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  • 1
    Electronic Resource
    Electronic Resource
    Numerical solutions for the deformation of a bubble rising in dilute polymeric fluids (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1315-1332 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The steady-state deformation of a bubble rising in polymeric liquid has been investigated using a general numerical technique for the solution of free-boundary problems in non-Newtonian fluid mechanics. The technique is based on a finite-difference solution of the governing equations on an orthogonal curvilinear coordinate system, which is constructed numerically and adjusted to fit the boundary shape exactly at any time. The problem was analyzed based on the constitutive equation proposed by Chilcott and Rallison [J. Non-Newtonian Fluid Mech. 29, 381 (1988)], which models a dilute polymer solution as a suspension of dumbbells with finite extensibility. Computations were carried out to investigate the effect of conformation change of polymer chains on the bubble deformation for various values of the Deborah number, maximum chain extensibility (i.e., roughly proportional to molecular weight), capillary number, and the Reynolds number. Numerical results show good agreement with existing experimental findings reported elsewhere. Especially, the tendency of transition from a prolate shape to a cusped shape has been observed in the creeping flow limit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858568
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  • 2
    Electronic Resource
    Electronic Resource
    Strong flows of dilute suspensions of microstructure (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1438-1438 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We consider dilute suspensions that have a microstructure that may be characterized by an axial state vector. Examples include axisymmetric particles, line elements of the fluid itself, or, as an approximation, droplets of fluid or polymer molecules. Past studies, in which sufficient conditions for stretch or coherent orientation of the microstructure are obtained for steady flows with homogeneous velocity gradient tensors are shown not to apply to the general situation. Instead, a careful analysis of the microdynamical equations reveals that stretching and orientation of the microstructure by the flow must be analyzed over a time interval. Using techniques from the theory of dynamical systems, a quantitative measure is developed to determine orientations and/or stretched lengths of the microstructure, that are robust and attractive to nearby states. This leads to a strong flow criterion for unsteady flows with inhomogeneous velocity gradient tensors in which the effects of history dependence are apparent.A particular model system is treated in the case of general two-dimensional flow. The sensitivity of the results to changes in the modeling assumptions is investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858026
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  • 3
    Electronic Resource
    Electronic Resource
    The onset of chaotic oscillations and rapid growth of a spherical bubble at subcritical conditions in an incompressible liquid (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 551-555 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recently developed techniques of Wiggins [SIAM J. Appl. Math. 48, 262 (1988)] are used to study the onset of chaotic oscillations and explosive growth of a spherical bubble in an otherwise quiescent, incompressible fluid. It is shown that bubbles forced with a quasiperiodic background pressure can respond chaotically and grow explosively at lower amplitudes of the primary component of the forcing than bubbles forced with a single frequency. The means of extension of these results to an arbitrary, but finite, number of forcing frequencies is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858116
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  • 4
    Electronic Resource
    Electronic Resource
    Time-resolved velocity gradient and optical anisotropy in linear flow by photon correlation spectroscopy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 3519-3534 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A time-resolved dynamic light scattering technique is presented for measuring the velocity gradient in transient but repeatable flows. The experimental technique is verified via measurements for a Newtonian fluid undergoing a known time-dependent flow. The method is then applied to the creeping flow of a Newtonian fluid in a corotating two-roll mill. It is demonstrated that the flow near the stagnation point can be accurately described by an analytical creeping flow solution for a two-roll mill in an unbounded fluid. The time dependence of the velocity gradient for a concentrated polymer solution in the startup of the two-roll mill has also been measured, it is believed, for the first time. The measurement provides direct evidence of the modification of the flow for the viscoelastic polymer liquid, and will ultimately lead to significant insights into the polymer dynamics for concentrated solutions in strong, extension-like flows. A second significant feature of the dynamic light scattering experiment is that the initial magnitude of the correlation function is related to the degree of optical anisotropy of the polymer molecules, i.e., to the geometric configuration of the polymer chains. Thus, it yields information on the time-dependent degree of polymer orientation and stretch that is equivalent to birefringence, but is obtained at the "point'' occupied by the scattering volume rather than as a two-dimensional average across the whole fluid as in birefringence. This measurement of polymer configuration is compared with birefringence data for the exact same flow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868411
