Effect of solute concentration on the number of NaCl particles generated by millimeter- and micron-sized droplets

Abstract

Salt particles generated by aerosol generator are commonly used in air filtration test. As a common phenomenon, the number of generated particles increases with the salt concentration in the atomization solution. Thus far, the dependence of the particle number on the concentration of the atomization solution is not fully understood. In this study, two hypotheses were proposed to explain this phenomenon: i) a single droplet generates multiple solid particles, and the generated particle number is influenced by the salt concentration, and ii) the original droplet number increases with an increase in the salt concentration of the atomization solution. By observing the particle formation process of the levitated millimeter-scale NaCl droplet, one droplet was found to generate one particle in free air. However, whether these results are applicable to micrometer-scale droplets remains to be determined. In situ measurements were performed to detect the size distributions of the original droplets generated by the atomization solutions with various salt concentrations. A more concentrated atomization solution induced a higher number of original droplets. Particle formation patterns of droplets on glass substrates and filaments were demonstrated. Traditional observation methods for droplet drying are unsuitable for studying the particle formation of atomized droplets because of the large difference in droplet size and the existence of external forces.

Keywords:

• Atomization
• droplets
• drying
• particle number
• solution concentration

Authors’ contributions

W. He: Conceptualization, Methodology, Investigation, Writing – original draft. Y. Guo: Investigation, Resources, Formal analysis. Q. Luo, Z. Zhou, and X. Zhou: Validation, Formal analysis. D. Chang and J. Liu: Formal analysis, Writing – review and editing.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China under Grant 52304210; the Project funded by China Postdoctoral Science Foundation under Grant 2023M740545; Fundamental Research Funds for the Central Universities under Grant N2301022; We also thank the Natural Science Foundation Liaoning Provincial (2023-BSBA-105) and the National Science and Technology Major Project of China (2022YFC2503200, 2022YFC2503201).