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Estimate of the critical exposure time based on 70 confirmed COVID-19 cases
Lee Handol,Ahn Kang-Ho 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.79 No.5
The transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) occurs via contact with contaminated surfaces and inhalation of large airborne droplets and aerosols. As growing evidence of airborne SARS-CoV-2 transmission has been reported worldwide, ventilation is an effective method of reducing the infection probability of SARS-CoV-2. This leads to such questions as “What is a sufficient ventilation rate for avoiding the risk of COVID-19 infection?” Therefore, this study evaluates the critical ventilation rates according to room size and exposure time when a susceptible person is in the same room as an infector. The analytical results were based on data obtained from 70 confirmed COVID-19 cases transmitted in confined spaces without an operational ventilation system. The results reveal that even with active ventilation (20 h− 1 air exchange rate), the critical exposure time for a susceptible person with a COVID-19 infector in a small space of 20 m3 is less than 1 h. For other cases (different space sizes), the estimated air exchange rates for avoiding the risk of infection are generally higher than various requirements for good indoor air quality. The findings of this study will provide guidelines for determining sufficient ventilation rates to protect against the highly contagious COVID-19.
Handol Lee,Se-Jin Yook,Kwan-Soo Lee Institute of Electrical and Electronics Engineers 2014 IEEE transactions on semiconductor manufacturing Vol.27 No.2
<P>Deposition velocity of charged particles onto a horizontal flat plate in parallel airflow in the presence of an electric field was numerically investigated by employing a Lagrangian particle tracking approach. The plate length was set as 450 mm, i.e., the characteristic length of the next generation wafer. Either the face-up or the face-down critical surface was considered. The electric field strength and the particle density were varied. The particle deposition velocity was greatly influenced by the electric field strength for particles smaller than approximately 0.1 μm. The influence of the particle density was significant for particles larger than about 0.1 μm. In case of the face-down critical surface, the deposition velocity was greatly reduced for micrometer-sized particles, whereas it was estimated to be relatively high for sub-micrometer sized particles due to attractive electrophoresis and Brownian diffusion.</P>
Ki-Tai Kang,Handol Lee,Hyeok Chung,Kang-Ho Ahn 대한환경공학회 2022 Environmental Engineering Research Vol.27 No.5
Low-cost optical dust sensors are widely used in air purifiers, air conditioners, and air-quality monitoring networks. However, the quality and reliability of these sensors have always been disputed because a standard calibration method has not been established. Low-cost dust sensors used by researchers are calibrated using the researchers’ own methods by applying, for example, a co-location test with reference instruments, a chamber test, or a low-speed duct test. In this study, a test method for the performance evaluation of low-cost sensors was developed using KCl particles with an exponentially decaying particle concentration. With this method, the testing time can be significantly reduced to less than 10 min, and the response characteristics of the sensors to rapidly changing concentrations can be determined. AirAssure from TSI Inc., AirBeam2 from HabitatMap LLC, and DC1100 from Dylos were tested accordingly. The linearities of the measured particulate matter concentrations were significantly good (R² > 0.95), except for the AirAssure sensors. It was also found that the response characteristics of the sensors depended on the particle concentration decay times.
Particle Deposition Velocity Onto EUVL Masks in Vertical Airflow
Won-Geun Kim,Handol Lee,Se-Jin Yook,Kwan-Soo Lee Institute of Electrical and Electronics Engineers 2014 IEEE transactions on semiconductor manufacturing Vol.27 No.3
<P>Extreme ultraviolet lithography (EUVL) masks are vulnerable to particulate contamination due to the unavailability of pellicles. Particle deposition velocity is used to assess the level of particulate contamination. The particle deposition velocity onto a circular disk or a square flat plate situated perpendicular to the airflow was investigated. The numerical and experimental methods employed in this paper were validated by comparing the numerically simulated mean Sherwood numbers or the experimentally determined particle deposition velocities with the theoretically predicted values for the circular disk, representing a wafer, exposed to vertical airflow. Then, an equation for predicting the particle deposition velocity onto a square flat plate, simulating a EUVL mask, in vertical airflow was suggested by numerically obtaining the mean Sherwood number correlation, and validated through experiments.</P>