Plume Shape Research Articles

Study of steam jet characteristics and regime maps for bevelled spray nozzles exhausting into quiescent water

Steam-water direct contact condensation phenomenon is being widely used in industrial applications due to its rapid heat and mass transfer rates. The present experimental study explores the underlying physics of the steam jet characteristics by condensing supersonic steam exhausting from five different bevelled nozzles into quiescent water tank. Based on the image processing approach, the effects of steam pressure, water temperature and nozzle exit inclination angle on the size and shape of the steam jet have been studied. The dimensionless steam jet length and maximum expansion ratio have been found in the range of 1.18–5.64 and 1.03–2.70, respectively. The results show that the dimensionless penetration length increases with the increase of steam pressure and water temperature, and decreases with increase in nozzle exit inclination angle. Similarly, maximum expansion ratio of steam jet increases with steam pressure, water temperature and nozzle exit inclination angle. It was observed that steam jet exhausting from bevel nozzle undergoes deflection from its nozzle symmetry axis. The deflected angle increases with steam pressure and nozzle exit inclination angle. A theoretical model of steam jet length for bevelled nozzle has also been presented whose accuracy is found to be within ±30% of the experimental data. Additionally, condensation regime diagrams have been proposed on the basis of steam pressure, water temperature and nozzle exit inclination angle. Existence of seven different plume shapes in regime maps have been identified.

MEASUREMENT OF COPPER SOLUTION TRANSPORT IN A SAND COLUMN BY MEANS OF A FIBRE-OPTIC SENSOR AND ANALYSIS OF THE BREAKTHROUGH CURVE

This paper deals with the measurement of copper contaminant migration in soils by means of a fibre-optic sensor operating with yellow light buried in the soil. The resulting breakthrough curve is compared with a numerical analysis using the advection-dispersion equation. In order to examine the copper adsorption properties, a batch experiment was carried out. It was found that the copper adsorption on silica sand follows a Langmuir model at high concentration. The copper dispersion coefficient was estimated from the plume shape, assuming that a Gaussian distribution of concentration is applicable to the copper plumes. It is demonstrated that the measured breakthrough curve is in reasonable agreement with the one calculated from the dispersion coefficient or the longitudinal dispersivity and retardation factor measured by the batch method. The retardation factor is observed to decrease sharply with increasing concentration of copper solution up to 10 (g/L).

Flow characteristic of steam jet condensed into a water pipe flow - a numerical study

• Numerical simulation of steam jet condensation in subcooled water flow is conducted. • Thermal hydraulic parameters of cone and cylinder-cone steam plumes are analyzed. • The total pressure in the centerline reaches maximum at steam volume fraction 0.01. • Heat transfer coefficients based on area and volume of two-phase region are obtained. Gas-liquid two-phase jet condensation has a property of high heat and mass transfer efficiency, thereby its theory and method becoming an urgent requirement for optimization design and safe operation of various industrial processes. Based on the experimental study of steam jet condensation in subcooled water flow in a vertical pipe, we have developed a numerical simulation method of steam-water two-phase jet condensation coupled with thermal phase change model and two-fluid model. Meanwhile, we emphasize on the shape of the steam plume, the distribution of pressure and velocity, and the heat and mass transfer of the two-phase interface. As the steam mass flux increases from subsonic to sonic, the steam plume becomes longer, and its shape transforms from cone to cylinder-cone gradually. The steam volume fraction is close to 0.01 at the end of the two-phase region, where the total pressure in the centerline approaches the total pressure of the water and reaches the maximum. The mass transfer process of steam condensed into liquid mainly occurs in the gas–liquid two-phase region, accompanied by drastic parameter change in pressure and velocity. Under the working conditions of this paper, the heat transfer coefficients based on the interfacial area of the steam plume and the volume of the two-phase region range from 1.71 MW/m 2 K to 3.51 MW/m 2 K, and from 2398.80 MW/m 3 K to 5040.07 MW/m 3 K, respectively.

