・ 試運転中のスーパーコンピュータ「富岳」と申請者らが理研で独自開発したシミュレーションソフトウェア「CUBE」を用いて、室内環境でのウイルス飛沫・エアロゾル感染のリスク評価を行い、感染リスク低減対策の提案を行った。
・ 「富岳」の膨大な計算資源を活用することで、2か月に一度程度の頻度で、社会の感染状況に合わせて必要な情報を提供し、感染拡大の防止に寄与した。
・ 具体的な解析対象は、マスクやフェースガード、パーティションの他、具体的な室内空間としては例えばオフィス、病室、教室、体育館、イベントホール、大規模コンサートホール、国立競技場、飲食店、カラオケボックス、通勤電車、航空機、バス、タクシー、救急車と多岐に渡り、広く社会のニーズに合わせた情報を提供した他、内閣官房、文科省、国交省、神戸市とも連携することで、社会活動の再開のためのガイドライン策定や改定に寄与した。

室内環境に関する代表的な国際ジャーナルIndoor and Built Environmentに掲載された以下の論文が，2020年に掲載された論文中で最高評価を受け，Best Paper Awardを受賞した．
Koki Nakahara, Mahbubul Muttakin, Kiyoshi Yamamoto, and Kazuhide Ito, CFD modeling of the visible light photocatalytic oxidation process of toluene for indoor building material with locally doped titanium dioxide, Indoor and Built Environment, 29 (2), 2019, 163-179
(doi.org/10.1177/1420326X19854499)

室内環境に関する代表的な国際ジャーナルIndoor and Built Environmentに掲載された以下の論文が，2018年に掲載された論文中で最高評価を受け，Best Paper Awardを受賞した．
Sung-Jun Yoo and Kazuhide Ito, Numerical Prediction of Tissue Dosimetry in Respiratory Tract using Computer Simulated Person integrated with physiologically based pharmacokinetic (PBPK)-computational fluid dynamics (CFD) Hybrid Analysis, Indoor and Built Environment, 2018, Vol. 27(7) 877–889 (doi: 10.1177/1420326X17694475)

室内での空気汚染物質の濃度分布予測や、人体の気道における曝露濃度の高精度予測および健康影響評価は、基礎研究から室内環境設計までの広範な知識と経験が必要な複合的な環境問題であるが、これまで的確な研究手法がなかった。伊藤一秀氏は、有機化合物の移流・拡散、吸脱着、化学反応、建材内拡散と、人体内気道での流れなど、空気汚染物質の各現象を総合的に組み込んだ連成解析モデルを提案、室内の空気汚染物質の濃度分布を解析し、室内環境を設計する手法を開発した。特に、人体の呼吸器における複雑な幾何形状を再現し、人体周辺の気流を高精度で再現できる数値人体モデルは、汚染物質が呼吸器系に至る経路と気道での曝露濃度の高精度予測につながる画期的なモデルである。また、研究成果は国際規格にも採用され、社会的にも高く評価されている。室内環境問題は、今後ますます重要になるものと予想され、伊藤氏が世界をリードする研究者となることが期待される。

中規模オフィスビルを対象とした全熱交換器の空調消費電力削減効果に関する実測研究

病院待合スペースを対象とした非定常不均一濃度分布解析と疫学モデルの連成解析による空気感染伝播予測

Numerical Prediction Model for Fungal Growth Coupled with Hygrothermal Transfer in Building Materials

Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

Publisher：Building and Environment  

To enhance the realism and precision of indoor environment assessments and the evaluation of human health risks using computational fluid dynamics (CFD), it is crucial to accurately replicate human shape and physiological functions. This study investigates the influence of micro-movements resulting from posture control on the human breathing zone (BZ) using CFD analysis. A Computer-Simulated Person (CSP) incorporating a sophisticated nasal cavity model and multi-node thermoregulation was employed to precisely predict the microclimate around the human body, including the BZ. Two types of movements were considered to replicate micro-movements of a standing human body: angular and linear movements. The BZs were evaluated based on the Scale for Ventilation Efficiency (SVE) 4 and 5 for exhalation and inhalation modes, respectively. While the distribution of exhaled air remained generally consistent, distinct differences were observed in inhaled air distribution. In a representative case with a maximum angular velocity of 4°/s, the horizontal length increased by 12 cm, and the vertical distance of the SVE5>10 % distribution decreased by 14 cm compared to the stationary case. Linear movement, particularly in the mediolateral (ML) direction, led to a horizontal expansion of the inhaled air distribution. The findings of this study suggest that replicating human micro-movements has a minimal impact on general indoor climate analysis but significantly enhances the accuracy of predicting breathing air quality.

DOI： 10.1016/j.buildenv.2024.111916

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Scopus

Language：English   Publisher：Computer Methods and Programs in Biomedicine  

Background and objective: Viral respiratory infections stand as a considerable global health concern, presenting significant risks to the health of both humans and animals. This study aims to conduct a preliminary analysis of the time series of viral load in the nasal cavity-nasopharynx (NC-NP) of the human and rhesus macaque (RM). Methods: Taking into account the random uniform distribution of virus-laden droplets with a diameter of 10 μm in the mucus layer, this study applies the computational fluid dynamics-host cell dynamics (CFD-HCD) method to 3D-shell NC-NP models of human and RM, analyzing the impact of initial distribution of droplets on the viral dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), estimating parameters in the HCD model based on experimental data, integrating them into simulations to predict the time series of viral load and cell counts, and being visualized. The reproductive number (R0) are calculated to determine the occurrence of infection. The study also considers cross-parameter combinations and cross-experimental datasets to explore potential correlations between the human and RM. Results: The research findings indicate that the uniform distribution of virus-laden droplets throughout the whole NC-NP models of human and RM is reasonable for simulating and predicting viral dynamics. The visualization results offer dynamic insights into virus infection over a period of 20 days. Studies involving parameter and dataset exchanges between the two species underscore certain similarities in predicting virus infections between the human and RM. Conclusions: This study lays the groundwork for further exploration into the parallels and distinctions in respiratory virus dynamics between humans and RMs, thus aiding in making more informed decisions in research and experimentation.

DOI： 10.1016/j.cmpb.2024.108354

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Scopus

PubMed

Publisher：Building and Environment  

Engineers have integrated general ventilation systems with personalized ventilation (PV) to achieve energy efficiency while providing good indoor air quality (IAQ) and thermal comfort. Previous studies conducted parametric analyses of PV by varying its flow rate and temperature, analyzing energy, IAQ, and thermal comfort while keeping main ventilation settings constant, even though the latter significantly affect the general flow field. Therefore, computational fluid dynamics simulation is performed to simultaneously optimize the above-mentioned three outputs in an office with displacement ventilation (DV) and PV by varying the DV supply flow rate and temperature, the fraction of outlet air being resupplied to inlet or DV recirculation, and PV supply flow rate and temperature. We utilize the Taguchi design to minimize the number of simulations as well as use the “technique for order preference by similarity to ideal solution” (TOPSIS) coupled with Taguchi's signal-to-noise ratio analysis for optimization. Four optimization cases are investigated by varying the thermal comfort and IAQ parameters from volume-averaged to occupant-centric values, such as the skin temperature and inhaled concentration. Results show that occupant-centric optimization presents low energy requirements with acceptable IAQ and thermal comfort compared with volume-averaged optimization, which can be attributed to imperfect mixing conditions. Furthermore, the DV settings and thermal plumes significantly affect the direction of jet released by the PV, which does not improve the IAQ. This underscores the importance of considering the aforementioned effects in maximizing the PV potential. Nevertheless, the PV system functions as intended under a flow rate of 6 L/s.

DOI： 10.1016/j.buildenv.2024.111837

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Scopus

Publisher：Building and Environment  

In a typical house with a mechanical ventilation system, a ventilation duct with a certain installation length is placed along the exterior walls or in the ceiling shed space. To effectively use this ventilation duct, we aimed to develop a novel ventilation duct system with sensible heat exchange and passive air purification mechanisms. The proposed ventilation duct comprises multiple layers of a counterflow heat recovery ventilator (HRV). Baffles were installed in the middle of the flow channel to collect particles in the outdoor air by forming a circulating flow associated with the separation flow and gravitational settling in a local domain in the flow channel. To optimize the design of this new ventilation duct concept in terms of particle removal and heat exchange efficiencies, we conducted a computational fluid and particle dynamics analysis as a function of design parameters such as airflow rate, particle size, and air temperature. Through a series of numerical analyses, differences in the heat exchange efficiency and effectiveness of particle removal corresponding to different baffle designs were quantitatively evaluated, and finally, the optimal design for the air channel as an HRV was determined.

DOI： 10.1016/j.buildenv.2024.111773

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Scopus

Language：Japanese   Publisher：Japan Association on Odor Environment  

<p>The assessment of odour and/or smell in indoor environments has basically relied on sensory testing by human volunteers. In recent years, there has been active development of olfactory sensing devices and electronic noses based on semiconductor sensors. On the other hand, the development of a digital twin, which mathematically describes the olfactory mechanism in the human nasal cavity and reproduces it on a computer, is also being researched. This paper presents the current status and future prospects for the development of an <i>in silico</i> nose based on computational fluid dynamics and physiologically based pharmacokinetic models.</p>

DOI： 10.2171/jao.55.211

CiNii Research

Publisher：Building and Environment  

Natural ventilation offers significant advantages, especially in terms of energy conservation. However, most published articles have focused on the ventilation flow rate to determine the average contaminant concentration, while few have examined local ventilation distributions. Therefore, isothermal steady-state Reynolds-averaged Navier–Stokes simulations were conducted to analyze the airflow and scalar concentration fields of a cross-ventilation model sheltered by buildings. Based on these fields, we generated the spatial distributions of ventilation indices, namely, the net escape velocity (NEV), point-to-point indices transfer probability (TP), and travel time (TT), to discuss the dispersion of scalars emitted from local points in a room with natural ventilation. The NEV, which indicates the direction of the scalar discharge from each cell, exhibited a distribution distinct from the advection velocity because of concentration gradient effect. Higher TPs were observed when evaluated from a contaminant source to a target point following the NEV streamlines. Meanwhile, lower TTs were observed when evaluated in a point near the source and also from a contaminant source to a target point following the NEV streamlines. Although TP and TT are independent ventilation indices, a negative correlation between them was observed. Instead of the ventilation flow rate, the detailed structure of scalar dispersion can now be described by simultaneously analyzing the ventilation efficiency indices, which provide information on the general contaminant transport direction, and the probability and duration of transfer from a source to a target point. This potentially helps in the design of ventilation system especially in room lay-out to avoid cross-contamination.

