Viscous Flow (viscous + flow)

Distribution by Scientific Domains

Kinds of Viscous Flow

  • incompressible viscous flow
  • three-dimensional viscous flow

  • Terms modified by Viscous Flow

  • viscous flow problem

  • Selected Abstracts


    Decoupling between Enthalpy Relaxation and Viscous Flow and Its Structural Origin in Fragile Oxide Glass-Forming Liquids

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2002
    Takayuki Komatsu
    The structural relaxation kinetics at the glass transition in tellurium oxide (TeO2)-based glasses has been examined from viscosity and heat-capacity measurements to clarify the features of the structural relaxation in fragile oxide glass-forming liquids. A large decoupling between enthalpy relaxation and viscous flow, i.e., a large discrepancy between the activation energies for the enthalpy relaxation (recovery), ,H, and viscous flow, E,, has been demonstrated in TeO2 -based glasses. The values in xK2OxMgO(100 , 2x)TeO2 glasses, for example, are ,919,1051 kJ/mol for ,H and , 577,701 kJ/mol for E,, given the ratio of ,H/E,, 1.44,1.59. Some viscosity and heat-capacity data (all data have been reported previously) obtained from similar experiments in Sb2O3,B2O3 glasses belonging to the category of strong glass-forming liquids have been reanalyzed in this paper for comparison; a strong coupling was found to exist between ,H and E,, i.e., ,H/E,, 0.98,1.18. An origin of decoupling between ,H and E, in fragile glass-forming systems such as TeO2 -based glasses has been discussed by considering the glass structure model for fragile glasses; strongly bonded correlated (highly constrained) regions are surrounded or connected by weakly bonded noncorrelated (unconstrained) parts. [source]


    Viscous flow in three-dimensional reconstructed porous media

    INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2003
    Marco Pilotti
    Abstract In a recent paper Masad et al. (Int. J. Numer. Methods Eng. 2000; 26: 53,74) have shown the possibility of numerically studying fluid flow within two-dimensional microscopic images of granular materials. In this paper we investigate the possibility of computing the flow field at the pore scale within numerically reconstructed three dimensional porous media, by coupling a physically based sedimentation algorithm for porous media generation and a Lattice Boltzmann Technique for solving Navier equations for the monophasic flow of a newtonian fluid inside the intergranular space. Since the adopted sedimentation algorithm can produce porous media with a controlled level of complexity, we believe that this type of approach provides an ideal numerical laboratory to probe the effect of void space topology and geometry on the flow field. This should allow to understand the fluid-dynamic implications of processes such as compaction and cementation. After showing that the Lattice Boltzmann Technique is effective in solving Navier equations in porous media also at moderately high Reynolds, where Darcy's flow does not strictly hold anymore, we investigate the distribution of velocity components within porous media of growing complexity, starting from two different periodic arrangements of spheres up to a mixture of log-normally distributed spheres. We observe that the distribution of velocity components is conditioned by the medium complexity and tends to an exponential pattern. Copyright 2003 John Wiley & Sons, Ltd. [source]


    Analysis of multicomponent adsorption kinetics on activated carbon

    AICHE JOURNAL, Issue 4 2003
    L. P. Ding
    An integrated mathematical model for the kinetics of multicomponent adsorption on microporous carbon was developed. Transport in this bidisperse solid is represented by balance equations in the macropore and micropore phases, in which gas-phase diffusion dominates the mass transfer in the macropores, with the phenomenological diffusivities represented by the generalized Maxwell,Stefan (GMS) formulation. Viscous flow also contributes to the macropore fluxes and is included in the MS expressions. Diffusion of the adsorbed phase controls the mass transfer in the micropore phase, which is also described in a similar way by the MS method. The adsorption isotherms are represented by a new heterogeneous modified vacancy solution theory formulation of adsorption, which has proved to be a robust method for adsorption on activated carbons. The model is applied to the coadsorption and codesorption of C2H6 and C3H8 on Ajax and Norit carbon, as well as the displacement on Ajax carbon. The effect of the viscous flow in the macropore phase is not significant for the cases studied. The model accurately predicts the overshoot behavior and rollup of C2H6 during coadsorption. The prediction for the heavier compound C3H8 is always satisfactory, though at higher C3H8 mole fraction, the overshoot extent of C2H6 is overpredicted, possibly due to neglect of heat effects. [source]


