Behavior Of Liquid Film Research Articles

C232 ガス溶解に伴う三相界線近傍の液膜挙動に関する研究(界面)

C232 ガス溶解に伴う三相界線近傍の液膜挙動に関する研究(界面)

Effect of mass transfer on the film drainage between colliding drops

The influence of mass transfer on the drainage behaviour of the thin liquid film between two drops immersed in another liquid colliding at constant approach velocity has been studied experimentally. The liquid–liquid system used is glycerol in silicone oil. The transferred solute is acetone and the volume concentration difference across the interface ranges from 1 to 5%. The film thickness evolution has been measured using a laser interferometry technique. The direction of mass transfer (from the drops towards the film phase and inversely) has been investigated and the results compared to the case with no mass transfer [E. Klaseboer, J.P. Chevaillier, C. Gourdon, O. Masbernat, J. Colloid Interface Sci. 229 (2000) 274–285]. When the solute transfers from the drops towards the continuous phase, the drainage rate is significantly higher than in the case with no mass transfer. This result is interpreted as a consequence of the mass transfer induced surface mobility in the film region (the so-called Marangoni effect) due to localized surface tension differences. This effect has been demonstrated by the visualization of the flow patterns in the drops and in the film phase (using a particle tracer technique). In this case, the slope of the film height as a function of time seems to be independent of the approach velocity condition imposed on the drop and appears to be controlled by the interfacial tension gradient. In the opposite case, when the solute transfers from the continuous phase towards the drops, the film drainage rate is lowered with respect to the case of no mass transfer, goes to zero or even changes its sign depending on the mass transfer intensity. The results also show that in the range of solute concentration studied, the effect of mass transfer on the film drainage process takes place at large distances compared to the scales at which lubrication theory is valid.

Hybrid Particle/Grid Method for Predicting Motion of Micro- and Macrofree Surfaces

We developed a method of hybrid particle/cubic interpolated propagation (CIP) to predict the motion of micro- and macrofree surfaces within gas-liquid flows. Microfree surfaces (smaller than the grid sizes) were simulated with the particle method, and macrofree surfaces (larger than the grid sizes) were simulated with the grid method (CIP is a kind of grid method). With the hybrid, velocities given by the advection part of the particle method were combined with those given by the advection part of CIP. Furthermore, the particles used with the particle method were assigned near the macrofree surfaces by using the volume fraction of liquid that was calculated with CIP. The method we developed was used to predict the collapse of a liquid column. Namely, it was simultaneously able to predict both large deformation in the liquid column and its fragmentation, and the predicted configurations for the liquid column agreed well with the experimentally measured ones. It was also used to predict the behavior of liquid films at the outlet of a fuel injector used for automobile engines. The particle method in the simulation was mainly used for liquid films in the air region and the grid method was used for the other regions to shorten the computational time. The predicted profile of the liquid film was very sharp in the air region where the liquid film became thinner than the grid sizes; there was no loss of liquid film with numerical diffusion.

On the Rayleigh–Taylor instability for confined liquid films with injection through the bounding surfaces

An experimental and numerical investigation has been conducted to evaluate the hydrodynamic characteristics of a thin liquid film bounded by a downward-facing flat wall through which the liquid is continually injected. Both horizontal and inclined surfaces have been examined. The effect of different parameters, namely, the film thickness, liquid injection velocity, inclination angle and liquid properties on liquid film behavior have been examined. Non-intrusive optical techniques have been used to follow the transient evolution of the film free surface. Specifically, the frequency of droplet detachment, the size of the detached droplets, and the penetration depth prior to droplet detachment have been measured. These data have been compared against predictions of a mechanistic numerical model based on the level contour reconstruction front tracking method. The numerical model predictions are in good agreement with the experimental data.

New Slip Regimes and the Shape of Dewetting Thin Liquid Films

We compare the flow behavior of liquid polymer films on silicon wafers coated with either octadecyl-(OTS) or dodecyltrichlorosilane (DTS). Our experiments show that dewetting on DTS is significantly faster than on OTS. We argue that this is tied to the difference in the solid/liquid friction. As the film dewets, the profile of the rim advancing into the undisturbed film is monotonically decaying on DTS but has an oscillatory structure on OTS. For the first time we can describe this transition in terms of a lubrication model with a Navier-slip condition for the flow of a viscous Newtonian liquid.

Behavior of ultrathin liquid lubricant films for contact sliders in hard disk drives

In this paper, we describe the behavior of ultrathin liquid lubricant films for contact sliders in hard disk drives. In the experiments, the ultrathin liquid lubricant film behavior is investigated using Zdol and cyclotriphosphazene-terminated PFPE lubricant which have different end groups as a function of lubricant film thickness. The disks are examined with a scanning microellipsometer before and after contact slider experiments. It is found that the lubricant film thickness profiles almost do not change, when the lubricant film thickness is less than one monolayer. It can also be observed that lubricant film thickness instability due to dewetting occurs as a result of slider-disk contacts for the tested lubricants and the films undergo spontaneous redistributions, resulting in significantly nonuniform film thickness profiles, when the lubricant film thickness is thicker than one monolayer. In addition, it is found that the observed behavior of ultrathin liquid lubricant films for cyclotriphosphazine-terminated PFPE lubricant contrasts markedly with that for Zdol. The difference between cyclotriphosphazene-terminated PFPE lubricant and Zdol is only the functional end group. Therefore, it may be concluded that their unstable lubricant behavior depends on the chemical structure of functional end groups.

