Small Liquid Droplets Research Articles

Pollination of Sarcandra glabra (Chloranthaceae) in Natural Populations in Japan

was investigated in its natural habitat in Japan. Flowers were protogynous and stigma receptivity dropped off significantly following anther dehiscence. Female-stage and bisexual-stage flowers were visited by beetles, bees, hemiptera, flies, and rarely ants that foraged for pollen and/or small droplets of liquid that occasionally were secreted by the carpels and inflorescence axes. At least the beetles, bees, and hemiptera commonly touched the stigmas and likely effected pollination. Flowers were self-compatible, and automatic selfing sometimes occurred when pollen fell from apical flowers onto the stigmas of lower flowers.

Review and experimental evaluation of runaway chemical reactor disposal design methods

Abstract This paper covers work carried out on the design of disposal systems for runaway chemical reactor relief, specifically horizontal gravity separators. Existing design methods are based on removing all but the very small liquid droplets (

Preparation of ultra-fine alumina powders by D. C. plasma jet

Ultra-fine alumina was prepared by DC thermal plasma. The influence of reactor configuration, input power and cooling conditions was investigated on properties such as particle diameter and phase composition. The powders synthesized without reaction tube were observed to be of two forms. One was metastable nano-sized powder with an average diameter of 30 nm due to rapid quenching of the vapor phase. The other form was larger-sized powder with an average diameter of 200 nm, and it was considered to be due to quenching of small liquid droplets, which had not fully vaporized in short residence time. With a reacting tube, the powder collected at the reaction tube was dominated by α-phase Al2O3, whereas the powder collected at the quenching chamber was mainly composed of intermediate γ- and δ-Al2O3. Input power and injection position of oxygen did not significantly affect the powder characteristics. To increase the conversion, aluminum powder should be vaporized completely. Most of the powders synthesized appeared fluffy spherical white powders with particle diameter of below 150 nm.

Experimental investigation of interaction processes between droplets and hot walls

A detailed experimental investigation of interaction processes of small liquid droplets with hot walls well above the Leidenfrost temperature has been carried out. The experimental method which uses monodisperse droplet streams in combination with a standard video camera allows very detailed observations and measurements with very high time resolution. The main intent of this paper is to study the mechanical behavior of liquid droplets impacting on hot walls well above the Leidenfrost temperature. A better understanding of this process may lead to a better modeling of two-phase flows, especially for applications in fuel preparation processes, combustion processes, and spray cooling. The loss of momentum of the droplets, the droplet deformation, and the onset of droplet disintegration have been investigated. For all experimental results correlations have been developed, which can be used to improve the numerical modeling of two-phase flows. Using the correlation for the loss of momentum a theoretical approximation for the maximum droplet deformation has been deduced, which yields a very good agreement with our own measurements as well as with results reported in the literature. A minimum impinging angle for droplet disintegration has been discovered for small impinging angles. Below this impinging angle no droplet disintegration is observed. This phenomenon is directly related to the energy dissipation at the wall during the interaction process. With the presented work the understanding of basic interaction processes between droplets and hot walls may be improved.

Small solid particles and liquid lenses at fluid/fluid interfaces

The behaviour of small solid particles and liquid droplets at fluid interfaces is of wide interest, in part because of the roles they play in the stability of foams and emulsions. Here we focus on solid particles at liquid interfaces, both singly and in highly structured monolayers. We briefly mention small oil lenses on water in connection with the determination of line tension, τ. Particles are surface-active in the sense that they often adhere quite strongly to liquid surfaces, although of course they are not usually amphiphilic. The three-phase contact line around a particle at an interface is associated with an excess free energy resulting in a tendency of the line to contract (positive τ, which is a 1D analogue of surface tension) or to expand (negative τ). Positive line tension acts so as to push the contact angle of a particle with the fluid interface further away from 90°, i.e. to force the particle towards the more “wetting” of the two bulk phases. It also leads to activation barriers to entry and departure of particles from an interface. The behaviour of particle monolayers at octane/water interfaces is also discussed . It is found that, for monodisperse spherical polystyrene particles containing ionisable sulphate groups at the surface, highly ordered monolayers are formed. This appears to result from very long range electrostatic repulsion mediated through the oil phase. Surface pressure–surface area isotherms are discussed for particle monolayers and it is shown, using light microscopy, that at monolayer “collapse” particles are not expelled from the monolayers but rather the monolayer folds, remaining intact. This has an important bearing on methods, involving the use of the Langmuir trough, for the experimental determination of contact angles and line tensions in particulate systems.