Water Enhancement of Si Self‐Diffusion in Wadsleyite

AbstractWe investigated the H2O‐content dependence of Si self‐diffusion coefficient in Fe‐free wadsleyite using multi‐anvil experiments at pressures of 19–20 GPa, temperatures of 1573–1873 K, and H2O‐content ranging from ∼10 to 5,300 wt. ppm by the isotopic thin‐film diffusion‐couple method. The 29Si‐doped diffusion profiles were measured by nanoscale secondary ion mass spectrometry in the depth profiling mode. The H2O contents in the samples were analyzed by Fourier transformation infrared spectroscopy. The experimental results show a H2O enhancement of Si diffusion coefficient with a H2O content exponent of 0.8 ± 0.1. The activation enthalpy was found to be 270 ± 40 kJ/mol. The diffusion coefficients in the [100], [010], and [001] directions are indistinguishable. The temperature and H2O‐content dependences of Si diffusion indicate that H2O incorporation dramatically reduces the rheological strength of wadsleyite, whereas temperature has a relatively small effect. The viscosity in the mantle transition zone could be significantly reduced by H2O incorporation in wadsleyite. The viscosity contrast between mantle plumes and surroundings may control the evolution of plume shapes at 410–660 km depths.

Assessing Impacts on Pressure Stabilization and Leasing Acreage for CO2 Storage Utilizing Oil Migration Concepts

Favorable geological storage for CO2 has long been pictured as large anticlines with thick sandstones, similar to oil reservoirs in the petroleum system. Unlike oil, however, stored CO2 does not need to be recoverable, which raises the possibility of using dissolution and residual trapping to augment the capacity of buoyant traps and tap more of the bulk rock volume. The work presented builds on that idea, asking the following question: If we inject CO2 down to a syncline – analogous to the carrier bed in the petroleum system – how would this injection mechanism impact storage capacity and plume shape, migration, and stabilization? To address this question, we built a reservoir model, based on seismic interpretation of Middle Miocene strata, offshore Galveston, Texas. 3-D seismic and well logs were used to characterize key intervals. Reservoirs chosen for modeling are progradational-aggradational sands with mud intercalation. They have a higher degree of heterogeneity than the more conventional reservoirs commonly targeted for CO2 storage. Modeling investigated how far the CO2 plume would migrate under two scenarios: (1) injecting CO2 at the base of the salt withdrawal basin (syncline scenario) and (2) injecting CO2 at the base of the structural closure, similar to a common injection well location for EOR purposes (base scenario). For each scenario, we separately simulated injection of 30 MT of CO2 and 60 MT of CO2 continuously for 30 years and observe the plume and pressure evolution for 100 years after the injection stops. The simulation shows that injecting the CO2 into a syncline limits the vertical migration of CO2, thus making synclinal injection more secure. In the syncline scenario, the geological layer around the injection point is more heterogeneous than the layer in the base scenario; thus, the CO2 tends to migrate laterally. Additionally, in the syncline scenario, the plume does not even reach the upper part of the anticline, allowing us to safely store an additional amount of CO2 into the reservoir. Moreover, the simulation also shows that in the syncline scenario, the times needed for the reservoir to reach its stabilized pressure after the end of injections are faster. To summarize, CO2 injection at the base of a syncline could provide additional storage, increase the safety of the project from the limited vertical plume migration, and expedite plume stabilization, which could result in the decrease of monitoring frequency as the project runs, thus lowering the operating cost of the project in the long run.

Near-infrared measurement of temperature fields formed by mixed convection from a small heating sphere in water

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.

Comparing heat and solute transport in a discrete rock fracture of variable aperture

In this study, we have compared heat and solute transport in a discrete fracture using numerical modeling. Fracture aperture heterogeneity was described using geostatistical properties with fracture aperture means of up to 1000 μm, variances of 10,000 µm2 and isotropic correlation lengths up to 10 m. Groundwater flow in the matrix was assumed to be negligible and flow in the fracture was set to values typical for natural groundwater conditions with velocities less than 100 m/day and associated hydraulic gradients of less than 0.05. A uniform isotropic thermal conductivity of 2 W/m °C was set for the matrix. Based on 50 realizations, three-dimensional and two-dimensional conduction in the matrix and in the fracture, respectively, play an important role in controlling the development and the shape of the thermal plume under natural flow conditions. In contrast, solute transport exhibits limited penetration depth in the matrix. The results of this research indicate that, contrary to solute transport in discrete fracture settings where channeling is sometimes a major contributor to solute migration rates, no significant thermal channeling is observed under natural groundwater flow conditions. The use of tracer experiments or the monitoring of solute transport in fractured rock will not therefore provide a reliable prediction of the migration of heat in the same setting.

