Comments on “Liquid Film Atomization on Wall Edges-Separation Criterion and Droplets Formation Model”

Abstract

In an intriguing paper (1), Maroteaux, Llory, Le Coz, and Habchi presented a separation criterion for a liquid film from sharp edges in a high-speed air flow. According to their model, the film of thickness hf and velocity Uf separates from a sharp edge of angle α if α>αcrit. The relation obtained for the critical angle isDisplay Formulaαcrit=Ufωmaxhflog(δδ0)crit (1) where δ∕δ0 is the amplitude ratio of the final to the initial perturbation of the film surface. When the wave amplitude reaches a critical value, the film stripping from an edge occurs. The critical value (δ∕δ0)crit is set equal to 20 as the best fit for their experimental data. The frequency ωmax is defined as the most unstable perturbation growth rate that causes the film separation. This maximum frequency is computed from the dispersion relation of Jain and Ruckenstein (JR) (2). The results of 12 tests with dodecane film flowing on springboard or straight step are reported. The geometrical edge angle α is equal to 135deg for all tests. The maximum film thickness hf is measured while the film velocity Uf is estimated. The fact of stripping is established from the visual observations. If the critical angle, computed from Eq. 1, takes values that are inferior to 135deg, the theory assumes to predict stripping. The experimental data are summarized in Table 1.