Research On Dynamics And Thermodynamic Characteristics Of Droplets On Surfaces With Uniform/Non-uniform Wettability

In recent years, with the rapid development of microelectronics technology, integration of electronic components result in higher heat flux. However, conventional cooling technology has been difficult to meet its cooling requirements. As a phase change heat cooling technology, spray cooling, which has efficient heat transfer capability and strict temperature control capabilities, has been used in more and more electronic components with high heat flux density. Spray Goofing is a complicated phase change heat transfer process. Free evaporation of droplet is a complex process with a transmission mechanism is not clear, the influence factors in addition to the droplet itself physical properties, evaporation conditions, including solid surface properties, is of great significance to explore the impact of surface wettability on a droplet free evaporation. This paper first through a facile hydrothermal method one step preparation of superhydrophobic surface, the surface infiltration effect of droplet dynamics followed by means of numerical simulation, through the visualization research of the droplet in different on the surface of the evaporation process, the main contents include: the evaporation of droplet is free the complex process of a transmission mechanism is not clear, the influence factors in addition to the droplet itself physical properties, evaporation conditions, including the surface properties, is of great significance to explore the impact of surface wettability on a droplet free evaporation. This paper first through a facile hydrothermal method one step preparation of super hydrophobic surface, the surface infiltration effect on droplet dynamics, by using numerical simulation technology, through the visualization research of droplet in different on the surface of the evaporation process, the main contents include:(1)Superhydrophobic cathodic cobalt and anodic copper surfaces were fabricated by one-step electrodeposition process. The superhydrophobicity properties, morphological features and chemical composition of the coatings were characterized. The results show that a short time of 0.5 min is sufficient to render superhydrophobicity on the cathodic cobalt deposit. The cathodic cobalt surface exhibits a contact angle of 160 o and a sliding angle of 6.2o when it is electrodeposited for 5 min. The corresponding anodic copper surface displays superhydrophobicity with a contact angle of 153 o and a sliding angle of 6.8o after electrodeposition for 2 h. Meanwhile, the cathodic cobalt surfaces show superhydrophobicity even for corrosive liquids with p H value ranging from 1.0 to 14.0. But, the anodic copper surfaces only have superhydrophobicity in the neutral, weak alkaline or acid aqueous solutions. The superhydrophobicity of the surfaces result from the formation of the myristate compounds on their surfaces and their special micro-/nanostructures.(2)Dynamic behavior of an impacting water droplet was simulated with the VOF(volume of fluid) method. Droplet diameter was 2.6 mm and impacting velocity was 0.5 m·s-1. Droplet dynamic behavior on simulated,hydrophilic and hydrophobic surfaces was simulated with an impacting angle of 60°, 90°, 120°and 160°. Simulation results showed reasonably good agreement with the experiment data Surface wettability seriously affected droplet dynamic behavior. Droplet spread well and then socked on the hydrophilic surface. On the surface with an impacting angle of 90° droplet partly rebounded away from the surface. While droplet totally rebounded when impacting on the hydrophobic surface. There was an edge liquid ring for liquid sticking on the droplet edge when contact line draw back. The maximum spreading factor and the time needed to arrive at the maximum spread diameter were reduced with increasing contact angle.(3)Droplet evaporation process dynamic contact angle and morphology were recorded by contact angle measurement, the temperature distribution inside the droplet were recorded by the thermal imager, the results show that: the droplet evaporation rate on the hydrophilic copper surface is higher than the hydrophobic copper surface, and the evaporating droplets on former one has a more uniform temperature distribution in the interior of the droplets.(4) A photolithography process was used in the preparation of indium tin oxide/octadecyltrichlorosilane(hydrophilic/hydrophobic) patterned surface on glass, and the droplets evaporation processes on a different patterned surface were recorded through the high-speed camera. The results show that:, the glass surface hydrophilic / hydrophobic patterning had a significant effect on the micro-droplet evaporation in the range of 50-110 ℃, evaporation rates up to a stripe pattern, hexagonal pattern, followed by the worst form of radiation; evaporation during a fixed time and a ratio of the droplets and the surface morphology of the total time of evaporation, but not to the temperature.