Chemical tracer measurements

As of this writing, it has not been possible to use the seismic data which defines the volume of the reservoir to also determine the joint stmcture. Extended flow testing is the most direct measure of the efficiency and sustainabiUty of energy recovery from the reservoir. The use of chemical tracers in the circulating fluid can also provide valuable supporting data with regard to the multiplicity of flow paths and the transit time of fluid within the reservoir (37). 

Given k fit) for nny reactor, you automatically have an expression for the fraction unreacted for a first-order reaction with rate constant k. Alternatively, given ttoutik), you also know the Laplace transform of the differential distribution of residence time (e.g., k[f(t)] = exp(—t/t) for a PER). This fact resolves what was long a mystery in chemical engineering science. What is f i) for an open system governed by the axial dispersion model Chapter 9 shows that the conversion in an open system is identical to that of a closed system. Thus, the residence time distributions must be the same. It cannot be directly measured in an open system because time spent outside the system boundaries does not count as residence but does affect the tracer measurements. 

Equations 11.1.33 and 11.1.39 provide the basis for several methods of estimating dispersion parameters. Tracer experiments are used in the absence of chemical reactions to determine the dispersion parameter )L this value is then employed in a material balance for a reactive component to predict the reactor effluent composition. We will now indicate some methods that can be used to estimate the dispersion parameter from tracer measurements. 

In order to provide AMS analyses to the broad ocean sciences research community, the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS) was established at Woods Hole Oceanographic Institution (Massachusetts) in 1989. Studies performed there include identification of sources of carbon-bearing materials in the water column and sediment, dating of sedimentary samples, investigations of paleocirculation patterns (e.g., from observations of differences in 14C relative abundances in planktonic and benthic foraminifera, and coral cores and cross sections), as well as studies of modern oceanic carbon cycling and circulation. In fact, much that is known about advective and diffusive processes in the ocean comes from measurements of chemical tracers, such as 14C, rather than from direct measurements of water mass flow. 

Ambient HO measurements have employed both chemical tracer and direct spectroscopic approaches, the latter including both fluorescence and absorbance. The history of ambient HO measurements has been one of uneven success, as might have been expected from the attempt to develop an analytical system for an important but difficult analyte. Nevertheless, real progress has been made, and all three approaches now provide viable alternatives for providing useful ambient HO data. 

Two dynamic alternatives to the static approach have been used in HO calibration and measurement. In the CSTR (continuously stirred tank reactor) approach, air containing the tracer or tracers flows into the reactor to balance the bulk flow out to the HO measuring devices, and the contents are stirred by a fan or other means. The HO chemical tracer is measured in the inlet flow to obtain [T]() and in the outlet flow to obtain [T], Mass balance requires... 

A further important conclusion is that for a given C-curve or residence time distribution obtained from tracer studies, a unique value of the conversion in a chemical reaction is not necessarily obtainable unless the reaction is first order. Tracer measurements can certainly tell us about departures from good macromixing. However, tracer measurements cannot give any further information about the extent of micromixing because the tracer stimulus-response is a first-order (linear) process as is a first-order reaction. 

A tracer usually is a solution of a standardized radionuclide that is an isotope of the analyte radionuclide. With the identical chemical behavior of tracer and analyte, the yield of the tracer, determined radiometrically, represents the yield of the analyte. In this respect, the radioactive tracer has the same function as the stable carrier. Furthermore, for alpha particles of the usual 4-10 MeV energy in a thin source, the ratio of net count rate to activity is the same for the tracer and the analyte, so that the analyte activity is directly calculated from the activity of the tracer and ratio of the net count rates at the peaks of the analyte relative to the tracer, measured with an alpha-particle spectrometer. 

Fluorescent tracer techniques hold the promise of improved accuracy in assessing dermal exposures, as they require no assumptions regarding the distribution of exposure across skin surfaces. However, this approach also has several limitations. First, it requires introduction of the tracer compound into the agricultural spray mix. Secondly, there must be demonstration of a correspondence between pesticide deposition and deposition of the fluorescent compound for the production, such that the fluorescence can indeed be considered a tracer of chemical deposition. Thirdly, range-finding and quality assurance studies may be needed to ensure the accuracy of tracer measurements. Fourthly, when protective clothing is worn by workers, the relative penetration of the pesticide and tracer needs to be characterized. All of these limitations make fluorescent tracer methods technically challenging. 

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... 

Identification of chemical tracers for the wide variety of organic combustion and secondary aerosol sources, which can be used to identify and quantify source contributions to ambient aerosol. For the health effects community, it would especially valuable to have simple indicators of sources, which need not be highly accurate but can be easily measured and used to correlate source contributions with health criteria. 

Irradiation of 1 g. of lithium carbonate in a thermal neutron flux of 1 X 10 neutrons cm. sec. produces approximately 0.5 millicurie of F at the time of removal from the reactor, but larger quantities of lithium carbonate or higher neutron fluxes will yield proportionately higher F activities. The efficiency of the 0 (f,n)F reaction in lithium carbonate is 1.6 X 10 . Decay measurements show that the F samples usually contain less than 0.01% of radioactive contaminants. Chemical tracer work is... 

Conventional Tracers. A survey of the history of environmental science will show that tracers are important tools for the environmental scientist. They have been used to measure flow rates and dispersion coefficients, to follow the movement of materials through the atmosphere, hydrosphere, and biosphere, and to characterize pollutant sources. Three principal types of tracer have been used in environmental science chemical tracers, such as NaCl, KHSO4, and K2CO3 radioactive tracers, such as H, and Br and fluorescent dyes, such as fluorescein, Rhodamine B, and Rhodamine WT. 

In such cases, it may be desirable to reproduce the actual sample with tracers for example, radioactive tracer is added to the roots of the growing vegetation that is to be analyzed. If going to such lengths is not feasible, all portions usually discarded during the testing of the procedure should be analyzed for the radionuclide to check for losses not indicated by chemical yield measurements. 

One can visualize RTD through an experiment with the use of chemical tracers, introducing them at a particular moment or since the beginning of the reaction. This chemical tracer should necessarily be a compound not reactive to the system under study, by measuring its concentration in the reactor outlet. In general, dye compounds are used, but also other materials can be used with conductive or radioactive material properties that can be measured quantitatively. 

Not all mixed valence compounds show intervalence bands. Those that show not the slightest evidence for them are often called class 1. In class 2 intervalence compounds the intervalence-transfer band may well dominate the visible spectrum, swamping the spectra of the individual ions. However, these may be seen the important point is that the different ions retain their chemical individuality. Soluble Prussian blue is a case in point. This contains Fe and Fe bridged by CN ligands. Isotopic tracer measurements show that there is no doubt—the Fe" is bonded to the N atom of the CN ligand and the Fe to the C. If radioactive Fe is used in the preparation and the compound subsequently decomposed, the activity remains in the iron of the same valence state in which it was incorporated. A class 3 also exists, exemplified by the IJ anion, in which it is not possible to associate a unique valence state to individual metal ions typically, but as our example shows, not always, they are structurally indistinguishable. When they form an... 

Reprinted with permission from Ind.Eng. Chem Fundamentals,14> 75-91(1975). Copyright 1975 American Chemical Society, profiles in the bed coupled with hydrodynamic measurements (38,39), selectivity determinations coupled with careful kinetic characterization (36,37), or unsteady state tracer measurements in columns of different scale (40). A comparison between experimental concentration profiles determined by Chavarie and Grace (38) and the three-phase (i.e. bubble, cloud and emulsion) (20) and two phase (19) bubbling bed models appears in Figure 7. 

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