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1.
For a study of nonlinear wave motion under an electrostatic field, the Korteweg-de Vries (KdV) equation for inviscid liquid
film flowing under gravity down an inclined plane has been derived, and the effect of the electric field on the stability
of a solitary wave as a solution of the KdV equation is examined. Under a constant electrostatic potential the stability of
the wave is not affected. However, with a slowly varying potential it becomes unstable. 相似文献
2.
The hydraulic-jump phenomenon of a thin fluid layer flowing down an inclined plane under an electrostatic field is explored
by using a global bifurcation theory. First, the existence of hydraulic-hump wave has been found from heteroclinic trajectories
of an associated ordinary differential equation. Then, the jump behavior has been characterized by introducing an intensity
function on the variations of Reynolds number and surfave-wave speed. Finally, we have investigated the nonlinear stability
of traveling shock waves triggered from a hydraulic jump by integrating the initial-value problem directly. At a given wave
speed there exists a certain value of Reynolds number beyond which a time-dependent buckling of the free surface appears.
Like the other wave motions such as periodic and pulse-like solitary waves, the hydraulic-jump waves are also found to become
more unstable as the electrostatic field is getting stronger. 相似文献
3.
For the study on the nonlinear dynamics of thin-film flow running down an inclined plane under the effect of an electrostatic
field, the mechanism of solitary waves has been examined by using a global bifurcation theory. First, the existence of solitary
waves has been chased by using an orbit homoclinic to a fixed point of saddle-focus type in a linearized third-order ordinary
differential equation which resulted from the evolution equation in a steady moving frame. Then, the trajectories with several
kinds of solitary waves have also been searched numerically for the nonlinear system. In addition, the behavior of these waves
has been directly confirmed by integrating the initial-value problem. The slightly perturbed waves at the inception eventually
evolve downstream into almost permanent pulse-like solitary waves through the processes of coalescence and repulsion of the
triggered subharmonics. In the global aspects the flow system at a given Reynolds number becomes more unstable and chaotic
than when there is no electrostatic force applied. 相似文献
4.
Stability of a thin viscous Newtonian fluid draining down a uniformly heated porous inclined plane is examined. The long-wave linear stability analysis is performed within the generic Orr-Sommerfeld framework both theoretically and numerically. An evolution equation for the local film thickness for two-dimensional disturbances is derived to analyze the effect of long-wave instabilities. The parameters governing the film flow system and the porous substrate strongly influence the wave forms and their amplitudes and hence the stability of the fluid. The long-time wave forms are either time-independent wave forms that propagate or time-dependent modes that oscillate slightly in the amplitude. The role of permeability and Marangoni number is to increase the amplitude of the disturbance leading to the destabilization state of the film flow system. The permeability of the porous medium promotes the oscillatory behavior. 相似文献
5.
Hyo Kim 《Korean Journal of Chemical Engineering》1997,14(1):41-48
The free-surface behavior of a viscous liquid layer flowing down an inclined plane by gravity and interacting with an overlying
uniform electrostatic field is examined in the limit of long-wave approximation. Both linear and nonlinear stability analyses
are performed to address two-dimensional surface-wave evolution initiating from a flat interface. The growth of a periodic
disturbance is first investigated for a linear analysis, and then to examine the nonlinear surface-wave instabilities the
evolution equation for film height is solved numerically by a Fourier-spectral method. For small evolution time the calculated
nonlinear modes of instability are consistent with the results obtained from the linear theory. The effect of an electrostatic
field increases the wavenumbers showing a maximum linear growth rate as well as a cutoff. A significant phenomenon as Reynolds
number is increasing is the appearance of the catastrophic surface waves in the long run whenever any initial wavenumber making
a traveling wave linearly unstable is employed into the initial simple-harmonic disturbance. 相似文献
6.
To answer the questions on the dynamics of thin liquid flow down an inclined plane at high Reynolds numbers subjected to a uniform normal electrostatic field, we have derived evolution equations describing the free-surface behavior by using the von Kármán-Pohlhausen approximation. The integration of the evolution equations is numerically performed to address two-dimensional finite-amplitude surface-wave propagation modes. The growth of a periodic disturbance is first examined to compare with the results linear-stability theory, and then to investigate the nonlinear surface-wave behavior the evolution equations are solved numerically by a Fourier-spectral method. For small evolution time the computed nonlinear modes of instability are well consistent with the results from the linear theory. The effect of an electrostatic field makes the flow system significantly unstable. 相似文献
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8.
