Surface Tension Effects Research Articles

Effect of Sodium Carboxymethyl Cellulose on the Dynamic Wetting Characteristics of the Dust Suppression Droplet Impacting the Coal Surface.

The dynamic wetting behavior of droplets impacting the coal surface directly affects the efficient application of water-based dust suppression materials in coal-related industrial production. In this paper, ultrapure water, Tween-80, and sodium carboxymethyl cellulose are taken as the research objects. Using high-speed photography technology, the spreading, oscillation process, and splash morphology of many kinds of droplets during impacting the coal surface are captured. The effects of viscosity, surface tension, and impact velocity on dynamic wetting characteristics were studied. The results show that with the decrease of surface tension, the retraction and oscillation of droplets are significantly reduced. For the same kind of droplets, the greater the impact velocity, the faster the droplet spread, and the dimensionless maximum spreading coefficient (βmax) and dimensionless steady-state spreading coefficient (βe) of droplets are bigger. With the increase of velocity, the time for different kinds of droplets to reach the βmax increases. At the same impact velocity, βmax and βe of droplets (0.2% Tween-80 + 0.1% sodium carboxymethyl cellulose) are the largest, indicating that adding a small amount of sodium carboxymethyl cellulose can promote droplet spreading. With the increase of sodium carboxymethyl cellulose content, βmax and βe decreased gradually. The results have a great significance to the research, development, and scientific utilization of water-soluble polymer dust inhibitors.

Superhydrophobic/Superoleophilic PDMS/SiO2 Aerogel Fabric Gathering Device for Self-Driven Collection of Floating Viscous Oil

The persistent challenge of removing viscous oil on water surfaces continues to pose a major concern and requires immediate attention. Here, a novel solution has been introduced in the form of a superhydrophobic/superoleophilic PDMS/SiO2 aerogel fabric gathering device (SFGD). The SFGD is based on the adhesive and kinematic viscosity properties of oil, enabling self-driven collection of floating oil on the water surface. The SFGD is able to spontaneously capture the floating oil, selectively filter it, and sustainably collect it into its porous fabric interior through the synergistic effects of surface tension, gravity, and liquid pressure. This eliminates the need for auxiliary operations such as pumping, pouring, or squeezing. The SFGD demonstrates exceptional average recovery efficiencies of 94% for oils with viscosities ranging from 10 to 1000 mPa·s at room temperature, including dimethylsilicone oil, soybean oil, and machine oil. With its facile design, ease of fabrication, high recovery efficiency, excellent reclaiming capabilities, and scalability for multiple oil mixtures, the SFGD represents a significant advancement in the separation of immiscible oil/water mixtures of various viscosities and brings the separation process one step closer to practical application.

Parasitic waves and micro-breaking on highly nonlinear gravity–capillary waves in a convergent channel

Gravity–capillary waves are waves influenced by both the effects of surface tension and gravity; these waves are at small scales with wavelength range from approximately 10 cm to less than 1 cm. Gravity–capillary waves play a significant role in air–sea interactions, and they exhibit much different features compared with gravity waves. They can be observed widely on the sea surface. Parasitic waves (capillary waves generated by and that ride on gravity and/or gravity–capillary waves) and micro-breaking can be observed on the water surface with winds; however, the presence of wind makes it difficult to analyse the mechanisms of the wave itself. In this paper, parasitic waves and micro-breaking on gravity–capillary waves are examined experimentally, both in the absence of wind. Parasitic waves and axisymmetric micro-breaking waves are generated mechanically in a convergent channel, where energy density increases due to spatial convergence. Three experimental techniques are used to measure wave properties: planar laser-induced fluorescence, particle image velocimetry and shadowgraphs. The wave profile evolution and vortices beneath the parasitic waves are studied. The micro-breaking of gravity–capillary waves is observed on a surface with added surfactant. The surfactant increases the Bond number, and makes breaking possible in these small-scale waves. Energy dissipation of parasitic waves and micro-breaking is quantified, and the enhanced dissipation caused by parasitic waves is identified through the experiments. In this study, mechanically generated breaking waves with wavelengths less than 10 cm are studied for the first time, without the effect of wind. The results yield insight into wave characteristics and energy dissipation on the air–sea interface at small scales.

