Particle size distribution is of utmost importance in spray dryers. Controlling the degree of agglomeration and coalescence is vital for manufacturing products that conform to the requirements. To predict the particle size accurately, this study presents a CFD model of particle agglomeration and droplet coalescence in a counter-current spray dryer. The stochastic agglomeration model was modified to incorporate more realistic droplet-droplet, droplet-particle and particle-particle interactions. Binary droplet collisions in the atomization zone of a spray dryer can result in either coalescence or separation. The boundaries between collision regimes were experimentally determined, and existing binary collision models were validated for water and milk concentrate to include the effect of viscous forces on collision outcomes. A high-speed camera was used to record the kinematic and physical properties of the droplets to identify various collision regimes. A suitable model was then incorporated in CFD simulations of spray drying. Using existing experimental data from a counter-current spray dryer with strong agglomeration, it is shown that the model can accurately predict product particle properties under different process conditions.

粒度分布在喷雾干燥器中至关重要。控制团聚和聚结的程度对于制造符合要求的产品至关重要。为了准确预测粒径，本研究提出了逆流喷雾干燥器中颗粒团聚和液滴聚结的 CFD 模型。对随机团聚模型进行了修改，以纳入更真实的液滴-液滴、液滴-颗粒和颗粒-颗粒相互作用。喷雾干燥器雾化区中的二元液滴碰撞可导致聚结或分离。碰撞机制之间的界限是通过实验确定的，并且针对水和牛奶浓缩物验证了现有的二元碰撞模型，以包括粘性力对碰撞结果的影响。高速相机用于记录液滴的运动学和物理特性，以识别各种碰撞方式。然后将合适的模型纳入喷雾干燥的 CFD 模拟中。使用来自具有强团聚性的逆流喷雾干燥器的现有实验数据，表明该模型可以准确预测不同工艺条件下的产品颗粒特性。