finding of the decrease in frequency/shear-rate ratio with shear rate and the increase of frequency with suspending viscosity. Moreover, based on the detailed information from our simulations, we are able to interpret the frequency dependency on shear rate and suspending viscosity using a simple two-fluid shear model. The information obtained in this study thus is useful for understanding experimental observations of RBCs in shear and other flow situations; the good agreement to experimental measurements also shows the potential usefulness of our model for providing reliable results for microscopic blood flows. PMID:26158788
Decruppe, J P; Ponton, A
2003-03-01
The flow birefringence and the rheological properties of four viscoelastic solutions having nearly the same zero shear viscosity and subjected to shear flows are investigated in the linear and non-linear domains. The surfactant used for the samples is the cetyltrimethylammonium chloride in water at the concentration of 100 mmol/l with an organic salt, the sodium salicylate. The low shear viscosity curve versus the salt concentration is non-monotonic and has two maxima separated by a minimum forming four domains in which the salt concentration is chosen. For the two solutions belonging to the inner branch, i.e. between the two maxima, a simple Maxwellian behaviour is observed and shear banding occurs as confirmed by the flow birefringence pictures. Contrary to the results of P. Fisher (1996) where the unstable flow regime is restricted to the first decreasing part of the low shear viscosity curve of a cetylpyridinium chloride solution, we show that shear banding exits in a wider domain of the salt concentration. PMID:15015102
A carbon-free lithium-ion solid dispersion redox couple with low viscosity for redox flow batteries
NASA Astrophysics Data System (ADS)
Qi, Zhaoxiang; Koenig, Gary M.
2016-08-01
A new type of non-aqueous redox couple without carbon additives for flow batteries is proposed and the target anolyte chemistry is demonstrated. The so-called "Solid Dispersion Redox Couple" incorporates solid electroactive materials dispersed in organic lithium-ion battery electrolyte as its flowing suspension. In this work, a unique and systematic characterization approach has been used to study the flow battery redox couple in half cell demonstrations relative to a lithium electrode. An electrolyte laden with Li4Ti5O12 (LTO) has been characterized in multiple specially designed lithium half cell configurations. The flow battery redox couple described in this report has relatively low viscosity, especially in comparison to other flow batteries with solid active materials. The lack of carbon additive allows characterization of the electrochemical properties of the electroactive material in flow without the complication of conductive additives and unambiguous observation of the electrorheological coupling in these dispersed particle systems.
Thermal and Mechanical Erosion by Low-Viscosity Lava Flows at Hrad Vallis, Mars
NASA Astrophysics Data System (ADS)
Hopper, J.; Leverington, D. W.
2012-12-01
involving lava flows with depths of 5 to 20 m and dynamic viscosities on the order of ~1 Pa s. These rates of incision are estimated to have been associated with lava discharges as great as ~100,000 to 600,000 cubic meters per second and Reynolds numbers well in excess of 10,000, suggesting fully turbulent flow. Consistent with the findings of recent modeling efforts (Hurwitz et al., 2012, Journal of Geophysical Research-Planets, v.117), incision rates by thermal mechanisms are estimated to have been especially significant at Hrad Vallis as a result of the low channel slopes typical of this system, and should have exceeded mechanical incision rates for slopes less than 0.09 degrees. A volcanic origin for the Hrad Vallis system is in accord with the volcanic origins recently suggested for other Martian outflow systems, and correspondingly has important implications regarding our understanding of the past nature of surface conditions on Mars, and the planet's near-surface volatile content.
NASA Astrophysics Data System (ADS)
Makinde, O. D.; Onyejekwe, O. O.
2011-11-01
The steady flow and heat transfer of an electrically conducting fluid with variable viscosity and electrical conductivity between two parallel plates in the presence of a transverse magnetic field is investigated. It is assumed that the flow is driven by combined action of axial pressure gradient and uniform motion of the upper plate. The governing nonlinear equations of momentum and energy transport are solved numerically using a shooting iteration technique together with a sixth-order Runge-Kutta integration algorithm. Solutions are presented in graphical form and given in terms of fluid velocity, fluid temperature, skin friction and heat transfer rate for various parametric values. Our results reveal that the combined effect of magnetic field, viscosity, exponents of variable properties, various fluid and heat transfer dimensionless quantities and the electrical conductivity variation, have significant impact on the hydromagnetic and electrical properties of the fluid.
Uddin, Mohammed J.; Khan, Waqar A.; Amin, Norsarahaida S.
2014-01-01
The unsteady two-dimensional laminar g-Jitter mixed convective boundary layer flow of Cu-water and Al2O3-water nanofluids past a permeable stretching sheet in a Darcian porous is studied by using an implicit finite difference numerical method with quasi-linearization technique. It is assumed that the plate is subjected to velocity and thermal slip boundary conditions. We have considered temperature dependent viscosity. The governing boundary layer equations are converted into non-similar equations using suitable transformations, before being solved numerically. The transport equations have been shown to be controlled by a number of parameters including viscosity parameter, Darcy number, nanoparticle volume fraction, Prandtl number, velocity slip, thermal slip, suction/injection and mixed convection parameters. The dimensionless velocity and temperature profiles as well as friction factor and heat transfer rates are presented graphically and discussed. It is found that the velocity reduces with velocity slip parameter for both nanofluids for fluid with both constant and variable properties. It is further found that the skin friction decreases with both Darcy number and momentum slip parameter while it increases with viscosity variation parameter. The surface temperature increases as the dimensionless time increases for both nanofluids. Nusselt numbers increase with mixed convection parameter and Darcy numbers and decreases with the momentum slip. Excellent agreement is found between the numerical results of the present paper with published results. PMID:24927277
NASA Astrophysics Data System (ADS)
Pfusterschmied, G.; Kucera, M.; Wistrela, E.; Manzaneque, T.; Ruiz-Díez, V.; Sánchez-Rojas, J. L.; Bittner, A.; Schmid, U.
2015-10-01
It is the objective of this paper to report on the performance of piezoelectric MEMS resonators for viscosity and density measurements at elevated temperatures. A custom-built temperature controlled measurement setup is designed for fluid temperatures up to 100 °C. Piezoelectric single-side clamped resonators are fabricated, excited in 2nd order of the roof tile-shaped mode (13-mode) and exposed to several liquids (i.e. D5, N10, N35, PAO8, olive oil, ester oil and N100). At the next step, these results are analysed applying a straightforward evaluation model, thus demonstrating that with piezoelectric MEMS resonators the density (i.e. from {ρ\\min}=785 kg m-3 to {ρ\\max}=916 kg m-3) and viscosity (i.e. from {μ\\min}=1.20 mPa s to {μ\\max}=286.36 mPa s) values of liquids can be precisely determined in a wide range. Compared to standard measurement techniques, the results show for the first parameter a mean deviation of about 1.04% at 100 °C for all the liquids investigated. For the second parameter, the standard evaluation model implies a systematic deviation in viscosity with respect to the calibration being N35 in this study. This inherent lack of strength has a significant influence on the accuracy, especially at 100 °C due to fluids having a viscosity reduced by a factor of 30 for N100 compared to room temperature. This leads to relative deviations of about 23% at 100 °C and indicates the limits of the evaluation model.
NASA Astrophysics Data System (ADS)
Sunil; Mahajan, Amit
2009-09-01
A rigorous nonlinear stability result is derived by introducing a suitable generalized energy functional for a magnetized ferrofluid layer heated and soluted from below with magnetic field-dependent (MFD) viscosity, for stress-free boundaries. The mathematical emphasis is on how to control the nonlinear terms caused by magnetic body and inertia forces. For ferrofluids, we find that there is possibility of existence of subcritical instabilities, however, it is noted that in case of non-ferrofluid, global nonlinear stability Rayleigh number is exactly the same as that for linear instability. For lower values of magnetic parameters, this coincidence is immediately lost. The effects of magnetic parameter, M3, solute gradient, S1 and MFD viscosity parameter, δ, on the subcritical instability region have also been analyzed.
An, Hongli; Yuen, Manwai
2014-05-15
In this paper, we investigate the analytical solutions of the compressible Navier-Stokes equations with dependent-density viscosity. By using the characteristic method, we successfully obtain a class of drifting solutions with elliptic symmetry for the Navier-Stokes model wherein the velocity components are governed by a generalized Emden dynamical system. In particular, when the viscosity variables are taken the same as Yuen [M. W. Yuen, “Analytical solutions to the Navier-Stokes equations,” J. Math. Phys. 49, 113102 (2008)], our solutions constitute a generalization of that obtained by Yuen. Interestingly, numerical simulations show that the analytical solutions can be used to explain the drifting phenomena of the propagation wave like Tsunamis in oceans.
Calculation of laminar and turbulent boundary layers for two-dimensional time-dependent flows
NASA Technical Reports Server (NTRS)
Cebeci, T.
1977-01-01
A general method for computing laminar and turbulent boundary layers for two-dimensional time-dependent flows is presented. The method uses an eddy-viscosity formulation to model the Reynolds shear-stress term and a very efficient numerical method to solve the governing equations. The model was applied to steady two-dimensional and three-dimensional flows and was shown to give good results. A discussion of the numerical method and the results obtained by the present method for both laminar and turbulent flows are discussed. Based on these results, the method is efficient and suitable for solving time-dependent laminar and turbulent boundary layers.
Investigating plasma viscosity with fast framing photography in the ZaP-HD Flow Z-Pinch experiment
NASA Astrophysics Data System (ADS)
Weed, Jonathan Robert
The ZaP-HD Flow Z-Pinch experiment investigates the stabilizing effect of sheared axial flows while scaling toward a high-energy-density laboratory plasma (HEDLP > 100 GPa). Stabilizing flows may persist until viscous forces dissipate a sheared flow profile. Plasma viscosity is investigated by measuring scale lengths in turbulence intentionally introduced in the plasma flow. A boron nitride turbulence-tripping probe excites small scale length turbulence in the plasma, and fast framing optical cameras are used to study time-evolved turbulent structures and viscous dissipation. A Hadland Imacon 790 fast framing camera is modified for digital image capture, but features insufficient resolution to study turbulent structures. A Shimadzu HPV-X camera captures the evolution of turbulent structures with great spatial and temporal resolution, but is unable to resolve the anticipated Kolmogorov scale in ZaP-HD as predicted by a simplified pinch model.
NASA Astrophysics Data System (ADS)
Alligné, S.; Decaix, J.; Nicolet, C.; Avellan, F.; Münch, C.
2015-12-01
The 1D modelling of cavitation vortex rope dynamics in Francis turbine draft tube is decisive for prediction of pressure fluctuations in the system. However, models are defined with parameters which values must be quantified either experimentally or numerically. In this paper a methodology based on CFD simulations is setup to identify these parameters by exciting the flow through outlet boundary condition. A simplified test case is considered to assess if 1D cavitation model parameters can be identified from CFD simulations. It is shown that a low wave speed and a second viscosity due to the cavitating flow can be identified.
NASA Astrophysics Data System (ADS)
Nadeem, S.; Ijaz, S.
2015-10-01
The present theoretical model deals with the analysis of variable viscosity and thermal conductivity of a single wall carbon nanotube within the considered base fluid flowing through multiple stenosed arteries. A mathematical model is presented for the mild stenosis case and then solved by using symmetry boundary conditions to determine the exact solution of temperature, axial velocity and pressure gradient. The main hemodynamics due to multiple stenosis is also computed under the influence of a SWCNT. Numerical simulations are presented for the SWCNT with different values of nanoparticles volume fraction. The behavior of fluid flow for blood based SWCNT is discussed through graphs and streamlines.
Sandhagen, Bo; Lind, Lars
2012-01-01
It has previously been shown that a high hemoglobin value, a major determinant of whole blood viscosity (WBV), predicts cardiovascular events. One putative mechanism might be an impaired endothelial function. Erythrocyte deformability is another rheologic feature of the erythrocyte being of importance for the flow properties of the blood, especially in the capillaries. The present study evaluates the relationships between blood viscosity, erythrocyte deformability assessed as erythrocyte fluidity (EF), coronary risk and endothelial vasodilatory function. In the population-based PIVUS study (1016 subjects aged 70); endothelium-dependent vasodilation (EDV) was evaluated by the invasive forearm technique with acetylcholine given in the brachial artery and the brachial artery ultrasound technique with measurement of flow-mediated dilatation (FMD). WBV, plasma viscosity (PV) and EF were measured in a random sample of 573 subjects. WBV and PV were positively and EF negatively related to Framingham risk score. EDV was inversely related to both whole blood and plasma viscosity. FMD was not related to any rheologic variable. In multiple regression analyses WBV and EF were significantly related to EDV independently of gender, hypertension, smoking, hypercholesterolemia, obesity and diabetes. Acetylcholine-induced vasodilation in the forearm, but not FMD, was negatively related to whole blood viscosity and positively related to EF independently of traditional risk factors in elderly subjects, indicating a pathophysiological link between impaired hemorheology and coronary risk. PMID:22240364
Laskowski, Gregory Michael
2005-12-01
Flows with strong curvature present a challenge for turbulence models, specifically eddy viscosity type models which assume isotropy and a linear and instantaneous equilibrium relation between stress and strain. Results obtained from three different codes and two different linear eddy viscosity turbulence models are compared to a DNS simulation in order to gain some perspective on the turbulence modeling capability of SIERRA/Fuego. The Fuego v2f results are superior to the more common two-layer k-e model results obtained with both a commercial and research code in terms of the concave near wall behavior predictions. However, near the convex wall, including the separated region, little improvement is gained using the v2f model and in general the turbulent kinetic energy prediction is fair at best.
