Experimental Investigations Of The Instability And Breakup Of Capillary Liquid Jets

The capillary instability has been an important subject in fluid mechanics since the19th century.Many researchers endeavored to explain the mechanism theoretically, while many others devisedthe experimental apparatuses and made their eforts to verify the theories. The primary aspectsof these researches refer to the liquid jet breakup, the control of the uniformity of droplets, thepropagation and development of the surface wave, and the formation of satellite droplets. Withthe investigation of these problems, the mechanism of the capillary instability is being graduallyrevealed.With the development of the experimental designs, the application of the disturbancemodulated with respect to the frequency, amplitude, and duty cycle of the electric signal pow-ering the piezoelectric actuator has been a new concept on the study of capillary instability.After this technology is applied, the control of droplets, especially the formation of satellitedroplets can be investigated. Another aspect afecting the liquid jet breakup is the nozzlegeometry. When the the complex nozzles manufactured with the laser drilling technology areutilized, the experiments referring to the liquid jet breakup of the unconventional liquid jets canbe implemented. In this project, the droplet generation system satisfying the specific require-ments of the project is designed and built to generate the monodispersed droplets. Moreover,the nozzles of diferent geometries mounted in the established experimental system are utilisedto investigate the liquid jet breakup with the modulated signal as the powering source.The experimental results based on the data derived from the images of liquid jet breakupcaptured by the fast-speed camera reveal that:(1) Among the nozzles of the same hydraulicdiameter, the jet breakup lengths of the liquid jets emanating from the non-circular nozzles arelonger than the one from the circular nozzle under the same experimental conditions.(2) Thesatellite droplets tend to form when the duty cycle is high or low.(3) The satellite droplet is afactor afecting the jet breakup length.(4) The diference of fluid properties is a factor afectingthe liquid jet breakup.(5) The application of dual-actuation mode is an efective method toreduce the jet breakup length.