Airflow Patterns Research Articles

Ventilation methods to prevent the spread of airborne pathogens from teachers to students

This study investigates different ventilation systems to prevent the spread of airborne pathogens from teachers in an elementary school classroom setting. The analyzed systems include a general mechanical ventilation system and a hybrid ventilation system. The hybrid ventilation system used a combination of natural ventilation, general mechanical ventilation, and local mechanical ventilation systems. For natural ventilation, wind velocities of 1.1 m/s and 0.11 m/s were considered. To analyze the patterns of the spread of airborne pathogens, the indoor airflow patterns and concentrations of airborne pathogens (passive scalar) were examined using Star-CCM + . Comparing the methods confirmed that natural ventilation was more effective than general mechanical ventilation in removing the airborne pathogens discharged from the teacher. The proposed hybrid ventilation method with combined natural and mechanical ventilation also showed promise in removing airborne pathogens. However, for natural ventilation with low wind velocity, the buoyancy effect around the occupants creates airflow vortices in the front of the classroom which spread airborne pathogens from the teacher toward the students seated in the front of the classroom. Furthermore, operating a local ventilation system close to the teacher reduced the spread of airborne pathogens that occurred under natural ventilation conditions with low wind velocity.

Electrostatic precipitator with Surface Dielectric Barrier Discharge ionizer

The performance of a two-stage electrostatic precipitator (ESP) with an ionizer with Surface Dielectric Barrier Discharge (SDBD), where the ionizer both generates the free charges and forces the airflow via the electrohydrodynamic (EHD) effect, was experimentally studied. The Particle Image Velocimetry Method (PIV) measurements revealed the airflow patterns and showed that the total flow rate generated by the ionizer (with both flat edge and saw-like high-voltage electrodes) increases with the applied discharge voltage up to a maximum of 73 l/min for 24 kV. These measurements, supported by Computational Fluid Dynamics (CFD) simulations, suggested that changing the airflow pattern with a flow guide would improve the filtration efficiency. This has been experimentally confirmed using an optical particle analyzer, and we recorded a maximum total mass filtration efficiency of 98% for the ionizer with a flat electrode and a flow guide with 3 mm inlet gap. We found that the filtration efficiency increases with the applied voltage up to about 14 kV, then decreases with the voltage due to a reduction in the particle charging rate caused by the high flow velocity of the particles through the discharge region. We also determined that, taking into account both flow rate and filtration efficiency, the ESP works optimally with an applied voltage of 18 kV–20 kV, achieving a filtration efficiency of 77% and simultaneously a flow rate of 63 l/min for the ionizer with the saw-like electrode and respectively 89% and 28 l/min for the ionizer with the flat electrode.

Experimental Study of an Industrial Tower-Type Supporting Frame with Facades Subjected to the Stationary Wind Effect

Aerodynamic studies of canceled structures are important for design of buildings, analysis of air flows inside buildings, evaluation of buildings’ effects on air flow patterns of the adjoining area, and optimal choice of enclosing structures. The analysis of wind effects during the design of canceled structures is governed by codes and standards of general purpose. These statutory documents do not regulate the mounting procedure of wind protection screens, nor do they contain the analysis of wind effects on structures with different angles of attack of an incident wind flow. The codes prescribe aeroelastic model testing in special civil engineering wind tunnels during the design of such structures. The purpose of this research project is to analyze wind effects on the force and torque specification of a canceled structure at different wind effect angles accounting for the mounting sequence of wind protection screens. The subject of the article is an experimental aeroelastic study of wind effects on a canceled structure accounting for sequential mounting of wind protection screens on the structure’s facade. The obtained data will allow for the analysis of effects of the wind flow angle on internal forces of the structure, given that a change in its permeability is taken into account. At the initial design stage, experimental modeling of wind effects in a wind tunnel is thereby considered a structure model validation step. The relevance of the paper lies in the need to identify optimum operating conditions of canceled structures, subjected to a wind effect, to ensure safe and comfortable work of people and reliable operation of process equipment installed inside the facility.