The complexity of falling film flow has been studied in many industrial applications. In this work, the velocity field of high-viscosity fluids falling film flow down clamped channels was investigated numerically and experimentally. The results show that the numerical simulation results are consistent with the experimental results, and the characteristics of the velocity field are related to the fluid properties, operating conditions, and structure of the clamped channels. When the fluid viscosity is greater than or equal to 10 Pa ⋅ s, the type of velocity field changes into I shape, U shape, and V shape. While the fluid viscosity drops to 0.89 Pa ⋅ s, the viscous force cannot resist the inertial force and gravity, resulting in a cardioid velocity field. By adjusting the structure of the clamped channels and operating conditions, the tension of the liquid film can be changed, and the velocity distribution of the liquid film can be manipulated. Significantly, under the fluctuating curtain flow, the liquid film coalesces and breaks frequently, which enlarges the surface area of the liquid film and strengthens the surface renewal frequency. Hence, this form of falling film flow can be applied to process intensification of high-viscosity materials. 相似文献
9.
We consider the flow of a thin liquid film over a spinning disc in the presence of an electric field. This is imposed by applying a potential between the disc and an electrode above the film. The integral method and lubrication theory are used to derive a coupled set of evolution equations for the film thickness, radial and azimuthal flow rates and the surface charge density. These equations are parameterized by a modified Weber number, a modified Masuda number, dimensionless conductivities and a dimensionless electrode separation. We focus on the limit of large liquid conductivity and explore the influence of the applied electric field on the film dynamics via numerical simulations. The effects of spatially and temporally varying electric fields and electrode geometry on the formation of waves are also examined. Our results indicate that increasing the intensity of the electric field or decreasing the electrode separation exerts a destabilizing effect, leading to the formation of interfacial waves of larger amplitude. Spatial and temporal variations of the electric field also lead to complex film dynamics which, beyond a certain threshold of the relevant parameter values, give rise to sustained formation of waves over a large fraction of the spinning disc. These results suggest that electric fields have the potential to enhance the degree of wave-induced process intensification. 相似文献
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11.
Eldin Wee Chuan Lim 《Chemical engineering science》2006,61(24):7889-7908
The pneumatic transport of granular materials through an inclined and vertical pipe in the presence of an electrostatic field was studied numerically using the discrete element method (DEM) coupled with computational fluid dynamics (CFD) and a simple electrostatic field model. The simulation outputs corresponded well with previously reported experimental observations and measurements carried out using electrical capacitance tomography and high-speed camera techniques in the present study. The eroding dunes and annular flow regimes, observed experimentally by previous research workers in inclined and vertical pneumatic conveying, respectively, were reproduced computationally by incorporating a simplified electrostatic field model into the CFD-DEM method. The flow behaviours of solid particles in these regimes obtained from the simulations were validated quantitatively by experimental observations and measurements. In the presence of a mild electrostatic field, reversed flow of particles was seen in a dense region close to the bottom wall of the inclined conveying pipe and forward flow in a more dilute region in the space above. At sufficiently high field strengths, complete backflow of solids in the inclined pipe may be observed and a higher inlet gas velocity would be required to sustain a net positive flow along the pipe. However, this may be at the expense of a larger pressure drop over the entire conveying line. In addition, the time required for a steady state to be attained whereby the solids flow rate remains substantially constant with respect to time was also dependent on the amount of electrostatic effects present within the system. The transient period was observed to be longer when the electrostatic field strength was higher. Finally, a flow map or phase diagram was proposed in the present study as a useful reference for designers of inclined pneumatic conveying systems and a means for a better understanding of such systems. 相似文献
12.
