Atomization of superheated liquids

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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.