Sampedro, José G.; Muñoz-Clares, Rosario A.; Uribe, Salvador
2002-01-01
The effect of increasing trehalose concentrations on the kinetics of the plasma membrane H+-ATPase from Kluyveromyces lactis was studied at different temperatures. At 20°C, increasing concentrations of trehalose (0.2 to 0.8 M) decreased Vmax and increased S0.5 (substrate concentration when initial velocity equals 0.5 Vmax), mainly at high trehalose concentrations (0.6 to 0.8 M). The quotient Vmax/S0.5 decreased from 5.76 μmol of ATP mg of protein−1 min−1 mM−1 in the absence of trehalose to 1.63 μmol of ATP mg of protein−1 min−1 mM−1 in the presence of 0.8 M trehalose. The decrease in Vmax was linearly dependent on solution viscosity (η), suggesting that inhibition was due to hindering of protein domain diffusional motion during catalysis and in accordance with Kramer's theory for reactions in solution. In this regard, two other viscosity-increasing agents, sucrose and glycerol, behaved similarly, exhibiting the same viscosity-enzyme inhibition correlation predicted. In the absence of trehalose, increasing the temperature up to 40°C resulted in an exponential increase in Vmax and a decrease in enzyme cooperativity (n), while S0.5 was not modified. As temperature increased, the effect of trehalose on Vmax decreased to become negligible at 40°C, in good correlation with the temperature-mediated decrease in viscosity. The trehalose-mediated increase in S0.5 was similar at all temperatures tested, and thus, trehalose effects on Vmax/S0.5 were always observed. Trehalose increased the activation energy for ATP hydrolysis. Trehalose-mediated inhibition of enzymes may explain why yeast rapidly hydrolyzes trehalose when exiting heat shock. PMID:12142408
Zyła, Gaweł; Cholewa, Marian; Witek, Adam
2012-01-01
: This work presents results of measurements of viscosity of suspensions including yttrium oxide (Y2O3), yttrium aluminum garnet (Y3Al5O12) and magnesium aluminum spinel (MgAl2O4) nanopowders in ethanol. Nanoparticles used in our research were either commercially available (Baikowski) or nanopowders newly developed in the Institute of Ceramics and Building Materials in Warsaw, Poland. The study was conducted in a wide range of shear rates (0.01 to 2,000 s-1) and temperature interval from -15°C to 20°C. A Haake Mars 2 rheometer from Thermo Fisher, Germany, was used in the Biophysics Laboratory at Rzeszów University of Technology. Most of the samples show a non-Newtonian behaviour. It was confirmed with a Rheo-NMR system from Bruker that 10% by weight of Y2O3 suspension is a non-Newtonian fluid. In this work, we also report an unexpected behaviour of the viscosity of some samples (Y2O3 and Y3Al5O12) due to sedimentation effect. PMID:22824064
2012-01-01
This work presents results of measurements of viscosity of suspensions including yttrium oxide (Y2O3), yttrium aluminum garnet (Y3Al5O12) and magnesium aluminum spinel (MgAl2O4) nanopowders in ethanol. Nanoparticles used in our research were either commercially available (Baikowski) or nanopowders newly developed in the Institute of Ceramics and Building Materials in Warsaw, Poland. The study was conducted in a wide range of shear rates (0.01 to 2,000 s−1) and temperature interval from -15°C to 20°C. A Haake Mars 2 rheometer from Thermo Fisher, Germany, was used in the Biophysics Laboratory at Rzeszów University of Technology. Most of the samples show a non-Newtonian behaviour. It was confirmed with a Rheo-NMR system from Bruker that 10% by weight of Y2O3 suspension is a non-Newtonian fluid. In this work, we also report an unexpected behaviour of the viscosity of some samples (Y2O3 and Y3Al5O12) due to sedimentation effect. PMID:22824064
Magnetic viscosity by localized shear flow instability in magnetized accretion disks
Matsumoto, R.; Tajima, T.
1995-01-01
Differentially rotating disks are subject to the axisymmetric instability for perfectly conducting plasma in the presence of poloidal magnetic fields. For nonaxisymmetric perturbations, the authors find localized unstable eigenmodes whose eigenfunction is confined between two Alfven singularities at {omega}{sub d} = {+-} {omega}{sub A}, where {omega}{sub d} is the Doppler-shifted wave frequency, and {omega}{sub A} = k{parallel}v{sub A} is the Alfven frequency. The radial width of the unstable eigenfunction is {Delta}x {approximately} {omega}{sub A}/(Ak{sub y}), where A is the Oort`s constant, and k{sub y} is the azimuthal wave number. The growth rate of the fundamental mode is larger for smaller value of k{sub y}/k{sub z}. The maximum growth rate when k{sub y}/k{sub z} {approximately} 0.1 is {approximately} 0.2{Omega} for the Keplerian disk with local angular velocity {Omega}. It is found that the purely growing mode disappears when k{sub y}/k{sub z} > 0.12. In a perfectly conducting disk, the instability grows even when the seed magnetic field is infinitesimal. Inclusion of the resistivity, however, leads to the appearance of an instability threshold. When the resistivity {eta} depends on the instability-induced turbulent magnetic fields {delta}B as {eta}([{delta}B{sup 2}]), the marginal stability condition self-consistently determines the {alpha} parameter of the angular momentum transport due to the magnetic stress. For fully ionized disks, the magnetic viscosity parameter {alpha}{sub B} is between 0.001 and 1. The authors` three-dimensional MHD simulation confirms these unstable eigenmodes. It also shows that the {alpha} parameter observed in simulation is between 0.01 and 1, in agreement with theory. The observationally required smaller {alpha} in the quiescent phase of accretion disks in dwarf novae may be explained by the decreased ionization due to the temperature drop.
ERIC Educational Resources Information Center
Victoria, L.; Arenas, A.
2004-01-01
A device designed to demonstrate the dependence of viscosity on temperature and to check the validity of the exponential relationship is described. The device has the advantage of versatility as it can be adapted to different types of viscosimeters.
NASA Astrophysics Data System (ADS)
Le Losq, Charles; Neuville, Daniel R.
2016-04-01
The rheological and thermodynamic properties of silicate melts played a crucial role in the formation and the evolution of the Earth. For instance, they influenced the evolution of a plausible primordial magma ocean, and, as a result, the differentiation of the Earth mantle and crust. Further, they control the dynamic of volcanic eruptions. Because of that, modelling the viscosity or the heat capacity of silicate melts is crucial in order to model the physical processes they are involved in. The Adam and Gibbs theory of viscous flow offers a thermodynamic framework that assumes that the viscosity η (Pa s) at a temperature T (K) of a melt can be expressed as: log(η) = A + ----Be--- e T Sconf(T) (1) with Ae a pre-exponential constant related to the viscosity at infinite temperature, Be (J mol‑1) a constant proportional to the potential energy barrier opposed to the cooperative rearrangement of the liquid structure and Sconf(T) (J mol‑1 K‑1) the melt configurational entropy. With expressing Sconf(T) as the sum of the residual entropy of the glass and of the variation in melt configurational heat capacity, it is possible to link existing thermodynamic and viscosity data for melts with various chemical composition, e.g., SiO2, NaAlSi3O8 or CaAl2Si2O8. Further, it also is possible to describe the viscosity variation induced by mixing Ca and Mg or Na and K in silicate melts, under the assumption that such mixing produces an ideal excess entropy of mixing. An interesting point in the Adam and Gibbs framework is that it assumes that viscous flow occurs through the cooperative re-arrangement of molecular sub-regions in the melt. From high temperature 29Si NMR and Raman spectroscopy data, it actually is known that viscous flow occurs because of the cooperative exchange of oxygen atoms between tetrahedral SiO2 units, allowing their motions. Therefore, it is tempting to link such structural knowledge to heat capacity and viscosity data through the use of equation 1. In
NASA Astrophysics Data System (ADS)
Morgan, J. P.; Hasenclever, J.; Shi, C.
2009-12-01
Computational studies of mantle convection face large challenges to obtain fast and accurate solutions for variable viscosity 3d flow. Recently we have been using parallel (MPI-based) MATLAB to more thoroughly explore possible pitfalls and algorithmic improvements to current ‘best-practice’ variable viscosity Stokes and D’Arcy flow solvers. Here we focus on study of finite-element solvers based on a decomposition of the equations for incompressible Stokes flow: Ku + Gp = f and G’u = 0 (K-velocity stiffness matrix, G-discretized gradient operator, G’=transpose(G)-discretized divergence operator) into a single equation for pressure Sp==G’K^-1Gp =G’K^-1f, in which the velocity is also updated as part of each pressure iteration. The outer pressure iteration is solved with preconditioned conjugate gradients (CG) (Maday and Patera, 1989), with a multigrid-preconditioned CG solver for the z=K^-1 (Gq) step of each pressure iteration. One fairly well-known pitfall (Fortin, 1985) is that constant-pressure elements can generate a spurious non-zero flow under a constant body force within non-rectangular geometries. We found a new pitfall when using an iterative method to solve the Kz=y operation in evaluating each G’K^-1Gq product -- even if the residual of the outer pressure equation converges to zero, the discrete divergence of this equation does not correspondingly converge; the error in the incompressibility depends on roughly the square of the tolerance used to solve each Kz=y velocity-like subproblem. Our current best recipe is: (1) Use flexible CG (cf. Notay, 2001) to solve the outer pressure problem. This is analogous to GMRES for a symmetric positive definite problem. It allows use of numerically unsymmetric and/or inexact preconditioners with CG. (2) In this outer-iteration, use an ‘alpha-bar’ technique to find the appropriate magnitude alpha to change the solution in each search direction. This improvement allows a similar iterative tolerance of
NASA Astrophysics Data System (ADS)
Cieśliński, Janusz T.; Ronewicz, Katarzyna; Smoleń, Sławomir
2015-12-01
In this study the results of simultaneous measurements of dynamic viscosity, thermal conductivity, electrical conductivity and pH of two nanofluids, i.e., thermal oil/Al2O3 and thermal oil/TiO2 are presented. Thermal oil is selected as a base liquid because of possible application in ORC systems as an intermediate heating agent. Nanoparticles were tested at the concentration of 0.1%, 1%, and 5% by weight within temperature range from 20 °C to 60 °C. Measurement devices were carefully calibrated by comparison obtained results for pure base liquid (thermal oil) with manufacturer's data. The results obtained for tested nanofluids were compared with predictions made by use of existing models for liquid/solid particles mixtures.
Leahy-Dios, Alana; Zhuo, Lin; Firoozabadi, Abbas
2008-05-22
New thermal diffusion coefficients of binary mixtures are measured for n-decane-n-alkanes and 1-methylnaphthalene-n-alkanes with 25 and 75 wt % at 25 degrees C and 1 atm using the thermogravitational column technique. The alkanes range from n-pentane to n-eicosane. The new results confirm the recently observed nonmonotonic behavior of thermal diffusion coefficients with molecular weight for binary mixtures of n-decane- n-alkanes at the compositions studied. In this work, the mobility and disparity effects on thermal diffusion coefficients are quantified for binary mixtures. We also show for the binary mixtures studied that the thermal diffusion coefficients and mixture viscosity, both nonequilibrium properties, are closely related. PMID:18438988
Jones, A Y; Jones, R D; Kwong, K; Burns, Y
2000-01-01
Gas flows of 2, 3, and 4 L/min were directed through a sputum-like gel with viscosities of 100, 150, and 200 P and placed in a tube similar in diameter to a human segmental bronchus (4 mm), which was immersed in a bath of water. The sound produced by gas flow through the gel was recorded with a hydrophone. Sound data were subjected to time-expanded waveforms and fast Fourier transform (FFT) analysis. This study demonstrated that the number of crackles generated was directly related to the flow rate and inversely related to gel viscosity. The initial deflection width (IDW), two-cycle duration (2 CD), and peak-to-peak amplitude of crackles were significantly affected by the gas flow rate but not the viscosity of the gel. A lower gas flow rate generated crackles with longer IDW and 2 CD, but higher gas flow rates generated crackles with higher amplitude. Peak sound intensity measured from FFT increased as flow rate increased but decreased as the viscosity of the gel increased. At low gas flows, no gel-induced crackle sound was generated within the data capture window when the most viscous gel was examined. A digital video image of gas flow through the gel was captured, and this confirmed the absence of bubbles or slug formation at low flows through 200 P gel during the 3 seconds of data acquisition. This study describes some characteristics of crackles generated from different combinations of gas flow and gel viscosity and suggests that "coarse crackles" results from the explosion of gas bubbles in pulmonary secretions. Health care practitioners should consider the combined effect of rate of inspiratory gas flow and sputum viscosity during auscultation of patients' lungs. PMID:10723718
Gai, Ya; Khor, Jian Wei; Tang, Sindy K Y
2016-08-21
This paper describes the dimensionless groups that determine the break-up probability of droplets in a concentrated emulsion during its flow in a tapered microchannel consisting of a narrow constriction. Such channel geometry is commonly used in droplet microfluidics to investigate the content of droplets from a concentrated emulsion. In contrast to solid wells in multi-well plates, drops are metastable, and are prone to break-up which compromises the accuracy and the throughput of the assay. Unlike single drops, the break-up process in a concentrated emulsion is stochastic. Analysis of the behavior of a large number of drops (N > 5000) shows that the probability of break-up increases with applied flow rate, the size of the drops relative to the size of the constriction, and the viscosity ratio of the emulsion. This paper shows that the break-up probability collapses into a single curve when plotted as a function of the product of capillary number, viscosity ratio, and confinement factor defined as the un-deformed radius of the drop relative to the hydraulic radius of the constriction. Fundamentally, the results represent a critical step towards the understanding of the physics governing instability in concentrated emulsions. Practically, the results provide a direct guide for the rational design of microchannels and the choice of operation parameters to increase the throughput of the droplet interrogation step while preserving droplet integrity and assay accuracy. PMID:27194099
Viscosity of confined inhomogeneous nonequilibrium fluids
NASA Astrophysics Data System (ADS)
Zhang, Junfang; Todd, B. D.; Travis, Karl P.
2004-12-01
We use the nonlocal linear hydrodynamic constitutive model, proposed by Evans and Morriss [Statistical Mechanics of Nonequilibrium Liquids (Academic, London, 1990)], for computing an effective spatially dependent shear viscosity of inhomogeneous nonequilibrium fluids. The model is applied to a simple atomic fluid undergoing planar Poiseuille flow in a confined channel of several atomic diameters width. We compare the spatially dependent viscosity with a local generalization of Newton's law of viscosity and the Navier-Stokes viscosity, both of which are known to suffer extreme inaccuracies for highly inhomogeneous systems. The nonlocal constitutive model calculates effective position dependent viscosities that are free from the notorious singularities experienced by applying the commonly used local constitutive model. It is simple, general, and has widespread applicability in nanofluidics where experimental measurement of position dependent transport coefficients is currently inaccessible. In principle the method can be used to predict approximate flow profiles of any arbitrary inhomogeneous system. We demonstrate this by predicting the flow profile for a simple fluid undergoing planar Couette flow in a confined channel of several atomic diameters width.
Viscosity of confined inhomogeneous nonequilibrium fluids.
