Long-Wave Interfacial Instabilities in Viscous Liquid Films

1994 ◽  
pp. 79-97
Author(s):  
Marc K. Smith
Keyword(s):  
Viscous Liquid ◽  
Liquid Films ◽  
Interfacial Instabilities ◽  
Long Wave

scholarly journals Falling liquid films with blowing and suction

2015 ◽  
Vol 787 ◽  
pp. 292-330 ◽  
Author(s):  
Alice B. Thompson ◽  
Dmitri Tseluiko ◽  
Demetrios T. Papageorgiou
Keyword(s):  
Travelling Waves ◽  
Liquid Films ◽  
Industrial Applications ◽  
Steady States ◽  
Interfacial Instabilities ◽  
Vertical Control ◽  
Long Wave ◽  
Thin Film Equations ◽  
Wide Range ◽  
Falling Liquid Films

Flow of a thin viscous film down a flat inclined plane becomes unstable to long-wave interfacial fluctuations when the Reynolds number based on the mean film thickness becomes larger than a critical value (this value decreases as the angle of inclination to the horizontal increases, and in particular becomes zero when the plate is vertical). Control of these interfacial instabilities is relevant to a wide range of industrial applications including coating processes and heat or mass transfer systems. This study considers the effect of blowing and suction through the substrate in order to construct from first principles physically realistic models that can be used for detailed passive and active control studies of direct relevance to possible experiments. Two different long-wave, thin-film equations are derived to describe this system; these include the imposed blowing/suction as well as inertia, surface tension, gravity and viscosity. The case of spatially periodic blowing and suction is considered in detail and the bifurcation structure of forced steady states is explored numerically to predict that steady states cease to exist for sufficiently large suction speeds since the film locally thins to zero thickness, giving way to dry patches on the substrate. The linear stability of the resulting non-uniform steady states is investigated for perturbations of arbitrary wavelength, and any instabilities are followed into the fully nonlinear regime using time-dependent computations. The case of small amplitude blowing/suction is studied analytically both for steady states and their stability. Finally, the transition between travelling waves and non-uniform steady states is explored as the amplitude of blowing and suction is increased.

The mechanism for the long-wave instability in thin liquid films

1990 ◽  
Vol 217 ◽  
pp. 469-485 ◽  
Author(s):  
Marc K. Smith
Keyword(s):  
Physical Mechanism ◽  
Thin Liquid Film ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
The Other ◽  
Wave Instability ◽  
Inclined Plane ◽  
Long Wave ◽  
The Many ◽  
Large Groups

A physical mechanism for the long-wave instability of thin liquid films is presented. We show that the many diverse systems that exhibit this instability can be classified into two large groups. Each group is studied using the model of a thin liquid film with a deformable top surface flowing down a rigid inclined plane. In the first group, the top surface has an imposed stress, while in the other, an imposed velocity. The proposed mechanism shows how the details of the energy transfer from the basic state to the disturbance are handled differently in each of these cases, and how a common growth mechanism produces the unstable motion of the disturbance.

scholarly journals Precise Determination of Liquid Layer Thickness with Downward Annular Two-Phase Gas-Very Viscous Liquid Flow

Energies ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 6529
Author(s):  
Krystian Czernek ◽  
Stanisław Witczak
Keyword(s):  
Viscous Liquid ◽  
Liquid Layer ◽  
Liquid Flow ◽  
Liquid Films ◽  
Measuring System ◽  
Image Analysis System ◽  
Oil Viscosity ◽  
Two Phase ◽  
Study Results

