THE ANALYSIS OF THE BINARY HOMOGENEOUS SOLUTION FILM BEHAVIOR UNDER THERMAL ACTION

2021 ◽  
Vol 7 (2) ◽  
pp. 43-59
Author(s):  
Kseniia A. BORODINA
Keyword(s):  
Free Surface ◽  
Local Heating ◽  
Thin Liquid Film ◽  
Volatile Component ◽  
Experimental Studies ◽  
Homogeneous Solution ◽  
Liquid Films ◽  
Surface Shape ◽  
Pressure Jump ◽  
Capillary Flows

Studying the processes occurring in liquid films under thermal influence allows improving a variety of technological systems, since a thin layer aids in providing a high intensity of heat and mass transfer and a significant surface of phase contact with a minimum liquid consumption. Many Russian and international works wrote about theoretical and experimental studies of film flows, though paid insufficient attention to the study of the behavior of films of a binary homogeneous solution. This article studies the behavior of a thin liquid film containing a volatile component during local heating of a solid horizontal substrate. The presented calculations were performed for an aqueous solution of isopropanol. The author describes the formation of a specific surface shape, which is formed with a sufficient increase in the substrate temperature and the initial film thickness — the so-called “liquid drop”, separated from the main volume of the liquid by a thin extended layer, which is explained by the sequential occurrence of thermal and concentration-capillary flows. The results show a significant influence of the Laplace pressure jump on the character of the entire process. In addition, the cooling of the substrate leads to multidirectional flows, but in the opposite directions. The analysis of the functions of the temperature of the film free surface, the volatile component concentration in the solution, and the vapor density over the free surface at different times is carried out. The velocity field in liquid and gas during the evolution of thermocapillary and concentration-capillary flows is illustrated.

MODEL OF THE EVOLUTION OF A BINARY HOMOGENEOUS SOLUTION FILM UNDER THERMAL ACTION

2020 ◽  
Vol 6 (4) ◽  
pp. 48-68
Author(s):  
Kseniia A. Borodina
Keyword(s):  
Saturated Vapor ◽  
Vertical Wall ◽  
Volatile Component ◽  
Homogeneous Solution ◽  
Thermal Action ◽  
Liquid Films ◽  
Medical Diagnostics ◽  
Liquid Volume ◽  
Pressure Jump ◽  
Uneven Heating

The research on the motion of liquid films has recently become increasingly important, which is associated with the expanding field of their practical application. For example, the promising methods of cooling include the technologies based on the evaporation of a thin layer of liquid. Based on the Marangoni effects, optical elements of medical diagnostics systems can be developed, the performance of which can be quickly reconfigured for the necessary tasks in comparison with the currently used movable lenses. Many authors in Russia and abroad are engaged in a comprehensive theoretical study of film flows, which should not lag behind the studies of the possibilities of their application. At the same time, the motion of films of a binary homogeneous solution has not been studied enough, and this is the object of this study. This paper considers the behavior of a liquid film containing a volatile component when it is heated. The importance of taking into account the Laplace pressure jump at the interface is indicated, as well as the effect of surface curvature on the saturated vapor pressure. Formulation of the problem is formalized in a limited volume. The stability of the numerical scheme was investigated by the harmonics method. The results confirm the reliability of the model by testing it on a number of problems with analytical solutions: preservation of a liquid volume when a film in a gravity field touches a vertical wall; determination of the profile of the liquid layer with uneven heating of the substrate; mass balance at uniform heating and cooling.

Three-dimensional surfactant-covered flows of thin liquid films on rotating cylinders

2018 ◽  
Vol 844 ◽  
pp. 61-91 ◽  
Author(s):  
Weihua Li ◽  
Satish Kumar
Keyword(s):  
Free Surface ◽  
Flow Visualization ◽  
Evolution Equations ◽  
Thin Liquid Film ◽  
Three Dimensional ◽  
Axial Direction ◽  
Liquid Films ◽  
Practical Applications ◽  
Rotation Rates ◽  
Visualization Experiments

The coating of discrete objects is an important but poorly understood step in the manufacturing of a broad variety of products. An important model problem is the flow of a thin liquid film on a rotating cylinder, where instabilities can arise and compromise coating uniformity. In this work, we use lubrication theory and flow visualization experiments to study the influence of surfactant on these flows. Two coupled evolution equations describing the variation of film thickness and concentration of insoluble surfactant as a function of time, the angular coordinate and the axial coordinate are solved numerically. The results show that surface-tension forces arising from both axial and angular variations in the angular curvature drive flows in the axial direction that tend to smooth out free-surface perturbations and lead to a stable speed window in which axial perturbations do not grow. The presence of surfactant leads to Marangoni stresses that can cause the stable speed window to disappear by driving flow that opposes the stabilizing flow. In addition, Marangoni stresses tend to reduce the spacing between droplets that form at low rotation rates, and reduce the growth rate of rings that form at high rotation rates. Flow visualization experiments yield observations that are qualitatively consistent with predictions from linear stability analysis and the simulation results. The visualizations also indicate that surfactants tend to suppress dripping, slow the development of free-surface perturbations, and reduce the shifting and merging of rings and droplets, allowing more time for solidifying coatings in practical applications.