Analysis of single-sided ventilation flows of a generic isolated building using particle tracking method in LES simulation

The main objective of this study is to investigate the airflow patterns in single-sided ventilation of isolated buildings in which the ventilation rate can not be easily predicted by the conventional Orifice equation. The research focuses on buildings with two openings located either at the front or back external wall, with building aspect ratios of 1:1 and 1:2.The study utilizes Large Eddy Simulation (LES) with the particle tracking technique validated by velocity data obtained from a wind tunnel experiment. Ventilation performance is evaluated by Airflow Rate (AFR) and Purging Flow Rate (PFR). AFR was obtained based on the instantaneous velocity over the openings, and PFR was determined by the tracer gas method. The results show that the influence of pulsation flow and eddy penetration both exist in single-sided ventilation. The comparison of AFR and PFR indicates part of the airflow through the opening does not contribute to effectively removing the indoor contaminants, which is quantitively evaluated by ventilation efficiency (εv) defined as the ratio of PFR and AFR. In order to explicitly observe and depict the airflow, the massless particles were emitted at the opening, and the trajectories were analysed. The Probability Density Function (PDF) of indoor residence and indoor travel distance was calculated. The high probability of short indoor travel distance and the residence time, which is mainly caused by the eddy at the openings and time-variant pulsation flow, can explain the difference between AFR and PFR.

Investigation of vertical thermal stratification and stratified air conditioning load for large space with low-sidewall supply air based on vertical temperature node model

Large space buildings often use stratified air conditioning, which has the advantages of reducing energy consumption and improving indoor air quality. The airflow pattern of low-sidewall supply air is a common technology for creating stratified air conditioning in large space. The vertical temperature dynamic distribution is a momentous feature in stratified air conditioning thermal environment, and it is also the key to attain energy saving. In order to explore the heat transfer evolution process for large space stratified air conditioning, a vertical temperature node model for predicting the thermal stratification was established based on the airflow pattern of low-sidewall supply air. In this node model, the large space indoor environment is divided into several air layers in the vertical direction. Each air layer is considered about the aspects of wall convection heat transfer, supply air heat transfer, airflow heat transfer between air layers, temperature differences heat transfer between air layers and so on. A series of heating balance equations are established, and the vertical temperature dynamic distribution results can be obtained by matrix iterative calculation. Based on the 24-h periodic heat flow, the calculated results of the node model were compared with the experimental results. Then, based on the vertical temperature node model, the heat transfer evolution process and dynamic cooling load calculation of large space stratified air conditioning with low-sidewall supply air were discussed and investigated quantitatively.

Study on bioaerosol diffusion and deposition in a mobile BSL-4 laboratory based on air age analysis

Biosafety issues have aroused global concern, especially after the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron strain of corona virus disease 2019 (COVID-19) caused incalculable human and property losses. Laboratory-acquired infections (LAIs) caused by improper operations or accidents are frequently reported. Research is urgently needed for a mobile biosafety level-4 (BSL-4) laboratory with a high risk for exposure. Deposition characteristics and the spatial distribution of bioaerosols under two typical cases were studied in this paper. Based on the age of air and simulation of airflow pattern, a detailed analysis of infection risk and the distribution of bioaerosols was conducted. The deposition characteristics of particles on different surfaces were analyzed based on particle tracking technology. The results showed that the removal rate of bioaerosols was lower in the space area of the laboratory from 1.6 m above the ground. The distribution of high-risk areas is affected by the coupling of equipment layout and pollution sources, mainly located downstream of the main airflow in the laboratory, and the particle concentration was eight times that of the low-risk areas. More than half of bioaerosol particles are deposited on laboratory equipment and walls. The number of particles deposited on the wall was the largest, accounting for 25.02% of the total. The unit area deposition ratio of the experimental table was the highest, which was 6.14 %/m2. The main deposition area of each surface was determined, which could be of guiding significance to the determination of the key disinfection location of the mobile BSL-4 laboratory.

Mitigation of breathing contaminants: Exhaust location optimization for indoor space with impinging jet ventilation supply

