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1.
E. Lorenceau N. Louvet F. Rouyer O. Pitois 《The European physical journal. E, Soft matter》2009,28(3):293-304
We perform forced-drainage experiments in aqueous foams and compare the results with data available in the literature. We
show that all the data can be accurately compared together if the dimensionless permeability of the foam is plotted as a function
of liquid fraction. Using this set of coordinates highlights the fact that a large part of the published experimental results
corresponds to relatively wet foams ( ∼ 0.1 . Yet, most of the foam drainage models are based on geometrical considerations only valid for dry foams. We therefore
discuss the range of validity of the different models in the literature and their comparison to experimental data. We propose
extensions of these models considering the geometry of foam in the relatively wet-foam limit. We eventually show that if the
foam geometry is correctly described, forced drainage experiments can be understood using a unique parameter --the Boussinesq
number. 相似文献
2.
Although extensively studied in the past, drainage of aqueous foams still offers major unaddressed issues. Among them, the
behaviour of foam films during drainage has great significance as the thickness of the films is known to control the Ostwald
ripening in foams, which in turn impacts liquid drainage. We propose a model relating the films’ behavior to the liquid flow
in foam channels. It is assumed that Marangoni-driven recirculation counterflows take place in the transitional region between
the foam channel and the adjoining films, and the Gibbs elasticity is therefore introduced as a relevant parameter. The velocity
of these counterflows is found to be proportional to the liquid velocity in the channel. The resulting channel permeability
is determined and it is shown that Marangoni stresses do not contribute to rigidify the channel’s surfaces, in strong contrast
with the drainage of horizontal thin liquid films. New experimental data are provided and support the proposed model. 相似文献
3.
The foam/emulsion analogy in structure and drainage 总被引:1,自引:0,他引:1
Hutzler S Péron N Weaire D Drenckhan W 《The European physical journal. E, Soft matter》2004,14(4):381-386
The often quoted analogy between foams and emulsions is experimentally tested by studying properties after settling and under forced drainage of oil-in-water emulsions of drop size similar as for bubbles generally used in foam experiments. Observations with regard to structure, water fraction and drainage wave properties confirm the expected similarity in the low flow rate range. However, while for foams a convective circulation on the scale of the container sets in for values of water fraction exceeding about 0.2, no such convection is found in emulsions. Here instabilities are only encountered at water fractions of about 0.4, close to the void fraction of random packings of spheres. These take on the form of descending pulses of increased water fraction and lead to the transition from a frozen to a locally agitated structure.Received: 12 December 2003, Published online: 24 August 2004PACS:
82.70.-y Disperse systems; complex fluids - 47.20.-k Hydrodynamic stability - 47.55.Dz Drops and bubbles 相似文献
4.
A. Saint-Jalmes M.U. Vera D.J. Durian 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):67-73
An apparatus is described for rapidly producing large quantities of foam via turbulent mixing of gas with a narrow jet of a surfactant solution inside a delivery tube. By controlling relative flow rates,
the gas volume fraction in the resulting foam may be easily varied across . Using such foams, we present a comprehensive set of data for free drainage as a systematic function of gas fraction and
sample geometry. The qualitative behavior can be understood in terms of simple theoretical considerations, emphasizing the
importance of controlling the initial foam conditions. Quantitative features are compared with two approximate versions of
the drainage equation, highlighting the crucial role of capillarity for very dry foams and small samples.
Received 15 February 1999 相似文献
5.
Physicochemical approach to the theory of foam drainage 总被引:1,自引:0,他引:1
We have investigated theoretically the effect of surface viscoelasticity on the drainage of an aqueous foam. Former theories
consider that the flow in Plateau borders is either Poiseuille flow or plug-flow. In the last case, the dissipation is attributed
to flow in the nodes connecting Plateau borders. Although we do not include this dissipation in our model, we obtain a drainage
equation that includes terms equivalent to those of the earlier models. We show that when the water solubility of the surfactant
stabilizing the foam is low, the control parameter M for the transition between the two regimes is the ratio , where μ is the bulk viscosity, D
s the surface diffusion coefficient, R the radius of curvature of the Plateau border and ɛ the surface elasticity. When the surfactant is more soluble M is rather related to the bulk diffusion coefficient. Within the frame of this approach and in view of the estimated M values, we show that the flow in Plateau borders is Poiseuille-like.
Received 26 June 2001 相似文献
6.