Viscous Liquid Films in Nonradial Rotating Pipes[1]

1980 ◽  
Vol 102 (2) ◽  
pp. 231-235
Author(s):  
J. T. Dakin
Keyword(s):  
Liquid Film ◽  
Centrifugal Force ◽  
Radial Direction ◽  
Thin Liquid Film ◽  
Film Surface ◽  
Liquid Films ◽  
Surface Shape ◽  
Pipe Axis ◽  
Viscous Forces ◽  
Secondary Motion

The dynamics of a thin liquid film flowing through a rotating pipe are studied. The flow is assumed to be fully developed and dominated by viscous forces. The fluid is drawn along the pipe by the centrifugal force. The pipe is tilted with respect to the radial direction so that the centrifugal force has a component perpendicular to the pipe axis. An approximate dynamic model is developed which describes the film surface shape, and which includes the effects of the Coriolis-induced secondary motion. Several simple, interesting solutions are presented.

scholarly journals Visualization of Surface Acoustic Waves in Thin Liquid Films

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
R. W. Rambach ◽  
J. Taiber ◽  
C. M. L. Scheck ◽  
C. Meyer ◽  
J. Reboud ◽  
...  
Keyword(s):  
Liquid Film ◽  
Acoustic Waves ◽  
Low Cost ◽  
Thin Liquid Film ◽  
Surface Acoustic Waves ◽  
Liquid Films ◽  
Theoretical Description ◽  
Propagation Path ◽  
Microfluidic Channels ◽  
Potential Applications

Abstract We demonstrate that the propagation path of a surface acoustic wave (SAW), excited with an interdigitated transducer (IDT), can be visualized using a thin liquid film dispensed onto a lithium niobate (LiNbO3) substrate. The practical advantages of this visualization method are its rapid and simple implementation, with many potential applications including in characterising acoustic pumping within microfluidic channels. It also enables low-cost characterisation of IDT designs thereby allowing the determination of anisotropy and orientation of the piezoelectric substrate without the requirement for sophisticated and expensive equipment. Here, we show that the optical visibility of the sound path critically depends on the physical properties of the liquid film and identify heptane and methanol as most contrast rich solvents for visualization of SAW. We also provide a detailed theoretical description of this effect.

Marangoni instability of a thin liquid film heated from below by a local heat source

2003 ◽  
Vol 475 ◽  
pp. 377-408 ◽  
Author(s):  
SERAFIM KALLIADASIS ◽  
ALLA KIYASHKO ◽  
E. A. DEMEKHIN
Keyword(s):  
Free Surface ◽  
Liquid Film ◽  
Discrete Spectrum ◽  
Essential Spectrum ◽  
Marangoni Number ◽  
Thin Liquid Film ◽  
Nonlinear Partial Differential Equations ◽  
Spanwise Direction ◽  
Surface Boundary ◽  
Integral Boundary

We consider the motion of a liquid film falling down a heated planar substrate. Using the integral-boundary-layer approximation of the Navier–Stokes/energy equations and free-surface boundary conditions, it is shown that the problem is governed by two coupled nonlinear partial differential equations for the evolution of the local film height and temperature distribution in time and space. Two-dimensional steady-state solutions of these equations are reported for different values of the governing dimensionless groups. Our computations demonstrate that the free surface develops a bump in the region where the wall temperature gradient is positive. We analyse the linear stability of this bump with respect to disturbances in the spanwise direction. We show that the operator of the linearized system has both a discrete and an essential spectrum. The discrete spectrum bifurcates from resonance poles at certain values of the wavenumber for the disturbances in the transverse direction. The essential spectrum is always stable while part of the discrete spectrum becomes unstable for values of the Marangoni number larger than a critical value. Above this critical Marangoni number the growth rate curve as a function of wavenumber has a finite band of unstable modes which increases as the Marangoni number increases.