Zhang, Junfang; Todd, B D; Travis, Karl P
2004-12-01
We use the nonlocal linear hydrodynamic constitutive model, proposed by Evans and Morriss [Statistical Mechanics of Nonequilibrium Liquids (Academic, London, 1990)], for computing an effective spatially dependent shear viscosity of inhomogeneous nonequilibrium fluids. The model is applied to a simple atomic fluid undergoing planar Poiseuille flow in a confined channel of several atomic diameters width. We compare the spatially dependent viscosity with a local generalization of Newton's law of viscosity and the Navier-Stokes viscosity, both of which are known to suffer extreme inaccuracies for highly inhomogeneous systems. The nonlocal constitutive model calculates effective position dependent viscosities that are free from the notorious singularities experienced by applying the commonly used local constitutive model. It is simple, general, and has widespread applicability in nanofluidics where experimental measurement of position dependent transport coefficients is currently inaccessible. In principle the method can be used to predict approximate flow profiles of any arbitrary inhomogeneous system. We demonstrate this by predicting the flow profile for a simple fluid undergoing planar Couette flow in a confined channel of several atomic diameters width. PMID:15549963
Predictions of axisymmetric free turbulent shear flows using a generalized eddy-viscosity approach
NASA Technical Reports Server (NTRS)
Morgenthaler, J. H.
1973-01-01
The generalized eddy viscosity approach is described and results are presented of test cases which show that predictions obtained by this approach are adequate for most engineering applications. Because of the importance of starting computations from the injection station where experimentally determined mean and turbulence parameters are rarely available, a very simple core model applicable to simple step-type (slug) profiles was developed. Agreement between predicted and experimental mean profiles was generally almost as good for calculations made by using this model throughout the core region and the transition model for all subsequent regions as predictions made by starting from experimental profiles in the transition region. The generalized eddy-viscosity model, which was developed in part through correlation of turbulence parameters, successfully predicted turbulent shear stress, turbulent intensity, and mean velocity profiles for a 0.040-inch-diameter microjet. Therefore, successful scaling by the model was demonstrated since data used in its development was for jet areas up to 90,000 times as large as the microjet and velocities only 1/20th as high.
NASA Astrophysics Data System (ADS)
Liu, Haihu; Ju, Yaping; Wang, Ningning; Xi, Guang; Zhang, Yonghao
2015-09-01
Contact angle hysteresis is an important physical phenomenon omnipresent in nature and various industrial processes, but its effects are not considered in many existing multiphase flow simulations due to modeling complexity. In this work, a multiphase lattice Boltzmann method (LBM) is developed to simulate the contact-line dynamics with consideration of the contact angle hysteresis for a broad range of kinematic viscosity ratios. In this method, the immiscible two-phase flow is described by a color-fluid model, in which the multiple-relaxation-time collision operator is adopted to increase numerical stability and suppress unphysical spurious currents at the contact line. The contact angle hysteresis is introduced using the strategy proposed by Ding and Spelt [Ding and Spelt, J. Fluid Mech. 599, 341 (2008), 10.1017/S0022112008000190], and the geometrical wetting boundary condition is enforced to obtain the desired contact angle. This method is first validated by simulations of static contact angle and dynamic capillary intrusion process on ideal (smooth) surfaces. It is then used to simulate the dynamic behavior of a droplet on a nonideal (inhomogeneous) surface subject to a simple shear flow. When the droplet remains pinned on the surface due to hysteresis, the steady interface shapes of the droplet quantitatively agree well with the previous numerical results. Four typical motion modes of contact points, as observed in a recent study, are qualitatively reproduced with varying advancing and receding contact angles. The viscosity ratio is found to have a notable impact on the droplet deformation, breakup, and hysteresis behavior. Finally, this method is extended to simulate the droplet breakup in a microfluidic T junction, with one half of the wall surface ideal and the other half nonideal. Due to the contact angle hysteresis, the droplet asymmetrically breaks up into two daughter droplets with the smaller one in the nonideal branch channel, and the behavior of
Liu, Haihu; Ju, Yaping; Wang, Ningning; Xi, Guang; Zhang, Yonghao
2015-09-01
Contact angle hysteresis is an important physical phenomenon omnipresent in nature and various industrial processes, but its effects are not considered in many existing multiphase flow simulations due to modeling complexity. In this work, a multiphase lattice Boltzmann method (LBM) is developed to simulate the contact-line dynamics with consideration of the contact angle hysteresis for a broad range of kinematic viscosity ratios. In this method, the immiscible two-phase flow is described by a color-fluid model, in which the multiple-relaxation-time collision operator is adopted to increase numerical stability and suppress unphysical spurious currents at the contact line. The contact angle hysteresis is introduced using the strategy proposed by Ding and Spelt [Ding and Spelt, J. Fluid Mech. 599, 341 (2008)JFLSA70022-112010.1017/S0022112008000190], and the geometrical wetting boundary condition is enforced to obtain the desired contact angle. This method is first validated by simulations of static contact angle and dynamic capillary intrusion process on ideal (smooth) surfaces. It is then used to simulate the dynamic behavior of a droplet on a nonideal (inhomogeneous) surface subject to a simple shear flow. When the droplet remains pinned on the surface due to hysteresis, the steady interface shapes of the droplet quantitatively agree well with the previous numerical results. Four typical motion modes of contact points, as observed in a recent study, are qualitatively reproduced with varying advancing and receding contact angles. The viscosity ratio is found to have a notable impact on the droplet deformation, breakup, and hysteresis behavior. Finally, this method is extended to simulate the droplet breakup in a microfluidic T junction, with one half of the wall surface ideal and the other half nonideal. Due to the contact angle hysteresis, the droplet asymmetrically breaks up into two daughter droplets with the smaller one in the nonideal branch channel, and the
The effect of temperature dependence of viscosity on a Brownian heat engine
NASA Astrophysics Data System (ADS)
Taye, Mesfin Asfaw; Duki, Solomon Fekade
2015-12-01
We modeled a Brownian heat engine as a Brownian particle that hops in a periodic ratchet potential where the ratchet potential is coupled with a spatially varying temperature. The strength for the viscous friction γ( x) is considered to decrease exponentially when the temperature T( x) of the medium increases ( γ( x) = B e - AT( x)) as proposed originally by Reynolds [O. Reynolds, Phil. Trans. R. Soc. London 177, 157 (1886)]. Our result depicts that the velocity of the motor is considerably higher when the viscous friction is temperature dependent than that of the case where the viscous friction is temperature independent. The dependence of the efficiency η as well as the coefficient of performance of the refrigerator P ref on model parameters is also explored. If the motor designed to achieve a high velocity against a frictional drag, in the absence of external load f, we show that Carnot efficiency or Carnot refrigerator is unattainable even at quasistatic limit as long as the viscous friction is temperature dependent A ≠ 0. On the contrary, in the limit A → 0 or in general in the presence of an external load (for any A) f ≠ 0, at quasistatic limit, Carnot efficiency or Carnot refrigerator is attainable as long as the heat exchange via kinetic energy is omitted. For all cases, far from quasistatic limit, the efficiency and the coefficient of performance of the refrigerator are higher for constant γ case than the case where γ is temperature dependent. On the other hand, if one includes the heat exchange at the boundary of the heat baths, Carnot efficiency or Carnot refrigerator is unattainable even at quasistatic limit. Moreover, the dependence for the optimized and maximum power efficiencies on the determinant model parameters is explored.
The effect of temperature dependence of viscosity on a Brownian heat engine
NASA Astrophysics Data System (ADS)
Asfaw Taye, Mesfin; Fekade Duki, Solomon
2015-12-01
We modeled a Brownian heat engine as a Brownian particle that hops in a periodic ratchet potential where the ratchet potential is coupled with a spatially varying temperature. The strength for the viscous friction γ(x) is considered to decrease exponentially when the temperature T(x) of the medium increases (γ(x) = Be- AT(x)) as proposed originally by Reynolds [O. Reynolds, Phil. Trans. R. Soc. London 177, 157 (1886)]. Our result depicts that the velocity of the motor is considerably higher when the viscous friction is temperature dependent than that of the case where the viscous friction is temperature independent. The dependence of the efficiency η as well as the coefficient of performance of the refrigerator Pref on model parameters is also explored. If the motor designed to achieve a high velocity against a frictional drag, in the absence of external load f, we show that Carnot efficiency or Carnot refrigerator is unattainable even at quasistatic limit as long as the viscous friction is temperature dependent A ≠ 0. On the contrary, in the limit A → 0 or in general in the presence of an external load (for any A) f ≠ 0, at quasistatic limit, Carnot efficiency or Carnot refrigerator is attainable as long as the heat exchange via kinetic energy is omitted. For all cases, far from quasistatic limit, the efficiency and the coefficient of performance of the refrigerator are higher for constant γ case than the case where γ is temperature dependent. On the other hand, if one includes the heat exchange at the boundary of the heat baths, Carnot efficiency or Carnot refrigerator is unattainable even at quasistatic limit. Moreover, the dependence for the optimized and maximum power efficiencies on the determinant model parameters is explored.
Nonlinear evolution of resistive tearing mode instability with shear flow and viscosity
NASA Technical Reports Server (NTRS)
Ofman, L.; Morrison, P. J.; Steinolfson, R. S.
1993-01-01
The effect of shear flow on the nonlinear evolution of the tearing mode is investigated via numerical solutions of the resistive MHD equations in slab geometry, using a finite-difference alternative-direction implicit method. It was found that, when the shear flow is small (V less than 0.3), the tearing mode saturates within one resistive time, whereas for larger flows the nonlinear saturation develops on longer time scales. The magnetic energy release decreases and the saturation time increases with increasing values of V for both small and large resistivity. Shear flow was found to decrease the saturated magnetic island width and to generate currents far from the tearing layer. Results suggest that equilibrium shear flow may improve the confinement of tokamak plasma.
Viscosity measurement techniques in Dissipative Particle Dynamics
NASA Astrophysics Data System (ADS)
Boromand, Arman; Jamali, Safa; Maia, Joao M.
2015-11-01
In this study two main groups of viscosity measurement techniques are used to measure the viscosity of a simple fluid using Dissipative Particle Dynamics, DPD. In the first method, a microscopic definition of the pressure tensor is used in equilibrium and out of equilibrium to measure the zero-shear viscosity and shear viscosity, respectively. In the second method, a periodic Poiseuille flow and start-up transient shear flow is used and the shear viscosity is obtained from the velocity profiles by a numerical fitting procedure. Using the standard Lees-Edward boundary condition for DPD will result in incorrect velocity profiles at high values of the dissipative parameter. Although this issue was partially addressed in Chatterjee (2007), in this work we present further modifications (Lagrangian approach) to the original LE boundary condition (Eulerian approach) that will fix the deviation from the desired shear rate at high values of the dissipative parameter and decrease the noise to signal ratios in stress measurement while increases the accessible low shear rate window. Also, the thermostat effect of the dissipative and random forces is coupled to the dynamic response of the system and affects the transport properties like the viscosity and diffusion coefficient. We investigated thoroughly the dependency of viscosity measured by both Eulerian and Lagrangian methodologies, as well as numerical fitting procedures and found that all the methods are in quantitative agreement.
NASA Technical Reports Server (NTRS)
Macaraeg, Michele G.; Streett, Craig L.
1987-01-01
Analytical and experimental techniques for modeling the aerothermodynamics of hypersonic flight are assessed, together with the problems which will be encountered in developing reusable hypersonic vehicles. Emphasis is placed on a numerical coupling between a nonequilibrium chemistry model and hypersonic flow kinematics. Finite difference and finite element descriptions of flow fields in which molecules encounter a shock wave and undergo various motion (and thereby energy) transformations are discussed. The effects of artificial smearing of the shock wave are considered in terms of the resulting effects on the distribution of the energies and chemical composition of the transition region. Results are provided from schlieren photographs of shock-tube experiments, Navier-Stokes calculations of axisymmetric flow over a conical body, and calculations using a spectral multidomain approach for chemically reacting flows.
NASA Astrophysics Data System (ADS)
Sanan, Patrick; May, Dave; Schenk, Olaf; Rupp, Karl
2016-04-01
Scalable solvers for mantle convection and lithospheric dynamics with highly heterogeneous viscosity structure typically require the use of a multigrid method. To leverage new hybrid CPU-accelerator architectures on leadership compute clusters, multigrid hierarchies which can reduce communication and use high available arithmetic intensity are at a premium, motivating more aggressive coarsening schemes and smoothers. We present results of a comparative study of two competitive GPU-enabled subdomain smoothers within an additive Schwarz method. Chebyshev-Jacobi smoothing has been shown to be an effective smoother, and its nature as a low-communication method built from basic linear algebra routines allows its use on a wide range of devices with current libraries. ILU smoothing is also of interest and is known to provide robust smoothing in some cases, but has traditionally been difficult to use in a fine-grained parallel environment. However, a recently-introduced variant by Chow and Patel allows for incomplete factorizations to be computed and applied in these environments, hence allowing us to study them as well. We use and extend the pTatin3D, PETSc, and ViennaCL libraries to integrate promising methods into a realistic application framework.
Beam energy dependence of the viscous damping of anisotropic flow
NASA Astrophysics Data System (ADS)
Lacey, Roy
2013-10-01
The flow harmonics v2 , 3 for charged hadrons, are studied for a broad range of centrality selections and beam collision energies in Au+Au (√{sNN} = 7 . 7 - 200 GeV) and Pb+Pb (√{sNN} = 2 . 76 TeV) collisions. They validate the characteristic signature expected for the system size dependence of viscous damping at each collision energy studied. The extracted viscous coefficients, that encode the magnitude of the ratio of shear viscosity to entropy density η / s , are observed to decrease to an apparent minimum as the collision energy is increased from √{sNN} = 7 . 7 to approximately 62.4 GeV; thereafter, they show a slow increase with √{sNN} up to 2.76 TeV. This pattern of viscous damping provides the first experimental constraint for η / s in the temperature-baryon chemical potential (T ,μB) plane, and could be an initial indication for decay trajectories which lie close to the critical end point in the phase diagram for nuclear matter. This research is supported by the US DOE under contract DE-FG02-87ER40331.A008.
Prestrain-dependent viscosity of a highly filled elastomer: experiments and modeling
NASA Astrophysics Data System (ADS)
Jalocha, D.; Constantinescu, A.; Neviere, R.