An instrument for determining the total water content in air when extinguishing fires

An instrument suitable for measuring the total water content both as small liquid droplets and as vapour in the air, in water mist total flooding extinguishing tests, is presented. The instrument consists of a heater and a Vaisala humidity meter. The Vaisala humidity meter is capable of measuring relative humidity at temperatures up to 180°C. The instrument has a measuring range of 0–600g/m3, a sample rate of 1 L/min, a time constant of 5–10 s and an accuracy of ±40 g/m3. Accurate results are obtained when used outside the direct spray from a nozzle. If the instrument is placed in the spray the total water content can be either over- or underdetermined, depending on which part of the instrument faces the spray. Copyright © 1999 John Wiley & Sons, Ltd.

Understanding protein crystallization on the basis of the phase diagram

The phase diagram of a protein–water system is described with a simple model with parameters for the interaction between the protein molecules in the crystal and in the solution. For a certain range of these parameters the phase diagram shows a metastable liquid–liquid immiscibility region. It is shown that this region corresponds to the “crystallization slot” for growing crystals, as proposed by George and Wilson [Acta Crystallogr. D 50 (1994) 361]. Nucleation in this region proceeds in two steps. First small liquid droplets with a high protein concentration are formed; then small crystalline nuclei grow inside these droplets. In the crystallization slot crystals are covered by a thin liquid film with a high protein concentration. We discuss NMR experiments on lysozyme, which show that nucleation is a transient process with an induction time.

Evidence of ferromagnetic behavior of small liquid droplets produced from amorphous alloys by laser ablation

Experimental evidence of ferromagnetic behavior of liquid droplets produced by laser ablation from amorphous alloys is presented. Thin films of amorphous magnetic materials were fabricated by laser ablation deposition in the presence and in the absence of a magnetic field. The difference in parameters of deposited films is attributed to ferromagnetic properties of small size liquid droplets.

Ferromagnetic liquid droplets

Experimental evidence for ferromagnetic behavior of liquid droplets produced by laser ablation from amorphous alloys is presented for the first time. Thin films of amorphous magnetic materials are fabricated by a laser deposition technique in the presence and in the absence of magnetic field. The differences in the parameters of deposited films are attributed to the ferromagnetic properties of small liquid droplets.

Dynamic Motion of Superfluid Bubble in Solid 4He

We have observed an interesting motion of a superfluid bubble in solid 4 He with the solid/liquid interface through the video camera. The host hcp crystal was formed at around 0.8 K with c-axis oriented approximately 45 degrees from the horizontal solid/liquid interface. When a fairly strong power of 10 MHz pulsed sound was applied to a transducer in the solid, a small rounded liquid droplet was nucleated at one spot on the transducer. The droplet became larger as the sound pulse continued to be applied, developing over the entire transducer, and finally began to grow upwards. As it increased in size, the c-facet was observed in the bubble. At this time the shape of the bubble became something like a pyramid. When a top of the pyramidal shape of the bubble touched the interface, it changed its shape drastically, rapidly merged into the superfluid phase. The detailed motion was determined by careful observation of the video records. When the bubble size became pretty large, the horizontal interface moved upward to compensate the lower density of the bubble in order that total number of atoms in the cell should be retained.

An Electrical Suspension Method for Measuring the Electric Charge on Small Silicone Oil Droplets Dispersed in Aqueous Solutions

