Tracer flow characterization

It is shown (Fig.3) a comparison of a model solution with the respective solids residence time distribution - the latter obtained by spectrophotometric registration of Ni-Al tracer concentration at the reactor outlet.From this and other curves generated by a computer it has been concluded that solids move essentially in backmixed flow,characterized by both liquid interstage backflow rates and solids settling velocities. 

Dunn et al. (D7) measured axial dispersion in the gas phase in the system referred to in Section V,A,4, using helium as tracer. The data were correlated reasonably well by the random-walk model, and reproducibility was good, characterized by a mean deviation of 10%. The degree of axial mixing increases with both gas flow rate (from 300 to 1100 lb/ft2-hr) and liquid flow rate (from 0 to 11,000 lb/ft2-hr), the following empirical correlations being proposed ... 

Schiesser and Lapidus (S3), in later studies, measured the liquid residencetime distribution for a column of 4-in. diameter and 4-ft height packed with spherical particles of varying porosity and nominal diameters of in. and in. The liquid medium was water, and as tracers sodium chloride or methyl orange were employed. The specific purposes of this study were to determine radial variations in liquid flow rate and to demonstrate how pore diffusivity and pore structure may be estimated and characterized on the basis of tracer experiments. Significant radial variations in flow rate were observed methods are discussed for separating the hydrodynamic and diffusional contributions to the residence-time curves. 

Glaser and Lichtenstein (G3) measured the liquid residence-time distribution for cocurrent downward flow of gas and liquid in columns of -in., 2-in., and 1-ft diameter packed with porous or nonporous -pg-in. or -in. cylindrical packings. The fluid media were an aqueous calcium chloride solution and air in one series of experiments and kerosene and hydrogen in another. Pulses of radioactive tracer (carbon-12, phosphorous-32, or rubi-dium-86) were injected outside the column, and the effluent concentration measured by Geiger counter. Axial dispersion was characterized by variability (defined as the standard deviation of residence time divided by the average residence time), and corrections for end effects were included in the analysis. The experiments indicate no effect of bed diameter upon variability. For a packed bed of porous particles, variability was found to consist of three components (1) Variability due to bulk flow through the bed... 

Dye structures of passive tracers placed in time-periodic chaotic flows evolve in an iterative fashion an entire structure is mapped into a new structure with persistent large-scale features, but finer and finer scale features are revealed at each period of the flow. After a few periods, strategically placed blobs of passive tracer reveal patterns that serve as templates for subsequent stretching and folding. Repeated action by the flow generates a lamellar structure consisting of stretched and folded striations, with thicknesses s(r), characterized by a probability density function, f(s,t), whose... 

TFSA-WATERFLOOD PILOT. A 36 acre (1.14 x lO m2) TFSA-waterflood pilot was recently conducted in the Torrance Field in the Los Angeles Basin of Southern California. To characterize the fluid floi patterns within the pilot, an interwell chemical tracer study was conducted with sodium thiocyanate. Results of the tracer study are shown in Table IV. Only 61.6 % of the injected tracer was recovered in the produced fluids, indicating that as much as 38.4 % of the injected fluids were flowing out of the pattern. Furthermore, since only 1604 bbl/d (255 m3/d) of brine was injected into the pattern, as much as 75.9 % of the total fluids produced by pilot wells were from outside the pattern. 

Fluid flow patterns within the pilot pattern were characterized by an interwell chemical tracer study which showed that as much as 38.4 % of the fluids injected into the pilot flowed out of the unconfined pattern and 75.9 % of the produced fluids are from outside the pattern. 

If it is suspected (or known) that the plug flow assumption does not hold, a separate tracer study is needed to characterize the flow distribution within the pipes. These data are then used to adjust both the concentration and the sampling time, as required. If the nature of flow and mixing in the vessel is independent of the flow characteristics in the pipes, then the o1 curve for the vessel may be calculated from... 