2015-08-01
Highly filled elastomers exhibit a complex microstructure made up of rigid fillers bounded by a thin layer polymeric matrix. The interactions between the fillers and the binder amplify locally the applied strains and induce a nonlinear viscoelastic behavior. The aim here is to analyze the influence of prestrain on the viscoelastic behavior. This paper proposes a prestrain-dependent viscoelastic constitutive model. The model is a superposition of three relaxation spectra, each corresponding to a family of polymer chains, and can be regarded in either its continuous or discrete expression. More specifically, one of these relaxation spectra is modified to assure the prestrain sensitivity. The parameters of the discrete model are identified from relaxation and DMA experiments performed on a solid propellant, and the obtained predictions match closely the experiments. The novelty of the analysis proposed in this paper is threefold. On the one hand, we report a new series of experimental measures, performed for a large range of frequencies for the DMA experiment and relaxation times for the relaxation experiment, and, on the other hand, we propose a constitutive law compatible with the principles of thermodynamics, which predicts closely the measurements. Finally, the analysis is performed comparing both relaxation and DMA experiments using the spectrum of relaxation times. A peculiarity of the present discussion is the novel identification method used, which identifies directly the relaxation times. This technique leads to models with smaller and optimum numbers of parameters than classical methods based on a logarithmic distribution of relaxation times.
A FLUENT simulation of buoyancy-driven flow in a square enclosure with variable viscosity effects
Choudhury, D.
1995-12-31
Numerical solutions of the Navier-Stokes and energy equations are presented for the fluid flow and heat transfer in a square enclosure with variable property effects, a benchmark test case for the 1995 ASME Winter Annual Meeting. Computations are carried out using FLUENT, a general-purpose CFD software package. The numerical method employed in the present study is briefly described. The results are then presented.
NASA Astrophysics Data System (ADS)
Wildenschild, D.; Herring, A. L.; Carey, J. W.; Young, I. M.
2010-12-01
measuring trapped non-wetting phase area as a function of varying interfacial tension, viscosity, and wetting flow rate. Experiments are repeated for a single sintered glass bead core using three different non-wetting phase fluids and varying concentrations of surfactants to explore and separate the effects of interfacial tension, viscosity, and fluid flow rate. Analysis of the data demonstrates distinct and consistent differences in the amount of initial (i.e. following CO2 injection) and residual (i.e. following flood or WAG scheme) nonwetting phase occupancy as a function of fluid properties and flow rate. Further experimentation and analyses is needed, but these preliminary results indicate trends that can guide design of injection scenarios such that both initial and residual trapped gas occupancy is optimized.
Duangthongsuk, Weerapun; Wongwises, Somchai
2009-04-15
Nanofluid is an innovative heat transfer fluid with superior potential for enhancing the heat transfer performance of conventional fluids. Many attempts have been made to investigate its thermal conductivity and viscosity, which are important thermophysical properties. No definitive agreements have emerged, however, about these properties. This article reports the thermal conductivity and dynamic viscosity of nanofluids experimentally. TiO{sub 2} nanoparticles dispersed in water with volume concentration of 0.2-2 vol.% are used in the present study. A transient hot-wire apparatus is used for measuring the thermal conductivity of nanofluids whereas the Bohlin rotational rheometer (Malvern Instrument) is used to measure the viscosity of nanofluids. The data are collected for temperatures ranging from 15 C to 35 C. The results show that the measured viscosity and thermal conductivity of nanofluids increased as the particle concentrations increased and are higher than the values of the base liquids. Furthermore, thermal conductivity of nanofluids increased with increasing nanofluid temperatures and, conversely, the viscosity of nanofluids decreased with increasing temperature of nanofluids. Moreover, the measured thermal conductivity and viscosity of nanofluids are quite different from the predicted values from the existing correlations and the data reported by other researchers. Finally, new thermophysical correlations are proposed for predicting the thermal conductivity and viscosity of nanofluids. (author)
Computational Relativistic Astrophysics Using the Flow Field-Dependent Variation Theory
NASA Technical Reports Server (NTRS)
Richardson, G. A.; Chung, T. J.
2002-01-01
We present our method for solving general relativistic nonideal hydrodynamics. Relativistic effects become pronounced in such cases as jet formation from black hole magnetized accretion disks which may lead to the study of gamma-ray bursts. Nonideal flows are present where radiation, magnetic forces, viscosities, and turbulence play an important role. Our concern in this paper is to reexamine existing numerical simulation tools as to the accuracy and efficiency of computations and introduce a new approach known as the flow field-dependent variation (FDV) method. The main feature of the FDV method consists of accommodating discontinuities of shock waves and high gradients of flow variables such as occur in turbulence and unstable motions. In this paper, the physics involved in the solution of relativistic hydrodynamics and solution strategies of the FDV theory are elaborated. The general relativistic astrophysical flow and shock solver (GRAFSS) is introduced, and some simple example problems for computational relativistic astrophysics (CRA) are demonstrated.
NASA Astrophysics Data System (ADS)
Ali, M.; Alim, M. A.; Nasrin, R.; Alam, M. S.
2016-07-01
An analysis is performed to study the free convection heat and mass transfer flow of an electrically conducting incompressible viscous fluid about a semi-infinite inclined porous plate under the action of radiation, chemical reaction in presence of magnetic field with variable viscosity. The dimensionless governing equations are steady, two-dimensional coupled and non-linear ordinary differential equation. Nachtsgeim-Swigert shooting iteration technique along with Runge-Kutta integration scheme is used to solve the non-dimensional governing equations. The effects of magnetic parameter, viscosity parameter and chemical reaction parameter on velocity, temperature and concentration profiles are discussed numerically and shown graphically. Therefore, the results of velocity profile decreases for increasing values of magnetic parameter and viscosity parameter but there is no effect for reaction parameter. The temperature profile decreases in presence of magnetic parameter, viscosity parameter and Prandtl number but increases for radiation parameter. Also, concentration profile decreases for the increasing values of magnetic parameter, viscosity parameter and reaction parameter. All numerical calculations are done with respect to salt water and fixed angle of inclination of the plate.
Nonequilibrium viscosity of glass
NASA Astrophysics Data System (ADS)
Mauro, John C.; Allan, Douglas C.; Potuzak, Marcel
2009-09-01
Since glass is a nonequilibrium material, its properties depend on both composition and thermal history. While most prior studies have focused on equilibrium liquid viscosity, an accurate description of nonequilibrium viscosity is essential for understanding the low temperature dynamics of glass. Departure from equilibrium occurs as a glass-forming system is cooled through the glass transition range. The glass transition involves a continuous breakdown of ergodicity as the system gradually becomes trapped in a subset of the available configurational phase space. At very low temperatures a glass is perfectly nonergodic (or “isostructural”), and the viscosity is described well by an Arrhenius form. However, the behavior of viscosity during the glass transition range itself is not yet understood. In this paper, we address the problem of glass viscosity using the enthalpy landscape model of Mauro and Loucks [Phys. Rev. B 76, 174202 (2007)] for selenium, an elemental glass former. To study a wide range of thermal histories, we compute nonequilibrium viscosity with cooling rates from 10-12 to 1012K/s . Based on these detailed landscape calculations, we propose a simplified phenomenological model capturing the essential physics of glass viscosity. The phenomenological model incorporates an ergodicity parameter that accounts for the continuous breakdown of ergodicity at the glass transition. We show a direct relationship between the nonequilibrium viscosity parameters and the fragility of the supercooled liquid. The nonequilibrium viscosity model is validated against experimental measurements of Corning EAGLE XG™ glass. The measurements are performed using a specially designed beam-bending apparatus capable of accurate nonequilibrium viscosity measurements up to 1016Pas . Using a common set of parameters, the phenomenological model provides an accurate description of EAGLE XG™ viscosity over the full range of measured temperatures and fictive temperatures.
Kimura, Y; Kida, Y; Matsushita, Y; Yasaka, Y; Ueno, M; Takahashi, K
2015-06-25
Translational diffusion coefficients of diphenylcyclopropenone (DPCP), diphenylacetylene (DPA), and carbon monoxide (CO) in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIm][NTf2]) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIm][NTf2]) were determined by the transient grating (TG) spectroscopy under pressure from 0.1 to 200 MPa at 298 K and from 298 to 373 K under 0.1 MPa. Diffusion coefficients of these molecules at high temperatures in tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide ([P4441][NTf2]), and tetraoctylphosphonium bis(trifluoromethanesulfonyl)imide ([P8888][NTf2]), and also in the mixtures of [BMIm][NTf2], N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide ([Pp13][NTf2]), and trihexyltetradecylphosphonium bis(trifluoromethanesulfonyl)imide ([P66614][NTf2]) with ethanol or chloroform have been determined. Diffusion coefficients except in ILs of phosphonium cations were well scaled by the power law of T/η, i.e., (T/η)(P), where T and η are the absolute temperature and the viscosity, irrespective of the solvent species, pressure and temperature, and the compositions of mixtures. The values of the exponent P were smaller for the smaller size of the molecules. On the other hand, the diffusion coefficients in ILs of phosphonium cations with longer alkyl chains were larger than the values expected from the correlation obtained by other ILs and conventional liquids. The deviation becomes larger with increasing the number of carbon atoms of alkyl-chain of cation, and with decreasing the molecular size of diffusing molecules. The molecular size dependence of the diffusion coefficient was correlated by the ratio of the volume of the solute to that of the solvent as demonstrated by the preceding work (Kaintz et al., J. Phys. Chem. B 2013 , 117 , 11697 ). Diffusion coefficients have been well correlated with the power laws of both T/η and the relative volume of the solute to the solvent
NASA Astrophysics Data System (ADS)
Odenbach, S.; Störk, H.
1998-03-01
Viscoelastic properties of ferrofluids are an upcoming field of scientific interest, since the magnetic control of the related fluid behavior would give rise to new applications as well as for new possibilities in basic research concerning viscoelasticity. We have constructed a specialized rheometer for the investigation of fluids under the influence of magnetic fields, to examine such effects in stable suspensions of magnetic particles. In particular we will report the change of field-induced increase of viscosity due to variation of the shear rate applied to the fluid. The results show that the available theoretical approach, namely the concept of rotational viscosity, is not valid for the description of the field-induced increase of viscosity in concentrated fluids at low shear rates.
Blume, K; Dietrich, K; Lilienthal, S; Ternes, W; Drotleff, A M
2015-04-15
Egg yolk and its main component, low-density lipoproteins (LDL), were consecutively pasteurised, optimally freeze-dried, and dispersed in various NaCl solutions (0-10%). Heat-induced changes in the protein secondary structures which accompanied viscosity-increasing aggregation processes were monitored using Fourier transform infrared spectroscopy (FTIR) to determine the intensities of intermolecular β-sheets (1622 cm(-1)) and results were compared with the temperature-dependent viscosities. Considerable changes in secondary structures observed after reconstitution of freeze-dried LDL had no detectable effect on the characteristic heat-induced viscosity curves but suggest that LDL plays a particular role in the unwanted gel formation of egg yolk after conventional freezing. For all egg yolk samples and all NaCl-containing LDL samples, the sigmoidal changes in the absorbance units vs. temperature curves corresponded with the first increase in heat-induced viscosity. Both analytical methods showed that the presence of ionic strength caused a shift in curve progressions towards higher temperatures, indicating increased thermal stability. PMID:25466063
Borovsky, Joseph E.
2006-05-15
The coefficient of magnetohydrodynamic (MHD) eddy viscosity of the turbulent solar wind is calculated to be {nu}{sub eddy}{approx_equal}1.3x10{sup 17} cm{sup 2}/s: this coefficient is appropriate for velocity shears with scale thicknesses larger than the {approx}10{sup 6} km correlation length of the solar-wind turbulence. The coefficient of MHD eddy viscosity is calculated again accounting for the action of smaller-scale turbulent eddies on smaller scale velocity shears in the solar wind. This eddy viscosity is quantitatively tested with spacecraft observations of shear flows in co-rotating interaction regions (CIRs) and in coronal-mass-ejection (CME) sheaths and ejecta. It is found that the large-scale ({approx}10{sup 7} km) shear of the CIR fractures into intense narrow ({approx}10{sup 5} km) slip zones between slabs of differently magnetized plasma. Similarly, it is found that the large-scale shear of CME sheaths also fracture into intense narrow slip zones between parcels of differently magnetized plasma. Using the solar-wind eddy-viscosity coefficient to calculate vorticity-diffusion time scales and comparing those time scales with the {approx}100-h age of the solar-wind plasma at 1 AU, it is found that the slip zones are much narrower than eddy-viscosity theory says they should be. Thus, our concept of MHD eddy viscosity fails testing. For the freestream turbulence effect in solar-wind magnetosphere coupling, the eddy-viscous force of the solar wind on the Earth's magnetosphere is rederived accounting for the action of turbulent eddies smaller than the correlation length, along with other corrections. The improved derivation of the solar-wind driver function for the turbulence effect fails to yield higher correlation coefficients between measurements of the solar-wind driver and measurements of the response of the Earth's magnetosphere.
Hall Viscosity II: Extracting Viscosity from Conductivity
NASA Astrophysics Data System (ADS)
Goldstein, Moshe; Bradlyn, Barry; Read, Nicholas
2012-02-01
When time reversal symmetry is broken, the viscosity tensor of a fluid can have non-dissipative components, similarly to the non-dissipative off-diagonal Hall conductivity. This ``Hall viscosity'' was recently shown to be half the particle density times the orbital angular momentum per particle. Its observation can thus help elucidate the nature of the more exotic quantum Hall states and related systems (e.g., p+ip superconductors). However, no concrete measurement scheme has hitherto been proposed. Motivated by this question we use linear response theory to derive a general relation between the viscosity tensor and the wave-vector dependent conductivity tensor for a Galilean-invariant quantum fluid. This relation enables one to extract the Hall viscosity, as well as other viscosity coefficients (shear and bulk) when relevant, from electromagnetic response measurements. We also discuss the connection between this result and a similar one recently derived by C. Hoyos and D. T. Son [arXiv:1109.2651].
NASA Astrophysics Data System (ADS)
Moorthy, M. B. K.; Senthilvadivu, K.
