What Determines the Breakup Length of a Jet?

Area of Science:

• Fluid Dynamics
• Surface Science
• Thermodynamics

Background:

• Capillary jet breakup is traditionally attributed to external disturbances like noise, turbulence, or nozzle imperfections.
• Exponential growth of surface disturbances is the presumed mechanism governing jet disintegration into droplets.
• The precise origin and scale of these initial disturbances remain a key question in fluid dynamics.

Purpose of the Study:

• To investigate the fundamental cause of initial surface disturbances in capillary jets.
• To determine if thermal fluctuations can act as a primary driver for jet breakup.
• To validate a new model for jet breakup across a wide range of experimental parameters.

Main Methods:

• Experimental manipulation of jet diameter, velocity, and fluid properties across diverse nozzle types.
• Quantitative comparison of observed initial disturbances with predictions from thermal capillary wave theory.
• Integration of experimental data with prior molecular dynamics simulations and stochastic hydrodynamics calculations for nanojets.

Main Results:

• Initial jet disturbances are quantitatively consistent with thermal capillary waves at the angstrom scale.
• No significant variation in breakup length was observed with different nozzle types, shapes, or roughness.
• The thermal disturbance model successfully predicts jet breakup length over 4 orders of magnitude experimentally, and 7 orders of magnitude including prior simulations.

Conclusions:

• Thermal noise, manifesting as angstrom-scale thermal capillary waves, is identified as a primary driver of capillary jet breakup.
• The findings challenge the necessity of external noise, turbulence, or nozzle defects as the sole initiators of jet breakup.
• A unified model based on thermal fluctuations provides a robust explanation for jet breakup phenomena across various scales.