共查询到20条相似文献,搜索用时 31 毫秒
1.
Strain recovery after the cessation of shear was studied in model immiscible blends composed of polyisobutylene drops (10–30%
by weight) in a polydimethylsiloxane matrix. Blends of viscosity ratio (viscosity of the drops relative to the matrix viscosity)
ranging from 0.3 to 1.7 were studied. Most of the strain recovery was attributable to interfacial tension, and could be well-described
by just two parameters: the ultimate recovery and a single retardation time. Both these parameters were found to increase
with the capillary number of the drops prior to cessation of shear. For blends that had reached steady shear conditions, the
ultimate recovery decreased with increasing viscosity ratio, whereas the retardation time increased with increasing viscosity
ratio. The retardation time was well-predicted, but the ultimate recovery was over-predicted by a linear viscoelastic model
developed previously by Vinckier et al. (Rheol Acta 38:65–72, 1999). 相似文献
2.
V. I. Pen'kovskii 《Journal of Applied Mechanics and Technical Physics》1998,39(6):922-927
Two mathematical models of filtration coalescence of oil drops when a water-oil mixture moves through a porous material are
proposed. In the first model, coalescence is interpreted as the process of sorption, i.e., the accumulation of the oil phase
on the pore surface up to a definite critical value above which the larger drops involved by a filtration flow stall. The
second model assumes that the motion of the sorbed oil and the entire mixture obeys the generalized Darcy laws.
Lavrent'ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from
Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 6, pp. 118–124, November–December, 1998. 相似文献
3.
4.
5.
B. Taboada L. Vega-Alvarado M. S. Córdova-Aguilar E. Galindo G. Corkidi 《Experiments in fluids》2006,41(3):383-392
Characterization of multiphase systems occurring in fermentation processes is a time-consuming and tedious process when manual methods are used. This work describes a new semi-automatic methodology for the on-line assessment of diameters of oil drops and air bubbles occurring in a complex simulated fermentation broth. High-quality digital images were obtained from the interior of a mechanically stirred tank. These images were pre-processed to find segments of edges belonging to the objects of interest. The contours of air bubbles and oil drops were then reconstructed using an improved Hough transform algorithm which was tested in two, three and four-phase simulated fermentation model systems. The results were compared against those obtained manually by a trained observer, showing no significant statistical differences. The method was able to reduce the total processing time for the measurements of bubbles and drops in different systems by 21–50% and the manual intervention time for the segmentation procedure by 80–100%. 相似文献
6.
H. Ó. Haraldsson H. X. Li Z. L. Yang T. N. Dinh B. R. Sehgal 《Heat and Mass Transfer》2001,37(4-5):417-426
This paper presents results of experimental and analytical investigation on molten alloy drop fragmentation in water pool.
Emphasis is directed towards delineating the roles which melt to coolant heat transfer and melt solidification play in the
fragmentation process. The strong impact of coolant temperature upon fragmentation process is addressed. A set of 23 drop
fragmentation experiments were performed, in which 8 experiments employed a low melting point alloy, cerrobend-70 and 15 experiments
using Pb–Bi eutectic alloy as drop fluid. The results show strong impact of coolant temperature on particle size distribution
of the fragmented drops. A linear stability analysis of the interface between the two liquid fluids with thin crust growing
between them, is performed. A modified dimensionless Aeroelastic number, for Kelvin–Helmholtz instability, is obtained and
used as a criteria for fragmentation of molten drops penetrating into another liquid coolant media with lower temperature.
The nondimensionalized mean diameter of the fragmented particles is correlated with the Aeroelastic number.
Received on 26 March 2000 相似文献
7.
High-speed tomographic PIV was used to investigate the coalescence of drops placed on a liquid/liquid interface; the coalescence
of a single drop and of a drop in the presence of an adjacent drop (side-by-side drops) was investigated. The viscosity ratio
between the drop and surrounding fluids was 0.14, the Ohnesorge number (Oh = μd/(ρdσD)1/2) was 0.011, and Bond numbers (Bo = (ρ
d
− ρ
s
)gD
2/σ) were 3.1–7.5. Evolving volumetric velocity fields of the full coalescence process allowed for quantification of the velocity
scales occurring over different time scales. For both single and side-by-side drops, the coalescence initiates with an off-axis
film rupture and film retraction speeds an order of magnitude larger than the collapse speed of the drop fluid. This is followed
by the formation and propagation of an outward surface wave along the coalescing interface with wavelength of approximately
2D. For side-by-side drops, the collapse of the first drop is asymmetric due to the presence of the second drop and associated
interface deformation. Overall, tomographic PIV provides insight into the flow physics and inherent three-dimensionalities
in the coalescence process that would not be achievable with flow visualization or planar PIV only. 相似文献
8.
