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Breakage of a drop of inviscid fluid due to a pressure fluctuation at its surface

Published online by Cambridge University Press:  26 April 2006

Shreekumar
Affiliation:
Department of Chemical Engineering, Indian Institute of Science, Bangalore 560012, India
R. Kumar
Affiliation:
Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India
K. S. Gandhi
Affiliation:
Department of Chemical Engineering, Indian Institute of Science, Bangalore 560012, India

Abstract

In this work, an attempt is made to gain a better understanding of the breakage of low-viscosity drops in turbulent flows by determining the dynamics of deformation of an inviscid drop in response to a pressure variation acting on the drop surface. Known scaling relationships between wavenumbers and frequencies, and between pressure fluctuations and velocity fluctuations in the inertial subrange are used in characterizing the pressure fluctuation. The existence of a maximum stable drop diameter dmax follows once scaling laws of turbulent flow are used to correlate the magnitude of the disruptive forces with the duration for which they act.

Two undetermined dimensionless quantities, both of order unity, appear in the equations of continuity, motion, and the boundary conditions in terms of pressure fluctuations applied on the surface. One is a constant of proportionality relating root-mean-square values of pressure and velocity differences between two points separated by a distance l. The other is a Weber number based on turbulent stresses acting on the drop and the resisting stresses in the drop due to interfacial tension. The former is set equal to 1, and the latter is determined by studying the interaction of a drop of diameter equal to dmax with a pressure fluctuation of length scale equal to the drop diameter. The model is then used to study the breakage of drops of diameter greater than dmax and those with densities different from that of the suspending fluid.

It is found that, at least during breakage of a drop of diameter greater than dmax by interaction with a fluctuation of equal length scale, a satellite drop is always formed between two larger drops. When very large drops are broken by smaller-length-scale fluctuations, highly deformed shapes are produced suggesting the possibility of further fragmentation due to instabilities. The model predicts that as the dispersed-phase density increases, dmax decreases.

Type
Research Article
Copyright
© 1996 Cambridge University Press

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