scholarly journals Using Computational Fluid Dynamics to Evaluate the Role of Air Purification in Reducing Fallow Time in Dentistry 

2020 ◽  
Author(s):  
Neha Raghava ◽  
Bojan Vidovic
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Particle Number ◽  
Air Purification ◽  
Particle Volume ◽  
Dental Surgery ◽  
Infection Transmission ◽  
Air Purifier ◽  
Total Particle ◽  
Open Window

Abstract AbstractIn dentistry, fallow time is a period which allows for airborne pathogens to settle out of the air and mitigate the risk of airborne infection transmission to dental professionals and staff. The current recommendation is a one hour period.Aims and Objectives We aim to show that air purification devices are an undervalued adjunctive measure to mitigate the risk of airborne transmission of pathogens, and so reduce fallow time.Methods Using a computational fluid dynamics software, we created a virtual dental surgery, and simulated a ten-minute aerosol generating procedure. We then modelled air flow in the room with no ventilation, and then the same room with an air purifier at a throughput of 430m3 h-1, and subsequently the room with one open window providing 6 ACH and no purifier. The particles released were monitored and their behaviour and airborne time measured and collated.Results and conclusions The room with no ventilation had a total particle number at 600s of 4.5million, which required 8400s to reduce by 99%. With an open window providing 6 ACH, we obtained a value of 2500s for a 99% reduction in airborne particles, and a similar peak particle volume. Conversely, when using an air purifier throughout the procedure, the peak particle number was ten times lower than the peak number without ventilation, or with an open window, and after the particle injection 99% airborne particle reduction was achieved 60s. Our findings suggest that the use of an air purifier greatly reduces the total particle volume in the air during the aerosol generating procedure, and the fallow period needed. The values found with 6 ACH and an open window are corroborated in other literature. The use of air purification could greatly reduce the risk of infection transmission in a dental surgery.

scholarly journals Using Computational Fluid Dynamics to Evaluate the Role of Air Purification in Reducing Fallow Time in Dentistry

2021 ◽  
Vol 7 (3) ◽  
Author(s):  
Raghava N ◽  
Vidovic B
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Air Purification ◽  
Current Recommendation ◽  
Infection Transmission ◽  
Airborne Infection ◽  
Dental Professionals

In dentistry, fallow time is a period which allows for airborne pathogens to settle out of the air and mitigate the risk of airborne infection transmission to dental professionals and staff. The current recommendation is a one-hour period.

scholarly journals Vertical marine snow distribution in the stratified, hypersaline, and anoxic Orca Basin (Gulf of Mexico)

Elem Sci Anth ◽  
2019 ◽  
Vol 7 ◽  
Author(s):  
Arne Diercks ◽  
Kai Ziervogel ◽  
Ryan Sibert ◽  
Samantha B. Joye ◽  
Vernon Asper ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Gulf Of Mexico ◽  
Particle Number ◽  
Sea Surface ◽  
Marine Snow ◽  
Particle Volume ◽  
Total Particle Number ◽  
Total Particle ◽  
Snow Distribution ◽  
Orca Basin

We present a complete description of the depth distribution of marine snow in Orca Basin (Gulf of Mexico), from sea surface through the pycnocline to within 10 m of the seafloor. Orca Basin is an intriguing location for studying marine snow because of its unique geological and hydrographic setting: the deepest ~200 m of the basin are filled with anoxic hypersaline brine. A typical deep ocean profile of marine snow distribution was observed from the sea surface to the pycnocline, namely a surface maximum in total particle number and midwater minimum. However, instead of a nepheloid (particle-rich) layer positioned near the seabed, the nepheloid layer in the Orca Basin was positioned atop the brine. Within the brine, the total particle volume increased by a factor of 2–3 while the total particle number decreased, indicating accumulation and aggregation of material in the brine. From these observations we infer increased residence time and retention of material within the brine, which agrees well with laboratory results showing a 2.2–3.5-fold reduction in settling speed of laboratory-generated marine snow below the seawater-brine interface. Similarly, dissolved organic carbon concentration in the brine correlated positively with measured colored dissolved organic matter (r2 = 0.92, n = 15), with both variables following total particle volume inversely through the pycnocline. These data indicate the release of dissolved organic carbon concomitant with loss in total particle volume and increase in particle numbers at the brine-seawater interface, highlighting the importance of the Orca Basin as a carbon sink.

scholarly journals Annual cycle of Antarctic baseline aerosol: controlled by photooxidation-limited aerosol formation

2014 ◽  
Vol 14 (6) ◽  
pp. 3083-3093 ◽  
Author(s):  
M. Fiebig ◽  
D. Hirdman ◽  
C. R. Lunder ◽  
J. A. Ogren ◽  
S. Solberg ◽  
...  
Keyword(s):  
Annual Cycle ◽  
Particle Number ◽  
Climate Models ◽  
Aerosol Formation ◽  
Particle Volume ◽  
Transport Pathway ◽  
Air Masses ◽  
Total Particle ◽  
The Antarctic ◽  
Aerosol Properties

