The lavatory is a fertile area for the transmission of infectious disease through bioaerosols between its users. In this study, we built a generic compact lavatory model with a vacuum toilet, and ...computational fluid dynamics (CFD) is used to evaluate the effects of ventilation and user behaviors on the airflow patterns, and the resulting fates of bioaerosols. Fecal aerosols are readily released into the lavatory during toilet flush. Their concentration rapidly decays in the first 20 s after flushing by deposition or dilution. It takes about 315 s to 348 s for fine bioaerosols (<10 µm in diameter) to decrease to 5% of the initial concentration, while it takes 50 and 100 µm bioaerosols approximately 11 and <1 s, respectively, to completely deposit. The most contaminated surfaces by aerosol deposition include the toilet seat, the bowl, and the nearby walls. The 10 µm aerosols tend to deposit on horizontal surfaces, while the 50 and 100 µm bioaerosols almost always deposit on the bowl. In the presence of a standing thermal manikin, the rising thermal plume alters the flow field and more bioaerosols are carried out from the toilet; a large fraction of aerosols deposit on the manikin’s legs. The respiratory droplets generated by a seated coughing manikin tend to deposit on the floor, legs, and feet of the manikin. In summary, this study reveals the bioaerosol dilution time and the easily contaminated surfaces in a compact lavatory, which will aid the development of control measures against infectious diseases.
•The simplification methods largely affect the thermal flow and contaminant fields.•The mesh decimating algorithm is promising to reduce cost but remain accuracy.•The recommended method is efficient ...for multi-occupant environment simulations.
While simplified computational thermal manikins (CTMs) are widely employed in CFD models of occupied indoor spaces in order to save the computational cost, a criterion of simplification is still absent and the effects of CTM simplification are yet not clear. In this study, six CTMs including a 3D scanned CTM and five simplified CTMs generated from various simplification approaches were employed to analyse the impact of CTM simplification on the prediction of airflow field and contaminant transport. Comparison of the predicted airflow field against the published data in the literature demonstrated that CTM simplification has a strong effect on the thermal airflow field prediction in the vicinity of manikin surfaces. For densely occupied indoor spaces such as a train cabin, the error induced by CTM simplification could be enlarged and further cause significant global error to the prediction of contaminant transport. This is especially true when contaminants are released from the CTMs. This study demonstrated that the mesh decimating algorithm is promising to simply CTMs that is not only able to reduce considerable computational cost but capable of maintaining an acceptable predictive error.
In confined spaces, such as vehicle cabins, airflow and temperature distribution are the most critical factors affecting thermal comfort and pollutant dispersion. To develop innovative and ...energy-efficient HVAC systems, a deep understanding of the interaction of the jet flow from the air diffusers on the development process of the human thermal plume became essential to improve the knowledge of airflow patterns for optimizing ventilation system design, thermal comfort, and, indirectly, the energy efficiency. The human thermal plume is one of the most challenging phenomena to capture with optical measurement methods and validate with complex numerical models, given its unsteady nature governed by the buoyancy forces. This study aims to validate the interaction of jet flows from classical and innovative air diffusers on the thermal plume by comparing measured data and numerical simulation results. This validation was made with a specific approach by comparing PIV fields from measurements and CFD results with boundary conditions of air velocity distribution from LDV data. The PIV measurements for flow distributions at the air vents and the thermal plume of an advanced thermal manikin in the driver’s seat were performed in a 1:1 scale mock-up of a Renault Megane car cabin in a climatic chamber. The results obtained with both methods showed good agreement regarding air velocity ranges and distributions. Despite the confined cabin space restricting the development of the thermal plume, a difference in maximum velocities of 0.08 m/s was observed when the distance between the top of the head and the ceiling was doubled. With innovative air diffusers, air velocity distribution showed a more uniform flow than classical diffusers.
•The effects of source intensity and axial ratio on the buoyant plume are analyzed.•The evolution characteristics of the plume's diffusion range are analyzed.•The cross-sectional flow rate equation ...for the axial ratio (ξ) > 5/3 is obtained.
