Title: Axisymmetric oscillation modes of a double droplet system

Abstract

A double droplet system (DDS) consists of a sessile and a pendant drop that are coupled through a liquid filled cylindrical hole in a plate of thickness d. For a small hole radius R, equilibrium shapes of both drops are sections of spheres. While DDSs have a number of applications in microfluidics, a DDS oscillating about its equilibrium state can be used as a fast focusing liquid lens. Here, a DDS consisting of an isothermal, incompressible Newtonian fluid of constant density p and constant viscosity u that is surrounded by a gas is excited by oscillating in time (a) the pressure in the gas surrounding either drop (pressure excitation), (b) the plate perpendicular to its plane (axial excitation), and (c) the hole radius (radial excitation). In contrast to previous works that assumed transient drop shapes are spherical, they are determined here by simulation and used to identify the natural modes of axisymmetric oscillations from resonances observed during frequency sweeps with DDSs for which the combined volume V of the two drops is less than (4/3)πR³. Pressure and axial excitations are found to have identical responses but axial and radial excitations are shown to excite different modes. These modes are comparedmore » to those exhibited by single pendant (sessile) drop systems. Specifically, while a single pendant (sessile) drop has one additional oscillation mode compared to a free drop, a DDS is found to exhibit roughly twice as many oscillation modes as a pendant (sessile) drop. The effects of dimensionless volume V/R³, dimensionless plate thickness d/R, and Ohnesorge number Oh =μ/√ρRσ , where σ is the surface tension of the DDS-gas interface, on the resonance frequencies are also investigated.« less

Authors:

Ramalingam, Santhosh K. ^[1]; Basaran, Osman A. ^[1]

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+ Show Author Affiliations

1. Purdue Univ., West Lafayette, IN (United States). School of Chemical Engineering.

Publication Date:

Mon Nov 15 00:00:00 EST 2010

Research Org.:

Purdue Univ., West Lafayette, IN (United States). Chemical Engineering

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1076456

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Fluids

Additional Journal Information:

Journal Volume: 22; Journal Issue: 11; Journal ID: ISSN 1070-6631

Publisher:

American Institute of Physics

Country of Publication:

United States

Language:

English

Subject:

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; fluid drops; free surface; free oscillations; liquid surfaces; surface tension