Study Of Tracer Dispersion Research Articles

Vertical and horizontal concentration profiles from a tracer experiment in a heterogeneous urban area

An atmospheric tracer dispersion study was conducted in a heterogeneous district of the city of Nantes, France, in May 2010 and June 2012 during the measurement campaigns FluxSAP. Vertical (0–100m) and horizontal (≈300m) profiles were measured at distances of 20 to 1200m from the tracer gas release location. The vertical profiles show vertical mixing occurring progressively with distance: the 0–100m air column is homogenous beyond 600m, whereas at shorter distances a maximum of concentration is observed, either at ground level for distances less than 200m, or at altitude for intermediate distances. Our measurements are compared with the Briggs-urban model which may be used in emergency situations: the model gives coherent results with our measurements in terms of vertical and horizontal dispersion parameters but we observe concentration differences up to an order of magnitude between model and measurements. Based on our results we propose new relationships for the horizontal and vertical dispersion parameters for distances from 0 to 1km. For emission–measurement distances above 1km, differences appear between the trends deduced from our measurements and those of the Briggs-urban model: it will be necessary to acquire data at greater distances, 2000m and more, to verify and validate these trends.

Validation of CALPUFF Applicability within Urban Area

An atmospheric tracer dispersion study known as Urban Meteorological and Tracer Experiment was carried out in Yuzhong County, Gansu province in northwest of China, during October of 2011. By using the observational data, the applicability of CALPUFF model based on Gaussian formula was verified within urban area. The results show that (i) CALPUFF model can reasonably reflect the actual observations on the whole, and the high value centers of tracer concentration was changed with wind direction over the urban canopy layer. (ii) The simulated plume central axis has a bias of 10-15° with observations, and the simulation error is very much big at the single point, especially at the ground.

The Viscoelastic Effect of Polymer on Tracer Dispersion

Polymer flooding works as the main enhance oil recovery method in China, but tracer test interpretation during and after polymer flooding still uses the technology of water flooding. And a lot of problems exposed in the application Experimental study of tracer dispersion in viscoelastic fluid through porous media isreported. We use different viscoelastic non-Newtonian fluid with the same shear shinning properties as the carrier fluid. It is evident that viscoelastic property is also the key factor influences the velocity field and the dispersivity in non-Newtonian fluid. High Peclet number yields the enhancement of the viscoelastic effect on the dispersivity of the tracer. Compared to pure viscous fluid, polymer viscoelasticity may lead to a larger vortex and, thus, a larger sweeping volume and speed field difference which leads to a higher dispersivity.

Effect of blockage of outlet nozzle on fluid flow and heat transfer in continuously cast multistrand billet caster tundish

