2025 AIChE Annual Meeting

(65e) Escape from Pinch-Off during Contraction of Low-Viscosity Liquid Sheets.

Authors

Hansol Wee - Presenter, Purdue University
Ajay Harishankar Kumar, Purdue University
Osman A. Basaran, Purdue University
Liquid sheets are thin films with two free surfaces and are omnipresent not only in industrial applications such as spraying, polymer processing, and coating flows, but also in everyday life and nature. The cross-sections of such sheets are rectangular in shape but with rounded ends, i.e. they resemble elongated 2D drops. The two ends, however, contract towards each other due to surface tension forces. If sufficiently thin (of the order of a few tens of nanometers), sheets can rupture due to the action of intermolecular van der Waals (vdW) forces. Such intermolecular forces are not operational with much thicker films. However, regardless of the thickness of the film, it has been shown by Burton and Taborek (PoF, 2007) that a contracting inviscid liquid sheet can break even when vdW forces are absent. Here, we demonstrate that in the presence of small yet finite viscosity, contracting liquid sheets can escape from pinch-off or rupture when vdW forces are absent. We investigate the problem using theory and 2D free-surface flow simulations. We demonstrate that there are two distinct mechanisms for contracting liquid sheets to escape from pinch-off. We further use scaling arguments to deduce how the minimum sheet thickness when escape occurs varies with Ohnesorge number (the ratio viscous stress to inertia and capillary stress) and show that the simulation results are in excellent accord with the theoretically obtained scaling laws.