Experimental investigation and modelling of coalescence and agglomeration for spray drying of suspensions

研究项目的主要目的是建立喷雾干燥过程相关条件下的液滴碰撞模型，从而建立不同干燥阶段的悬浮液和溶液液滴碰撞模型。因此，考虑了粘度占主导地位的液滴的碰撞和碰撞结果以及高粘度液滴与由此产生的团聚的碰撞。因此，应描述所生产粉末的性质，例如粒度分布和结块结构。开发的模型将在内部欧拉/拉格朗日代码中实现，以便为允许设计和优化杂散干燥过程提供工具。为实现项目目标，将在项目后期进行高粘性液滴碰撞的进一步测量。在这里，使用上一个项目期间开发的新液滴发生器可以实现高达约6 Pa s的粘度范围。在如此高的液滴粘度下，预计会有部分渗透，产生二元团聚体。穿透深度将由高速摄像机测量，并使用相关的无量纲参数进行总结。在广泛的参数研究（即冲击参数，碰撞速度和粘度比）的基础上，将详细阐述并结合适当的建模概念。在此基础上，将根据新的发现对Sommerfeld and st<s:1> bing（2012）的穿透和结构模型进行回顾和调整。所开发的液滴碰撞模型以及干燥模型将在内部欧拉/拉格朗日代码（FASTEST/Lag 3D）中实现。为了验证，将在改进的实验室喷雾干燥机上进行测量，该干燥机位于进口处，配有两个风扇式雾化器。为了确定喷雾相互作用区域，可以改变雾化器的分离。在喷嘴的近场，通过光学测量记录了由于液滴碰撞而产生合并或分离的液滴尺寸的变化。这是可能的，因为风扇喷雾相当稀释，因此光学方法，如高速摄像机，可以用来确定所有相关参数。使用大喷嘴分离，喷雾相互作用发生在远场，液滴已经干燥到很大程度，因此将观察到团聚。高速成像将再次记录团聚过程。此外，粉末探针将在测试段结束时取样，以便进行尺寸和形状分析。验证后，模拟工具将可用于预测喷雾干燥过程的粉末特性。

The main objective of the research project is related to the modelling of droplet collisions under conditions relevant for spray drying processes, thus for suspension and solution droplets with different drying stage. Consequently, the collision of viscosity dominated droplets and the collision outcome as well as the collision of high viscous droplets with the resulting agglomeration is considered. As a result, the properties of the produced powders, e.g. particle size distribution and agglomerate structure shall be described. The developed models will be implemented in an inhouse Euler/Lagrange code in order to provide a tool for allowing the design and optimisation of stray drying processes.For the realisation of the project goals further measurements of high viscous droplet collisions will be carried out in the last project period. Here a viscosity range up to about 6 Pa s can be achieved with the new droplet generators developed during the last project period. At such high droplet viscosity a partial penetration is expected, yielding binary agglomerates. The penetration depths will be measured by high-speed cameras and summarised using the relevant dimensionless parameters. On the basis of extensive parameter studies (i.e. impact parameter, collision velocity and viscosity ratio) the dependencies will be elaborated and combined to appropriate modelling concepts. On this basis the penetration and structure model of Sommerfeld and Stübing (2012) will be reviewed and adapted according the new findings.The developed droplet collision models as well as a drying model will be implemented in the inhouse Euler/Lagrange code (FASTEST/Lag 3D). For validation, measurements at the modified laboratory spray dryer will be conducted, which is at the inlet equipped with two fan-type atomisers. The separation of the atomisers may be varied in order to determine the spray interaction region. In the near field of the spray nozzles a change of the droplet size due to droplet collisions yielding coalescence or separation, are recorded via optical measurements. This is possible since the fan sprays are rather dilute, so that optical methods, such as high-speed cameras, can be utilised to determine all relevant parameters. Using large nozzle separations spray interaction takes place in the far field where the droplets have dried to a large extent so that agglomeration will be observed. The agglomeration process will be again recorded by high-speed imaging. Moreover, powder probes will be sampled at the end of the test section for allowing a size and shape analysis. After the validation, a simulation tool will be available for predicting the powder properties of spray drying processes.