Break-up, coalescence and catastrophic phase inversion in turbulent contactors

下降(电信) 机械 湍流 叶轮 间歇性 聚结(物理) Péclet编号 化学 热力学 材料科学 物理 计算机科学 电信 天体生物学
作者
Alvin W. Nienow
出处
期刊:Advances in Colloid and Interface Science [Elsevier BV]
卷期号:108-109: 95-103 被引量:38
标识
DOI:10.1016/j.cis.2003.10.020
摘要

When a low concentration of immiscible phase is dispersed, break-up in the impeller region controls the drop size. The traditional application of Kolmogoroff's theory of local isotropic turbulence has been moderately successful in relating equilibrium drop sizes to the physical properties and the turbulent flow, with low power number impellers giving smaller drops at equal mean specific energy dissipation rates, ε̄T. However, to explain the reduction in drop size at equal ε̄T on scale-up, the concept of intermittency must be introduced leading to a scale-up rule close to constant tip speed. With increasing concentration, coalescence generally becomes important and drop sizes increase. Modelling of coalescence involves collision frequency and coalescence efficiency. The latter is dependent on the type of drop interface, the establishment of which type for a particular system being difficult. The difficulty is compounded since in clean systems, at concentrations of the aqueous phase >∼20% by volume, droplets of oil appear in the aqueous drops whilst the converse is not found. At sufficiently high concentrations, where the concept of collision frequency is questionable, catastrophic phase inversion (CPI) occurs because coalescence becomes so high. Anything that enhances coalescence, e.g. surfactants, particles that bridge interfaces, wettable surfaces, bulk flow patterns, encourages CPI to occur at lower concentrations of dispersed phase. Satisfactory models for CPI are not available.
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