DOI： 10.1016/j.buildenv.2024.111668

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Scopus

Language：Japanese   Publisher：公益社団法人におい・かおり環境協会  

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DOI： 10.2171/jao.55.147

CiNii Research

Language：English   Publisher：Computer Methods and Programs in Biomedicine  

Background and objective: Respiratory diseases caused by respiratory viruses have significantly threatened public health worldwide. This study presents a comprehensive approach to predict viral dynamics and the generation of stripped droplets within the mucus layer of the respiratory tract during coughing using a larynx-trachea-bifurcation (LTB) model. Methods: This study integrates computational fluid-particle dynamics (CFPD), host-cell dynamics (HCD), and the Eulerian wall film (EWF) model to propose a potential means for seamless integrated analysis. The verified CFPD-HCD coupling model based on a 3D-shell model was used to characterize the severe acute respiratory syndrome, coronavirus 2 (SARS-CoV-2) dynamics in the LTB mucus layer, whereas the EWF model was employed to account for the interfacial fluid to explore the generation mechanism and trace the origin site of droplets exhaled during a coughing event of an infected host. Results: The results obtained using CFPD delineated the preferential deposition sites for droplets in the laryngeal and tracheal regions. Thus, the analysis of the HCD model showed that the viral load increased rapidly in the laryngeal region during the peak of infection, whereas there was a growth delay in the tracheal region (up to day 8 after infection). After two weeks of infection, the high viral load gradually migrated towards the glottic region. Interestingly, the EWF model demonstrated a high concentration of exhaled droplets originating from the larynx. The coupling technique indicated a concurrent high viral load in the mucus layer and site of origin of the exhaled droplets. Conclusions: This interdisciplinary research underscores the seamless analysis from initial exposure to virus-laden droplets, the dynamics of viral infection in the LTB mucus layer, and the re-emission from the coughing activities of an infected host. Our efforts aimed to address the complex challenges at the intersection of viral dynamics and respiratory health, which can contribute to a more detailed understanding and targeted prevention of respiratory diseases.

DOI： 10.1016/j.cmpb.2024.108073

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Scopus

PubMed

Publisher：Sustainable Cities and Society  

This paper presents a comprehensive numerical investigation to predict the human breathing zones (BZs) in crowded semi-outdoor environments. The computational domain consisted of a nine-human block array with integrated nasal cavities subjected to the lower part of the atmospheric boundary layer. Five crowding levels, seven wind directions, and inflow ambient air temperatures (ranging from 10 to 31 °C) were tested to examine the horizontal and vertical formations of the BZs. Validation and verification tests were performed through comparisons with experimental results, a grid independence test, and an evaluation of various randomized distribution scenarios to minimize the uncertainties of the computational fluid dynamics analyses. The horizontal extension of the BZs tripled as the crowding level increased from 0.325 to 4.0 m2/capita. However, the lateral extension was insensitive and remained within 10 cm of the nostrils. Human models can inhale air close to the cheek, neck, and shoulders when an oblique flow is assumed. As the air temperature increased, individuals tended to inhale air from the upper regions, which was influenced by the interrelated thermal properties of the human body. Consequently, under high-temperature conditions, there may be an increased probability of gas-phase contaminant inhalation over greater horizontal distances.

DOI： 10.1016/j.scs.2024.105274

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Scopus

Publisher：Building and Environment  

The assessment of potential health risks from exposure to airborne contaminants and the inhalability of microparticles through human nasal breathing is crucial for the design of ventilation systems. In this study, using a standing computer-simulated person (CSP) directly linked to a numerical model of the respiratory tract, we investigated the aspiration efficiency (AE) of microparticles ranging between 1 and 80 μm under steady and transient breathing conditions. Two ventilation scenarios with displacement and mixed ventilation systems (DV and MV) were assumed for AE calculations. To determine the appropriate particle injection location, we investigated the position of highly inhaled particles corresponding to the breathing zone using a reverse particle-tracking simulation with reversed time progression. Additionally, the total and regional deposition fractions (TDF and RDF) of the inhaled microparticles on the respiratory wall surfaces were evaluated using the Lagrangian approach. The results indicate that the transient breathing cycle showed relatively higher AE and TDF rates compared to the assumed steady inhalation conditions, particularly for the size range 1–10 μm. An insignificant variation was observed in the AE and RDF results between different ventilation systems. However, microparticles in the MV room showed slightly higher AE than the DV system. Moreover, AE and penetration ratio were highly sensitive to the initially assumed particle density. For a comprehensive and accurate assessment of inhalation exposure to microparticles, we should predict the heterogeneous flow field formed around the human body and then analyze the AE and TDF in the respiratory tract during realistic transient breathing.

DOI： 10.1016/j.buildenv.2023.111114

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Scopus

Language：English  

DOI： 10.1093/nar/gkad1149

Web of Science

PubMed

Publisher：Building and Environment  

There is a growing demand for more advanced and diverse computer-simulated persons (CSPs) to accurately evaluate the indoor environmental quality and analyze the human body interactions with environmental factors. This study aimed to develop a CSP targeting the ANDI thermal manikin, which regulates skin temperature and thermal functions through a multi-node thermoregulation model, that is, the development of a digital twin for the ANDI thermal manikin. Additionally, to ensure the prediction reliability of the numerical thermoregulation model applied to the CSP using computational fluid dynamics (CFD) analysis, the CFD results were compared with those from the chamber experiment using an ANDI thermal manikin. We conducted integrated analyses of the CSP using the Fiala thermoregulation model to calculate the metabolic heat production, at transfer between different layers and sections, and skin surface temperature. The CFD analysis was performed using the CSP under the same environmental conditions as those used in the experiment. The CSP analysis results reproduced the experimental results obtained using the thermal manikin in the thermal comfort evaluation with acceptable accuracy, and the root mean square deviation of the predicted mean skin temperature was approximately 0.195. Furthermore, the importance of detailed clothing geometry was highlighted by confirming that the thickness of the ventilation layer between the skin and clothing has a significant effect on the thermal performance. The comprehensive prediction method for indoor environments based on the advanced CSP developed in this study can contribute to human-centered indoor environmental planning through parametric analyses under various environmental scenarios.

DOI： 10.1016/j.buildenv.2023.111105

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Scopus

Language：English  

Infectious respiratory diseases have long been a serious public health issue, with airborne transmission via close person-to-person contact being the main infection route. Coughing episodes are an eruptive source of virus-laden droplets that increase the infection risk of susceptible individuals. In this study, the droplet generation process during a coughing event was reproduced using the Eulerian wall film (EWF) model, and the absorption/expulsion of droplets was tracked using the discrete phase model (DPM). A realistic numerical model that included the oral cavity with teeth features and the respiratory system from the throat to the first bifurcation was developed. A coughing flow profile simulated the flow patterns of a single coughing episode. The EWF and DPM models were coupled to predict the droplet formation, generation, absorption, and exhalation processes. The results showed that a large droplet number concentration was generated at the beginning of the coughing event, with the peak concentration coinciding with the peak cough rate. Analysis of the droplet site of origin showed that large amounts of droplets were generated in the oral cavity and teeth surface, followed by the caudal region of the respiratory system. The size of the expelled droplets was 0.25–24 μm, with the peak concentration at 4–8 μm. This study significantly contributes to the realm on the site of origin and localized number concentration of droplets after a coughing episode. It can facilitate studies on infection risk assessment, droplet dispersion, and droplet generation mechanisms from other sneezing or phonation activities.

CiNii Research

Publisher：Building and Environment  

We numerically analyzed odorant transportation from a sniffing device (funnel) to the olfactory region of the nasal cavity during breathing. We followed the procedure for the perceived air quality evaluations described in the ISO 16000-28 standard, and used acetone defined as the standard test substance for pi-scale evaluations in this standard; we also used ammonia and acetic acid, as acetone also emitted by humans. We modelled two breathing conditions: normal breathing (through nose) and sniffing. We evaluated olfactory receptor access under these breathing conditions. The acetone absorption flux to the olfactory epithelial tissues was analyzed using a computer-simulated person with a numerical respiratory tract model and a physiologically based pharmacokinetic model that was used to validate the prediction accuracy. The absorption flux and sensible/latent heat flux to the olfactory epithelial tissue were analyzed quantitatively. We also analyzed the impact of flow through the ortho- and retro-nasal pathways on the absorption flux to the olfactory region. The transient inhalation/exhalation airflow profile, breathing, and sniffing conditions had a significant impact on the absorption flux to the olfactory region of the nasal cavity. We observed two peaks of odorant absorption flux in one breath one during inhalation and one during exhalation. For example, 0.5μg/(m2s) of peak acetone absorption flux in the olfactory region during inhalation and 0.1μg/(m2s) during exhalation was observed.

DOI： 10.1016/j.buildenv.2023.110868

Web of Science

Scopus

Publisher：Physics of Fluids  

Infectious respiratory diseases have long been a serious public health issue, with airborne transmission via close person-to-person contact being the main infection route. Coughing episodes are an eruptive source of virus-laden droplets that increase the infection risk of susceptible individuals. In this study, the droplet generation process during a coughing event was reproduced using the Eulerian wall film (EWF) model, and the absorption/expulsion of droplets was tracked using the discrete phase model (DPM). A realistic numerical model that included the oral cavity with teeth features and the respiratory system from the throat to the first bifurcation was developed. A coughing flow profile simulated the flow patterns of a single coughing episode. The EWF and DPM models were coupled to predict the droplet formation, generation, absorption, and exhalation processes. The results showed that a large droplet number concentration was generated at the beginning of the coughing event, with the peak concentration coinciding with the peak cough rate. Analysis of the droplet site of origin showed that large amounts of droplets were generated in the oral cavity and teeth surface, followed by the caudal region of the respiratory system. The size of the expelled droplets was 0.25-24 μm, with the peak concentration at 4-8 μm. This study significantly contributes to the realm on the site of origin and localized number concentration of droplets after a coughing episode. It can facilitate studies on infection risk assessment, droplet dispersion, and droplet generation mechanisms from other sneezing or phonation activities.

DOI： 10.1063/5.0174014

Web of Science

Scopus

Publisher：Building and Environment  

To address the problem of airborne transmission caused by droplets/droplet nuclei containing infectious viruses such as influenza A, tuberculosis, and SARS-CoV-2, the transmission dynamics of infectious droplets in indoor environments, from the generation/emission from an infected subject to the exposure of the target subject via indoor air, must be comprehended seamlessly and accurately. Research on indoor airborne transmission requires rigorous prior ethical review, and experimental studies on humans (in vivo and/or in vitro) are severely limited. Therefore, research methods based on in silico models; i.e., numerical modeling and analysis approaches, are preferred, owing to their flexibility for case and sensitivity analyses. In this study, assuming airborne transmission of SARS-CoV-2 in an indoor environment, we develop and perform a seamless and continuous numerical analysis of infectious droplet dispersion from a coughing infected subject and the subsequent inhalation exposure of a target subject (via the respiratory tract) through transient breathing. We focus on the effects of respiration patterns, particle-size changes due to evaporation, and indoor physical distance between the subjects, on the exposure concentration and distribution of inhaled droplets in the respiratory tract. The results show that, when an infected person coughs within a physical distance of 1 m, inhalation exposure results in significant differences in the inhalation–exhalation timing of breathing, and local environmental conditions have a dominant effect on the inhalation exposure. In short-range airborne transmission, the particle-size change due to evaporation has a dominant effect on the estimation of the inhalation exposure concentration in the respiratory tract.

DOI： 10.1016/j.buildenv.2023.110748

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Scopus

Publisher：Fluids  

The transport and prediction of the concentration of particles in confined spaces are crucial for human well-being; this has become particularly evident during the current worldwide pandemic. Computational fluid dynamics (CFD) has been widely used for such predictions, relying on Eulerian–Eulerian (EE) and Eulerian–Lagrangian (EL) models to study particle flow. However, there is a lack of research on industrial factories. In this study, a scaled laboratory in an industrial factory was established for oil mist particles in a machining factory, and oil mist dispersion experiments were conducted under roof exhaust and mixed ventilation conditions. After that, the oil mist concentration distribution in the factory under the same working conditions was calculated by Eulerian and Lagrangian methods, and the corresponding calculation errors and resource consumption were compared. It was found that the simulation results of both methods are acceptable for mixed ventilation and roof exhaust ventilation systems. When there are more vortices in the factory, the Lagrangian method increases the computation time by more than 53% to satisfy the computational accuracy, and the computational error between the Eulerian and Lagrangian methods becomes about 10% larger. For oil mist particles with an aerodynamic diameter of 0.5 μm, both Eulerian and Lagrangian methods have reliable accuracy. Based on the same flow field, the Lagrangian method consumes more than 400 times more computational resources than the Eulerian method. This study can provide a reference for the simulation of indoor particulate transport in industrial factories.

