Gravitational Drainage Research Articles

Experimental Investigation of Eletrokinetic Stabilization of Gravitational Drainage of Ionic Surfactants Films

Gravitational drainage of vertical films of ionic surfactants supported on a frame with the upper and lower parts being electrodes is studied experimentally. The electric field introduces three additional physical phenomena: (i) the surface charge redistribution, which eventually changes surface elasticity, (ii) the electroosmotic flow in the diffuse layer, and (iii) pressure build-up near the electrode toward which the electroosmotic flow is directed. It is shown that stabilization of the films is possible either due to the traction imposed by the electroosmotic flow directed upward (against gravity), or due to the pressure build-up near the lower end of the frame, in cases where the electroosmotic flow is directed downward (in the gravity direction) and enters a dead end at the lower electrode.

Effect of Nd:Yag Laser Hyaloidotomy for Premacular Subhyaloid Haemorrhage

INTRODUCTION: Premacular subhyaloid hemorrhage is a common condition leading to severe sudden vision loss in various conditions.This study investigated the effects of drainage of premacular subhyaloid hemorrhage into the vitreous with Nd:YAG laser treatment. Photodisruption with Zeiss Nd.Yag laser done in the inferior part of the the hemorrhage to create hole in ILM for gravitational drainage of blood in vitreous. A rapid resolution of subhyaloid hemorrhage with improvement of visual acuity was achieved in all patients treated with Nd:YAG laser posterior hyaloidotomy, without evidence of damage to the retina or choroid. Nd:YAG laser posterior hyaloidotomy is simple, effective, safe and non invasive procedure for draining a premacular hemorrhage into the vitreous cavity and to avoid vitreoretinal surgery and complication related to long standing macular toxicity by blood.Journal of Universal College of Medical Sciences Vol. 3, No. 1, 2015: 51-53

How antifoams act: a microgravity study.

Antifoams are widely used to control or to avoid foam production. In order to work, antifoam particles need to break foam films efficiently, which many antifoams do very well. However, once they have broken a film, to continue to be effective they need to be transported to the next film. We show, for the first time, that buoyancy has an important part in the transport of the antifoam particles. In microgravity, where buoyancy and gravitational drainage are strongly slowed down, diffusion leads to poor antifoam performance. The foam is stable for the duration of the experiment, whereas on Earth the foam starts to disappear immediately. Indeed, microgravity renders highly efficient antifoam practically useless.

Dynamics of a spreading thin film with gravitational counterflow using slip model

Thin liquid films can be made to spread along a solid surface by application of temperature gradients at the liquid–gas interface. The surface tension of usual liquids decreases linearly with temperature thus producing the driving thermocapillary stresses due to the applied temperature gradient. These spreading films are susceptible to a fingering instability at the advancing solid–liquid–vapor contact line, which is linked to the development of a capillary ridge near the advancing front. A thin film climbing up on a vertical substrate against gravity shows interesting dynamics due to strong opposing gravitational counterflow. At the contact-line of the spreading film, slip-model is used to alleviate the stress-singularity due to more usual no-slip boundary condition. It is shown that depending upon the magnitude of a gravitational drainage parameter the steady-profiles of the spreading films show qualitatively different dynamics. The dynamics is in agreement with the experimentally observed profiles in the literature as well as computed profiles using precursor-film model at the contact-line in some earlier theoretical studies. Briefly, their stability behavior is also discussed.

The effect of shear-thickening on liquid transfer from an idealized gravure cell

Gravure printing is an economical roll-to-roll processing technique with potential to revolutionize the fabrication of nano-patterned thin films at high throughput. In the present study, we investigated the impact of shear-thickening on the liquid transfer from an idealized gravure cell by a combination of experiments and numerical computations. We chose as a model system fumed silica nanoparticles dispersed in polypropylene glycol; these dispersions exhibit shear and extensional thickening as verified by steady shear and filament stretching extensional rheometry. Model gravure printing experiments were conducted using a linear motor to pick out the fluid vertically up from a truncated conical shaped idealized gravure cell cavity; the cell size is large enough that gravity is important, and therefore experiments were also conducted to pickout the fluid vertically down from the cavity-on-top. The amount liquid transfer from the cavity was studied with varying stretch velocities and dispersion concentrations. The filament profile evolution during the pickout process was examined using a high speed camera. Beyond a critical stretch rate, shear-thickening of the fluid, manifested by the formation of long stable filaments, exacerbates gravitational drainage during pickout. Beyond a second critical stretch rate, shear-thinning induces conical profile evolutions that result in pickout insensitive to stretch rate. All of these observations were qualitatively predicted by finite element computations using a generalized Newtonian fluid model, where the shear rheology was modeled explicitly. We showed that under the influence of gravity, wetting/de-wetting may be a critical phenomenon in determining pickout at low stretch rates.

