Breakup Processes and Droplet Characteristics of Liquid Jets Injected into Low-Speed Air Crossflow

Spatial reorganization of analytes in charged aqueous microdroplets

Imprinted charged aqueous droplets of micrometer dimensions containing spherical gold and silver nanoparticles, gold nanorods, proteins and simple molecules were visualized using dark-field and transmission electron microscopies. With such studies, we hoped to understand the unusual chemistry exhibited by microdroplets. These droplets with sizes in the range of 1-100 μm were formed using a home-built electrospray source with nitrogen as the nebulization gas. Several remarkable features such as mass/size-selective segregation and spatial localization of solutes in nanometer-thin regions of microdroplets were visualized, along with the formation of micro-nano vacuoles. Electrospray parameters such as distance between the spray tip and surface, voltage and nebulization gas pressure influenced particle distribution within the droplets. We relate these features to unusual phenomena such as the enhancement of rates of chemical reactions in microdroplets.

Interferometric laser imaging for droplet-size measurement in spray

An upgraded droplet-size measurement method, based on laser interference particle imaging (IPI) technology, is applied to accomplish high-precision measurement of particle size and spatial distribution of gas-liquid two-phase flow in the atomization field. In this study, an improved morphological-Hough transform interference fringe location algorithm is applied to IPI measurement. The particle size of the standard particle field with a diameter of 24 µm is measured by the upgraded IPI measurement experimentally, whose absolute error and relative error are 0.14 µm and 0.58%, respectively. The atomization field of the 400 µm centrifugal nozzle under different pressures is demonstrated by direct imaging and IPI technology, where the assessment results are evaluated by SMD value and particle size distribution, and the results exhibit good agreement.

Development of a Semi-Empirical Model for Droplet Size Determination of a Three-Channel Spray Nozzle for Pellet Coating Based on the Optical Method Concept

The purpose of this study was to investigate the droplet size obtained with a three-channel spray nozzle typically used in fluid bed devices and to construct a semi-empirical model for prediction of droplet size. With the aid of a custom-made optical method concept, the impact of the type of polymer and solvents used through dispersion properties (viscosity, density, and surface tension), dispersion flow rate, atomization pressure, and microclimate pressure on droplet size was investigated. A semi-empirical model with adequate predictability for calculating the average droplet size (R2 = 0.90, Q2 = 0.73) and its distribution (R2 = 0.84, Q2 = 0.61) was constructed by employing dimensional analysis and design of experiments. Newtonian and non-Newtonian dispersion and process parameters on laboratory and on production scale were included, thereby enabling constant droplet size irrespective of the scale. Based on the model results, it would be possible to scale-up the atomization process (e.g., coating process) from laboratory to production scale in a systematic fashion, regardless of the type of solvent or polymer used. For the system investigated, this can be performed by understanding the dispersion properties, such as viscosity, density, and surface tension, as well as the following process parameters: dispersion flow rate, atomization, and microclimate pressure.

Special Issue “Fluid Dynamics, Multi-Phase Flow, and Thermal Recovery Methods”

Intricate fluid flow and transport phenomena in porous media are ubiquitous in natural processes and engineering systems [...]