DOI： 10.3390/fluids8100264

Web of Science

Scopus

Publisher：Building and Environment  

This study investigates outdoor public health by predicting the airflow fields and probabilistic size of breathing zones. Computational fluid dynamics (CFD) simulations were performed in a simplified semi-outdoor domain, utilizing a validated computer-simulated person (CSP) with an integrated nasal cavity. The simulations were conducted for eight wind orientations (0°, 90°, 180°, 270°, 45°, 135°, 225°, and 315°), four wind velocities (Uref = 0.25, 0.5, 0.75, and 1.0 m/s), and one inhalation flow rate (18.7 L/min), considering both steady and transient conditions. The RANS-based equations were solved using the SST k-omega turbulence model. Breathing zones were computed and visualized using the scale for ventilation efficiency 5 (SVE5) and reverse time-traced vector techniques. The results indicated that wind orientation influenced the air velocity, temperature, and breathing zone distribution. The steady-state condition tended to overestimate breathing zones, whereas, under transient conditions, they assumed a semi-cylindrical form that extended horizontally, with a slight slope from the nostrils towards the direction of the wind source. The horizontal extension of the breathing regions increased at high wind speeds and with a smaller cylinder radius compared to calm conditions. Eventually, this study proposed new definitions of the breathing zone in the semi-outdoor environment in different SVE5 values. These findings can contribute to air quality management and aid in assessing the probability of airborne transmission in public spaces.

DOI： 10.1016/j.buildenv.2023.110672

Web of Science

Scopus

Language：English   Publisher：Experimental and Computational Multiphase Flow  

Commuter buses have a high passenger density relative to the interior cabin volume, and it is difficult to maintain a physical/social distance in terms of airborne transmission control. Therefore, it is important to quantitatively investigate the impact of ventilation and air-conditioning in the cabin on the airborne transmission risk for passengers. In this study, comprehensive coupled numerical simulations using computational fluid and particle dynamics (CFPD) and computer-simulated persons (CSPs) were performed to investigate the heterogeneous spatial distribution of the airborne transmission risk in a commuter bus environment under two types of layouts of the ventilation system and two types of passenger densities. Through a series of particle transmission analysis and infection risk assessment in this study, it was revealed that the layout of the supply inlet/exhaust outlet openings of a heating, ventilation, and air-conditioning (HVAC) system has a significant impact on the particle dispersion characteristics inside the bus cabin, and higher infection risks were observed near the single exhaust outlet in the case of higher passenger density. The integrated analysis of CFPD and CSPs in a commuter bus cabin revealed that the airborne transmission risk formed significant heterogeneous spatial distributions, and the changes in air-conditioning conditions had a certain impact on the risk.

DOI： 10.1007/s42757-022-0146-6

Web of Science

Scopus

PubMed

Publisher：Fluids  

Highway buses are used in a wide range of commuting services and in the tourist industry. The demand for highway bus transportation has dramatically increased in the recent post-pandemic world, and airborne transmission risks may increase alongside the demand for highway buses, owing to a higher passenger density in bus cabins. We developed a numerical prediction method for the spatial distribution of airborne transmission risks inside bus cabins. For a computational fluid dynamics analyses, targeting two types of bus cabins, sophisticated geometries of bus cabins with realistic heating, ventilation, and air-conditioning were reproduced. The passengers in bus cabins were reproduced using computer-simulated persons. Airflow, heat, and moisture transfer analysis were conducted based on computational fluid dynamics, to predict the microclimate around passengers and the interaction between the cabin climate and passengers. Finally, droplet dispersion analysis using the Eulerian–Lagrangian method and an investigation of the spatial distribution of infection/spread risks, assuming SARS-CoV-2 infection, were performed. Through parametric analyses of passive and individual countermeasures to reduce airborne infection risks, the effectiveness of countermeasures for airborne infection was discussed. Partition installation as a passive countermeasure had an impact on the human microclimate, which decreased infection risks. The individual countermeasure, mask-wearing, almost completely prevented airborne infection.

DOI： 10.3390/fluids8090253

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Scopus

Language：English   Publisher：Computer Methods and Programs in Biomedicine  

Background and Objective: Respiratory diseases caused by viruses are a major human health problem. To better control the infection and understand the pathogenesis of these diseases, this paper studied SARS-CoV-2, a novel coronavirus outbreak, as an example. Methods: Based on coupled computational fluid and particle dynamics (CFPD) and host-cell dynamics (HCD) analyses, we studied the viral dynamics in the mucus layer of the human nasal cavity-nasopharynx. To reproduce the effect of mucociliary movement on the diffusive and convective transport of viruses in the mucus layer, a 3D-shell model was constructed using CT data of the upper respiratory tract (URT) of volunteers. Considering the mucus environment, the HCD model was established by coupling the target cell-limited model with the convection-diffusion term. Parameter optimization of the HCD model is the key problem in the simulation. Therefore, this study focused on the parameter optimization of the viral dynamics model, divided the geometric model into multiple compartments, and used Monolix to perform the nonlinear mixed effects (NLME) of pharmacometrics to discuss the influence of factors such as the number of mucus layers, number of compartments, diffusion rate, and mucus flow velocity on the prediction results. Results: The findings showed that sufficient experimental data can be used to estimate the corresponding parameters of the HCD model. The optimized convection-diffusion case with a two-layer multi-compartment low-velocity model could accurately predict the viral dynamics. Conclusions: Its visualization process could explain the symptoms of the disease in the nose and contribute to the prevention and targeted treatment of respiratory diseases.

DOI： 10.1016/j.cmpb.2023.107622

Scopus

PubMed

Language：English   Publisher：Computer Methods and Programs in Biomedicine  

Background and objectives: Suspended respirable airborne particles are associated with human health risks and especially particles within the range of ultrafine (< 0.1 μm) or fine (< 2.5 μm) have a high possibility of penetrating the lung region, which is concerned to be closely related to the bronchial or alveoli tissue dosimetry. Nature complex structure of the respiratory system requires much effort to explore and comprehend the flow and the inhaled particle dynamics for precise health risk assessment. Therefore, this study applied the computational fluid-particle dynamics (CFPD) method to elucidate the deposition characteristics of ultrafine-to-coarse particles in the human respiratory tract from nostrils to the 16th generation of terminal bronchi. Methods: The realistic bronchi up to the 8th generation are precisely and perfectly generated from computed tomography (CT) images, and an artificial model compensates for the 9th-16th bronchioles. Herein, the steady airflow is simulated at constant breathing flow rates of 7.5, 15, and 30 L/min, reproducing human resting-intense activity. Then, trajectories of the particle size ranging from 0.002 – 10 μm are tracked using a discrete phase model. Results: Here, we report reliable results of airflow patterns and particle deposition efficiency in the human respiratory system validated against experimental data. The individual-related focal point of ultrafine and fine particles deposition rates was actualized at the 8th generation; whilst the hot-spot of the deposited coarse particles was found in the 6th generation. Lobar deposition characterizes the dominance of coarse particles deposited in the right lower lobe, whereas the left upper-lower and right lower lobes simultaneously occupy high deposition rates for ultrafine particles. Finally, the results indicate a higher deposition in the right lung compared to its counterpart. Conclusions: From the results, the developed realistic human respiratory system down to the terminal bronchiole in this study, in coupling with the CFPD method, delivers the accurate prediction of a wide range of particles in terms of particle dosimetry and visualization of site-specific in the consecutive respiratory system. In addition, the series of CFPD analyses and their results are to offer in-depth information on particle behavior in human bronchioles, which may benefit health risk assessment or drug delivery studies

DOI： 10.1016/j.cmpb.2023.107589

Web of Science

Scopus

PubMed

Publisher：E3S Web of Conferences  

We conducted isothermal large-eddy simulations to generate the velocity and concentration distributions to investigate the air pollution transport from outside to inside of a space surrounded by urban-like block arrays. Contrary to previous study, we assumed that the pollution in the form of scalars are generated outdoors and not indoors which we placed at: 1) middle of window, 2) near window wall, 3) middle of street canyon at ground level, and 4) middle of street canyon at window level. Results showed that regardless of scalar source location, the scalars accumulated inside the indoor space which can be explained by the downdraft effect that are typically found in urban environments. The downdraft effect produced vortices outside and inside the indoor space. For scalars near window, indoor vortex drove the concentration to indoors. On the other hand, outdoor vortex transported the scalars located at street canyon to reach the window where they were eventually transported to indoors also due to indoor vortex. The average normalized indoor concentrations found in this study are 1.25 -1.50, 1.00 -1.75, 0.25 -0.50, and 0.0 -0.25 for scalars C1, C2, C3, and C4, respectively. Our study suggests that for natural ventilation studies of urban environments where air pollution is significant, outdoor effects should also be carefully considered.

DOI： 10.1051/e3sconf/202339602004

Scopus

Publisher：E3S Web of Conferences  

Natural and cross ventilation is recognized as an important measure for introducing outdoor fresh air to indoor without the use of mechanical equipment. Plenty of fruitful studies for elucidating natural and cross ventilation mechanisms have been reported adopting experimental and computational methods. Field and wind tunnel experiments could provide substantial flow information on indoor-outdoor interaction in actual or reduced model conditions. However, these approaches were relatively costly and time-consuming and limited in terms of spatial and temporal resolutions. Computational fluid dynamics approaches are promising complementary technique to these methods. In this study, we performed isothermal CFD simulations for both airflow and concentration fields for cross-ventilation conditions sheltered by surrounding buildings with two different opening conditions. ANSYS/Fluent was utilized to perform CFD using RANS simulation. Heterogeneity of ventilation efficiencies determined by concentration distributions in cross-ventilated room model were quantitatively analyzed using ventilation efficiencies, e.g., age of air. The results showed that the location of the openings had a significant impact on the cross-ventilation rate, creating completely different concentration fields, and ventilation efficiencies indices could quantitatively demonstrate the formation mechanisms of scalar concentration distributions in an indoor space.

DOI： 10.1051/e3sconf/202339602015

Scopus

Publisher：E3S Web of Conferences  

The airflow balance test to confirm the physical performance of biological safety cabinets (BSC) is standardized by JIS K 3800 in accordance with NSF/ANSI 49 in Japan. In the test, Bacillus atrophaeus spores are used as an evaluation index, which poses a few limitations, such as their dependence on the environmental conditions to be tested. The aim of this study is to develop BSC digital twins and discuss reasonable alternatives for performance evaluation tests while maintaining the accuracy of the bacterial test performance. Herein, we provide the outline of a digital twin model for BSCs and the results of a numerical analysis, where a passive scalar is used as an alternative pollutant in the evaluation index.

