Continuous droplet impinging on the heated nano-coating surface

• Main Author: Ni, Qiming
• Other Authors: Fei Duan
• Format: Final Year Project
• Language: English
• Published: 2017
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/71407
• Institution: Nanyang Technological University

With aid of high-speed imaging method, the boiling phenomena of a single droplet and droplet train on the heated surface can be identified. As the development of nano-coating technology, nowadays the solid surfaces with nanotubes are widely used in industry. The nanotubes can improve the surface properties, and increase the nucleation sites to enhance the boiling, which can be applied on the impingement cooling for CPU. Experiments were designed to understand the fluid dynamics and heat transfer mechanisms of the liquid droplet impinging on the solid titanium surface with anodic titanium nanotubes. For single droplet impingement test, the boiling regimes can be classified as film evaporation regime, nucleate boiling regime (include gentle nucleate boiling and violent nucleate boiling) and film boiling regime. The changes of contact height and contact diameter corresponding with time were found in the experiments. Contact height reduced linearly as evaporate time increasing, and the contact diameter remained stable at first, and the decreasing rate of contact diameter was very large at the end of evaporation. The total evaporation time decreased as the weber number (We) increase. For droplet train test, different boiling phenomena were observed as the temperature increasing. The interesting unsymmetrical splashing angle was observed, the differences of splashing appearance and amount of heat transferred between temperature increasing and decreasing process were found, and the complicated heat transfer and temperature distribution of the heated surface were also discussed in the report. For future works, contrast experiment needs to be conducted by using pure titanium surface, the surface should be polished and have small surface resistance. By comparing the results, the further understanding can be made for the influence of nano-arrays on heat transfer and fluid dynamics mechanisms.