The electric charge on small liquid droplets dispersed in another immiscible liquid is of fundamental interest in various colloidal and interfacial phenomena and industrial processes. In this paper, the authors present a new experimental method to measure the charge on small silicone oil droplets in aqueous solutions. Basically, an oil droplet was kept stationary inside a test cell between two electrode plates by application of an electric field of an appropriate polarity and strength. Thus, the electric charge on the oil droplet was determined from the force balance among the electrical force, the gravitational force, and the buoyancy force exerted on it. By using the electrical suspension method, the effects of two different silicone oils, pH values, valences, and concentrations of three different electrolytes on the measured electric charge were investigated. One of the two silicone oils is heavier (ρ1= 1050 kg m−3) and the other is lighter (ρ2= 963 kg m−3) than the aqueous solutions. There was an appreciable difference between the measured electric charges for the two silicone oils. The point of zero charge (pzc) for the heavier oil droplets was found to be pH ≈5.0, which is essentially the same as the value for the mineral oil droplets in the oil-in-water (O/W) emulsions reported by other researchers. It was also observed that the electric charge depends strongly on not only the concentrations but also the ionic valences of electrolytes added to the solutions. More specifically, divalent and trivalent cations, such as Ca2+and Al3+, were more readily adsorbed on the oil–water interface. Therefore, their effects were more pronounced than that of monovalent cations, Na+, on reducing the negative charge or even reversing the charge polarity as their ionic concentrations increase, in accordance with the valence difference.

Performance Characteristics of Mechanical Foam-Breakers with Rotating Parts Fitted to Bubble Column

The characteristics of four mechanical foam-breakers (a six-blade turbine (F-B), a six-blade vaned disk (V-D), a two-blade paddle (T-P) and a conical rotor (C-R) having six-blades fixed internally) with rotating parts fitted to a bubble column (BC) treating various foaming liquids were examined. In the BC with different foam-breakers, the average liquid hold-up in foam, ϕL, was both a typical parameter reflecting the foaming intensity of the BC, and a parameter related to the difficulty or ease of foam-breaking. The value of power consumption, Pkc, for foam-breaking in the C-R was the largest amongst the foam-breakers. Furthermore, it was demonstrated that in the four foam-breakers with rotating parts a considerable amount of very small liquid droplets was entrained with the exhaust air. © 1997 SCI.

Droplet-target laser-plasma source for proximity x-ray lithography

A compact, high-brightness and practically debris-free laser-plasma soft x-ray source for proximity x-ray lithography is described. The target of the source is small liquid fluorocarbon droplets injected into vacuum with a piezoelectrically vibrated nozzle. Emission from helium- and hydrogenlike fluorine in the 1.2–1.7 nm wavelength range was determined to ∼2×1012 photons/(sr-pulse), which corresponds to a conversion efficiency of ∼5% of the 70 mJ laser pulse. Exposure of a copolymer of PMMA–MAA confirms the measured photon flux. Debris production was approximately 70 pg/sr pulse. The applicability of the source for dedicated lithography systems is discussed.

Determination of Contact Angles and Surface Tensions with the Quartz Crystal Microbalance

A method based on the quartz crystal microbalance (QCM) for measuring the sessile contact angles and surface energies of liquid−air and liquid−liquid interfaces is described. The method involves measurement of the frequency change accompanying the introduction of a small liquid droplet to the center of a vibrating quartz resonator, which comprises an AT-cut quartz crystal sandwiched between two gold electrodes. If the density and viscosity of the liquid are known, the contact angle between the droplet and the gold substrate surface can be determined directly. QCM measurements of contact angles formed between aqueous droplets and gold surfaces modified with various organosulfur monolayers having different surface energies agree with sessile contact angles determined by optical goniometry. Furthermore, the QCM method can be used to measure the contact angle formed between an aqueous droplet and the QCM surface when both are submerged under an immiscible solvent such as hexadecane. In this case, the frequenc...

The fundamental equations of gas-droplet multiphase flow

This paper describes the derivation of an equation set for the multiphase flow of small polydispersed liquid droplets in a continuous gas-phase consisting of either a pure vapour (of the same chemical species as the liquid droplets) or a mixture of pure vapour and an inert gas. Some difficulties of previous formulations are resolved by more judicious definitions of the interphase transfer terms. The analysis includes a consistent model to represent the surface energy and entropy of the liquid droplets. Surface effects are normally neglected but must be included if consistency is to be maintained with droplet growth models in which the droplet temperature depends on its radius due to the effects of capillarity. A derivation of the equation for the rate of entropy creation due to departures from equilibrium is also presented. Entropy production in non-nucleating flows can be represented by precisely four terms, three of which are associated individually with the interphase transfer of mass, momentum and energy. The fourth term represents the entropy change due to the homogeneous nucleation of liquid droplets from the vapour and is in exact agreement with the results of classical nucleation theory. The form of the entropy creation equation allows an interpretation using the methods of linear irreversible thermodynamics and indicates that some mathematical models of droplet growth in common use, derived on an informal basis, may not be physically realistic in certain circumstances.

