Record Details

Coalescence in a surfactant-less emulsion under simple shear flow

DSpace at IIT Bombay

View Archive Info
 
 
Field Value
 
Title Coalescence in a surfactant-less emulsion under simple shear flow
 
Creator NANDI, A
MEHRA, A
KHAKHAR, DV
 
Subject colloidal dispersions
stabilized emulsions
polymer blends
linear flow
drops
efficiency
suppression
coagulation
diffusion
fields
emulsion
coalescence
smoluchowski
shear flow
drop size distribution
population balance
 
Description Shear-induced coalescence is investigated in a neutrally buoyant, surfactant-less oil-in-water emulsion containing an electrolyte. Emulsion drops are large enough for Brownian motion-induced coalescence to be negligible. The emulsion is subjected to a simple shear flow in a tangential Couette apparatus with a rotating inner cylinder, and the evolution of the drop size distribution with time is obtained using optical microscopy and image analysis. The effect of varying the shear rate and the dispersed phase holdup is studied. The evolving drop size distributions become bimodal with increasing coalescence and are not found to be self-similar. A population balance model with an empirical coalescence efficiency (ratio of the actual coalescence rate to the Smoluchowski rate), function containing four fitting parameters describes the time evolution of the experimental drop size distribution reasonably well. The coalescence rate, inferred qualitatively from the measured drop size distributions at different times as well as obtained from the fitted coalescence efficiency, is found to increase with increasing shear rate and dispersed-phase holdup. The coalescence efficiency also increases with holdup, although it decreases with increasing shear rates. The fitted coalescence efficiency results indicate the existence of a critical drop diameter of 12 Am at which the coalescence efficiency is maximum. The computed magnitude of the coalescence efficiency is of the order of 10(-2) for all cases and is about 100-fold larger than that obtained earlier for surfactant-stabilized emulsions. The results indicate that coalescence in surfactant-less emulsions is qualitatively different from that in emulsions containing surfactant. The experimental findings are discussed in the light of recent theories and experimental work in this field. (c) 2005 American Institute of Chemical Engineers.
 
Publisher JOHN WILEY & SONS INC
 
Date 2011-08-04T11:53:22Z
2011-12-26T12:54:42Z
2011-12-27T05:42:54Z
2011-08-04T11:53:22Z
2011-12-26T12:54:42Z
2011-12-27T05:42:54Z
2006
 
Type Article
 
Identifier AICHE JOURNAL, 52(3), 885-894
0001-1541
http://dx.doi.org/10.1002/aic.10682
http://dspace.library.iitb.ac.in/xmlui/handle/10054/9350
http://hdl.handle.net/10054/9350
 
Language en