Linear Stability Analysis of Falling Liquid Films

1974 ◽  
Vol 13 (3) ◽  
pp. 289-291 ◽  
Author(s):  
E. Marschall ◽  
R. Salazar
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Liquid Films ◽  
Falling Liquid Films

Effect of Longitudinal Minigrooves on Flow Stability and Wave Characteristics of Falling Liquid Films

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Klaus Helbig ◽  
Ralph Nasarek ◽  
Tatiana Gambaryan-Roisman ◽  
Peter Stephan
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Film Flow ◽  
Flow Direction ◽  
Wave Theory ◽  
Liquid Films ◽  
Falling Film ◽  
Wave Characteristics ◽  
Falling Liquid Films

Falling liquid films are used in many industrial apparatuses. In many cases the film flow along a wall with topography is considered advantageous for intensification of the heat and mass transport. One of the promising types of the wall topography for the heat transfer intensification is comprised of minigrooves aligned along the main flow direction. The wall topography affects the development of wavy patterns on the liquid-gas interface. Linear stability analysis of the falling film flow based on the long-wave theory predicts that longitudinal grooves lead to the decrease in the disturbance growth rate and therefore stabilize the film. The linear stability analysis also predicts that the frequency of the fastest growing disturbance mode and the wave propagation velocity decrease on a wall with longitudinal minigrooves in comparison with a smooth wall. In the present work the effect of the longitudinal minigrooves on the falling film flow is studied experimentally. We use the shadow method and the confocal chromatic sensoring technique to study the wavy structure of falling films on smooth walls and on walls with longitudinal minigrooves. The measured film thickness profiles are used to quantify the effect of the wall topography on wave characteristics. The experimental results confirm the theoretical predictions.

AC electrohydrodynamic instabilities in thin liquid films

2009 ◽  
Vol 631 ◽  
pp. 255-279 ◽  
Author(s):  
SCOTT A. ROBERTS ◽  
SATISH KUMAR
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Electric Fields ◽  
Linear Stability Analysis ◽  
Floquet Theory ◽  
Thin Liquid Film ◽  
Liquid Films ◽  
Dielectric Films ◽  
High Frequencies ◽  
Ac Electric Fields

When DC electric fields are applied to a thin liquid film, the interface may become unstable and form a series of pillars. In this paper, we apply lubrication theory to examine the possibility of using AC electric fields to exert further control over the size and shape of the pillars. For perfect dielectric films, linear stability analysis shows that the influence of an AC field can be understood by considering an effective DC field. For leaky dielectric films, Floquet theory is applied to carry out the linear stability analysis, and it reveals that high frequencies may be used to inhibit the accumulation of interfacial free charge, leading to a lowering of growth rates and wavenumbers. Nonlinear simulations confirm the results of the linear stability analysis while also uncovering additional mechanisms for tuning overall pillar height and width. The results presented here may be of interest for the controlled creation of surface topographical features in applications such as patterned coatings and microelectronics.

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