共查询到20条相似文献,搜索用时 15 毫秒
1.
The resonant modes of sessile water drops on a hydrophobic substrate subjected to a small-amplitude lateral vibration are
investigated using computational fluid dynamic (CFD) modeling. As the substrate is vibrated laterally, its momentum diffuses
within the Stokes layer of the drop. Above the Stokes layer, the competition between the inertial and Laplace forces causes
the formation of capillary waves on the surface of the drop. In the first part of this paper, the resonant states of water
drops are illustrated by investigating the velocity profile and the hydrostatic force using a 3d simulation of the Navier-Stokes
equation. The simulation also allows an estimation of the contact angle variation on both sides of the drop. In the second
part of the paper, we investigate the effect of vibration on a water drop in contact with a vertical plate. Here, as the plate
vibrates parallel to gravity, the contact line oscillates. Each oscillation is, however, rectified by hysteresis, thus inducing
a ratcheting motion to the water droplet vertically downward. Maximum rectification occurs at the resonant states of the drop.
A comparison between the frequency-dependent motion of these drops and the variation of contact angles on their both sides
is made. The paper ends with a discussion on the movements of the drops on a horizontal hydrophobic surface subjected to an
asymmetric vibration. 相似文献
2.
An original set-up is used to study the adhesive properties of two hemispherical soap bubbles put into contact. The contact
angle at the line connecting the three films is extracted by image analysis of the bubbles profiles. After the initial contact,
the angle rapidly reaches a static value slightly larger than the standard 120° angle expected from Plateau rule. This deviation is consistent with previous experimental and theoretical studies: it can
be quantitatively predicted by taking into account the finite size of the Plateau border (the liquid volume trapped at the
vertex) in the free energy minimization. The visco-elastic adhesion properties of the bubbles are further explored by measuring
the deviation Δθd(t) of the contact angle from the static value as the distance between the two bubbles supports is sinusoidally modulated. It
is found to linearly increase with Δr
c/r
c , where rc is the radius of the central film and Δr
c the amplitude of modulation of this length induced by the displacement of the supports. The in-phase and out-of-phase components
of Δθd(t) with the imposed modulation frequency are systematically probed, which reveals a transition from a viscous to an elastic
response of the system with a crossover pulsation of the order 1rad · s^-1. Independent interfacial rheological measurements,
obtained from an oscillating bubble experiment, allow us to develop a model of dynamic adhesion which is confronted to our
experimental results. The relevance of such adhesive dynamic properties to the rheology of foams is briefly discussed using
a perturbative approach to the Princen 2D model of foams. 相似文献
3.
4.
P. Snabre F. Magnifotcham 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):369-377
The continuous emission of gas bubbles from a single ejection orifice immersed in a viscous fluid is considered. We first
present a semi empirical model of spherical bubble growth under constant flow conditions to predict the bubble volume at the
detachment stage. In a second part, we propose a physical model to describe the rise velocity of in-line interacting bubbles
and we derive an expression for the net viscous force acting on the surrounding fluid. Experimental results for air/water-glycerol
systems are presented for a wide range of fluid viscosity and compared with theoretical predictions. An imagery technique was used to determine the bubble size and rise velocity.
The effects of fluid viscosity, gas flow rate, orifice diameter and liquid depth on the bubble stream dynamic were analyzed.
We have further studied the effect of large scale recirculation flow and the influence of a neighbouring bubble stream on
the bubble growth and rising velocity.
Received: 23 July 1997 / Revised: 16 December 1997 / Accepted: 11 May 1998 相似文献
5.
6.
P. Snabre F. Magnifotcham 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):379-386
The recirculation flow induced by the rising motion of a bubble stream in a viscous fluid within an open-top rectangular enclosure
is studied. The three-dimensional volume averaged conservation equations are solved by a control-volume method using a hybrid
finite differencing scheme to describe the liquid phase hydrodynamics. The momentum exhange between the bubbles and the liquid
phase is modeled with a source term equals to the volumetric buoyancy force acting on the gas in the bubble stream. The volumetric
buoyancy force accounts for in line interactions between bubbles through the average gas volume fraction in the gas liquid
column which depends on the size and the rising velocity of bubbles. The fluid flow within an open-top rectangular enclosure
is further investigated by particle image velocimetry for a bubble stream rising in a water-glycerol solution. The measured
fluid velocities in a vertical plane are compared with the predictions of the numerical model over a wide range of fluid viscosity
(43 mPa s-800 mPa s) and gas flow rates. Finally, the recirculation flows resulting from the interaction of two neighbouring
vertical bubble streams are studied.
Received: 23 July 1997 / Revised: 19 December 1997 / Accepted: 11 May 1998 相似文献
7.
