Understanding the influence of the human body's thermal plume on exhaled airflow is crucial for accurately assessing indoor infection risks. This study employs numerical simulations and a jet ...integral modeling method to investigate the airflow dispersion patterns of a single thermal manikin during sustained expiration. It was found that the thermal plume formed a two-stage evolution in exhaled airflow. Initially, the airflow was weakened by the thermal plume in the horizontal dispersion, and subsequently it was bent due to the entrainment of the surrounding air in the upward dispersion of the exhaled airflow. The thermal plume changes the trajectory and lateral dispersion distance of exhaled airflow. When the exhalation velocity is 1 m/s, the airflow is fully deflected towards the head plume region. When the exhalation velocity is between 1.5 and 2 m/s, the airflow is partially deflected, with only part of the upper airflow deflected towards the head plume region. In addition, it is interesting to note that the plume changes the dispersion trajectory of the exhaled airflow, while still adhering to the distributions of buoyant jet flow. This study suggests that the thermal effect of the human body is a significant factor in characterizing the dispersion of exhalation airflow and aerosols. Considering the thermal plume in indoor infection risk assessment is expected to yield more reliable data for theoretical modeling of respiratory airflow transport.
•Penetration of exhaled airflow from thermal plume was numerically studied.•Equivalent model based on an integral jet model is proposed to modify plume's effect.•A two-stage evolution mode of the exhaled airflow was found with plume considered.•Trajectory and deflection angle of exhaled flow were predicted with plume intensity.
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•Comparative study of human thermal plume under different air supply velocity.•Simulated flow fields agree well with experiment.•Human thermal plume affects the diffusion of ...bacteria-carrying particles.•The range of air supply velocity for effective control of thermal plume is proposed.
In the operating room (OR), ventilation and thermal plumes can affect the distribution of bacteria-carrying particles (BCPs). Especially in the operating microenvironment, the development of human thermal plumes cannot be ignored. Therefore, in this study, six different air supply velocities were used to study human thermal plumes and the diffusion of BCPs. The numerical simulation based on computational fluid dynamics was verified by experiments, and the realizable k-ε turbulence model and Lagrangian particle tracking model were used. The results show that the interaction of the thermal plumes and ventilation significantly affected the diffusion of BCPs in the operating area, which cannot be ignored. The maximum thermal plumes in the ORs are markedly higher than those in other rooms. The strong thermal plumes caused BCPs to reach the operating area and infect the wound of the patient. For most ORs with a vertical unidirectional air supply, ventilation and thermal plumes achieve a good offset when the air supply velocity reaches 0.25 m/s. In addition, increasing the air supply velocity alone cannot effectively control the effect of thermal plumes on BCPs. This study can provide a practical guideline for controlling the diffusion and distribution of BCPs in ORs.
Effective infection prevention and control measures are required in the intensive care units of hospitals, as these areas have a high incidence of nosocomial infections. Adopting proper ventilation ...pattern that is efficient in pollutant removal is important for controlling the spread of infectious diseases. In this study, the computational fluid dynamics (CFD) simulation approach is used to investigate the airflow pattern, fates of respiratory particles, and patients' intake fraction in a four-bed model intensive care unit under three types of ventilation: impinging jet ventilation and two forms of mixing ventilation. The results show that in contrast to mixing ventilation, the airflow trend of impinging jet ventilation is consistent with the thermal plume of the human body. Accordingly, impinging jet ventilation can efficiently remove pollutants at the ceiling level, thereby reducing cross-infection. Our results also show that fine particles are greatly affected by the ventilation pattern, whereas large particles are primarily removed by surface deposition. The maximum intake fraction of susceptible patients under the three types of ventilation are 8.24 × 10−5 (impinging jet ventilation); 4.5 × 10−4 (ceiling air ventilation; a type of mixing ventilation) and 5.3 × 10−4 (side air ventilation; a type of mixing ventilation). Impinging jet ventilation appears to be the most effective ventilation system for removing particles and reducing susceptible patients’ intake fraction under our investigated scenarios, and exhibits great potential as a ventilation method in intensive care units.
•This study first proposes the use of IJV for ICUs to reduce cross-infection.•An appropriate airflow structure efficiently removes fine particles (<20 μm).•Large particles are primarily removed by gravitational deposition.•The removal efficiency of IJV for fine particles can reach twice that of MV.•The highest intake fraction under IJV is 8.24×10-5, while it is 5.3×10-4 under MV.