2013-02-01
The aim of this paper is to investigate the effect of thermal stratification together with variable viscosity on free convection flow of non- Newtonian fluids along a nonisothermal semi infinite vertical plate embedded in a saturated porous medium. The governing equations of continuity, momentum and energy are transformed into nonlinear ordinary differential equations using similarity transformations and then solved by using the Runge-Kutta-Gill method along with shooting technique. Governing parameters for the problem under study are the variable viscosity, thermal stratification parameter, non-Newtonian parameter and the power-law index parameter.The velocity and temperature distributions are presented and discussed. The Nusselt number is also derived and discussed numerically.
NASA Astrophysics Data System (ADS)
Song, Mijung; Liu, Pengfei F.; Hanna, Sarah J.; Zaveri, Rahul A.; Potter, Katie; You, Yuan; Martin, Scot T.; Bertram, Allan K.
2016-07-01
To improve predictions of air quality, visibility, and climate change, knowledge of the viscosities and diffusion rates within organic particulate matter consisting of secondary organic material (SOM) is required. Most qualitative and quantitative measurements of viscosity and diffusion rates within organic particulate matter have focused on SOM particles generated from biogenic volatile organic compounds (VOCs) such as α-pinene and isoprene. In this study, we quantify the relative humidity (RH)-dependent viscosities at 295 ± 1 K of SOM produced by photo-oxidation of toluene, an anthropogenic VOC. The viscosities of toluene-derived SOM were 2 × 10-1 to ˜ 6 × 106 Pa s from 30 to 90 % RH, and greater than ˜ 2 × 108 Pa s (similar to or greater than the viscosity of tar pitch) for RH ≤ 17 %. These viscosities correspond to Stokes-Einstein-equivalent diffusion coefficients for large organic molecules of ˜ 2 × 10-15 cm2 s-1 for 30 % RH, and lower than ˜ 3 × 10-17 cm2 s-1 for RH ≤ 17 %. Based on these estimated diffusion coefficients, the mixing time of large organic molecules within 200 nm toluene-derived SOM particles is 0.1-5 h for 30 % RH, and higher than ˜ 100 h for RH ≤ 17 %. As a starting point for understanding the mixing times of large organic molecules in organic particulate matter over cities, we applied the mixing times determined for toluene-derived SOM particles to the world's top 15 most populous megacities. If the organic particulate matter in these megacities is similar to the toluene-derived SOM in this study, in Istanbul, Tokyo, Shanghai, and São Paulo, mixing times in organic particulate matter during certain periods of the year may be very short, and the particles may be well-mixed. On the other hand, the mixing times of large organic molecules in organic particulate matter in Beijing, Mexico City, Cairo, and Karachi may be long and the particles may not be well-mixed in the afternoon (15:00-17:00 LT) during certain times of the
NASA Astrophysics Data System (ADS)
Read, Nicholas
2015-03-01
Viscosity is a transport coefficient relating to transport of momentum, and usually thought of as the analog of friction that occurs in fluids and solids. More formally, it is the response of the stress to the gradients of the fluid velocity field, or to the rate of change of strain (derivatives of displacement from a reference state). In general, viscosity is described by a fourth-rank tensor. Invoking rotation invariance, it reduces to familiar shear and bulk viscosity parts, which describe dissipation, but it can also contain an antisymmetric part, analogous to the Hall conductivity part of the conductivity tensor. In two dimensions this part is a single number, the Hall viscosity. Symmetry of the system under time reversal (or, in two dimensions, reflections) forces it to vanish. In quantum fluids with a gap in the bulk energy spectrum and which lack both time reversal and reflection symmetries the Hall viscosity can be nonzero even at zero temperature. For integer quantum Hall states, it was first calculated by Avron, Seiler, and Zograf, using a Berry curvature approach, analogous to the Chern number for Hall conductivity. In 2008 this was extended by the present author to fractional quantum Hall states and to BCS states in two dimensions. I found that the general result is given by a simple formula ns / 2 , where n is the particle number density, and s is the ``orbital spin'' per particle. The spin s is also related to the shift S, which enters the relation between particle number and magnetic flux needed to put the ground state on a surface of non-trivial topology with introducing defect excitations, by S = 2 s ; the connection was made by Wen and Zee. The values of s and S are rational numbers, and are robust--unchanged under perturbations that do not cause the bulk energy gap to collapse--provided rotation as well as translation symmetry are maintained. Hall viscosity can be measured in principle, though a simple way to do so is lacking. It enters various
NASA Astrophysics Data System (ADS)
Schug, Kai-Uwe; King, Hubert E.; Cummins, Herman Z.; Sillescu, Hans
1996-03-01
Glass-forming by supercooling the van-der-Waals-liquids Salol (salicylic acid phenyl ester) and OTP (ortho-terphenyl) has been studied over many years with a wide range of techniques. Mode-coupling and free-volume theories are very often used to describe the molecular behavior in the liquid and the supercooled state. To investigate such theories we used pressure as a new parameter. This allows one to change the density at constant temperature. We will present viscosity measurements in an diamond anvil cell done with the rolling ball technique. We superpressed the liquids at constant temperatures and have measured viscosities up to 10^8 cP in the temperature range from 30 to 130 Celsius with pressures up to 10 kBar. We will show free-volume and mode-coupling fits of the data and discuss the results. Based on a modified Angell-plot we will scale liquids with a different fragility and show the influence of pressure / temperature on the fragility.
Hutcheson, I R; Smith, J A; Griffith, T M
1994-01-01
1. We have used a pulsatile cascade bioassay system to investigate the effects of dietary-induced hypercholesterolaemia on EDRF release evoked by acetylcholine and by the oscillatory and time-averaged components of flow, in isolated segments of rabbit abdominal aorta. 2. Flow pulsatility (frequency range 0.1-10 Hz) was studied with constant flow (9 ml min-1) at a pulse pressure amplitude of 2 mmHg. Frequency-related EDRF release, maximal at 6 Hz, was slightly attenuated after 4 weeks and abolished after 8 weeks of cholesterol feeding. 3. Time-averaged shear stress was manipulated with dextran (1-4% w/v, 80000 mol. wt.), to increase perfusate viscosity. EDRF release induced by increased perfusate viscosity was unaffected after 4 weeks but abolished after 8 weeks of cholesterol feeding. 4. Endothelium-dependent relaxations to acetylcholine (0.1-10 microM) were not influenced after 4 weeks and only partially attenuated (by 60% of the maximal response, EC50 unchanged at 6.45 +/- 0.04 vs. 6.4 +/- 0.1 microM) after 8 weeks of cholesterol feeding. 5. Blood cholesterol levels were significantly (P < 0.001) increased after 4 weeks (26 +/- 3.6 vs 2.6 +/- 0.6 mmol l-1) and 8 weeks (56.2 +/- 3.8 vs 1.3 +/- 0.1 mmol l-1) of cholesterol feeding but after 8 weeks plasma L-arginine levels were not significantly different from the age-matched controls (0.2 +/- 0.05 vs. 0.19 +/- 0.04 mmol l-1). 6. We conclude that hypercholesterolaemia impairs flow-related (pulsatile- and time-averaged shear-induced) EDRF release earlier than acetylcholine-induced relaxation in rabbit aorta.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7529109
NASA Astrophysics Data System (ADS)
Sawale, R. T.; Deosarkar, S. D.; Kalyankar, T. M.
2015-07-01
Density ( ρ), viscosity ( η) and refractive index ( n D) of an antiemetic drug metoclopramide (4-amino-5-chloro- N-(2-(diethylamino)ethyl)-2-methoxybenzamide hydrochloride) solutions containing amino acids (glycine, D-alanine, L-cystine and L-histidine) were measured in the concentration range 0.01-0.17 mol/dm3 at 303.15 K. The apparent molar volume (φv) of this drug in aqueous amino acid solutions was calculated from the density data and fitted to the Massons relation, and the partial molar volume φ{v/0} of the drug was determined graphically. The partial molar volumes of transfer (Δtrφ{v/0}) of drug at infinite dilution from pure water to aqueous amino acid solutions were calculated and interpreted in terms of different interactions between the drug and amino acids.
Viscosity of Hydrous Rhyolitic Melts
NASA Astrophysics Data System (ADS)
Zhang, Y.; Xu, Z.; Liu, Y.
2002-12-01
It is critical to understand and to be able to predict viscosity of hydrous silicate melts for understanding magma transport, bubble growth, volcanic eruptions, and magma fragmentation. We report new viscosity data for hydrous rhyolitic melt in the viscosity range of 109 to 1015 Pa s based on the kinetics of hydrous species reaction in the melt upon cooling (i.e., based on the equivalence between the glass transition temperature and the apparent equilibrium temperature). We also report viscosity data obtained from bubble growth experiments. Our data show that the viscosity model of Hess and Dingwell (1996) systematically overestimates the viscosity of hydrous rhyolitic melt at the high viscosity range by a factor of 2 to 4 (still within their stated 2σ uncertainty). Another problem with the model of Hess and Dingwell is that the functional dependence of viscosity on total H2O content cannot be extended to dry melt: as total H2O content decreases to zero, the viscosity would first increase, and then decrease to zero. A zero viscosity for a dry melt makes no sense. Hence we need a mixing law for hydrous melt viscosity that is extendible to dry melts. By examining the viscosity of rhyolitic melts containing 6 ppm to about 8.0 wt% total H2O (both our own data and literature data), we propose the following relation for the dependence of viscosity on total H2O content: 1/η = 1/η 1+(1/η 2-1/η 1)xn ≈ 1/η 1+xn/η 2 where η is viscosity and 1/η is fluidity, η 1 is the viscosity of the dry melt, x is the mole fraction of total dissolved H2O, n and η 2 are two fitting parameters, and η 2 can be identified to be the viscosity of the hypothetical melt consisting of pure H2O (η 2 cannot be directly measured since such a melt does not exist). The above equation appears to work well for the viscosity of hydrous rhyolitic melts. By fitting hydrous rhyolitic melt viscosity with the above equation, we find that rhyolitic melt viscosity vary by 1.2 orders of magnitude
NASA Astrophysics Data System (ADS)
Ebaid, A.
2008-08-01
In this Letter, we considered a numerical treatment for the solution of the hydromagnetic peristaltic flow of a bio-fluid with variable viscosity in a circular cylindrical tube using Adomian decomposition method and a modified form of this method. The axial velocity is obtained in a closed form. Comparison is made between the results obtained by only three terms of Adomian series with those obtained previously by perturbation technique. It is observed that only few terms of the series expansion are required to obtain the numerical solution with good accuracy.
Viscosity Measurement for Tellurium Melt
NASA Technical Reports Server (NTRS)
Lin, Bochuan; Li, Chao; Ban, Heng; Scripa, Rosalia N.; Su, Ching-Hua; Lehoczky, Sandor L.
2006-01-01
The viscosity of high temperature Te melt was measured using a new technique in which a rotating magnetic field was applied to the melt sealed in a suspended ampoule, and the torque exerted by rotating melt flow on the ampoule wall was measured. Governing equations for the coupled melt flow and ampoule torsional oscillation were solved, and the viscosity was extracted from the experimental data by numerical fitting. The computational result showed good agreement with experimental data. The melt velocity transient initiated by the rotating magnetic field reached a stable condition quickly, allowing the viscosity and electrical conductivity of the melt to be determined in a short period.
Grissom, C.B.; Cleland, W.W.
1988-04-19
The role of the metal ion in the oxidative decarboxylation of malate by chicken liver NADP malic enzyme and details of the reaction mechanism have been investigated by /sup 13/C isotope effects. With saturating NADP and the indicated metal ion at a total concentration 10-fold higher than its K/sub m/, the following primary /sup 13/C kinetic isotope effects at C/sub 4/ of malate (/sup 13/(VK/sub mal/)) were observed at pH 8.0: Mg/sup 2 +/, 1.0336; Mn/sup 2 +/, 1.0365; Cd/sup 2 +/, 1.0366; Zn/sup 2 +/, 1.0337; Co/sup 2 +/, 1.0283; Ni/sup 2 +/, 1.025. Knowing the partitioning of the intermediate oxalacetate between decarboxylation to pyuvate and reduction to malate allows calculation of the intrinsic carbon isotope effect for decarboxylation to pyuvate and reduction to malate allows calculation of the intrinsic carbon isotope effect for decarboxylation. For Mg/sup 2 +/ as activator, this was 1.049 with NADP and 1.046 with 3-acetylpyridine adenine dinucleotide phosphate, although the intrinsic primary deuterium isotope effects on dehydrogenation were 5.6 and 4.2, and the partition ratios of the oxalacetate intermediate for decarboxylation as opposed to hydride transfer were 0.11 and 3.96. It was not possible to calculate reasonable intrinsic carbon isotope effects with the other metal ions by use of the partitioning ratio of oxalacetate because of decarboxylation by another mechanism. The variation of /sup 13/(VK/sub mal/) with pH was used to dissect the total forward and external components. When the authors attempted to use the variation of /sup 13/(VK/sub mal/) with solution viscosity to determine the internal and external commitments, incorrect values were obtained because of a specific effect of the viscosogen in decreasing the K/sub m/ for malate, so that VK/sub mal/ actually increased with viscosity instead of decreasing, as theory predicts.
Scale dependent dynamic capillary pressure effect for two-phase flow in porous media
NASA Astrophysics Data System (ADS)
Abidoye, Luqman K.; Das, Diganta B.
