Experimental investigation of particle–droplet–substrate interaction

Abstract

The impact of droplets on non-fixed spherical particles placed on a plane polymethyl methacrylate (PMMA) substrate is investigated. This interaction is a highly abstracted level of a high-pressure spray cleaning process. Water droplets in a diameter range between 0.68 and 1.66mm and spherical particles (PMMA) with a diameter of 1.55 mm are used. The droplet velocity range of 1.05≤vd≤2.0m/s results in a Weber number range of 13≤We≤94. The particle-droplet-substrate interactions are investigated for different Weber numbers, droplet-to-particle diameter ratios and eccentricities. Different droplet impact scenarios are identified: A—Lift-off during initial recoil; B—Lift-off during a later recoil; C—No Lift-off, deposition of the droplet and D—No Lift-off, wetting of the substrate. The behavior of the particle-droplet-substrate interaction is determined depending on Weber number and particle-to-droplet diameter. Additionally, the analysis of the eccentricity in relation to the lift-off behavior shows that the lift-off height and duration increases with the centrality. The investigation of temporal change of the half-spread and contact angle results in a criterion for the point in time at which the lift-off takes place. Finally, a simplified analytical model is provided quantifying the probability of the lift-off of the particle-droplet system after the interaction. Experimental and analytical results are used to create a map of occurring impact regimes in terms of the particle-droplet configuration.