Densely occupied spaces (e.g., classrooms) are generally over-crowded and pose a high risk of cross-infection during the pandemic of COVID-19. Among various ventilation systems, impinging jet ventilation (IJV) system might be promising for such spaces. However, the exhaust location of the IJV system used for densely occupied classrooms is unclear. This study aims to investigate the effects of exhaust location on the removal of exhaled contaminants in a classroom (15 × 7 × 5 m3) occupied by 50 students. Exhaled contaminants are modeled by a tracer gas released at the top of each manikin. The reference case has three exhausts evenly distributed in the ceiling. The results indicate that: a) a recirculation airflow entraining exhaled contaminants exists above the occupied zone; b) this recirculation air flow entrains contaminants and accumulates them at the upper part of the room near the diffuser; c) locating merely one exhaust on the same side of the supply diffuser leads to the best indoor air quality, i.e., it reduces the mean age of air from 278 s to 243 s, the mass fraction of CO2 from 753 ppm to 726 ppm, and the concentration of tracer gas from 305 ppm to 266 ppm; d) this layout still performs the best when the supply velocity drops to 0.5 m/s. It is worth noting that the proposed layout has fewer exhausts than the reference case but performs better. These results conclude that the exhaust for large spaces is not evenly distributed but depends on the indoor airflow pattern: the key is locating the exhaust near the region with high contaminant concentration. Factors determining the recirculation airflow are suggested to be further studied.

Impact of Internal Wall Barriers on Airflow Pattern in Natural Cross-Ventilation of the Common Houses in Bhubaneswar City, India

Impact of Internal Wall Barriers on Airflow Pattern in Natural Cross-Ventilation of the Common Houses in Bhubaneswar City, India

Numerical Analysis of the Impact of the Use of Personal Protective Equipment on the Face in the Process of Pollutants Spreading Emitted During Breathing

Abstract The study presents the results of a numerical analysis of the effectiveness of the use of personal protective equipment of various designs on the spread of pollutants marked with CO2 emitted during human breathing. In the study of 3D geometry the upper part of the human torso and head was developed. The simulated person was supplied with different personal protective equipment covering the human face (PPE). Two types of face shields worn at a different distance from the face and one fabric face mask was analysed. The reference geometry with no personal protective equipment was also analysed. Transient calculation with full breathing model including breath-in and breath-out and species transport were simulated. The results showed that different PPE generates different airflow patterns in the vicinity of the human face. The most efficient in reducing infection risk is by wearing a face mask or face shields at a small distance from the face, as they most effectively reduce CO2 concentration in the surrounding air. However, they also increase the re-inhalation risk of high CO2 concentration which affects human well-being.

Research on the cross-contamination in the confined conference room with the radiant floor heating system integrated with the down-supply ventilation

The performance of a confined conference room under radiant heat floor combined with down-supply ventilation (RFDS) is investigated. The purpose of the study is to reveal the mechanism of indoor contaminants transmission from infected person and to protect the occupants. The exhaled contaminant dispersion was simulated using a CFD model and experimentally validated in an office with the down-supply ventilation (DS). The effects of radiant floor (RF) combined with down-supply ventilation on airflow and contaminant distribution in the room was evaluated with regard to different RF temperatures and inlet velocities. The influence of downdraft from the envelope on the airflow pattern of the room is also discussed. It is proved that the exposure risk of pollutants can be reduced by strengthening the insulation of the envelope.The simulation results showed that the proposed RFDS system could significantly reduce the level of exposure to contaminants in the breathing zone (BZ) of occupants. In this research case, the RFDS reduced the average exposure rates by more than 50% relative to the case with the only down-supply warm air heating. Furthermore, With improved envelope insulation, the probability of infection can be reduced by more than 80% only by avoiding a simultaneous inlet velocity of 0.3 m/s at RF temperatures no less than 27 °C. The results suggested an improved fresh air heating mode for passive ultra-low energy consumption buildings with good thermal insulation and air tightness.

Impact of high‐permeability preferential flow zones on pumping‐induced airflow in unconfined aquifer

AbstractWhen the unsaturated zone of the unconfined aquifer is covered by a low‐permeability upper layer, significant airflow will be generated in the unsaturated zone during water pumping. However, high permeability preferential flow zones (PFZs) such as fractures and macropores are frequently present in the unsaturated zone, forming the preferential fluid flow paths, which may change the original airflow pattern in the unsaturated zone during the pumping test and consequently affect the precision of obtained aquifer hydraulic parameters. The main objective of this paper is to investigate the effect of PFZs in low‐permeability upper layer on pumping‐induced airflow in the unsaturated zone by numerical simulations of transient three‐dimensional air‐water two‐phase flow and to quantify errors in the aquifer hydraulic parameters obtained during pumping test. The results demonstrate that a large amount of air flows quickly from the atmosphere into the unsaturated zone through the PFZs, and that the PFZs can draw some air from the nearby low‐permeability soils as well. The significant influx of air through PFZs also reduces the negative air pressure in the unsaturated zone and decreases the drawdown in the saturated zone at intermediate times, which are nevertheless still greater than the results obtained in the homogeneous aquifer. Estimations of the aquifer hydraulic parameters reveal that errors of these parameters obtained are smaller when the PFZs with favourable combinations of permeability, width and quantities facilitate more air to flow into the unsaturated zone.