Abstract. This article investigates the annual cycle observed in the Antarctic baseline aerosol scattering coefficient, total particle number concentration, and particle number size distribution (PNSD), as measured at Troll Atmospheric Observatory. Mie theory shows that the annual cycles in microphysical and optical aerosol properties have a common cause. By comparison with observations at other Antarctic stations, it is shown that the annual cycle is not a local phenomenon, but common to central Antarctic baseline air masses. Observations of ground-level ozone at Troll as well as backward plume calculations for the air masses arriving at Troll demonstrate that the baseline air masses originate from the free troposphere and lower stratosphere region, and descend over the central Antarctic continent. The Antarctic summer PNSD is dominated by particles with diameters <100 nm recently formed from the gas-phase despite the absence of external sources of condensible gases. The total particle volume in Antarctic baseline aerosol is linearly correlated with the integral insolation the aerosol received on its transport pathway, and the photooxidative production of particle volume is mostly limited by photooxidative capacity, not availability of aerosol precursor gases. The photooxidative particle volume formation rate in central Antarctic baseline air is quantified to 207 ± 4 μm3/(MJ m). Further research is proposed to investigate the applicability of this number to other atmospheric reservoirs, and to use the observed annual cycle in Antarctic baseline aerosol properties as a benchmark for the representation of natural atmospheric aerosol processes in climate models.

scholarly journals Aerosol–computational fluid dynamics modeling of ultrafine and black carbon particle emission, dilution, and growth near roadways

2014 ◽  
Vol 14 (23) ◽  
pp. 12631-12648 ◽  
Author(s):  
L. Huang ◽  
S. L. Gong ◽  
M. Gordon ◽  
J. Liggio ◽  
R. Staebler ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Boundary Layer ◽  
Computational Fluid Dynamics ◽  
Atmospheric Boundary Layer ◽  
Urban Areas ◽  
Particle Number ◽  
Carbon Particle ◽  
Particle Growth ◽  
Horizontal Gradient ◽  
Computational Domain

Abstract. Many studies have shown that on-road vehicle emissions are the dominant source of ultrafine particles (UFPs; diameter < 100 nm) in urban areas and near-roadway environments. In order to advance our knowledge on the complex interactions and competition among atmospheric dilution, dispersion, and dynamics of UFPs, an aerosol dynamics–computational fluid dynamics (CFD) coupled model is developed and validated against field measurements. A unique approach of applying periodic boundary conditions is proposed to model pollutant dispersion and dynamics in one unified domain from the tailpipe level to the ambient near-road environment. This approach significantly reduces the size of the computational domain, and therefore allows fast simulation of multiple scenarios. The model is validated against measured turbulent kinetic energy (TKE) and horizontal gradient of pollution concentrations perpendicular to a major highway. Through a model sensitivity analysis, the relative importance of individual aerosol dynamical processes on the total particle number concentration (N) and particle number–size distribution (PSD) near a highway is investigated. The results demonstrate that (1) coagulation has a negligible effect on N and particle growth, (2) binary homogeneous nucleation (BHN) of H2SO4–H2O is likely responsible for elevated N closest to the road, and (3) N and particle growth are very sensitive to the condensation of semi-volatile organics (SVOCs), particle dry deposition, and the interaction between these processes. The results also indicate that, without the proper treatment of the atmospheric boundary layer (i.e., its wind profile and turbulence quantities), the nucleation rate would be underestimated by a factor of 5 in the vehicle wake region due to overestimated dilution. Therefore, introducing atmospheric boundary layer (ABL) conditions to activity-based emission models may potentially improve their performance in estimating UFP traffic emissions.

scholarly journals Modelling the contribution of biogenic VOCs to new particle formation in the Jülich plant atmosphere chamber

2014 ◽  
Vol 14 (20) ◽  
pp. 27973-28018 ◽  
Author(s):  
L. Liao ◽  
M. Dal Maso ◽  
D. Mogensen ◽  
P. Roldin ◽  
A. Rusanen ◽  
...  
Keyword(s):  
Organic Compounds ◽  
Particle Number ◽  
Particle Formation ◽  
Oxidation Products ◽  
New Particle Formation ◽  
Particle Volume ◽  
Aerosol Dynamics ◽  
Total Particle Number ◽  
Total Particle ◽  
Air Chemistry

