Occurrence of Finite-Amplitude Surface Waves on Falling Liquid Films

1970 ◽  
Vol 13 (8) ◽  
pp. 1918 ◽  
Author(s):  
B. Gjevik
Keyword(s):  
Surface Waves ◽  
Liquid Films ◽  
Finite Amplitude ◽  
Falling Liquid Films

Wave Effects on the Transport to Falling Laminar Liquid Films

1978 ◽  
Vol 100 (1) ◽  
pp. 143-147 ◽  
Author(s):  
R. A. Seban ◽  
A. Faghri
Keyword(s):  
Surface Waves ◽  
Liquid Films ◽  
Wave Effects ◽  
Falling Liquid Films ◽  
The Waves ◽  
Film Absorption ◽  
Existing Data

Existing data for the transport to falling liquid films are reviewed to show the effect of augmented transport by surface waves in the cases of heating of the film, absorption by the film from the surrounding gas, and evaporation from the film. It is shown that, while the effect of the waves can be partially rationalized, the nature of the waves themselves is not known exactly enough to provide a consistent specification for all of the available data.

Three-dimensional flow structures in laminar falling liquid films

2014 ◽  
Vol 743 ◽  
pp. 75-123 ◽  
Author(s):  
Georg F. Dietze ◽  
W. Rohlfs ◽  
K. Nährich ◽  
R. Kneer ◽  
B. Scheid
Keyword(s):  
Surface Waves ◽  
Stokes Equations ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Liquid Films ◽  
Capillary Waves ◽  
Flow Structures ◽  
Two Dimensional ◽  
Viscous Forces ◽  
Falling Liquid Films

AbstractFull numerical simulations of the Navier–Stokes equations for four cases of vertically falling liquid films with three-dimensional surface waves have been performed. Flow conditions are based on several previous experimental studies where the streamwise and spanwise wavelengths were imposed, which we exploit by simulating periodic wave segments. The considered flows are laminar but approach conditions at which intermittent wave-induced turbulence has been observed elsewhere. Working liquids range from water to silicone oil and cover a large interval of the Kapitza number ($\textit {Ka}=18\mbox{--}3923$), which relates capillary to viscous forces. Simulations were performed on a supercomputer, using a finite-volume code and the volume of fluid and continuum surface force methods to account for the multiphase nature of the flow. Our results show that surface waves, consisting of large horseshoe-shaped wave humps concentrating most of the liquid and preceded by capillary ripples on a thin residual film, segregate the flow field into two regions: an inertia-dominated one in the large humps, where the local Reynolds number is up to five times larger than its mean value, and a visco-capillary region, where capillary and/or viscous forces dominate. In the inertial region, an intricate structure of different-scale vortices arises, which is more complicated than film thickness variations there suggest. Conversely, the flow in the visco-capillary region of large-$\textit {Ka} $ fluids is entirely governed by the local free-surface curvature through the action of capillary forces, which impose the pressure distribution in the liquid film. This results in flow separation zones underneath the capillary troughs and a spanwise cellular flow pattern in the region of capillary wave interference. In some cases, capillary waves bridge the large horseshoe humps in the spanwise direction, coupling the two aforementioned regions and leading the flow to oscillate between three- and two-dimensional wave patterns. This persists over long times, as we show by simulations with the low-dimensional model of Scheid et al. (J. Fluid Mech., vol. 562, 2006, pp. 183–222) after satisfactory comparison with our direct simulations at short times. The governing mechanism is connected to the bridging capillary waves, which drain liquid from the horseshoe humps, decreasing their amplitude and wave speed and causing them to retract in the streamwise direction. Overall, it is observed that spanwise flow structures (not accounted for in two-dimensional investigations) are particularly complex due to the absence of gravity in this direction.