Confined thermo-capillary flows in a double free-surface film with small Marangoni Numbers

2014 ◽  
Vol 78 ◽  
pp. 1060-1067 ◽  
Author(s):  
B. Messmer ◽  
T. Lemee ◽  
K. Ikebukuro ◽  
I. Ueno ◽  
R. Narayanan
Keyword(s):  
Free Surface ◽  
Surface Film ◽  
Capillary Flows

Foam mechanics: spontaneous rupture of thinning liquid films with Plateau borders

2010 ◽  
Vol 658 ◽  
pp. 63-88 ◽  
Author(s):  
ANTHONY M. ANDERSON ◽  
LUCIEN N. BRUSH ◽  
STEPHEN H. DAVIS
Keyword(s):  
Thin Liquid Film ◽  
Liquid Films ◽  
Two Dimensions ◽  
Metallic Foams ◽  
Film Rupture ◽  
Drainage Flow ◽  
Curved Boundaries ◽  
Capillary Suction ◽  
Aqueous Foams ◽  
Foam Mechanics

Spontaneous film rupture from van der Waals instability is investigated in two dimensions. The focus is on pure liquids with clean interfaces. This case is applicable to metallic foams for which surfactants are not available. There are important implications in aqueous foams as well, but the main differences are noted. A thin liquid film between adjacent bubbles in a foam has finite length, curved boundaries (Plateau borders) and a drainage flow from capillary suction that causes it to thin. A full linear stability analysis of this thinning film shows that rupture occurs once the film has thinned to ‘tens’ of nanometres, whereas for a quiescent film with a constant and uniform thickness, rupture occurs when the thickness is ‘hundreds’ of nanometres. Plateau borders and flow are both found to contribute to the stabilization. The drainage flow leads to several distinct qualitative features as well. In particular, unstable disturbances are advected by the flow to the edges of the thin film. As a result, the edges of the film close to the Plateau borders appear more susceptible to rupture than the centre of the film.

scholarly journals The oscillatory longwave Marangoni convection in a thin film heated from below

2021 ◽  
Vol 3 (10) ◽  
Author(s):  
Anna Samoilova ◽  
Alexander Nepomnyashchy
Keyword(s):  
Thin Film ◽  
Free Surface ◽  
Large Scale ◽  
Marangoni Convection ◽  
Thin Liquid Film ◽  
Stationary Regime ◽  
Oscillatory Regime ◽  
Oscillatory Flows ◽  
The Past ◽  
Heating From Below

Abstract A novel type of Marangoni convection was predicted theoretically a decade ago. The thin liquid film atop a substrate of low thermal conductivity was considered. In the case of heating from below, the Marangoni convection emerges not only in a conventional stationary regime, but also as oscillatory flows. Specifically, the oscillatory Marangoni convection emerges if (1) the heat flux from the free surface is small, and (2) the large-scale deformation of the free surface is allowed. During the past decade, this novel Marangoni convection was detected and investigated in several other theoretical works. The review discusses the recent achievements in studying the oscillatory Marangoni convection in a thin film heated from below. The guiding data for observation of the oscillatory regime are also provided.

scholarly journals Study of non-isothermal liquid evaporation in synthetic micro-pore structures with hybrid lattice Boltzmann model

2019 ◽  
Vol 866 ◽  
pp. 33-60 ◽  
Author(s):  
Feifei Qin ◽  
Luca Del Carro ◽  
Ali Mazloomi Moqaddam ◽  
Qinjun Kang ◽  
Thomas Brunschwiler ◽  
...  
Keyword(s):  
Lattice Boltzmann ◽  
Evaporation Rate ◽  
Experimental Studies ◽  
Liquid Films ◽  
Lattice Boltzmann Model ◽  
Layer By Layer ◽  
Pore Structures ◽  
Liquid Evaporation ◽  
Cooling Effects ◽  
Boltzmann Model

Non-isothermal liquid evaporation in micro-pore structures is studied experimentally and numerically using the lattice Boltzmann method. A hybrid thermal entropic multiple-relaxation-time multiphase lattice Boltzmann model (T-EMRT-MP LBM) is implemented and validated with experiments of droplet evaporation on a heated hydrophobic substrate. Then liquid evaporation is investigated in two specific pore structures, i.e. spiral-shaped and gradient-shaped micro-pillar cavities, referred to as SMS and GMS, respectively. In SMS, the liquid receding front follows the spiral pattern; while in GMS, the receding front moves layer by layer from the pillar rows with large pitch to the rows with small one. Both simulations agree well with experiments. Moreover, evaporative cooling effects in liquid and vapour are observed and explained with simulation results. Quantitatively, in both SMS and GMS, the change of liquid mass with time coincides with experimental measurements. The evaporation rate generally decreases slightly with time mainly because of the reduction of liquid–vapour interface. Isolated liquid films in SMS increase the evaporation rate temporarily resulting in local peaks in evaporation rate. Reynolds and capillary numbers show that the liquid internal flow is laminar and that the capillary forces are dominant resulting in menisci pinned to the pillars. Similar Péclet number is found in simulations and experiments, indicating a diffusive type of heat, liquid and vapour transport. Our numerical and experimental studies indicate a method for controlling liquid evaporation paths in micro-pore structures and maintaining high evaporation rate by specific geometry designs.

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