How wind direction and building spacing influences airflow patterns and sediment transport patterns around a row of beach buildings: A numerical study

How wind direction and building spacing influences airflow patterns and sediment transport patterns around a row of beach buildings: A numerical study

Numerical investigation of indoor air quality in health care facilities: A case study of an intensive care unit

The risk of healthcare-associated infections (HAIs) is higher in patients admitted to intensive care units (ICU) and high dependency units (HDU). Currently, most ventilation studies focus on specialized areas, mainly isolation rooms and operating rooms. This paper focuses on the ventilation of multiple-bed hospital wards in developing countries. This study uses computational fluid dynamics (CFD) simulation to model and investigate airflow and the spread of pollutants. The study aims to investigate ICUs with various ventilation system designs. These predicted behaviors and characteristics were compared numerically to determine compliance with the requirements of airflow patterns, airborne contaminant distribution, and current international standards. The case study simulations were carried out using ANSYS Fluent simulation software as a solution tool. Three different ventilation systems, Vertical Laminar Airflow Ventilation (VLAF), Horizontal Laminar Airflow Ventilation (HLAF), and Temperature-Controlled Airflow Ventilation (TcAF), were modeled within five different designs to determine the most effective possible distribution of air inside the patient's room, based on different categories, primarily temperature distribution, CO2 concentration, and airflow distribution. The authors applied the TcAF technique in an ICU room, comparing the results of the proposed technique with those of other common techniques (HLAF and VLAF). It was found that TcAF showed the most effective airflow distribution around patients, isolating each patient from the others. However, the temperature distribution was excluded from the ASHRAE standard. HLAF with two exhausts is the most suitable option, with a lower CO2 concentration than the alternatives and a temperature that meets ASHRAE standards.

Airflow Mitigation and Pollutant Purification in an Idealized Urban Street Canyon with Wind Driven Natural Ventilation: Cooperating and Opposing Effects of Roadside Tree Plantings and Non-uniform Building Heights

A refined CFD research was reported, concerning on the individual characteristics of different roadside tree planting and street canyon with non-uniformity of buildings. In this work, airflow field and pollutant dispersion were simulated by the use of a full three-dimensional simulations. Ventilation air exchange rate (ACH) and net escape velocity (NEV) were, respectively applied to assess ventilation exchange and pollutant dispersion in the street canyons. Numerical results show that the airflow patterns within the street canyon varies significantly with canopy leaf area density (LAD) and trunk height (Htb), whereas the distribution of pollutants at pedestrian level in the street canyon is mainly determined by the symmetrical inverse vortex structure of the street canyon. Promotions of LAD and Htb of the road trees simultaneously reduce the wind velocity, ACH and NEV of the street canyon, deteriorating the ventilation exchange conditions as well as the pollutant dispersion performance. As the value of the Htb becomes larger, NEV of the step-up canyon is approximately approaching to that of the step-down canyon. In addition, as the value of standard deviation (σH) of the street canyon increases, the vortex structure of the canyon disappears and promotes the diffusion of pollutants inside canyons. As σH further increases, ACH of the step-down canyon also boosts, indicating better ventilation performance of street canyon, whereas the step-up canyon only tops the best ventilation performance at the value of σH= 33.3%. The best dispersion of pollutants is observed at σH= 16.7% in the step-down canyon while in the step-up canyon the dispersion of pollutants becomes better continuously with increasing σH. In particular, as σH= 66.7% was maintained, the dispersion of pollutants is better in the step-up canyon compared to the street canyon without trees. At the same time, the difference between the NEV of the step-down canyon and the step-up canyon increases as σH increases, which indicates that the difference in pollutant dispersion performance between adjacent street canyons becomes greater. This research provides a theoretical reference for urban design and vegetation planning in urban areas to improve the habitat.

