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.
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.
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.
•Experimental assessment of Personal Protective Equipment (PPE) for medical care.•The PPE uses a face shield combined with an air-sealed curtain.•The maximum efficiency was 82% when exposed to a ...uniform polluted environment.•Human thermal plume reduces the velocity and affects the device efficiency by 2%.•Human breathing process improves the PPE efficiency by 32%.
This paper presents the performance assessment of a novel air-sealed visor for medical care based on experiments. This Personal Protective Equipment (PPE) provides effective aerodynamic sealing of the breathing zone, thus reducing the risk of inhaling droplets and aerosols carrying a potential viral load. The air curtain supply system was designed after computational fluid dynamics exploratory simulations to determine suitable airflow conditions. The main parameters under study are the air curtain velocities and the fraction of contaminated air in the breathing zone. The impact of different airflow rates, human breathing, thermal plume and lateral barriers to reduce the risk of leakage, was investigated. For the designed airflow rate and considering the worst-case scenario with a contaminated environment, results indicate that this PPE can reduce the contaminated air in the breathing zone by 31% and 82%, without and with lateral physical barriers, respectively. Although the human body thermal plume has a high impact on the air curtain velocity profile, it just affects the device efficiency by 2%. The breathing process increases the air curtain velocities improving the PPE efficiency by 32%. This study shows the potential of using a visor with aerodynamic sealing as an infection control barrier for healthcare workers.
The impinging jet ventilation has addressed extensive attention in recent years because it can be used as both cooling and heating modes, which greatly affect the resultant indoor environment like ...thermal comfort and air quality. Previous works have explored the effects of geometrical parameters (e.g., supply duct shape and discharge height) while leaving the ceiling exhaust location unexplored yet. This study aims to investigate the effects of ceiling exhaust location on thermal comfort and mean age of air (MAA) under such impinging jet cooling pattern. Firstly, two locations both far from a heating source are compared (i.e. exhaust located on the same side as or the opposite of the inlet, named Room-U and Room-D respectively). Secondly, locating the exhaust right above the heating source (named Room-M) is compared with Room-U and Room-D. The results indicate that Room-M has the least neutral predictive mean vote (PMV) and the longest MAA. Thirdly, the steps to locate ceiling exhaust near the thermal plume are proposed and verified by applying them to improve the PMV of Room-M further (including a case with three heat sources). PMV decreases from 0.35 of Room-M to 0.28 of the further improved under the case with a sole source located on the floor center, and decreases from 0.88 of Room-M to 0.84 of an improved case when there are three sources uniformly distributed on the floor. In summary, locating the ceiling exhaust near the thermal plume removes heat efficiently in respect of cooling while locating it on the ceiling center may result in a longer age of air.
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This study proposed a method for reconstructing three-dimensional (3D) non-axisymmetric temperature fields in water formed by mixed convection surrounding a small heating sphere. The proposed method ...is based on the temperature dependence of the absorption coefficient of water at a wavelength of 1150 nm in the near-infrared (NIR) region. The absorbance images of a 10-mm-thick water cell containing a 1-mm diameter steel sphere heated via electromagnetic induction were acquired using a two-orthogonal-direction NIR imaging system. The 3D reconstruction was implemented by applying a non-axisymmetric inverse Abel transform to the absorbance images. In addition, particle tracking velocimetry (PTV) was applied to the same images to visualize and quantify the flow field. The results indicated that the temperature distribution within the plume was distorted compared to an axisymmetric one, and the plume shape, length, and angle were dependent on the forced flow and heating power. Further, employing a thermal balance model with temperature distributions, the heat production rates were determined and discussed based on the plume characteristics. The PTV results revealed a mixed convection field inconsistent with the plume shape, which was also verified by comparison with numerical simulations.
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•Simultaneous measurement of temperature and flow fields employing two-orthogonal-direction near-infrared imaging method.•Reconstruction of three-dimensional non-axisymmetric laminar thermal plumes.•Determination of heat production rate in the sphere.•Particle tracking velocimetry using near-infrared absorbance images.
•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.
Wearable devices have been introduced for research purposes and especially for environmental monitoring, with the aim of collecting large amounts of data. In a previous study, we addressed the ...measurement reliability of low-cost thermohygrometers. In this study, we aim to find out how human thermal plume could affect the measurement performance of thermohygrometers. For this purpose, we used a Do-It-Yourself device that can be easily replicated. It consists of 10 iButtons with 3D-printed brackets to position them at different distances from the body. The device was attached to the user’s belt in a seated position. We considered two scenarios: a summer scenario with an air temperature of 28 °C and a clothing thermal resistance of 0.5 clo and an autumn scenario with an air temperature of 21 °C and a clothing thermal resistance of 1.0 clo. The results show that the proximity of the measurement station to the body significantly affects the accuracy of the measurements and should be considered when developing new wearable devices to assess thermal comfort. Therefore, we recommend that at least two thermohygrometers be considered in the development of a new wearable device if it is to be worn on a belt, with one positioned as close to the body as possible and the other at least 8 cm away, to determine if and how the standard thermal comfort assessment differs from the user’s personal perception and whether spatial proximity might also play a role.
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