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Experimental Analysis of Surface Temperature and Geometry Effects for Drop Impact on Solid Surfaces

Jowkar, Saeed | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52539 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Morad, Mohammad Reza
  7. Abstract:
  8. When a liquid drop impacts on a hot non-flat surface the curvature of the surface and its geometrical characteristics transmute the physical regimes and their boundary compared to a flat surface impact. The present experimental study is focused on water drop impingement on the mimetic solid semi-cylindrical convex and concave hot surfaces. The thermal versus inertia map of generated regimes is obtained, while some well-known regimes associated with a flat surface are not observed for the present non-flat impacts. The maximum spreading of the droplet is measured at different surface temperatures and impact Weber numbers for the case of droplet impingement on the convex surface. In directrix direction it is independent of temperature at both partial contacted and breakup regions but reduces upon transitioning at high Weber numbers. Moreover, since the spreading is asymmetric, its aspect ratio is obtained and has shown a considerable rise at partial contacted high Weber numbers. On the other hand, for the case of droplet impingement on the concave surface, it is shown that asymmetric spreading of lamella on the surface has a considerable impact on the drop bouncing which leads to suppression of maximum height of drop rebound. Furthermore, it is demonstrated that the behavior of the lamella during the spreading to its maximum diameter has a considerable impact on the maximum height of the drop bouncing. Results indicate that the thermal atomization mid-regime was eliminated in the case of drop impact on the concave surface in a wide range of impact Weber numbers and surface temperatures. The variations in rebounding and maximum heights at different regions of the maps are quantified and discussed. The morphology of drop impact on the concave surface was captured and the influence of its asymmetric deformation on extensive suppression of drop bouncing was discussed. Finally, the amount of dissipated energy due to drop deformation was obtained based on an energy balance analysis
  9. Keywords:
  10. Droplet Impact ; Rebound Effect ; Nuclear Boling ; Film Boiling Regime ; Leidenfrost Temperature ; Asymmetric Spreading

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