Dynamic Surface Wetting and Heat Transfer in a Droplet-Particle System of Less Than Unity Size Ratio

Abstract

Dynamic surface wetting of particles in contact with droplet is a complex phenomenon ubiquitously encountered in many multiphase systems of industrial importance. In this study, we address this aspect by investigating impact behavior of a water droplet (diameter = 2.9 ± 0.1 mm) in the Weber number (We) range from ~4 to 104 on a stationary spherical brass particle (diameter = 10 mm) with and without heat transfer using a combination of high speed imaging and computational fluid dynamics (CFD) modeling approach. In cold state interactions (20°C), droplet exhibited oscillatory interfacial motion comprising periodic spreading and recoiling motion. Interactions involving heat transfer were studied in film boiling regime (350°C) and two outcomes were noted—droplet rebound and disintegration. A coupled Level Set and Volume of Fluid (VOF) approach based multiphase CFD model was utilized to predict the dynamic spread ratio and transient evolution of droplet shape during the interaction. To capture the complex contact line motion realistically, a continuous time varying profile of experimentally measured dynamic contact angles was used as a wall boundary condition for the cold interactions which provided good agreement with experimentally measured droplet spread ratio. In film boiling regime, droplet spread ratio was correlated to impact Weber number and a power law trend was obtained. Rebound and disintegration outcomes were characterized by the droplet-particle contact time. For simulating interactions in film boiling regime, a constant contact angle in the limit of super-hydrophobic surface was implemented in the CFD model to account for the apparent non-wetting effect due to vapor film formation at the contact area. A sensitivity analysis was performed involving three different contact angle boundary conditions (θs = 150, 160, and 170°) to represent the surface hydrophobicity. CFD model predicted interaction outcomes and droplet spread ratios were in reasonable agreement with the experiment at different impact Weber numbers. Increase in spherical surface heat flux and corresponding rise in droplet temperature at different impact Weber numbers were also quantified which showed an increasing trend up to a critical Weber number for droplet disintegration.

Review of Research Related to Fluid Cokers

“…The jet cavity undergoes an expansion–contraction cycle: as large gas bubbles detach from the jet cavity tip, the jet cavity shrinks and expands again as gas enters the cavity from the nozzle and bubbles are captured by the cavity . Particles are entrained from the bed into the low-pressure cavity zone, just downstream of the nozzle tip. , The spray droplets mix imperfectly with the entrained particles and impact the bed particles at the end of the jet cavity. − This accumulation of wet solids at the tip of the jet cavity means that the exact nature of the interactions between individual droplets and particles within the jet cavity is less critical than in processes such as FCC. − Wet solids are continuously removed from the tip of the jet cavity in the wake of bubbles detaching from the cavity, in the form of wet agglomerates Figure shows X-ray pictures of a bubbling fluidized bed into which a tracer liquid is injected; the figure on the left-hand side shows the poor distribution that is obtained without atomization gas, while the figure on the right-hand side shows that with atomization gas.…”

Maximum spreading of droplet-particle collision covering a low Weber number regime and data-driven prediction model

“…Seven collision scenarios mapped against the outcome regime maps, 29 and a theoretical model for droplet rebound criterion 30 have been presented. Malgarinos et al, 31,32 Mitra et al, 33 and Mitra and Evans, 34 studied droplet collisions with a particle focusing on heat transfer and phase change behavior during a collision process. Various effects of impact conditions on collision phenomena have been investigated in the film boiling regime mainly based on numerical simulations.…”

“…Various effects of impact conditions on collision phenomena have been investigated in the film boiling regime mainly based on numerical simulations. [31][32][33][34] Even though these studies mentioned above have significantly shed light on our understanding of fundamental knowledge associated with droplet impact with a particle, they have mostly focused on the behaviors of film thickness, lamella structure, collision outcomes, heat transfer and phase change characteristics rather than on the maximal spreading of dropletparticle collision.…”

Experimental characterization of liquid film behavior during droplets–polyethylene particle collision

“…They also studied the droplet–particle with the size ratio close to 1 under normal and elaborated on the nucleate boiling, and gave a time‐dependent scheme for different stages. They then studied heat transfer in the film boiling state and measured dynamic contact angles, whose continuous time varying profile was used as a wall boundary condition for the cold interactions. They even experimented with glass particles hitting fixed larger‐diameter stationary water droplets.…”