Numerical analysis of particle deposition during normal impact of diluted suspension droplets

Abstract

Suspension droplet wall impacts are important for numerous technical applications, as for example spray painting in automotive industry, layering in material science, erosive surface cleaning and pharmaceutical coatings. Therefore, a numerical framework for the investigation of suspension droplet impact processes based on the coupling between the Volume of Fluid (VOF) method and a Lagrangian Particle Tracking (LPT) algorithm is implemented in OpenFOAM. A dynamic contact angle model is used to account for contact angle hysteresis effects during the impact process, with advancing, receding and equilibrium phases, coupled with a partial-slip boundary condition. Particle deposition at the substrate is modelled considering energy balances accounting for the adhesive van der Waals force acting at the particle-substrate interface. Three dimensional simulations are carried out to analyse the effects of impact conditions for the impingement of diluted water suspension droplets (diameter in the mm-range and Weber numbers in the range of 2.8 – 64.30) composed by micrometre-sized Polystyrene particles with a 0.5 % volume fraction onto a Polycarbonate substrate. The numerical results are validated by comparing the droplet’s spread factor and contact angle dynamics with own experimental data, obtaining a good agreement during the spreading phase of the impact. The influence of the droplet’s impact morphology on the particle distribution and particle-substrate interactions is discussed. A fixed impact condition test case is used to evaluate the influence of particle inertia on particle-substrate interactions by considering different particle size and density values, as well as distinct particle deposition models.