Divergent Stiffness of One-Dimensional Growing Interfaces.

When a spatially localized stress is applied to a growing one-dimensional interface, the interface deforms. This deformation is described by the effective surface tension representing the stiffness of the interface. We present that the stiffness exhibits divergent behavior in the large system size limit for a growing interface with thermal noise, which has never been observed for equilibrium interfaces. Furthermore, by connecting the effective surface tension with a space-time correlation function, we elucidate the mechanism that anomalous dynamical fluctuations lead to divergent stiffness.

The influence of flexible bottom on wave generation by an oscillatory disturbance in the presence of surface tension

The two-dimensional problem of wave generation by a time-harmonic pressure distribution on the surface in a finite-depth ocean is studied in this article. Here, it is considered that the ocean has a flexible base, which is modelled as a thin elastic plate and is governed by the Euler–Bernoulli beam equation. The effect of surface tension at the free surface is also taken into account. Within the framework of the linearised theory of water waves, the initial boundary value problem is solved using the Laplace–Fourier transform technique and the integral form of the free surface elevation is obtained. The method of stationary phase is used to evaluate the asymptotic solutions of the free surface elevation for large time and distance. Different forms of the surface elevation have been demonstrated graphically for variation of parameters in a number of figures, and appropriate conclusions are drawn. Moreover, the dispersion relation associated with the wave motion is also derived and analysed using contour plots to understand the characteristics of the roots. Further, the phase and group velocities of the wave motion have also been investigated in this study for both shallow and deep water.

Inertial effects in just-saturated axisymmetric column collapses

This work introduces a scaling analysis of sub-aerial axisymmetric column collapses of glass beads and Newtonian glycerol-water solutions mimicking some of the behaviours of debris flows. The beads were in a size range where their inertia partly decouples their collapse behaviour from the water column. Experiments explored a range of viscous, surface tension and particle inertia effects through systematic variation of particle size and fluid viscosity. Crucially a geotechnical centrifuge was used to access elevated effective gravitational accelerations driving the collapse, allowing field-scale viscous and surface tension effects to be replicated. Temporal pore pressure and run out front position evolution data was extracted using a pressure transducer and high speed imaging, respectively. A least-squares fitted scale analysis demonstrated that all characteristic dimensionless quantities of the acceleration phase could be described as a function of the column-scale Bond number text{ Bo }, the Capillary number text{ Ca }, the system size r^*, and the grain-fluid density ratio rho ^*. This analysis demonstrated that collapses as characterised by pore pressure evolution and front positions were controlled by the ratio of text{ Bo}/text{Ca}. This indicates that grain-scale surface tension effects are negligible in such inertial column collapses where they may dominate laboratory-scale granular-fluid flow behaviour where geometric similarity between grain and system size is preserved.Graphical abstract

SOME FEATURES OF CAPILLARY WAVE ENERGY CONVERSION ON LIQUID SURFACE IN THE PRESENCE OF DYNAMIC SURFACE TENSION

The effect of dynamic surface tension on capillary oscillations of a droplet is studied in the theoretical asymptotic calculations of the first order of smallness with respect to the dimensionless amplitude of oscillations of charged droplets of a polar liquid. The calculations are carried out within the framework of a model of an ideal incompressible electrically conducting liquid. It has been shown that allowance for the effect of dynamic surface tension increases the order of the dispersion equation, which acquires one more damping root relevant to the destruction of the near-surface electrical double layer (disordering of molecules in the near-surface layer). What is interesting about the revealed damping is that it takes place in an ideal liquid, while the characteristic damping time coincides with that measured experimentally. Free energy transformations occur between mechanical, thermal, electromagnetic, and mechanical again forms of energy, with all of the transformations being caused by the effect of the dynamic surface tension. It has been shown that the dynamic surface tension has a weak effect on the low-frequency oscillations of the droplets, while it essentially affects the high-frequency oscillations causing their rapid damping.

