Liquid jet stability through elastic planar nozzles

An extensive number of processes require liquid jets such as cleaning, waterjet cutting, hydroentanglement, and atomization in combustion. The coherence and stability of the jet highly depend on the characteristics of the nozzle. Jet breakup lengths have been extensively studied for a multitude of nozzle characteristics and external stimuli, yet jets issuing from deformable, elastic nozzles have not been considered. In this study, we take the enduring topic of jet breakup into a new realm by introducing nozzles that passively deform when exposed to liquid flow by making an approximately 500 mu m orifice in thin sheets. We perform the experiments with nozzles of varying hardness and thickness, starting with a rigid BeCu nozzle, and continuing with shore hardness 70A, 65A, 35A and 20A. We observe nozzle dilation scales well with Reynolds number and that softer nozzles experiences greater dilation, as expected. We introduce a modification to linear stability theory to describe the break-up length of deformable nozzles to account for the dilation, a scaling which works best for our stiffer nozzles. The three softest materials provide the most stable jets through the range of flow rates in which they can operate before failure. For all nozzles, breakup is highly variable with time and jet velocity.