    On singularities in the solution of three-dimensional Stokes flow and incompressible elasticity problems with corners

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2004
    A. Dimitrov
    Abstract In this paper, a numerical procedure is presented for the computation of corner singularities in the solution of three-dimensional Stokes flow and incompressible elasticity problems near corners of various shape. For obtaining the order and mode of singularity, a neighbourhood of the singular point is considered with only local boundary conditions. The weak formulation of this problem is approximated using a mixed u, p Galerkin,Petrov finite element method. Additionally, a separation of variables is used to reduce the dimension of the original problem. As a result, the quadratic eigenvalue problem (P+,Q+,2R)d=0 is obtained, where the saddle-point-type matrices P, Q, R are defined explicitly. For a numerical solution of the algebraic eigenvalue problem an iterative technique based on the Arnoldi method in combination with an Uzawa-like scheme is used. This technique needs only one direct matrix factorization as well as few matrix,vector products for finding all eigenvalues in the interval ,,(,) , (,0.5, 1.0), as well as the corresponding eigenvectors. Some benchmark tests show that this technique is robust and very accurate. Problems from practical importance are also analysed, for instance the surface-breaking crack in an incompressible elastic material and the three-dimensional viscous flow of a Newtonian fluid past a trihedral corner. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Three-dimensional viscous flow over rotating periodic structures

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2003
    Kyu-Tae Kim
    Abstract The three-dimensional Stokes flow in a periodic domain is examined in this study. The problem corresponds closely to the flow inside internal mixers, where the flow is driven by the movement of a rotating screw; the outer barrel remaining at rest. A hybrid spectral/finite-difference approach is proposed for the general expansion of the flow field and the solution of the expansion coefficients. The method is used to determine the flow field between the screw and barrel. The regions of elongation and shear are closely examined. These are the two mechanisms responsible for mixing. Besides its practical importance, the study also allows the assessment of the validity of the various assumptions usually adopted in mixing and lubrication problems. Copyright 2003 John Wiley & Sons, Ltd. [source]


    Bifurcation and stability analysis of laminar flow in curved ducts

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2010
    Werner Machane
    Abstract The development of viscous flow in a curved duct under variation of the axial pressure gradient q is studied. We confine ourselves to two-dimensional solutions of the Dean problem. Bifurcation diagrams are calculated for rectangular and elliptic cross sections of the duct. We detect a new branch of asymmetric solutions for the case of a rectangular cross section. Furthermore we compute paths of quadratic turning points and symmetry breaking bifurcation points under variation of the aspect ratio , (,=0.8,1.5). The computed diagrams extend the results presented by other authors. We succeed in finding two origins of the Hopf bifurcation. Making use of the Cayley transformation, we determine the stability of stationary laminar solutions in the case of a quadratic cross section. All the calculations were performed on a parallel computer with 3232 processors. Copyright 2009 John Wiley & Sons, Ltd. [source]


    Numerical simulation of viscous flow interaction with an elastic membrane

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2008
    Lisa A. Matthews
    Abstract A numerical fluid,structure interaction model is developed for the analysis of viscous flow over elastic membrane structures. The Navier,Stokes equations are discretized on a moving body-fitted unstructured triangular grid using the finite volume method, taking into account grid non-orthogonality, and implementing the SIMPLE algorithm for pressure solution, power law implicit differencing and Rhie,Chow explicit mass flux interpolations. The membrane is discretized as a set of links that coincide with a subset of the fluid mesh edges. A new model is introduced to distribute local and global elastic effects to aid stability of the structure model and damping effects are also included. A pseudo-structural approach using a balance of mesh edge spring tensions and cell internal pressures controls the motion of fluid mesh nodes based on the displacements of the membrane. Following initial validation, the model is applied to the case of a two-dimensional membrane pinned at both ends at an angle of attack of 4 to the oncoming flow, at a Reynolds number based on the chord length of 4 103. A series of tests on membranes of different elastic stiffness investigates their unsteady movements over time. The membranes of higher elastic stiffness adopt a stable equilibrium shape, while the membrane of lowest elastic stiffness demonstrates unstable interactions between its inflated shape and the resulting unsteady wake. These unstable effects are shown to be significantly magnified by the flexible nature of the membrane compared with a rigid surface of the same average shape. Copyright 2007 John Wiley & Sons, Ltd. [source]