We analyze the flow of a liquid foam between two plates separated by a gap of the order of the bubble size (2D foam). We concentrate
on the salient features of the flow that are induced by the presence, in an otherwise monodisperse foam, of a single large
bubble whose size is one order of magnitude larger than the average size. We describe a model suited for numerical simulations
of flows of 2D foams made up of a large number of bubbles. The numerical results are successfully compared to analytical predictions
based on scaling arguments and on continuum medium approximations. When the foam is pushed inside the cell at a controlled
rate, two basically different regimes occur: a plug flow is observed at low flux whereas, above a threshold, the large bubble
migrates faster than the mean flow. The detailed characterization of the relative velocity of the large bubble is the essential
aim of the present paper. The relative velocity values, predicted both from numerical and from analytical calculations that
are discussed here in great detail, are found to be in fair agreement with experimental results from the preprint Experimental evidence of flow destabilization in a 2D bidisperse foam by the present authors (2005). 相似文献
7.
J.-P. Raven P. Marmottant F. Graner 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(1):137-143
We present an experimental investigation of the agglomeration of
microbubbles into a 2D microfoam and its flow in a rectangular microchannel. Using a
flow-focusing method, we produce the foam in situ on a
microfluidic chip for a large range of liquid fractions, down to a few percent in liquid.
We can monitor the transition from separated bubbles to the desired
microfoam, in which bubbles are closely packed and separated by thin films.
We find that bubble formation frequency is limited by the liquid flow rate, whatever the gas pressure. The formation frequency
creates a modulation of the foam flow, rapidly damped along the channel. The average foam flow rate depends non-linearly on
the applied gas pressure,
displaying a threshold pressure due to capillarity.
Strong discontinuities in the flow rate appear when the number of bubbles in the channel width changes, reflecting the discrete
nature of the foam topology.
We also produce an ultra flat foam, reducing the channel height from 250 μm to 8 μm, resulting in a height to diameter ratio
of 0.02; we notice a marked change in bubble shape during the flow. 相似文献
8.
Denkov ND Tcholakova S Golemanov K Ananthapadmanabhan KP Lips A 《Physical review letters》2008,100(13):138301
We present a model for the viscous friction in foams and concentrated emulsions, subject to steady shear flow. First, we calculate the energy dissipated due to viscous friction inside the films between two neighboring bubbles or drops, which slide along each other in the flow. Next, from this energy we calculate the macroscopic viscous stress of the sheared foam or emulsion. The model predictions agree well with experimental results obtained with foams and emulsions. 相似文献
9.
P. Grassia J.J. Cilliers S.J. Neethling E. Ventura-Medina 《The European physical journal. E, Soft matter》2001,6(4):325-348
Foam drainage is considered in a froth flotation cell. Air flow through the foam is described by a simple two-dimensional
deceleration flow, modelling the foam spilling over a weir. Foam microstructure is given in terms of the number of channels
(Plateau borders) per unit area, which scales as the inverse square of bubble size. The Plateau border number density decreases
with height in the foam, and also decreases horizontally as the weir is approached. Foam drainage equations, applicable in
the dry foam limit, are described. These can be used to determine the average cross-sectional area of a Plateau border, denoted
A, as a function of position in the foam. Quasi-one-dimensional solutions are available in which A only varies vertically, in spite of the two-dimensional nature of the air flow and Plateau border number density fields.
For such situations the liquid drainage relative to the air flow is purely vertical. The parametric behaviour of the system
is investigated with respect to a number of dimensionless parameters: K (the strength of capillary suction relative to gravity), α (the deceleration of the air flow), and n and h (respectively, the horizontal and vertical variations of the Plateau border number density). The parameter K is small, implying the existence of boundary layer solutions: capillary suction is negligible except in thin layers near
the bottom boundary. The boundary layer thickness (when converted back to dimensional variables) is independent of the height
of the foam. The deceleration parameter α affects the Plateau border area on the top boundary: weaker decelerations give larger
Plateau border areas at the surface. For weak decelerations, there is rapid convergence of the boundary layer solutions at
the bottom onto ones with negligible capillary suction higher up. For strong decelerations, two branches of solutions for
A are possible in the K = 0 limit: one is smooth, and the other has a distinct kink. The full system, with small but non-zero capillary suction,
lies relatively close to the kinked solution branch, but convergence from the lower boundary layer onto this branch is distinctly
slow. Variations in the Plateau border number density (non-zero n and h) increase individual Plateau border areas relative to the case of uniformly sized bubbles. For strong decelerations and negligible
capillarity, solutions closely follow the kinked solution branch if bubble sizes are only slightly non-uniform. As the extent
of non-uniformity increases, the Plateau border area reaches a maximum corresponding to no net upward velocity of foam liquid.
