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

该研究项目的主要目标是与喷雾干燥过程相关条件下的液滴碰撞建模有关，因此对于具有不同干燥阶段的悬浮液和溶液液滴。因此，粘度为主的液滴的碰撞和碰撞的结果，以及高粘度液滴与所产生的团聚的碰撞被认为是。因此，应描述所生产粉末的性质，例如粒度分布和团聚体结构。开发的模型将在内部欧拉/拉格朗日代码中实现，以提供一种工具，允许设计和优化杂散干燥过程。为了实现项目目标，将在最后一个项目期间对高粘度液滴碰撞进行进一步测量。在这里，粘度范围高达约6帕秒，可以实现与新的液滴发生器在最后一个项目期间开发。在如此高的液滴粘度下，预期部分渗透，产生二元附聚物。将通过高速摄像机测量穿透深度，并使用相关无量纲参数进行汇总。在广泛的参数研究（即撞击参数、碰撞速度和粘度比）的基础上，将详细阐述各种相关性，并将其与适当的建模概念结合起来。在此基础上，对Sommerfeld和Stübing（2012）的渗透和结构模型进行了回顾，并根据新的研究结果进行了调整。所开发的液滴碰撞模型以及干燥模型将在内部Euler/拉格朗日程序（FASTEST/Lag 3D）中实现。为了验证，将在改进的实验室喷雾干燥器中进行测量，该干燥器位于配备两个风扇式雾化器的入口处。为了确定喷雾相互作用区域，可以改变雾化器的间隔。在喷嘴的近场中，通过光学测量记录由于液滴碰撞产生聚结或分离而引起的液滴尺寸的变化。这是可能的，因为扇形喷雾是相当稀释的，所以光学方法，如高速摄像机，可以用来确定所有相关参数。使用大的喷嘴间隔，喷雾相互作用发生在远场，其中液滴已经干燥到很大程度，使得将观察到团聚。团聚过程将再次通过高速成像记录。此外，将在试验部分结束时对粉末探针进行取样，以进行尺寸和形状分析。验证后，一个模拟工具将可用于预测喷雾干燥过程中的粉末性质。

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.