Graduate Thesis Or Dissertation
 

Effects of a thin, flexible nozzle on droplet formation and impingement

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/0z7090295

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  • The droplet formation process in the vicinity of the nozzle exit and the behavior of a spreading droplet during impingement on a smooth glass surface were studied. Two nozzle geometries were tested. The first case was a stiff stainless steel nozzle plate 0.787 mm thick. The second case was a flexible stainless steel nozzle plate 0.102 mm thick. In each case, two different waveforms were used to drive the piezoelectric element in the droplet generator. This resulted in different meniscus behavior at the nozzle exit in each case. Leading and trailing edge velocities and the position of the leading edge relative to the nozzle were measured through use of double-frame images taken with a high-speed camera to describe the formation process at the nozzle. This data was displayed in both dimensional and non-dimensional form using capillary parameters. At the impingement surface, the high speed camera was used to record the spread rate and contact angle of the droplets. This research concluded that the flexible nozzle had a significant impact on droplet formation. Exit velocities were more than double those of the stiff nozzle, and break-off times were shorter for the flexible nozzle. One drawback of the flexible nozzle was that satellite droplets were produced along with the main droplet, which did not happen with a stiff nozzle. Behavior at the impingement surface was also noted to be different in each case. However, this is not directly related to the different nozzles themselves, but rather the fact that the nozzles resulted in different droplet velocities. The spread rate of the droplets was observed to increase as the impingement velocity was increased. The dynamic contact angles were also measured and compared to existing models found in the literature. Although there were discrepancies, it is likely that these are due to the difference in Weber numbers between this experiment and the models.
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file details Mechanical_Engineering_Masters_Thesis__Hawke_.pdf 2017-08-14 Pubblico Scaricare