HEAT TRANFER PHENOMENA IN FALLING LIQUID FILMS: A SYNERGISTIC EXPERIMENTAL AND COMPUTATIONAL STUDY

2018 ◽  
Author(s):  
Alexandros Charogiannis ◽  
Fabian Denner ◽  
Berend G. M. van Wachem ◽  
Serafim Kalliadasis ◽  
Christos N. Markides
Keyword(s):  
Computational Study ◽  
Liquid Films ◽  
Falling Liquid Films

Dynamics of Developing Laminar Non-Newtonian Falling Liquid Films With Free Surface

1978 ◽  
Vol 45 (1) ◽  
pp. 19-24 ◽  
Author(s):  
V. Narayanamurthy ◽  
P. K. Sarma
Keyword(s):  
Liquid Film ◽  
Power Law ◽  
Mathematical Formulation ◽  
Liquid Films ◽  
Interfacial Shear ◽  
Newtonian Liquid ◽  
Power Law Model ◽  
Falling Liquid Film ◽  
Falling Liquid Films ◽  
Special Case

The dynamics of accelerating, laminar non-Newtonian falling liquid film is analytically solved taking into account the interfacial shear offered by the quiescent gas adjacent to the liquid film under adiabatic conditions of both the phases. The results indicate that the thickness of the liquid film for the assumed power law model of the shear deformation versus the shear stress is influenced by the index n, the modified form of (Fr/Re). The mathematical formulation of the present analysis enables to treat the problem as a general type from which the special case for Newtonian liquid films can be derived by equating the index in the power law to unity.

Capillary Flow Separation in 2- and 3-Dimensional Laminar Falling Liquid Films

2010 ◽  
Author(s):  
Georg F. Dietze ◽  
Reinhold Kneer
Keyword(s):  
Heat Transfer ◽  
Flow Separation ◽  
Capillary Flow ◽  
Capillary Wave ◽  
Liquid Films ◽  
Transport Processes ◽  
Gravitational Acceleration ◽  
3 Dimensional ◽  
Wave Region ◽  
Falling Liquid Films

Due to the selective use of liquid films in specialized technical equipment (e.g. new generation nuclear reactors), a fundamental understanding of underlying momentum and heat transport processes inside these thin liquid layers (with a thickness of approximately 0.5 mm) is required. In particular, the influence of surface waves (which develop due to the film’s natural instability) on these transport processes is of interest. For a number of years, experimental and numerical observations in wavy falling liquid films have suggested that momentum and heat transfer in the capillary wave region, preceding large wave humps, undergo drastic modulations. Indeed, some results have indicated that upward flow, i.e. counter to the gravitational acceleration, takes place in this region. Further, evidence of a substantial increase in wall-side and interfacial transfer coefficients has also been noted. Recently, Dietze et al. [1,2] have established that flow separation takes place in the capillary wave region of 2-dimensional laminar falling liquid films, partially explaining the above mentioned observations. Thereby, it was shown that the strong third order deformation (i.e. change in curvature) of the liquid-gas interface in the capillary wave region causes an adverse pressure gradient sufficiently large to induce flow detachment from the wall. In the present paper, a detailed experimental and numerical account of the capillary flow separation’s kinematics and governing dynamics as well as its effect on heat transfer for two different 2-dimensional flow conditions is presented. Experimentally, velocity measurements (using Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV)) and film thickness measurements (using a Confocal Chromatic Imaging technique) were performed in a specifically designed optical test setup. On the numerical side, simulations of the full Navier-Stokes equations as well as the energy equation using the Volume of Fluid (VOF) method were performed. In addition to the 2-dimensional investigations, the characteristics of capillary flow separation under 3-dimensional wave dynamics were studied based on the 3-dimensional numerical simulation of a water film, which was previously investigated experimentally by Park and Nosoko [3]. Results show that flow separation persists over a wide area of the 3-dimensional capillary wave region, with multiple capillary separation eddies occurring in the shape of vortex tubes. In addition, strong spanwise flow induced by the same governing mechanism is shown to occur in this region, which could explain the drastic intensification of transfer to 3-dimensional liquid films.

Sign in / Sign up

Export Citation Format

Share Document