    Numerical analysis of a 3D hydrodynamic contact

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2006
    Costin Alin Caciu
    Abstract We study here the numerical analysis of a hydrodynamic contact in a particular configuration: the 3D incompressible viscous flow of a fluid dragged by a smooth plate over a rough surface. The mathematical model takes into account and discretizes the local topography of the rough profile. The simulation outcome will be the 3D velocity and pressure fields of the fluid film within the contact borders. This work is limited to the study of numerical resolution methods working solely in finite differences. The algorithms will be tested by analysing and comparing their results with analytically known flows. Copyright 2006 John Wiley & Sons, Ltd. [source]


    Numerical analysis on the propulsive performance and vortex shedding of fish-like travelling wavy plate

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2005
    Gen-Jin Dong
    Abstract Numerical analysis is carried out to investigate viscous flow over a travelling wavy plate undergoing lateral motion in the form of a streamwise travelling wave, which is similar to the backbone undulation of swimming fish. The two-dimensional incompressible Navier,Stokes equations are solved using the finite element technique with the deforming-spatial-domain/stabilized space,time formulation. The objective of this study is to elucidate hydrodynamic features of flow structure and vortex shedding near the travelling wavy plate and to get into physical insights to the understanding of fish-like swimming mechanisms in terms of drag reduction and optimal propulsive performance. The effects of some typical parameters, including the phase speed, amplitude, and relative wavelength of travelling wavy plate, on the flow structures, the forces, and the power consumption required for the propulsive motion of the plate are analysed. These results predicted by the present numerical analysis are well consistent with the available data obtained for the wave-like swimming motion of live fish in nature. Copyright 2005 John Wiley & Sons, Ltd. [source]


    A complete boundary integral formulation for compressible Navier,Stokes equations

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2005
    Yang ZuoshengArticle first published online: 29 DEC 200
    Abstract A complete boundary integral formulation for compressible Navier,Stokes equations with time discretization by operator splitting is developed using the fundamental solutions of the Helmholtz operator equation with different order. The numerical results for wall pressure and wall skin friction of two-dimensional compressible laminar viscous flow around airfoils are in good agreement with field numerical methods. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Solving high Reynolds-number viscous flows by the general BEM and domain decomposition method

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2005
    Yongyan Wu
    Abstract In this paper, the domain decomposition method (DDM) and the general boundary element method (GBEM) are applied to solve the laminar viscous flow in a driven square cavity, governed by the exact Navier,Stokes equations. The convergent numerical results at high Reynolds number Re = 7500 are obtained. We find that the DDM can considerably improve the efficiency of the GBEM, and that the combination of the domain decomposition techniques and the parallel computation can further greatly improve the efficiency of the GBEM. This verifies the great potential of the GBEM for strongly non-linear problems in science and engineering. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Control strategies for timestep selection in finite element simulation of incompressible flows and coupled reaction,convection,diffusion processes

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2005
    A. M. P. Valli
    Abstract We propose two timestep selection algorithms, based on feedback control theory, for finite element simulation of steady state and transient 2D viscous flow and coupled reaction,convection,diffusion processes. To illustrate performance of the schemes in practice, we solve Rayleigh,Benard,Marangoni flows, flow across a backward-facing step, unsteady flow around a circular cylinder and chemical reaction systems. Numerical experiments confirm that the feedback controllers produce in some cases a very smooth stepsize variation, suggesting that robust control algorithms are possible. These experiments also show that parameter selection can improve timesteps when co-ordinated with the convergence control of non-linear iterations. Further, computational cost of the selection procedures is negligible, since they involve only storing a few extra vectors, computation of norms and evaluation of kinetic energy. Copyright 2004 John Wiley & Sons, Ltd. [source]


    A promising boundary element formulation for three-dimensional viscous flow

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2005
    Xiao-Wei Gao
    Abstract In this paper, a new set of boundary-domain integral equations is derived from the continuity and momentum equations for three-dimensional viscous flows. The primary variables involved in these integral equations are velocity, traction, and pressure. The final system of equations entering the iteration procedure only involves velocities and tractions as unknowns. In the use of the continuity equation, a complex-variable technique is used to compute the divergence of velocity for internal points, while the traction-recovery method is adopted for boundary points. Although the derived equations are valid for steady, unsteady, compressible, and incompressible problems, the numerical implementation is only focused on steady incompressible flows. Two commonly cited numerical examples and one practical pipe flow problem are presented to validate the derived equations. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Meshfree weak,strong (MWS) form method and its application to incompressible flow problems

