Influence of the liquid film thickness on the coefficient of restitution for wet particles

TL;DR

This study experimentally investigates how the liquid film thickness affects the coefficient of restitution for wet particles and proposes an analytical model to predict energy loss during impact.

Contribution

It introduces a model linking the wet COR to the Stokes number and liquid film thickness, enabling prediction of impact behavior based on these parameters.

Findings

Wet COR decays linearly with inverse Stokes number at fixed film ratios.

The model accurately predicts the impact energy loss considering inertia and viscosity.

Parameters depend systematically on the ratio of film thickness to particle diameter.

Abstract

The normal coefficient of restitution (COR) for a spherical particle bouncing on a wet plane is investigated experimentally and compared with a model characterizing the energy loss at impact. For fixed ratios of liquid film thickness $\delta$ to particle diameter $D$, the wet COR is always found to decay linearly with St$^{-1}$, where St, the Stokes number, measures the particle inertia with respect to the viscous force of the liquid. Such a dependency suggests a convenient way of predicting the wet COR with two fit parameters: A critical COR at infinitely large St and a critical St at zero COR. We characterize the dependency of the two parameters on $\delta/D$ and compare it with a model considering the energy loss from the inertia and the viscosity of the wetting liquid. This investigation suggests an analytical prediction of the COR for wet particles.