Biomass burning nitrogen dioxide emissions derived from space with TROPOMI: methodology and validation

Abstract. Smoke from wildfires is a significant source of air pollution, which can adversely impact air quality and ecosystems downwind. With the recently increasing intensity and severity of wildfires, the threat to air quality is expected to increase. Satellite-derived biomass burning emissions can fill in gaps in the absence of aircraft or ground-based measurement campaigns and can help improve the online calculation of biomass burning emissions as well as the biomass burning emissions inventories that feed air quality models. This study focuses on satellite-derived NOx emissions using the high-spatial-resolution TROPOspheric Monitoring Instrument (TROPOMI) NO2 dataset. Advancements and improvements to the satellite-based determination of forest fire NOx emissions are discussed, including information on plume height and effects of aerosol scattering and absorption on the satellite-retrieved vertical column densities. Two common top-down emission estimation methods, (1) an exponentially modified Gaussian (EMG) and (2) a flux method, are applied to synthetic data to determine the accuracy and the sensitivity to different parameters, including wind fields, satellite sampling, noise, lifetime, and plume spread. These tests show that emissions can be accurately estimated from single TROPOMI overpasses. The effect of smoke aerosols on TROPOMI NO2 columns (via air mass factors, AMFs) is estimated, and these satellite columns and emission estimates are compared to aircraft observations from four different aircraft campaigns measuring biomass burning plumes in 2018 and 2019 in North America. Our results indicate that applying an explicit aerosol correction to the TROPOMI NO2 columns improves the agreement with the aircraft observations (by about 10 %–25 %). The aircraft- and satellite-derived emissions are in good agreement within the uncertainties. Both top-down emissions methods work well; however, the EMG method seems to output more consistent results and has better agreement with the aircraft-derived emissions. Assuming a Gaussian plume shape for various biomass burning plumes, we estimate an average NOx e-folding time of 2 ±1 h from TROPOMI observations. Based on chemistry transport model simulations and aircraft observations, the net emissions of NOx are 1.3 to 1.5 times greater than the satellite-derived NO2 emissions. A correction factor of 1.3 to 1.5 should thus be used to infer net NOx emissions from the satellite retrievals of NO2.

Response of a Small River Plume on Wind Forcing

Wind forcing is the main driver of river plume dynamics. Direction and magnitude of wind determine position, shape, and size of a river plume. The response of river plumes on wind forcing was simulated in many numerical modeling studies; however, in situ measurements of this process are still very scarce. In this study, we report the first direct measurements of frontal movement of a small river plume under variable wind forcing conditions. Using quadcopters, we performed nearly continuous daytime aerial observations of the Bzyb river plume located in the non-tidal Black Sea. The aerial remote sensing was accompanied by synchronous in situ measurements of wind forcing. We assessed spreading patterns of the plume and evaluated movement velocity of its outer border with unprecedentedly high spatial (∼10 m) and temporal (∼1 min) resolution, which was not available in previous studies based on in situ measurements and satellite observations. Based on the collected data, we evaluated the time of response of plume spreading dynamics on changes in wind forcing conditions. The advection velocity of the outer plume border shows linear relation to wind speed with very small response time (10–20 min). The reversal between upstream/downstream plume spreading occurs during several hours under moderate wind forcing conditions. These reversals involve only near-field part of the plume, which cause detachment of the far-field part of the plume. The obtained results are crucial for understanding and simulating spreading dynamics of small river plumes worldwide.