Stability of drawing of microstructured optical fibres

We consider the stability of the drawing of a long and thin viscous thread with an arbitrary number of internal holes of arbitrary shape that evolves due to axial drawing, inertia and surface tension effects. Despite the complicated geometry of the boundaries, we use asymptotic techniques to determine a particularly convenient formulation of the equations of motion that is well-suited to stability calculations. We will determine an explicit asymptotic solution for steady states with (a) large surface tension and negligible inertia, and (b) large inertia. In both cases, we will show that complicated boundary layer structures can occur. We will use linear stability analysis to show that the presence of an axisymmetric hole destabilises the flow for finite capillary number and which answers a question raised in the literature. However, our formulation allows us to go much further and consider arbitrary hole structures or non-axisymmetric shapes, and show that any structure with holes will be less stable than the case of a solid axisymmetric thread. For a solid axisymmetric thread, we will also determine a closed-form expression that delineates the unconditional instability boundary in which case the thread is unstable for all draw ratios. We will determine how the detailed effects of the microstructure affect the stability, and show that they manifest themselves only via a single function that occurs in the stability problem and hence have a surprisingly limited effect on the stability.

Effects of liquid surface tension on gas capillaries and capillary forces at superamphiphobic surfaces

The formation of a bridging gas capillary between superhydrophobic surfaces in water gives rise to strongly attractive interactions ranging up to several micrometers on separation. However, most liquids used in materials research are oil-based or contain surfactants. Superamphiphobic surfaces repel both water and low-surface-tension liquids. To control the interactions between a superamphiphobic surface and a particle, it needs to be resolved whether and how gas capillaries form in non-polar and low-surface-tension liquids. Such insight will aid advanced functional materials development. Here, we combine laser scanning confocal imaging and colloidal probe atomic force microscopy to elucidate the interaction between a superamphiphobic surface and a hydrophobic microparticle in three liquids with different surface tensions: water (73 mN m−1), ethylene glycol (48 mN m−1) and hexadecane (27 mN m−1). We show that bridging gas capillaries are formed in all three liquids. Force-distance curves between the superamphiphobic surface and the particle reveal strong attractive interactions, where the range and magnitude decrease with liquid surface tension. Comparison of free energy calculations based on the capillary menisci shapes and the force measurements suggest that under our dynamic measurements the gas pressure in the capillary is slightly below ambient.

Effect of Wall Proximity and Surface Tension on a Single Bubble Rising near a Vertical Wall

Path instability of a rising bubble is a complex phenomenon. In many industrial applications, bubbles encounter walls, and the interactions between the bubbles and the wall have a significant impact on flow physics. A single bubble rising near a vertical wall was experimentally observed to follow a bouncing trajectory. To investigate the near-wall dynamics of rising bubbles, 3D numerical simulations were performed based on the volume of fluid (VOF) method using the open source solver OpenFOAM. The effect of wall proximity and surface tension on the bubble trajectory was investigated. Previous studies have focused on the near-wall rising dynamics of bubbles for higher Eotvos numbers (Eo) and varied the Galilei number (Ga). The physical properties of the flow were chosen such that the free-rising bubble lies in the rectilinear regime. The Ga number was fixed and the Eo number was varied to analyze its effect on the bubble’s rising trajectory. It was found that the presence of the wall increases the drag experienced by the bubble and induces an early transition from rectilinear to a planar zigzagging regime. We identify the maximum wall distance and the critical Eo number for the bubble to follow a bouncing trajectory. The amplitude, frequency and wavelength of the bouncing motion are independent of the initial wall distance, but they decrease with decreasing surface tension.