Effect of Acid Treatment on Interfacial and Foam Properties of Soy Proteins

Abstract: The goal of the present work was to study the effects of acid treatment on the foaming properties of a soybean protein isolate (SPI) and its fractions, glycinin (11S) and β-conglycinin (7S). The structural characteristics, interfacial properties, foaming capacity and stability of the treated proteins were studied. Results from surface hydrophobicity and differential scanning calorimetry (DSC) showed that the acid treatment caused the complete denaturation of 11S and a partial denaturation of 7S. This protein unfolding affected their interfacial properties, which led to an improvement in the foaming properties of both protein fractions and isolate. Treated 7S showed the best behavior in the rearrangement process, probably due to its smaller size and its modified structural characteristics. All treated proteins showed stronger interfacial films. The foams of treated proteins were destabilized mostly due to gravitational drainage rather than Ostwald ripening. Key words: Soy proteins, foams, gravitational drainage, Ostwald ripening.

Robust liquid-infused surfaces through patterned wettability

Liquid-infused surfaces display advantageous properties that are normally associated with conventional gas-cushioned superhydrophobic surfaces. However, the surfaces can lose their novel properties if the infused liquid drains from the surface. We explore how drainage due to gravity or due to an external flow can be prevented through the use of chemical patterning. A small area of the overall surface is chemically treated to be preferentially wetted by the external fluid rather than the infused liquid. These sacrificial regions disrupt the continuity of the infused liquid, thereby preventing the liquid from draining from the texture. If the regions are patterned with the correct periodicity, drainage can be prevented entirely. The chemical patterns are created using spray-coating or deep-UV exposure, two facile techniques that are scalable to generate large-scale failure-resistant surfaces.

Enhanced foamability of sodium dodecyl sulfate surfactant mixed with superspreader trisiloxane-(poly)ethoxylate.

Gravitational drainage from thin vertical surfactant solution films and gravitational drainage in a settler column are used to study the behavior of foams based on two-surfactant mixtures. Namely, solutions of the anionic sodium dodecyl sulfate (SDS) and nonionic superspreader SILWET L-77, and their mixtures at different mixing ratios, are studied. It is shown, for the first time, that solutions having a longer lifetime in the vertical film drainage process also possess a higher foamability. An additional and unexpected unique result is that when using a mixed surfactant system, the foamability can be much greater than the foamabilities of the individual components.

Influence of boundary slip on the dynamics and stability of thermocapillary spreading with a significant gravitational counterflow

Applied temperature gradients produce thermocapillary stresses that can force liquid films to spread along solid surfaces. These films are susceptible to a rivulet instability at the advancing solid-liquid-vapor contact line, which is linked to the development of a capillary ridge near the advancing front. The application of a sufficiently strong gravitational counterflow has been shown to drain fluid from the ridge and stabilize the film against rivulet formation and lead to interesting spreading dynamics. In this work, the dynamics and stability of thermocapillary driven films are analyzed for the entire range of drainage. Boundary slip is allowed at the solid-liquid interface, which introduces the static contact angle and slip coefficient as parameters that can typically be specified independently. The contact angle of the spreading film is allowed to depend on the velocity of the contact line, and the effects of this dependence on the film profile, linear stability, and transient response of perturbations are examined. Increasing the influence of gravitational drainage relative to the thermocapillary stress from zero has a stabilizing influence on the traveling wave solutions but is accompanied by an increase in the amplitude of the capillary ridge, which is contrary to stability results for spreading films with only one driving force. Results for the different spreading regimes are generally consistent with predictions based on the more extensively used precursor film model of the contact line, although some differences are observed due to the additional parameters in the slip model that are relevant to partially wetting fluids.