Migration of Co, Cd, Cu, Pb to the groundwater in the area of underground coal gasification experiment in a shallow coal seam in the experimental mine ‘Barbara’ in Poland

A numerical model of inorganic pollutants migration in the area of ​​ underground coal gasification (UCG) reactor in the post-operational phase was constructed in this study. Also the deceleration of migration and the shape of the contaminant plume in individual geological formations of the reactor surroundings, resulting from different values ​​of sorption affinity, were compared. The simulations were carried out for four selected metals (Co, Cd, Cu, Pb), which in relation to the raw coal and post-process char showed different sorption properties. The sorption parameters of the tested systems were determined experimentally on the basis of the Freundlich isotherm equation. The retardation coefficients were calculated and the degree of sorption intensity in hydrogeological media was classified from II (in the cobalt-char and metals-coal systems) to the IV class of sorption intensity (in the copper-char system).The modeling was carried out using the finite element method (FEM) in the COMSOL Multiphysics computing environment in a two-dimensional plane. The simulation of pollutant migration was carried out for the transient state, with the assumed time horizon up to 20 years after the termination of the UCG experiment. The bottom of the cavity formed due to the coal gasification in situ (10 m × 20 m ellipse) was assumed as the source of contamination and the spread of metals in a horizontal plane 200 m long and 200 m wide was analyzed.To compare the extent to which sorption phenomena affect the spread of pollutants, an additional model was constructed, taking into account only the advection–dispersion movement of the contaminant plume. The consequence of sorption interactions for the tested systems was the delay of the contaminant plume migration depending on time since the termination of the gasification process and depending on the distance from the source of pollution. Due to high sorption affinities, the post-process char acts as an effective buffer for inorganic pollutants and slows down the migration of analyzed metals even 20 years after UCG experiment. The greatest slowdown in migration in relation to the velocity of groundwater flow as a result of sorption occurred for copper transport in the char layer.

Deep learning inversion of gravity data for detection of CO2 plumes in overlying aquifers

We developed an effective U-Net based deep learning (DL) model for inversion of surface gravity data on a rectangular grid to predict 2-D high-resolution subsurface CO2 distribution along a vertical cross-section due to CO2 leakage through a wellbore within a deep CO2 storage reservoir. We used synthetic data to model two types of CO2 leakage scenarios: one CO2 plume in a shallow aquifer (single plume case), and two plumes present at different depths (double plume case). The 3-D synthetic plume samples were created by sampling among predetermined CO2 plume depths, saturations, and volumes. The corresponding surface gravity data on a rectangular grid were generated by a 3-D forward model. The U-Net model detected 72% of single-plume samples, and one or both plumes in 75% of double-plume samples. Most of the undetected single plumes have small gravity field strengths below the typical noise level of 5 μGal. This model generated reproducible, reliable predictions with acceptable errors and demonstrated improved spatial resolution over the conventional least-squares inversion. In contrast to the conventional least-squares inversion, which often overestimates the size of its target and underestimates its density, this U-Net model accurately delineated the boundary of a target. Furthermore, this DL inversion detected deep, small, or low saturation CO2 plumes that are often more difficult to resolve with conventional gravity inversion methods. We note the limitations of this feasibility study, including the use of synthetic data with regular CO2 plume shapes, and the prediction of a 2-D plume cross-section rather than the full 3-D plume, as well, we recognize the lower detection fraction for double-plume scenarios. Nevertheless, this study demonstrates that DL gravity inversion is a promising and potentially superior method to conventional least-squares inversion. Our U-Net based deep learning inversion approach may be adapted for inversion of other types of geophysical data. DL inversion can facilitate near real-time monitoring of geologic carbon sequestration to provide site operators with prompt information about subsurface CO2 distribution for risk management and mitigation.

