Study of Dynamics of Water Droplet Freezing

• Author / Creator

  Komaragiri, Lalitha Ganesh Prabhu

• This thesis delves into the intricate dynamics of water droplet freezing, a phenomenon with profound implications across a spectrum of fields including climate science, anti-icing technologies, and cryogenic 3D printing. The influence of heat transfer on the wettability and freezing processes of water droplets was investigated. Utilizing a jet-based dosing system, droplets were deposited onto precooled substrates of varying thermal conductivities. The simultaneous spreading and freezing dynamics of a water droplet was investigated. The spreading and freezing stages of droplets created by a continuous jet have been outlined. Thermal imaging showed that the effect of supercooling was absent in the dosing with jet-based methods. A theoretical model was proposed to elucidate the temporal evolution of the three-phase contact line (TPCL). The model was nondimensionalized using appropriate length, time, and temperature scales. The findings demonstrate a pivotal relationship between the Stefan number and the spreading rate. The time delay at the beginning of freezing is significantly influenced by the Ste number. The universal behavior of the tip-cone angle created by the frozen water droplet was also analyzed. It was observed that, for a particular density ratio, the ratio between the height of the solidified droplet and the liquid droplet remains constant, irrespective of the droplet's shape. This can be considered as the true universality of the frozen droplet. This was observed for the case of symmetric and asymmetric droplets. A series of parabolic flights were performed that simulate microgravity, martian gravity, and hypergravity to investigate the influence of body forces on the universal behavior of the frozen water droplets. In the present study, a more general theoretical model that can predict the solid-liquid height ratio, called the``two triangle" approach, was proposed. Finally, the current study aims to investigate the freezing dynamics and morphology by examining the process of successive droplet dosing onto a cold substrate and the formation of column-like ice structures at a macroscopic level. Using a jet-based dosing mechanism, we meticulously controlled the deposition of water droplets onto a smooth copper substrate maintained at subzero temperatures. The experimental design systematically varied the volume and frequency of the droplets. Different final column structures were observed under different experimental conditions. Real-time shadowography and thermal imaging were utilized to capture morphological and thermal changes during the freezing process. The effects of remelting and heat accumulation on the bonding and the form of the column-ice structure were investigated. Lastly, an optimized volume and frequency sequence was suggested to obtain ideal bonding conditions.

• Subjects / Keywords

  • Droplet freezing
  • Droplet spreading
  • Overall Energy Balance
  • Column-ice structures

• Graduation date

  Spring 2024

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-6ctj-kf29

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.