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.
This study numerically investigated the thermal effect of human body on the time-dependent dispersion of cough droplets with evaporation process. The thermal flow of human body was imitated using a ...3D thermal manikin with real body features, while a recent developed multi-component Eulerian-Lagrangian approach was used to address the effects of inhomogeneous temperature and humidity fields on droplet evaporation. By comparing the results yielded without and with the human body heat, the outcomes demonstrated strong impact of human body heat on the droplets mass fraction and local air velocity distributions. Inspirable droplets could potentially drop into respirable droplets by evaporation, although the evaporation rate was not significantly affected by body heat. The thermal effect of human body revealed its vital impacts on the time-dependent droplets dispersion. Due to the buoyancy driven thermal flow, both the vertical velocity and displacement of small droplets (≤20 μm) were completely reversed from descending to ascending, while the deposition time of large droplets (≥50 μm) were significantly delayed. With the reduced droplet size by evaporation and droplets lifted into breathing zone by human thermal effect, the inhalability and infection risks of cough droplets would be much higher in real occupied indoor spaces.
•Inspirable droplets could drop into respirable droplets through evaporation process.•Human body heat strongly affects the local droplets mass fraction.•Evaporation rate is not sensitive to human body heat but to the RH and droplet size.•Cough droplets could be lifted to breathing zone by buoyancy driven thermal flow.•Human thermal effect promotes evaporation process by delaying droplets deposition.
•Experimental-numerical study on the transmission of bacteria-carrying particles.•Clean air is the result of the interaction between thermal plume and ventilation.•The performance of four ventilation ...systems was compared.•Temperature-controlled airflow ventilation is effective ventilation.
During surgery, the release of bacterial-carrying particles (BCPs) by surgeons is one of the major pollution sources in operating rooms (ORs), which may cause surgical site infection (SSIs) or health problems. The human thermal plume emitted by the human body may affect the airflow in the surgical micro-environment, leading to the further spread of BCPs. Therefore, this paper aimed to evaluate and compare the diffusion of human thermal plume and BCPs under the design conditions of four ventilation systems (vertical laminar airflow ventilation (VLAF1), horizontal laminar airflow ventilation (HLAF), vertical laminar airflow ventilation (VLAF2), and temperature-controlled airflow ventilation (TAF)). The experiments of airspeed measurements and biological particle emission were carried out in a standard vertical laminar ventilation operating room. Computational fluid dynamics (CFD) was used to extend the investigation of the different ventilation systems. In summary, both the VLAF and TAF systems were able to interact effectively with the human thermal plume, and the TAF ventilation system was superior to the other three systems in reducing BCPs levels in the air of the operating room. The TAF system was able to control the BCPs concentration in the surgical area to 20 CFU/m3. The interaction between human thermal plume and ventilation plays an important role in the clearance of BCPs in the operating room, so it is significant to systematically compare the performance of different ventilation systems.
The prediction of heat transfer in natural convection is crucial for various engineering applications, including building heating and natural ventilation. CFD study of heat transfer in elements with ...complex geometries, like radiators, increase the computational effort and could turn inviable the study of natural ventilation in large rooms with heating radiators. This study aimed to develop a CFD methodology and validate a simplified model to study natural convection and plumes above heat sources like heating radiators. The model uses porous media to simulate heat sources without compromising thermal plume development in large spaces. It enables cost-effective exploration of solutions, reducing computational costs while accurately modelling thermal plume effects. The CFD model was validated using a full-scale model experimental, ensuring its accuracy and reliability. The experimental measurements showed consistent evolutions for inlet and outlet water temperatures, indicating stable heat transfer processes. The study includes 5 heating scenarios in which the inlet and outlet water temperature (Ti/To) is varied, namely: 64/58 °C, 67/41 °C, 73/68 °C, 50/35 °C, and 39/29 °C. With the experiments and the CFD results, it was also concluded that the air temperature and velocity profiles in radiators configured in parallel are asymmetrical. The CFD simulations with the simplified model incorporating a porous medium demonstrated the effectiveness of the proposed methodology. Notably, the computational time for the simplified model was reduced by approximately 70 % compared to the detailed model. The developed CFD methodology has potential applications in optimizing natural ventilation systems for different radiators and environmental conditions, contributing to energy efficiency and occupant comfort.
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•Simplified Porous Media model predicts thermal plume in large spaces.•Rigorous validation of CFD model's using comprehensive full-scale experimental data.•Results with less the 15 % error comparing experimental to simplified CFD model.•Simplified Model reduces computation time by 70 % versus detailed model.
Groundwater Heat Pumps (GWHPs) are increasingly adopted for air conditioning in urban areas, thus reducing CO2 emissions, and this growth needs to be managed to ensure the sustainability of the ...thermal alteration of aquifers. However, few studies have addressed the propagation of thermal plumes from open-loop geothermal systems from a long-term perspective. We provide a comprehensive sensitivity analysis, performed with numerical finite-element simulations, to assess how the size of the thermally affected zone is driven by hydrodynamic and thermal subsurface properties, the vadose zone and aquifer thickness, and plant setup. In particular, we focus the analysis on the length and width of thermal plumes, and on their time evolution. Numerical simulations are compared with two simplified methods, namely (i) replacing the time-varying thermal load with its yearly average and (ii) analytical formulae for advective heat transport in the aquifer. The former proves acceptable for the assessment of plume length, while the latter can be used to estimate the width of the thermally affected zone. The results highlight the strong influence of groundwater velocity on the plume size and, especially for its long-term evolution, of ground thermal properties and of subsurface geometrical parameters.
The compositional models currently used for cough droplet transport and dispersion simulations typically consider water and inorganic salts, ignoring the organics in the droplets. In this study, an ...organics-ignoring two-composition model and an organics-containing three-composition model of cough droplets are investigated. Computational fluid dynamic (CFD) numerical simulations are conducted to compare the dispersions in the two compositional droplet models under the effect of transient cough jets, and the influences of the compositional model on the transport of cough droplets are revealed. The results show that in the range of 5–50 μm, the two compositional droplet models have essentially the same droplet transport. However, in the range of 50–130 μm, the two models show significant differences in terms of the droplet distribution. The three-composition droplet model has a shorter sedimentation time and fewer suspended droplets than the two-composition model. Therefore, to accurately track the transport process of cough droplets, the organics-containing three-composition droplet model should be used in relevant research. The results of this study provide a scientific basis for accurately predicting the risk of cough droplet propagation and contribute to the development of rational epidemic prevention measures.
•Organic is considered in the cough droplet model, and this composition is ignored by most current numerical studies.•The distribution difference between the organics-ignoring and organics-containing droplet models is studied by CFD.•Evaporation processes and the number above the mouth of two compositional droplet models are analyzed.•Two compositional models smaller than 140 μm can evaporate as droplet nuclei before deposition.•The suspension number and settling time of the organics-ignoring model are higher than another (40–130 μm).
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