Shop floor problems like strand breakout, mechanical or electrical failure in the strand or inadequate availability of molten steel from coming ladle sometimes lead to closing one/two strand in a continuous casting unit. Closing any of the outlets affects the flow distribution inside the tundish and so it is important to study which of the outlets should be closed to have proper results in terms of residence time distribution (RTD) and thermal behaviour of the tundish. The present study aims at finding the effect of closing one or two outlets on flow behaviour and heat transfer in a multistrand tundish. Navier–Stokes equation has been solved using standard K–ϵ turbulence model with the help of educational version of computational fluid dynamics software PHOENICS to find the steady state velocity field inside the tundish. Furthermore, tracer dispersion study was carried out using pulse input technique of the tracer to find the RTD curve of the tundish. Mixing parameters, namely ratio of actual to theoretical mean residence time and ratio of mixed volume to dead volume have been found out for different cases when either all the outlets are open or one/two outlets are closed. It was found that closing the near outlet increases the mixing capability of the tundish the most as compared with far or middle outlet. A larger recirculation zone created in the half of the tundish results in better mixing when near outlet is closed. Numerical code was validated against the experimental observation by performing the tracer dispersion study inside a multistrand tundish and reasonably good match between the experimental and numerical results in terms of RTD curves is observed.Des problèmes d’atelier comme la percée du cordon, la défaillance mécanique ou électrique du cordon ou la disponibilité inadéquate de l’acier fondu de la poche d’arrivée mènent quelquefois à la fermeture d’un ou deux cordons d’une unité de coulée en continu. La fermeture de n’importe laquelle des orifices de sortie affecte la distribution de l’écoulement dans le panier de coulée. Il est donc important de déterminer lequel des orifices de sortie devrait être fermé pour avoir des résultats appropriés par rapport au RTD et au comportement thermique du panier de coulée. La présente étude vise à trouver l’effet de la fermeture d‘un ou deux orifices de sortie sur le comportement de l’écoulement et sur le transfert de chaleur dans un panier de coulée à plusieurs lignes. On a résolu l’équation de Navier-Stokes en utilisant le modèle normal de turbulence K-ϵ, avec l’aide de la version éducationnelle du logiciel de CFD PHOENICS, afin de trouver le champ de vitesse à régime constant à l’intérieur du panier de coulée. En plus, on a effectué une étude de dispersion de traceur en utilisant une technique d’entrée de l’impulsion du traceur afin de trouver la courbe de Distribution du Temps de Séjour (RTD) du panier de coulée. On a trouvé le paramètre de mélange, soit le rapport du temps de séjour moyen actuel à théorique et le rapport de volume mélangé à volume mort, pour différents cas où soit que toutes les sorties étaient ouvertes, soit qu’une ou deux sorties étaient fermées. On a trouvé que la fermeture de la sortie la plus proche augmentait davantage la capacité de mélange du panier de coulée par rapport à la sortie la plus éloignée ou à celle du milieu. Une plus grande zone de re-circulation créée dans la moitié du panier de coulée avait pour résultat un meilleur mélange lorsque la sortie la plus proche était fermée. On a validé le code numérique contre l’observation expérimentale en effectuant l’étude de dispersion du traceur à l’intérieur d’un panier de coulée à plusieurs lignes. On a observé une correspondance raisonnable entre les résultats expérimentaux et numériques par rapport aux courbes de la RTD.

Numerical investigation of the effect of transitory strand opening on mixing in a multistrand tundish

In a multistrand, the outlet near the inlet produces short circuiting flow. This leads to the formation of dead zones inside the tundish, and consequently, the mean residence time decreases. In the present study, numerical investigation of mixing inside a delta shaped tundish with sloping boundaries was carried out by solving the Navier-Stokes equation and employing the standard turbulence model. To decrease the dead zone volume inside the tundish, the effect of closing the outlet near the inlet for a small amount of time and further opening it on the mixing behavior of the tundish was studied. The outlets near the inlet were closed for varying amount of time, and the transient analysis of fluid flow and the tracer dispersion study were carried out to find the mixing parameters of the tundish, namely, mean residence time and the ratio of mixed to dead volume of the tundish. An optimum closure time of the near outlet has been found, which yields best mixing inside the tundish. The numerical code was validated against the experimental observation by performing the tracer dispersion study inside a multistrand tundish and the reasonably good match between the experimental and numerical results in terms of residence time distribution (RTD) curves. The results obtained from the present study confirm the strong role of choosing the right time for opening and closing the outlets to get improved characteristics for the fluid flow and mixing behavior of the tundish. The educational version of computational fluid dynamics (CFD) software PHOENICS was used to solve the governing equations and interpret the results in different forms.

Modeling Energy Dissipation in Slag-Covered Steel Baths in Steelmaking Ladles

Physical and mathematical modeling of energy dissipation phenomena in a gas-stirred ladle with, and without, an overlying second-phase liquid have been carried out at relatively low gas flow rate and specific energy input rate. Data from the literature are applied to infer the extent of energy dissipation caused by various mechanisms. An analysis reveals that bubble slippage and friction at the vessel walls dominate energy dissipation in such systems, each contributing roughly one third of the input energy. The remainder is dissipated because of turbulence in the bulk of the liquid, the formation of a spout, and interactions between the upper phase and the bulk liquid when an overlying liquid is present. Remarkably, the overlying liquid despite its small volume (~3 pct to 13 pct of the bulk), is found to dissipate about 10 pct of input energy. To understand the way the total input energy is dissipated via the overlying liquid, flow and mixing studies were carried out with different types of upper phase liquids. Tracer dispersion studies conducted with Petroleum ether as the overlying liquid show reasonably intense flow within the upper phase with no noticeable entrainment around the spout. In contrast, a thick layer of highly viscous upper phase liquid such as mustard oil shows extensive deformation of the upper phase around the spout, but no discernable motion within. However, remarkably, the thickness of the upper phase rather than its physical properties was found to influence bath hydrodynamics and mixing most significantly. A mechanism based on the rerouting of the surfacing plume and the attendant reversal of flow in the vicinity of the spout is advocated to explain energy dissipation caused by the overlying liquid. This finding is rationalized with our experimental results on composition adjustment with sealed argon bubbling (CAS) alloy addition procedures reported more than two decades ago, wherein flow reversal caused by the baffle in the immediate vicinity of the surfacing plume was shown to cause significant energy dissipation, leading to much sluggish flow and slower mixing in the bulk of the liquid, in comparison with an equivalent unbaffled situation.