DOI： 10.1051/e3sconf/202339602008

Scopus

Publisher：E3S Web of Conferences  

This study aims to develop a vertical air duct which is embedded inside the building envelop. It is also designed as a counter-flow heat recovery ventilator (HRV). The vertical air duct model in this study adopted baffle structure considering two methods to suppress the inflow of the particulate matters from outdoor: 1) trapping by wall surface and airflow structure and 2) gravitational sedimentation in the air duct. Design parametric analyses are conducted using computational fluid dynamics to determine optimal design of vertical air duct. Three types of analytical case with various set-up of baffles inside air passages are prepared, and heat exchange efficiency is estimated by heat transfer analysis inside ventilator. In addition, particulate pollutants' behaviour inside air passages is predicted based on Euler-Lagrange particle transport analysis. Through the series of numerical analysis, differences in heat exchange efficiency and effectiveness of particulate pollutant removal corresponding to different baffle design are quantitatively discussed, and finally optimal design for air passages in HRV is determined. The building-integrated HRV introduced in this study could contribute to sustainable design of building environment.

DOI： 10.1051/e3sconf/202339603006

Scopus

Publisher：E3S Web of Conferences  

In recent years, the plastics pollution of 5mm or less size (microplastics) in marine ecosystems has been a global issue. The presence of microplastics (microfibers) is also a major concern in indoor environments of the residetial house. Many sources of microplastics in the marine environment also exist in the indoor environment. In the modern age where we spend most of our time indoors, the indoor environment is related to the health of residents, so it is important to investigate the presence and contamination status of microplastics in the indoor environment. There is limited the number of studies on microplastics in the indoor environment. In our previous studies have confirmed the presence of microplastics in indoor environments Kanto area including Tokyo of Japanese residential houses. The purpose of this study is to investigate the concentration of indoor microplastics in four regions; Kanto area including Tokyo, Chubu area, Tohoku area, and Kansai area. We focused on the indoor microplastics in settled dust on the floor of residential houses, and the survey was conducted on the 16 residential houses. Micro-Fourier transform infrared (μ-FT-IR) spectrophotometry was used for the qualitative analysis of microplastics. The detected components in the settled dust were cellulose, polyamide (PA), polyacrylamide (PAM), polyacrylonitrile (PAN), polybutylene terephthalate (PBT), polyethylene (PEs), polyester (PE), polyethylene terephthalate (PET), polypropylene (PP), polyvinyl acetate (PVAL).

DOI： 10.1051/e3sconf/202339601120

Scopus

Publisher：E3S Web of Conferences  

The behavior of airborne particles in the human respiratory system is closely related to local tissue dosimetry and its associated health risks. The inhalation of these particles is known to be the origin of lung diseases, such as lung cancer, chronic obstructive pulmonary disease, and cardiovascular disease. To compensate for the difficulty of experiments involving volunteers, in silico studies using numerical models have been adopted as promising alternatives. Therefore, this study applied the computational fluid and particle dynamics technique to investigate the deposition of ultrafine particles in the human respiratory tract from the nostrils to the ninth generation of bronchi. A computational model was created using computed tomography images. The airflow patterns were simulated under steady and incompressible conditions at breathing flow rates of 7.5 and 15 L/min, respectively. The discrete phase was simulated for ultrafine particles with aerodynamic diameters of 2-100 nm. Consequently, the validation work confirmed the simulation accuracy for particle sizes > 25 nm. In the lower respiratory system, the total deposition fraction decreased as the particle size increased. In addition, the eighth generation is a focal point of the deposited particles, elucidated by the local deposition fraction. The results of this study will benefit further studies involving health risk assessments and drug delivery.

DOI： 10.1051/e3sconf/202339601017

Scopus

Publisher：E3S Web of Conferences  

To analyse the interaction between the indoor environment and the human body, various computer-simulated persons (CSP) which can treat specific characteristics of the human body have been suggested as a "digital twin"for experimental thermal manikin. However, previous studies simplified or ignored the reproduction of the clothing function. In this study, a digital twin based on ANDI thermal manikin integrated with a multi-node thermoregulation model was developed in a naked and clothed state. In addition, to validate the prediction accuracy of numerical thermoregulatory analysis coupled with CSPCFD simulation, the analysis results were compared with the experimental results using thermal manikin. The computational model was generated based on 3D scan data of ANDI manikin and clothe. Moreover, the user subroutine program for coupled simulation of CSP and Fiala thermoregulation model was developed and applied into CSP to estimate the heat generation by metabolism, heat transfer between layers and parts, and skin surface temperature. CFD analysis was performed using CSP under identical environmental condition with the experiment, by setting CFD boundary conditions based on the data measured in the experiment. Through a series of numerical analyses, we confirmed that the analysis result of CSP corresponds well with experimental results using thermal manikin.

DOI： 10.1051/e3sconf/202339601019

Scopus

Publisher：E3S Web of Conferences  

Respiratory diseases, such as COVID-19 (coronavirus disease 2019) caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), have posed a threat to human health. For infection control and a better understanding of the pathogenesis, this study mainly focused on elucidating the virus dynamics in the mucus layer of the human nasal cavity-nasopharynx, using coupled computational fluid-particle dynamics (CFPD) and host-cell dynamics (HCD) analyses. To reproduce virus transportation in the mucus layer by mucociliary motion, a three-dimensional-shell model was created using the data obtained from computed tomography (CT) of the human upper airway. By considering the mucus milieu, the target-cell-limited model was coupled with the convection-diffusion term to develop the HCD model. Parameter optimization has been shown to have a great impact on the accuracy of model prediction; therefore, this study proposes a method that divides the geometric model into multiple regions and uses Monolix for nonlinear mixed effects modeling for pharmacometrics. The results showed that data from human inoculation challenge trials could be used to estimate the corresponding parameters. The models developed and used with optimized parameters can provide relatively accurate predictions of virus dynamics, which could contribute to the prevention and treatment of respiratory diseases.

DOI： 10.1051/e3sconf/202339601008

Scopus

Language：English   Publisher：Computer Methods and Programs in Biomedicine  

Background and objective: From various perspectives (e.g. inhalation exposure and drug delivery), it is important to provide insights into the behavior of inhaled particles in the human respiratory system. Although most of the experimental and numerical studies have relied on an assumption of steady inhalation, the transient breathing profile is a key factor in particle deposition in the respiratory tract. In this study, particle transportation and deposition were predicted in a realistic human airway model during a breathing cycle and the effects of steady-state and transient flows on the deposition fraction were observed using computational fluid dynamics. Methods: Two transient breathing cycles with different respiratory durations were considered to evaluate the effects of respiration duration on particle transport and deposition characteristics. Two types of steady breathing conditions with corresponding steady-state respiratory volumes were reproduced. The Lagrangian discrete phase model approach was used to investigate particle transportation and deposition under transient breathing conditions. Additionally, the Eulerian approach was used to analyze the transport of nanoparticles in the gas phase. A total of >50,000 monodispersed particles with aerodynamic diameters ranging between 2 nm and 10 μm were selected for comprehensive deposition predictions for particle sizes ranging from the nano- to microscale. Results: The predicted results were compared with the experimental data. The particle deposition fraction in the nasal cavity and tracheal regions showed differences between the steady and transient simulations. In addition, particle analysis under steady inhalation conditions cannot accurately predict particle transportation and deposition in the lower airway. Furthermore, the breathing cycle had a significant effect on the deposition fraction of the particles and the behavior of the inhaled particles. Conclusions: Transient simulation mimicking the breathing cycle was observed to be an important factor in accurately predicting the transportation and deposition of particles in the respiratory tract.

DOI： 10.1016/j.cmpb.2023.107501

Web of Science

Scopus

PubMed

Language：Japanese   Publisher：Architectural Institute of Japan  

<p>Recently, health risk assessment of chemical substances has become a legal requirement, and accordingly, estimation of indoor gas concentrations and their impact on workers has taken on increasing importance. Therefore, we have developed a numerical model based on CFD (Computational Fluid Dynamics) methods to predict transient and non-uniform concentration distributions for chemical substances in enclosed spaces. This paper (Part 2) reports on the heterogeneous concentration distributions of ethanol and aqueous ammonia solutions formed in a full-scale environment, the microclimate around the human body, and the risk assessment of trans-airway exposure.</p>

DOI： 10.3130/aije.88.307

Scopus

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publisher：PLoS Computational Biology  

As evidenced by the worldwide pandemic, respiratory infectious diseases and their airborne transmission must be studied to safeguard public health. This study focuses on the emission and transport of speech-generated droplets, which can pose risk of infection depending on the loudness of the speech, its duration and the initial angle of exhalation. We have numerically investigated the transport of these droplets into the human respiratory tract by way of a natural breathing cycle in order to predict the infection probability of three strains of SARSCoV-2 on a person who is listening at a one-meter distance. Numerical methods were used to set the boundary conditions of the speaking and breathing models and large eddy simulation (LES) was used for the unsteady simulation of approximately 10 breathing cycles. Four different mouth angles when speaking were contrasted to evaluate real conditions of human communication and the possibility of infection. Breathed virions were counted using two different approaches: the breathing zone of influence and direction deposition on the tissue. Our results show that infection probability drastically changes based on the mouth angle and the breathing zone of influence overpredicts the inhalation risk in all cases. We conclude that to portray real conditions, the probability of infection should be based on direct tissue deposition results to avoid overprediction and that several mouth angles must be considered in future analyses.

DOI： 10.1371/journal.pcbi.1010972

Web of Science

Scopus

PubMed

Publisher：Building Simulation  

A significant feature of the indoor environment is the heterogeneity of airflow and pollutant distributions, which are primarily dependent on ventilation systems. In the case of short- and high-concentration exposures to hazardous chemical pollutants, it may be necessary to precisely determine the concentration in the breathing zone or, more directly, the inhalation exposure concentration in the respiratory tract, rather than the representative room average concentration in an indoor environment, because of the non-uniformity of pollutant concentration distributions. In this study, we developed a computer-simulated person with a detailed respiratory system to predict inhalation exposure concentration and inhalation dose via transient breathing and reported a demonstrative numerical simulation for analyzing acetone concentration distributions in a simplified model room. Our numerical analysis revealed that the ventilation efficiency distribution in a room could change significantly by changing the design of the ventilation system, and that the inhalation exposure concentration estimated by a computer-simulated person could differ from the representative concentration, such as perfect-mixing or volume-averaged acetone concentration, by a factor of two or more.

DOI： 10.1007/s12273-022-0954-4

Web of Science

Scopus

Language：English   Publisher：Computer Methods and Programs in Biomedicine  

Background and objective: Brachycephalic obstructive airway syndrome (BOAS) susceptible dogs (e.g., French bulldog), suffer health complications related to deficient breathing primarily due to anatomical airway geometry. Surgical interventions are known to provide acceptable functional and cosmetic results; however, the long-term post-surgery outcome is not well known. In silico analysis provides an objective measure to quantify the respiratory function in postoperative dogs which is critical for successful long-term outcomes. A virtual surgery to open the airway can explore the ability for improved breathing in an obstructed airway of a patient dog, thus supporting surgeons in pre-surgery planning using computational fluid dynamics. Methods: In this study five surgical interventions were generated with a gradual increment of decongested levels in a bulldog based on computed tomography images. The effects of the decongested airways on the breathing function of a patient bulldog, i.e., airflow characteristics, pressure drop, wall shear stress, and air-conditioning capacity, were quantified by benchmarking against a clinically healthy bulldog using computational fluid dynamics (CFD) method. Results: Our findings demonstrated a promising decrease in excessive airstream velocity, pressure drop, and wall shear stress in virtual surgical scenarios, while constantly preserving adequate air-conditioning efficiency. A linear fit curve was proposed to correlate the reduction in the pressure drop and decongested level. Conclusions: The in silico analysis is a viable tool providing visual and quantitative insight into new unexplored surgical techniques.