In the case of vertical variation of number density, liquid content profiles and Plateau border area profiles cease to be
simply proportional to one another. Plateau border areas match at the top of the foam independent of h, implying a considerable difference in liquid content for foams which exhibit different number density profiles.
Received 3 July 2001 相似文献
10.
G. Guéna J. Corde S. Fouilloux J. -B. d’Espinose F. Lequeux L. Talini 《The European physical journal. E, Soft matter》2009,28(4):463-468
The present work deals with emulsions of volatile alkanes in an aqueous clay suspension, Laponite, which forms a yield stress
fluid. For a large enough yield stress (i.e. Laponite concentration), the oil droplets are prevented from creaming and the emulsions are thus mechanically stabilized.
We have studied the evaporation kinetics of the oil phase of those emulsions in contact with the atmosphere. We show that
the evaporation process is characterized by the formation of a sharp front separating the emulsion from a droplet-free Laponite
phase, and that the displacement of the front vs. time follows a diffusion law. Experimental data are confronted to a diffusion-controlled model, in the case where the limiting
step is the diffusion of the dissolved oil through the aqueous phase. The nature of the alkane, as well as its volume fraction
in the emulsion, has been varied. Quantitative agreement with the model is achieved without any adjustable parameter and we
describe the mechanism leading to the formation of a front. 相似文献
11.
P. Poulin J. Bibette D.A. Weitz 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):277-281
Aggregation mechanisms of emulsions at high initial volume fractions () is studied using light scattering. We use emulsion droplets which can be made unstable towards aggregation by a temperature
quench. For deep quenches and , the aggregation mechanism is identified as diffusion-limited cluster aggregation (DLCA). An ordering of the clusters, which
is reflected by a peak in the scattering intensity, is shown to result from the intercluster separation, exhibiting different
scaling than that observed at lower volume fractions. This manifests an increasing similarity to spinodal decomposition observed
as is increased. For and shallow quenches, different mechanisms, closer to spinodal decomposition, are observed. These results allow the subtle
boundaries between DLCA and spinodal decomposition to be explored.
Received: 7 April 1998 / Revised: 19 August 1998 / Accepted: 21 August 1998 相似文献
12.
Saint-Jalmes A Marze S Ritacco H Langevin D Bail S Dubail J Guingot L Roux G Sung P Tosini L 《Physical review letters》2007,98(5):058303
We report the results of fluid transport experiments in aqueous foams under microgravity. Using optical and electrical methods, the capillary motion of the foam fluid and the local liquid fractions are monitored. We show that foams can be continuously wetted up to high liquid fractions ( approximately 0.3), without any bubble motion instabilities. Data are compared to drainage models: For liquid fractions above 0.2, discrepancies are found and identified. These new results on foam hydrodynamics and structure can be useful for other poroelastic materials, such as plants and biological tissues. 相似文献
13.
P. Frick S. Khripchenko S. Denisov D. Sokoloff J.-F. Pinton 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):399-402
A fully developed turbulent flow is capable to mix and homogenize a suspension of heavy macroscopic particles even at a high
concentration of particles. If the particles are ferromagnetic, a kind of “turbulent ferrofluid" can be obtained. In the present
work, we present a direct measurements of the effective magnetic permeability in a turbulent fluid with suspended ferromagnetic
particles of typical size 0.01-0.1 mm and volume fraction c up to 25%. We show that the effective permeability can be fitted by the linear law = 1 + 5.3c for c? 10%. For higher volume fractions the permeability exceeds this linear relation.
Received 11 January 2002 相似文献
14.
15.
A new finite volume-based numerical algorithm for predicting incompressible and compressible multi-phase flow phenomena is presented. The technique is equally applicable in the subsonic, transonic, and supersonic regimes. The method is formulated on a non-orthogonal coordinate system in collocated primitive variables. Pressure is selected as a dependent variable in preference to density because changes in pressure are significant at all speeds as opposed to variations in density, which become very small at low Mach numbers. The pressure equation is derived from overall mass conservation. The performance of the new method is assessed by solving the following two-dimensional two-phase flow problems: (i) incompressible turbulent bubbly flow in a pipe, (ii) incompressible turbulent air–particle flow in a pipe, (iii) compressible dilute gas–solid flow over a flat plate, and (iv) compressible dusty flow in a converging diverging nozzle. Predictions are shown to be in excellent agreement with published numerical and/or experimental data. 相似文献
16.
