Showing papers on "Ohnesorge number published in 2005"

Retraction dynamics of aqueous drops upon impact on non-wetting surfaces

Abstract: We study the impact and subsequent retraction of liquid droplets upon high-speed impact on hydrophobic surfaces. Extensive experiments show that the drop retraction rate is a material constant and does not depend on the impact velocity. We show that on increasing the Ohnesorge number, Oh = η/ √ ρRIγ , the retraction, i.e. dewetting, dynamics crosses from a capillary–inertial regime to a capillary–viscous regime. We rationalize the experimental observations by a simple but robust semi-quantitative model for the solid–liquid contact line dynamics inspired by the standard theories for thin-film dewetting.

Retraction dynamics of aquous drops upon impact on nonwetting surfaces

Abstract: We study the impact and subsequent retraction dynamics of liquid droplets upon high-speed impact on hydrophobic surfaces. Performing extensive experiments, we show that the drop retraction rate is a material constant and does not depend on the impact velocity. We show that when increasing the Ohnesorge number, $\Oh=\eta/\sqrt{\rho R_{\rm I} \gamma}$, the retraction, i.e. dewetting, dynamics crosses over from a capillaro-inertial regime to a capillaro-viscous regime. We rationalize the experimental observations by a simple but robust semi-quantitative model for the solid-liquid contact line dynamics inspired by the standard theories for thin film dewetting.

Laminar jet dispersion and jet atomization in pressurized carbon dioxide

Abstract: Laminar jet dispersion and more particularly jet atomization of water, methylene chloride and ethyl alcohol into pressurized carbon dioxide are investigated under experimental conditions of pressure, temperature and liquid flow rate commonly used for supercritical anti solvent (SAS) precipitation processes. The different modes of dispersion are characterized as a function of the jet velocity. Axisymmetrical, asymmetrical and atomized jets are observed at 308 K, under a pressure ranging from 6 to 9 MPa, and for a liquid jet velocity ranging from to 0.14 to 8.02 m s −1 . A new correlation is given between the jet Reynolds number and the Ohnesorge number, determining the transition to the atomization regime. Experimental values of dynamic interfacial tensions are used to elaborate the correlation.

Nonlinear oscillations and collapse of elongated bubbles subject to weak viscous effects

Abstract: The weak viscous oscillations of a bubble are examined, in response to an elongation that perturbs the initial spherical shape at equilibrium. The flow field in the surrounding liquid is split in a rotational and an irrotational part. The latter satisfies the Laplacian and can be obtained via an integral equation. A hybrid boundary-finite element method is used in order to solve for the velocity potential and shape deformation of axisymmetric bubbles. Weak viscous effects are included in the computations by retaining first-order viscous terms in the normal stress boundary condition and satisfying the tangential stress balance. An extensive set of simulations was carried out until the bubble either returned to its initial spherical shape, or broke up. For a relatively small initial elongation the bubble returned to its initial spherical state regardless of the size of the Ohnesorge number; Oh=μ∕(ρRσ)1∕2. For larger initial elongations there is a threshold value in Oh−1 above which the bubble eventually bre...

Wave-turbulence interaction of a low-speed plane liquid wall-jet investigated by particle image velocimetry

Abstract: The surface-wave amplitude (free-surface level) and the turbulent velocity field of the liquid phase of a plane wall-jet flow have been simultaneously measured by means of particle image velocimetry, which allows for the investigation of surface waves and wave-turbulence interaction. The Reynolds number, Weber number, and Ohnesorge number of the tested flow, based on the bulk velocity, height of the closed channel, and physical properties of water, were 3.6×104, 1.2×103, and 9.5×10−4, respectively. Based on the measured datasets of the velocity field and free-surface level, the characteristics of the wave-turbulence interaction as well as the statistics of surface waves and turbulent velocity field were studied. The characteristics of the turbulent velocity field near the wavy free surface obtained in this study were different from those obtained previously for open-channel flows with no shear at the interface or negligible deformation of the free surface. It was found that reverse vortex motion was predo...

Study on the Mechanism of Liquid Jet Breakup under Heating Conditions

Abstract: A temporal linear instability analysis on a viscous liquid jet with temperature gradient subjected to a gas stream is presented in this paper, and the effects from various dimensionless numbers, including Weber number (We), Density ratio (Q), Marangoni number (Ma) and Ohnesorge number (Z), on the growth rate and dominant frequency of surface wave of a liquid jet was numerically studied. It was found that the thermo-capillary force induced by the temperature gradient was a significant destabilizing factor for the breakup of a liquid jet. The results also showed that the influence by Taylor regime was more remarkable to liquid jet than by Rayleigh regime, and the breakup dimension of a liquid jet decreased dramatically with the increase of temperature gradient.

Important Parameters in Drop Coalescence at Planar Surfaces

Abstract: An experimental study has been performed to establish the principal elements that govern drop coalescence. The study consisted of placing drops of various sizes and physical properties on a planar interface. The coalescence process was recorded with the aid of a high speed digital camera. The experimental portion of the project was aimed at capturing the time of coalescence and the size of the secondary drop that formed after coalescence had finished. Results of the experiments, when scaled properly, showed clear patterns with respect to inertial and viscous terms. Dimensional analysis indicated that Ohnesorge number, Oh, had a strong influence on the behavior of drop coalescence. The ratio of secondary drop radius to primary drop radius, ri , was calculated to be approximately constant when Oh was much smaller than unity. However, as Oh approached unity from the lower bound, the value of ri decayed. No secondary drop was observed when Oh was greater than unity. Normalized coalescence times confirmed this trend by being properly scaled with inertial time scales for small Ohnesorge number and preferring viscous time scales when Ohnesorge number was greater than unity.Copyright © 2005 by ASME