DOI： 10.1016/j.cmpb.2022.107243

Web of Science

Scopus

PubMed

Publisher：Healthy Buildings 2023: Asia and Pacific Rim  

In this study, we investigated the aspiration efficiency of microparticles in both steady and transient breathing in a ventilated room with a displacement ventilation system. The flow patterns in the vicinity of the CSP and the effects of the thermal plume on the particle aspiration by the CSP were simulated using the computational fluid dynamics (CFD) technique. In order to set the appropriate particle injection position, the high inhaled particle position corresponding to the breathing zone was investigated using the reverse particle tracking method. In addition, the overall and regional deposition efficiencies of inhaled microparticles on the respiratory wall surfaces were evaluated. As a result, the thermal plume around the CSP and the assumption of breathing conditions (steady vs transient) significantly affect the aspiration efficiency of microparticles, the high inhaled particle position, and the overall and regional deposition efficiencies of particles in the respiratory surface depending on the particle size.

Scopus

Publisher：Healthy Buildings 2023: Asia and Pacific Rim  

Acetone is an organic chemical solvent with widespread industrial applications. Inhaling a lot of acetone in a short time or long-term exposure to acetone may have severe effects and permanent damage to human health. This study combined CFD and the physiologically based pharmacokinetic (PBPK) models, coupled with a computer-simulated person (CSP) embedded in the respiratory model, and conducted precise prediction of the transport pathway of acetone-containing air from indoor emission sources to the respiratory tract via inhalation and dermal absorption. A series of numerical methods for analyzing the acetone concentration in the nasal passages and acetone dermal adsorption to the local tissue cells were presented, coupled with the analysis of the acetone concentration distributions in a simple room model as functions of typical ventilation modes. It is believed that the numerical method proposed in this study would provide a feasible prediction method and risk assessment for acetone applications.

Scopus

Publisher：Environmental Science and Engineering  

Fibrous-particle (asbestos) exposure induces lung cancer, mesothelioma, and fibrosis. Man-made vitreous fibers (MMVFs) share some similarities, and so their related health effects need to be determined. Computational fluid dynamics (CFD) was used to simulate the airflow patterns (Eulerian method) and to predict the particle behaviors (Lagrangian method) in human upper airways. Results of the simulation showed high agreement with the experimental data. A higher deposition of spherical particles was observed at a specific aerodynamic diameter. The nasal vestibule and turbinate had the highest regional deposition fractions for both spherical and fibrous particles. Fibrous particles present a greater exposure health risk than spherical particles under similar breathing conditions and aerodynamic sizes.

DOI： 10.1007/978-981-19-9822-5_195

Scopus

Publisher：Healthy Buildings 2023: Asia and Pacific Rim  

Although the current ventilation design is defined only by the time-averaged flow rate, turbulence intensity of airflow at the supply inlet may be one of the major factors forming the concentration distribution of contaminants. In this study, we investigated the effects of turbulent intensity at the supply inlet on the indoor flow field and contaminant concentration distribution for three different contaminant generation methods. As a result, the turbulence intensity at the supply inlet affected the separation point of the airflow from the inlet. In both uniform and regional spatial generation, the peak contaminant concentrations and the effect of the turbulent intensity on the emission rate from the wall surfaces were dependent on the turbulent intensity at the inlet. In conclusion, we should consider not only the time-averaged ventilation rate but also the turbulent inlet boundary condition for indoor contamination control.

Scopus

Publisher：Environmental Science and Engineering  

The purpose of this study was to analyze the transport dynamics of inhaled gaseous odorants in the respiratory tract and investigate the characteristics of the adsorption flux on the olfactory epithelium tissue. Following the procedure of the perceptive air quality test described in ISO 16000–28, we analyzed the adsorption flux on the olfactory epithelium tissue under transient breathing conditions using a coupled computational fluid dynamics and physiologically based pharmacokinetic (CFD-PBPK) model. In the calculations, a comprehensive model that integrates human body geometry with realistic airway geometry was used. Through the analysis, we obtained the following results: (1) The inhaled odorant concentration varied with the unsteady breathing cycle. (2) The adsorption flux on the olfactory epithelium tissue was low compared to that in the other nasal regions. (3) The difference in the adsorption fraction in the olfactory epithelium region was confirmed between the orthonasal and retronasal pathways. Thus, the two different pathways might have a significant impact on the efficiency of odorant transportation to the olfactory epithelial region.

DOI： 10.1007/978-981-19-9822-5_186

Scopus

Publisher：Healthy Buildings 2023: Asia and Pacific Rim  

To better understand the infection dynamics of respiratory viruses, this study conducted a comparative analysis of the factors affecting the SARS-CoV-2 infection dynamics through the mucociliary movement of the human nasal cavity-nasopharynx based on coupled computational fluid and particle dynamics (CFPD) and host-cell dynamics (HCD) analysis. The viral infection dynamics were predicted by combining a 3D shell model with the mucus layer, droplet deposition distribution, droplet virus content, and developed HCD model. The findings showed that the diffusive rate, mucus flow velocity, and layer mode have a significant influence, which may contribute to the accurate prediction of viral dynamics and disease prevention.

Scopus

Publisher：Healthy Buildings 2023: Asia and Pacific Rim  

This study investigated the characteristics of drug particle deposition in the human lower respiratory tract based on spontaneous respiration with the application of endotracheal tube (ETT). This study was carried out using Computational Fluid and Particle Dynamics (CFPD). The results showed that particle size and flow rate affected the deposition fraction (DF) in the human lung to different degrees. The drug particle distribution characteristics over different particle sizes based on the application of the newly designed ventilator were numerically identified, which can serve as a reference for clinical treatments.

Scopus

Publisher：Healthy Buildings 2023: Asia and Pacific Rim  

We performed large-eddy simulation (LES) of airflow within an urban building to estimate net escape velocity (NEV) distribution - a velocity scale that describes contaminant transport integrating both convection and diffusion effects, which we superimposed on contaminant concentration distribution. Results showed that at different flow times, contaminant accumulations may appear in local domains of indoor space that were higher than the mean contaminant concentration. These instantaneous accumulations, though happen in short periods, should be infomative in optimized indoor environmental design to avoid cross-contamination.

Scopus

Publisher：Environmental Science and Engineering  

The purpose of this study is to reproduce CO2 emission from a human in the chamber experiment and investigate a relationship between CO2 emission rate and indoor air environment. A “digital-twin” model of the experiments for estimation of CO2 emission rate was developed by CSP integrated with CFD technique. As a result, the inhaled CO2 level depended on the flow patterns around the occupants. Additionally, the reasonable reduction of tidal volume by low IAQ could explain the reduction of CO2 emission rate in the chamber experiment.

DOI： 10.1007/978-981-19-9822-5_210

Scopus

Publisher：Healthy Buildings 2023: Asia and Pacific Rim  

This study aimed to compare the flow physics obtained using large eddy simulation (LES) and Reynolds averaged Navier-Stokes (RANS) simulations in a realistic human respiratory system using a computational fluid dynamics (CFD) method. The results demonstrate the homogeneous fidelity of the flow patterns using LES and RANS, while discrepancies in magnitude and secondary flow can be observed. LES can precisely capture detailed flow profiles, which is consistent with the experimental data. Although RANS is widely applied in the industrial sector, the use of LES can benefit detailed studies concerning respiratory physiology.

Scopus

Publisher：Environmental Science and Engineering  

This study focused on the impact of the reproduction of oral cavity shape on the droplets dispersion dynamics, and compared the coughing dynamics between human models with and without oral cavity by using computational fluid dyanmics (CFD) technique. In this analysis, droplets were released from mouth opening surface or from the trachea via oral cavity. The results showed these models made differences of exhaled airflow pattern, the droplets dispersion and the rate of inhalation and deposition depending on the oral cavity shape. In conclusion, the droplets dispersion dynamics with consideration of oral cavity shape might contribute to accurately predict the dispersion characteristics of droplets and infection risk caused by coughing.

DOI： 10.1007/978-981-19-9822-5_169

Scopus

Publisher：Healthy Buildings 2023: Asia and Pacific Rim  

The physical performance of biological safety cabinets (BSCs) is confirmed and standardized by an airflow balance test (JIS K 3800) in accordance with the standard NSF/ANSI 49 in Japan. In JIS K 3800, the use of Bacillus atrophaeus spores as an evaluation index poses a few limitations, such as their dependence on the test environmental conditions and the skill level of the bacteriological test examiner. This study aimed to discuss reasonable alternatives to this bacterial test to improve or at least maintain its accuracy. Thus, we provided the outline of a digital twin model for BSCs and results of a numerical analysis where a particle was used as an alternative pollutant in the evaluation index.

Scopus

Publisher：Environmental Science and Engineering  

Inhalation exposure to various types of airborne particles is an important risk factor for human health. This study predicted particle transport and deposition in a realistic human airway model during breathing and observed the effects of steady-state flow and transient flow on the deposition fraction using computational fluid dynamics (CFD). To evaluate the effect of the transient breathing profile on particle transport and deposition in the respiratory tract, we reproduced two unsteady breathing cycles with different breathing time scales. The particle dispersion analysis targeted approximately 50,000 or 75,000 particles, with aerodynamic diameters ranging from 2 nm to 10 µm, randomly placed near the nostril. Under transient breathing conditions, a total of approximately 50,000 or 75,000 particles were continuously released at each time step during the inhalation period. As a result, a significant difference in particle deposition and transport to the lower airway region was confirmed for different breathing patterns.

DOI： 10.1007/978-981-19-9822-5_173

Scopus

Publisher：Environmental Science and Engineering  

The purpose of this study was to accurately predict the dynamics of SARS-CoV-2 infection–based on a 3D shell model and combining computational fluid and particle dynamics (CFPD) and host-cell dynamics–along the mucus layer of the upper airway. Assuming that a healthy person inhaled droplets coughed up by an infected individual via nasal inhalation, we focused on the infection dynamics of the virus deposited in the nasal cavity and nasopharynx. The distribution of the cough droplets deposited was preliminarily analyzed using CFPD. Using this distribution as an initial condition, we predicted the time series distribution for SARS-CoV-2 concentration in the mucus milieu depending on diffusion, mucociliary motion, and virus production. These results form an initial elucidation of an aspect of the virus’ transmission mechanism in the upper airway.