Nonuniformly Filled Vortex Rings in Nonlinear Optics

A new type of long-lived solitary structures for paraxial optics with two circular polarizations of light in a homogeneous defocusing Kerr medium with an anomalous group velocity dispersion has been revealed numerically in the coupled nonlinear Schrödinger equations. A found hybrid three-dimensional soliton is a vortex ring against the background of a plane wave in one of the components, and the core of the vortex is filled with another component nonuniformly in azimuth angle. The existence of such quasistationary structures with a reduced symmetry in a certain parametric region is due to the saturation of the so-called sausage instability caused by the effective surface tension of a domain wall between two polarizations.

Effects of SDS surface-active agents on hydrodynamics and oxygen mass transfer in a square bubble column reactor: Experimental and CFD modeling study

This work examined experimentally and numerically the effects of sodium dodecyl sulfate (SDS) surfactant agent on mass transfer coefficients kLaL and kL in a high-aspect square bubble column reactor. To this end, SDS aqueous solutions at concentrations between 5 ppm and 30 ppm were prepared. Superficial gas velocity was varied from 0.74 cm.s−1 to 9.44 cm.s−1 covering all flow regimes to analyze the interaction between different phases and the effect of liquid surface tension on gas-liquid interfaces. Experimental data indicated that the presence of the SDS in the liquid phase augmented the overall gas holdup up to 25% at a constant gas velocity (Ug = 7.3 cm.s−1) in the transition regime, which is due to the role of SDS in bubble interactions. The impact of SDS addition on the mass transfer is twofold. Firstly, it reduced kL because the SDS molecules migrate towards the bubble-liquid interface thanks to the lower O2 diffusivity in water, thus hindering the O2 transfer from one phase to the other. Secondly, it increased aL owing to the inhibition of bubbles coalescence and, therefore, the lower mean bubble size. Among these two effects, the latter is prevailing, which led to an increase in kLaL in contaminated systems. In the second part of this work, a population balance model (PBM) was coupled with a computational fluid dynamics (CFD) model based on large-eddy simulation (LES) to analyze the effect of both tap water and SDS contaminated systems on the breakage phenomena, local flow pattern, and the resulting hydrodynamics and mass transfer features in the reactor. Ultimately, experiments and numerical simulations agreed well in terms of global gas holdup and kLaL coefficient. In particular, the transition points in the case of the SDS media (except for foam formation) provided the model with adequate PBM definitions for the dispersed phase.

Generation mechanism of lack of fusion in X70 steel welded joint by fully automatic welding under steep slope conditions based on numerical simulation of flow field

X70 pipeline steel is butt welded by fully automatic welding at 25° slope, and the characteristic information of welding process is collected. A 3D transient heat and mass transfer model of weld pool is established. This model was verified by means of the shape of the weld pool and the two-dimensional shape of the weld, and then, the flow field of the fully automatic welding process under steep slope conditions was simulated to clarify the mechanism of the lack of fusion defect. The results show that the welding arc is deflected when it stays on both side walls of the groove. The slope makes the liquid metal tend to gather at the lower groove. When gravity plays a leading role in the flow of the molten pool, some liquid metal begins to flow out from the lower groove to the front end, resulting in an overflow phenomenon. The generation of overflow phenomenon and arc deflection cause the formation of a “void zone” at the structure mutation position in front of the groove. In the welding process, the liquid metal tends to flow to the side walls for heat transfer under various thermal effects, and forms a large range of eddy current at the side walls. This has a positive effect on sidewall melting. In addition, the effect of surface tension at the lower groove is more obvious than that at the upper groove, and the trend of upward flow along the side wall is stronger, so it is difficult for the high-temperature liquid metal in the arc center to flow to the “void area” located at the bottom of the side wall of the lower groove. Therefore, the bottom of the lower groove is more likely to cause lack of fusion defect.