Vertical Tracer Concentration Profiles Measured during the Joint Urban 2003 Dispersion Study

Abstract An atmospheric tracer dispersion study known as Joint Urban 2003 was conducted in Oklahoma City, Oklahoma, during July of 2003. As part of this field program, vertical concentration profiles were measured at approximately 1 km from the downtown ground-level tracer gas release locations. These profiles showed that the urban landscape was very effective in mixing the plume vertically. In general, the lowest concentration measured along the profile was within 50% of the highest concentration in any given 5-min measurement period. The general slope of the concentration profiles was bounded by a Gaussian distribution with Briggs’s urban equations (stability classes D and E/F) for vertical dispersion. However, measured concentration maxima occurred at levels above the surface, which would not be predicted by Gaussian formulations. Variations in tracer concentration observed in the time series between different release periods were related to changes in wind direction as opposed to changes in turbulence. This was demonstrated using data from mobile analyzers that captured the width of the plume by traveling east to west along nearby streets. These mobile-van-analyzer data were also used to compute plume widths. Plume widths increased for wind directions at larger angles to the street grid, and a simple model comprising adjusted open-country dispersion coefficients and a street channeling component, were used to describe the measured widths. This dispersion dataset is a valuable asset not only for developing advanced tools for emergency-response situations in the event of a toxic release but also for refining air-quality models.

Web site on marine connectivity around Australia

The Commonwealth Scientific and Industrial Research Organisation (CSIRO), with support from the Western Australian Government, has developed an online tool for marine scientists and managers to investigate the largescale patterns of spatial connectivity around Australia that are associated with ocean current transport (Figure l). This tool, referred to as the Australian Connectivity Interface, or Aus‐Connle, is expected to find applications in areas such as tracer dispersion studies (see example by Ridgway and Condie [2004]), larval dispersion and recruitment, and the development of scenarios and preliminary risk assessments for contaminant dispersion in the marine environment.After selecting a region of interest, users can investigate where material carried into that region comes from, or where material originating in that region goes to, over a range of timescales (weeks to months). These connectivity statistics are based on large numbers of particle trajectories (one million at any given time) estimated from satellite altimeter data, coastal tide‐gauge data, and winds from meteorological models ]Condie et al., 2005]. Users can save the results in a variety of formats (CSV, Excel, or XML) and, as an option, may save their sessions by first registering.

Study of tracer dispersion in self-affine fractures using lattice–gas automata

This paper studies the problem of hydrodynamic dispersion of a tracer in a fluid flowing through a two-dimensional rough channel bounded by self-affine surfaces. Changing the surface roughness exponent H, rough walls having different microstructure are obtained. In order to simulate hydrodynamics, a lattice–gas automata modified to introduce two different species of particles is used. In the studied range of Péclet numbers (20–50), the concentration profiles along the channel are well described by Gaussian-type dispersion. A clear enhancement of the dispersion due to roughness is observed. For the studied regime of Péclet numbers, a simple approach is proposed which allows us to interpret the dispersion enhancement in terms of surface roughness. It is shown that the dispersion enhancement in the rough channel is due to the presence of two characteristic lengths, the hydraulic diameter δH which determines the velocity in the channel and the average aperture δav which determines the transverse diffusion length; next shown is that the dispersion in the rough channel varies as D∥∼(δav/δH)2. The values of δH obtained from the dispersion results are compared with those obtained from permeability measures and a good agreement is observed. In the studied domain of Péclet numbers, the roughness exponent H has only a weak influence on the dispersion.