2014-12-01
Causes and effects of non-uniqueness in capillary pressure and saturation (Pc-S) relationship in porous media are of considerable concern to researchers of two-phase flow. In particular, a significant amounts of discussion have been generated regarding a parameter termed as dynamic coefficient (τ) which has been proposed for inclusion in the functional dependence of Pc-S relationship to quantify dynamic Pc and its relation with time derivative of saturation. While the dependence of the coefficient on fluid and porous media properties is less controversial, its relation to domain scale appears to be dependent on artefacts of experiments, mathematical models and the intra-domain averaging techniques. In an attempt to establish the reality of the scale dependency of the τ-S relationships, we carry out a series of well-defined laboratory experiments to determine τ-S relationships using three different sizes of cylindrical porous domains of silica sand. In this paper, we present our findings on the scale dependence of τ and its relation to high viscosity ratio (μr) silicone oil-water system, where μr is defined as the viscosity of non-wetting phase over that of the wetting phase. An order of magnitude increase in the value of τ was observed across various μr and domain scales. Also, an order of magnitude increase in τ is observed when τ at the top and the bottom sections in a domain are compared. Viscosity ratio and domain scales are found to have similar effects on the trend in τ-S relationship. We carry out a dimensional analysis of τ which shows how different variables, e.g., dimensionless τ and dimensionless domain volume (scale), may be correlated and provides a means to determine the influences of relevant variables on τ. A scaling relationship for τ was derived from the dimensionless analysis which was then validated against independent literature data. This showed that the τ-S relationships obtained from the literature and the scaling
NASA Astrophysics Data System (ADS)
Yamasaki, Tadashi
2016-04-01
Development of the satellite observations (GPS and/or InSAR) has allowed us to precisely measure surface deformation. However any geodetic observation by itself does not tell us a mechanism of the deformation. All we can do the most is to compare such an observation to some quantitative predictions, only from which we can deduce a possible deformation mechanism. We therefore need to understand characteristic deformation pattern for a given source mechanism. This study particularly pays attention to magmatic activity in depth as the source, aiming to distinguish magma-induced crustal deformation by better knowing how the activity can be reflected in geodetically observable surface deformation. A parallelized 3-D finite element code, OREGANO_VE [e.g., Yamasaki and Houseman, 2015, J. Geodyn., 88, 80-89], is used to solve the linear Maxwell visco-elastic response to an applied internal inflation/deflation of magma chamber. The rectangular finite element model is composed with a visco-elastic layer overlaid by an elastic layer with thickness of H, and the visco-elastic layer extends over the rest of crust and the uppermost mantle. The visco-elastic crust has a depth-dependent viscosity (DDV) as an exponential function of depth due to temperature-dependent viscosity: hc = h0 exp[c(1 - z/L0)], where h0 is the viscosity at the bottom of the crust, c is a constant; c > 0 for DDV model and c = 0 for uniform viscosity (UNV) model, z is the depth, and L0 is a reference length-scale. The visco-elastic mantle has a spatially uniform viscosity hm. The inflation and/or deflation of sill-like magma chamber is implemented by using the split node method developed by Melosh and Raefsky [1981, Bull. Seism. Soc. Am., 71, 1391-1400]. UNV model with c = 0 employed in this study shows that the inflation-induced surface uplift would abate with time by visco-elastic relaxation. The post-inflation subsidence would erase the uplift in ~ 50 - 100 times Maxwell relaxation time of the crust
Effective viscosity of magnetic nanofluids through capillaries
NASA Astrophysics Data System (ADS)
Patel, Rajesh
2012-02-01
The simultaneous effect of magnetic field and temperature on the capillary viscosity of magnetic nanofluid is an important parameter for a new class of applications such as nanoduct flow, nanomotors, micro- and nanofluidic devices, for transformer cooling, magnetic targeted drug delivery, etc. The effective viscosity of a nanofluid is explained based on the rotation of the particles and the effect of torque on it due to an externally applied magnetic field. Two types of fluids are used here, temperature-sensitive and non-temperature-sensitive magnetic nanofluids. In both types of fluids, decrease in effective viscosity with temperature is observed, but in both cases the mechanism for the decrement is quite different. One is due to temperature dependence of the magnetic moment and the other is due to removal of the secondary surfactant. For temperature-sensitive magnetic nanofluids, a Curie temperature of ˜80 ∘C is extracted from this study. For non-temperature-sensitive magnetic nanofluids ˜65% of the secondary surfactant is removed for a change in temperature, ΔT = 40 ∘C. This is analogous with removal of a drug from magnetic particles for targeted drug delivery. Further, a linear dependence of effective viscosity with different capillary size and ξ (angle between magnetic field and flow direction, ξ∈[0,π/2]) is also observed. This linear dependence can also be a good approximation for the study of magnetic drug targeting, as in the human body the capillaries are of different sizes, and the externally applied magnetic field is not always parallel or perpendicular to the drug flow direction.
Effective viscosity of magnetic nanofluids through capillaries.
Patel, Rajesh
2012-02-01
The simultaneous effect of magnetic field and temperature on the capillary viscosity of magnetic nanofluid is an important parameter for a new class of applications such as nanoduct flow, nanomotors, micro- and nanofluidic devices, for transformer cooling, magnetic targeted drug delivery, etc. The effective viscosity of a nanofluid is explained based on the rotation of the particles and the effect of torque on it due to an externally applied magnetic field. Two types of fluids are used here, temperature-sensitive and non-temperature-sensitive magnetic nanofluids. In both types of fluids, decrease in effective viscosity with temperature is observed, but in both cases the mechanism for the decrement is quite different. One is due to temperature dependence of the magnetic moment and the other is due to removal of the secondary surfactant. For temperature-sensitive magnetic nanofluids, a Curie temperature of ~80 °C is extracted from this study. For non-temperature-sensitive magnetic nanofluids ~65% of the secondary surfactant is removed for a change in temperature, ΔT = 40 °C. This is analogous with removal of a drug from magnetic particles for targeted drug delivery. Further, a linear dependence of effective viscosity with different capillary size and ξ (angle between magnetic field and flow direction, ξε[0,π/2]) is also observed. This linear dependence can also be a good approximation for the study of magnetic drug targeting, as in the human body the capillaries are of different sizes, and the externally applied magnetic field is not always parallel or perpendicular to the drug flow direction. PMID:22463326
Magnetic effect in viscosity of magnetorheological fluids
NASA Astrophysics Data System (ADS)
Fonseca, H. A.; Gonzalez, E.; Restrepo, J.; Parra, C. A.; Ortiz, C.
2016-02-01
In this work the study of viscosity is presented for a magnetorheological fluid made from iron oxides micrometre, under an external magnetic field. The material was characterized by magnetic loops in a vibrating sample magnetometer and its crystal structure by X-ray diffraction. The results show that saturation magnetization and coercive field have dependence with the powder size. The material has different crystal structure which lattice parameters were determined by Rietveld refinement. The viscosity of the magnetorheological fluid was measured by a viscometer with rotational symmetry with and without external field. This result evidence a dependency on the size, percentage iron oxide and the applied magnetic field, it is due to the hydrodynamic volume of iron oxide interacts with the external magnetic field, increasing the flow resistance.
Feasibility of density and viscosity measurements under ammonothermal conditions
NASA Astrophysics Data System (ADS)
Steigerwald, Thomas G.; Alt, Nicolas S. A.; Hertweck, Benjamin; Schluecker, Eberhard
2014-10-01
With an eye on numerical simulations of ammonothermal growth of group III-V bulk single crystals, precise data for viscosity and density are strongly needed. In this work, changes in viscosity depending on temperature and pressure are traced in the developed ball viscometer. There, the falling time is detected by acquiring the acoustic signal of the ball using a high temperature borne-noise acceleration sensor. The results for the viscosity of pure ammonia at ammonothermal conditions already show good accuracy. The apparatus is designed to measure the density in addition to the viscosity, by the substitution of the rolling ball material in later experiments. This is important because the density of the flowing fluid is not constant due to the solubility change of GaN in ammonia by the mineralizers obligatory in ammonothermal process.
NASA Technical Reports Server (NTRS)
2001-01-01
The Critical Viscosity of Xenon Experiment (CVX-2) on the STS-107 Research 1 mission in 2002 will measure the viscous behavior of xenon, a heavy inert gas used in flash lamps and ion rocket engines, at its critical point. Shear thirning will cause a normally viscous fluid -- such as pie filling or whipped cream -- to deform and flow more readily under high shear conditions. In shear thinning, a pocket of fluid will deform and move one edge forward, as depicted here.
Harris, M R; Davis, D J; Durham, B; Millett, F
1997-04-11
The temperature and viscosity dependence of the photo-induced electron-transfer reaction between plastocyanin and cytochrome c labeled at Lys13 with Ru(4,4'-dicarboxybipyridine)(bipyridine)(2+)2 have been investigated. In these studies, a short pulse of 450 nm light was used to excite the ruthenium complex which was oxidatively quenched by the iron center of cytochrome c. The resulting Fe(II) cytochrome c was then rapidly reoxidized by plastocyanin. The reactions were investigated over a temperature range of 3.5 to 37 degrees C under low ionic strength conditions such that protein/protein complex formation was favored. The enthalpy of activation was 7 kcal mol-1 and the entropy of activation was -20 cal mol-1 K-1. Increasing the viscosity by the addition of sucrose up to 70% resulted in a 4-fold decrease in the rate constant for electron transfer. The overall results suggest a rate-limiting step that involves either dissociation of the dominant protein/protein complex or surface diffusion of the associated proteins. PMID:9131042
Viscosity of sodium-borate melts containing mechanically activated REM oxide additions
NASA Astrophysics Data System (ADS)
Ryabov, V. V.; Istomin, S. A.; Khokhryakov, A. A.; Ivanov, A. V.; Paivin, A. S.
2015-08-01
The viscosity of sodium-borate melts containing 1 wt % mechanically activated lanthanide group REM oxide is measured in the temperature range 950-1650 K using an oscillating viscometer. The dependences of the viscosity on temperature and composition are determined. The logarithmic dependences have high- and low-temperature portions with different viscous flow activation energies. It is found that the melt structure changes as a function of composition and temperature.
NASA Astrophysics Data System (ADS)
Henry, Eric J.; Smith, James E.
2006-09-01
SummarySurface infiltration line sources can deliver surfactant solutions for agricultural purposes or for use in subsurface remediation. Though the prediction of water distribution below a line source has received considerable attention in the scientific literature, little has been has been reported on how infiltration of surfactant solution from a line source differs from water infiltration. Few numerical models are capable of simulating surfactant-induced changes in moisture characteristic and hydraulic conductivity properties of unsaturated soil, so it is difficult to assess the importance of these effects when designing surfactant application schemes. We investigated surfactant infiltration behavior by using the variably-saturated flow and transport model HYDRUS-2D [Simunek, J., Sejna, M., van Genuchten, M.Th., 1999. The HYDRUS-2D software package for simulating the two-dimensional movement of water, heat, and multiple solutes in variably-saturated media, Version 2.0. IGWMC-TPS-53C. International Ground Water Modeling Center, Colorado School of Mines, Golden, CO] which was modified by [Henry, E.J., Smith, J.E., Warrick, A.W., 2002. Two-dimensional modeling of flow and transport in the vadose zone with surfactant-induced flow. Water Resour. Res. 38. DOI: doi:10.1029/2001WR000674] to incorporate surfactant effects on unsaturated flow. Significant differences were found between pure water and surfactant solution infiltration into a fine sand that was initially at residual moisture content. The surfactant solution wetted a larger area, both horizontally and vertically, relative to water, while the distribution of water within the wetted zone was more uniform than in the surfactant system. The surfactant system exhibited transient localized drainage and rewetting caused by surfactant-induced capillary pressure gradients within the wetting front. A standard unsaturated flow model (i.e., one that does not include surfactant effects on flow) is not capable of
Time-Dependence and Pattern Formation in Flowing Granular Media.
NASA Astrophysics Data System (ADS)
Baxter, George William, III
1990-01-01
We study the time dependence and pattern formation of gravity driven flows of granular media in three experiments. In three dimensional flows of sand, the normal stress on the wall of a conical hopper is measured. There is no evidence of characteristic time scales predicted by a linear stability analysis of a current continuum theory of granular media. Instead, the signal is characterized by a power law power spectrum, and the time variation of the normal stress obeys a scaling law consistent with fractional Brownian motion with H ~ 0.2. As one of the best examples to date of fractional Brownian motion in a physical experiment, this provides a unique opportunity for a study of the theory's application. In digital subtraction radiography studies of sand flow through a thin (nearly two dimensional) wedge, density waves are found. The formation and motion of these depends on the geometry of the wedge and the roughness of the sand grains. The waves form in rough sand but not in smooth sand of the same approximate size, demonstrating that grain structure has a dramatic effect on the flow. Also, the position of stagnant regions along the sides of the wedge is found to scale as a power law of the wedge angle. Neither the density waves nor the position of the stagnant regions are predicted by current theories. Finally, a cellular automata model is proposed to model the two dimensional flow of ellipsoidal grains (such as grass seed) through a wedge. By including particle shape and orientation as degrees of freedom, this model is able to capture many features of real physical flows. In sum, these experiments demonstrate that flows of even simple materials like sand or grass seed contain time dependent patterns that are not predicted by current theoretical models. This demonstrates the need to include particle structure and orientation. Finally, the cellular automata model shows that even relatively simple models which include these added degrees of freedom can reproduce the
Shear viscosity of shocked metals at mega-bar pressures
NASA Astrophysics Data System (ADS)
Liu, Fu-Sheng
2013-06-01
Viscosity of metals at high pressures and temperatures has been one of the most concerned problems in weapon physics and geophysics, e.g., the shear viscosity coefficients of substances in earth's mantle and earth's core at mega-bar pressures are needed for understanding the core mantle convection in deep earth. But the experimental data is very scarce because the conventional measurement methods can hardly be applied to such compression conditions [1]. In this talk, the principle of small-disturbance perturbation method [2] is re-investigated based on both the analytic solution and the numerical solution of the two-dimentional shock flow of sinusoidal distubance on front. In numerical solution, the real viscosity, which governs the flow behind the shock front and the perturbation damping feature, and the artificial viscosity, whick controls the numerical oscillation, separately treated. The relation between the viscosity of flow and the damping features of perturbation amplitude is quantitatively established for the loading situations of Sakharov's [3] and a flyer-impact situation with a finite disturbance. The later is the theoretical basis to develop a new experimental method, called the flyer-impact small-disturbance method [4]. In the flyer-impact small-disturbance method, the two-stage light-gas gun is used to launch a metal flyer. When the flyer directly impacts on the wedge-shaped sample with a sinusoidal surface, a two-dimensional shock flow of sinusoidal distubance on its front is generated. The amplitude of disturbance and its dependance with propagation distance is measured by use of an electric pin-array probe or a fibre-array probe. Correspondingly, the solution of the flow is given by numerically solving the hydrodynamic equations by the finite difference technique to find out the quantative correlations among the amplitude decay, the initial distribution of flow, the amplitude of initial disturbance, the shear viscosity of the flow, and the material
Endothelial-dependent vasodilators preferentially increase subendocardial blood flow
Pelc, L.R.; Gross, G.J.; Warltier, D.C.
