Since the outbreak of COVID‐19 in December 2019, the severe acute respiratory syndrome coronavirus 2 (SARS CoV‐2) has spread worldwide. This study summarized the transmission mechanisms of COVID‐19 ...and their main influencing factors, such as airflow patterns, air temperature, relative humidity, and social distancing. The transmission characteristics in existing cases are providing more and more evidence that SARS CoV‐2 can be transmitted through the air. This investigation reviewed probabilistic and deterministic research methods, such as the Wells–Riley equation, the dose‐response model, the Monte‐Carlo model, computational fluid dynamics (CFD) with the Eulerian method, CFD with the Lagrangian method, and the experimental approach, that have been used for studying the airborne transmission mechanism. The Wells–Riley equation and dose‐response model are typically used for the assessment of the average infection risk. Only in combination with the Eulerian method or the Lagrangian method can these two methods obtain the spatial distribution of airborne particles' concentration and infection risk. In contrast with the Eulerian and Lagrangian methods, the Monte‐Carlo model is suitable for studying the infection risk when the behavior of individuals is highly random. Although researchers tend to use numerical methods to study the airborne transmission mechanism of COVID‐19, an experimental approach could often provide stronger evidence to prove the possibility of airborne transmission than a simple numerical model. All in all, the reviewed methods are helpful in the study of the airborne transmission mechanism of COVID‐19 and epidemic prevention and control.
To control the transport of particles such as the SARS-CoV-2 virus in airliner cabins, which is a significant concern for the flying public, effective ventilation systems are essential. Validated ...computational fluid dynamics (CFD) models are frequently and effectively used to investigate air distribution and contaminant transportation. The complex geometry and airflow characteristics in airliner cabins pose a challenge to numerical CFD validation. The objective of this investigation was to identify accurate and affordable validation processes for studying the airflow field and particulate contaminant distribution in airliner cabins during the design process for different ventilation systems. This study quantitatively evaluated the effects of ventilation system, turbulence model, particle simulation method, geometry simplification, and boundary condition assignment on airflow and particulate distributions in airliner cabins with either a mixing ventilation (MV) system or a displacement ventilation (DV) system calculated by CFD. The results showed that among four turbulence models, the standard k-ε, RNG k-ε, realizable k-ε and SST k-ω models, the prediction by the realizable k-ε model agreed most closely with the experimental data. Meanwhile, the steady Eulerian method provided a reasonable prediction of the particle concentration field with low computing cost. The computational domain should be simplified differently for the DV system and the MV system with consideration of the simulation accuracy and computing cost. For more accurate modeling results, the boundary conditions should be assigned in greater detail, taking into account the uniformity on the boundary.
•Evaluation of various factors in the accuracy of CFD simulations.•Factors include ventilation system, turbulence model, particle simulation method, geometric model, and boundary conditions.•Comparison of CFD results with experimental data from the literature.
Detachment of fungal spores from growing colonies results in human exposure. Thus far, the distribution of the binding forces of the spores in a fungal unit is unknown, so that precise prediction of ...the spores detachment is quite challenging. This investigation used centrifugal separation to measure the binding forces of the spores. Aspergillus niger (A. niger) colonies on a culture plate were placed in a centrifuge, the detached spores were counted, and this number was used to obtain the distribution of binding forces. Next, the air-blowing of an A. niger unit was modeled by computational fluid dynamics (CFD). A spore was judged to be detached if the air-imposed drag force was greater than the binding force. For model validation, the predicted spore detachment ratios were compared with the ratios measured in a wind tunnel test. The results revealed that the binding forces of the spores obeyed the log-normal distribution. The binding forces of the distal spores from colonies with a growth age of 66 h ranged from 0 nN to 4.0 nN and had a mean of 0.65 nN. The CFD modeling predicted the detachment ratios of the distal spores with good accuracy.
•Binding forces of spores on the whole vesicle unit obey the log-normal distribution.•Relative deviation between the measured and predicted spore detachment ratios is <25 %.•Local air velocity surrounding a spore must be used to calculate the exerted drag force.