DOI： 10.1007/978-981-19-9822-5_170

Scopus

Language：Japanese   Publisher：(一社)室内環境学会  

環境中にゴミとして流出した一部のプラスチック類は,海洋中で力学的・光化学的作用により崩壊・微細化し,ミリメートル(mm)からマイクロメートル(μm)スケール以下の粒子となり海洋中に蓄積することが明らかとなっており,所謂,海洋マイクロプラスチック問題として社会的関心事となっている。一方,室内には多くのマイクロプラスチックの発生源となるプラスチック類製品が多様に存在し,室内環境中でのマイクロプラスチック汚染の可能性や健康影響への懸念が完全には否定できないにも関わらず,現時点では十分な議論が行われておらず,全国規模の実態調査の実績も無い。本報を含む一連の研究は,室内環境中(空気中もしくはダスト中)に存在するマイクロプラスチックの調査法(サンプリング法),ならびに定性・定量分析法を確立した上で,全国規模の調査を行うことで室内マイクロプラスチック汚染問題の実態把握を行うことを最終目標とする。特に本報はその第一歩として,既存のハウスダストサンプリング法と海洋マイクロプラスチック成分の分析法を組み合わせることで,室内環境を対象としたマイクロプラスチック調査への適用可能性に関して基礎的な検討を行った結果を報告する。(著者抄録)

Publisher：Building and Environment  

Although ventilation effectiveness varies in different sections of indoor spaces owing to imperfect mixing condition, previous studies on cross-ventilation in a model sheltered by urban-like arrays were limited to the computation of boundary-based volume flow rates and air exchange rate. To evaluate the local ventilation efficiency in the cross-ventilation model, we conducted large-eddy simulations (LESs) to generate the velocity and concentration fields of an indoor space surrounded by blocks arranged in a staggered manner to compute local ventilation using the age of air, purging flow rate, and net escape velocity (NEV*). We solved the distributions of seven scalars with corresponding sources positioned at the inlet of the indoor space (flow fluctuation is intermittent), indoor corners (flow stagnation is present), and downwind location, for two window-opening cases: parallel and perpendicular to the flow direction. The results indicated that the location of scalar sources significantly affects the ventilation of the scalar, resulting in different concentration fields, even when the sources are near each other. Additionally, we pioneered the use of NEV* for an unsteady simulation using LES and the decomposition of NEV* into two components: advection (NEVA) and turbulent diffusion (NEVT). The NEVA field appeared to be the velocity field, whereas the NEVT field appeared to be the induced or equivalent velocity field owing to turbulent diffusion. NEVT significantly affected local ventilation and even surpassed the effect of advection in regions with low mean velocities. This study reinforced the use of ventilation indices over boundary-based ventilation rates when analyzing the sheltering effect.

DOI： 10.1016/j.buildenv.2022.109759

Web of Science

Scopus

Publisher：Indoor and Built Environment  

The establishment of a healthy indoor environment requires the accurate evaluation of an individual’s exposure to pollutants. The concentration of indoor chemical pollutants is a representative indicator for such evaluation and is generally measured on-site. Moreover, material flow analysis (MFA), using macroscopic statistical data, is a reasonable method for objectively evaluating pollution on a wide scale; however, no effective strategy exists for the prediction of indoor air pollution, nor for the assessment of an individual’s exposure from social stock data. Accordingly, we developed a novel integration method comprising MFA and computational fluid dynamics (CFD) with a computer-simulated person (CSP) to establish a framework for evaluating indoor pollutant concentration and individual exposure of residents. We focused on diethyl-hexyl phthalate (DEHP) and first estimated the amount of DEHP-containing product accumulation in Japan by MFA. Second, we conducted a thorough survey and measurement of DEHP emission rates. Using these results as boundary conditions for indoor CFD with CSP, the individual exposure of a resident, in a standard residential house, was quantitatively evaluated. The total daily exposure per unit of body weight was estimated to be more than 100 (μg/kg/d) in the worst-case scenario which was considered the upper limit for exposure in this analysis.

DOI： 10.1177/1420326X221092613

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Scopus

Language：English   Publisher：Interdisciplinary Graduate School of Engineering Sciences, Kyushu University  

Understanding the deposition of inhaled toxic particles is critical in evaluating numerous health risks, especially in the lower airway. Recently, the computational fluid dynamics (CFD) method has been introduced as a promising method to facilitate the accurate prediction of airflow and particle behavior in complex geometry. Therefore, this study applied the CFD method to investigate the deposition characteristic of fine particles in the human respiratory tract from the nostrils to the 7th generation. The airflow pattern was simulated using the Eulerian method at breathing flow rates of 7.5 and 30 L/min, and was followed by particle (aerodynamic diameter 1 to 10μm) deposition simulation using the Lagrangian method. In general, the results were comparable with experimental data. The high deposited concentration of particles was found at the 5-7th generation, and a specific deposition hot-spot was observed at the carina ridge.

DOI： 10.5109/5909118

Scopus

CiNii Research

Publisher：Journal of Building Engineering  

There have been serious hazardous liquid chemical leakage cases in factories, chemical plants, and laboratories owing to natural disasters or contingent human accidents. Regarding risk management, when high-risk liquid chemical substances are assumed to leak inside enclosed indoor spaces, reasonable prediction of transient and heterogeneous concentration distributions formed around the human body is necessary to develop an appropriate evacuation plan. In particular, understanding the air-phase concentration level in the breathing zone and its duration for inhalation exposure is essential for short-term and high-concentration exposure health risk assessment. Transient and non-uniform concentration distributions can be predicted using computational fluid dynamics (CFD) and in silico human body analysis. However, the development of practical chemical emission models considering internal diffusion and direct evaporative diffusion from floor materials and their seamless boundary conditions must be addressed for practical application. In this study, liquid toluene was assumed to be a representative hazardous chemical substance for risk assessment, and fundamental experiments and corresponding numerical analyses of liquid toluene leaks on mortar materials were conducted. The experimental results suggest that the effective diffusion coefficient of the mortar sample has a significant effect on the sorption timescales of liquid toluene into the materials and significantly changes the air-phase toluene concentrations. The three-dimensional CFD analysis incorporating the practical toluene emission models reproduces the external and internal emission characteristics of leaked toluene on the mortar material and reasonably agrees with the experimental data.

DOI： 10.1016/j.jobe.2022.104976

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Scopus

Publisher：Japan Architectural Review  

Computer-simulated persons (CSPs) with respiratory systems have been developed for microclimate analysis around the human body and inhalation exposure analysis, for detailed assessment of comfort and health risks in indoor spaces. This study examined and validated the prediction accuracy of a CSP, for precise estimation of indoor environmental quality (IEQ). The flow-field prediction accuracy was thoroughly examined in a grid analysis using the CSP and a thermal manikin for benchmarking. The model incorporated unsteady breathing and human postural sway, and assessed their impact on the microclimate around the human body. The numerically estimated flow field was validated using experimental particle image velocimetry (PIV) data, with a detailed grid independence test. Considering the practical use of the respiratory tract model for the inhalation exposure risk assessment, the prediction accuracy of particle transport and deposition analysis was examined using previously published in vivo experimental results. This analysis revealed that the impact of transient breathing and body vibrations on the reproduction of the thermal plume around the human body is quite weak; consequently, these conditions can be ignored from the macroscopic perspective of indoor airflow analysis.

DOI： 10.1002/2475-8876.12301

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Scopus

Publisher：Building and Environment  

The evaluation of inhalation exposure of workers in industrial production environments is significant. Current studies on inhalation exposure in industrial workshops are quite limited and lack experimental data validation. This study established a scaled experimental cabin and performed inhalation exposure experiments. Subsequently, the validated numerical model was used to study the influences of different factors on human inhalation exposure prediction. The factors emphasize the meshing strategy, the manikin geometry and the thermal plume of the manikin. The results show that the polyhedron grid offers a greater advantage and that the required grids and computing time represent only 20% and 33% of the tetrahedral grid. CFD results are more consistent with human inhalation exposure experimental results when a 5% mean computational error is used as a criterion to verify grid independence. The inhalation exposure computational results of different manikin models differed by only about 2%. And compared with the 3D scanned model, the humanlike multi-box and single cuboid models are easier to build and consume fewer resources. Therefore, using humanlike multi-box and single cuboid models to compute human inhalation exposure in the industrial workshop is more recommended. The Ri number evaluates the intensity of the human thermal plume. The computational errors between the isothermal and thermal manikin models are 1.76%, 5.14%, 9.18%, and 14.95% for inhalation exposures with 20, 15, 10 and 5 ACH (air changes per hour), respectively, and the corresponding Ri numbers are 0.09, 0.16, 0.34, and 1.41.The computational error between the isothermal and thermal manikin models is less than 10% when the ACH is larger than 10. This study can provide a reference for the prediction of inhalation exposure of workers in industrial workshops.

DOI： 10.1016/j.buildenv.2022.109573

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Scopus

Publisher：Japan Architectural Review  

DOI： 10.1002/2475-8876.12291

Web of Science

Scopus

Publisher：Japan Architectural Review  

A fume hood is a local ventilation system that is typically installed in a laboratory space to ensure the safety of workers from chemical exposure. A fume hood is designed to capture hazardous gas-phase pollutants generated inside a box-like enclosure, and the pollutant capture efficiency is regulated by the average opening surface air velocity. However, few cases exist in which the pollutant capture efficiency inside the fume hood is precisely analyzed and quantitatively visualized. In this study, the capture performance of a fume hood under actual use conditions was evaluated using computational fluid dynamics (CFD). The factors that could affect the performance, that is, the exhaust airflow rate, experimental instruments inside, worker in front, and heat source within the fume hood, were parametrically considered. The numerical analyses revealed that experimental instruments near the opening surface significantly affected the airflow into the fume hood and decreased its capture performance. Under the inadequate condition of a low exhaust airflow rate, pollutant leakage inside the chamber was observed due to the presence of a worker in front of the fume hood and the heat source inside. Furthermore, the pollutant capture performance was slightly improved by changing the layout/position of the experimental instrument.

DOI： 10.1002/2475-8876.12300

Web of Science

Scopus

Publisher：Japan Architectural Review  

In the existing ventilation design, the ventilation rate is defined by the time-averaged flow rate, and the fluctuating (turbulence) component is not typically considered. However, inlet turbulent conditions are also assumed to have some influence on the formation of contaminant distributions. Therefore, the influence of turbulent kinetic energy at the inlet boundary on scalar transportation in an indoor environment needs to be elucidated when discussing the ventilation rate setpoint via the supply inlet in terms of local contaminant concentration control. This study discusses the impact of turbulent kinetic energy in the ventilation design on scalar transfer and its distribution within an enclosed space. To understand the influence of various inlet turbulent boundary conditions on scalar transfer, a computational fluid dynamics analysis was conducted using two different room models: a simple room and a room with a ventilation system that creates a large velocity gradient. The results indicate that scalar transfer within the room is not solely dominated by the averaged velocity input at the inlet boundary but is also strongly affected by the turbulence conditions at the inlet boundary. The numerical results indicate the possibility of a new ventilation design strategy that simultaneously considers the transfer of turbulent components and contaminants.

DOI： 10.1002/2475-8876.12299

Web of Science

Scopus

Publisher：Japan Architectural Review  

Assuming the leakage of hazardous liquid chemicals in factories and chemical plants caused by natural disasters or human error, it is important to precisely estimate exposure risk and design appropriate evacuation plans and risk-reduction measures. The exposure risk of indoor residents to leaked chemicals may be estimated using direct measurements or theoretical/numerical estimations of gas-phase concentrations. Although mathematical models of gas-phase concentration in the workplace are essential for predicting exposure concentrations at the design stage, practical models have not yet been fully established. We previously proposed practical numerical models to assess indoor gas-phase concentration distributions after the accidental leakage of liquid chemicals using liquid toluene as a representative hazardous chemical. In this study, the leakage of liquid ethyl acetate, a commonly used organic solvent, into mortar flooring was reproduced in a small test chamber, and numerical analysis was performed. The results showed that the time history of the chamber exhaust concentration had a sharp peak and differed significantly from that of toluene. Three-dimensional computational fluid dynamics (CFD) analysis incorporating practical ethyl acetate emission models reproduced the external and internal emission characteristics of leaked ethyl acetate on the mortar material. The models showed reasonable agreement with the experimental data.