For isothermal, first-order chemical reactions, the mole balances form a system of linear equations. A non-ideal reactor can then be modeled as a collection of Lagrangian fluid elements moving independe n tly through the system. When parameterized by the amount of time it has spent in the system (i.e., its residence time), each fluid element behaves as abatch reactor. The species concentrations for such a system can be completely characterized by the inlet concentrations, the chemical rate constants, and the residence time distribution (RTD) of the reactor. The latter can be found from simple tracer experiments carried out under identical flow conditions. A brief overview of RTD theory is given below. 

If a pulse of tracer is injected into a flowing stream, this discontinuity spreads out as it moves with the fluid past a downstream measurement point. For a fixed distance between the injection point and measurement point, the amount of spreading depends on the intensity of dispersion in the system, and this spread can be used to characterize quantitatively the dispersion phenomenon. Levenspiel and Smith (L16) first showed that the variance, or second moment, of the tracer curve conveniently relates this spread to the dispersion coefficient. 

PET offers the possibility to quantitatively measure the myocardial blood flow (MBF). MBF tracers can be divided into two groups. The first group is freely diffusible and represented by [ 0]H20. These tracers do not show any specific absorption and their distribution is completely determined by diffusion. Consequently, the measurement of the MBF is based on the first-pass extraction and clearance data. Because of the low heart-to-blood radioactivity ratio, the freely diffusible tracers provide myocardial images with low signal-to-background ratios. The second class is composed of highly extractable heart tracers. The tracer p NjNHs belongs to this family. These radiolabeled compounds are characterized by a selective extraction and retention in the myocardium. The... 

Rivers are close to the perfect environmental flow for describing the flow as plug flow with dispersion. The flow is confined in the transverse and vertical directions, such that a cross-sectional mean velocity and concentration can be easily defined. In addition, there is less variation in rivers than there is, for example, in estuaries or reactors - both of which are also described by the plug flow with dispersion model. For that reason, the numerous tracer tests that have been made in rivers are useful to characterize longitudinal dispersion coefficient for use in untested river reaches. A sampling of the dispersion coefficients at various river reaches that were... 

The best way to characterize this behavior is by tracer-response techniques. This can identify such ailments as short circuiting, stagnant flow regions, shear forces which decrease droplet sizes and make separation me a difficult, and others. 

For mono-disperse pore size distributions a combination of steady state diffusion and flow permeability measurements can be used to characterize the structural parameters which enable consistent values for tortuosity to be defined. These results can be used to predict the dynamic response of a Wicke-Kallenbach cell to short pulses of a tracer gas having a comparatively high diffusivity and enable a reasonable estimate of the effective diffusion coefficient to be obtained. 

A well-known traditional approach adopted in chemical engineering to circumvent the intrinsic difficulties in obtaining the complete velocity distribution map is the characterization of nonideal flow patterns by means of residence time distribution (RTD) experiments where typically the response of apiece of process equipment is measured due to a disturbance of the inlet concentration of a tracer. From the measured response of the system (i.e., the concentration of the tracer measured in the outlet stream of the relevant piece of process equipment) the differential residence time distribution E(t) can be obtained where E(t)dt represents... 

The ZLC method offers advantages of speed and simplicity and requires only a very small adsorbent sample thus making it useful for characterization of new materials. The basic experiment using an inert carrier (usually He) measures the limiting transport difiiisivity (Do) at low concentration. A variant of the technique using isotopically labeled tracers (TZLC) yields the tracer diffiisivity and counter diffusion in a binary system may also be studied by this method. To obtain reliable results a number of preliminary experiments are needed, e.g. varying sample quality, nature of the purge gas, the flow rate and, if possible, particle size to confirm intracrystalline diffusion control. 

The proportionality of t] to Q/D in both cases and the absence of any dependence on the cross section area of the channel are easy to understand. First, the molecules which are initially near the tube walls reach the surface by diffusion in a short time they are also carried by the laminar flow only a small distance. The layers near the surface are soon depleted, and the resulting steady shape of the concentration profile of the tracer over the radius no longer depends on that profile at the inlet of the channel. Then the probability of deposition per unit length gets constant and only one exponential term must characterize the density profile of the deposit. Second, the respective mean deposition length must be proportional to the flow velocity multiplied by the time of diffusion across the tube section For circular... 

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