Influence of emission inventory resolution on the modeled spatio-temporal distribution of air pollutants in Buenos Aires, Argentina, using WRF-Chem

The temporal and spatial resolution of the emission inventory included into an air quality model plays a key role in the appropriate representation of air pollution events and background atmospheric chemistry. Here, we use the Weather Research and Forecasting coupled with Chemistry (WRF-Chem v4.0) model to perform high-resolution air quality simulations over the city of Buenos Aires, Argentina, with two different anthropogenic emissions datasets: the High-resolution Emissions Inventory of Argentina (GEAA-AEI) and the Emissions Database for Global Atmospheric Research - Hemispheric Transport of Air Pollution (EDGAR-HTAP). A local optimized configuration considering 3 nested domains with a horizontal grid size of 20 × 20 km, 4 × 4 km, and 1.3 × 1.3 km and the MOZART chemical scheme was used. The model performance for NO2, PM10, PM2.5, and O3 concentrations was validated against measurements from the existing air quality monitoring stations in the Buenos Aires Metropolitan Area (AMBA) during austral fall 2018. Our results show that the daytime concentrations of air pollutants are influenced by the shape and shift of the hourly emissions profile, especially for NO2 where the reduction in nighttime emissions decreased the mean model bias by ∼50%. PM10 and PM2.5 generally satisfied the model performance criteria, but underestimation tended to occur in the GEAA-AEI simulations and overestimation for the EDGAR-HTAP case. Comparison with TROPOMI-derived tropospheric NO2 columns showed a high positive correlation (r > 0.75) and a positive bias. We found large discrepancies between the spatial distribution patterns of the simulations within the innermost high-resolution domain centered on AMBA, mostly in suburban areas where no observations are available. We propose additional monitoring sites to address such differences and determine the size and shape of the main pollutant plume. We conclude that high-resolution air quality modeling is important within underdeveloped or developing South American cities that lack continuous air quality measurements, as it represents a powerful tool in supporting the design of governmental monitoring networks and air pollution mitigation policies.

131Spatio-temporal analysis to assess health effects of landscape fire smoke: an empirical model

Abstract Background Understanding the health effects of smoke from landscape fires (LFs), including wildfires and prescribed burns, is limited due to lack of adequate smoke exposure measures. Methods We used the reported LFs to determine smoke plume shapes from satellite images. Daily remotely sensed fire radiative power, aerosol optical depth, smoke plumes, fire danger rating, venting index and previous day PM 2.5 were then used to estimate smoke-related particulate matter 2.5 (PM2.5). A population based time series design was used to assess associations between smoke-related PM2.5 and selected adverse health outcomes such as hospital admissions, emergency department visits and ambulance callouts. Results We found a significant dose-response relationship between increased smoke-related PM2.5 concentration and 1% to 5% increase for total emergency department attendances and total hospital admissions on the same day and the lag effects of 3 days where the PM2.5 was at medium level (95-98th percentile) and high level ( > =99th percentile) compared to the low level (<95th percentile). There was also 1% to 25% increased risk for individuals who were exposed to high level LF smoke with selected respiratory and cardiovascular diseases in selected health care utilisations. Conclusions Exposure to LF smoke at a high level was spatio-temporally associated with a wide range of adverse respiratory and cardiovascular diseases in selected health care utilisations. Key messages

Small pigmented eukaryote assemblages of the western tropical North Atlantic around the Amazon River plume during spring discharge

Small pigmented eukaryotes (⩽ 5 µm) are an important, but overlooked component of global marine phytoplankton. The Amazon River plume delivers nutrients into the oligotrophic western tropical North Atlantic, shades the deeper waters, and drives the structure of microphytoplankton (> 20 µm) communities. For small pigmented eukaryotes, however, diversity and distribution in the region remain unknown, despite their significant contribution to open ocean primary production and other biogeochemical processes. To investigate how habitats created by the Amazon river plume shape small pigmented eukaryote communities, we used high-throughput sequencing of the 18S ribosomal RNA genes from up to five distinct small pigmented eukaryote cell populations, identified and sorted by flow cytometry. Small pigmented eukaryotes dominated small phytoplankton biomass across all habitat types, but the population abundances varied among stations resulting in a random distribution. Small pigmented eukaryote communities were consistently dominated by Chloropicophyceae (0.8–2 µm) and Bacillariophyceae (0.8–3.5 µm), accompanied by MOCH-5 at the surface or by Dinophyceae at the chlorophyll maximum. Taxonomic composition only displayed differences in the old plume core and at one of the plume margin stations. Such results reflect the dynamic interactions of the plume and offshore oceanic waters and suggest that the resident small pigmented eukaryote diversity was not strongly affected by habitat types at this time of the year.