DOI： 10.1002/2475-8876.12297

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Scopus

Publisher：Japan Architectural Review  

Although microplastic (size ≤5 mm) pollution in marine ecosystems has received global attention, the presence of microplastics and microfibers in indoor environments is also a major concern. Compared to the available field survey data on microplastics in the ocean, such information remains limited for indoor environments. Microplastics in indoor environments may act as adsorbents for chemical compounds, which may result in multiple adverse health effects on residents. Establishment of reproducible sampling and analysis methods aiding comprehensive field measurements of indoor microplastics in Japan is required. This study conducted the first field survey of indoor microplastics in settled dust in 10 residential houses in the Kanto area of Japan and explored their composition and morphology. Micro-Fourier transform infrared (μ-FT-IR) spectrophotometry and laser direct infrared (LDIR) analysis were used for the qualitative analysis of microplastics. The μ-FT-IR and LDIR analyses revealed the presence of large quantities of microplastics in the settled dust. The samples were composed of cellulose, polyethylene terephthalate, polyethylene, alkyd resins, polysulfone, polyvinyl alcohol, and polyamides. The μ-FT-IR and LDIR analyses were suitable for identifying large fibrous materials and small particles, respectively. Thus, the two methods are complementary for the comprehensive identification of microplastic composition in settled dust.

DOI： 10.1002/2475-8876.12298

Web of Science

Scopus

Publisher：Japan Architectural Review  

Particles longer than 5 μm and with a length/diameter ratio >3 are defined as fibers. Asbestos or other fibers are still identified in residential environments due to the emission from asbestos-used building materials. The respiratory system is the primary route of asbestos exposure; under a longer residence time, asbestos-related adverse health effects are inevitable. Currently, asbestos fibers have been replaced with man-made vitreous fibers (MMVFs); however, studies have revealed some similar biological effects of MMVFs with asbestos. Therefore, MMVFs-induced diseases need to be determined by analyzing their deposition characteristics and foci in human respiratory tracts. In this study, we used computational fluid dynamics method to investigate fibers' airflow and deposition patterns in two realistic human respiratory models. Two drag models were used to predict the deposition of uniform 1 μm (asbestos) and 3.66 μm (carbon fiber-CF) diameter, 15–300 μm long fibers. Two drag models provided comparable results with the experimental data. Comparatively, asbestos deposition was independent of fiber length, while CF deposition increased proportionally to fiber length. The highest level of local deposition was detected in the anterior nasal cavity. The results obtained from this study can extend current knowledge of human vitreous fiber exposure-related lung diseases.

DOI： 10.1002/2475-8876.12277

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Scopus

Language：English   Publishing type：Research paper (scientific journal)  

Publisher：E3S Web of Conferences  

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to the worldwide spread of coronavirus disease-2019 (COVID-19) since its emergence in 2019. Virus replication and infection dynamics after its deposition on the respiratory tissues require detailed studies for infection control. This study focused primarily on SARS-CoV-2 dynamics in the mucus layer of the nasal cavity and nasopharynx, based on coupled computational fluid-particle dynamics (CFPD) and host-cell dynamics (HCD) analyses. Considering the mucus milieu, we coupled the target-cell limited model with the convection-diffusion term to develop an improved HCD model. The infection dynamics in the mucus layer were predicted by a combination of the mucus flow field, droplet deposition distribution, and HCD. The effect of infection rate, β, was investigated as the main parameter of HCD. The results showed that the time series of SARS-CoV-2 concentration distribution in the mucus layer strongly depended on diffusion, convection, and virus production. β affected the viral load peak, its arrival time, and duration. Although the SARS-CoV-2 dynamics in the mucus layer obtained in this study have not been verified by appropriate clinical data, it can serve as a preliminary study on the virus transmission mode in the upper respiratory tract.

DOI： 10.1051/e3sconf/202235605021

Scopus

Publisher：E3S Web of Conferences  

In recent years, an integrated analysis of computational fluid dynamics (CFD) and computer simulation person (CSP), especially to reproduce the shape of the human body, has been conducted to estimate the interaction between the human body and its surrounding indoor environment. Meanwhile, clothing is often treated in a simplified manner, as a means of resistance to heat and pollutant transfer, and there is sufficient room for improvement in the hygrothermal and scalar transfer phenomena in and around clothing with a complex geometry. In this study, some garment models with complex geometry and others with simplified geometry were created with a CSP, and airflow, temperature, and humidity were investigated along with the CSP. It was assumed that only heat and water vapor were transported in the garment. As a result, the naked model was found to be over-or underestimated with respect to all airflow, temperature, and water vapor. It was also found that models with a simple garment shape produced the same results as models with a complex geometry on a macroscopic scale. Models with different regions and smaller air gaps between the clothes and the human body should be confirmed.

DOI： 10.1051/e3sconf/202235603004

Scopus

Language：Japanese   Publisher：Architectural Institute of Japan  

<p>In this study, following the procedure of the perceptive air quality test described in ISO 16000-28 and ISO 16000-30, we numerically analyzed the odorant transportation from the odorant generator to human breathing zone using acetone which is considered as a standard substance for pi-scale evaluation. For the evaluation of access to olfactory receptors under a transient breathing cycle, the acetone adsorption flux to the olfactory epithelial cells was calculated by using computer simulated person (CSP) with numerical respiratory tract model and physiologically based pharmacokinetic (PBPK) model.</p>

DOI： 10.3130/aije.87.541

Scopus

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publisher：Indoor Air  

Accurate prediction of inhaled CO2 concentration and alveolar gas exchange efficiency would improve the prediction of CO2 concentrations around the human body, which is essential for advanced ventilation design in buildings. We therefore, developed a computer-simulated person (CSP) that included a computational fluid dynamics approach. The CSP simulates metabolic heat production at the skin surface and carbon dioxide (CO2) gas exchange at the alveoli during the transient breathing cycle. This makes it possible to predict the CO2 distribution around the human body. The numerical model of the CO2 gas exchange mechanism includes both the upper and lower airways and makes it possible to calculate the alveolar CO2 partial pressure; this improves the prediction accuracy. We used the CSP to predict emission rates of metabolically generated CO2 exhaled by a person and assumed that the tidal volume will be unconsciously reduced as a result of exposure to poor indoor air quality. A reduction in tidal volume resulted in a decrease in CO2 emission rates of the same magnitude as was observed in our published experimental data. We also observed that the predicted inhaled CO2 concentration depended on the flow pattern around the human body, as would be expected.

DOI： 10.1111/ina.13079

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Scopus

PubMed

Language：Japanese   Publisher：Architectural Institute of Japan  

<p>The purpose of this study is to investigate the effect of supply air return from the HVAC system on indoor air quality. We discuss the structure of the formation mechanism in local pollutant concentration distributions using various indices on the ventilation efficiency of a local domain in 3 rooms with different layout of the exhaust outlet location. As a result, when the percentage of the return air at the supply inlet becomes large, visitation frequency of pollutants on a target local domain increases exponentially, and then the averaged concentration of the pollutants of the local domain also increases exponentially.</p>

DOI： 10.3130/aije.87.439

Scopus

CiNii Research

Language：English   Publisher：Indoor Air  

Net escape velocity (NEV) and net escape probability (NEP) are concepts that describe that scalar quantity discharged from a source in an indoor air environment is expressed by the unique velocity scales of the returning and escaping populations. Despite the conceptual description and applications of several numerical simulations, the definitions were not precisely explained using a mathematical formula. Here, we derive rigorous mathematical formulations of the NEV and NEP. These formulations provide us with the physical interpretation of NEV, clarify the sufficient condition of perfect escape, and lead to a further formulation of the transfer probability of the scalar. To justify and apply the derived relationships, two simple problems were numerically solved: One was a diffusion equation, and the other was an advection–diffusion equation. The results of the diffusion problem clearly demonstrate that only the outgoing scalar flux exists on the surface of the control volume, covering the source at any location. In contrast, the advection–diffusion problem reveals that there is a returning population of the scalar in most locations, despite both diffusion and turbulent parts working to remove the scalar. This rigorous formulation contributes to apply NEV as an appropriate air quality index with the clear physical interpretation to determine the local scalar concentration.

DOI： 10.1111/ina.13072

Web of Science

Scopus

PubMed

Publisher：Indoor and Built Environment  

Several studies regarding indoor environmental quality assessments based on computational human models have been reported. Recently, various computer-simulated persons for computational fluid dynamics (CFD) simulations that reproduce a detailed human body geometry has been developed. However, clothing is usually treated with simplification as a resistance to heat/contaminant transfer, and detailed hygro-thermo-chemical transfer phenomena in clothing-centred area with complex geometry have not been fully discussed. It is also important to investigate the ventilation characteristics inside the air gap between the clothing and the human body. Thus, this study aimed to develop an analytical method of three-dimensional clothing model that can be applied to a computer-simulated person (CSP) for indoor computational fluid dynamics analysis. To identify the impact of the clothing model on the human and the microclimate around the body, hygro-thermo-chemical transfer analyses were conducted in a virtual simplified model room. By reproducing the detailed clothing geometry, ventilation inside the air gap and clothing-centred hygro-thermo-chemical transfer characteristics were quantitatively investigated. The data analysis technique established in this study could contribute to preparing foundational data for simplification of numerical modelling of clothing.

DOI： 10.1177/1420326X211059449

Web of Science

Scopus

Publisher：Indoor and Built Environment  

Fume hoods are an indispensable instrument for experimental operations dealing with hazardous chemicals, wherein safety operations are strictly adherent to regulations. Within this context, few cases exist wherein the ventilation efficiency and pollutant capture efficiency inside fume hoods are precisely analyzed and quantitatively visualized. In this study, the pollutant capture efficiencies of a fume hood were analyzed by computational fluid dynamics as functions of exhaust airflow rate and according to the posture of workers in front of the fume hood. The indices for ventilation efficiencies, that is, age of air (SVE3), net escape velocity (NEV), and local purging flow rate (L-PFR), were adopted to quantitatively evaluate the pollutant concentration distributions formed inside the fume hood. NEV analysis revealed that the presence of a worker at the front of the fume hood did not significantly affect the pollutant capture efficiency at the opening surface of the fume hood. Changing the exhaust airflow rate resulted in changes in the size of the circulation flow formed in the upper part of the chamber. The circulation flow was found to have a dominant effect on the distribution of SVE3 and on the formation of the pollutant concentration distribution in the chamber.

DOI： 10.1177/1420326X211066538

Web of Science

Scopus

Publisher：Sustainability (Switzerland)  

A thorough understanding of the inhalation dynamics of infectious aerosols indoors and infection dynamics within the host by inhaled viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) plays an important role in the assessment and control of infection risks indoors. Here, by combining computational fluid–particle dynamics (CFPD) and host–cell dynamics (HCD), SARS-CoV-2 infection dynamics in the mucus layer of the human upper airway were studied. To reproduce the diffusive and convective transport of the virus in the nasal cavity–nasopharynx by mucociliary motion, a three-dimensional (3D)-shell model with a mucus layer was developed. The initial virus concentrations for HCD calculation were estimated based on the deposition distribution of droplets with representative sizes analyzed by CFPD. To develop a new HCD model, the target-celllimited model was integrated with the convection–diffusion equation. Additionally, the sensitivity of the infection rate β to the infection dynamics was systematically investigated. The results showed that the time series of SARS-CoV-2 concentration in the mucus layer strongly depended on diffusion, convection, and β. Although the SARS-CoV-2 dynamics obtained here have not been verified by corresponding clinical data, they can preliminarily reveal its transmission mode in the upper airway, which will contribute to the prevention and treatment of coronavirus disease 2019.

