Formation Of Secondary Droplets Research Articles

Spray impingement on a wall in the context of the upper airways

We here address the modelling of an aerosol hitting the walls of the airways or an endotra- cheal tube used for a mechanical ventilation, and the possible creation of secondary droplets that may follow. We present a kinetic modelling of the spray-wall interaction and propose a boundary term that takes into account the possible formation of secondary droplets. Next we answer the following ques- tion: when, modelling the delivery of solute therapeutic aerosols, is it necessary to take into account the apparition of secondary droplets? A study of empirical models of drop-wall interaction allows us to conclude that in usual respiratory conditions, no secondary droplets appear. Finally, we perform numerical simulations of an aerosol delivered in an endotracheal tube, in the mechanical ventilation case. The idea is to compare our numerical results to in silico experiments from aerosols specialists. We study the trajectories and the deposition locations of spray droplets.

Three-dimensional numerical investigation of a droplet impinging normally onto a wall film

The paper presents a three-dimensional numerical investigation of a droplet impinging normally onto a wall film. The numerical method is based on the finite volume solution of the Navier–Stokes equations coupled with the volume of fluid method (VOF) and utilizing an adaptive local grid refinement technique for tracking more accurately the liquid–gas interface. The results are compared with available experimental data for integral quantities such as the lamella temporal development. Two mechanisms are identified leading to secondary droplet formation; in the initial and intermediate stages of splashing secondary droplet formation is according to Rayleigh instability while at later times surface tension effects contribute further to secondary atomization. Moreover, the influence of Weber number on the impingement process is investigated and correlations for the diameter and number of secondary droplets are proposed.

Investigation of secondary droplet characteristics produced by an isooctane drop chain impact onto a heated piston surface

The physics of the impingement process of small hydrocarbon droplets is mostly unknown due to the difficulties of obtaining experimental data. In this publication, the impingement of small isooctane droplets on a hot piston surface is studied. The emphasis was put on the image-based investigation of the process of successive impingements and its influence on secondary droplet formation. The diameter and velocity of the secondary droplets were found to depend on the wall temperature and impingement frequency. Thus, the temporal interaction has a significant influence on the secondary droplet characteristics.

The impact of a single drop on a wetted solid surface

The impact of single drops on a thin liquid film was studied to understand the mechanism of secondary atomisation of sprays colliding on a wetted, cold, solid surface. To span a wide range of conditions various mixtures of water and glycerol were used. The use of Weber number, Ohnesorge number and non-dimensional film thickness to describe the peculiarities of the phenomenon allowed to carry out the experiments under appropriate similarity conditions. The impact of millimetric drops was analysed in detail by photographic means, using both still photography to study impact morphology, and laser sheet visualisation to investigate secondary droplet formation. Two mechanisms of splash were identified, depending essentially on the liquid viscosity (Ohnesorge number), a parameter which appears to play an important role also in defining the splash morphology. A photographic documentation is annexed. The characteristic times of the crown formation, the non-linear evolution of cusps (jet formation) and the surface roughness influence are further discussed. The experimental results allow to propose an empirical correlation for the splashing/deposition limit, for a wide range of conditions, and a comparison to available previous works is presented. The influence of the film thickness and liquid viscosity on the splash is confirmed and quantified.

The velocity change of ethanol droplets during collision with a wall analysed by image processing

Monodisperse droplet streams are used to study the droplet wall interaction of ethanol droplets in the micrometer range. Qualitative results are given for different regimes of droplet wall interaction. The phenomena observed range from complete wetting to almost elastic reflection of the droplets. Complete wetting is observed for low wall temperatures, whereas reflection occurs for wall temperatures above the Leidenfrost temperature. For high impact velocities and high wall temperatures above the Leidenfrost temperature the formation of secondary droplets can be observed. Image processing is used to obtain quantitative results for the loss of momentum during wall interaction for cases of droplet reflection without formation of secondary droplets.

The formation of secondary droplets in a dispersion at a phase boundary

The formation of secondary droplets in a dispersion at a phase boundary