Energy dissipation rate

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Droplet Break-Up By In-Line Silverson Rotor–Stator Mixer

Journal Title, Volume, Page: 
Chemical Engineering Science Volume 66, Issue 10, 15 May 2011, Pages 2068-2079
Year of Publication: 
2011
Authors: 
A.El-Hamouz
Department of Chemical Engineering, An-Najah National University, Nablus, West Bank, PO Box 7, The Palestinian Authority, Occupied Palestinian Territory
Current Affiliation: 
Department of Chemical Engineering, An-Najah National University, Nablus, Palestine
S. Hall
School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
M.Cooke
School of Chemical Engineering & Analytical Science, The University of Manchester, Sackville Street, PO Box 88, Manchester,
A.J.Kowalski
Unilever Research & Development, Port Sunlight Laboratory, Quarry Road East, Bebington, Wirral, CH63 3JW, UK
Preferred Abstract (Original): 
Silverson high shear in-line rotor–stator mixers are widely applied in industry for the manufacture of emulsion-based products but the current understanding of droplet breakage and coalescence in these devices is limited. The aim of this paper is to increase the understanding of droplet break-up mechanisms and to identify appropriate literature correlations for in-line rotor–stator mixers. Silicone oils with viscosities ranging from 9.4 to 969 mPa s were emulsified with surfactant in an in-line Silverson at rotor speeds up to 11,000 rpm and flow rates up to 5 tonnes/h. The effect of rotor speed, flow rate, dispersed phase fraction up to 50 wt%, inlet drop size and viscosity ratio on droplet size was investigated. It was found that rotor speed and dispersed phase viscosity have a significant effect on the droplet size, while flow rate, inlet droplet size, viscosity ratio and dispersed phase volume have a lesser effect. The results indicate that low viscosity droplets are broken by turbulent inertial stresses, while droplets smaller than the Kolmogorov length scale are broken by a combination of inertial and viscous stresses. It also appears that the weak dependence of drop size on flow rate enables the energy efficiency of an in-line high shear Silverson to be significantly improved by operating at as high a flow rate as possible.
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