Modeling The Maximum Deposition of a Core-shell Compound Droplet Impacting a Solid Surface

Compound droplets composed of core and shell liquids have earned significant attention in recent years, owing to their potential advantages in various industrial applications including inkjet printing, 3D printing, pharmaceutics and food industry. Predicting and controlling the maximum deposition of such drops after impact on solid surfaces is crucial for these applications. The maximum spreading factor, which is the maximum deposition normalized by the initial droplet diameter, is determined by the energy budget of the falling droplet before impact and at the maximum spreading. A semi-analytical model has been derived using the energy balance of the primary driving forces of the spreading phase namely, kinetic energy, interfacial energy and viscous dissipation. To solve the energy balance equation, simplifications are utilized, particularly concerning the geometry and viscous dissipation terms for the two segments of the compound drop. The model has been validated with the experimental investigations of the low Weber number water-in-oil drop impact events within a wide range of core sizes and viscosity values of the core and the shell layers.