静态混合器中液液分散的实验及CFD模拟

Experimental and numerical study on liquid-liquid dispersion in static mixer

在SK型静态混合器上进行甲苯-水两相混合实验,采用截面直接拍摄法获得分散混合性能指标Sauter平均直径(SMD)。利用Box-Behnken响应面分析设计实验,在Design Expert 7.0平台上拟合实验数据,获得SMD的多项式形式的表达式。建立了与实验相同的静态混合器物理模型,使用Mixture多相流模型、k-ε湍流模型进行了CFD模拟研究,获得了浓度场云图及分布混合指标不均匀系数。模拟所得压降与实验值的相对误差在15%以内,表明模拟结果与实验结果吻合较好。结果表明,静态混合器中液液分散过程是分散混合和分布混合共同作用的结果,两种混合经过6～8个混合单元后共同达到充分发展。充分发展后的SMD受表观流速、分散相分率和静态混合器直径三因素影响,且表观流速的影响最为显著;充分发展后的不均匀系数均达0.05以下,表明静态混合器自身具有较好的分布混合性能。

Distributive mixing and dispersive mixing for the dispersion of toluene in water in a Kenics static mixer were investigated by means of numerical modelling tools and experimental study.Dispersive mixing performance was described as Sauter mean diameter（SMD）,which was measured by photographic technique（direct shooting method on a cross-section）.Polynomial expression of SMD was built by three factor Box-Behnken design and response surface analysis,which was based on Design Expert 7.0 code.A physical model of the static mixer was built,which was the same as the experimental apparatus.Mixture multiphase model and standard k-ε turbulence model were chosen for CFD modeling.The contours of concentration field and non-uniform coefficient were obtained.Distributive mixing performance was described as non-uniform coefficient,which was calculated by contours of concentration field.The total deviation between simulated and experimental pressure drops was less than 15% in this way.Thus,the simulated results showed good agreement with the experimental results.The results showed that liquid-liquid dispersion in static mixer could be attributed to the combination of distributive mixing and dispersive mixing.A fully developed state for both mixing processes could be achieved through 6—8 mixing units.The influences of superficial velocity,volume fraction of dispersed phase and pipe diameter on fully developed SMD were obvious,but the influence of superficial velocity was most significant.The non-uniform coefficient in fully developed section decreased to below 0.05,so that the static mixer had excellent performance on distributive mixing under wider experimental conditions.