A three-dimensional ISPH-FVM coupling method for simulation of bubble rising in viscous stagnant liquid

The bubble rising problem has always been one of the research hotpots in the field of multiphase flow simulation due to the complex topological evolution of the phase interface. In this paper, an approach of coupling incompressible smoothed particle hydrodynamic (ISPH) and finite volume method (FVM) in three-dimensional space (abbreviated as 3D ISPH-FVM coupling method) is developed to simulate the bubble rising in viscous stagnant liquid. In the 3D ISPH-FVM coupling method, the coupling framework between the two numerical schemes is established through the information exchange at the overlapping regions. The effect of surface tension is evaluated by implementing the 3D continuum surface force model (CSF). To verify the interface capture accuracy of the 3D ISPH-FVM coupling method, several benchmark cases are tested. Then, the single bubble rising in viscous fluid is simulated by 3D ISPH-FVM coupling method, in which the results are compared with the experimental data and other numerical results in the literatures. To further explore the ability of 3D ISPH-FVM coupling method in bubble rising simulation, the effect of some parameters (including numerical and physical parameters) on single bubble rising is investigated. Afterwards, the dynamics phenomena of two bubbles coalescence are also studied. Numerical results validate the robustness and stability of the present coupling model in simulating the bubble rising.

Inclusion complexation of surfactant with β-cyclodextrin and its effect on the mixed micellization of cationic/anionic surfactants

Inclusion complexation of surfactant with β-cyclodextrin (β-CD) is an active research topic in supramolecular chemistry. For the mixed system of β-CD and cationic/anionic surfactants, the thermodynamic and molecular dynamics (MD) simulation studies can provide valuable information about synergism between cationic and anionic surfactants and competition between inclusion complexation and mixed micellization. Experimental results indicated a synergistic effect between CTAB and SL in surface tension reduction efficiency and effectiveness, and in mixed micelle formation. The surface tension experiments indicated that for single surfactant CTAB or SL, the binding stoichiometry was β-CD:surfactant = 1:1. For the 1:1 β-CD/surfactant inclusion complexes, umbrella sampling simulation results indicated that SL bound preferentially to the wide rim of β-CD, while, CTAB had a similar probability of binding to either rim of β-CD. Both experimental and simulation results indicated that the inclusion affinity of β-CD with CTAB was significantly stronger than that of β-CD with SL. Due to the electrostatic attraction between the oppositely charged headgroups, the distance between adjacent CTA+ and L− ions was significantly shorter than that between two adjacent CTA+ (or L−) ions. It encouraged us to explore whether the 1:1:1 β-CD/CTAB/SL inclusion complex could form. The MD simulation results indicated that all four possible initial 1:1:1 conformations were unstable. The final stable inclusion complexes were in 1:1 β-CD/CTAB and 1:1 β-CD/SL forms consistent with the umbrella sampling simulation results of the single surfactant. The results suggested that the inclusion interaction becomes less competitive with mixed micellization as the composition approaches the equimolar ratio of CTAB and SL.

Semi-empirical model for the liquid fuel film formed by an oblique jet impinging on a curved wall

The operating conditions and the properties of the liquid have great effects on the shape and size of the liquid film and eventually affect the efficiencies of the atomization of alternative fuels, liquid jet impingement cooling, and equipment cleaning processes. The shape and size of the liquid film are dominated by the distance from the stagnation point to the liquid film edge(rmax). In this study, after deducing the thickness profile and the theoretical rather than the numerical solution of the initial velocity profile of the liquid film, a set of semi-empirical models about the shape, size of the liquid film, and the width of the raised zone formed by an oblique jet impinging on curved walls have been developed. In order to validate the theoretical model, a corresponding experiment has been developed, in which the jet velocities, impingement angles, liquid viscosity, surface tension, and radius of curvature have been included. The comparisons showed the theoretical results are in good agreement with the experimental data. The error for the location of the inner and outer border lines are less than 14.9% and 13.5%, respectively, except for the location in the upstream part of the film. And the effects of jet velocity, impingement angle, surface tension, dynamic viscosity, and radius of curvature were also theoretically discussed. The outer border line of the liquid film is dominated by the impingement angle and the impingement velocity, which affect the rmax exponentially and linearly, respectively. And the liquid viscosity and surface tension coefficient also affect the rmax approximately linearly. But the effects of the liquid viscosity and surface tension coefficient on the rmax are much less than the impingement velocity. The radius of curvature has little effect on the outer border lines and width of the raised zone when gravity is ignored.