The results of an experimental investigation of staggered tube bundle heat transfer to upward and downward moving vertical foam flow are presented in this article. It was determined that a dependency exists between tube bundle heat transfer intensity on foam volumetric void fraction, foam flow velocity and direction, and liquid drainage from foam. In addition to this, the influence of tube position of the bundle on heat transfer was investigated. Experimental results were summarized by criterion equations, which can be applied in the design of foam type heat exchangers. 相似文献
17.
H. Caps H. Decauwer M.-L. Chevalier G. Soyez M. Ausloos N. Vandewalle 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):115-119
We report an experimental study of aqueous foam imbibition in microgravity with strict mass conservation. The foam is in a
Hele-Shaw cell. The bubble edge width ℓ is measured by image analysis. The penetration of the liquid in the foam, the foam
imbibition, the foam inflation, and the rigidity loss are shown all to obey strict diffusion processes. The motion of bubbles
needed for the foam inflation is a slow two-dimensional process with respect to the one-dimensional capillary rise of liquid.
The foam is found to imbibes faster than it inflates.
Received 20 May 2002 / Received in final form 21 January 2003 Published online 23 May 2003
RID="a"
ID="a"e-mail: herve.caps@ulg.ac.be 相似文献
18.
Bénito S Bruneau CH Colin T Gay C Molino F 《The European physical journal. E, Soft matter》2008,25(3):225-251
A variety of complex fluids consists in soft, round objects (foams, emulsions, assemblies of copolymer micelles or of multilamellar
vesicles--also known as onions). Their dense packing induces a slight deviation from their prefered circular or spherical
shape. As a frustrated assembly of interacting bodies, such a material evolves from one conformation to another through a
succession of discrete, topological events driven by finite external forces. As a result, the material exhibits a finite yield
threshold. The individual objects usually evolve spontaneously (colloidal diffusion, object coalescence, molecular diffusion),
and the material properties under low or vanishing stress may alter with time, a phenomenon known as aging. We neglect such
effects to address the simpler behaviour of (uncommon) immortal fluids: we construct a minimal, fully tensorial, rheological
model, equivalent to the (scalar) Bingham model. Importantly, the model consistently describes the ability of such soft materials
to deform substantially in the elastic regime (be it compressible or not) before they undergo (incompressible) plastic creep--or
viscous flow under even higher stresses. 相似文献
19.
Raufaste C Dollet B Cox S Jiang Y Graner F 《The European physical journal. E, Soft matter》2007,23(2):217-228
We study the two-dimensional flow of foams around a
circular obstacle within a long channel. In experiments, we
confine the foam between liquid and glass surfaces. In
simulations, we use a deterministic software, the Surface
Evolver, for bubble details and a stochastic one, the extended
Potts model, for statistics. We adopt a coherent definition of
liquid fraction for all studied systems. We vary it in both
experiments and simulations, and determine the yield drag of the
foam, that is, the force exerted on the obstacle by the foam
flowing at very low velocity. We find that the yield drag is
linear over a large range of the ratio of obstacle to bubble
size, and is independent of the channel width over a large range.
Decreasing the liquid fraction, however, strongly increases the
yield drag; we discuss and interpret this dependence. 相似文献
20.
Mader MA Vitkova V Abkarian M Viallat A Podgorski T 《The European physical journal. E, Soft matter》2006,19(4):389-397
The dynamics of giant lipid vesicles under shear flow is experimentally investigated. Consistent with previous theoretical
and numerical studies, two flow regimes are identified depending on the viscosity ratio between the interior and the exterior
of the vesicle, and its reduced volume or excess surface. At low viscosity ratios, a tank-treading motion of the membrane
takes place, the vesicle assuming a constant orientation with respect to the flow direction. At higher viscosity ratios, a
tumbling motion is observed in which the whole vesicle rotates with a periodically modulated velocity. When the shear rate
increases, this tumbling motion becomes increasingly sensitive to vesicle deformation due to the elongational component of
the flow and significant deviations from simpler models are observed. A good characterization of these various flow regimes
is essential for the validation of analytical and numerical models, and to relate microscopic dynamics to macroscopic rheology
of suspensions of deformable particles, such as blood. 相似文献