Sergey Aktershev Sergey Alekseenko Aleksey Bobylev 《American Institute of Chemical Engineers》2021,67(1):e17002
In the long-wave approximation, a theoretical model is developed to describe waves in a rivulet flowing down the lower surface of an inclined cylinder. The model equations are derived by the weighted residual method by projecting the Navier–Stokes equations onto the constructed system of basic orthogonal polynomials. The simplest case of quasi-two-dimensional waves is studied in detail. The stability of the rivulet flow is analyzed and dispersion dependences for linear waves are obtained. The characteristics of nonlinear steady-state traveling waves have been obtained by numerical method for the first time, and the spatial development of forced waves has been studied. The results of calculations are in good agreement with the available experimental data for various liquids in a wide range of parameters. 相似文献
13.
Hyo Kim 《Korean Journal of Chemical Engineering》2011,28(11):2122-2129
This research examines rupture phenomena of a horizontal static thin viscous layer on a solid plate under an electrostatic
field generating from a charged foil above the film. The dynamics of the electrified liquid film is formulated to derive a
long-wave evolution equation of local film thickness. It determines two-dimensional nonlinear behavior of the film subject
to surface tension, viscous, electrically induced forces, and van der Waals attractions. Linear stability analysis is used
to obtain the maximum growth rate of a periodic disturbance and its corresponding wavenumber. To see the development of film
rupture the strongly nonlinear partial differential equation is numerically solved for the unlimited or limited foil length
as part of an initial-value problem with spatially periodic boundary conditions. The stronger electric forces make the thin
layer more unstable and speed up its rupture. 相似文献
14.
The paper presents an analytical study which describes the laminar accelerating flow of a thin film along an inclined wall. When interfacial shear is taken into consideration it is found that the non-dimensional film thickness depends on two parameters (Fr/Re) and ρu-ratio, the effect of the latter being more pronounced for larger values of the former. The results are compared with those of earlier workers. 相似文献
15.
利用VOF法建立了液膜在倾斜波纹板上的气-液两相流CFD模型,并根据液膜流动特点提出了表面张力动量源项和气液界面作用力动量源项.模拟结果与文献实验值吻合较好,表明本文提出的CFD液膜流动模型具有一定的可靠性.通过模拟不同性质的液体在不同表面结构波纹板上的流动过程发现,波纹板表面微观结构以及液体性质尤其是液体的表面张力对连续液膜的形成有重要作用,表明通过改变波纹板面微观结构以及降低液体的表面张力可以促进连续液膜的形成,对提高气液之间的传质效率有重要意义. 相似文献
16.
The behavior of dry particulate solids during unconfirmed flow over inclined surfaces has been investigated. The motion of individual particles is found to depend strongly on the nature of the surface over which they flow. For smooth surfaces, flow occurs primarily by sliding at the surface, and little or no shear is introduced into the stream. In the case of highly roughened surfaces consisting of, for example, a stationary layer of the same particles, there appears to be no slip at the surface, and flow occurs entirely by shear within the flowing stream. Surfaces of intermediate roughness lead to flow in which both slip at the surface and shear within the bed contribute significantly.Velocity profiles have been measured experimentally under a variety of conditions, and the effects of such variables as roughness and inclination of the surface, depth of the flowing stream and particle size have been evaluated quantitatively. Empirical relationships have been obtained which describe the flow behavior in all cases studied. 相似文献
17.
H. Boutebila 《Desalination》2009,249(3):1249-1258
This analysis is used to investigate a free flow inclined flat plate solar still.To study the effect of significant parameters on a laminar falling liquid solution over an inclined long flat plate solar still, a mathematical two dimensional flow analysis is carried out based on continuity, momentum and energy equations for liquid and vapor phases together with the interface. As far as the liquid film is concerned, the velocity, film thickness, pressure, temperature and the hourly evaporated water volume profiles are found. It is shown that the significant parameters which affect the solar still are the initial film thickness (i.e, the initial mass flow rate), the plate inclination, the still length and the absorber heat flux (i.e., the solar radiation reaching the plate). It is also shown that the variation in liquid film thickness down the still has a significant effect on the evaporation rate (i.e., the condensed water) and should not be neglected particularly in the case of a long inclined solar still. 相似文献
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20.
在斜面上布置管路时,虽然设计上满足了管子自重下滑力与其摩擦力的平衡,但工程实际中管子仍会下滑从而造成变形破坏。详细分析了破坏的原因,认为是由于温差引起管子在斜面上蠕动而造成的。 相似文献