DOI： 10.3390/su14073896

Web of Science

Scopus

Publisher：Aerosol and Air Quality Research  

The recognition that the spread of COVID-19 is primarily through airborne transmission has brought renewed urgency to understand the spread of aerosols generated from patients. Viral-laden aerosols generated from oral coughs have been well studied; however, aerosols generated from nasal sneezing has been overlooked. This scenario arises from patients who suffer allergenic rhinosinusitis, or the nasal cavity is irritated, particularly during naso-endoscopy. Nasal sneezing is characterised by an explosive blast of air exiting the nostrils, which can be considered as dual jets, resulting in the spread of viral-laden aerosols remaining suspended in the air. This study used computational fluid dynamics consisting of a hybrid RANS-LES turbulence method to model the airflow and the discrete phase model to track aerosol dispersion during nasal sneezing. The results demonstrated that the exhaled airflow jets during nasal sneezing resemble the flow characteristics of two parallel jets in co-flow. These two jets interfere with each other in the merging zone, and after they merge, the sneeze plume expands radially. The nasal sneeze forms a V-shaped plume with smaller particles in the core region. At the end of the sneeze, when the exhaled jets have lost their initial momentum, the large particle dispersion is dominated by gravity. We detected the presence of a ‘sneeze puff’ that transport droplets away from the body, similar to the buoyant puff observed in recent COVID-19 studies of oral coughs.

DOI： 10.4209/aaqr.210338

Web of Science

Scopus

Publisher：Building and Environment  

We determined carbon dioxide (CO2) emission rates from sedentary subjects performing light work on tablets or smartphones in controlled chamber exposures. Five groups, each consisting of four people (four groups with two females and two males and one with three males and one female), stayed in a 22.5 m3 stainless steel chamber under different environmental conditions for 3 h in the morning and then 2,5 h in the afternoon after having a light lunch. Three groups consisted of young adults (college students), one of seniors, and one of teenagers. The chamber was ventilated with outdoor air at 3.2 h−1 (per person rate was 5 L/s). The CO2 emission rates per person were calculated using a single-zone mass-balance equation and the measured CO2 concentration once steady state had been reached. Per person emission rates varied between 14.1 and 16.8 L/h in the morning and 15.9–17.8 L/h in the afternoon; higher levels in the afternoon were probably caused by the increased metabolism from diet-induced thermogenesis (DIT). Emission rates were higher with increased temperature when the participants felt warm, but did not change with increased relative humidity or ozone concentration. They differed to some extent from those estimated using ISO 8996 and ASTM DS 6245, but were similar to published measured CO2 emission rates. The present results require confirmation with more people and measurements of CO2 emission rates using the calorimetric method.

DOI： 10.1016/j.buildenv.2021.108735

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Scopus

Publisher：Indoor and Built Environment  

In factories where high-risk chemical pollutants are treated, it is essential to anticipate response measures in the event of chemical pollutant leakage to minimize adverse health effects on workers. When high-risk liquid chemical pollutants are assumed to be leaked inside enclosed spaces, it becomes crucial to predict the non-uniform concentration distributions in enclosed spaces and evaluate the health impacts and risks of short-time exposure to prevent large-scale accidents. Therefore, we have developed an emergency ventilation system for controlling the inhaled contaminant dose of factory workers. In this study, assuming a worst-case scenario liquid chemical pollutant leak in an enclosed factory space, the advantages and performance of a hybrid ventilation system that combines displacement and push–pull type ventilation systems were numerically investigated. Installation of wall materials that facilitate photocatalytic oxidation (PCO) reactions for background passive concentration control was also discussed. Based on the demonstrative numerical analyses for a realistic factory space, push–pull type ventilation system was confirmed to effectively suppress chemical pollutant diffusion in enclosed spaces with a low ventilation rate. Wall materials with the PCO mechanism had a certain contribution to the control of peak concentration.

DOI： 10.1177/1420326X211026360

Web of Science

Scopus

Publisher：Japan Architectural Review  

Advances in next-generation sequencing (NGS) technologies since 2005 have revolutionized biological science. One particular application of NGS technologies is to elucidate microbiomes in built environments. We are currently conducting a series of studies on the elucidation and control of mass infection mechanisms based on dynamic measurement of environment microbiomes. The objective of this study is to clarify the dispersion characteristics of oral bacteria in the built environment. Bacterial communities from occupants’ hands and oral cavities, doorknobs, desk and keyboard surfaces, and air in laboratories were investigated in seven Japanese universities. The median relative abundances of Firmicutes, Proteobacteria, Actinobacteria, Bacteroidetes, and Fusobacteria were 41%, 31%, 12%, 7%, and 3%, respectively. Moreover, the main genera detected were Streptococcus (27.6%), Haemophilus (7.0%), Staphylococcus (5.6%), Neisseria (5.6%), Corynebacterium (4.7%), Rothia (3.2%), Prevotella (3.0%), Fusobacterium (2.6%), Veillonella (1.7%), Leptotrichia (1.7%), Enhydrobacter (1.7%), Lactobacillus (1.3%), Acinetobacter (1.3%), and Actinomyces (1.1%). The oral bacteria Actinomyces, Corynebacterium, Fusobacterium, Haemophilus, Leptotrichia, Neisseria, Prevotella, Rothia, and Streptococcus were observed in indoor air and on surfaces as well as in oral cavities. Furthermore, Prevotella melaninogenica and Rothia mucilaginosa were observed in all samples, including those from hands and oral cavities, doorknobs, desk and PC keyboard surfaces, and air in laboratories, in all seven universities.

DOI： 10.1002/2475-8876.12261

Web of Science

Scopus

Publisher：Building and Environment  

Ten healthy young adults slept one by one in a specially designed and constructed sleep capsule located in a climate chamber at two temperatures (24 °C and 28 °C) and two ventilation rates that ensured that the resulting CO2 concentrations were 800 and 1700 ppm. Subjectively rated sleep quality was reduced at 28 °C and reduced ventilation, while sleep onset latency was longer under these conditions. Sleep efficiency was lower at 28 °C. Subjectively rated fatigue and sleepiness decreased after sleeping under all conditions but less so after sleeping at 28 °C. The subjects indicated that their work performance improved after sleeping at 24 °C but not when ventilation was reduced and the temperature increased. Both objectively measured and subjectively rated work performance was worse after sleeping in the condition with increased temperature. The subjects felt warmer at 28 °C although the thermal environment was still rated as acceptable but the air in the capsule was rated stuffier, the acceptability of the air quality decreased and the rated odour intensity increased at this condition. The wrist skin temperature was always higher at 28 °C with reduced ventilation but only during the sleep onset latency period. The subjects felt slightly warm and rated the air stuffier when ventilation was reduced. The present results, albeit from a small exploratory pilot study, show that increased temperature and reduced ventilation both have negative effects on sleep quality, which may have consequences for next-day work performance. These pilot experiment results require validation due to the low number of subjects.

DOI： 10.1016/j.buildenv.2021.108666

Web of Science

Scopus

Language：English   Publisher：Indoor Air  

The breathing zone of an individual indoors is usually defined as a finite region steadily formed in front of a face. Assuming the steady formation of the breathing zone, we propose a procedure for quantitatively identifying a breathing zone formed in front of a human face in the transient condition. This assumption is reasonable considering that the ventilation time scale of human respiration is sufficiently short compared to the ventilation time scale of a room. We used steady-state computational fluid dynamics (CFD) and a computationally simulated person (CSP). We present the probabilistic size of the breathing zone for various postures and breathing conditions. By analyzing unsteady inhalation and exhalation airflow characteristics via a CSP with a respiratory system, we also estimated the direct re-inhalation rate of the exhaled air. The results can be used for developing methods to control the long-term and low-contaminant concentration exposures.

DOI： 10.1111/ina.13003

Web of Science

Scopus

PubMed

Language：Japanese   Publisher：The Society of Heating,Air-Conditioning&Sanitary Engineers of Japan  

DOI： 10.18948/shasetaikai.2022.7.0_157

CiNii Research

Language：Japanese   Publisher：The Society of Heating,Air-Conditioning&Sanitary Engineers of Japan  

DOI： 10.18948/shasetaikai.2022.7.0_153

CiNii Research

Language：Japanese   Publisher：Society of Indoor Environment, Japan  

The issue of marine pollution caused by micro-plastics has emerged and has attracted worldwide attention. If the source of micro-plastic is routine plastic waste and products, they will be located very close to the living environment, and there is a concern about the risk of micro plastic contamination even in the residential environment. However, the actual micro plastic conditions of the indoor environment, and the presence or absence of micro-plastic contamination in residential environments, as well as their concentrations, have not been well investigated so far. In this study, we firstly classified and defined micro-plastic present in indoor environment, and proposed a standard sampling and measurement method of indoor micro-plastic concentration by way of a preliminary field survey in residential houses.

DOI： 10.7879/siej.25.225

CiNii Research

Publisher：17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022  

We summarize our three recent studies that determined CO2 emission rates from humans using the mass-balance model and the measured steady-state CO2 concentration. One study determined CO2 emission rates from sleeping adults; they were on average 11 L/h/person, 30-45% than for awake people at a light activity. They were relatively stable and similar to the published work and estimations using models. Two studies determined CO2 emission rates from the sedentary awake people at a light activity; they were on average 12.9-17.8 L/h/person. They were not significantly different between teenagers, young adults, and the elderly, nor when ozone and relative humidity increased. Reduced ventilation and increased CO2 significantly reduced CO2 emission rates; the changes in respiration could be the plausible reason. CO2 emission rates increased at thermal sensation departing from neutrality; increased metabolic activity could be the plausible reason. The emission rates were different from published results and estimations using models.

Scopus

Publisher：17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022  

This study examined the impact of room temperature on carbon dioxide (CO2) emission rates from humans at three different physical activity levels: sitting, standing, and walking. Six volunteers (four males and two females) stayed in a temperature-controlled classroom. Four room temperature conditions were examined: 15, 20, 25, and 28℃. Indirect calorimetry was used to measure CO2 emission rates and additionally respiratory parameters such as ETCO2 and respiration rate. CO2 emission rates increased significantly with the physical activity level increased, and it was lower when thermally neutral compared to thermally warm and cool. The room temperature effect on CO2 emission rate depended on the physical activity levels.

Scopus

Language：Japanese   Publisher：The Society of Heating,Air-Conditioning&Sanitary Engineers of Japan  

DOI： 10.18948/shasetaikai.2022.7.0_1

CiNii Research

Publisher：17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022  

In this study, the pollutant capture efficiency of the laboratory fume hood was analyzed by computational fluid dynamics (CFD) as functions of the exhaust airflow rate, the presence of a worker in front of the fume hood, and a heat source within the fume hood. We confirmed that heat generation within the fume hood significantly affected the pollutant capture efficiency distribution in the fume hood under low exhaust airflow rate conditions.

Scopus

Publisher：17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022  

The issue of marine pollution caused by micro-plastics has emerged and has attracted worldwide attention. If the source of micro-plastics is routine plastic waste and products, they will be located very close to our living environment, and there is a concern about the risk of micro plastic contamination even in the residential environment. However, the actual microplastics conditions of the indoor environment, and the presence or absence of micro-plastics contamination in residential environments, as well as their concentrations, have not been well investigated so far. We conducted a preliminary survey on indoor microplastics contamination in house dust, targeting four general residential houses in Kanto area of Japan.

Scopus

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Responsible for pages：2.2.3節担当 (分担執筆)、pp 49-56   Language：Japanese   Book type：Scholarly book

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Venue：Kyoto   Country：Japan