The thermal plume formed by the high-temperature elliptical heat source surface during the smelting process is often captured and removed by the local exhaust system. Accurately mastering the flow-field characteristics of such high-temperature elliptical heat plumes is helpful for efficient design of local exhaust systems. In this paper, the effects of the ratio of long and short axes (5/4 ≤ ξ ≤ 5/1) and the intensity of heat source (80 ≤ F ≤ 160 W) on the axial and radial velocity distribution of thermal plume in an elliptical heat source are investigated by numerical simulation combined with experimental validation. The results show that in the range of ξ ≤ 5/1, the axial dimensionless velocity distribution of the elliptical plume field and the spreading range of the plume field are mainly affected by ξ instead of F. For 5/4 ≤ ξ ≤ 5/1, the maximum axial velocity Um appears at 1.7 to 2.7 times Z/L (plume height to heat source long axis ratio). For ξ ≤ 5/2, the height at which the cross-sectional velocity field transitions to a circular distribution aligns with the height of Um. It is found that the plume velocity field is characterized by applying the point source model for ξ ≤ 5/3, and vice versa for the linear source model. The plume flow rate formulation obtained by modifying the linear source model for ξ > 5/3 has a better predictive ability in the Z/L ≤ 5 region. This study provides a reference for the design of ventilation systems for elliptical surface heat sources.
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Airflow distribution in the operating room plays an important role in ensuring a clean operating microenvironment and preventing surgical site infections (SSIs) caused by airborne contaminations. The ...objective of this study was to characterize the airflow distribution in proximity to a patient in an orthopedic operating room.
Experimental measurements were conducted in a real operating room at St. Olav's Hospital, Norway, with a laminar airflow system. Omnidirectional anemometers were used to investigate the air distribution in the operating zone, and 4 different cases were examined with a real person and a thermal manikin.
This study showed that the downward airflow from the laminar airflow system varies in each case with different surgical arrangement, such as the position of the operating lamp. The results indicate that the interaction of thermal plumes from a patient and the downward laminar airflow may dominate the operating microenvironment.
The airflow distribution in proximity to a patient is influenced by both the surgical facility and the presence of medical staff. A thermal manikin may be an economical and practical way to study the interaction of thermal plumes and downward laminar airflow. The provision of higher clean airflow rate in the operating microenvironment may be an effective way to prevent the development of SSIs caused by indoor airborne contamination.
The purpose of this study is to investigate the influence of the heat dissipation of thermal manikins on the flow field in a seven-row cabin mockup that was fully occupied by thermal manikins. ...Temperature data from the cabin mockup, as measured by thermocouples, were analyzed using statistical methods for elucidation of the turbulence characteristics of the thermal plumes of manikins. The characteristics of the thermal plumes are illustrated by the skewness factors of the temperature signal. The results indicate the characteristics of the thermal plume from the torso differ from those from the thigh. A thin layer (approximately 5 mm) of the thermal plume was observed around the human torso. Further, thermal plumes were more fully developed at the thigh than the torso. The results contribute to the understanding of airflow patterns influenced by thermal plumes near the head, chest, abdomen and thigh.
•Through using the dynamic thermal turbulence measurements investigate the thermal plume of passenger in cabin.•A thin layer of torso thermal plume was observed around the human body in cabin.•The thermal plumes have influence on the flow field and enhanced turbulent fluctuation at abdomen region.
Elevated exposure to airborne particulate matter is linked to deleterious health and well-being outcomes. Exposure assessment can be improved through enhanced understanding of source-receptor ...relationships, for example as expressed in the inhalation intake fraction metric. This study provides new knowledge about how inhalation intake of airborne particles varies with spatially varying indoor emissions. In a controlled environmental chamber with low background particle levels, we monitored the time- and size-resolved particle concentrations at multiple locations including the subject's breathing zone. We investigated two types of particle emissions: (i) controlled releases from several specific indoor locations; and (ii) natural release from skin and clothing for a range of simulated occupant activities. Findings show that particles released proximate to the human envelope caused a total inhalation intake fraction of 7–10 per thousand, which was 1.5–16 × higher than the intake fraction for other indoor release locations. These outcomes reflect the influence of emissions-receptor proximity combined with the efficient transport of particles by means of the thermal plume to the breathing zone. The results show that the well-mixed representation of an indoor environment could underestimate the inhalation intake by 40–90% for various localized indoor emissions, and by up to 3 × for particles emitted from the human envelope. The post-release exposure period contributed substantially to total inhalation intake. For particles released naturally from the human envelope, inhalation intake fractions varied with activity type and were higher for a subject when seated rather than walking.
•We study how intake fraction (iF) of airborne particles varies with the location of indoor emissions.•Source position, thermal plume, and exposure duration considerably influence inhalation iF.•Near-occupant releases cause much higher inhalation iF compared to other indoor release locations.•For near-occupant releases, inhalation iF while walking was lower than for a seated person.•Well-mixed assumption could underestimate inhalation iF for certain indoor pollutant releases.