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2004
    G. R. Liu
    Abstract A meshfree weak,strong (MWS) form method has been proposed by the authors' group for linear solid mechanics problems based on a combined weak and strong form of governing equations. This paper formulates the MWS method for the incompressible Navier,Stokes equations that is non-linear in nature. In this method, the meshfree collocation method based on strong form equations is applied to the interior nodes and the nodes on the essential boundaries; the local Petrov,Galerkin weak form is applied only to the nodes on the natural boundaries of the problem domain. The MWS method is then applied to simulate the steady problem of natural convection in an enclosed domain and the unsteady problem of viscous flow around a circular cylinder using both regular and irregular nodal distributions. The simulation results are validated by comparing with those of other numerical methods as well as experimental data. It is demonstrated that the MWS method has very good efficiency and accuracy for fluid flow problems. It works perfectly well for irregular nodes using only local quadrature cells for nodes on the natural boundary, which can be generated without any difficulty. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Biomagnetic fluid flow in a 3D rectangular duct

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2004
    E. E. Tzirtzilakis1
    Abstract The laminar, incompressible, three-dimensional, fully developed viscous flow of a non-conducting biomagnetic fluid in a impermeable rectangular duct is numerically studied in the presence of an applied magnetic field. It is assumed that the magnetic field strength is sufficiently strong to saturate the biofluid and the magnetization is given as a function of the magnetic field intensity. The system of the partial differential equations, resulting after the introduction of appropriate non-dimensional variables, is solved applying an efficient numerical technique based on a pressure-linked pseudotransient method on a common grid. Results concerning the existence and the uniqueness of the solution, are also given. The obtained results, for different values for the parameters entering into the problem under consideration, show that the flow is appreciably influenced by the presence of the magnetic field. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Indirect boundary element method for unsteady linearized flow over prolate and oblate spheroids and hemispheroidal protuberances

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2004
    Lisa F. Shatz
    Abstract The indirect boundary element method was used to study the hydrodynamics of oscillatory viscous flow over prolate and oblate spheroids, and over hemispheroidal bodies hinged to a plate. Analytic techniques, such as spheroidal coordinates, method of images, and series representations, were used to make the numerical methods more efficient. A novel method for computing the hydrodynamic torque was used, since for oscillatory flow the torque cannot be computed directly from the weightings. Instead, a Green's function for torque was derived to compute the torque indirectly from the weightings. For full spheroids, the method was checked by comparing the results to exact solutions at low and high frequencies, and to results computed using the singularity method. For hemispheroids hinged to a plate, the method for low frequencies was checked by comparing the results to previous results, and to exact solutions at high frequencies. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Numerical method for calculation of the incompressible flow in general curvilinear co-ordinates with double staggered grid

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2003
    A. Shklyar
    Abstract A solution methodology has been developed for incompressible flow in general curvilinear co-ordinates. Two staggered grids are used to discretize the physical domain. The first grid is a MAC quadrilateral mesh with pressure arranged at the centre and the Cartesian velocity components located at the middle of the sides of the mesh. The second grid is so displaced that its corners correspond to the centre of the first grid. In the second grid the pressure is placed at the corner of the first grid. The discretized mass and momentum conservation equations are derived on a control volume. The two pressure grid functions are coupled explicitly through the boundary conditions and implicitly through the velocity of the field. The introduction of these two grid functions avoids an averaging of pressure and velocity components when calculating terms that are generated in general curvilinear co-ordinates. The SIMPLE calculation procedure is extended to the present curvilinear co-ordinates with double grids. Application of the methodology is illustrated by calculation of well-known external and internal problems: viscous flow over a circular cylinder, with Reynolds numbers ranging from 10 to 40, and lid-driven flow in a cavity with inclined walls are examined. The numerical results are in close agreement with experimental results and other numerical data. Copyright 2003 John Wiley & Sons, Ltd. [source]


    A new stable space,time formulation for two-dimensional and three-dimensional incompressible viscous flow

