Title: Turbulent coagulation model considering effects of London-van der Waals force and wettability

Authors: Takehiro Nakaoka, Katsutoshi Matsumoto, Shoji Taniguchi

Addresses: Mechanical Engineering Research Laboratory, Kobe Steel Ltd., 1-5-5 Takatsukadai, Nishi-ku, Kobe 651-2271, Japan. ' Department of Environmental Studies, Graduate School of Environmental Studies, Tohoku University, 6-6-02 Aoba-yama, Aoba-ku, Sendai 980-8579, Japan. ' Department of Environmental Studies, Graduate School of Environmental Studies, Tohoku University, 6-6-02 Aoba-yama, Aoba-ku, Sendai 980-8579, Japan

Abstract: In this study, coagulation rates of various particles observed in agitated water were analysed by a mathematical model of turbulent coagulation. This model is based on the Saffman-Turner model of turbulent collision modified by Higashitani to take into account, van der Waals-London force between a pair of particles under collision. The Higashitani model could not account for the retardation of coagulation rate at high concentrations of suspended particles, which was observed in our precious studies. The new model proposed in this study considered the breakup of coagulating particles due to collision with other particles, and the turbulent shear force. Two parameters were introduced in the model; one was the film-thinning time and the other the breakup frequency. By choosing suitable values of the two parameters, the estimated coagulation curves fitted well with the observed curves. In addition, the film-thinning time increased with increasing wettability of particle and the breakup frequency increased with increasing turbulent intensity.

Keywords: non-metallic inclusion; turbulent coagulation; coagulation coefficient; clean metal; Hamaker constant; Saffman-Turner model; Higashitani model; film thinning models; particle size grouping method; coagulation modelling; agitated water; coagulating particles; London-van der Waals force; wettability; turbulent shear force.

DOI: 10.1504/PCFD.2008.019480

Progress in Computational Fluid Dynamics, An International Journal, 2008 Vol.8 No.5, pp.270 - 275

Published online: 14 Jul 2008 *

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