Efforts are made to elucidate a three-dimensional (3D) computational work on laminar free/natural convection flows around the isothermally heated inclined hollow cylinder immersed in the quiescent ...ambient air negligible wall thickness. The thermofluidic characterization is performed by solving three-dimensional governing differential equations i.e. continuity, momentum, and energy equations over the following ranges of pertinent parameters: Rayleigh number, 10
4
≤ Ra ≤ 10
8
; cylindrical aspect ratio, 1 ≤ L/D ≤ 20; tube inclination, 0°≤θ ≤ 90°. Detailed behaviors of thermal and flow fields are delineated with the help of visualization technique like temperature contours and velocity vectors in order to identify the regions of low/high temperature gradient and fluid velocity. The influence of Ra, L/D, and θ on the local and average Nusselt number is predicted and it is seen that the average Nusselt number on outer and inner surface increases and decreases, respectively with the reduction in tube inclination for a particular Ra and L/D. A couple of correlation has been developed for the average Nusselt number on outer and inner surface of the hollow cylinder as a function of Ra, L/D, and θ based on the computed data points which would be helpful for various academic and industrial purposes.
•The process of smoke settling in the long channel is analyzed.•The temperature and flow field distributions in channels are shown.•The maximum ceiling temperature with various fire positions is ...analyzed.
This paper aims to study the characteristics of smoke flow in a long-closed channel with one lateral opening at one end. A series of full-scale experiments with different longitudinal positions and heat release rates of fire sources were carried out. And, the corresponding numerical simulations were conducted to help explain the law of smoke flow field. The characteristics of the smoke spread on both sides of the fire source, the thermal plume distribution within the channel, and the maximum ceiling excess temperature were analyzed. Results show that the existence of the end walls in the long channel causes the smoke to accumulate, which further results in the smoke settlement going through three stages. The lateral opening causes a significant difference of smoke flow and other characteristics from the channel with both ends open. When the fire source approaches the closed end without opening, the vertical fire-induced plume inclines to the closed end because of the asymmetrical air supplementation. Due to the limited air supply, the combustion will change to ventilation-controlled as the fire source heat release rate increases. The maximum ceiling excess temperature is higher than that with both ends open and is basically not influenced by fire positions studied in this work. It has been verified that the dimensionless maximum ceiling excess temperature of the smoke is also proportional to the dimensionless heat release rate. This study can provide a reference for fire prevention and smoke exhaust strategies for long channels.
•The validity of general assumption on thermal dispersivity ratio was investigated.•Small-scale heterogeneity causes the scatter in dispersion-velocity relationships.•The dispersivity ratio affects ...the time evolution and geometry of thermal plumes.•Injection increases the dispersivity ratio effect in the downstream direction.•It is needed to evaluate the dispersivity magnitude and ratio in the design stage.
Studies on shallow geothermal applications have demonstrated that mechanical thermal dispersion is an important heat transport mechanism in saturated porous media. However, most previous studies have assumed the thermal dispersivity ratio, which has not been sufficiently examined. This study investigates the validity of the general assumption that the transverse dispersivity is one-tenth of the longitudinal dispersivity. For this purpose, heat transport experiments, specifically designed at the laboratory scale for estimating dispersivity, were conducted using two different heat sources at Darcy fluxes of 4.74 to 37.47 m/d (Reynolds number Re < 0.3). The results from the analytical models showed that the dispersivity ratios differed from the thermal dispersivity assumption, indicating that the ratio can vary depending on the properties of the porous media. Additionally, heat transport modeling was performed to confirm the influence of the dispersivity ratio on the temperature plumes that develop from the thermal use of shallow aquifers, such as groundwater heat pump systems. We found that, under steady-state conditions, the decrease in the dispersivity ratio led to smaller plume dimensions in all directions, owing to the increased heat dissipation in the transverse direction. Transient simulations for flow and heat transport indicated that the effect of the thermal dispersivity ratio was time-dependent and heterogeneous and increased with the injection rate. These results suggest that the thermal dispersivity ratio is crucial for assessing the environmental impacts of aquifer thermal use, especially for long-term and large-scale applications. Therefore, the magnitude and ratio of thermal dispersivity should be evaluated at the design stage for more efficient and sustainable use of shallow geothermal resources.
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