共查询到20条相似文献,搜索用时 390 毫秒
1.
S. Residori E. Pampaloni P.K. Buah-Bassuah F.T. Arecchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):331-334
As a drop of fluid is deposited on the surface of a miscible fluid (that we call the solvent), it undergoes a strong pulling
due to its surface rupture and it acquires a kinetic energy independently of gravity. For the drop and the solvent being of
the same fluid we observe a drop injection at an initial velocity which scales as the square root of the surface tension of
the drop against air. Once injected, the drop develops a transverse instability giving rise to an expanding ring. Viscosity
terminates the process and stops the ring. We show that the final ring height follows a scaling law whereas two asymptotical
scaling regimes can be identified for the ring radius.
Received 31 August 1999 相似文献
2.
W. Nörenberg G. Papp P. Rozmej 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):327-343
The diabatic approach to dissipative collective nuclear motion is reformulated in the local-density approximation in order
to treat the normal modes of a spherical nuclear droplet analytically. In a first application the adiabatic isoscalar modes
are studied and results for the eigenvalues of compressional (bulk) and pure surface modes are presented as function of density
and temperature inside the droplet, as well as for different mass numbers and for soft and stiff equations of state. We find
that the region of bulk instabilities (spinodal regime) is substantially smaller for nuclear droplets than for infinite nuclear
matter. For small densities below 30% of normal nuclear matter density and for temperatures below 5 MeV all relevant bulk
modes become unstable with similar growth rates. The surface modes have a larger spinodal region, reaching out to densities
and temperatures way beyond the spinodal line for bulk instabilities. Essential experimental features of multifragmentation,
like fragmentation temperatures and fragment-mass distributions (in particular the power-law behavior) are consistent with
the instability properties of an expanding nuclear droplet, and hence with a dynamical fragmentation process within the spinodal
regime of bulk and surface modes (spinodal decomposition).
Received: 4 September 2000 / Accepted: 14 November 2000 相似文献
3.
We analyze the stability and dynamics of toroidal liquid droplets. In addition to the Rayleigh instabilities akin to those
of a cylindrical droplet there is a shrinking instability that is unique to the topology of the torus and dominates in the
limit that the aspect ratio is near one (fat tori). We first find an analytic expression for the pressure distribution inside
the droplet. We then determine the velocity field in the bulk fluid, in the Stokes flow regime, by solving the biharmonic
equation for the stream function. The flow pattern in the external fluid is analyzed qualitatively by exploiting symmetries.
This elucidates the detailed nature of the shrinking mode and the swelling of the cross-section following from incompressibility.
Finally the shrinking rate of fat toroidal droplets is derived by energy conservation. 相似文献
4.
Numerical investigation of the deformation mechanism of a bubble or a drop rising or falling in another fluid 下载免费PDF全文
A numerical method for simulating the motion and deformation of an axisymmetric bubble or drop rising or falling in another infinite and initially stationary fluid is developed based on the volume of fluid (VOF) method in the frame of two incompressible and immiscible viscous fluids under the action of gravity, taking into consideration of surface tension effects. A comparison of the numerical results by this method with those by other works indicates the validity of the method. In the frame of inviseid and incompressible fluids without taking into consideration of surface tension effects, the mechanisms of the generation of the liquid jet and the transition from spherical shape to toroidal shape during the bubble or drop deformation, the increase of the ring diameter of the toroidal bubble or drop and the decrease of its cross-section area during its motion, and the effects of the density ratio of the two fluids on the deformation of the bubble or drop are analysed both theoretically and numerically. 相似文献
5.
Borcia R Menzel S Bestehorn M Karpitschka S Riegler H 《The European physical journal. E, Soft matter》2011,34(3):24-9
Mixing of droplets with a body of different liquids shows an interesting behavior for small contact angles at solid substrate.
The droplets interact with each other, a liquid exchange appears between the approaching drops owing to surface tension gradients
at the droplets interface. But the drops remain separated for some seconds (up to minutes), until the merging into a single
drop occurs (Langmuir 24, 6395 (2008)). We investigate this phenomenon using lubrication approximation and phase field approach. For both methods,
2D quantitative computer simulations for delayed fusion of perfectly miscible thin liquid films/droplets with low contact
angles are reported. 相似文献
6.
用热力学方法证明了壁面上球冠形液滴的内外压差同样遵循经典的Laplace方程,并用力学方法给予了验证.液滴的内外压差与固液接触角无关,只取决于液体的表面张力和液滴半径;液滴的临界半径也与接触角无关,其值可用经典的Kalvin公式计算
关键词:
滴状冷凝
液滴
压差
临界半径 相似文献
7.
8.