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2001
    Donatien N'dri
    Abstract A space,time finite element method for the incompressible Navier,Stokes equations in a bounded domain in ,d (with d=2 or 3) is presented. The method is based on the time-discontinuous Galerkin method with the use of simplex-type meshes together with the requirement that the space,time finite element discretization for the velocity and the pressure satisfy the inf,sup stability condition of Brezzi and Babu,ka. The finite element discretization for the pressure consists of piecewise linear functions, while piecewise linear functions enriched with a bubble function are used for the velocity. The stability proof and numerical results for some two-dimensional problems are presented. Copyright 2001 John Wiley & Sons, Ltd. [source]


    Numerical simulation of the unsteady flow over an elliptic cylinder at different orientations

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2001
    H. M. Badr
    Abstract A numerical method is developed for investigating the two-dimensional unsteady viscous flow over an inclined elliptic cylinder placed in a uniform stream of infinite extent. The direction of the free stream is normal to the cylinder axis and the flow field unsteadiness arises from two effects, the first is due to the flow field development following the start of the motion and the second is due to vortex shedding in the wake region. The time-dependent flow is governed by the full conservation equations of mass and momentum with no boundary layer approximations. The parameters involved are the cylinder axis ratio, Reynolds number and the angle of attack. The investigation covers a Reynolds number range up to 5000. The minor,major axis ratio of the elliptic cylinder ranges between 0.5 and 0.6, and the angle of attack ranges between 0 and 90. A series truncation method based on Fourier series is used to reduce the governing Navier,Stokes equations to two coupled infinite sets of second-order differential equations. These equations are approximated by retaining only a finite number of terms and are then solved by approximating the derivatives using central differences. The results reveal an unusual phenomenon of negative lift occurring shortly after the start of motion. Various comparisons are made with previous theoretical and experimental results, including flow visualizations, to validate the solution methodology. Copyright 2001 John Wiley & Sons, Ltd. [source]


    A three-dimensional vortex particle-in-cell method for vortex motions in the vicinity of a wall

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2001
    Chung Ho Liu
    Abstract A new vortex particle-in-cell method for the simulation of three-dimensional unsteady incompressible viscous flow is presented. The projection of the vortex strengths onto the mesh is based on volume interpolation. The convection of vorticity is treated as a Lagrangian move operation but one where the velocity of each particle is interpolated from an Eulerian mesh solution of velocity,Poisson equations. The change in vorticity due to diffusion is also computed on the Eulerian mesh and projected back to the particles. Where diffusive fluxes cause vorticity to enter a cell not already containing any particles new particles are created. The surface vorticity and the cancellation of tangential velocity at the plate are related by the Neumann conditions. The basic framework for implementation of the procedure is also introduced where the solution update comprises a sequence of two fractional steps. The method is applied to a problem where an unsteady boundary layer develops under the impact of a vortex ring and comparison is made with the experimental and numerical literature. Copyright 2001 John Wiley & Sons, Ltd. [source]


    Polymer Viscoelasticity and Residual Stress Effects on Nanoimprint Lithography,

    ADVANCED MATERIALS, Issue 10 2007
    Y. Ding
    The decay kinetics of polystyrene (PS) gratings are monitored by tracking the intensity of the first-order laser diffraction peak as a function of annealing time. For low-molecular-mass PS (24,kg,mol,1, blue circles), an exponential response suggests that the pattern decay is a surface-tension- driven viscous flow. In high-molecular-mass PS (1007,kg,mol,1, green circles) a complicated response includes a rapid elastic recovery, a power-law creep, and a viscouslike flow (see figure). [source]


    Reducing energy availability losses with open parallel microchannels embedded in a micropatterned surface

    INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2005
    G. F. Naterer
    Abstract This article develops a new technique of reducing exergy losses of external viscous flow over surfaces, based on optimized microchannels embedded within the surface. The rate of entropy production and loss of available optimized energy are formulated by an integral solution and modified Blasius profiles of boundary layer flow. The optimized number of microchannels, width and height of each microchannel and spacing between microchannels involve a selective compromise between added heat exchange due to surface area, together with reduced friction through slip conditions within each microchannel. Mixed Knudsen numbers across each microchannel require simultaneous modelling of both slip-flow and no-slip conditions at the wall. Results involving the minimal entropy production and optimized microchannel profiles are presented and compared to other benchmark results involving classical macro-scale configurations. Copyright 2005 John Wiley & Sons, Ltd. [source]


    Plastic energy dissipation and its role on heating/melting of single-component polymers and multi-component polymer blends

    ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2003
    Bainian Qian
    Abstract Plastic energy dissipation (PED) of polymer particulates is, essentially, the energy dissipated during large and repeated plastic deformations of compacted polymer particulates while still in the solid state. PED is higher or much higher than VED, the viscous energy dissipation source of polymeric melts, because the stresses necessary to plastically deform viscoelastic polymer solids are orders of magnitude higher than the stresses needed to support viscous flow. In the last few years our group has demonstrated experimentally the dominant role which PED plays in the heating/melting of solid polymer (compacted) particulate beds in compounding processing equipment, such as twin-screw extruders and counterrotating continuous mixers/melters, in which the deformation of solid polymers is mandatory. We have also developed simple empirical methods of predicting the total axial distance needed for melting a given polymer in specific processing/compounding machines and processing. conditions, as well as the melting rates, all based on the mechanical energy dissipated during solid particulate compression. This work explores the more complex issue of how the PED behavior of single-component polymers may affect the PED (and the heating/melting) behavior of multi-component polymer blends. 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 85,95, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10039 [source]


    Competitive plasticization in ternary plasticized starch biopolymer system

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010
    Deeptangshu S. Chaudhary
    Abstract Two plasticizers namely, glycerol and xylitol, based on their similar molecular diameter (, 6.3 ) but different molecular weights (glycerol-92; xylitol-152) were selected were selected for studying the plasticization of starch biopolymer containing 70% amylopectin structure via glass transition measurements carried over a wide range of water activity. A standard calorimetry was used to determine the onset temperature of polymeric viscous flow. For both glycerol and xylitol, typical antiplasticization was evident at low plasticizer concentrations, whereas at higher concentration, there was significant reduction in glass transition temperature. Water activity isotherms showed that equilibrium moisture content of the starch biopolymer (no plasticizer) steadily increases up to 11%, however, for plasticized biopolymer, the moisture content was nearly double than that of biopolymer. We used a modified Gordon-Taylor model, using a new interaction parameter, to understand the competitive plasticization of glycerol and xylitol in presence of water, and determined 8 wt % water as a threshold amount of matrix water for strong three-way interactions: starch-plasticizer, plasticizer-plasticizer/water and starch-water. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]


    Analysis of multicomponent adsorption kinetics on activated carbon

    AICHE JOURNAL, Issue 4 2003
    L. P. Ding
    An integrated mathematical model for the kinetics of multicomponent adsorption on microporous carbon was developed. Transport in this bidisperse solid is represented by balance equations in the macropore and micropore phases, in which gas-phase diffusion dominates the mass transfer in the macropores, with the phenomenological diffusivities represented by the generalized Maxwell,Stefan (GMS) formulation. Viscous flow also contributes to the macropore fluxes and is included in the MS expressions. Diffusion of the adsorbed phase controls the mass transfer in the micropore phase, which is also described in a similar way by the MS method. The adsorption isotherms are represented by a new heterogeneous modified vacancy solution theory formulation of adsorption, which has proved to be a robust method for adsorption on activated carbons. The model is applied to the coadsorption and codesorption of C2H6 and C3H8 on Ajax and Norit carbon, as well as the displacement on Ajax carbon. The effect of the viscous flow in the macropore phase is not significant for the cases studied. The model accurately predicts the overshoot behavior and rollup of C2H6 during coadsorption. The prediction for the heavier compound C3H8 is always satisfactory, though at higher C3H8 mole fraction, the overshoot extent of C2H6 is overpredicted, possibly due to neglect of heat effects. [source]


    RHEOLOGICAL BEHAVIOUR OF CLARIFIED MANGO JUICE CONCENTRATES

    JOURNAL OF TEXTURE STUDIES, Issue 3 2000
    NGASEPPAM IBOYAIMA SINGH
    ABSTRACT The rheological behaviour of clarified mango juice was measured at temperatures 15,85C and concentrations 15,66 Brix, using a rotoviscometer. Mango juice free of pectin and pulp behaves as a Newtonian fluid. The effect of temperature can be described by an Arrhenius-type equation. The activation energy for viscous flow was in the range of 1.64,8.44 kcal/g-mol, depending on the concentration. The effect of concentration was modelled better by an exponential relationship than a power-law relationship. Simple equations are proposed for describing the combined effect of temperature and soluble solids content on the juice viscosity. [source]


