On the thinnest steady threads obtained by gravitational stretching of capillary jets

TL;DR

This study combines experiments and stability analysis to determine the conditions under which a highly stretched capillary jet remains steady, revealing that increasing nozzle diameter can produce thinner steady threads due to axial curvature effects.

Contribution

It extends previous work by providing a detailed theoretical and experimental analysis of the stability of capillary jets, highlighting the stabilizing role of axial curvature.

Findings

Critical flow rate for jet stability identified

Axial curvature significantly stabilizes the jet

Thinner steady threads achievable with larger nozzle diameters

Abstract

Experiments and global linear stability analysis are used to obtain the critical flow rate below which the highly stretched capillary jet generated when a Newtonian liquid issues from a vertically oriented tube, is no longer steady. The theoretical description, based on the one-dimensional mass and momentum equations retaining the exact expression of the interfacial curvature, accurately predicts the onset of jet self-excited oscillations experimentally observed for wide ranges of liquid viscosity and nozzle diameter. Our analysis, which extends the work by Sauter & Buggisch (2005), reveals the essential stabilizing role played by the axial curvature of the jet, being the latter effect especially relevant for injectors with a large enough diameter. Our findings allow us to conclude that, surprisingly, the size of the steady threads produced at a given distance from the exit can be reduced by increasing the nozzle diameter.