Wearing of face masks has been identified as an essential means of reducing COVID-19 infection during the pandemic. However, air leakage into ordinary face masks decreases the protection they ...provide. Wearing a mask also causes both CO2 and humidity to accumulate inside, imposing breathing difficulty and discomfort. To remedy the above problems, this investigation proposed to ventilate ordinary masks by supplying additional HEPA filtered air. The N95, surgical, and cotton masks available on the market, were modified into ventilated masks. The air inside the masks was extracted for measurement of the PM2.5, CO2, and water vapor concentrations. The protection provided by the masks was evaluated in terms of their effectiveness in shielding wearers from ambient PM2.5. Mask comfort was examined in terms of both CO2 concentration and humidity ratio. In addition, a mathematical model was established to solve for the exchanged air flow rates via different routes. Subjective voting by 20 mask wearers was also conducted. Performance of the ventilated face masks were compared against the non-ventilated ones. It was found that the protection provided by the ordinary non-ventilated masks is much lower than that claimed for the filter materials alone due to significantly total inward leakage. The accumulated CO2 and humidity inside masks resulted in discomfort and complaints. For contrast, the ventilated face masks not only enhanced protection by suppressing the inward leakage of ambient airborne particles, but also significantly improved comfort. The wearers preferred a filtered air flow rate ranging from 18 to 23 L/min.
•Ordinary face masks were provided with additional HEPA filtered air for ventilation.•The masks were comprehensively evaluated by measurement, modeling, and voting.•Ordinary non-ventilated face masks have significant inward leakage.•The ventilated face masks enhanced protection and comfort.•The appropriate filtered air flow rate into the face masks was determined.
Squat toilets are widely used in developing countries due to local customs and low costs. The flushing of a squat toilet can entrain strong airflow and produce aerosols. This investigation ...constructed a lavatory mock-up with a squat toilet. The flushing-induced airflow was both visualized and quantitatively measured by particle image velocimetry. The maximum height of the impacted airflow was identified by an ultrasonic anemometer. For inference of the particle emission rate, the toilet bowl was covered by an enclosed box for particle concentration measurement. The risks from skin contact of the deposited particles on the flushing button and the door handle and the possible inhalation of the released aerosols were evaluated. The results revealed that flushing a squat toilet can drive toilet plume to rise up to 0.9 m above the toilet bowl. A single flushing process can produce 0.29 million particles with diameters greater than 0.3 μm, among which 90% of the particles are submicron-sized. The flushing may cause particles to deposit on the flushing button and lavatory door handle as well as inhalation exposure even remaining in the lavatory for half a minute after flushing, especially for those lavatory users whose respiratory zones are below 1.0 m.
Dining tables may present a risk to diners by transmitting bacteria and/or viruses. Currently, there is a lack of an environmental-friendly and convenient means to protect diners when they are ...sitting together. This investigation constructed far-UVC excimer lamps to disinfect dining-table surfaces. The lamps were mounted at different heights and orientations, and the irradiance on table surfaces was measured. The irradiation doses to obtain different inactivation efficiencies for Escherichia coli (E. coli) were provided. In addition, numerical modeling was conducted for irradiance and the resulting inactivation efficiency. The surface-to-surface (S2S) model was validated with the measured irradiance. The germicidal performance of far-UVC irradiation, the far-UVC doses to which diners were exposed, and the risk of exposure to the generated ozone were evaluated. The results revealed that an irradiation dose of 12.8 mJ/cm
can disinfect 99.9% of E. coli on surfaces. By varying the lamp irradiance output, the number and positions of the lamps, the far-UVC irradiation can achieve a 3-log reduction for a dining duration of 5 min. Besides, the far-UVC lamp has a low damage risk to diners when achieving an effective inactivation rate. Moreover, there is virtually no ozone exposure risk in a mechanically ventilated dining hall.
Aspergillus niger (A. niger) spores can induce numerous health problems. Once the airflow-imposed drag force on an A. niger spore exceeds its binding force with the colony, the spore is detached. ...Turbulent flow may considerably increase the spore detachment. No method is currently available for prediction of the drag force on a spore and its detachment in turbulent flows. This investigation measured the turbulent velocities and detachment of A. niger colonies in a wind tunnel. Computational fluid dynamics (CFD) was employed to model an A. niger unit subjected to turbulent flow blowing. The top 1 % quantile instantaneous velocity of the turbulent flow was specified as the steady entry flow boundary condition for solving the peak velocity distribution and the peak drag forces onto spores. The predicted spore detachment ratios were compared with the measurement data for model validation. The results revealed that the spore detachment ratios with a turbulence intensity of 17 % to 20 % can be twice to triple the ratio with a turbulence intensity of approximately 1 %, when the average velocity for blowing remains the same. The proposed CFD model can accurately predict the detachment ratios of the A. niger spores.
