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We study the fragmentation of pre-perforated thin liquid films using three-dimensional numerical simulations, focusing on droplet formation following hole collisions. An air–water system with film thickness e0=25 μm and varying hole spacings (dh/e0=3−20) is considered. The liquid bridge formed between colliding holes undergoes oscillation and stretching before breakup. The outcome depends on the spacing: for small dh, ligaments recoil into single droplets, while for larger dh, ligaments fragment via end-pinching and Rayleigh–Plateau (RP) instabilities. Droplet size distributions are compared with RP predictions and show improved agreement when a 40% reduction in ligament diameter due to stretching is accounted for. The results also compare favorably with experimental data from air-blasted films. This work provides new insight into the fundamental mechanisms controlling droplet formation from perforated films and highlights the critical role of hole spacing in determining ligament dynamics and droplet size distributions.
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Prediction of the Atomization Process in Respimat® Soft MistTM Inhalers Using a Volume of Fluid-to-Discrete Phase Model
This study investigates the atomization process in Respimat® Soft MistTM Inhalers (SMIs) using a validated Volume of Fluid (VOF)-to-Discrete Phase Model (DPM) to simulate the transition from colliding liquid jets to aerosolized droplets. Key parameters, including colliding jet inlet velocity, surface tension, and liquid viscosity, were systematically varied to analyze their impact on the atomization, i.e., aerosolized droplet size distributions. The VOF-to-DPM simulation results indicate that higher jet inlet velocities enhance ligament fragmentation, producing finer and more uniform droplets while reducing total atomized droplet mass. The relationship between surface tension and atomization performance in colliding jet atomization is not monotonic. Reducing surface tension plays a complex dual role in the atomization process. On the one hand, lower surface tension enhances the likelihood of liquid jet breakup into a liquid sheet, leading to the formation of smaller ligaments under the same airflow conditions and shear forces. This increases the probability of generating more secondary droplets. On the other hand, reduced surface tension also destabilizes the liquid surface shape, decreasing the formation of fine, high-sphericity droplets in regimes where surface tension is a dominant force. Viscosity also influences atomization through complex mechanisms, i.e., lower viscosity reduces resistance to ligament breakup but promotes droplet interactions and coalescence, while higher viscosity suppresses ligament fragmentation, generating larger droplets and reducing atomization efficiency. The validated VOF-to-DPM framework provides critical insights for enhancing the performance and efficiency of inhalation therapies. Future work will incorporate nozzle geometry, jet impingement angles, and surfactant effects to better understand and optimize the atomization process in SMIs, focusing on achieving preferred droplet size distributions and emitted doses for enhanced drug delivery efficiency in human respiratory systems.
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- PAR ID:
- 10587508
- Publisher / Repository:
- MDPI Bioengineering
- Date Published:
- Journal Name:
- Bioengineering
- Volume:
- 12
- Issue:
- 3
- ISSN:
- 2306-5354
- Page Range / eLocation ID:
- 264
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.3390/bioengineering12030264
