Break-up, coalescence and catastrophic phase inversion in turbulent contactors.
Break-up, coalescence and catastrophic phase inversion in turbulent contactors.
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DOI：
10.1016/j.cis.2003.10.020
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发表时间：
2004-05
影响因子：
15.6
通讯作者：
A. Nienow
中科院分区：
文献类型：
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作者：
A. Nienow
当分散低浓度的不混溶相时，在叶轮区域中的破碎控制液滴尺寸。Kolmogoroff局部各向同性湍流理论的传统应用在将平衡液滴尺寸与物理性质和湍流联系起来方面取得了一定的成功，低功率数叶轮在相等的平均比能量耗散率ε <$T下产生较小的液滴。 然而，为了解释液滴尺寸在等ε/Ton放大时的减小，必须引入不连续性的概念，从而导致接近恒定尖端速度的放大规则。随着浓度的增加，聚结通常变得重要并且液滴尺寸增加。聚结的建模涉及碰撞频率和聚结效率。后者取决于分接接口的类型，为特定系统建立哪种类型是困难的。困难是复杂的，因为在清洁的系统中，在水相浓度> 20%体积时，油滴出现在水滴中，而没有发现匡威的情况。在足够高的浓度下，其中碰撞频率的概念是有疑问的，灾难性的相转化（CPI）发生，因为聚结变得如此之高。任何增强聚结的物质，例如表面活性剂、桥接界面的颗粒、表面活性剂、整体流动模式，都会促使CPI在较低浓度的分散相下发生。没有令人满意的CPI模型。
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, ε ̄T. However, to explain the reduction in drop size at equal ε ̄Ton 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.