The interaction between ambient airflow and human thermal plume may affect airflow distribution in human micro-environment and then personal exposure. This study aims to investigate this interaction ...and to determine what dominates personal exposure: ambient airflow pattern or local human thermal plume. A computational fluid dynamics (CFD) method was employed in a downward ventilated room with a standing person below the supply grill. The research has taken into consideration the effects of room height, supply air opening area on the interaction. Results showed that the airflow was dominated by the downward jet from supply grill when the downward jet velocity was higher than high turning point of 0.275 m/s, but was dominated by the upward human thermal plume when the downward jet velocity was lower than low turning point of 0.075 m/s in the Case where room height is 2.7 m and supply air opening size is 0.6 m × 0.6 m. Dual steady flows were found when the downward jet velocity was between low and high turning point in the same case, indicating that the airflow pattern was determined by initialized airflow field with same boundary conditions. Besides, a higher downward jet velocity, larger air supply opening area and lower height were more likely to produce downward airflow pattern. This study may help to develop appropriate ventilation strategies to reduce personal exposure and save energy.
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•Supply air velocity higher than high turning point downward jet dominates airflow.•Supply air velocity lower than low turning point thermal plume dominates airflow.•Supply air velocity between low and high turning points, dual solutions were found.•Both room height and supply area had significant impacts on multiple solutions.
Solar radiation plays a crucial role in the formation of sea-land breeze (SLB) circulation in coastal areas, and the SLB circulation in turn influences the atmospheric diffusion of pollutants in ...coastal cities. Therefore, the characteristics of the SLB and its impacts on the pollutant distributions in Shanghai, China, are numerically investigated for three (low, medium, and high) daily solar radiation intensities (DSRIs). The results show that the pollutant dispersion is affected by both the horizontal flow of SLB circulation and the vertical thermal plume (TP). The SLB only transports pollutants within the near-ground layer, while TP removes pollutants from the boundary layer and then improves near-ground air quality. Both the intensities of the SLB and TP increase with the increase of DSRI, however, the relative strength of the two are different at different DSRIs. When the DSRI is high (28.35 MJ/m2/day) or low (9.45 MJ/m2/day) during the daytime, the sea breeze (SB) is much stronger than the TP, so the prevailing flow direction on the land is horizontal, causing large amounts of pollutants to be blown inland. For the medium DSRI (18.90 MJ/m2/day), the TP is more powerful in the early stage of the SB period, so the airflow across the land is dominated by the rising TP. Pollutants are mainly transported to the upper atmosphere and the best air quality can be achieved in the residential region. At night, the worst air quality occurs at low DSRI, because when the DSRI is low, the speed of the land breeze is also low and this decelerates the diffusion of pollutants to the sea by the wind.
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•Effect of daily solar radiation intensity (DSRI) on the sea-land breeze (SLB) is studied.•Pollutant dispersion patterns for different SLB intensities are compared.•The height of the low-speed region (i.e., pollutant accumulation) depends on DSRI.•Thermal plume facilitates the pollutant vertical transport at medium DSRI.•Pollutants accumulated on the sea surface are re-blown to land only in case of low DSRI.
The purpose of this study was to investigate the influence of large-scale circulation on the flow field in a cabin mockup. The velocity was measured by ultrasonic anemometers (UA). Then, this study ...analyzed the turbulence kinetic energy spectra of the velocity fluctuation signal. The turbulence kinetic energy spectra of the measurement points reflect the flow characteristic of the large-scale circulation in the cabin mockup. The results contribute to the understanding of the role of the thermal plume on the large-scale circulation in the cabin. The large-scale circulation's impact on air quality was also investigated, and the contaminant distribution was measured using tracer gas in the cabin. The two large-scale circulation interactions made the air flow mixing approximately uniform.
•The turbulence kinetic energy spectrum analysis method can reveal the effect of thermal plumes on large-scale circulation.•The thermal plume transmitted energy to the large-scale circulation through the process of circulation entrainment.•The two large-scale circulation interactions made the air flow mixing approximately uniform.
•The interaction of respiratory activities with thermal plume was investigated.•Human subject data were used to verify the accuracy of thermal plumes generated by a thermal manikin.•The direction of ...breathing airflow was visualized under undisturbed conditions.•Nose breathing mode may improve the inhaled air quality in breathing zone.
