Atomization of superheated liquids

在过热雾化过程中，要分解的液体相对于环境加热到蒸发温度以上。因此，除了通常的压力能之外，还给出了流体解体的另一个能量分量(热)。利用该工艺，可以根据喷嘴几何形状、工艺条件和所施加流体的性质来产生具有不同尺寸分布的喷雾。与过冷喷雾相比，必须考虑其他影响，如喷嘴内流体的局部蒸发或由于粘度随温度降低而增强流体流动。在拟议的项目中，将用无量纲量来分析和描述产品特性对工艺和材料特性的依赖关系。应用项目的重点是研究复杂流变液的雾化行为以及用这些物质合成颗粒。驱动温差的方向可以通过改变环境温度来设置，环境温度对生成的粒子的形貌有很大影响。将专门设置环境温度，以分析该参数对产生的颗粒的影响。在计划的调查中，将使用聚乙烯吡咯烷酮(PVP)溶液、悬浮液(例如含水的玻璃珍珠)、两者的混合物和甘露醇溶液。这些物质的溶解度随着温度的升高而增加。因此，与过冷喷涂相比，更高的浓度(更高的过饱和度)可以被雾化，产生细小的结晶颗粒。将对合成的颗粒进行尺寸分布和形貌分析。由于对于粘度较高的流体(如PVP溶液)，液滴尺寸增大，因此将使用中空锥形喷嘴，以便即使在粘度较高的介质中也能生成细小的液滴。与迄今使用的圆柱形喷嘴相比，中空锥形喷嘴产生的水滴的中等尺寸较小；因此，可以预期PVP溶液的中等尺寸(在25℃时粘度高达514 mPas)。在带有光学通道的逆压室中，将研究雾化与较高逆压的行为。在SPP 1423中，采用了不同的喷雾工艺(气泡雾化、二氧化碳溶解雾化、外置混合喷嘴雾化)。将对这些进程的有效性进行比较，并讨论不同之处。

In the process of superheated atomization the fluid which is to be disintegrated is heated up above the evaporation temperature in respect to the ambient. Accordingly, another energy component (heat) is given for the fluid disintegration in addition to the usual pressure energy. With this process it is possible to generate sprays with varying size distributions in dependence of the nozzle geometry, process conditions and the properties of the applied fluid. In comparison to subcooled spraying additional effects like local evaporation of fluid inside the nozzle or the enhancement of fluid flow due to a viscosity reduction with temperature have to be taken into account. In the proposed project the dependency of the product properties on process and material properties will be analyzed and described by dimensionless quantities. The focus of the applied project is set on the investigation of the atomization behavior of rheologically complex fluids and the synthesis of particles with these substances. The direction of the driving temperature difference can be set by varying the ambient temperature which has significant influence on the morphology of the generated particles. The temperature of the ambient will be set specifically in order to analyze the impact of this parameter on the produced particles. For the planned investigations Polyvinylpyrrolidone (PVP) solutions, suspensions (for example glass pearls with water), mixtures of both and solutions of Mannitol will be used. The solubility of those substances increases with temperature. Accordingly higher concentrations (higher supersaturation) in comparison to subcooled spraying can be atomized yielding finely crystallized particles. The synthesized particles will be analyzed regarding size distribution and morphology. Since for higher viscous fluids (like PVP solutions) the droplet size is enhanced hollow cone nozzles will be used in order to generate fine droplets even for higher viscous media. The medium size of the water droplets is smaller for droplets generated by hollow cone nozzles in comparison to those made with a cylindrical nozzle which have been applied thus far; hence the same can be expected for PVP-solutions (viscosity up to 514 mPas at 25°C). In a counter pressure chamber with an optical access the behavior of the atomization versus a higher counter pressure will be investigated. In the SPP 1423 different spraying processes are applied (effervescent atomization, atomization by dissolution of CO2, atomization with external mixing nozzles). These processes will be compared in respect to their effectiveness and differences will be discussed.