Comparison of Experimental and Numerical Transient Drop Deformation during Transition through Orifices in High-Pressure Homogenizers

Abstract

The droplet deformation in dispersing units of high-pressure homogenizers (HPH) is examined experimentally and numerically. Due to the small size of common homogenizer nozzles, the visual analysis of the transient droplet generation is usually not possible. Therefore, a scaled setup was used. The droplet deformation was determined quantitatively by using a shadow imaging technique. It is shown that the influence of transient stresses on the droplets caused by laminar extensional flow upstream the orifice is highly relevant for the droplet breakup behind the nozzle. Classical approaches based on an equilibrium assumption on the other side are not adequate to explain the observed droplet distributions. Based on the experimental results, a relationship from the literature with numerical simulations adopting different models are used to determine the transient droplet deformation during transition through orifices. It is shown that numerical and experimental results are in fairly good agreement at limited settings. It can be concluded that a scaled apparatus is well suited to estimate the transient droplet formation up to the outlet of the orifice.

Influence of the droplet trajectory on the resulting droplet deformation and droplet size distribution in high‐pressure homogenizer orifices

“…However, the effect was smaller than expected, probably because the emulsifier molecules did not adsorb fast enough at the newly created interface during deformation and Gibbs-Marangoni effects. Besides, it was observed that the influence of the interfacial tension on the droplet deformation is more prominent at lower viscosity ratios, which was already experimentally shown for low and slow deformation [4] as well as in simulations [12] with fast-changing stresses as applied in this study. However, the effect was again less prominent than that expected from the work of Taylor [4] and Mutsch et al [12] due to the discussed emulsifier adsorption kinetics-induced effects.…”

“…Walzel [10] simulated the droplet deformation inside a passage through an orifice on the centreline using an approach stated by Cox [6] and Kalb et al [11] These findings were later validated using experimental data from a scaled orifice setup whereby a good agreement was found between the simulation and the experiment at limited settings. [12] Among others, Feigl et al [13] and Hövekamp [14] used computational fluid dynamics (CFD) simulations to determine the stress history on the droplet streamline with changing stress loads and constant interfacial tension, which was subsequently correlated with the droplet deformation from simulations and experimental data. In all investigated setups, droplets that travel on a trajectory close to the wall are exposed to higher stresses and are thus more deformed.…”

“…Walzel [ 10 ] simulated the droplet deformation inside a passage through an orifice on the centreline using an approach stated by Cox [ 6 ] and Kalb et al [ 11 ] These findings were later validated using experimental data from a scaled orifice setup whereby a good agreement was found between the simulation and the experiment at limited settings. [ 12 ]…”