1986-03-05
Interference with arachidonic acid metabolism on the effect of acetylcholine (Ach) or arachidonic acid (AA) to preferentially increase subendocardial perfusion was investigated in anesthetized dogs. Hemodynamics, regional myocardial blood flow (MBF (ml/min/g):radioactive microspheres) and the left ventricular transmural distribution of flow (endo/epi) were measured. Intracoronary infusion of Ach (10 ..mu..g/min) and AA (585 ..mu..g/min) significantly (P < .05*) increased myocardial perfusion and selectively redistributed flow to the subendocardium (increased endo/epi) without changes in systemic hemodynamics. Inhibition of phospholipase A/sub 2/ by quinacrine (Q; 600 ..mu..g/min, ic) attenuated the increase in myocardial perfusion produced by Ach but not by AA and inhibited the redistribution of flow to the subendocardium. The present results suggest that endothelium-dependent vasodilators produce a preferential increase in subendocardial perfusion via a product of AA metabolism.
NASA Technical Reports Server (NTRS)
Cline, M. C.
1974-01-01
The steady flow in two-dimensional and axisymmetric nozzles was computed using a time-dependent method. In this method the interior mesh points were computed using the MacCormack finite-difference scheme, while a characteristic scheme was used to calculate the boundary mesh points. No explicit artificial viscosity term was included. The fluid was assumed to be a perfect gas. This method was used to compute the flow in a 45 deg - 15 deg conical, converging-diverging nozzle, a 15 deg conical, converging nozzle, and a 10 deg conical, plug nozzle. Good agreement between the numerical solution and experimental data was found. In contrast to previous time-dependent methods, the computational times were less than one minute on a CDC 6600 computer.
Finite element simulation of temperature dependent free surface flows
NASA Technical Reports Server (NTRS)
Engelman, M. S.; Sani, R. L.
1985-01-01
The method of Engelman and Sani (1984) for a finite-element simulation of incompressible surface flows with a free and/or moving fluid interface, such as encountered in crystal growth and coating and polymer technology, is extended to temperature-dependent flows, including the effect of temperature-dependent surface tension. The basic algorithm of Saito and Scriven (1981) and Ruschak (1980) has been generalized and implemented in a robust and versatile finite-element code that can be employed with relative ease for the simulation of free-surface problems in complex geometries. As a result, the costly dependence on the Newton-Raphson algorithm has been eliminated by replacing it with a quasi-Newton iterative method, which nearly retains the superior convergence properties of the Newton-Raphson method.
Heat flux viscosity in collisional magnetized plasmas
Liu, C.; Fox, W.; Bhattacharjee, A.
2015-05-15
Momentum transport in collisional magnetized plasmas due to gradients in the heat flux, a “heat flux viscosity,” is demonstrated. Even though no net particle flux is associated with a heat flux, in a plasma there can still be momentum transport owing to the velocity dependence of the Coulomb collision frequency, analogous to the thermal force. This heat-flux viscosity may play an important role in numerous plasma environments, in particular, in strongly driven high-energy-density plasma, where strong heat flux can dominate over ordinary plasma flows. The heat flux viscosity can influence the dynamics of the magnetic field in plasmas through the generalized Ohm's law and may therefore play an important role as a dissipation mechanism allowing magnetic field line reconnection. The heat flux viscosity is calculated directly using the finite-difference method of Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], which is shown to be more accurate than Braginskii's method [S. I. Braginskii, Rev. Plasma Phys. 1, 205 (1965)], and confirmed with one-dimensional collisional particle-in-cell simulations. The resulting transport coefficients are tabulated for ease of application.
Heat flux viscosity in collisional magnetized plasmas
NASA Astrophysics Data System (ADS)
Liu, C.; Fox, W.; Bhattacharjee, A.
2015-05-01
Momentum transport in collisional magnetized plasmas due to gradients in the heat flux, a "heat flux viscosity," is demonstrated. Even though no net particle flux is associated with a heat flux, in a plasma there can still be momentum transport owing to the velocity dependence of the Coulomb collision frequency, analogous to the thermal force. This heat-flux viscosity may play an important role in numerous plasma environments, in particular, in strongly driven high-energy-density plasma, where strong heat flux can dominate over ordinary plasma flows. The heat flux viscosity can influence the dynamics of the magnetic field in plasmas through the generalized Ohm's law and may therefore play an important role as a dissipation mechanism allowing magnetic field line reconnection. The heat flux viscosity is calculated directly using the finite-difference method of Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], which is shown to be more accurate than Braginskii's method [S. I. Braginskii, Rev. Plasma Phys. 1, 205 (1965)], and confirmed with one-dimensional collisional particle-in-cell simulations. The resulting transport coefficients are tabulated for ease of application.
Viscosity of Campi Flregrei (Italy) magmas
NASA Astrophysics Data System (ADS)
Misiti, Valeria; Vetere, Francesco; Scarlato, Piergiorgio; Behrens, Harald; Mangiacapra, Annarita; Freda, Carmela
2010-05-01
Viscosity is an important factor governing both intrusive and volcanic processes. The most important parameters governing silicate melts viscosity are bulk composition of melt and temperature. Pressure has only minor effect at crustal depths, whereas crystals and bubbles have significant influence. Among compositional parameters, the water content is critical above all in terms of rheological behaviour of melts and explosive style of an eruption. Consequently, without an appropriate knowledge of magma viscosity depending on the amount of dissolved volatiles, it is not possible to model the processes (i.e., magma ascent, fragmentation, and dispersion) required to predict realistic volcanic scenarios and thus forecast volcanic hazards. The Campi Flegrei are a large volcanic complex (~150 km2) located west of the city of Naples, Italy, that has been the site of volcanic activity for more than 60 ka and represents a potential volcanic hazard owing to the large local population. In the frame of a INGV-DPC (Department of Civil Protection) project devoted to design a multidisciplinary system for short-term volcano hazard evaluation, we performed viscosity measurements, under dry and hydrous conditions, of primitive melt compositions representative of two Campi Flegrei eruptions (Minopoli-shoshonite and Fondo Riccio-latite). Viscosity of the two melts have been investigated in the high temperature/low viscosity range at atmospheric pressure in dry samples and at 0.5 GPa in runs having water content from nominally anhydrous to about 3 wt%. Data in the low temperature/high viscosity range were obtained near the glass transition temperature at atmospheric pressure on samples whose water contents vary from 0.3 up to 2.43 wt%. The combination of high- and low-viscosity data permits a general description of the viscosity as a function of temperature and water content using a modified Tamman-Vogel-Fulcher equation. logν = a+ --b--+ --d--×exp(g × w-) (T - c) (T - e) T (1) where
Gas flow dependence of atmospheric pressure plasma needle discharge characteristics
NASA Astrophysics Data System (ADS)
Qian, Muyang; Yang, Congying; Liu, Sanqiu; Chen, Xiaochang; Ni, Gengsong; Wang, Dezhen
2016-04-01
In this paper, a two-dimensional coupled model of neutral gas flow and plasma dynamics is presented to explain the gas flow dependence of discharge characteristics in helium plasma needle at atmospherics pressure. The diffusional mixing layer between the helium jet core and the ambient air has a moderate effect on the streamer propagation. The obtained simulation results present that the streamer shows the ring-shaped emission profile at a moderate gas flow rate. The key chemical reactions which drive the streamer propagation are electron-impact ionization of helium neutral, nitrogen and oxygen molecules. At a moderate gas flow rate of 0.5 slm, a significant increase in propagation velocity of the streamer is observed due to appropriate quantity of impurities air diffuse into the helium. Besides, when the gas flow rate is below 0.35 slm, the radial density of ground-state atomic oxygen peaks along the axis of symmetry. However, when the gas flow rate is above 0.5 slm, a ring-shaped density distribution appears. The peak density is on the order of 1020 m-3 at 10 ns in our work.
NASA Astrophysics Data System (ADS)
Berndt, Thomas; Muxworthy, Adrian R.; Paterson, Greig A.
2015-11-01
A new method to determine the atomic attempt time τ0 of magnetic relaxation of fine particles, which is central to rock and soil magnetism and paleomagnetic recording theory, is presented, including the determination of its temperature dependence, and simultaneously the grain size distribution of a sample. It is based on measuring a series of zero-field magnetic viscous decay curves for saturation isothermal remanent magnetization at various different temperatures that are later joined together on a single grain size scale from which the grain size distribution and attempt time are determined. The attempt time was determined for three samples containing noninteracting, single-domain titanomagnetites of different grain sizes for temperatures between 27 K and 374 K. No clear temperature-dependent trend was found; however, values varied significantly from one sample to the other: from 10-11 to 10-8s; in particular, the sample containing multiple magnetic phases had an effective attempt time significantly lower than the more homogeneous samples, thereby questioning the applicability of the simple Néel-Arhennius equation for magnetic relaxation for composite materials.
Role of salt sources in density-dependent flow
NASA Astrophysics Data System (ADS)
Hidalgo, Juan J.; Carrera, Jesús; Medina, AgustíN.
2009-05-01
Flow equation expresses mass conservation for a fluid phase. In density-dependent problems, fluid consists of at least two components, termed salt and water here. Salt sources are usually properly accounted for when salt is dissolved in water (i.e., as a solute) but are neglected otherwise. An analysis of the effect of neglecting pure salt sources on flow regime and concentration distribution is performed. Two test cases are used to illustrate the issue. The first one is the saltwater bucket problem, which consists of adding salt to an otherwise isolated domain. The second one is the Elder problem. Discrepancies in concentrations are moderate for reasonably small salt mass fractions. However, currently available codes yield head drops in response to the addition of salt because fluid mass is kept constant while its density increases. Such results contradict basic physical principles and lead to an inversion in the flow direction.
NASA Astrophysics Data System (ADS)
Baratoux, D.; Baumgartner, R. J.; Gaillard, F.; Fiorentini, M. L.
2015-12-01
Archean and Proterozoic komatiites and ferropicrites are mantle plume-related, low-viscosity, high-temperature, mafic to ultramafic lava flows. They are hosts to Ni-Cu±(PGE) sulphide mineralisation, which generally formed due to the segregation of sulphides following thermo-mechanical erosion and assimilation of sulphur-rich crustal rocks. We numerically simulated erosion and assimilation during the turbulent emplacement of iron-rich Martian lavas displaying chemical and rheological analogies with terrestrial mafic to ultramafic lavas, on a variety of basaltic and sedimentary sulphate-rich substratum. With the adoption of the lava flow and erosion model of Williams et al. (JGR, 1998), thermodynamic simulations were implemented to (semi-) quantify the potential changes in melt parameter (i.e., chemistry, temperature, and oxygen fugacity) that dictate the sulphur capacity of silicate melts. Modelling was also performed to assess the role of volatile degassing (Gaillard et al., SSR, 2013) on the sulphur inventory of Martian lavas. Our modelling show that lavas emplacing over basaltic crust are governed by low cooling rates, as well as low erosion and assimilation capacities, thus resulting in calculated near-cotectic proportions of sulphides segregating relatively late upon lava emplacement (usually > 100 km flow distance). The rapid assimilation of highly erodible and sulphate-rich Martian regolith may trigger sulphide supersaturation and batch segregation of sulphides well above cotectic proportions relatively early during the establishment of magmatic flow (<100 km flow distance). However, the assimilation of sulphate, which serves as a strongly oxidising agent, could result in dramatic sulphur loss due to increased volatile degassing rates. This process may limit or even counteract the overall positive effect of sulphate assimilation on achieving sulphide supersaturation, sulphide segregation and the genesis of Ni-Cu±(PGE) sulphide mineralisation.
Distributed energy storage: Time-dependent tree flow design
NASA Astrophysics Data System (ADS)
Bejan, A.; Ziaei, S.; Lorente, S.
2016-05-01
This article proposes "distributed energy storage" as a basic design problem of distributing energy storage material on an area. The energy flows by fluid flow from a concentrated source to points (users) distributed equidistantly on the area. The flow is time-dependent. Several scenarios are analyzed: sensible-heat storage, latent-heat storage, exergy storage vs energy storage, and the distribution of a finite supply of heat transfer surface between the source fluid and the distributed storage material. The chief conclusion is that the finite amount of storage material should be distributed proportionally with the distribution of the flow rate of heating agent arriving on the area. The total time needed by the source stream to "invade" the area is cumulative (the sum of the storage times required at each storage site) and depends on the energy distribution paths and the sequence in which the users are served by the source stream. Directions for future designs of distributed storage and retrieval are outlined in the concluding section.
Concentration Dependence of VO2+ Crossover of Nafion for Vanadium Redox Flow Batteries
Lawton, Jamie; Jones, Amanda; Zawodzinski, Thomas A
2013-01-01
The VO2+ crossover, or permeability, through Nafion in a vanadium redox flow battery (VRFB) was monitored as a function of sulfuric acid concentration and VO2+ concentration. A vanadium rich solution was flowed on one side of the membrane through a flow field while symmetrically on the other side a blank or vanadium deficit solution was flowed. The blank solution was flowed through an electron paramagnetic resonance (EPR) cavity and the VO2+ concentration was determined from the intensity of the EPR signal. Concentration values were fit using a solution of Fick s law that allows for the effect of concentration change on the vanadium rich side. The fits resulted in permeability values of VO2+ ions across the membrane. Viscosity measurements of many VO2+ and H2SO4 solutions were made at 30 60 C. These viscosity values were then used to determine the effect of the viscosity of the flowing solution on the permeability of the ion. 2013 The Electrochemical Society. [DOI: 10.1149/2.004306jes] All rights reserved.
Time-dependent local density measurements in unsteady flows
NASA Technical Reports Server (NTRS)
Mckenzie, R. L.; Monson, D. J.; Exberger, R. J.
1979-01-01
A laser-induced fluorescence technique for measuring the relative time-dependent density fluctuations in unsteady or turbulent flows is demonstrated. Using a 1.5-W continuous-wave Kr(+) laser, measurements have been obtained in 0.1-mm diameter by 1-mm-long sampling volumes in a Mach 3 flow of N2 seeded with biacetyl vapor. A signal amplitude resolution of 2% was achieved for a detection frequency bandwidth of 10 kHz. The measurement uncertainty was found to be dominated by noise behaving as photon statistical noise. The practical limits of signal-to-noise ratios have been characterized for a wide range of detection frequency bandwidths that encompasses those of interest in supersonic turbulence measurements.
Time-dependent local density measurements in unsteady flows
NASA Technical Reports Server (NTRS)
Mckenzie, R. L.; Monson, D. J.; Exberger, R. J.
