Numerical Study on the Impact of Large Air Purifiers, Physical Distancing, and Mask Wearing in Classrooms

Abstract

The risk of COVID-19 infection from virulent aerosols is particularly high indoors. This is especially true for classrooms, which often do not have pre-installed ventilation and are occupied by a large number of students at the same time. It has been found that precautionary measures, such as the use of air purifiers (AP), physical distancing, and the wearing of masks, can reduce the risk of infection. To quantify the actual effect of precautions, it is not possible in experimental studies to expose subjects to virulent aerosols. Therefore, in this study, we develop a computational fluid dynamics (CFD) model to evaluate the impact of applying the aforementioned precautions in classrooms on reducing aerosol concentration and potential exposure in the presence of index or infected patients. A CFD-coupled Wells–Riley model is used to quantify the infection probability (IP) in the presence of index patients. Different cases are simulated by varying the occupancy of the room (half/full), the volumetric flow rate of the AP, two different locations of the AP, and the effect of wearing masks. The results suggest that using an AP reduces the spread of virulent aerosols and thereby reduces the risk of infection. However, the risk of the person sitting adjacent to the index patient is only marginally reduced and can be avoided with the half capacity of the class (physical distancing method) or by wearing face masks of high efficiencies.

Computational Fluid Dynamics-Based Calculation of Aerosol Transport in a Classroom with Window Ventilation, Mechanical Ventilation and Mobile Air Purifier

“…Based on the transient observations presented so far, we can derive several correlations and interactions between various effects discussed in this section. Our results mainly confirm the findings of investigations conducted by other authors (see [14][15][16][17][18]21,22]), we also show that an air purifier leads to a significant reduction in the aerosol concentration in the room air. We extend the existing knowledge by highlighting the additional impact of transient, intermittent window ventilation.…”

“…They observed a significant reduction in inhaled particle doses when operating the mobile air purifier at high volume flow rates. In their study, Jain et al [15] investigate a classroom setting where a large air purifier is operated at different positions and volume flow rates. Under the assumption of steady-state conditions, neglecting any transient effects, they calculate an infection risk originating from varying index patients.…”

Numerical Evaluation of the Efficiency of an Indoor Air Cleaner under Different Heating Conditions

“…The indoor airflow and air purification has been studied numerically using CFD, which provides much more detailed information regarding the temperature and velocity fields compared to experimentation [8] and allows parametric studies to be carried out, e.g., to evaluate the efficiency of different air purifier setups [1,4,9]. Medium and large rooms such as offices, classrooms, auditoriums, and patient rooms are typically considered [1,4,5,8,[10][11][12][13][14][15][16][17], although smaller spaces may be of interest as well [18,19].…”

“…While a large number of CFD studies have considered the steady-state airflow [4,5,8,11,12,16,17,20,21], the transient flow, which is computationally more demanding, has been modelled as well [1,5,9,10,[13][14][15]18,19,21]. For the modelling of turbulence, the k-ε and k-ω models or their variations [4,5,[8][9][10][11][12][15][16][17][18]20,21] are typically employed, while more advanced approaches such as Large Eddy Simulation, Detached Eddy Simulation, and the Reynolds Stress Model are suitable for the transient cases [11,14,19,21]. Regarding prediction of the particle concentration, the Eulerian approach [5,8,11,13,14,17,[20][21][22] deals with the continuous aerosol concentration field, while the computationally more expensive Lagrangian approach [1,…”

“…For the modelling of turbulence, the k-ε and k-ω models or their variations [4,5,[8][9][10][11][12][15][16][17][18]20,21] are typically employed, while more advanced approaches such as Large Eddy Simulation, Detached Eddy Simulation, and the Reynolds Stress Model are suitable for the transient cases [11,14,19,21]. Regarding prediction of the particle concentration, the Eulerian approach [5,8,11,13,14,17,[20][21][22] deals with the continuous aerosol concentration field, while the computationally more expensive Lagrangian approach [1,4,9,10,12,13,15,16,18,19,21,22] tracks the trajectories of individual particles. Further considerations on the choice of a CFD model are presented in Section 2.1.…”