Influence of indoor airflow on airborne disease transmission in a classroom

It has been widely accepted that the most effective way to mitigate airborne disease transmission in an indoor space is to increase the ventilation airflow,measured in air change per hour(ACH).However,increasing ACH did not effectively prevent the spread of COVID-19.To better understand the role of ACH and airflow large-scale patterns,a comprehensive fully transient computational fluid dynamics(CFD)simulation of two-phase flows based on a discrete phase model(DPM)was performed in a university classroom setting with people present.The investigations encompass various particle sizes,ventilation layouts,and flow rates.The findings demonstrated that the particle size threshold at which particles are deemed airborne is highly influenced by the background flow strength and large-scale flow pattern,ranging from 5µm to 10µm in the cases investigated.The effects of occupants are significant and must be precisely accounted for in respiratory particle transport studies.An enhanced ventilation design(UFAD-CDR)for university classrooms is introduced that places a premium on mitigating airborne disease spread.Compared to the baseline design at the same ACH,this design successfully reduced the maximum number density of respiratory particles by up to 85%.A novel airflow-related parameter,Horizontality,is introduced to quantify and connect the large-scale airflow pattern with indoor aerosol transport.This underscores that ACH alone cannot ensure or regulate air quality.In addition to the necessary ACH for air exchange,minimizing horizontal bulk motion is essential for reducing aerosol transmissibility within the room.

CFD modeling of methane distribution at a continuous miner face with various curtain setback distances

Knowledge of the airflow patterns and methane distributions at a continuous miner face under different ventilation conditions can minimize the risks of explosion and injury to miners by accurately forecasting potentially hazardous face methane levels. This study focused on validating a series of computational fluid dynamics(CFD) models using full-scale ventilation gallery data that assessed how curtain setback distance impacted airflow patterns and methane distributions at an empty mining face(no continuous miner present). Three CFD models of face ventilation with 4.6, 7.6 and 10.7 m(15, 25, and 35 ft) blowing curtain setback distances were constructed and validated with experimental data collected in a full-scale ventilation test facility. Good agreement was obtained between the CFD simulation results and this data.Detailed airflow and methane distribution information are provided. Elevated methane zones at the working faces were identified with the three curtain setback distances. Visualization of the setback distance impact on the face methane distribution was performed by utilizing the post-processing capability of the CFD software.

Numerical simulation of particle deposition in obstructive human airways

To investigate airflow pattern and its impact on particle deposition, finite-volume based computational fluid dynamics （CFD） simulations were conducted in the diseased triple-bifitrcation airways. Computations were carried out for twenty Reynolds numbers ranging from 100 to 2 000 in the step of 100. Particles in the size range of 1-10 μm were conducted. Two particle deposition mechanisms （gravitational sedimentation and inertial impaction） were considered. The results indicate that there are strong relationship between airflow structures and particle deposition patterns. Deposition efficiency is different for different particles in the whole range of the respiratory rates. Particles in different sizes can deposit at different sites. Smaller particles can be uniformly deposited at the inside wall of the considered model. Larger particles can be mainly deposited in the proximal bifurcations. Deposition fraction varies a lot for different inlet Reynolds numbers. For lower Reynolds numbers, deposition fraction is relatively small and varies a little with varying the diameters. For Reynolds number to target the aerosols at the specific site. higher Reynolds numbers, there is a most efficient diameter for each

Numerical simulation of micro-particle deposition in a realistic human upper respiratory tract model during transient breathing cycle

An more reliable human upper respiratory tract model that consisted of an oropharynx and four generations of asymmetric tracheo-bronchial （TB） airways has been constructed to investigate the micro-particle deposition pattern and mass distribution in five lobes under steady inspiratory condition in former work by Huang and Zhang （2011 ）. In the present work, transient airflow patterns and particle deposition during both inspiratory and expiratory processes were numerically simulated in the realistic human upper respiratory tract model with 14 cartilaginous rings （CRs） in the tracheal tube. The present model was validated under steady inspiratory flow rates by comparing current results with the theoretical models and pub- lished experimental data. The transient deposition fraction was found to strongly depend on breathing flow rate and particle diameter but slightly on turbulence intensity. Particles were mainly distributed in the high axial speed zones and traveled basically following the secondary flow. ＂Hot spots＂ of deposition were found in the lower portion of mouth cavity and posterior wall of pharynx/larynx during inspiration, but transferred to upper portion of mouth and interior wall of pharynx/larynx during expiration. The deposition fraction in the trachea during expiration was found to be much higher than that during inspiration because of the stronger secondary flow.