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research-article

Computational Modeling of Adiabatic Bubble Growth Dynamics from Submerged Capillary-Tube Orifices in Aqueous Solutions of Surfactants

[+] Author and Article Information
Sanjivan Manoharan

249 Kennedy Hall of Engineering, Grand Valley State University, Grand Rapids, MI 49504
manohars@gvsu.edu

Anirudh Deodhar

Thermal-Fluids & Thermal Processing Laboratory, Department of Mechanical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221
anirudh.deodhar@gmail.com

Raj M. Manglik

ASME Fellow, Thermal-Fluids & Thermal Processing Laboratory, Department of Mechanical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221
raj.manglik@uc.edu

Dr. Milind A. Jog

ASME Fellow, Thermal-Fluids & Thermal Processing Laboratory, Department of Mechanical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221
Milind.Jog@uc.edu

1Corresponding author.

ASME doi:10.1115/1.4042700 History: Received September 24, 2018; Revised January 16, 2019

Abstract

The growth dynamics of isolated gas bubbles from a submerged capillary-tube orifice in a pool of an aqueous surfactant (sodium dodecyl sulfate/SDS) solution is computationally investigated. The governing equations for surfactant mass transport in the bulk liquid and interfacial adsorption-desorption are solved simultaneously with Navier-Stokes equations, employing the volume-of-fluid (VOF) technique to track the deforming interface. The VOF method tends to spread the liquid-air interface over two to three cells creating an interface region with finite thickness. A numerical treatment is developed to determine the surfactant transport and adsorption/desorption in the interface region. From the surfactant interfacial concentration, the spatio-temporal variation in interfacial tension and the bubble shape are predicted. For model validation, measurements of bubble shape and size are carried out using high speed videography. Because of the decrease in surface tension with surface age, bubble departure diameters in SDS solutions are smaller than those obtained in pure water, and they are a function of bubble frequency. At higher air flow rates (smaller surface age), the departure diameters tend towards those in pure water. Whereas, at low flow rates (larger surface age), they are significantly smaller than those in water and are closer to those in a pure liquid having surface tension equal to the equilibrium value in SDS solution. Furthermore, the nonuniform surfactant adsorption at the evolving interface results in variation in interfacial tension, and thus their shapes in surfactant solution are different from those in a pure liquid.

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