English

Medical paradox of induced hypotension has arisen because bleeding during operative interventions has become a problem of increasing importance during the past few years. Certain surgical procedures are now so vastly extensive and that other operations have penetrated so deeply into the vital structure of the body. A number of workers, both on this continent and abroad, have suggested that one effective method of controlling either gross hemorrhage or excessive vascular ooze may be by the reduction of systemic arterial pressure. When such a deliberate hypotension is combined with proper posturing of the patient so that the operative site is superior, permitting gravitational venous drainage away from the wound to the dependent portions of the body, the technique has been called “controlled hypotension,” and has been employed to achieve a relatively ischemic operative field.

Use of inorganic substrates and composted green waste in growing media for green roofs

Inorganic substrates are used as the primary component in green roof growing media because they can provide the desired physical properties and are thought to be physically, chemically and structurally stable over time. Inorganic substrates can be amended with organic matter to help establish vegetation on green roofs but there is little information on how this affects the physical properties; dry bulk density, water holding capacity and air filled porosity; of the resulting growing medium or whether the effects are the same for all inorganic substrates. Nine crushed brick and three crushed tile substrates obtained from five UK suppliers of aggregates were amended with 30% v/v composted green waste. The physical properties of the substrates and growing media mixes were determined using the gravitational drainage technique. Amending the inorganic substrates with composted green waste significantly improved the physical properties by reducing the dry bulk density and increasing the water holding capacity. Air filled porosity of inorganic substrates decreased with addition of fine composted green waste but aeration was always adequate for plant growth and survival. This provides evidence of the beneficial effects of inclusion of composted green waste on the physical properties of inorganic substrates for green roof growing media but highlights the fact that the responses to inclusion of composted green waste may be different for different inorganic substrates or grades of substrate.

Superspreaders Versus “Cousin” Non-Superspreaders: Disjoining Pressure in Gravitational Film Drainage

Gravitational drainage of vertical films supported on a wire frame of two superspreaders SILWET L-77 and BREAK-THRU S 278 and their respective "cousin" non-superspreaders SILWET L-7607 and BREAK-THRU S 233 revealed drastic differences. The superspreader films showed complicated dynamic "turbulent"-like interferometric patterns in distinction from the ordered color bands of the "cousin" non-superspreaders, which resembled those of the ordinary surfactants. Nevertheless, the superspreader films stabilized themselves at the thickness about 35 nm and revealed an order of magnitude longer lifetime before bursting compared to that of the "cousin" non-superspreaders. Notably, the superspreaders revealed drastic differences from the non-superspreaders in aqueous solutions with no contact with any solid hydrophobic surface. The self-stabilization of the superspreader films is attributed to significant disjoining pressure probably related to long superspreader bilayers hanging from the free surfaces. The scaling law for the disjoining pressure was found as p(disj)(h) ~ h(-m) (with m ≈ 9-11) for the sufficiently concentrated superspreader solutions, and as p(disj)(h) ~ h(-s) (with s ≈ 6) for more dilute solutions (in both cases, concentrations were above the critical micelle concentration). The non-superspreaders do not possess any significant disjoining pressure even in the films with thicknesses in the 35-100 nm range. The results show that gravitational drainage of vertical films is a useful simple tool for measuring disjoining pressure.

Dynamics of a pre-lens tear film after a blink: Model, evolution, and rupture

A mathematical model is developed to investigate the dynamics and rupture of a pre-lens tear film on a contact lens. The contact lens is modeled as a saturated porous medium of constant, finite thickness and is described by the Darcy-Brinkman equations with stress-jump condition at the interface. The model incorporates the influence of capillarity, gravitational drainage, contact lens properties such as the permeability, the porosity, and the thickness of the contact lens on the evolution and rupture of a pre-lens tear film, when the eyelid has opened after a blink. Two models are derived for the evolution of a pre-lens tear film thickness using lubrication theory and are solved numerically; the first uses shear-free surface condition and the second, the tangentially immobile free surface condition. The results reveal that life span of a pre-lens tear film is longer on a thinner contact lens for all values of permeability and porosity parameter considered. An increase in permeability of contact lens, porosity or stress-jump parameter increases the rate of thinning of the film and advances the rupture time. The viscous-viscous interaction between the porous contact lens and the pre-lens tear film increases the resistance offered by the frictional forces to the rate of thinning of pre-lens tear film. This slows down the thinning process and hence delays the rupture of the film as compared to that predicted by the models of Nong and Anderson [SIAM. J. Appl. Math. 70, 2771–2795 (2010)] derived in the framework of Darcy model.