1979-01-01
A laser-induced fluorescence technique for measuring the relative time-dependent density fluctuations in unsteady or turbulent flows is demonstrated. Using a 1.5-W continuous-wave Kr(+) laser, measurements have been obtained in 0.1-mm-diameter by 1-mm-long sampling volumes in a Mach 3 flow of N2 seeded with biacetyl vapor. A signal amplitude resolution of 2% was achieved for a detection frequency bandwidth of 10 kHz. The measurement uncertainty was found to be dominated by noise behaving as photon statistical noise. The practical limits of signal-to-noise ratios have been characterized for a wide range of detection frequency bandwidths that encompasses those of interest in supersonic turbulence measurements.
Numerical modeling of a fast-axial-flow CO2 laser with considering viscosity and ambipolar diffusion
NASA Astrophysics Data System (ADS)
Galeev, Ravil S.; Fedosov, A. A.
1996-03-01
A numerical method for analysis of a fast axial flow glow discharge carbon dioxide laser is developed. The method is based on the self-consistent solution to the two-dimensional steady- state Navier-Stokes equations in thin-shear-layer approximation (slender channel equations), the parabolized glow discharge equations, and the vibrational relaxation equations. The discharge equations include the continuity equations for the electrons, the positive and negative ions. The one-mode relaxation model for the vibrational kinetics and the plane-parallel optical resonator model are used. The present model is based on the assumption of the charge neutrality and limited by consideration of the positive column of discharge without taking into account the cathode-fall and anode-fall regions.
Zhou, Yang; Li, Yixue; Qian, Wen; He, Bi
2016-09-01
Based on dissipative particle dynamics (DPD) methods and experimental data, we used an empirical relationship between the DPD temperature and the real temperature to build a model that describes the viscosity of molten TNT fluids. The errors in the predicted viscosity based on this model were no more than 2.3 %. We also studied the steady-state shear rheological behavior of molten TNT fluids containing nanoparticles ("nanofluids"). The dependence of the nanofluid viscosity on the temperature was found to satisfy an Arrhenius-type equation, η = Ae (B/T) , where B, the flow activation energy, depends on particle content, size, and shape. We modified the Einstein-type viscosity model to account for the effects of nanoparticle solvation in TNT nanofluids. The resulting model was able to correctly predict the viscosities of suspensions containing nano- to microsized particles, and did not require any changes to the physical background of Einstein's viscosity theory. Graphical Abstract The revised Einstein viscosity model that correctly predict the viscosity of TNT suspensions containing nanoparticles. PMID:27553301
A self-adjusting flow dependent formulation for the classical Smagorinsky model coefficient
NASA Astrophysics Data System (ADS)
Ghorbaniasl, G.; Agnihotri, V.; Lacor, C.
2013-05-01
In this paper, we propose an efficient formula for estimating the model coefficient of a Smagorinsky model based subgrid scale eddy viscosity. The method allows vanishing eddy viscosity through a vanishing model coefficient in regions where the eddy viscosity should be zero. The advantage of this method is that the coefficient of the subgrid scale model is a function of the flow solution, including the translational and the rotational velocity field contributions. Furthermore, the value of model coefficient is optimized without using the dynamic procedure thereby saving significantly on computational cost. In addition, the method guarantees the model coefficient to be always positive with low fluctuation in space and time. For validation purposes, three test cases are chosen: (i) a fully developed channel flow at {mathopRenolimits} _tau = 180, 395, (ii) a fully developed flow through a rectangular duct of square cross section at {mathopRenolimits} _tau = 300, and (iii) a smooth subcritical flow past a stationary circular cylinder, at a Reynolds number of {mathopRenolimits} = 3900, where the wake is fully turbulent but the cylinder boundary layers remain laminar. A main outcome is the good behavior of the proposed model as compared to reference data. We have also applied the proposed method to a CT-based simplified human upper airway model, where the flow is transient.
NASA Astrophysics Data System (ADS)
Decaix, J.; Alligné, S.; Nicolet, C.; Avellan, F.; Münch, C.
2015-12-01
1D hydro-electric models are useful to predict dynamic behaviour of hydro-power plants. Regarding vortex rope and cavitation surge in Francis turbines, the 1D models require some inputs that can be provided by numerical simulations. In this paper, a 2D cavitating Venturi is considered. URANS computations are performed to investigate the dynamic behaviour of the cavitation sheet depending on the frequency variation of the outlet pressure. The results are used to calibrate and to assess the reliability of the 1D models.
NASA Astrophysics Data System (ADS)
Olyanina, N. V.; Bel'tyukov, A. L.; Lad'yanov, V. I.
2016-02-01
The temperature and concentration dependences of the kinematic viscosity of Co-B melts with a boron content up to 50 at % are studied by torsional vibrations. The viscosity polytherms are satisfactorily described by the Arrhenius equation. An increase in the viscosity with an increase in the boron content from 15 to 36 at % is observed in the concentration dependence of the viscosity. The viscosity of the melt is almost independent of the boron content in concentration ranges of 0-15 and 36-50 at %. The concentration dependence of the melt viscosity of the system is calculated using various equations. The best coincidence with the experimental data is obtained for the calculation using the Kaptay equation.
Tracking the permeable porous network during strain-dependent magmatic flow
NASA Astrophysics Data System (ADS)
Kendrick, J. E.; Lavallée, Y.; Hess, K.-U.; Heap, M. J.; Gaunt, H. E.; Meredith, P. G.; Dingwell, D. B.
2013-06-01
Rheological variations have been postulated as the cause of transitions from effusive to explosive volcanic eruption style. Rheology is integrally linked to the composition and textural state (porosity, crystallinity) of magma as well as the stress, temperature and strain rate operative during flow. This study characterises the rheological behaviour and, importantly, the evolution of physical properties of two magmas (with different crystallinity and porosity) from Volcán de Colima (Mexico) - a volcanic system known for its rapid fluctuations in eruption style. Magma samples deformed in a uniaxial press at a constant stress of 2.8, 12 or 24 MPa, a constant temperature of 940-945 °C (comparable to upper conduit or lava dome conditions) to strains of 20 or 30% displayed different mechanical behaviour and significant differences in measured strain rates (10- 2-10- 5 s- 1). The evolution of porosity, permeability, dynamic Young's modulus and dynamic Poisson's ratio illustrate a complex evolution of the samples manifested as strain-hardening, visco-elastic, constant-rate and strain-weakening deformation. Both magmas behave as shear-thinning non-Newtonian liquids and viscosity decreases as a function of strain. We find that strain localisation during deformation leads to the rearrangement and closure of void space (a combination of pores and cracks) followed by preferentially aligned fracturing (in the direction of the maximum principal stress) to form damage zones as well as densification of other areas. In a dome setting, highly viscous, low permeability magmas carry the potential to block volcanic conduits with a magma plug, resulting in the build-up of pressures in the conduit. Above a certain threshold of strain (dependent upon stress/strain rate), the initiation, propagation and coalescence of fractures leads to mechanical degradation of the magma samples, which then supersedes magmatic flow and crystal rearrangement as the dominant form of deformation. This
NASA Astrophysics Data System (ADS)
Lacey, Roy A.; Taranenko, A.; Jia, J.; Reynolds, D.; Ajitanand, N. N.; Alexander, J. M.; Gu, Yi; Mwai, A.
2014-02-01
The flow harmonics v2,3 for charged hadrons are studied for a broad range of centrality selections and beam collision energies in Au+Au (√sNN =7.7-200 GeV) and Pb +Pb (√sNN =2.76 TeV) collisions. They validate the characteristic signature expected for the system size dependence of viscous damping at each collision energy studied. The extracted viscous coefficients that encode the magnitude of the ratio of shear viscosity to entropy density η/s are observed to decrease to an apparent minimum as the collision energy is increased from √sNN =7.7 to approximately 62.4 GeV; thereafter, they show a slow increase with √sNN up to 2.76 TeV. This pattern of viscous damping provides the first experimental constraint for η/s in the temperature-baryon chemical potential (T, μB) plane and could be an initial indication for decay trajectories that lie close to the critical end point in the phase diagram for nuclear matter.
Surface dilatational viscosity of Langmuir monolayers
NASA Astrophysics Data System (ADS)
Lopez, Juan; Vogel, Michael; Hirsa, Amir
2003-11-01
With increased interest in microfluidic systems, interfacial phenomena is receiving more attention. As the length scales of fluid problems decrease, the surface to volume ratio increases and the coupling between interfacial flow and bulk flow becomes increasingly dominated by effects due to intrinsic surface viscosities (shear and dilatational), in comparison to elastic effects (due to surface tension gradients). The surface shear viscosity is well-characterized, as cm-scale laboratory experiments are able to isolate its effects from other interfacial processes (e.g., in the deep-channel viscometer). The same is not true for the dilatational viscosity, because it acts in the direction of surface tension gradients. Their relative strength scale with the capillary number, and for cm-scale laboratory flows, surface tension effects tend to dominate. In microfluidic scale flows, the scaling favors viscosity. We have devised an experimental apparatus which is capable of isolating and enhancing the effects of dilatational viscosity at the cm scales by driving the interface harmonically in time, while keeping the interface flat. In this talk, we shall present both the theory for how this works as well as experimental measurements of surface velocity from which we deduce the dilatational viscosity of several monolayers on the air-water interface over a substantial range of surface concentrations. Anomalous behavior over some range of concentration, which superficially indicates negative viscosity, maybe explained in terms of compositional effects due to large spatial and temporal variations in concentration and corresponding viscosity.
Cline, M.C.
1981-08-01
VNAP2 is a computer program for calculating turbulent (as well as laminar and inviscid), steady, and unsteady flow. VNAP2 solves the two-dimensional, time-dependent, compressible Navier-Stokes equations. The turbulence is modeled with either an algebraic mixing-length model, a one-equation model, or the Jones-Launder two-equation model. The geometry may be a single- or a dual-flowing stream. The interior grid points are computed using the unsplit MacCormack scheme. Two options to speed up the calculations for high Reynolds number flows are included. The boundary grid points are computed using a reference-plane-characteristic scheme with the viscous terms treated as source functions. An explicit artificial viscosity is included for shock computations. The fluid is assumed to be a perfect gas. The flow boundaries may be arbitrary curved solid walls, inflow/outflow boundaries, or free-jet envelopes. Typical problems that can be solved concern nozzles, inlets, jet-powered afterbodies, airfoils, and free-jet expansions. The accuracy and efficiency of the program are shown by calculations of several inviscid and turbulent flows. The program and its use are described completely, and six sample cases and a code listing are included.
NASA Technical Reports Server (NTRS)
Cline, M. C.
1981-01-01
A computer program, VNAP2, for calculating turbulent (as well as laminar and inviscid), steady, and unsteady flow is presented. It solves the two dimensional, time dependent, compressible Navier-Stokes equations. The turbulence is modeled with either an algebraic mixing length model, a one equation model, or the Jones-Launder two equation model. The geometry may be a single or a dual flowing stream. The interior grid points are computed using the unsplit MacCormack scheme. Two options to speed up the calculations for high Reynolds number flows are included. The boundary grid points are computed using a reference plane characteristic scheme with the viscous terms treated as source functions. An explicit artificial viscosity is included for shock computations. The fluid is assumed to be a perfect gas. The flow boundaries may be arbitrary curved solid walls, inflow/outflow boundaries, or free jet envelopes. Typical problems that can be solved concern nozzles, inlets, jet powered afterbodies, airfoils, and free jet expansions. The accuracy and efficiency of the program are shown by calculations of several inviscid and turbulent flows. The program and its use are described completely, and six sample cases and a code listing are included.
NASA Astrophysics Data System (ADS)
Brunei, David; Machetel, Philippe
1998-03-01
A more general expression for the mantle vorticity equation is proposed for convection using axisymmetrical spherical geometry. Both the main mantle phase changes and radial and lateral variations of viscosity due to temperature and pressure. Four series of computations have been performed with (1) both the latent heat releases of the 400 km exothermic and the 670 km endothermic phase change and uniform and constant mantle viscosity; (2) the 670 km phase change alone and viscosity jumps of 10 or 30 between upper and lower mantle phases; (3) the 670 km endothermic phase change, a viscosity contrast of 30, and temperature and pressure dependent viscosity law; and (4) both 400 km and 670 km phase changes, a viscosity jump of 30, and a temperature and pressure dependent viscosity. The 400 km exothermic phase change modifies the global structure from partly layered to whole mantle convection. This effect is opposite to the effect obtained by increasing the viscosity jump at 670 km. However, both effects induce unrealistic thermal behavior which will not appear with temperature dependent laws for viscosity. The mantle avalanches which suddenly inject huge quantities of cold material into the lower mantle have effects at the surface and at the core-mantle boundary (CMB). They induced heat flow crises which explain the huge volcanic events, high rates of mid-oceanic ridge accretion, and periods of low-frequency magnetic reversal. The surface heat flow proceeds directly from the upper mantle return flow along with the avalanches. The temperature dependent viscosity tends to decrease the strength of the avalanches. The bottom heat flow and the birth of CMB plumes may be considered as the consequences of cold upper mantle material arrival at the CMB. The lower mantle and the upper mantle transit times depend on the thickness of upper and lower mantles but also on the phase changes and on the viscosity. The CMB and surface perturbations may be simultaneous (to a few tens of
Percolation velocity dependence on local concentration in bidisperse granular flows
NASA Astrophysics Data System (ADS)
Jones, Ryan P.; Xiao, Hongyi; Deng, Zhekai; Umbanhowar, Paul B.; Lueptow, Richard M.
The percolation velocity, up, of granular material in size or density bidisperse mixtures depends on the local concentration, particle size ratio, particle density ratio, and shear rate, γ ˙. Discrete element method computational results were obtained for bounded heap flows with size ratios between 1 and 3 and for density ratios between 1 and 4. The results indicate that small particles percolate downward faster when surrounded by large particles than large particles percolate upward when surrounded by small particles, as was recently observed in shear-box experiments. Likewise, heavy particles percolate downward faster when surrounded by light particles than light particles percolate upward when surrounded by heavy particles. The dependence of up / γ ˙ on local concentration results in larger percolation flux magnitudes at high concentrations of large (or light) particles compared to high concentrations of small (or heavy) particles, while local volumetric flux is conserved. The dependence of up / γ ˙ on local concentration can be incorporated into a continuum model, but the impact on global segregation patterns is usually minimal. Partially funded by Dow Chemical Company and NSF Grant No. CBET-1511450.