The mechanical model was established for the anti-plane fracture problem of a functionally graded coating–substrate system
with a coating crack inclined to the weak/micro-discontinuous interface. The Cauchy singular integral equation for the crack
was derived using Fourier integral transform, and the Lobatto–Chebyshev collocation method put up by Erdogan and Gupta was
used to get its numerical solution. Finally, the effects of the weak/micro-discontinuity of the interface on SIFs were analyzed,
the “affected regions” corresponding to the two crack tips have been obtained and their engineering significance was discussed.
It was indicated that, for the crack tip in the corresponding “affected region”, to reduce the weak-discontinuity of the interface
and to make the interface micro-discontinuous are the two effective ways to reduce the SIF, and the latter way always has
more remarkable SIF-reduction effect. For the crack tip outside the “affected region”, its SIF is mainly influenced by material
stiffness, and to prevent such a tip from growing toward the interface “softer coating and stiffer substrate” is a more advantageous
combination than “stiffer coating and softer substrate”. 相似文献
9.
We consider the effects of 2.7-μm-diameter hydrophobic silica particles added to droplet–matrix blends of polyethylene oxide
(PEO) and polyisobutylene (PIB). The particles adsorb on the surface of the PEO drops but protrude considerably into the PIB
phase. Hence, it is possible for a single particle to adsorb onto two PEO drops simultaneously. Such particles are called
“bridging” particles, and they the glue drops into noncoalescing clusters. Flow visualization studies show that shearing the
sample promotes bridging-induced clustering of drops and that the structure of the clusters depends on the shear rate. Rheologically,
the most significant consequence of bridging-induced drop clustering appears to be a plateau in G′ at low frequencies characteristic of gel-like behavior. The gel-like behavior develops fully after shearing the sample,
and the kinetics of gel formation are faster with increasing shear stress or increasing drop volume fraction. The gel-like
behavior suggests that the bridging-induced drop clusters form a weak network. Apart from particle bridging, optical microscopy
also reveals that particles can organize into a hexagonal lattice on the drops’ surfaces, a phenomenon that has only been
noted in aqueous systems previously. Finally, rheology and flow visualization both suggest that particles promote coalescence
of drops. This is surprising in light of much past research that shows that particles that are preferentially wetted by the
continuous phase generally hinder coalescence in droplet–matrix systems. 相似文献
10.
In this article, we describe some aspects of the diffuse interface modelling of incompressible flows, composed of three immiscible
components, without phase change. In the diffuse interface methods, system evolution is driven by the minimisation of a free
energy. The originality of our approach, derived from the Cahn–Hilliard model, comes from the particular form of energy we
proposed in Boyer and Lapuerta (M2AN Math Model Numer Anal, 40:653–987,2006), which, among other interesting properties, ensures
consistency with the two-phase model. The modelling of three-phase flows is further completed by coupling the Cahn–Hilliard
system and the Navier–Stokes equations where surface tensions are taken into account through volume capillary forces. These
equations are discretized in time and space paying attention to the fact that most of the main properties of the original
model (volume conservation and energy estimate) have to be maintained at the discrete level. An adaptive refinement method
is finally used to obtain an accurate resolution of very thin moving internal layers, while limiting the total number of cells
in the grids all along the simulation. Different numerical results are given, from the validation case of the lens spreading
between two phases (contact angles and pressure jumps), to the study of mass transfer through a liquid/liquid interface crossed
by a single rising gas bubble. The numerical applications are performed with large ratio between densities and viscosities
and three different surface tensions. 相似文献
11.
Steady convective mass transfer to or from fluid interfaces in pores of angular cross-section is theoretically investigated.