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  • 5
    Electronic Resource
    Electronic Resource
    An experimental study of drop deformation and breakup in extensional flow at high capillary number (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 1568-1576 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An experimental study is reported of the flow-induced stretching of drops in a four-roll mill at low Reynolds number, but for capillary numbers that are large compared to the critical capillary number for onset of stretching. We mainly consider Newtonian drops in a Newtonian suspending fluid, but also present a brief study of Newtonian drops in a viscoelastic (Boger fluid) suspending fluid. The stability of the drops following cessation of flow is determined, in either case, by the ratio of their extended length to the undeformed radius. If this ratio is large enough, the drops will break into two or more parts via the capillary flow process known as end-pinching. However, for Newtonian drops in a Newtonian suspending fluid, it is shown that the critical degree of stretch for breakup increases sharply with increase of the capillary number that characterizes the stretching process. Furthermore, it is shown, in this case, that the critical stretch ratio is not unique, but that there can be a discrete range of stretch ratios above the first (or smallest) critical value where the drop is again stable before it encounters a second larger "critical" stretch ratio. This "restabilization" is associated with the transition from two to three drops in the breakup process. Newtonian drops in the viscoelastic Boger fluid are found to be slightly more stable than the same drops in a Newtonian fluid when stretched at strain rates just exceeding the critical value. By this we mean that the critical elongation ratio necessary for the drops to break upon cessation of flow is increased by about 20%. When stretched at a higher strain rate, approximately 2.15 times the critical value, large drops in the viscoelastic fluid (above 100 microns in radius for this particular suspending fluid) are destabilized relative to their counterpart in a Newtonian suspending fluid, while smaller drops are strongly stabilized. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1358306
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  • 6
    Electronic Resource
    Electronic Resource
    Experimental trajectories of two drops in planar extensional flow (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 971-981 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we map the experimental trajectories of two deformable drops in planar extensional flow and compare the experimental results with theoretical calculations for spherical drops. We examine the effects that deformation, initial position, and viscosity ratio have on the interaction of two drops and the necessity of incorporating deformation into trajectory calculations, which can be used to estimate the collision rates, the collision efficiencies, and the collision interaction times. For drops which do not come into close contact, the existing theoretical calculations for spherical drops accurately predict the symmetric trajectories and capture the increased hydrodynamic interaction for higher viscosity ratios. For drops which come into close contact, the spherical drop theory accurately predicts the approach and exit trajectories and with a slight empirical modification adequately predicts the interaction times for deformable drops with a Taylor deformation parameter up to 0.22. The experimental results show that for drops with close contact, the collision trajectories are asymmetric and irreversible with a minimum separation between the centers of mass that is less than the minimum separation of two spheres. This minimum separation corresponds to the minor axis of the deformed drop and is not captured by the spherical theory. However, overall, the modified trajectory theory based upon the hydrodynamic mobility for spherical drops does provide a reasonable estimate for the trajectories and the interaction times for two deformable drops in planar extensional flow. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869969
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  • 7
    Electronic Resource
    Electronic Resource
    Flow-aligning and tumbling in small-molecule liquid crystals: pure components and mixtures (1999)
    Springer
    Rheologica acta 38 (1999), S. 183-197 
    Details
    ISSN: 1435-1528
    Keywords: Key words Liquid crystal ; Conoscopy ; Flow-aligning ; Tumbling ; Mixtures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract  The results of an experimental study to measure the tumbling parameter, λ, for various small-molecule liquid crystals and their mixtures are presented. The methods used include textural observations (twist walls), a direct method, a rheological method, and the oscillatory method developed by Mather, Pearson, and Burghardt in 1995. The single-component results are compared with a molecular theory derived in 1995 by Archer and Larson as well as Kröger and Sellers, which predicts the temperature dependence of λ, while the results from the binary mixtures are compared to a continuum theory derived by Rey in 1996, giving the concentration dependence of λ. The results from the four experimental methods agree with each other for single-component liquid crystals, but not for mixtures. This suggests a failure of the single director Leslie-Ericksen theory to describe the rheology of liquid crystal mixtures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003970050168
