Interaction Dynamics of a Spherical Particle with a Suspended Liquid Film Subhasish Mitra, Elham Doroodchi, and Geoffrey M. Evans Discipline of Chemical Engineering, School of Engineering, University of Newcastle, Callaghan, NSW 2308 Australia Vishnu Pareek Dept. of Chemical Engineering, Curtin University, Perth, WA 6102, Australia Jyeshtharaj B. Joshi Dept. of Chemical Engineering, Homi Bhabha National Institute, Anushaktinagar, Mumbai 400 094, Maharashtra India DOI 10.1002/aic.15027 Published online September 21, 2015 in Wiley Online Library (wileyonlinelibrary.com) Hydrodynamics of collision interactions between a particle and gas-liquid interface such as droplet/film is of keen inter- est in many engineering applications. The collision interaction between a suspended liquid (water) film of thickness 3.41 6 0.04 mm and an impacting hydrophilic particle (glass ballotini) of different diameters (1.1–3.0 mm) in low parti- cle impact Weber number (We 5 q l v 2 p d p =r) range (1.4–33) is reported. Two distinct outcomes were observed—particle retention in the film at lower Weber number and complete penetration of the film toward higher Weber number cases. A collision parameter was defined based on energy balance approach to demarcate these two interaction regimes which agreed reasonably well with the experimental outcomes. It was shown that the liquid ligament forming in the complete penetration cases breaks up purely by “dripping/end pinch-off” mechanism and not due to capillary wave instability. An analytical model based on energy balance approach was proposed to determine the liquid mass entrainment associ- ated with the ligament which compared well with the experimental measurements. A good correlation between the %film mass entrained and the particle Bond number (Bo 5 q l gd 2 p =r) was obtained which indicated a dependency of Bo 1.72 . Computationally, a three-dimensional CFD model was developed to simulate these interactions using different contact angle boundary conditions which in general showed reasonable agreement with experiment but also indicated deficiency of a constant contact angle value to depict the interaction physics in entirety. The computed force profiles from compu- tational fluid dynamics (CFD) model suggest dominance of the pressure force over the viscous force almost by an order of magnitude in all the Weber number cases studied. V C 2015 American Institute of Chemical Engineers AIChE J, 62: 295–314, 2016 Keywords: particle-film collision, interface, ligament, end pinching-off, liquid entrainment, CFD Introduction In-depth understanding of collision interaction of particles with gas-liquid interface is the key to successful design and opti- mization of many process engineering applications. Some of these applications include but not limited to coating of particles; scrubbing of dust-laden off gases; mixing of feed droplets and catalyst particles in the vaporization zone of fluidized catalytic cracking reactors; 1–3 fluid coking of bitumen, spray drying, 4 fab- rication of ceramic reinforced metal composites, 5 recovery of valuable minerals by film flotation process, 6 and many more. In all of these interactions involving multiple interfaces, two distinct geometry of gas-liquid interface can be identi- fied—planar interface and curved interface. Depending on the geometry of interface and impacting particle, different interac- tion outcomes are observed. A significant number of studies are available on the interactions of cylindrical 7 and spheri- cal 8–10 objects on a large planar interface reporting phenom- ena like floating, sinking, and rebounding. These studies focused on explaining the load carrying capacity of liquid under different combinations of solid surface hydrophobicity and physical properties of liquid citing relevance to biological instances like insects walking on water. 8 Among other applica- tions, recovery of valuable mineral particles from gangue materials is also reported utilizing the suitable interactions of hydrophilic particles with planar gas-liquid interface in film floatation process. 6 However, relatively fewer studies are indeed reported on interaction of a particle with a curved interface, that is, droplet which include applications like feed droplet vaporization in contact with hot catalyst particles in fluid catalytic cracking (FCC) unit, 1–3 interactions of fine particles from recycled exhaust stream with feed droplets in spray drying system, 4 and Additional Supporting Information may be found in the online version of this article. Correspondence concerning this article should be addressed to G. M. Evans at Geoffrey.Evans@newcastle.edu.au V C 2015 American Institute of Chemical Engineers AIChE Journal 295 January 2016 Vol. 62, No. 1