Investigation of liquid film behavior at the onset of flooding during adiabatic counter-current air–water two-phase flow in an inclined pipe

The liquid film characteristics at the onset of flooding in an inclined pipe (16 mm i.d. and 2.2 m in length) have been investigated experimentally. A constant electric current method and visual observation were utilized to elucidate the flow mechanisms at the onset of flooding. Two mechanisms are clarified to control the flooding in lower flooding and upper flooding, respectively. The lower flooding occurred at lower liquid flow rate and high pipe inclination angle. In this mechanism, the liquid film does not block the pipe cross-section. On the other hand, the upper flooding occurred at higher liquid flow rate and low pipe inclination angle. In this case, blocking of the pipe cross-section by large wave and entrainment plays an important role. The experimental data indicated that there was no reversal motion of liquid film at the onset of flooding during the operation of both lower flooding and upper flooding. The effects of pipe inclination angle on the onset of flooding are also discussed.

Exploratory studies of flowing liquid metal divertor options for fusion-relevant magnetic fields in the MTOR facility

Abstract This paper reports on experimental findings on liquid metal (LM) free surface flows crossing complex magnetic fields. The experiments involve jet and film flows using GaInSn and are conducted at the UCLA MTOR facility. The goal of this study is to understand the magnetohydrodynamics (MHD) features associated with such a free surface flow in a fusion-relevant magnetic field environment, and determine what LM free surface flow option is most suitable for lithium divertor particle pumping and surface heat removal applications in a near-term experimental plasma device, such as NSTX. Experimental findings indicate that a steady transverse magnetic field, even with gradients typical of NSTX outer divertor conditions, stabilizes a LM jet flow—reducing turbulent disturbances and delaying jet breakup. Important insights into the MHD behavior of liquid metal films under NSTX-like environments are also presented. It is possible to establish an uphill liquid metal film flow on a conducting substrate, although the MHD drag experienced by the flow could be strong and cause the flow to pile-up under simulated NSTX magnetic field conditions. The magnetic field changes the turbulent film flow so that wave structures range from 2D column-type surface disturbances at regions of high magnetic field, to ordinary hydrodynamic turbulence wave structures at regions of low field strength at the outboard. Plans for future work are also presented.

Thin liquid films on a slightly inclined heated plate

The behavior of a thin liquid film on a uniformly heated substrate is considered. When the substrate is horizontal and the Marangoni number sufficiently large the film breaks up into a periodic array of drops. When the substrate is slightly inclined this drop-like state slides down the substrate. The relation between these states is discussed and their stability properties with respect to longitudinal perturbations are determined. The results shed light on the multiplicity of states accessible to systems of this type and on the possible transitions among them.

マイクロチャネル式蒸気発生器における薄液膜挙動と伝熱特性(一般セッション 液膜挙動)

マイクロチャネル式蒸気発生器における薄液膜挙動と伝熱特性(一般セッション 液膜挙動)

233 液体膜の水平方向力(摩擦力)発生機構に関する研究 水平方向力と液膜挙動

233 液体膜の水平方向力(摩擦力)発生機構に関する研究 水平方向力と液膜挙動

ON INTERACTION OF A LIQUID FILM WITH AN OBSTACLE

In this paper are discussed mathematical models for the liquid film generated by impinging jets. These models describe only the film shape under special assumptions about processes. Attention is stressed on the interaction of the liquid film with some obstacle. The idea is to generalize existing models and to investigate qualitative behavior of liquid film using numerical experiments. G.I. Taylor [Proc. R. Soc. London Ser. A 253, 313 (1959)] found that the liquid film generated by impinging jets is very sensitive to properties of the wire which was used as an obstacle. The aim of this presentation is to propose a modification of the Taylor's model, which allows to simulate the film shape in cases when the angle between jets is different from 180°. Numerical results obtained by discussed models give two different shapes of the liquid film similar as in Taylors experiments. These two shapes depend on the regime: either droplets are produced close to the obstacle or not. The difference between two regimes becomes larger if the angle between jets decreases. Existence of such two regimes can be very essential for some applications of impinging jets, if the generated liquid film can have a contact with obstacles.

B141 気液相変化過程における表面ぬれ性, 表面張力効果と熱伝達

As is well known, wettability of solid surface and surface tension of liquid have an important role in the field of heat transfer with phase change. Those are remarkably related upon the behavior of liquid thin films that are dominant factor in the heat transfer phenomena. Several phenomena concerning thin liquid film, which is in contact with a heat transfer surface, are discussed. That is, the measurement of condensate thickness for water-ethanol solutal Maragoni dropwise condensation, the condensation of water vapor on outer surface of vertical thin tubes on which the surface tension instability occurs and the vaporization in micro-channel type high density vapor generator.

Surface patterns of laterally extended thin liquid films in three dimensions.