First Concurrent Observations of NO2 and CO2 From Power Plant Plumes by Airborne Remote Sensing

AbstractCombined NO2 and CO2 observations have the potential to constrain the identification of the locations and strength of urban CO2 emissions, in particular, point sources such as power plants. We report the first results of airborne spectroscopic NO2 and CO2 observations over an urban area in Japan in February 2018. Inversed emission rates of two stacks of the coal‐fired power plant for CO2 showed relatively good agreement with those estimated by a bottom‐up inventory—the Regional Emission inventory in ASia (REAS) v3.1—within −7% to 40% because the plume shapes were well identified due to constraint by NO2 measurements. The estimated NOx emission rates showed discrepancies more than 80% with those estimated by the REAS v3.1, mainly due to the uncertainties in activity data and emission factors, or in the greatly varying NO/NO2 ratios in fresh plumes, which warrant further investigations when estimating NOx emissions from satellite NO2 observations on km‐scales.

Dynamics of laser produced plasma from foam targets for future nanolithography devices and X-ray sources

Foam targets are expected to be more efficient candidates than solid targets for laser produced plasma (LPP) for extreme ultraviolet (EUV) and X-ray radiation sources due to the expected plasma conditions that can be optimized regarding plasma opacities, volumetrics heating effects, and the produced ions debris characteristics. In this paper, a comparison of ion dynamics between low-density foam and solid Ni plasma was systematically investigated at CMUXE. The foam Ni target (density 0.6 g/cm3) and solid Ni target (density 8.9 g/cm3) were irradiated with 1064 nm Nd:YAG laser in vacuum. A Faraday cup (FC) was used to record the ion flux and time-of-flight (TOF) signals. A lower and wider TOF signal was observed for foam Ni plasma on the time scale. The average ion energy and peak of the TOF signal of solid Ni plasma were much higher than that of the foam Ni plasma. However, the total charge values between foam and solid Ni plasma were comparable indicating a more volumetric absorption of laser energy for foam Ni. The average ion energy and peak of the TOF signal of solid Ni showed a stronger angular and laser energy dependence than that of foam Ni. The plume shape of the solid Ni plasma appeared as an oblong ellipse at each time, while that of foam Ni plasma tended to be more circular, especially at early times. The results of mass ablation rate were consistent with the FC signals and showed a more intense plasma shielding for solid Ni.

Numerical investigation on submerged steam jet condensation in subcooled water flow in a restricted channel with the presence of non-condensable gas

Submerged steam jet in subcooled water flow is widely used in many industrial processes. When non-condensable gas is involved in the steam jet, the mechanisms of heat and mass transfer become more complicated due to the added non-condensable components and the strong effect of water turbulence. In present work, a three-dimensional steady numerical simulation is conducted to study the steam jet condensation in subcooled water flow in a vertical pipe with the presence of non-condensable gas based on inhomogeneous multiphase model. The effects of non-condensable gas on steam plume shapes, distributions of static pressure, velocity, temperature and heat transfer characteristics are investigated. As air contents increases, steam plume transforms from ellipsoidal shape to divergent shape and the peak value of static pressure decreases. The mechanism of the peak phenomenon of static pressure at the end of steam plume is revealed to be the squeezing effect of water flow towards the nozzle axis. Since air mass fraction rises to 1%–9%, the average heat transfer coefficient declines by 24.5%–54.9%. The local heat transfer coefficient is evaluated by using thermal equilibrium model at phase interface. Numerical results show a self-intensifying effect on heat transfer, indicating that the distribution of local heat transfer coefficient is highly similar to that of water turbulent kinetic energy near phase interface, decreasing first and then rising to a high level at the tail of steam plume. The local heat transfer coefficient and steam condensation rate decrease with air concentration and increase with water mass flow rate.

Quantifying SARS-CoV-2 Infection Risk Within the Google/Apple Exposure Notification Framework to Inform Quarantine Recommendations.