Calculating the thermodynamic properties of planar and spherical liquid-vapour interface

We present results of calculations of the equilibrium density profile and related surface properties for liquid-vapour interface of simple fluids. The interface has been considered to be (i) planar and (ii) spherical, with some attention paid to the stability of small liquid droplets. These calculations are based on density functional theory, in particular the gradient approximation, in conjunction with the simplified random phase approximation Bhatia-Young model for the bulk liquid.

Initial investigation of the homogeneous nucleation of cesium vapor

Initial measurements of the homogeneous nucleation of supersaturated cesium vapors using an upward thermal diffusion cloud chamber specially designed for use with highly reactive materials are presented. Comparison of the supersaturations measured at higher temperatures (greater than 455 K) with the supersaturations predicted by Classical nucleation theory show for the first time that the nucleation behavior of simple normal metals can be described by Classical theory. This agreement implies that the description of relatively large clusters of simple metal atoms (more than 25 atoms) as small liquid droplets with bulk metallic properties is valid. However, as the temperature decreases below 455 K, an increasingly larger supersaturation than that predicted by theory is required. This deviation from theory is so sharp that by 430 K the difference is an order of magnitude, and below 420 K nucleation cannot be observed. The deviation is discussed in the context of loss of bulk metallic properties with decreasing critical nuclei size. Other possible reasons for a deviation towards larger supersaturations are also considered.

Spreading of a droplet on a solid surface

AbstractThe spontaneous spreading of small liquid droplets on solid surfaces is examined with the objective of developing closed‐form expressions for the spreading dynamics, both for the case in which there is complete equilibrium spreading, that is the equilibrium contact angle is 0°, and for the case in which equilibrium spreading is incomplete. Such solutions are obtained using a simple hydrodynamic model. The results are consistent with the format of the universal Hoffman–Voinov–Tanner law (for complete spreading) and the modified Hoffman–Voinov–Tanner law for incomplete spreading. In the latter case, concurrence is found only when the dynamic contact angle is close to the equilibrium angle throughout the spreading process. © 1994 John Wiley & Sons, Inc.

On the thermodynamic stability of small droplets at positive line tension

The thermodynamic formalism with the Ω potential is applied for finding the conditions of mechanical equilibrium (Laplace's law and Young's equation) in the case of small liquid droplets attached at a plane surface. The conditions of stability of the equilibrium drops are examined. It is shown that at positive values of the line tension of the contact perimeter there exists a supersaturation above which no heterogeneous nucleation occurs. Below this maximum value of the supersaturation two equilibrium cap-shaped drops could coexist. They are both in unstable equilibrium with their surroundings. No range of supersaturations exists where the smaller equilibrium drop would be in stable equilibrium with the surroundings. Such a conclusion has been proposed (V.C. Noninski, Colloids Surfaces, 42 (1989) 205; J. Colloid Interface Sci., 143 (1991) 374) on the basis of the incorrect assumption that the stability of the equilibrium could be referred to the slope of the Thomson—Gibbs dependence of vapour pressure on drop size. Positive slopes of this dependence imply stability equilibrium in the case of free drops only. For the case of cap-shaped drops where the Ω potential is a function of two (or more) geometrical variables, the determination of the stability conditions follows another procedure shown in the present paper.

Formation of microparticulate protein powder using a supercritical fluid antisolvent

Gas antisolvent (GAS) expansion of dimethylsulfoxide (DMSO) and N,N-dimethylformamide (DMFA) solutions with supercritical carbon dioxide was used to produce biologically active powders of insulin. Powders with 90% of the particles smaller than 4 mum and 10% smaller than 1 mum were obtained under all conditions tested when the process was operated continuously, with small liquid droplets sprayed into a flowing supercritical continuum. Slow pressurization of the stagnant protein solution resulted in larger particles. In vivo tests on rats revealed no differences between the biological activity of processed and unprocessed insulin, GAS processing of organic solution appears to be a reliable and effective method for the production of dry, biologically active microparticulate powders of peptides and proteins.