Tracer test

On the laboratory scale, it is usually safe to assume that a batch reactor is stirred to uniform composition, but for critical cases such as high viscosities this could be checked with tracer tests. 

Real reactors deviate more or less from these ideal behaviors. Deviations may be detected with re.sidence time distributions (RTD) obtained with the aid of tracer tests. In other cases a mechanism may be postulated and its parameters checked against test data. The commonest models are combinations of CSTRs and PFRs in series and/or parallel. Thus, a stirred tank may be assumed completely mixed in the vicinity of the impeller and in plug flow near the outlet. 

The distribution of residence times of reactants or tracers in a flow vessel, the RTD, is a key datum for determining reactor performance, either the expected conversion or the range in which the conversion must fall. In this section it is shown how tracer tests may be used to estabhsh how nearly a particular vessel approaches some standard ideal behavior, or what its efficiency is. The most useful comparisons are with complete mixing and with plug flow. A glossary of special terms is given in Table 23-3, and major relations of tracer response functions are shown in Table 23-4. 

The unsteady material balances of tracer tests are represented by linear differential equations with constant coefficients that relate an input function Cj t) to a response function of the form... 

The chief quantities based on tracer tests are summarized in Table 23-4. Effluent concentrations resulting from impulse and step inputs are designated Cg and C , respectively. The initial mean concentration resulting from an impulse of magnitude m into a vessel of volume is C = mfVr- The mean residence time is the ratio of the vessel volume to the volumetric flow rate, t = V fV or t = jo tCg dt/jo Cg dt. The reduced time is t = t/t. 

Comparison of Models Only scattered and inconclusive results have been obtained by calculation of the relative performances of the different models as converiers. Both the RTD and the dispersion coefficient require tracer tests for their accurate determination, so neither method can be said to be easier to apply The exception is when one of the cited correlations of Peclet numbers in terms of other groups can be used, although they are rough. The tanks-in-series model, however, provides a mechanism that is readily visualized and is therefore popular. 

Axial Dispersion and the Peclet Number Peclet numbers are measures or deviation from phig flow. They may be calculated from residence time distributions found by tracer tests. Their values in trickle beds are fA to Ve, those of flow of liquid alone at the same Reynolds numbers. A correlation by Michell and Furzer (Chem. Eng. /., 4, 53 [1972]) is... 

Thierrin J, GB Davis, C Barber (1995) A ground-water tracer test with deuterated compounds for monitoring in situ biodegradation and retardation of aromatic hydrocarbons. Ground Water 33 469-475. 

A sharp breakthrough of tracers in a two-well tracer test is achieved by the following method [1672] ... 

Fenske, R.A., Wong, S.M., Leffingwell, J.T., and Spear, R.C. (1986b) A video imaging technique for assessing dermal exposure. II. Fluorescent tracer testing, Am. Ind. Hygiene Assoc.., 47 771-775. 

Reductions in expiration flow rate are indicative of bronchial disease, such as asthma or bronchitis. Reductions in FVC are due to reduction in the lung or chest volume, possibly as a result of fibrosis (an increase in the interstitial fibrous tissue in the lung). The air remaining in the lung after exhalation is called the residual volume (RV). An increase in the RV is indicative of deterioration of the alveoli, possibly because of emphysema. The RV measurement requires a specialized tracer test with helium. 

Quantification of injection fluids effects to Mindanao Geothermal Production Field productivity through a series of tracer tests,... 

The first and second tracer tests used 20 kgs of sodium flourescein dye in March 1998 and 1 curie of T31 in December 1998. The results of these tests... 

The 2003 tracer tests were conducted in two wells by injecting 400 kg of 1,6 NDS into MT2RD on March 28, 2003 and... 

Tracer test in KN2RD suggests a permeability barrier rather than limited... 

Delfin, F.G. Jr., Malate, R.C.M., Aragon, G.M. 1999. Tracer tests and injection returns at MGPF. PNOC-EDC Internal Report, 1999. 