An in-silico proof-of-concept of electrohydrodynamic air amplifier for low-energy airflow generation

Electrohydrodynamic (EHD) technology generates airflow without moving parts, making it a reliable solution for various low-energy applications. EHD-based airflow devices enhance airflow patterns, resulting in significant energy savings in air-moving systems. This airflow, also known as ionic wind, is created through Corona discharge, which accelerates electrically charged air molecules in a strong electric field. Currently, EHD's low electrical-to-mechanical energy conversion rate still limit its ability to generate large flow rates. The objective of this study is to enhance the flow rate of EHD-based devices, for applications where EHD can be used as an effective auxiliary technology with low pressure lift, to enhance airflow distribution and circulation. To this end, a novel bladeless air propulsion device is proposed that combines ionic wind with air amplification based on the Coanda phenomenon to amplify EHD-generated flow rates. We assess the performance of the bladeless air propulsion device to generate airflow by investigating fluid dynamics, electrostatics, and energy consumption. We demonstrate the proof-of-concept with an innovative fully-coupled simulation approach for corona discharge and EHD modeling. We explore different design parameters on the conceptual EHD air amplifier, such as the electric potential (10–30 kV) of the discharge electrode, the electrode spacing (5–25 mm), and the channel height (30–150 mm). The studies are performed on a 2D constrained channel flow and a 2D-axisymmetric open space design, respectively. In order to quantify the benefit of air amplification on EHD, the results are benchmarked to a regular EHD setup without amplifying vane as well as to a comparable commercial axial fan. We assess the performance in terms of flow rate per electric power input. Here, the EHD air amplifier in the constrained flow configuration increases the total flow rate by 59% compared to regular EHD and 48% compared to the axial fan for the same electrical energy input. Amplification factors of 16.5–19 are achieved for the constrained configuration and 5.5 to 6.4 for the open space configuration. The predicted energy consumption is 4–17.5 W for the open space configuration, resulting in flow rates up to 140 m3 h−1. These results show that EHD air amplification is a promising way to generate high flow rates with low pressure rise at a low electrical cost, by which it can provide a more sustainable alternative to conventional fans in specific applications..

Zone of flow: A new finding on the characteristics of airflow within the zone of influence during air sparging in aquifers

Air sparging (AS) is a popular technology for the in-situ remediation of groundwater contaminated by volatile organic compounds. The scope of the zone within which injected air exists, i.e., zone of influence (ZOI) and the airflow characteristics within ZOI are of great interest. However, few studies have shed light on the scope of the zone within which air flows, namely, the zone of flow (ZOF) and its relation with the scope of ZOI. This study focuses on the ZOF characteristics and its relation with ZOI based on quantitative observations of ZOF and ZOI using a quasi-2D transparent flow chamber. The relative transmission intensity obtained by the light transmission method presents a rapid and continuous increasing near the ZOI boundary, providing a criterion for the quantitative determination of ZOI. An integral airflow flux approach is proposed to determine the scope of ZOF based on the airflow flux distributions through aquifers. The ZOF radius decreases with the growth of particle sizes of aquifers; while it increases first and then keeps constant with the increase of sparging pressure. The ZOF radius is around 0.55– 0.82 times of the ZOI radius, which depends on air flow patterns related to particle diameters dp, that is, 0.55– 0.62 for channel flow (dp < 1– 2 mm), while 0.75– 0.82 for bubble flow (dp > 2– 3 mm). The experimental results show that the sparged air is entrapped with little flowing inside ZOI regions that are outside the ZOF, which should be considered carefully in the design of AS.

Selecting the Safe Area and Finding Proper Ventilation in the Spread of the COVID-19 Virus

Coughing and sneezing are the main ways of spreading coronavirus-2019 (SARS-CoV-2). People sometimes need to work together at close distances. This study presents the results of the computational fluid dynamics (CFD) simulation of the dispersion and transport of respiratory droplets emitted by an infected person who coughs in an indoor space with an air ventilation system. The resulting information is expected to help in risk assessment and development of mitigation measures to prevent the infection spread. The turbulent flow of air in the indoor space is simulated using the k-ε model. The particle equation of motion included the drag, the Saffman lift, the Brownian force and gravity/buoyancy forces. The innovation of this study includes A: Using the Eulerian–Lagrangian CFD model for the simulation of the cough droplet dispersion. B: Assessing the infection risk by the Wells–Riley equation. C: A safer design for the ventilation system (changing the ventilation supplies and exhausts in the indoor space and choosing the right location for air ventilation). The droplet distribution in the indoor space is strongly influenced by the air ventilation layout. The air-curtain flow pattern significantly reduces the dispersion and spreading of virus-infected cough droplets. When the ventilation air flow occurs along the room length, it takes about 115 s for the cough droplets to leave the space. However, when the ventilation air flow is across the width of the indoor space and there are air curtain-type air flow patterns in the room, it takes about 75 s for the cough droplets to leave the space.

