DRYING OF MOIST POROUS MEDIA WITH ELECTROHYDRODYNAMICS AND DEVELOPMENT OF NOVEL ATOMIZER FOR SPRAY DRYING

Yang, Mengqiao

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DRYING OF MOIST POROUS MEDIA WITH ELECTROHYDRODYNAMICS AND DEVELOPMENT OF NOVEL ATOMIZER FOR SPRAY DRYING

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Drying of moist porous media, such as food, forest products, chemicals and pharmaceuticals is an energy-intensive process. Traditional drying technologies have disadvantages, including high and inefficient energy consumption, large carbon footprint, thermal degradation of the products, as well as high capital cost. In addition, commercial spray dryers have the disadvantage of nonuniform particle size distribution. To improve the above-mentioned issues, in this dissertation, a fundamental understanding of drying of moist porous media with electrohydrodynamics (EHD) mechanisms is investigated. Furthermore, the ultrasonically actuated radial jet reattachment (RJR) atomizer is studied. This dissertation is organized in three major parts as follows: The first part focuses on the improvement of an existing impinging jet nozzle with the ionic wind. Specifically, the performance of the Slot Jet Reattachment (SJR) nozzle is numerically investigated by the application of an ionic wind, generated in the corresponding recirculation region. The simulation results show a significant secondary flow induced under the nozzle, due to ionic wind. A significant enhancement of local and average heat transfer coefficients is achieved. In the second part, a new novel technology, making use of the Dielectrophresis (DEP) mechanism, is introduced, to enhance the drying process of moist porous media. The experimental setup is designed and fabricated to experimentally determine the impact of DEP extraction force on the drying of moist hand-sheet papers. The experimental results show a significant impact of the DEP force on the temperature profile and drying rate. In addition, the results also show extremely low energy consumption and high energy efficiency associated with the application of DEP force for drying. Furthermore, a detailed two factorial design experiment is carried out to statistically obtain a correlation for drying of moist porous media in the presence of DEP force, an in-depth analysis at sheet formation level is provided for explaining the experimental results. The third part focuses on development and understanding an ultrasonically actuated RJR atomizer through a detailed experimental study. Specifically, the piezo mesh-based atomizer shows a significant production rate and uniform droplet size distribution. The high-speed visualization provides a fundamental understanding of the atomization process excited by ultrasonic waves. Additionally, the influence of liquid viscosity is studied for atomization performance.

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