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  • 8
    Electronic Resource
    Electronic Resource
    Interfacial resistance to interphase mass transfer in quiescent two-phase systems (1978)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 24 (1978), S. 246-254 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Interfacial resistance to solute mass transfer between two unstirred immiscible fluids is theoretically calculated. Solute molecules are modeled as Brownian particles, bathed by homogeneous fluid continua when wholly immersed in either fluid, or else by heterogeneous fluid continua when instantaneously straddling the interface. These diffusing particles are assumed to be subjected to either repulsive or attractive conservative forces exerted on them by the interface. Additionally, their mobility is supposed affected by proximity to the interface. Circumstances are found to exist under which the interface may offer significant resistance to interphase transport. Surprisingly, conditions also exist in which the interface may actually offer a negative resistance to such solute transfer. In such cases, the presence of the interface enhances the overall interphase mass transfer rate.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690240213
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  • 9
    Electronic Resource
    Electronic Resource
    Flow birefringence studies of a concentrated polystyrene solution in a two-roll mill. I. Steady flow and start-up of steady flow (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 30 (1992), S. 1329-1349 
    Details
    ISSN: 0887-6266
    Keywords: flow birefringence of concentrated polystyrene solution in two-roll mill ; polystyrene, flow birefringence of concentrated solution in shear flow ; melt rheology and birefringence of concentrated polystyrene solution ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We have studied a 4.8 volume percent solution of a narrow distribution polystyrene with molecular weight 3.84 × 106 in flows generated by a co-rotating two-roll mill. These flows have a stagnation point at the midpoint between the roller axes. Further, they are linear, two-dimensional, and the magnitudes of the strain-rates are greater than the vorticity. The overall objective of our studies is to explore the dynamics of concentrated polymer solutions which are in the highly deformed state that is generated in the two-roll mill. Birefringence data are presented for both steady flow and start-up of steady flow in the two-roll mill. The steady and transient data are used to analyze the linear and nonlinear viscoelastic regions of material behavior. In the nonlinear regime, the birefringence upon start-up shows an initial overshoot followed by a strong undershoot that is enhanced as the ratio of elongation to rotation is increased (i.e., the flow becomes increasingly extensional in character.) We attribute this undershoot, which does not seem to appear in simple shear flows, or flows close to simple shear flow, to polymer segment stretching following an initial period of segment reorientation. Model studies are currently underway to test this notion. © 1992 John Wiley & Sons, Inc.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1992.090301204
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  • 10
    Electronic Resource
    Electronic Resource
    The response of entangled polymer solutions to step changes of shear rate: Signatures of segmental stretch? (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 265-280 
    Details
    ISSN: 0887-6266
    Keywords: entangled polymer solution ; double-step strain rate ; flow birefringence ; tube model ; segmental stretch ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Experiments measuring the orientation angle and birefringence in startup and double-step strain rate flows were conducted on a 3.0 wt % 8.42 × 106 molecular weight polystyrene solution in a Couette flow cell. A phase-modulated flow birefringence apparatus was used to noninvasively probe the sample. Upon startup from rest, the orientation angle undershoots its final steady-state value, as seen by earlier investigators. When the shear rate undergoes a step increase from one nonzero value to another, the amplitude of this undershoot is decreased. However, a more significant effect is a shorter time scale overshoot in the orientation angle that is highly counterintuitive in the sense that an increase of shear rate initially produces a rotation of chain segments away from the flow direction. Similarly, a step decrease in shear rate yields an initial transient rotation toward the flow direction. In both cases, the height of the peaks depends upon the magnitude of the shear rate jump, and the width of the peaks is a function of the final shear rate. The longer time transients in the startup and step increase experiments reflect an apparent change in the relaxation time for segment orientation, which we tentatively attribute to a combination of tube dilation and convective constraint release. The shorter time scale over- and undershoots in the orientation angle appear to be qualitatively explained by considering the differences in extension or contraction of segments along the polymer chain. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 265-280, 1998
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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