Some people are sensitive to the Aspergillus niger (A. niger) spores, and excessive exposure can cause nasal congestion, skin tingling, coughing, and even asthma. Turbulent flow can considerably increase the spore detachment, due to the increased airflow-imposed drag force on the spores during turbulence. This investigation developed a numerical model to solve for the peak velocity distribution and the peak drag forces onto spores in turbulent flows to predict the spore detachment. With the numerical tool, the airborne fungal spore concentrations would be predictable, which paves a way for intelligent and precise control of fungal aerosol pollution.
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•Detachment of A. niger spores in turbulent flow was measured and predicted.•Peak drag force by turbulent flow was solved to predict the spore detachment.•The top 1 % quantile of the instantaneous velocity can be deemed the peak velocity.•Turbulence can increase the spore detachment ratio by several times.
In case airborne pollutants have been accidentally released indoors, knowing release locations and rate profiles of the pollutant sources is always beneficial. Current inverse models can locate a ...pollutant source but have difficulty quantifying its temporal release rate. This study proposes an inverse method based on Tikhonov regularization and least-squares optimization using computational fluid dynamics (CFD) to quantify the temporal release rate of a gaseous pollutant source. The Tikhonov regularization adds a regularized term to the objective function of the concentration and imposes a bound on the solution. The release rate can then be solved based on the inverse matrix operation with the monitored concentration series at a particular location. To accelerate the solving procedure, the gas concentration is expressed as the convolution integral between the concentration response of a unit impulse release (response factor) and the arbitrary release profile. This study finds that the developed inverse method can accurately and efficiently quantify the intermittent gas release in both constant and sinusoidal forms. The only prerequisites to implement the proposed inverse method are a steady flow field, a known fixed source location and the monitored temporal concentration at a point in space.
•Inverse quantification of the temporal pollutant release rate by only one sensor.•Tikhonov regularization coupled with least-squares optimization.•Convolution integral with response factors to accelerate solution.•Identified release type in both constant and intermittent sinusoidal forms.
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The high-speed jet discharged by hand dryers with brushed motors may release hazardous particles. In this study, the particles released from the hand dryer were trapped using high-efficiency ...particulate air filters for chemical composition analysis in a small test room. A manikin was placed to mimic a user standing in front of the dryer. Number and mass concentrations of the released particles were measured to estimate the particle emission rates and inhalation exposure. The particle emission rate reached 2.64 × 106 particles/s when starting the dryer. The released particles were found to contain a copper element, subsequently extrapolated to copper oxide. Secondly, in the large test room, jet airflows were measured using a three-dimensional ultrasonic anemometer. The results revealed that the horizontally placed palms caused the discharged jets to bend toward the human body, resulting in an upward motion of the air into the breathing zone. After running the dryer for 30 s, the peak mass concentration in the breathing zone for particles with a less than 2.5-μm diameter was 13.1 µg/m3. Installing high-efficiency particulate air filters to the air outlets of hand dryers was found to be effective in minimizing the exposure to CuO.
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•Induced airflows from a hand dryer were measured.•The chemical compositions of the self-generated particles were analyzed.•The self-generated particle emission rates and spectra were reported.•Installing HEPA filters to the air outlets of hand dryers is recommended.
According to the World Health Organization (https://covid19.who.int/), more than 651 million people have been infected by COVID-19, and more than 6.6 million of them have died. COVID-19 has spread to ...almost every country in the world because of air travel. Cases of COVID-19 transmission from an index patient to fellow passengers in commercial airplanes have been widely reported. This investigation used computational fluid dynamics (CFD) to simulate airflow and COVID-19 virus (SARS-CoV-2) transport in a variety of airliner cabins. The cabins studied were economy-class with 2-2, 3-3, 2-3-2, and 3-3-3 seat configurations, respectively. The CFD results were validated by using experimental data from a seven-row cabin mockup with a 3-3 seat configuration. This study used the Wells-Riley model to estimate the probability of infection with SARS-CoV-2. The results show that CFD can predict airflow and virus transmission with acceptable accuracy. With an assumed flight time of 4 h, the infection probability was almost the same among the different cabins, except that the 3-3-3 configuration had a lower risk because of its airflow pattern. Flying time was the most important parameter for causing the infection, while cabin type also played a role. Without mask wearing by the passengers and the index patient, the infection probability could be 8% for a 10-h, long-haul flight, such as a twin-aisle air cabin with 3-3-3 seat configuration.
•Proposed a CFD based method to study airborne infectious diseases in an air cabin.•Validated the CFD results by experimental data obtained from a cabin mockup.•Evaluated infection probabilities in different airplanes and seats to COVID-19.•Found flight time is the most important factor in the infection probability.
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