This situation is relevant to a variety of mass transport process in porous media, including the fate of residual non-aqueous
phase liquid ganglia and gas bubbles. The model incorporates the essential physics of capillarity and solute mass transfer
by convection and diffusion in corner fluid filaments. The geometry of the corner filaments, characterized by the fluid–fluid
contact angle, the corner half-angle and the interface meniscus curvature, is accounted for. Boundary conditions of zero surface
shear (‘perfect-slip’) and infinite surface shear (‘no-slip’) at the fluid–fluid interface are considered. The governing equations
for laminar flow within the corner filament and convective diffusion to or from the fluid–fluid interface are solved using
finite-element methods. Flow computations are verified by comparing the dimensionless resistance factor and hydraulic conductance
of corner filaments against recent numerical solutions by Patzek and Kristensen (J. Colloid Interface Sci 236, 305–317 2001). Novel results are obtained for the average effluent concentration as a function of flow geometry and pore-scale
Peclet number. These results are correlated to a characteristic corner length and local pore-scale Peclet number using empirical
equations appropriate for implementation in pore network models. Finally, a previously published “2D-slit” approximation to
the problem at hand is checked and found to be in considerable error. 相似文献
12.
A PIV based technique is developed to perform flow measurements in the vicinity of the air–water interface of a submerged
confined jet. Both the interface movement and the velocity field immediately beneath it are measured simultaneously. A detailed
turbulence structure in the surface influence region is thus obtained. Flow parameters evaluated without and w.r.t. the interface
are quantified and compared against previous works obtained using the conventional Eulerian-based instrumentation which do
not account for the interface fluctuation, and checked against analytical model characterising the turbulence close to a assumed
flat air–water interface.
Received: 15 March 1998/Accepted: 19 October 1998 相似文献
13.
We investigate the steady compressible Navier–Stokes system of equations in the isentropic regime in a domain with several
conical outlets and with prescribed pressure drops. Existence of weak solutions is proved and estimate of these solutions
with respect to the pressure drops is derived under the hypothesis γ > 3 where γ is the adiabatic constant. 相似文献
14.
Impact of water drops on a stainless steel surface comprising rectangular shaped parallel grooves is studied experimentally.
Geometric parameters of the surface groove structure such as groove depth, groove width and solid pillar width separating
any two successive grooves were kept at 7.5, 136 and 66 μm, respectively. The study was confined to the impact of drops in
inertia dominated flow regime with Weber number in the range 15–257. Experimental results of drop impact process obtained
for the grooved surface were compared with those obtained for a smooth surface to elucidate the influence of surface grooves
on the impact process. The grooves definitely influence both spreading and receding processes of impacting liquid drops. A
more striking observation from this study is that the receding process of impacting liquid drops is dramatically changed by
the groove structure for all droplet Weber number. 相似文献
15.
Viscoelasticity in inkjet printing 总被引:1,自引:0,他引:1
We investigate the effects of viscoelasticity on drop generation in inkjet printing. In drop-on-demand printing, individual
ink ‘drops’ are ejected from a nozzle by imposed pressure pulses. Upon exiting the nozzle, the shape of each ‘drop’ is that
of a nearly spherical bead with a long thin trailing ligament. This ligament subsequently breaks up under the Rayleigh instability,
typically into several small droplets (known as satellite drops). These satellite drops can create unwanted splash on the
target substrate and a reduction in printing quality. Satellite drops can potentially be eliminated by adding polymer to the
ink; elastic stresses can act to contract the trailing ligament into the main drop before capillary breakup occurs. However,
elasticity can also reduce the drop velocity and can delay or even prevent the break-off of the drop from the ink reservoir
within the nozzle. To achieve optimal drop shape and speed, non-Newtonian parameters such as the polymer concentration and
molecular weight must be chosen correctly. We explore this parameter space via numerical simulations, using the Lagrangian–Eulerian
finite-element method of Harlen et al. (J Non-Newtonian Fluid Mech 60:81–104, 1995). Results are compared with experimental observations taken from real printheads. 相似文献
16.
The behavior of glycerin–water jets flowing into immiscible ambients of Dow Corning 200 fluid was investigated using laser
induced fluorescence (LIF). Undistorted images were obtained by matching the index of refraction of the fluids. A sinusoidal
perturbation was superposed on the flow to phase lock the drop formation. The forcing frequency dramatically affected the
size, spacing, and number of drops that formed within a forcing cycle and the angle between drops and the jet interface just
before pinch-off. Two fluid combinations were studied with similar density ratios, but viscosity ratios differing by a factor
of 20. The viscosity ratio affected the jet stability as well as pinch-off angles and drop size.
