Xiaole Chen

The traditional Discrete Element Method (DEM) can track the motion details of individual particles, but its computational cost becomes excessively high when simulating large-scale systems involving millions or even billions of particles. In this study, a coarse-grained DEM approach was employed to analyze the flow behavior of mixed particles in a coal powder silo. This method maintains reasonable simulation accuracy while effectively reducing the total number of computational particles and significantly improving computational efficiency. After conducting investigations on the mesh-to-particle size ratio and model validation, this paper focuses on examining the effects of coal particle size distribution and mixing ratio on the characteristics of particle motion. The results indicate that during the discharge process of mixed particles, the downward velocity of particles in the central axis region near the outlet is significantly higher than that in the wall region, exhibiting typical funnel flow characteristics. The particle size distribution has a notable impact on the particle descent velocity. The uniform distribution case shows the highest descent velocity, the linear distribution case the lowest, while the normal distribution case falls between the two. Notably, in the normal distribution case, the descent velocity in the central axis region is similar to that of the uniform distribution, while the descent velocity in the wall region approaches that of the linear distribution. This presents a combined characteristic of the two extreme distributions rather than a simple transitional state. In contrast, the particle mixing ratio has a relatively minor influence on the overall motion characteristics. The mass flow rate of particles and the cross-sectional velocity distribution remain largely consistent, with only slight differences observed in the velocity within the central axis region.

This study presents the first known successful in vitro measurement of both deposition fractions (DFs) and spatial deposition patterns of nebulized droplets in a realistic human upper respiratory tract model. The model, based on computed tomography scan data of a healthy adult male, accurately replicates the complex geometries of the oral and pharyngeal regions. Experiments were conducted using three different vibrating mesh nebulizer (VMN) systems at varying inhalation flow rates (15–60 l/min). Fluorescein-tagged saline solutions were nebulized, with deposition patterns—representing the spatial distribution of deposited droplets—visualized through ultraviolet fluorescence and DFs quantified based on the absorbance of the rinsate solution. Results show that the DFs and patterns are significantly influenced by flow rate, with deposition shifting from the oral cavity to the oropharyngeal region as flow rate increases. This study provides new insight into aerosol transport and deposition in realistic human airways and offers valuable data for optimizing nebulizer design and improving aerosol drug delivery efficiency in clinical applications.

The exchange of water vapor between high-concentration droplets and air significantly influences droplet deposition in the upper airway model during nebulizer use. This study employed a two-way coupled Eulerian–Lagrange method to quantify nebulized droplet evaporation and relative humidity (RH) variations within an idealized mouth–throat (MT) airway model, utilizing validated numerical models. The water vapor interaction between high-concentration droplets and inhaled air was computed using a multiplier based on the particle parcel method. Simulations of normal saline droplet flow inhalation in the MT airway were conducted under two environmental conditions: indoor (26.5 °C, RH = 50%) and warm and wet (30 °C, RH = 75%), with various inhalation flow rates mirroring previous experiments. Droplet deposition fractions (DFs) and deposition patterns were recorded. The results indicated that DF initially decreased and then increased with rising inhalation flow rates. The largest discrepancy between predicted and measured DFs was 10.86%. These findings support the theory that the balance between droplet evaporation and elevated air RH dictates the deposition of nebulized droplets in the airway. Additionally, simulations revealed that environmental conditions significantly affect droplet DF, with variations up to 20.78%. The deposition hotspot shifted from the anterior to the posterior pharynx.

The vibrating mesh nebulizer (VMN) has gained popularity for its compactness and noiselessness. This study investigates the impact of different air inlet structures on the deposition fraction (DF) of droplets generated by VMNs in an idealized mouth–throat (MT) airway model. Three homemade VMNs with semi-circular inlet, symmetrical four-inlet, and multiple-orifice inlet structures were evaluated through simulations and experiments. The changes in droplet DF of 0.9% w/v concentration of nebulized sodium chloride (NaCl) droplets as a function of inertial parameters were acquired under different inhalation flow conditions. Additionally, flow field distributions in models with different inlet structures were analyzed at a steady inspiratory flow rate of 15 L/min. The results indicate that optimizing the VMN’s air inlet structure significantly enhances droplet delivery efficiency. The multiple–orifice inlet structure outperformed the other designs, directing the airflow from the inlet position to the center of the mouthpiece and then into the oral cavity, achieving a DF of up to 20% at an inhalation flow rate of 15 L/min. The region of high airflow velocity between the mouthpiece and oral cavity proved to be a favorable VMN inlet optimization, reducing direct droplet–wall collisions and improving delivery efficiency. These findings offer insights for VMN design and optimization to enhance pulmonary drug delivery effectiveness and therapeutic outcomes.

Accurate measurement of droplet/particle deposition fraction and spatial distribution is vital for understanding various inhalation processes, including nebulized therapy, inhalation of atmospheric pollutants, and exposure risk assessment to aerosols such as airborne SARS-COV-2-laden droplets. This paper presents a novel method to measure the deposition fraction and spatial distribution of the deposited particulate phase (i.e., deposition pattern) of droplets through a single experiment. The experiment employs an idealized mouth-to-throat model as a test platform for two vibrating mesh nebulizers to deposit droplets. By utilizing a nebulized solution of normal saline containing the fluorescein, the qualitative observation of droplet deposition pattern on the internal surfaces is achieved under ultraviolet excitation. Furthermore, through rinsing the experimental components and quantitatively determining the deposition fraction based on rinsate absorbance, experimental results indicate that the deposition fraction of nebulized droplets decreases initially and then increases with increasing inspiratory flow rate from 15 to 60 l/min. Additionally, the deposition hotspots gradually shift from the bottom of the oral cavity to the throat as the inhalation flow rate increases. In addition to providing validation data for the transport and deposition of high-concentration droplets, this experimental method has the potential for extension to research on aerosol transmission and exposure risk assessment. It offers valuable insight into the behavior of nebulized droplets, aiding in developing effective strategies for aerosolized therapies and mitigating transmission risks in various applications.

Nebulizer is one of inhalation therapy’s most widely used aerosol generation devices. Nowadays, the vibrating mesh nebulizer has become popular owing to its compactness and noiselessness. In this study, an experimental system is proposed to measure the deposition fraction (DF) of nebulized sodium chloride (NaCl) droplets in an idealized mouth-throat airway model. The results show that before the DF increases to 58.6% with an increasing flow rate to 60 L/min, there is a decrease in DF from 42.4% to 15.5% when the inhalation flow rate increases from 15 to 22.5 L/min for a normal saline solution. These results substantially differ from the conclusions of dry powder or particle experiments and simulations, which monotonously increases with increasing inhalation flow rate. This suggests that droplet evaporation during aerosol generation and transport in the airway plays an important role. The experiment also showed that droplets generated from solutions with a higher NaCl concentration have higher DFs.

Basic analysis of the flow field and aerosol deposition under different conditions when a spreader contains an upper airway tract is important to accurately predict the transmission of virus-laden aerosols. An upper airway was included to simulate aerosol transport and deposition. A flow field was simulated by the Transition SST model for validation. The simulation results show that, in the absence of the upper airway structure, an over-predicted aerosol deposition rate will occur. Higher upper-stream air velocity enhanced the intensity but added complexity to the recirculating flow between two manikins and increased the deposition rate of aerosol in the disseminator. A low-temperature environment can reduce the deposition rate of aerosol particles on the body of the disseminator due to a strong thermal plume. Therefore, the structure of the upper airway should be considered when predicting respiratory aerosol in order to increase the accuracy of aerosol propagation prediction.