Pulse tracer experiment

This provides an important check on the accuracy of the pulse-tracer experiment, since the area under the response curve represents the same quantity, if the tracer is completely accounted for by a material balance. Thus,... 

We describe two approximate methods of determining the value of N in the TIS model from pulse-tracer experiments. One is based on the first moment or mean 0, and the other on the variance a as determined from the tracer data. 

The accompanying table gives values of trace height at various times as read from a recorder for a pulse-tracer experiment (Thurier, 1977). In this experiment 1.5 cm3 of N2 was injected into a stream of He flowing steadily at 150 cm 3 s-1 through a stirred-tank reactor of volume 605 cm3. A thermal conductivity detector was used to compare the outlet stream (N2 + He) with the He feed stream, and the output fiom this as a trace on a recorder is a measure of the concentration of N2 in the outlet stream. 

A pulse-tracer experiment for a particular flow rate in a certain vessel (assume closed ) shows that the first (i) and the second (aj) moments of the RID are 15.4 min and 0.670, respectively. If a pseudo-first-order reaction, A + B products, with fcA = 0.299 min-1 at... 

A system of N continuous stirred-tank reactors is used to carry out a first-order isothermal reaction. A simulated pulse tracer experiment can be made on the reactor system, and the results can be used to evaluate the steady state conversion from the residence time distribution function (E-curve). A comparison can be made between reactor performance and that calculated from the simulated tracer data. 

Use the E curve from a pulse tracer experiment to calculate the first-order conversion. 

The dispersion coefficient can be detennined from a pulse tracer experiment. Here, we will use / and a to solve for the dispersion coefficient D, and then the Peclet number, Pe Here the effluent concentration of the reactor is measured as a function of time. From the effluent concentration data, the mean residence time. and variance, o, are calculated, and these values are then used to determine Dg. To show how this is accomplished, we will write... 

Activity. A comparison of the global rates of CO conversion on a per gram of catalyst or on a per gram of cobalt in the catalyst at 500 K shows that the activities of the chromium- and zirconium-doped catalysts were substantially higher than any of the other catalysts studied. (Specific rates on a per active catalyst site basis (13,21) are not available for these catalysts. Such measurements will be undertaken for the more promising catalysts in the near future (22). Justification for this use of the continuous stirred-tank reactor (CSTR) design equation was provided by pulse tracer experiments (20).) These are followed by the activated carbon-... 

Hee, C.A. et al.. Dissolved organic carbon production and consumption in anoxic marine sediments a pulsed-tracer experiment, Limnol. Oceanogr., 46(8), 1908, 2001. 

McCullough et al heated NO/Ar mixtures to temperatures in the range 1750-2100 K in an alumina flow tube reactor and monitored the fractional decomposition of NO as a function of flow rate (residence time) in the reactor using a commercial chemiluminescent analyzer. Experiments at low temperatures were also performed but the data were excluded because of the influence of surface reactions. The high-temperature central section of the reactor was packed with small pieces of alumina to promote uniform flow, and pulsed tracer experiments were conducted to determine deviations from plug flow. A detailed kinetic and flow model was used, with some simplifications to reduce computing time, to calculate the fractional removal of NO versus flow rate. A... 

Ross (R2) measured liquid-phase holdup and residence-time distribution by a tracer-pulse technique. Experiments were carried out for cocurrent flow in model columns of 2- and 4-in. diameter with air and water as fluid media, as well as in pilot-scale and industrial-scale reactors of 2-in. and 6.5-ft diameters used for the catalytic hydrogenation of petroleum fractions. The columns were packed with commercial cylindrical catalyst pellets of -in. diameter and length. The liquid holdup was from 40 to 50% of total bed volume for nominal liquid velocities from 8 to 200 ft/hr in the model reactors, from 26 to 32% of volume for nominal liquid velocities from 6 to 10.5 ft/hr in the pilot unit, and from 20 to 27 % for nominal liquid velocities from 27.9 to 68.6 ft/hr in the industrial unit. In that work, a few sets of results of residence-time distribution experiments are reported in graphical form, as tracer-response curves. 

Since tracer experiments are used to obtain RTD functions, we wish to establish that the response to a pulse-tracer input is related to (r) or E(0). For this purpose, c(t) must be normalized appropriately. We call c(t), in arbitrary units, the nonnormalized response, and define a normalized response C(t) by... 

In the case of trace metals, adsorption is typically much faster than the time intervals for which it is practically possible to separate the cells. Therefore, in practice, values of kf and kr are most often estimated by assuming that water loss from the hydrated cation is rate-limiting (Eigen-Wilkins mechanism, see Section 4.3.1 above). In some cases, uptake transients can be observed at the start of a short-term uptake experiment or by using pulse-chase experiments for which a metal solution containing a radioactive tracer is replaced by a solution... 

The program is formulated in vector form, allowing for any number of tanks N in the cascade but with all N tanks having an equal volume, V. The function PULSE is used in the program in relation to the tracer experiments, and the calculation of the actual conversion based on the E curve data is made by the program. Instructions on its use are found within the program. 

Array programming is used here which allows the graphing of the axial profile. Closed-end boundary conditions are used for the first and last segments. Also included is a PULSE function for simulating tracer experiments. Thus it should be possible to calculate the E curve and from that the reaction conversion obtained on the basis of tracer experiment. The example CSTRPULSE should be consulted for this. 

Brackets can be set or removed for the pulse of tracer. Set K = 0 to make a tracer experiment with no reaction. ... 

The above example demonstrates that treatment of the basic data by different numerical methods can produce distinctly different results. The discrepancy between the results in this case is, in part, due to the inadequacy of the data provided the data points are too few in number and their precision is poor. A lesson to be drawn from this example is that tracer experiments set up with the intention of measuring dispersion coefficients accurately need to be very carefully designed. As an alternative to the pulse injection method considered here, it is possible to introduce the tracer as a continuous sinusoidal concentration wave (Fig. 2.2c), the amplitude and frequency of which can be adjusted. Also there is a variety of different ways of numerically treating the data from either pulse or sinusoidal injection so that more weight is given to the most accurate and reliable of the data points. There has been extensive research to determine the best experimental method to adopt in particular circumstances 7 " . 

Two types of tracer experiments are commonly employed and they are the input of a pulse or a step function. Figure 8.2.1 illustrates the exit concentration curves and thus the shape of the (f)-curves (same shape as exit concentration curve) for an impulse input. Figure 8.2.2 shows the exit concentration for a step input of tracer. The (r)-curve for this case is related to the time derivative of the exit concentration. 

To determine the model parameters, a minimum of three injection experiments with tracers plus one for each solute have to be carried out. The evaluation of these experiments is sketched in Fig. 6.11, together with the symbols of the measured first moments. The injected signal for all experiments is represented by a rectangular pulse. The first tracer experiment detects the dead time of the plant while the column is replaced by a zero volume connector. The other experiments are carried out with the column in place, using a tracer that cannot get into the pores (Tracerl) and... 

Family of pulses and the Impulse or delta function.. 437 83 CSTR and tracer experiment.. 439... 

Chemical engineers also use this kind of experiment. It can be utilized to great advantage in chemical reactors to find the "residence time distribution" of the reactor, a crucial piece of information which links microscopic flow behavior, that is, fluid dynamics, to measurables of the system, such as chemical conversion and selectivity. For vessels that are not used for reaction processes, but are used for other operations that are also critically dependent upon mixing, this tracer experiment provides a great deal of insight into how the system behaves. We can analyze how a pulse of injected tracer would behave in the well-stirred vessel we have been analyzing here. 

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