Received: 28 January 1999/Accepted: 20 January 2000 相似文献
17.
The interaction of an electrically charged liquid-drop dispersed phase with a turbulent air-steam jet in a "water drop generator
(capillary)-jettarget" system is investigated. The experimental conditions were as follows: volume flow of water through the
capillary 0.01 cm3/s. capillary inside diameter 0.8 mm, electric potential applied to the capillary 20 kV. When the electric field is absent,
condensation does not develop in the jet despite the existence of oversaturation zones. Two regimes of interaction between
the charged dispersed phase and the jet are detected. The first regime (for ϕ<8 kV) is characterized by the regular launching
of fairly large charged drops (0.5<r<2 mm) from the capillary and the absence of condensation in thejet. As the potential ϕ increases, the drop size decreases,
whereas the drop charge increases. This regime made it possible to model the motion of individual charged clusters of different
charge and size in aircraft engine jets. The second regime (ϕ>8 kV) is characterized by the irregular launching of drops from
the capillary, drop dispersion with respect to size, a sharp increase in the target current, and the sudden appearance of
condensation in the air-steam jet. The possible electrohydrodynamic and heterophase processes are qualitatively analyzed.
Moscow, e-mail: vatazhin@ciam.ru.likhter@ciam.ru. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti
i Gaza, No. 4, pp. 102–114, July–August, 2000.
The work received financial support from the Russian Foundation for Basic Research (project No. 99-01-00983). 相似文献
18.
The flow and heat transfer in an inclined and horizontal rectangular duct with a heated plate longitudinally mounted in the
middle of cross section was experimentally investigated. The heated plate and rectangular duct were both made of highly conductive
materials, and the heated plate was subjected to a uniform heat flux. The heat transfer processes through the test section
were under various operating conditions: Pr ≈ 0.7, inclination angle ϕ = −60° to +60°, Reynolds number Re = 334–1,911, Grashof number Gr = 5.26 × 102–5.78 × 106. The experimental results showed that the average Nusselt number in the entrance region was 1.6–2 times as large as that
in the fully developed region. The average Nusselt numbers and pressure drops increased with the Reynolds number. The average
Nusselt numbers and pressure drops decreased with an increase in the inclination angle from −60° to +60° when the Reynolds
number was less than 1,500. But when the Reynolds number increased to over about 1,800, the heat transfer coefficients and
pressure drops were independent of inclination angles. 相似文献
19.
In this study, we carried out a numerical simulation of transient heat transfer in a composite passive system consisting of
air–phase change material–air, arranged as a rectangular enclosure. The vertical boundaries of the enclosure are isothermal
and the horizontal ones adiabatic. The enthalpy formulation with a fixed grid is used to study the process of phase change
with liquid–solid interface zone controlled by natural convection. The flow in this zone is simulated by a model based on
the Darcy porous medium. The numerical solution of the mathematical model is done using finite difference–control volume algorithm.
The influence of the geometrical and thermal parameters is studied. It is found that subcooling coefficient is the most important
parameter influencing heat transfer, and for a given subcooling, there is an optimum phase change partition thickness. 相似文献
20.
Pasqua D'Ambra 《Continuum Mechanics and Thermodynamics》1997,9(2):97-114
In this work we present some results of the numerical simulation of the growth of a crystal from its melt, taking into account
faceting. The simulation is based on a numerical solution of a three–dimensional generalized Stefan problem. That problem
arises from a non–local thermomechanical theory applied to a continuous system with an interface and embodies ideas from the
dislocation theory of crystal growth. In the model, the crystal surface is an isotherm and the growth velocity of a crystal
face depends on the velocities of the other faces and on the whole crystal configuration as well as on the temperature gradient.
A front fixing formulation of the model is considered. This is a conservative form of the Isotherm Migration Method [6, 7,
8, 9, 10, 11] in spherical coordinates. The numerical solution is based on an explicit finite difference discretization of
the resulting non–linear equations. We develop a theoretical analysis of the interface equations that drive the crystal face
motion. Numerical results, showing evolution of complex crystals with configuration changing during the growth, are in accord
with experimental results. Furthermore, numerical experiments offer useful information on the influence of certain parameters
in the model on the growth process.
Received: March 21, 1996 相似文献