Possible, Impossible, and Expected Diameters and Production Rates of Droplets in Aerosols and Sprays

TL;DR

This paper develops a theoretical framework and atomization diagrams to predict droplet sizes and flow rates in aerosols and sprays, validated by experiments across various liquids and atomization methods.

Contribution

It introduces a first-principles-based theoretical description and atomization diagrams for droplet size and flow rate prediction in liquid atomization processes.

Findings

Reasonable agreement between theory and experiments for submicron and micron droplets.

Theoretical framework applies across a wide range of Ohnesorge numbers.

Atomization diagrams help compare different atomization techniques.

Abstract

Liquid atomization processes generating sprays and aerosols of droplets are used in many delivery and coating systems involving pure solvents, solutions, and suspensions. In our recent experimental work, we introduced a novel liquid atomization process generating micro-sprays and aerosols of submicron-diameter droplets for pure solvents, solutions, and suspensions: gas jets disintegrate thin liquid films that are formed as bubbles approach a liquid surface. Here we develop a theoretical description of droplet sizes and flow rates, using the first principles of conservation of mass and energy, and accounting for the ratios of specific energies and the ratios of specific energy rates provided by the atomizing gas and dissipated by the atomized liquid. We introduce atomization diagrams as a graphical tool to determine possible, impossible, and expected droplet diameters and specific flow rates in aerosols and sprays produced under various conditions. We find a reasonable agreement between the theory and experiments for five different liquids converted into aerosols of submicron-diameter droplets by an atomization process where gas jets disintegrate thin liquid films that are formed as bubbles approach a liquid surface, and also for five traditional pressure nozzles that produce sprays of droplets of hundreds of microns in diameter. Our study explored the overall range of Ohnesorge number between 0.01-100, and the analysis and atomization diagrams contribute to understanding of liquid atomization and can serve as a theoretical framework for comparing different liquid atomization techniques.