Process modeling gas atomization of close-coupled ring-hole nozzle for 316L stainless steel powder production 下载免费PDF全文
《中国物理 B》2021,30(5):57502-057502
The paper aims at modeling and simulating the atomization process of the close-coupled ring-hole nozzle in vacuum induction gas atomization(VIGA) for metallic powder production. First of all, the primary atomization of the ring-hole nozzle is simulated by the volume of fluid(VOF) coupled large eddy simulation(LES) model. To simulate the secondary atomization process, we use the method of selecting the droplet sub-model and the VOF model. The results show that the ring-hole nozzle forms a gas recirculation zone at the bottom of the delivery tube, which is the main reason for the formation of an annular liquid film during the primary atomization. In addition, the primary atomization process of the ring-hole nozzle consists of three stages: the formation of the serrated liquid film tip, the appearance and shedding of the ligaments, and the fragmentation of ligaments. At the same time, the primary atomization mainly forms spherical droplets and long droplets, but only the long droplets can be reserved and proceed to the secondary atomization. Moreover,increasing the number of ring holes from 18 to 30, the mass median diameter(MMD, d50) of the primary atomized droplets decreases first and then increases, which is mainly due to the change of the thickness of the melt film. Moreover, the secondary atomization of the ring-hole nozzles is mainly in bag breakup mode and multimode breakup model, and bag breakup will result in the formation of hollow powder, which can be avoided by increasing the gas velocity. 相似文献
9.
It is shown that the critical self-charge for the onset of instability of a charged drop in a flow of an ideal fluid decreases
as the flow velocity of the fluid past the drop increases, i.e., a complex instability arises which is a superposition of
the instabilities of the free surface of the drop with respect to the tangential discontinuity of the velocity field at the
free surface of the drop and with respect to the self-charge.
Zh. Tekh. Fiz. 69, 7–14 (May 1999) 相似文献
10.
Holography is capable of three-dimensional (3D) representation of spatial objects such as fluid interfaces and particle ensembles. Based on this, we adapt it into a 3D flow visualization tool called Holographic Flow Visualization (HFV). This technique provides a novel means of studying spatially and temporally evolving complex fluid flow structures marked by a disperse phase or interfaces of different fluids. This paper demonstrates that HFV is a straightforward technique, especially when the In-line Recording Off-axis Viewing (IROV) configuration is used. The technique can be applied either as a stand-alone experimental tool for studying scalar-based coherent structures, flow instabilities, interactions of different fluids driven by fluid dynamics, interfacial phenomena, or as a precursor to volumetric 3D velocity vector field measurement of complex transient flow dynamics. Experimental results in several complex fluid flows and flames demonstrate the effectiveness of HFV. Different methods are used to mark flow structures undergoing different instabilities: 1) a vortex ring grown out of a drop of polymer suspension falling in water, 2) cascade of a bag-shaped drop of milk in water, and 3) internal flow structures of a jet diffusion flame. 相似文献
11.
In the quadratic approximation with respect to the amplitudes of capillary oscillation and velocity field of the liquid moving inside a charged drop of a perfectly conducting fluid, it is shown that the liquid drop oscillates about a weakly prolate form. This refines the result obtained in the linear theory developed by Lord Rayleigh, who predicted oscillation about a spherical form. The extent of elongation is proportional to the initial amplitude of the principal mode and increases with the intrinsic charge carried by the drop. An estimate is obtained for the characteristic time of instability development for a critically charged drop. 相似文献
12.
Sessile drops sitting on highly wettable solid substrates fuse in qualitatively different ways after contact, depending on
the surface tension gradients between the mixing droplets. In early time evolution the drop coalescence can be fast or delayed
(intermittent). In long time evolution a secondary drop formation can occur. We study numerically droplet dynamics during
coalescence in two and three spatial dimensions, within a phase field approach. We discuss criteria to distinguish different
coalescence regimes. A comparison with recent experiments will be done. 相似文献
13.
《Physics letters. A》2014,378(5-6):539-548
Experiments involving heating of liquid droplets which are acoustically levitated, reveal specific modes of oscillations. For a given radiation flux, certain fluid droplets undergo distortion leading to catastrophic bag type breakup. The voltage of the acoustic levitator has been kept constant to operate at a nominal acoustic pressure intensity, throughout the experiments. Thus the droplet shape instabilities are primarily a consequence of droplet heating through vapor pressure, surface tension and viscosity. A novel approach is used by employing Legendre polynomials for the mode shape approximation to describe the thermally induced instabilities. The two dominant Legendre modes essentially reflect (a) the droplet size reduction due to evaporation, and (b) the deformation around the equilibrium shape. Dissipation and inter-coupling of modal energy lead to stable droplet shape while accumulation of the same ultimately results in droplet breakup. 相似文献
14.
A dispersion relation for the capillary oscillations of a charged spherical drop of a viscous incompressible finite-conductivity liquid is derived and analyzed. It is found that electric currents inside the charged drop equalize its potential and produce liquid flows interacting with both potential and eddy poloidal liquid flows inside the drop that are due to drop oscillations. Taking into account the finiteness of the rate of potential equalization over the drop surface leads to an additional damping of the capillary oscillations that arises because of the increased role of energy dissipation. 相似文献
15.