The Effects of the Exhaust Fan Position to Indoor Air Pollution Distribution in Enclosed Parking Garage

Nowadays, lack of space in city center has forced the architects a propose a vertical construction to provide public facility, including the parking garage. Generally, this vertical parking garage has enclosed environment condition, which could be constructed under the building or in the middle of other buildings. This environment causes the parking garage will not have an adequate fresh air circulation or air change rate and gives a more risk due to the accumulation of air pollutants which is emitted from the cars inside. In this research, it observes a simple enclosed parking garage which normally can accommodate six cars. The air pollutant, particularly Carbon Monoxide (CO), from three gasoline cars is extracted by an exhaust fan in a proper location. Two location of exhaust fan are proposed to investigate better air circulation and better air pollutant extraction from the parking garage. The first option (Position of A) installs the exhaust fan near to the parking space units and the other installs the exhaust fan near to the pathway. Each option will follow two worst condition of simulations which are predicted will give a significant impact to Indoor Air Quality (IAQ). Each simulation has to extract the emission from three idle cars with same rate of air circulation of six air change per hour. The results show the influence of air flow pattern to the dispersion of air pollutant. An adequate air flow near to the emission source will cause the increase the maximum of air pollutant concentration. On the other hand, it can minimize the spread of air pollutant dispersion.

Morphology of pig nasal structure and modulation of airflow and basic thermal conditioning.

Mammals have presumably evolved to adapt to a diverse range of ambient environmental conditions through the optimized heat and mass exchange. One of the crucial biological structures for survivability is the nose, which efficiently transports and thermally preconditions the external air before reaching the internal body. Nasal mucosa and cavity help warm and humidify the inhaled air quickly. Despite its crucial role, the morphological features of mammal noses and their effect in modulating the momentum of the inhaled air, heat transfer dynamics, and particulate trapping remain poorly understood. Tortuosity of the nasal cavity in high-olfactory mammalian species, such as pigs and opossum, facilitates the formation of complex airflow patterns inside the nasal cavity, which leads to the screening of particulates from the inhaled air. We explored basic nasal features in anatomically realistic nasal pathways, including tortuosity, radius of curvature, and gap thickness; they show strong power-law correlations with body weight. Complementary inspection of tortuosity with idealized conduits reveals that this quantity is central in particle capture efficiency. Mechanistic insights into such nuances can serve as a tipping point to transforming nature-based designs into practical applications. In-depth characterization of the fluid-particle interactions in nasal cavities is necessary to uncover nose mechanistic functionalities. It is instrumental in developing new devices and filters in a number of engineering processes.

Effect of ceiling fan in mitigating exposure to airborne pathogens and COVID-19

Ceiling fans are the ubiquitously used electrical appliance in indoor spaces that affect the local airflow pattern and, consequently, transmission of airborne pathogens and respiratory droplets. This study numerically investigated the effect of airflow induced by the ceiling fan and ventilation rate on aerosol distribution to mitigate exposure to airborne pathogens and COVID-19. A full-scale room with a ceiling fan, natural ventilation and an occupant was modelled through transient computational fluid-particle dynamics (CFPD). To analyze the relationship between the ceiling fan rotation speed and the aerosol distribution, a ceiling fan was operated with 160, 265 and 365 revolutions per minute (RPM). The effect of the ceiling fan on particles was analyzed for particles of different sizes. The increasing ceiling fan rotation speed, the percentage deposition of the aerosol particles with diameters &gt;40 μm was increased. The effect of different ventilation rates on aerosol distribution was evaluated. The increased ventilation rate, the percentage of the total aerosol particles flushed out was increased. The effectiveness of the mask in mitigating the exposure risk of airborne pathogens was also investigated. In combination with the natural ventilation and mask, the ceiling fan was demonstrated to have the potential to reduce airborne pathogen transmission in indoor spaces.