Showing papers on "Laplace pressure published in 2002"

Structure formation at the interface of liquid liquid bilayer in electric field

Abstract: Subjecting a liquid/liquid interface to an electrohydrodynamic pressure enhances fluctuations with a characteristic wavelength leading to an instability and the formation of well-defined columnar structures An extension of a linear stability analysis for a single fluid interface to the bilayer case produced general arguments applicable to any interface Countering the electrohydrodynamic pressure is the Laplace pressure, which for films is dictated by the surface energy; whereas for a bilayer, it is given in terms of the interfacial energy Consequently, the characteristic length scale is reduced in the case of bilayers Results are presented for different polymer bilayers under a wide range of experimental conditions showing quantitative agreement with the generalized theory with no adjustable parameters Over 4 orders of magnitude in reduced wavelength and field strength can be described by these arguments These results point to a viable route by which structures can be produced over a wide range of length scales

Electrostatic stabilization of fluid microstructures

Abstract: A liquid surface of arbitrary shape is, in general, dynamically unstable due to gradients in Laplace pressure This greatly limits the class of morphologies eligible for artificial fluid microstructures In this work, we demonstrate that a wide class of these otherwise unstable surface morphologies can be stabilized using electrostatic fields Complex stable fluid microstructures were generated in a conventional electrowetting setup operated at high voltage We present an electrostatic model that explains the stability and the scale of the stable structures as a function of external control parameters The stability as well as the universality of these structures naturally leads to novel concepts in microfluidic technology

Method and instrument for measuring surface tension

Abstract: For measuring the surface tension between a liquid and fluid such as a gas, a capillary (3, 3') is used in which the liquid slowly flows and at the end of which drops (11) are formed, falling off into a closed space (7) containing the fluid. Using a pressur esensor (5, 5') the pressure is measured which can be the absolute pressure of a fluid volume enclosed in teh closed space or alternatively a differential pressure measured as the pressure difference between the liquid in the capillary and fluid contained in theclosed space. The pressure is measured when one or more drops are formed and fall off. The obtained pressure curves are evaluated electronically (12) and provide a value of the surface tension. The measurement can be made within a fairly short time with a high operational reliability. The temperature difference between the drop and the surrounding fluid is small resulting in a little precipitation of salts dissolved in the liquid, reducing the risk that the liquid capillary with be blocked. A pump can be connected (9) to the closed space to create a subatmospheric pressure therein and thereby assist in restarting the liquid flow through the capillary if it would be blocked. The velocity of the liquid flow to the drop can be controlled using the pump.

Dynamics of liquid meniscus bridge of intermittent contact slider

Abstract: The dynamics of a liquid meniscus bridge between solid plane surfaces were analyzed assuming small vibrations of the spacing. The geometries of the meniscus considered in this study were the infinite-width meniscus and the finite meniscus ring. The time-dependent Reynolds equation was solved under a boundary condition considering the Laplace pressure, assuming that the contact angle of the liquid-solid interface remains zero and the mass of the liquid-in the meniscus is conserved, so that the boundary position moves parallel to the plane. By solving a linearized Reynolds equation under the assumption of small vibration, it was found that the pressure and the load carrying capacity has three terms, i.e. time-dependent squeeze term by the viscosity of the liquid, spring term by the dynamic Laplace pressure, and the static meniscus force term.

Computer simulation of thin water films in nonwettable capillaries. The Laplace pressure and disjoining pressure

Abstract: The behavior of water in flat unwettable microcapillaries was studied as a function of their width by the methods of Monte Carlo and molecular dynamics. The conditions of the coexistence of liquid–vapor phases in capillaries were found, and the values of the coefficient of isothermal compressibility were determined by the calculated supercritical and subcritical adsorption isotherms. The profiles of local density and energy were calculated. The Laplace pressure and disjoining pressure, whose values and signs manifest strong hydrophobic attraction of solid surfaces, were estimated.

Theory of Initial Microcavity Growth in a Liquid Metal Around a Gas - Releasing Particle. Part 2. Bubble Initiation Conditions and Growth Kinetics

Abstract: A theory is presented that includes capillary, hydrodynamic, and diffusion aspects. The main attention is devoted to capillary and hydrodynamic effects. The hydrodynamic process (bubble growth) is governed by a nonlinear integrodifferential equation, whose coefficients are dependent on the surface tension, density, and viscosity of the liquid, and also on the difference between the pressure in the gas within the bubble and that in the surrounding liquid. The gas pressure in the bubble is dependent on the rate of gas release from the inclusion (source). An expression is derived for the bubble radius as a function of time. The theory can be useful for developing the technology of powder materials and foam metals.

Surface Tension Measurement at High Pressure

Abstract: A non-intrusive method, based on the properties of capillary waves, is used to measure surface tension at high pressure. Results are given for diesel fuel, gasoline and n-heptane. Large variations with pressure are showed. A model is proposed to understand the influence of pressure upon the liquid-gas interface. Results of both approaches are in good agreement.Copyright © 2002 by ASME

Pressure difference between inside and outside of a drop and its critical radius in dropwise condensation

Abstract: It was proved using the thermodynamic method that the pressure difference between the inside and outside of a liquid drop sitting on a solid surface follows the classical Laplace equation, and this was further validated using the mechanics method. Such a pressure difference depends only on the surface tension of the liquid and the radius of the drop but is independent of the liquidsolid contact angle.Similarly, the critical radius of a drop in dropwise condensation is also independent of the contact angle and can be calculated using the classical Kalvin equation.

Research on homogeneous reservoir pressure performance

Abstract: In this paper,the Laplace space solution to dimensionless reservoir pressure and dimensionless bottom hole pressure of variable flow problem is studied,which takes into consideration the effect of two types of inner boundary conditions(wellbore storage,skin factor)and three kinds of outer boundary conditions(constant pressure outer boundary,closed outer boundary,infinite boundary)by using the homogeneous reservoir model.The inter-relation among these pressure distribution formula is studied emphatically,a general formula is induced from it,and then a further discussion is carried out.All these work in this paper has profound meaning to well test analysis theory,so to well test analysis software applying.

Dynamic stability of the liquid-gas interface in micron-sized pores

Abstract: This paper investigates the dynamic stability of a liquid-gas (or vapor) interface, which occurs in very small diameter pores. The interface is examined under conditions of a static pressure difference across it and a static pressure difference along with a sinusoidal one-dimensional oscillation. The Navier-Stokes equations are applied to the liquid side with assumed no-slip conditions, while the Young-Laplace equation is used to formulate the shape of the interface. This theoretical model calculates both velocity profiles in the liquid side and transient profiles of the interface itself; and of particular interest, it predicts the pressure difference, oscillation frequency and amplitude required to burst this interface (sometimes referred to as bubble burst through).