Effects of surface tension reduction on wind-wave growth and air–water scalar transfer

Effects of surface tension reduction on wind-wave growth are investigated using direct numerical simulations of air–water two-phase turbulent flows. The incompressible Navier–Stokes equations for air and water sides are solved using an arbitrary Lagrangian–Eulerian method with boundary-fitted moving grids. The wave growth of finite-amplitude and non-breaking gravity–capillary waves, whose wavelength is less than 0.07 m, is simulated for two cases of different surface tensions under a low-wind-speed condition of several metres per second. The results show that significant wave height for the smaller surface tension case increases faster than that for the larger surface tension case. Energy fluxes for gravity and capillary wave scales reveal that when the surface tension is reduced, the energy transfer from the significant gravity waves to capillary waves decreases, and the significant waves accumulate more energy supplied by wind. This results in faster wave growth for the smaller surface tension case. The effect on the scalar transfer across the air–water interface is also investigated. The results show that the scalar transfer coefficient on the water side decreases due to the surface tension reduction. The decrease is caused by suppression of turbulence in the water side. In order to support the conjecture, the surface tension effect is compared with laboratory experiments in a small wind-wave tank.

An Experimental Investigation of the Impact of Surface Tension and Viscosity on the Atomization Effect of a Solid Cone Nozzle

To investigate the influence of surface tension and viscosity on the atomization performance of solid cone nozzles and improve their dust reduction efficiency in industrial and mining enterprises, this study employed a self-built PDPA dust-fog coupling experimental system to explore the effects of different surface tension and viscosity solutions on atomization performance from three aspects: axial, radial, and fog field distribution. The experimental results indicate that compared with surface tension, surface tension has a greater influence on droplet size and velocity in the axial direction. In the radial direction, increasing surface tension and reducing viscosity within a certain range can make the droplet size and velocity distribution more uniform. Additionally, surface tension and viscosity significantly affect the fog field distribution. It was found that a decrease in surface tension can result in a closer proximity of the droplet velocity and size expansion area to the nozzle, while an increase in viscosity can lead to a more prolonged stable area. Furthermore, optimizing the surface tension and viscosity can significantly enhance the efficacy of dust reduction for respirable dust. Consequently, the application of the aforementioned atomization principles to regulate the fog field characteristics of solid cone nozzles can effectively mitigate dust in the production process and augment the dust reduction rate of industrial and mining enterprises.

Similarity characteristics in the morphology of radial viscous fingers

We conduct nonlinear simulations to investigate the radial growth of viscous fingers in a Hele–Shaw cell by performing a wide parametric study on the two dimensionless parameters that govern the dynamics. These are the viscosity contrast, A, and the effective surface tension, B, which compares the influence of surface tension with the injection rate that drives instability. It is well known that the surface tension between the fluids has a stabilizing influence on pattern formation leading to slower fingering growth and a reduced number of fingers. Moreover, the current results show that, for fixed A values, larger values of the effective surface tension lead to the formation of fingering patterns that are similar to each other. As such, the calculated interfacial shapes are larger and take longer to develop. Furthermore, the calculated shapes offer a visually striking portrait of instability evolution, and comparison to our experimental measurements highlights the close resemblance between the two with a few discrepancies pointed out. Finally, we observe how changes to the initial nearly circular interface affect both the morphology of viscous fingers and the timescale for pattern formation.

Dynamics of electrified liquid metal surface using shallow water model

A shallow water model that incorporates surface tension and electric field effects is developed to investigate the dynamics of an electrified liquid surface. The computational model is verified against the Zakharov–Kuznetsov equation and is applied to study the growth and damping of the electrified liquid surface. A linear wave analysis is performed under a shallow water theory assuming an analytic solution of the electric field, similar to the Tonks–Frenkel instability. The electrified liquid surface grows or dampens based on the balance of the electric field, surface tension, and gravitational forces. The numerical results obtained from the electrified shallow water solver are in good agreement with the theoretical analysis.