Acute Bacterial Sinusitis in Children

On the basis of strong research evidence, the pathogenesis of sinusitis involves 3 key factors: sinusostia obstruction, ciliary dysfunction, and thickening of sinus secretions. On the basis of studies of the microbiology of otitis media, H influenzae is playing an increasingly important role in the etiology of sinusitis, exceeding that of S pneumoniae in some areas, and b-lactamase production by H influenzae is increasing in respiratory isolates in the United States. On the basis of some research evidence and consensus,the presentation of acute bacterial sinusitis conforms to 1 of 3 predicable patterns; persistent, severe, and worsening symptoms. On the basis of some research evidence and consensus,the diagnosis of sinusitis should be made by applying strict clinical criteria. This approach will select children with upper respiratory infection symptoms who are most likely to benefit from an antibiotic. On the basis of some research evidence and consensus,imaging is not indicated routinely in the diagnosis of sinusitis. Computed tomography or magnetic resonance imaging provides useful information when complications of sinusitis are suspected. On the basis of some research evidence and consensus,amoxicillin-clavulanate should be considered asa first-line agent for the treatment of sinusitis.

Fickian Diffusion in Discrete-Fractured Media from Chemical Potential Gradients and Comparison to Experiment

Fickian diffusion can be an important oil recovery mechanism from fractured reservoirs by gas injection, especially when gravitational drainage is inefficient. Without diffusion, injected gas will flow predominantly through the fractures, resulting in early breakthrough and low oil recovery, but compositional gradients between the fractures and the matrix can drive considerable cross-flow. Additionally, this species exchange can lead to favorable phase behavior, such as swelling and viscosity reduction of oil in the matrix. The modeling of Fickian diffusion in fractured reservoirs has been hampered by two deficiencies in existing simulators. The first is the use of the generalized classical Fick’s law for multicomponent mixtures, which violates molar balance. The second is the computation of diffusive fluxes across grid edges aligned with phase boundaries. Traditionally, diffusive fluxes are derived from gradients in compositions, computed by finite differencing of compositions in neighboring grid cells. ...

English

BACKGROUND: Caldwell Luc procedure was designed to remove irreversibly damaged mucosa of the maxillary sinus and to facilitate gravitational drainage and aeration via an inferior meatal antrostomy. Though the frequency of Caldwell Luc procedure has reduced with the advent of the more conservative functional endoscopic sinus surgery, it is still indicated in cases of irreversible scarring, polypoidal mucosal inflammation and chronic inflammation associated with mucociliary dysfunction. Although initially confined to the treatment of maxillary sinusitis, nowadays, it is also indicated in case of removal of foreign bodies from maxillary sinus, as an access to pterygomaxillary fissure and pterygo-palatine fossa, evaluation and stabilization of orbital floor fracture or removal of orbital floor in decompression. In spite of its effectiveness and variety of indication, it can be associated with complications, such as numbness, pain, paresthesia, damage to teeth and oro antral fistula. OBJECTIVES: This study aims to know the possible indications of Caldwell Luc procedure and to understand the effectiveness and the complication that can be associated with the procedure.

Measurement of retention functions with hysteresis using ground‐penetrating radar

ABSTRACTThe non‐invasive measurement of water retention functions employing geophysical methods involves the determination of the timely variation of water content using parametrized petrophysical models. Over the last two decades several methods have been published, which are based on the dielectric constant derived from ground‐penetrating radar measurements and their relation to the water content. While it is error‐prone to ascertain true radar traveltimes from radar reflection data, ground wave or diffraction analysis, transmission measurements are quite accurate. Soil water content is classically estimated by a simple equation or a mixing law derived from small‐scale laboratory analysis, which may deny clarification of hydraulic constraints. However, the application of these relationships for the in situ determination of retention functions from water content may lead to non‐representative results.For this reason, the aim of this study was to measure non‐invasively representative retention functions including their hysteresis of large sand samples using radar transmission data. Experiments were conducted in a two metre high rectangular Plexiglas© tank with a sample volume of 0.6 m3, being the main component of the set up. Implemented radar transmission measurements provided profiles of the dielectric constant across the transition between the water saturated zone and unsaturated soil zone. The spatiotemporal variations of water content induced by the multi‐step‐outflow/ inflow method were monitored with fixed transmitter‐receiver‐positions.A new petrophysical model, applicable to sand and incorporating the dielectric effect of hydraulic residual water, was developed to transform radar traveltimes into volumetric water content. This model can be easily calibrated on the basis of the monitored water contents at a fixed site because it includes the defined hydraulic conditions of fully gravitational drainage and full water saturation. Even the consideration of just two water phases with different dielectric properties allowed a satisfactory fitting. Following from the study, a complete retention function was obtained for each sand sample and characterized by a set of van‐Genuchten‐parameters. The work demonstrated that if a reference level of the water table is known from independent measurements, it is possible to determine retention functions reliably. Despite the fact, however, that further experiments are required, the results of this investigation offer a powerful tool for in situ determination of retention functions and the estimation of van‐Genuchten parameters with radar measurements, either in boreholes or from the surface.