This study characterized the interaction between human thermal plume and breathing air flow while people are sitting in a quiescent indoor environment. A sitting breathing thermal manikin was developed to mimic a real human, and data from real human subjects was collected to verify the breathing thermal manikin. In this study the velocity and temperature were measured in front of and above the breathing thermal manikin with and without breathing. In addition, the breathing modes through mouth and nose were studied to investigate the influence of breathing mode on the development of thermal plume, respectively. The ambient temperature was set at 23 ± 0.5 °C, and the surface temperature of manikin varied between 33–34 °C. Without breathing, a maximum value of 0.19 m/s was reached at around 35 cm height above the head which was similar with the mouth-breathing case (0.19 m/s) and higher than the nose breathing case (0.17 m/s). However, the two breathing mode would mitigate the thermal gradient and lower the maximum velocity and had little influence on the height of maximum velocity. Above the manikin's head, non-breathing thermal manikin can produce very similar velocity distribution compared to the breathing modes. But the velocity above the head in the non-breathing case reported the highest maximum value and developed faster to reach the maximum velocity. Breathing through the nose had much more impact on thermal plumes around manikin than breathing through the mouth, even change the flow direction.
Adjacent near-wall heat sources are widely used in indoor environments. It is important to investigate the particle deposition under the influence of coupled thermal plumes arising from adjacent ...near-wall heat sources to improve indoor air quality and control harmful particle deposition. Thus, this study scrutinizes the behavior of thermal plumes emanating from adjacent near-wall heat sources, focusing on the deposition of particles with diameters of 0.3 μm, 0.5 μm, 1.0 μm and 3.0 μm on the wall behind the heat sources. These findings are juxtaposed with the pattern of particles with varying sizes situated above the single near-wall heat source and away from the heat sources. The study delves into the impact of varying surface temperatures and the distance from the wall behind the heat sources, as well as the top surface of the heat source, on particle deposition in 29 distinct cases. The results indicate that the deposition velocity of particles with the same size is highest above the adjacent near-wall heat sources, followed by that of a single near-wall heat source, and finally, locations away from the near-wall heat source. Also, the decay rate loss coefficient of particles with the same size above the adjacent near-wall heat sources increases with a decrease in the distance of the heat sources from the wall behind them, an increase in the temperature of the heat sources, and a reduction in distance from the top surface of heat sources.
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•The particle deposition under twenty-nine cases with diferent heat sources configurations were studied experimentally.•The adjacent near-wall heat sources accelerated the particle deposition more significant than single near-wall heat source.•The β above adjacent near-wall heat sources decreases as the distance between the heat source and the back wall increases.
The solar radiation can heat the building outer surface, and then cause the upward natural convection flows adjacent to the wall. This phenomenon is especially obvious on a windless sunny day. The ...near wall thermal plume can drive gaseous pollutants released from lower floors to upper floors. Combined with the effect of ambient approaching wind, the transmission routes will be very complicated. The paper aims to investigate the airflow patterns and pollutant transmission within a building under the effects of wind and thermal forces. A hypothetical twenty-storey slab-shape high-rise building in Shanghai with single-sided natural ventilation is set as the research object in the present study. The intensity of solar radiation on a typical day during transition season is theoretically analysed. The temperature difference between the heated building envelope and the ambient air is calculated by a simplified heat balance model. Finally, the tracer gas method is employed in the numerical simulation to analyse the influence of the wind and wall thermal plume flow on the inter-flat pollutant transmission characteristics. The results show that, the temperature difference between sunward and shady side wall is about 10 K at noon on the designate day. When the source is set as a point with steady intensity and the buoyancy is stronger than or approximately equivalent to the wind, the reentry ratio of the flat immediately above the source can be around 25%.
•The impact of solar radiation on pollutant transmission is considered.•The interactive effects of wind and buoyancy forces on pollutant transmission are investigated.•The differences of inter-flat transmission characteristics between thermal and isothermal conditions are compared.
A survey around a recently-fueled MMRTG in the terrestrial atmosphere finds a warm air plume with a characteristic updraft velocity of ~1 m/s and a temperature rise of ~4 K. Additionally, a roughly ...hundredfold enhancement in ion density to ~70,000/cm3 in the vicinity (<~1 m) of the generator was observed: air electrical conductivity was measured to be ~10−13 S/m. No evidence of ozone production was detected. These observations inform the electrical charging environment and possible local perturbation to meteorological measurements on Mars or Titan on MMRTG-powered landers or rovers. On Mars, the effects of any electrical conductivity enhancement are likely small, but on Titan they may be significant.
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•In-situ measurements of heat plume and ionization by a radioisotope generator.•Atmospheric electrical conductivity is enhanced by ~100x near generator.•Effects on Mars or Titan lander measurements are discussed.•Titan conductivity enhancement is significant but very localized.
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