Abstract. We used the MALTE-BOX model including near-explicit air chemistry and detailed aerosol dynamics to study the mechanisms of observed new particle formation events in the Jülich Plant Atmosphere Chamber. The modelled and measured H2SO4 (sulfuric acid) concentrations agreed within a factor of two. The modelled total monoterpene concentration was in line with PTR-MS observations, and we provided the distributions of individual isomers of terpenes, when no measurements were available. The aerosol dynamic results supported the hypothesis that H2SO4 is one of the critical compounds in the nucleation process. However, compared to kinetic H2SO4 nucleation, nucleation involving OH oxidation products of monoterpenes showed a better agreement with the measurements, with R2 up to 0.97 between modelled and measured total particle number concentrations. The nucleation coefficient for kinetic H2SO4 nucleation was 2.1 × 10−11 cm3 s−1, while the organic nucleation coefficient was 9.0 × 10−14 cm3 s−1. We classified the VOC oxidation products into two sub-groups including extremely low-volatility organic compounds (ELVOCs) and semi-volatile organic compounds (SVOCs). These ELVOCs and SVOCs contributed approximately equally to the particle volume production, whereas only ELVOCs made the smallest particles to grow in size. The model simulations revealed that the chamber walls constitute a major net sink of SVOCs on the first experiment day. However, the net wall SVOC uptake was gradually reduced because of SVOC desorption during the following days. Thus, in order to capture the observed temporal evolution of the particle number size distribution, the model needs to consider reversible gas-wall partitioning.

scholarly journals Annual cycle of Antarctic baseline aerosol: controlled by photooxidation-limited aerosol formation

2013 ◽  
Vol 13 (9) ◽  
pp. 23057-23088
Author(s):  
M. Fiebig ◽  
D. Hirdman ◽  
C. R. Lunder ◽  
J. A. Ogren ◽  
S. Solberg ◽  
...  
Keyword(s):  
Annual Cycle ◽  
Particle Number ◽  
Climate Models ◽  
Aerosol Formation ◽  
Particle Volume ◽  
Transport Pathway ◽  
Air Masses ◽  
Total Particle ◽  
The Antarctic ◽  
Aerosol Properties

Abstract. This article investigates the annual cycle observed in the Antarctic baseline aerosol scattering coefficient, total particle number concentration, and particle number size distribution (PNSD) as measured at Troll Atmospheric Observatory. Mie-theory shows that the annual cycles in microphysical and optical aerosol properties have a common cause. By comparison with observations at other Antarctic stations, it is shown that the annual cycle is not a local phenomenon, but common to Central Antarctic baseline air masses. Observations of ground-level ozone at Troll as well as backward plume calculations for the air masses arriving at Troll demonstrate that the baseline air masses originate from the free troposphere and lower stratosphere region, and descend over the Central Antarctic continent. The Antarctic summer PNSD is dominated by particles with diameters < 100 nm recently formed from the gas-phase despite the absence of external sources of condensible gases. The total particle volume in Antarctic baseline aerosol is linearly correlated with the integral insolation the aerosol received on its transport pathway, and the photooxidative production of particle volume is mostly limited by photooxidative capacity, not availability of aerosol precursor gases. The photooxidative particle volume formation rate in Central Antarctic baseline air is quantified to 207 ± 4 μm3/(MJ m). Further research is proposed to investigate the applicability of this number to other atmospheric reservoirs, and to use the observed annual cycle in Antarctic baseline aerosol properties as a benchmark for the representation of natural atmospheric aerosol processes in climate models.

Investigation in the Characteristics of the Personal Ventilation Using Computational Fluid Dynamics

2011 ◽  
Vol 21 (6) ◽  
pp. 749-771 ◽  
Author(s):  
Mitja Mazej ◽  
Vincenc Butala
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Numerical Models ◽  
Personal Exposure ◽  
Convection Flow ◽  
Pv System ◽  
Infection Transmission ◽  
Airborne Infection ◽  
Increased Risk ◽  
Exhaled Air

Detailed information of transient exhaled air dispersion and recirculation in the breathing zone can be obtained using computational fluid dynamics (CFD) to generate detailed numerical models and obtain the necessary information. In this study, interaction of free convection flow around human body with respiration flow of breathing and vertical personalized flow from personalized ventilation (PV) system was simulated using a commercial CFD package. Impact of breathing process on personal exposure effectiveness εp was evaluated for different operating and environmental conditions. Re-inhaled exposure index εRI for exhaled CO2 was used to assess the amount of exhaled air re-inhaled due to the interaction between personalized and exhaled airflows. Another objective of this study was to consider the risk of airborne infection transmission, caused by undesirable transport and dispersion of exhaled pathogens to surrounding air when infected individual uses PV. Results show that calculation of personal exposure effectiveness would be sufficiently accurate to give proper information about the protection of occupant with a PV system also without the breathing simulation included. The operating mode of a PV proved as the main factor for dispersion of exhaled air and its transport to the background room air, resulting in an increased risk of airborne infection transmission.

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