Abstract
In this study, the air core dynamics inside of a pressure swirl nozzle and its effect on the resulting spray were examined. To do this, a transparent, 10 times scaled-up version of a pressure swirl nozzle which is used in industry is examined at different flow rates, with the transparency of the nozzle ensuring the air core dynamics can be readily observed, as well as the cone-shaped spray that is ejected from the nozzle.For this, the use of High-Speed Shadowgraphy and Phase Doppler Anemometry (PDA) was important to find the air core size, break-up length of the coned spray, and the cone angle of this spray, in addition to a mean axial velocity profile and a droplet size distribution found in the spray area. The high-speed shadowgraphy was used to determine at which flow rates the air core start to form in the different parts of the nozzle, and to find the cone angle and average break-up length of the resulting coned spray. The resulting flow rates are a minimum of 1.4 L/min to force the air core into existence in the exit orifice and is fully developed in this area at 3.0 L/min. The flow rate where the air core is fully developed in the whole nozzle has yet to be found, and thus new studies will need to be done to find this. The relation between the flow rate and the air core size and development is positive and stagnates at a relatively constant value. The average break-up length of the spray increases with increasing flow rate, and to starts to stagnate at higher flow rates. However, the behavior above 5.0 L/min was not looked into and thus has to be done in the new research. Finally, the cone angle once more has a positive relationship and increases with increasing flow rate and air core size.
For the mean axial velocity distribution, droplet size distribution, and the determination of the second break-up length, PDA was used. Here, velocity distribution found that the velocity outside of the coned spray is higher than inside. Due to limitations of the setup, the whole velocity distribution could not be determined and thus needs to be measured in a different setup. The droplet size distribution was not found, as the mean droplet size and spherical validity were not correct, due to limitations of the Phase Doppler Anemometry technique itself; the droplets resulting from the spray being too large to be effectively measured. This was proven using imaging of the droplets with high-resolution (mm/pixel) high-speed shadowgraphy and thus concludes that PDA is insufficient at measuring the droplet size from this coned spray.
| Date of Award | 26 May 2023 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Vivekanand Swami (Supervisor 1), Kay A. Buist (Supervisor 1), J.A.M. (Hans) Kuipers (Supervisor 2) & Maike W. Baltussen (Supervisor 2) |