Investigation of capillary wave formation on water jets with internally propagating ultrasound

The formation and control of capillary waves on jets are of importance in applications such as ink-jet printing, atomization of fuel, etc. External control of jet breakup processes is generally based on the ultrasonic atomization principle (used on jets of diameter in micrometer order) with transducers placed on nozzle tips. The present work investigates the formation of capillary waves and subsequent jet breakup on 10 mm and 15 mm diameter water jets with ultrasound propagating at either 121 kHz or 135 kHz. Experimental observations of the jet breakup process with a high speed camera are reported. The input signal to the transducer was controlled to investigate the formation and growth of capillary waves, leading to the breakup of the jet. It was observed that once the waves are formed on jet surface, they grow in size leading to a necking zone. Once necking zone is formed, the capillary waves then just propagate along the jet (with the flow) with no further growth in their amplitude. Spraying of the jet was also observed at the same time. The measurement of capillary wavelength and jet breakup length are measured and presented in an attempt to understand the nature of the breakup process.