We develop a theory of axisymmetric surfaces minimizing a combination of surface tension and nematic elastic energies which
may be suitable for describing simple film and bubble shapes. As a function of the elastic constant and the applied tension
on the bubbles, we find the analogues of the unduloid, sphere, and nodoid in addition to other new surfaces. 相似文献
8.
We compare extensive experimental results for the
gravity-driven steady drainage of oil-in-water emulsions with two
theoretical predictions, both based on the assumption of Poiseuille flow.
The first is from standard foam drainage theory,
applicable at low aqueous volume fractions, for which a
correction is derived to account for the effects
of the confinement of the emulsion. The second arises
from considering the permeability of a model porous
medium consisting of solid sphere packings, applicable
at higher aqueous volume fractions. We find quantitative
agreement between experiment and the foam drainage theory at low
aqueous volume fractions. At higher aqueous volume
fractions, the reduced flow rate calculated from the
permeability theory approaches the master curve
of the experimental data. Our experimental data
demonstrates the analogy between the problem of electrical flow and liquid
flow through foams and emulsions. 相似文献
9.
We present a mesoscopic model for simulating the dynamics of a non-volatile liquid on a solid substrate. The wetting properties
of the solid can be tuned from complete wetting to total non-wetting. This model opens the way to study the dynamics of drops
and liquid thin films at mesoscopic length scales of the order of the nanometer. As particular applications, we analyze the
kinetics of spreading of a liquid drop wetting a solid substrate and the dewetting of a liquid film on a hydrophobic substrate.
In all these cases, very good agreement is found between simulations and theoretical predictions. 相似文献
10.
J. de Vries S. Luther D. Lohse 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):503-509
When a 2-4 mm diameter bubble rising with constant velocity hits a thin wire, bubble shape oscillations can be induced. As
a consequence also the bubble rise velocity strongly oscillates. With the help of a force balance we show that these velocity
oscillations are an added-mass effect.
Received 9 April 2002 / Received in final form 11 July 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: lohse@tn.utwente.nl 相似文献
11.
T. Hamida T. Babadagli 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(4):447-462
This paper aims at identifying and analyzing the influence of
high-frequency, high-intensity ultrasonic radiation at the interface between
immiscible (different types of oils and aqueous solutions) and miscible
(different types of oil and solvent) fluids. An extensive set of Hele-Shaw
type experiments were performed for several viscosity ratios, and
interfacial tension. Fractal analysis techniques were applied to quantify
the degree of fingering and branching. This provided a rough assessment of
the degree of perturbation generated at the interface when the capillary
forces along with the viscous forces are effective. Miscible Hele-Shaw
experiments were also presented to isolate the effect of viscous forces. We
found that ultrasound acts to stabilize the interfacial front, and that such
effect is most pronounced at low viscosity ratios.
An erratum to this article is available at . 相似文献
12.
Saikat Chakraborty Prabhu R. Nott J. Ravi Prakash 《The European physical journal. E, Soft matter》2000,1(4):265-273
This paper considers the segregation of a granular mixture in a rotating drum. Extending a recent kinematic model for grain
transport on sandpile surfaces to the case of rotating drums, an analysis is presented for radial segregation in the rolling
regime, where a thin layer is avalanching down while the rest of the material follows rigid body rotation. We argue that segregation
is driven not just by differences in the angle of repose of the species, as has been assumed in earlier investigations, but
also by differences in the size and surface properties of the grains. The cases of grains differing only in size (slightly
or widely) and only in surface properties are considered, and the predictions are in qualitative agreement with observations.
The model yields results inconsistent with the assumptions for more general cases, and we speculate on how this may be corrected.
Received 4 June 1999 and Received in final form 28 September 1999 相似文献
13.
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
14.
J.P. Vishwakarma 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):369-372
The variation of flow-variables with distance, in the flow-field behind a shock wave propagating in a dusty gas with exponentially
varying density, are obtained at different times. The equilibrium flow conditions are assumed to be maintained, and the results
are compared with those obtained for a perfect gas. It is found that the presence of small solid particles in the medium has
significant effects on the variation of density and pressure.
Received 20 October 1999 and Received in final form 9 March 2000 相似文献
15.
Magnetic separation from superparamagnetic particle suspensions 总被引:1,自引:0,他引:1
We investigate the magnetophoretic separation of magnetic microparticles from a non-dilute flow in a microfluidic channel and their subsequent field-induced aggregation under the influence of an externally applied magnetic force. This force induces dipolar interactions between the particles that aid in their separation from the flow. Existing analytical models for dilute suspensions cannot be extended to non-dilute suspensions in which interparticle magnetic interactions play an important role. We therefore conduct a parametric investigation of the mechanics of this problem in a microcapillary flow through simulations and experimental visualization. When a magnetic field is applied, the magnetic microparticles form an aggregate on the channel wall that is influenced by the competition between the holding magnetic force and the aggregate-depleting flow shear force. Microparticle collection in the aggregate increases linearly with increasing magnetic field strength and is characterized by distinct buildup and washaway phases. The collected microparticle volume fraction in an aggregate is found to depend on a single dimensional group that depends upon characteristic system parameters. 相似文献
16.