The Effect of Tracer Density on Melt Flow Characterization in Continuous Casting Tundishes. A Modeling Study.

Mathematical and physical modeling have been extensively used to study the fluid flow phenomena taking place in continuous casting tundishes. Tracer dispersion studies are commonly carried out to characterize the overall fluid flow behavior within the tundish. It is shown in this paper that the buoyancy forces introduced by using a tracer whose density is different from that of the fluid in the tundish may have a significant effect on the fluid flow behavior within the tundish. A three-dimensional mathematical model for solving fluid flow equations incorporating the buoyancy force has been developed to study the fluid flow behavior in continuous casting tundishes. Water modeling experiments have also been carried out to verify the mathematical model.

Echo tracer dispersion in model fractures with a rectangular geometry

We report an experimental study of tracer dispersion in model rectangular fractures with rough or smooth walls and with different mean apertures. We use an echo dispersion technique in which tracer is first injected into the fracture and then pumped back through a detector. In a parallel flow regime, echo dispersion combines a geometrical mechanism due to the fracture roughness and a Taylor mechanism related to the parabolic velocity profile between walls. The latter effect is dominant at high velocities and the dispersivity variations with velocity allow one to determine the effective aperture of the fracture. The low-velocity dispersivity limit that should be related to the geometrical characteristics of the roughness was found to be independent of the mean fracture thickness for the two models that were studied. We show experimentally and numerically that velocity variations in the direction perpendicular to the flow lines result in additional dispersion resulting from molecular diffusion of the tracer particles across the flow lines.

Experimental study of tracer dispersion in flow through two-dimensional networks of etched capillaries

The authors analyse experimentally the relation between the length scales characterising the heterogeneity of a porous medium and the tracer dispersion coefficient D at a velocity U. Experiments are performed on two-dimensional lattices of millimetric channels. For a partly connected network with a percolation geometry they find D=Uld log(Uld/Dm)ld is close to the percolation correlation length and much larger than the individual channel size. This variation is in agreement with the Saffman model for mechanical dispersion. Experimental curves are non-Gaussian and no U2 contribution to D associated with zero-velocity zones could be detected because of the long exchange times with them. For a well connected network with channels of variable width, one has D=Uld+U2 tau ;ld is close to the individual channel length, and tau is close to the value for Taylor dispersion in capillary tubes of similar diameter.

Experimental study of tracer dispersion in sintered glass porous materials of variable compaction

Experimental measurements of tracer dispersion in sintered glass samples of variable compaction are reported. The results are compared to measurements in nonconsolidated packings of the same glass beads used to prepare the sintered material. While normal ‘‘Gaussian’’ dispersion is obtained in nonconsolidated samples (37% porosity), clear-cut anomalies (such as dispersion ‘‘tails’’ at long times) are observed in sintered materials even with a very low degree of compaction (34% porosity). Experimental curves are analyzed with a ‘‘capacitance’’-type model. The effective dispersion coefficient increases by a factor of 60 when the porosity decreases from 37% to 14% at higher degrees of compaction. The characteristic exchange time between the low-velocity regions and the main flow varies linearly with the transit time through the sample. These results are interpreted by the presence of inhomogeneities with a size of several grain diameters.

GENERALIZATION AND APPLICATIONS OF TRACER DISPERSION DATA1

ABSTRACT: The U.S. Geological Survey has performed hundreds of time‐of‐travel and tracer dispersion studies in streams and estuaries nationwide. This paper presents an approach to unitizing this type of data to make it more universally usable in predicting the behavior of soluble contaminants entering waterways. Practical application of the superposition principle and of the scalene triangle as an approximation of the response curve from a slug injection of a solute are demonstrated to be a means of simulating the downstream effects of any form of soluble contaminant release.

A tracer dispersion study of the drag-reduction effect in a turbulent pipe flow

Remarkable differences in dispersion of a tracer material injected into turbulent pipe flows of water and water containing as little as 2·5 parts per million by weight of a soluble high-molecular-weight drag-reducing polyoxyethylene additive have been measured. Analysis of the tracer response curves in terms of a simple one-parameter model shows that the observed results are compatible with a drag-reduction mechanism based on thickening of the viscous sublayer adjoining the wall. Other experiments, reported briefly, suggest that polymer adsorption on to the wall is responsible for this thickening.