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Experimental Investigation of Velocity Field Due to Liquid Droplet Impingement Onto the Surface af a Molten Phase Change Material

Asadi, Mohammad Reza | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56913 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Shafii, Mohammad Behshad; Ghahremani, Amir Reza
  7. Abstract:
  8. The impact of droplets is a widely used method for creating direct heat transfer between two fluids. This method enhances heat transfer between the working fluid and the phase change material (PCM). Therefore, a thorough investigation has been carried out on the impact of an acetone droplet on the surface of a pool of molten paraffin, which leads to the simultaneous boiling of the acetone droplet and solidifying part of the paraffin in contact with the acetone. The dynamics of impact, the depth and width of the crater, the jet, and the crown formed as a result of the impact have been reported with varying Weber numbers (ranging from 74 to 375), and the temperature of the pool surface of the molten phase change material (ranging from 65 to 90). Furthermore, the experimental data obtained for the crater depth has been compared with theoretical equations. Six regimes have been observed by changing the Weber number and the temperature of the molten PCM pool surface. It has been observed that an increase in the Weber number or the surface temperature leads to an increase in the depth and width of the crater and the height of the jet and crown. The velocity field resulting from the impact around the crater has been obtained using the particle image velocimetry (PIV) method and high-speed imaging from two different angles (perpendicular and parallel to the pool surface), and the effect of impact parameters on the velocity field has been reported quantitatively and qualitatively. At the moment of impact (at 90℃), maximum velocity is at the lowest point of the crater and equal to approximately 10% of the impact velocity. It has also been observed that the area of solidified paraffin generally increases with an increase in the Weber number (up to We = 297) and a decrease in the surface temperature. Solidified area at this Weber number at T = 90℃ is 9.3% of that at 65℃ Finally, the acetone vapor has been visualized using Z-type Schlieren imaging and compared in different conditions. Acetone evaporation rate, is increased with Weber number increment
  9. Keywords:
  10. Droplet Dynamics ; Particle Image Velocimetery (PIV) ; Phase Change Material (PCMs) ; Solidification ; Velocity Field ; Boiling Droplet Impact

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