We examine the fully nonlinear behavior of a thin liquid film in three spatial dimension for a large lateral extension. A partial differential equation is used for the spatiotemporal evolution of the height of the film. To take intermolecular forces in the liquid into account, we concentrate on a recently formulated model of Pismen and Pomeau, who derived an expression for the disjoining pressure only from the wetting properties of the fluid. Finally, the motion of a falling film on an inclined plane is studied within this model.

Spinodal dewetting of thin liquid films at soft interfaces

We study theoretically the behavior of nanoscopic liquid films L (thickness e) intercalated between a solid S and a rubber R (elastic modulus μ). Thickness modulations involve a healing length \(\), which results from a competition between elastic and disjoining pressure. With van der Waals interactions, \(\), where a is a molecular size and h0 the rubber capillary length ( \(\), \(\) interfacial tension). If the Hamaker constant of the intercalated liquid is negative, the film dewets by amplification of peristaltic fluctuations (“spinodal dewetting”). The typical size of the \(\) contacts is predicted to scale like \(\) for films of thicknesses \(\). The rise time \(\) of the fastest mode, predicted to scale like \(\), should be very sensitive to the film thickness.

Wetting behaviour of solid and liquid hydrogen films

Adsorbates on strong binding substrates like H 2 on Au show triple-point dewetting. To study this phenomenon in detail, we have reduced the van der Waals interaction of the H 2 films with the Au surface, by preplating the substrate with Ne, Ar or CH 4. From a theoretical model, which considers the deformation of the adsorbate by the attractive van der Waals potential and the lattice mismatch due to different lattice constants of adsorbate and substrate, complete wetting is expected when preplating the substrate. Our experiments show, however, that for all combinations of preplated material the equilibrium H 2 film thickness is – apart from small differences – the same as without preplating. This indicates that the present picture of the triple-point wetting of H 2 is incomplete.

Investigation of Thin Aqueous Films on Silica Using a Modified Interferometric Technique

The thinning behavior of liquid films between free bubbles and silica is investigated using the interferometric technique. Stable films were obtained at higher salt concentrations compared to previous studies because of the improved cleaning procedure. In contrast to the captive bubble technique used in the past, the free bubble method employed more closely approximates such processes as flotation. The results obtained for aqueous films at low and high ionic strengths are in better agreement with theoretical predictions than those in previous studies.

Direct Observation of Foam Film Rupture by Several Types of Antifoams Using a Scanning Laser Microscope

It is well known that the stability of a pseudoemulsion film, a thin liquid film formed between an antifoam particle and air, can be important during defoaming action. We have compared the bursting behavior of a two-dimensional thin liquid film from an aqueous surfactant solution on a glass plate, in which six types of antifoam particles have been dispersed, using laser microscopic techniques. The used antifoams were a silicone oil, a mixed-type antifoam (mixture of silicone oil and hydrophobic solid particles), a hydrophobic silica, and a silicone-based solid antifoam (prepared by interfacial polymerization with oil and water). The antifoaming performance of these six types of antifoams, measured by the glass cylinder shaking test, was in the order: the mixed-type antifoam ≧ the silicone-based solid antifoam > the hydrophobic silica ≧ the silicone oil. Pseudoemulsion film rupture was observed at the film thickness less than 0.1 μm for both the silocone oil and the hydrophobic silica. In the case of particles with rough edges (the silicone-based antifoam), pseudoemulsion film on the top of the particles can be easily ruptured at a convex part of the solid surface. Furthermore, solid particles existing on the surface of an oil droplet in the mixed-type antifoams form marked projections and these projections give rise to distortion of the thinning film. As soon as the distortion of the thinning film took place on the top of the antifoam droplet, the pseudoemulsion film can be instantaneously ruptured. Referring to the antifoaming mechanisms for mixed-type antifoams, both steps from the pseudoemulsion film formation to the lens formation and from the counter pseudoemulsion film formation to the bridge formation would be very fast and cause a very high antifoaming efficiency.

Drainage behaviour of aqueous liquid films on mica

The time dependent thinning of liquid films on a mica substrate has been examined. Aqueous solutions of glycerol, with and without potassium chloride present, were used to form the liquid film. The results were examined in the light of the Reynolds’ equation for hydrodynamic thinning. Several features of the results were as predicted by the equation but the viscosity of the liquid in the film was found to be larger than the bulk value.

Time Variation of the Thin Liquid Film Thickness under the Boiling Bubbles.

The high heat flux region near the burnout heat flux has recently been utilized not only in the nuclear power plant and the boiler system but also in the electrical and laser equipments. Since the mechanisms of the burnout heat flux modeled so far has some unclear aspects in predicting the dynamics behavior of thin liquid films under the boiling bubbles, the thickness of the boiling bubbles has been challenged to measure in this paper. To measure the thickness of the liquid film on the heat transfer surface under the boiling bubble, a capacitance probe has been newly devised. The thickness of the thin liquid film under the boiling bubble was obtained, and the relationship between the bubble shape around the bottom rim and the thickness of the thin liquid film under the bubbles (micro layer) was clarified for predicting the critical heat flux mechanism.