Increasing Nebulizer Spray Efficiency Using a Baffle with a Conical Surface: A Computational Fluid Dynamics Analysis

Abstract

Breath-actuated nebulizers used in aerosol therapy are vital to children and patients with disabilities and stand out for their ability to accurat ely deliver medication while minimizing waste. Their performance can be measured according to the mass output and droplet size. This study aimed to analyze how the baffle impact surface geometries affect the pressure and flow streamlines inside the nebulizer using computational fluid dynamics (CFD). Computer-aided design models of conical symmetric, conical asymmetric, and arc-shaped baffle designs were analyzed using CFD simulations, with the optimal spray output validated through the differences in mass. Conical baffles exhibited superior pressure distribution and output streamlines at 0.25 cm protrusion, suggesting that the nebulizer spray performance can be enhanced by using such a conical baffle impact surface. This result serves as a valuable reference for future research.

Keywords: CFD; baffle; breath-actuated nebulizer.

Figure 1

Geometric model of the nebulizer flow chamber. (a) CAD software model. (b) Internal flow channel structure. (c) Model cross-section. (d) Simulated outer cuboid boundary.

Figure 2

CFD model of the nebulizer flow. (a) Model meshed using tetrahedral elements. (b) Meshed outer cubic wall. (c) The outlet flow rate is set as the negative value of the flow into the nebulizer. (d) The entire model with the boundary conditions.

Figure 3

(a) Baffle location within the nebulizer. The baffles exhibit (b) traditional flat, (c) conical symmetric, (d) arc, and (e) conical asymmetric impact surface geometries. The red arrow identifies the location of the baffle tip.

Figure 4

(a) Three-dimensional-printed baffles used for mass difference experiments. Conical symmetric baffles with protrusions of (b) 0.15 cm, (c) 0.25 cm, and (d) 0.35 cm. (e) Arc surface design.

Figure 5

Experimental setup of the spray distance. The vertical line on the background provided reference markers (6 cm between red lines). The data measured the distance from the start to the final points of the background markers.

Figure 6

Flow lines in the simulated nebulizer with a traditional flat baffle. (a) Upper air inlet port and lower compressed air input, side view. (b) Flow lines within the nebulizer pass through the lower medication part and approach the inner wall of the nebulizer (blue arrows). (c) Three-dimensional view, (d) sagittal view, and (e) top view of the stream film created by the jet flow hitting the baffle (red arrows).

Figure 7

Side view of the pressure contour. (A) Pressure distribution at the sagittal plane. (B,C) Pressure patterns at the parasagittal planes.

Figure 8

Top view of the pressure contour. (A) Pressure along the outlet port central plane. (B) Pressure patterns at the nozzle plane and the surrounding areas (C,D).

Figure 9

Flow lines with (a–c) flat, (d–f) conical asymmetric, (g–i) arc, and (j–l) conical baffles. Red arrows indicate vortex locations.

Figure 10

(a) Streamline and (b) pressure contours due to the nozzle jet flow. The Con-0.25 baffle exhibited the most (a) output flow lines and (b) the largest negative pressure area near the nozzle (black arrow). The Con-0.15 and Con-0.35 outlet pressures were positive and equal to or greater than the nebulizer internal pressure (blue arrows).

Figure 11

The Con-0.25 baffle had the greatest aerosol output distance, approximately 41% greater than the output distance of the flat baffle.

Figure 12

(a) No statistical difference in the mass change was found between the absorbent papers at the spray outlet when a flat baffle was used in the nebulizer. (b) The Con-0.25 baffle exhibited the greatest spray mass compared to the other baffle designs. * and ** denote p values lower than 0.05 and 0.01.