Research On Dynamic Characteristics Of Bubble/Droplet Impacting On Hydrophobic Surface

The phenomenon of droplet/bubble impacting on solid wall can be widely found in many fields,such as chemical engineering,aerospace and hydraulic project.Therefore the study of droplet/bubble dynamics characteristics is of great significance for the effective use and control of droplet/bubble and the application of hydrophobic surface.In this paper,dynamics characteristics of droplet/bubble impacting on hydrophobic surface is studied systematically.The main contents are as follows:By using the technology of laser manufacture and self-assemble,hydrophobic surfaces with different wettability were obtained.In addition,the impacting process of droplet on hydrophobic surfaces was recorded by the high speed camera system.The effects of surface temperature,wettability and dripping height on droplet dynamics were emphatically studied.The experiment results indicated that with the increase of temperature,the spreading coefficient decreases but the rebounding coefficient increases.This is consistent with the effect of enhanced surface hydrophobicity.The boiling time is shortened and affected weakly by dripping height when the surface hydrophobicity becomes weaker.As the dripping height becomes larger,the boiling time is shortened.The way of ventilation was used to produce bubble in water.Bubble moved upward under buoyancy and impacted the upper wall finally.The heating plate was attached to upper wall to control the temperature by loading current.The influences of wall temperature,rising distance and wettability were studied.The results show that with the increase of wall temperature and the rising distance,the spreading coefficient increases but the rebounding coefficient decreases.The stronger the surface hydrophobicity,the stronger the influence of temperature on spreading coefficient and rebounding coefficient.Hydrophobic surfaces were attached as walls of micro channel.The state of bubble was recorded by the high speed camera system.The effects of temperature,flow velocity,liquid viscosity and wall wettability on bubble dynamics were studied.The results measured by micro channel and sessile drop method were compared.The following results can be obtained.With the increase of wall temperature,the real static contact angle increases,the wall hydrophobicity becomes stronger and the pressure at the entrance decreases.The greater the fluid viscosity,the greater the change of pressure value.The results of sessile drop method are smaller than those in micro channel.