    Particle Rearrangement and Pore Space Coarsening During Solid-State Sintering

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2009
    Hans Eckart Exner
    Coarsening of porosity during sintering has been observed in powder compacts of metallic, ceramic, and amorphous materials. Monitoring and modelling of the growth of individual (closed) pores in the late sintering stages are well established. Porosity is interconnected up to very high densities. Coarsening of the continuous pore space takes place during the initial and intermediate sintering stages. This coarsening is caused by localized transport of atoms or molecules (diffusion or viscous flow) as well as by bulk particle movement (rearrangement). Its quantitative exploration poses problems both experimentally and theoretically. Ways to characterize the geometry of the interconnected pore space and of closed pores are discussed with emphasis on stereological parameters. Recent and classical approaches, experimental findings with 2D model arrangements (as the formation and opening up of particle contacts, pore coarsening, and particle rearrangement) and some advances of computer simulations are discussed together with open questions. [source]


    Joining of Calcium Phosphate Invert Glass-Ceramics on a ,-Type Titanium Alloy

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2003
    Toshihiro Kasuga
    A bioactive calcium phosphate invert glass-ceramic containing ,-Ca3(PO4)2 crystals could be joined strongly with a Ti,29Nb,13Ta,4.6Zr alloy consisting of a ,-titanium phase by heating the metal on which the mother glass powders with a composition 60CaO30P2O57Na2O3TiO2 (mol%) were placed, at 800C for 1 h in air; the tensile joining strength was estimated to be ,26 MPa on average. A compositionally gradient layer was developed on the metallic substrate during the heating. When the metal with glass powders on it was heated at 850C in air, the phosphate glassy phase flowed viscously, permeating the oxide layer formed around the surface of the metal, which was thicker than that formed by heating at 800C; a compositionally gradient layer was not developed, and a strong joining was not realized. The joining between the glass-ceramic and the metal is suggested to be controlled by viscous flow of the glassy phase in the glass-ceramic and by reaction of the glassy phase with the oxide phase formed around the surface layer of the metal. [source]


    Properties of Nitrogen-Containing Yttria,Alumina,Silica Melts and Glasses

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003
    Noritaka Saito
    The viscosity and solubility of nitrogen in Y2O3,Al2O3,SiO2 melts have been systematically examined. The effects of nitrogen content on viscosity for Y-Al-Si-O-N melts and on Vickers hardness of oxynitride glasses also have been examined. Although the viscosity of Y2O3,Al2O3,SiO2 melts was decreased, the solubility of nitrogen into the melts was increased with increased Y2O3 content. These results indicated that the yttrium ion behaved as a network modifier. Therefore, the structural units for viscous flow became small, and the amount of nonbridging oxygen increased in the melts when the Y2O3 content increased. The viscosity of Y-Al-Si-O-N melts and Vickers hardness of oxynitride glasses remarkably increased with increased nitrogen content. These results suggested that the substitution of nitrogen for oxygen in the melts may have led to a high average coordination of nonmetal atoms and that the increased cross-linking produced a more rigid glass network. [source]


    Decoupling between Enthalpy Relaxation and Viscous Flow and Its Structural Origin in Fragile Oxide Glass-Forming Liquids

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2002
    Takayuki Komatsu
    The structural relaxation kinetics at the glass transition in tellurium oxide (TeO2)-based glasses has been examined from viscosity and heat-capacity measurements to clarify the features of the structural relaxation in fragile oxide glass-forming liquids. A large decoupling between enthalpy relaxation and viscous flow, i.e., a large discrepancy between the activation energies for the enthalpy relaxation (recovery), ,H, and viscous flow, E,, has been demonstrated in TeO2 -based glasses. The values in xK2OxMgO(100 , 2x)TeO2 glasses, for example, are ,919,1051 kJ/mol for ,H and , 577,701 kJ/mol for E,, given the ratio of ,H/E,, 1.44,1.59. Some viscosity and heat-capacity data (all data have been reported previously) obtained from similar experiments in Sb2O3,B2O3 glasses belonging to the category of strong glass-forming liquids have been reanalyzed in this paper for comparison; a strong coupling was found to exist between ,H and E,, i.e., ,H/E,, 0.98,1.18. An origin of decoupling between ,H and E, in fragile glass-forming systems such as TeO2 -based glasses has been discussed by considering the glass structure model for fragile glasses; strongly bonded correlated (highly constrained) regions are surrounded or connected by weakly bonded noncorrelated (unconstrained) parts. [source]