FIerras, E.B. 2004. The Naphthalene Disulfonate Tracer Test in the Mahanagdong Field, Leyte. Proceedings, 25th Annual PNOC-EDC Geothermal Conference. 2005. 

In the Type III pile, an apparent wetting front created by several artificial rainfall events conducted in late 2006 led to an elevated zone of moisture in the upper 3 m of the pile. Rainfall events late in the summer 2007, linked to two tracer tests, resulted in a wetting front that penetrated to a depth of approximately 8 m. This moisture was subsequently mobilized through the summer 2008 season as the pile warmed above 0°C (Neuner et al. 2009). 

A number of quantities based on tracer tests are used for the... 

Two tests were made on a vessel packed with catalyst particles, (a) A tracer test that led to the RTD... 

An impulse tracer tracer test gave the response represented by given equations. A first order reaction with k = 0.8 is conducted in this vessel. Find conversions by three models (a)... 

A tracer test on a packed vessel with "closed ends" gave the data of the first two columns of the table. Find conversion of a second order reaction with kC0 - 2 in segregated flow (a) with the direct data (b) with a Gamma distribution of the same variance. 

Tracer tests on a packed open end vessel has an RTD with a variance reaction with rate equation r = qf/U+kjjqf)... 

Meinardus, H. W., Jackson, R. E., Jin, M., Londergan, J. T., Taffinder, S., and Ginn, J. S., 1998, Characterization of a DNAPL Zone with Partitioning Interwell Tracer Tests In Nonaqueous-Phase Liquids, Remediation of Chlorinated and Recalcitrant Compounds (edited by G. B. Wickramanayake and E. Hinchee), Battelle Press, Columbus, OH, pp. 143-148. 

Chen, L. and Knox, R. C., 1997, Using Vertical Circulating Wells for Partitioning Tracer Test and Remediation of DNAPLs GroundWater Monitoring Remediation, Summer, pp. 161-168. 

OBSERVATIONS ON TRANSIENT TESTING TECHNIQUES. AN EXAMPLE OF A TRACER TEST... 

Tracer tests are extremely difficult to conduct and process so as to give accurate moments. Most errors are associated either with the start of the transient, where undesired pulses in pressure or flow rate accompany the tracer transient, or they arise from the tail, where small drifts in baseline of the instruments used to detect and record tracer transients mean that high-order moments fail to converge satisfactorily. In practice, experimental moments of higher order than second can seldom be used for parameter extraction Sect. 6 is a brief introduction to alternative techniques for estimating parameters. 

Conventional tracer tests can reveal nothing of the extent of micromixing present in a chemical reactor. In theory, a choice of reacting tracers could be made which would enable the degree of segregation to be determined but, in practical situations, the complexities of such techniques... 

The conversion achieved in most reactors lies between that which would be expected from a PFR or CSTR of the same size. The tanks-in-series model can be used to predict this level of conversion once tracer test data have been recorded and processed. The following extimple illustrates typical calculations. 

Note that, in a laminar-flow tubular reactor, the material on the reactor centre line has the highest velocity, this being exactly twice the average velocity, Q/A, for the whole reactor. This means that, following any tracer test, no response will be observed until the elapsed time exceeds one half of the reactor space time or mean residence time. The following values for 0 and F(0) emphasise the form of the cumulative RTD and the fact that, even up to 10 residence times after a tracer impulse test, 0.25% of the tracer will not have been eluted from the system. 

A pipeline (10 cm I.D., 19.1 m long) simultaneously transports gas and liquid from here to there. The volumetric flow rate of gas and liquid are 60 000 cm /s and 300 cm /s, respectively. Pulse tracer tests on the fluids flowing through the pipe give results as shown in Fig. PI 1.6. What fraction of the pipe is occupied by gas and what fraction by liquid ... 

The second order aqueous reaction A + B R + Sis run in a large tank reactor (V = 6 m ) and for an equimolar feed stream (C o = Qo) conversion of reactants is 60%. Unfortunately, agitation in our reactor is rather inadequate and tracer tests of the flow within the reactor give the flow model sketched in Fig. P12.ll. What size of mixed flow reactor will equal the performance of our present unit ... 

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