Zerstäubung überhitzter Fluide - Einfluss der Durchflusscharakteristik auf das Spray

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Doctoral Thesis
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Günther, Astrid

The scope of this work is the characterization of the process of super- heated atomization. Therefore, the flow through the nozzle is charac- terized applying Shadowgraphy, pressure measurements and mass flux measurements. The obtained results provide the basis for the resulting spray properties, which are analyzed as well. The characterization of the sprays is mostly conducted with optical measurement techniques (Shadowgraphy, Particle Image Velocimetry, Laser diffraction and Ra- man-Scattering). In addition, temperature measurements applying thermocouples and acoustical measurements for the determination of spray pulsation are conducted. The aim is a dimensionless characteri- zation of the whole process, including nozzle throughput and spray properties. Deionisied water as model fluid, as well as more complex fluids like polymer solutions and suspensions are atomized. In order to quantify the influence of process parameters, the liquid pressure and liquid temperature are varied. Furthermore different nozzle types are used, including hollow cone nozzles (lamella breakup) and plain orifice noz- zles (jet breakup). The geometry of the latter is varied regarding nozzle diameter, L/D-ratio, inner capillary roughness and outlet geometry. The dimensionless characterization of the superheated atomization is executed with known dimensionless numbers like the discharge coeffi- cient C D or the Pressure Number p * . Thereby it is possible to estimate the superheated throughput based on the subcooled mass flux. Fur- thermore the medium droplet size can be derived from known process parameter and mass flux values. With regard to the effectiveness, su- perheated atomization ranges in below pneumatic atomizers. Howev- er, the atomization effectiveness is only considering the droplet size as characteristic target quantity.

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