Date of Award
December 2024
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Mechanical Engineering
First Advisor
Hallie Chelmo
Abstract
Ice crystal aggregates are observed in upper stratospheric clouds. The crystal aggregates can form in different orientations, geometry, and shapes which are not well studied. These crystal aggregations are found in the clouds as crystal chains of various lengths and cause damage to hypersonic vehicles which include missiles, re-entry vehicles, and jet aircraft. The reasons behind such damage by atmospheric crystal chains to hypersonic bodies are unknown. That is why studying these ice crystals and their behavior in the hypersonic environment is necessary. Ice crystals form in the atmosphere in two different ways which are homogenous and heterogenous. Heterogenous freezing has been widely researched compared to homogenous freezing but cannot answer the ice crystal aggregation phenomena. Homogenous freezing is difficult to achieve in a lab environment due to its freezing nature. In this research, the adoption of two different methods to levitate water and microdroplets for initiating homogeneous freezing is discussed. These two different methods are the acoustic levitator and the dual balance electrodynamic trap (DBET). Acoustic levitator traps water droplets with the help of acoustic force and the DBET uses electrodynamic force to trap a micrometer-sized water droplet. With the incorporation of cooling systems along with these devices, the levitated water droplet can be frozen. In this research, the freezing procedure, size measurements, and images of different levitated ice shapes using an acoustic levitator are shown. This research also discusses the components, troubleshooting procedure, and a merging experiment of two charged 2.5wt% NaCl droplets using a DBET instrument in detail. A Cu coil tube has also been designed, incorporated, and insulated with the DBET to make ice crystals from levitated microdroplets which is a future work. The future work also includes ice crystals dropping from the acoustic levitator inside the shock tube to study and understand ice crystal behavior in the shock wave region. In relation to that a fall time calculation for spherical droplets inside the shock tube from several nodes of the acoustic levitator has also been presented here. For studying the ice crystal and shockwave interaction, precise time calculation between several components such as the time delay of myler bursting after entering the command, time for the shockwave to reach the viewing window, ice crystal falling time to the viewing window, high-speed camera recording etc. to be done inside the shock tube. This research also talks about the upcoming challenges and plans in brief to overcome those.
Recommended Citation
Osmani, Imteaz, "Experimental Investigation Of Freezing Microdroplets For Understanding Chain Crystal Aggregates Observed In Atmospheric Clouds" (2024). Theses and Dissertations. 6557.
https://commons.und.edu/theses/6557