The Effect of Viscosity on The Puddle Dynamics in Low Gravity Environment

Abstract

Enormous liquid puddles are observed to jump spontaneously from non-wetting substrates when exposed to the nearly step-reduction in body force common to drop tower test facilities. The phenomenon is similar to the second half of terrestrial drop bounce experiments except that (1) the initial static equilibrium configuration satisfies the static contact angle condition, (2) the initial height of the puddle is limited to the capillary height, and (3), for drop tower test durations on the order of seconds, puddle volumes can be over 104 times larger in mass (volume). The passive puddle jump mechanism provides a no-moving-parts deployment method for subsequent large drop dynamics investigations using drop towers. The effects of viscosity dampen large amplitude oscillations such that large spherical drops are quickly established from the initially flat viscous puddles. An experimental and numerical investigation of viscous puddle jump phenomena is pursued herein. A large drop tower data set is collected for puddle jump times, velocities, and character for viscosities 0.001 ≤ µ ≤ 1.18 kg/m·s, non-wetting contact angles 145º ≤ θ ≤ 160º, and puddle volumes 0.1 ≤ V ≤ 100 mL. We find that the jump time and velocity are weak and strong functions of viscosity, respectively. We benchmark the Gerris code for the contact line-driven flow and construct a combined experimental and numerical regime map for viscous puddle jump. We identify and distinguish the 'viscous jump' puddle volume limit, V ≈ (µ2/ρσ)3, below which puddles do not jump, but remain spherical wall-bound drops.