In a wind-blown sand layer, it has been found that wind transport of
particles is always associated with separation of electric charge. This
electrification in turn produces some electrostatic forces in addition to
the gravitational and fluid friction forces that affect the movement of
saltating sand particles, further, the wind-blown sand saltation. To
evaluate this effect quantitatively, this paper presents a simulation of
evolution of wind-blown sand grains after the electrostatic forces exerted
on the grains are taken into account in the wind feedback mechanism of
wind-blown saltation. That is, the coupling interaction between the wind
flow and the saltating sand particles is employed in the simulation to the
non-stationary wind and sand flows when considering fluid drag, gravitation,
and a kind of electrostatic force generated from a distribution of electric
field changing with time in the evolution process of the sand saltation. On
the basis of the proposed simulation model, a numerical program is given to
perform the simulation of this dynamic process and some characteristic
quantities, e.g., duration of the system to reach the steady state, and
curves of the saltating grain number, grain transport rate, mass-flux
profile, and wind profile varying with time during the non-stationary
evolution are displayed. The obtained numerical results exhibit that the
electrostatic force is closely related to the average charge-to-mass ratio
of sand particles and has obvious influence on these characteristic
quantities. The obtained results also show that the duration of the system
to reach the steady state, the sand transport rate and the mass flux profile
coincide well with experimental results by Shao and Raupach (1992) when the
average charge-to-mass ratio of sand particles is 60 μC/kg for the sand
particles with average diameter of 0.25 mm. When the average charge-to-mass
ratios of sand particles are taken as some other certain values, the
calculation results still show that the mass flux profiles are well in
agreement with the experimental data by Rasmussen and Mikkelsen (1998) for
another category of sand particles, which tell us that the electrostatic
force is one of main factors that have to be considered in the research of
mechanism of wind-blown sand saltation. 相似文献
17.
An Experimental Study of In-Situ Phase Fraction in Jet Pump Using Electrical Resistance Tomography Technique 下载免费PDF全文
We perform the experiments to investigate in-situ phase fraction in a jet pump using the electrical resistance tomography (ERT) technique. A new jet pump with ERT sensors is designed to measure in-situ phase fraction and flow regime. The study is based on laboratory experiments that are carried out on a 50-mm vertical flow rig for various gas and liquid phase superficial velocities. The different flow patterns of gas liquid in the jet pump and vertical pipe are studied using the ERT technique. The results suggest that the ERT system can be used to successfully produce images of gas-liquid flow patterns with frames rates of 58 fps and the in-situ phase fraction with frame rates of 5 fps can be obtained. The visualizations of a rapid mixing process in the throat of a jet pump obtained in this work provide a reliable basis for theoretical study and optimal design of jet pumps. 相似文献
18.
For an ordered array of critical volatile wetting droplets the formation of a super lattice by an Ostwald-ripening-like competition
process is considered. The underlying diffusion problem is treated within a quasistatic approximation and to first order in
the inverse droplets distance. The approach is rather general but a square lattice and a triangular lattice are studied explicitly.
Dispersion relations for the super lattice growth of these arrays are calculated.
Received 29 November 1999 and Received in final form 15 February 2000 相似文献
19.
Bong Jae Chung 《Physica D: Nonlinear Phenomena》2008,237(22):2945-2951
We study the steady terminal orientation of a fore-aft symmetric body as it settles in a viscous fluid. An optimal principle for the settling behavior is discussed based upon entropy production in the system, both in the Stokes limit and the case of near equilibrium states when inertial effects emerge. We show that in the Stokes limit, the entropy production in the system is zero allowing any possible terminal orientation while in the presence of inertia, the particle assumes a horizontal position which coincides with the state of maximum entropy production. Our results are seen to agree well with experimental observations. 相似文献
20.
Mechanism of thermal conductivity of nanofluids is analysed and calculated, including Brownian motion effects, particle agglomeration and viscosity, together influenced by temperature. The results show that only Brown- Jan motion as reported is not enough to describe the temperature dependence of the thermal conductivity of nanofluids. The change of particle agglomeration and viscosity with temperature are also important factors. As temperature increases, the reduction of the particle surface energy would decrease the agglomeration of nanopartieles, and the reduction of viscosity would improve the Brownish motion. The results egree well with the experimental data reported. 相似文献