Most early Bluetooth‐based exposure notification apps use three binary classifications to recommend quarantine following SARS‐CoV‐2 exposure: a window of infectiousness in the transmitter, ≥15 minutes duration, and Bluetooth attenuation below a threshold. However, Bluetooth attenuation is not a reliable measure of distance, and infection risk is not a binary function of distance, nor duration, nor timing. We model uncertainty in the shape and orientation of an exhaled virus‐containing plume and in inhalation parameters, and measure uncertainty in distance as a function of Bluetooth attenuation. We calculate expected dose by combining this with estimated infectiousness based on timing relative to symptom onset. We calibrate an exponential dose–response curve based on infection probabilities of household contacts. The probability of current or future infectiousness, conditioned on how long postexposure an exposed individual has been symptom‐free, decreases during quarantine, with shape determined by incubation periods, proportion of asymptomatic cases, and asymptomatic shedding durations. It can be adjusted for negative test results using Bayes' theorem. We capture a 10‐fold range of risk using six infectiousness values, 11‐fold range using three Bluetooth attenuation bins, ∼sixfold range from exposure duration given the 30 minute duration cap imposed by the Google/Apple v1.1, and ∼11‐fold between the beginning and end of 14 day quarantine. Public health authorities can either set a threshold on initial infection risk to determine 14‐day quarantine onset, or on the conditional probability of current and future infectiousness conditions to determine both quarantine and duration.

The wind-driven response of the Zambezi River plume along the Sofala Bank: A numerical model study

The Zambezi River plume constitutes a sizable feature in the horizontal distribution of both surface salinity and suspended sediments, and it spreads both downstream and upstream, influencing substantially the coastal ecosystems. Here we present the results of several numerical experiments conducted using the Regional Oceanic Modeling System, to investigate the plume’s response to impulsive wind forcing. The model uses realistic geometry and bathymetry, as well as constant discharges emanated from three point sources. Different wind directions and magnitudes were explored, including a daily oscillating wind field. In the absence of wind forcing, a modest discharge generates a plume that propagates northeastwards trapped to the coast. A constant wind field can alter the plume shape to become either a “coastal current” or a “large bulge”, depending on the predominant wind direction. The “coastal current” characterized by a northeastward (downstream) spreading of the plume reaching up to 180 km was directly related to a downwelling favorable winds. While the “large bulge” characterized by an increased upstream penetration is related to upwelling-favorable winds. Diurnal breezes were effective in transforming the trajectories of surface water particles into ellipsoids, as well as promoting additional mixing of the plume and ambient waters. The realistic wind field can transport plume waters to nearly 120 km downstream, 75 km upstream, and 65 km seaward.

Oil/gas jets in water crossflow: The impact of the droplet size

AbstractDuring undersea oil blowout in crossflow conditions, the oil droplets entrained horizontally which increased the residence time of droplets in the water column. Knowledge of the trajectory of an oil plume is important for predicting the pathways of hydrocarbons and to devise countermeasures. We conducted large-scale experiments in the Ohmsett tank where we released oil from a one-inch vertical orifice that was towed to produce the behavior of a jet in crossflow. The average oil velocity at the orifice was 1.36 m/s and the crossflow velocity was around 0.27 m/s which resulted in a jet-to-crossflow velocity ratio of 5.0. The results were simulated numerically using the Large Eddy Simulation (LES) turbulence model and the mixture multiphase model within the open-source software OpenFOAM. The instruments including ADVs, LISSTs, shadowgraph cameras, holographic camera, and fluorometers were employed. The oil jet released from the nozzle started to meander in the vertical direction most probably due to weak crossflow. The trajectory and meandering behavior of the oil jet, wavy pattern along the leading edge of the jet and column breakup observed in the experiments were captured well with the numerical simulation. The surface breakup just above the orifice created ligaments and droplets downstream of the jet. Larger oil droplets were observed near the upper boundary of the plume due to their higher buoyancy while the smaller droplets were suspended in the water column and they were entrained by water crossflow. This work reveals that different size of droplets determines the overall shape of plumes mostly the upper and lower boundaries of the plume.