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

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## Abstract

**:**

## 1. Introduction

^{−1}reduced the aerosol concentration by more than 90% in less than 30 min compared to a classroom where no AP was used and the windows and doors were closed. However, small APs generates noise of a sound level higher than 40 db(A) [21], which are considered disturbing for lessons in a classroom. Parhizkar et al. [22] carried out controlled clinical trials with 11 participants placed individually in a room and asked to carry out their daily activities such as walking on a treadmill, standing, sitting silently, or attending the online conferences and recorded the viral aerosol load at different locations inside the room. The authors found that increasing the air-exchange rate from outside or using APs yielded a reduced aerosol viral load and were likely to reduce the inhalation dose and the probability of infection in indoor spaces.

## 2. Materials and Methods

#### 2.1. Simulation Model

#### 2.2. Cases Simulated

## 3. Results

#### 3.1. Validation

#### 3.2. Airflow Pattern

#### 3.3. Effect of Using an Air Purifier

#### 3.4. Effect of Location of an Air Purifier

#### 3.5. Effect of Wearing a Face Mask

#### 3.6. Effect of Physical Distancing

## 4. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Abbreviations

CFD | Computational Fluid Dynamics |

AP | Air Purifier |

IP | Infection Probability |

HVAC | Heating, Ventilation, and Air Conditioning) |

WRM | Wells–Riley Model |

HEPA | High-Efficiency Particle Arresting |

DEHS | di-ethyl hexyl sebacate |

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**Figure 1.**The basic geometry of the classroom with (

**a**) the AP on the short side of the room operating at full capacity (24 students + 1 teacher). (

**b**) AP on the long side of the room operating at half capacity (12 students + 1 teacher).

**Figure 2.**Sketches of the four considered scenarios: (

**a**) Scenario 1 (

**b**) Scenario 2 (

**c**) Scenario 3 (

**d**) Scenario 4. The person in red is the index patient and the color purple denotes the student adjacent to the index patient. Green color denotes the students in the same row as the index patient and yellow color denotes the students in the adjacent row.

**Figure 4.**Aerosol concentration for position (

**a**) MP1 and (

**b**) MP2. The key exp refers to the experimental data and coarse, medium, and fine refer to the mesh size of simulations.

**Figure 5.**A snapshot of the flow field in the classroom for the two configurations: (

**a**) AP on the short side of the room. (

**b**) AP on the long side of the room. The colour of the streamlines and velocity vectors represents the magnitude of velocity.

**Figure 6.**Effect of using AP for (

**a**) Scenario 1, (

**b**) Scenario 2, (

**c**) Scenario 3, (

**d**) Scenario 4. The keys in the legend with prefix ’S’ and ’L’ refer to the AP placed on the short side and long side of the room, respectively. The numerical suffix refers to the volumetric flow rate level of the AP.

**Figure 7.**Quanta concentration and velocity vectors on the plane at the level of the mouths of students after 1 h in the classroom for Scenario 3 when the AP is on (

**a**) the short side of the room, (

**b**) the long side of the room.

**Figure 8.**Quanta concentration and velocity vectors on the plane at the level of the mouths of students after 1 h in the classroom for Scenario 4 when the AP is on (

**a**) the short side of the room, (

**b**) the long side of the room.

**Figure 9.**Effect of wearing a mask of different efficiencies for (

**a**) Scenario 1, (

**b**) Scenario 2, (

**c**) Scenario 3, (

**d**) Scenario 4. The keys in the legend with prefix ’S’ and ’L’ refer to AP placed on the short side and long side of the room, respectively. The suffixes ’NM’, ’C’, ’S’, and ’N95’ refer to cases with no mask, cloth masks, surgical masks, and N95 masks, respectively.

**Figure 10.**Effect of physical distancing for (

**a**) Scenario 1, (

**b**) Scenario 2, (

**c**) Scenario 3, (

**d**) Scenario 4. The keys in the legend with prefix ‘S’ and ‘L’ refer to AP placed on the short side and long side of the room, respectively. The numerical suffix refers to the volumetric flow rate level of the AP. The suffixes ‘F’, ‘H’, and ‘M’ refer to cases with the classroom operating at full capacity, half capacity, and full capacity with surgical masks, respectively.

Parameters | Values |
---|---|

Scenarios | 1, 2, 3, 4 as shown in Figure 2 |

Position of AP | Short side at the back of the room |

Long side of the room | |

Volumetric flow rate of AP | Level 0: 200 m${}^{3}/\mathrm{h}$ (0% efficiency) |

Level 1: 800 m${}^{3}/\mathrm{h}$ (100% efficiency) | |

Level 2: 1000 m${}^{3}/\mathrm{h}$ (100% efficiency) | |

Level 3: 1200 m${}^{3}/\mathrm{h}$ (100% efficiency) | |

Number of students | Half capacity: 12 students |

Full capacity: 24 students | |

Masks | No mask (0% efficiency) |

Cloth mask (20% efficiciency) | |

Surgical mask (40% efficiency) | |

N95 mask (95% efficiency) |

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**MDPI and ACS Style**

Jain, A.; Duill, F.F.; Schulz, F.; Beyrau, F.; van Wachem, B.
Numerical Study on the Impact of Large Air Purifiers, Physical Distancing, and Mask Wearing in Classrooms. *Atmosphere* **2023**, *14*, 716.
https://doi.org/10.3390/atmos14040716

**AMA Style**

Jain A, Duill FF, Schulz F, Beyrau F, van Wachem B.
Numerical Study on the Impact of Large Air Purifiers, Physical Distancing, and Mask Wearing in Classrooms. *Atmosphere*. 2023; 14(4):716.
https://doi.org/10.3390/atmos14040716

**Chicago/Turabian Style**

Jain, Aman, Finn F. Duill, Florian Schulz, Frank Beyrau, and Berend van Wachem.
2023. "Numerical Study on the Impact of Large Air Purifiers, Physical Distancing, and Mask Wearing in Classrooms" *Atmosphere* 14, no. 4: 716.
https://doi.org/10.3390/atmos14040716