Selective recovery of gold(III) via continuous counter-current foam separation from hydrochloric acid solution – Effects of foam and column sizes on separation performance

Continuous counter-current foam separation with simultaneous injections of metal and surfactant solutions into rising foam bed was applied to Au(III) recovery from hydrochloric acid solutions containing binary metals of Au(III) and Cu(II). A nonionic surfactant, poly(oxyethylene) nonylphenyl ether, used in this study showed a strong affinity to Au(III) and played a double role of foam-producer and metal collector. The effect of an average foam diameter (from 0.026 to 0.28cm) was investigated on the separation performance. It is noteworthy that a larger foam enhances gravitational drainage dramatically while decreasing of the adsorption capacity for Au(III). Increasing the foam diameter from 0.07 to 0.22cm improves Au(III)/Cu(II) separation factor successfully from 64 to 1060 under keeping the complete recovery of Au(III). Based on the results obtained, a parameter chart of the operational conditions on the separation performance was presented. Usage of a larger foam is essential for the metal separation under the optimized counter-current flow balance in the foam bed. Furthermore, enlargement of a bubble column diameter from 3.0 to 6.0cm enhances the separation factor as much to 3840 while keeping the complete recovery of Au(III), indicating that the size of the column is also crucial to the separation.

Computational study of viscoelastic effects on liquid transfer during gravure printing

High speed roll-to-roll coating and printing are important in both classical and novel processes, e.g., in the emergent flexible electronics industry. Gravure in particular is attractive for its application to printing as well as its high quality and throughput in coating continuous thin films. Despite its long standing use, gravure is still poorly understood especially in the liquid transfer regime and when the coating liquid has a complex rheology. As with any coating flow, the dynamics are governed by many complex phenomena including free surfaces, (de)-wetting, and non-Newtonian rheology; these present observational, modeling, and computational challenges. Accordingly, modeling and computational work are usually limited by the level of detail in describing the physical phenomena. In this work, we compute the influence of viscoelasticity on the transfer of polymer solutions in an idealized gravure process: the liquid is held between a cavity and a flat disk that moves away at a constant velocity, with pinned contact lines on both the disk and cavity. Our computations show that when the disk separation velocity is sufficiently high as measured by the Weissenberg number—i.e., the consequent strain rate in the liquid bridge is high compared to the rate of polymer relaxation—large elastic stresses are activated at early times and induce an adverse drainage into the cavity. Gravity or other forces eventually overwhelm this elastic drainage at later times when stretching dynamics decay in importance. When gravitational and elastic drainage act in concert, they compete with the viscous forces that promote liquid transfer; this competition manifests as an optimum disk velocity for maximal liquid transfer. With the appropriate scaling, we find that the optimal disk velocities over a range of parameters reduce to an optimal Weissenberg number of about 0.1, which agrees well with experiments in the literature.

Gravitational Drainage of Foam Films

Gravitational drainage from thick plane vertical soap films and hemispherical bubbles is studied experimentally and theoretically. The experiments involve microinterferometry kindred to the one used in the experiments in the Scheludko cell. The following surfactants were used in the experiments: cationic dodecyltrimethylammonium bromide (DTAB), anionic sodium dodecyl sulfate (SDS), anionic Pantene shampoo which primarily contains sodium lauryl sulfate, nonionic tetraethylene glycol monooctyl ether (C8E4), and nonionic Pluronic (P-123) surfactants at different concentrations. The theoretical results explain the drainage mechanism and are used to develop a new method of measurement of the surface elasticity and to test it on the above-mentioned surfactants.