Correlations to predict droplet size in ultrasonic atomisation. 总被引:2,自引:0,他引:2
In conventional two fluid nozzles, the high velocity air imparts its energy to the liquid and disrupts the liquid sheet into droplets. If the energy for liquid sheet fragmentation can be supplied by the use of ultrasonic energy, finer droplets with high sphericity and uniform size distribution can be achieved. The other advantage of ultrasound induced atomisation process is the lower momentum associated with ejected droplets compared to the momentum carried by the droplets formed using conventional nozzles. This has advantage in coating and granulation processes. An ultrasonic probe sonicator was designed with a facility for liquid feed arrangement and was used to atomise the liquid into droplets. An ingenious method of droplet measurement was attempted by capturing the droplets on a filter paper (size variation with regard to wicking was uniform in all cases) and these are subjected to image analysis to obtain the droplet sizes. This procedure was evaluated by high-speed photography of droplets ejected at one particular experimental condition and these were image analysed. The correlations proposed in the literature to predict droplet sizes using ultrasound do not take into account all the relevant parameters. In this work, a truly universal correlation is proposed which accounts for the effects of physico-chemical properties of the liquid (flow rate, viscosity, density and surface tension), and ultrasonic properties like amplitude, frequency and the area of vibrating surface. The significant contribution of this work is to define dimensionless numbers incorporating ultrasonic parameters, taking cue from the conventional numbers that define the significance of different forces involved in droplet formation. The universal correlations proposed are robust and can be used for designing ultrasonic atomisers for different applications. Among the correlations proposed here, those ones that are based on the dimensionless numbers and Davies approach predict droplet sizes within acceptable limits of deviation. Also, an empirical correlation from experimental data has been proposed in this work. 相似文献
16.
The factors influencing the state and wetting transition of droplets on a rough surface are both complex and obscure. The
change in wetting is directly reflected by changes under the contact condition of the droplets with the surface. The recent
study about the wettability of the superhydrophobic surface under the condensing condition arouses the new understanding about
the apparent state of droplets on a rough surface. In this work, to validate the existence of droplets in an intermediate
state, a microscale pillar topological polydimethylsiloxane (PDMS) surface was manufactured and its wettability under various
conditions was studied. According to the experimental data, it is proposed that the wetting state of a rough surface may be
embodied using the contact area ratio of a solid/liquid/gas droplet with the projective plane. A general calculation model
for the apparent contact angle of droplets is given and expressed diagrammatically. It is found that the measured apparent
contact angles of droplets at different states on the surface falls within the range predicted by our proposed equation.
Supported by the National Natural Science Foundation of China (Grant No. 50606025) 相似文献
17.
P. V. Kashtanov R. Hippler B. M. Smirnov S. R. Bhattacharyya 《Journal of Experimental and Theoretical Physics》2010,110(3):521-528
The fragmentation of silver liquid clusters deposited onto a silicon surface is observed after heating the clusters to 1073
K and subsequent annealing with the exposition time 3 min. This contradicts macroscopic models of a liquid drop deposited
on a surface if we use critical parameters of bulk silver. Some versions are analyzed that are based on cluster properties
and may explain the phenomenon of cluster fragmentation. An experiment is suggested for clarifying the nature of the cluster
fragmentation phenomenon and cluster critical phenomena. 相似文献
18.
本文采用自由落体实验技术和格子玻尔兹曼计算方法研究了低重力条件下液态Fe-Sn-Si/Ge合金的相分离过程. 实验发现, 二种合金液滴在自由下落过程中均发生显著的液相分离, 形成了壳核和弥散组织. 当Fe-Sn-Si合金中的Si元素被等量的Ge元素替换后, 壳核组织中富Fe区和富Sn区的分布次序会发生反转. 计算表明, 在液相分离过程中冷却速率、Marangoni对流和表面偏析对壳核构型的选择和弥散组织的形成起决定性作用. 相似文献
19.
《Journal of Electrostatics》2006,64(7-9):513-519
New flows and instabilities are demonstrated for magnetic fluids and by dual analogy to dielectric fluids. If a fluid drop is contained in a thin gap between two glass plates (Hele–Shaw cell) with a simultaneously applied in-plane rotating field and a DC axial field, smooth spirals or an abrupt transformation to many small droplets can occur. A preliminary minimum magnetization and surface energy analysis is presented to model the abrupt transformation in ferrofluids. An analysis of effective DC magnetoviscosity is also presented for planar Couette flow with an applied uniform DC field transverse to a duct axis with the effective magnetoviscosity and flow spin velocity calculated as a function of field strength. Related Couette viscometer measurements of ferrofluid viscosity show zero and negative magnetoviscosity values for rotating magnetic fields. 相似文献
20.