The paper presents the characteristics of the original optoelectronic system for measuring the values of hydrodynamics of two-phase downward gas-very viscous liquid flow. The measurement methods and results of the research on selected values describing gas–oil two-phase flow are presented. The study was conducted in vertical pipes with diameters of 12.5, 16, 22, and 54 mm. The research was conducted with the superficial velocities of air jg = 0–29.9 m/s and oil jl = 0–0.254 m/s, which corresponded to the values of gas stream density gg = (0–37.31) kg/(m2s) and of liquid gl = (0.61–226.87) kg/(m2s), in order to determine the influence of air and oil streams on the character of liquid films. The variations in oil viscosity were applied in the range ηl = (0.055–1.517) Pas. The study results that were obtained with optical probes along with computer image analysis system revealed vast research opportunities in terms of the identification of gas–liquid two-phase downward flow structures that were generated as well as the determination of the thickness of liquid film with various level of interfacial surface area undulation. The designed and constructed proprietary measuring system is also useful for testing the liquid layer by determining the parameters of the resulting waves. It is considered that the apparatus system that is presented in the article is the most effective in examining the properties of liquid layers of oil and other liquids with low electrical conductivity and a significant degree of monochromatic light absorption. In view of noninvasive technique of measuring characteristic values of liquid films being formed, the above measuring system is believed to be very useful for industry in the diagnostics of the apparatus employing such flows.

scholarly journals Dynamics of liquid films on vertical fibres in a radial electric field

2014 ◽  
Vol 752 ◽  
pp. 66-89 ◽  
Author(s):  
Zijing Ding ◽  
Jinlong Xie ◽  
Teck Neng Wong ◽  
Rong Liu
Keyword(s):  
Electric Field ◽  
Wave Speed ◽  
Nonlinear Evolution ◽  
Radial Electric Field ◽  
Liquid Films ◽  
Asymptotic Model ◽  
Nonlinear Behaviour ◽  
Wave Instability ◽  
Long Wave ◽  
Evolution Study

AbstractThe long-wave behaviour of perfectly conducting liquid films flowing down a vertical fibre in a radial electric field was investigated by an asymptotic model. The validity of the asymptotic model was verified by the fully linearized problem, which showed that results were in good agreement in the long-wave region. The linear stability analysis indicated that, when the ratio (the radius of the outer cylindrical electrode over the radius of the liquid film) $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\beta <e$, the electric field enhanced the long-wave instability; when $\beta >e$, the electric field impeded the long-wave instability; when $\beta =e$, the electric field did not affect the long-wave instability. The nonlinear evolution study of the asymptotic model compared well with the linear theory when $\beta <e$. However, when $\beta =e$, the nonlinear evolution study showed that the electric field enhanced the instability which may cause the interface to become singular. When $\beta >e$, the nonlinear evolution studies showed that the influence of the electric field on the nonlinear behaviour of the interface was complex. The electric field either enhanced or impeded the interfacial instability. In addition, an interesting phenomenon was observed by the nonlinear evolution study that the electric field may cause an oscillation in the amplitude of permanent waves when $\beta \ge e$. Further study on steady travelling waves was conducted to reveal the influence of electric field on the wave speed. Results showed that the electric field either increased or decreased the wave speed as well as the wave amplitude and flow rate. In some situations, the wave speed may increase/decrease while its amplitude decreased/increased as the strength of the external electric field increased.

scholarly journals Stability of liquid films down an inclined plane

2006 ◽  
Vol 28 (4) ◽  
pp. 219-224
Author(s):  
Phan Thi Thu Phuong ◽  
Tran Van Tran
Keyword(s):  
Experimental Data ◽  
Finite Difference ◽  
Finite Difference Method ◽  
Linear Stability ◽  
Viscous Liquid ◽  
Difference Method ◽  
Liquid Films ◽  
Inclined Plane ◽  
Wave Numbers

In this paper, the problem of linear stability of viscous liquid films down an inclined plane is solved by finite difference method. It is applicable for moderate values of Reynolds and wave numbers. The obtained results by this method is compared with ones of some papers and with experimental data.

scholarly journals Designing soft materials with interfacial instabilities in liquid films

2018 ◽  
Vol 9 (1) ◽  
Author(s):  
J. Marthelot ◽  
E. F. Strong ◽  
P. M. Reis ◽  
P.-T. Brun
Keyword(s):  
Soft Materials ◽  
Liquid Films ◽  
Interfacial Instabilities

scholarly journals Viscous liquid films on a porous vertical cylinder: Dynamics and stability

2013 ◽  
Vol 25 (6) ◽  
pp. 064101 ◽  
Author(s):  
Zijing Ding ◽  
Teck Neng Wong ◽  
Rong Liu ◽  
Qiusheng Liu
Keyword(s):  
Viscous Liquid ◽  
Vertical Cylinder ◽  
Liquid Films
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