As for the RTD study in the gas phase, we have used the method of two injections. The response of the conductimetric probe to the input and output injections, with a Dirac tracer impulse, is shown in figure 6. In order to model the liquid flow, several theoretical models were tested. The liquid flow corresponded to plug flow with axial dispersion as shown in figure 7. [Pg.683]

An RTD study on gas flows in a microchannel reactor specially designed for periodic operation with a y-alumina catalyst deposited on the reactor channels was performed [20]. Argon (in nitrogen) was used as a tracer. The concentration of argon was [Pg.374]

Shetty et al. (1992) studied gas-phase backmixing for the air-water system in bubble-column reactors by measuring RTDs of pulse-injected helium tracer. [Pg.493]

In an often quoted study Overcashier et. al. (156) used inert nonadsorbing tracers and showed that the use of horizontal baffles in the bed allows one to approach the plug flow RTD for the gas. [Pg.172]

Since the RTD of a particular reactor type does not describe its performance uniquely for nonlinear reactions, it is customary to develop flow models for the reactor. The parameters of the model are then determined from tracer studies and the structure of the model is used to calculate reactor performance. [Pg.133]

In the vast majority of experimental studies, the backmixing characteristics of a flowing phase are examined using a -pulse tracer input. For the fixed-bed systems shown in Fig. 3-2, if a perfect pulse input is used, then, as shown by Levenspiel,5 6 the axial dispersion coefficient or the Peclet number can be obtained from the variance of the RTD curve. For example, for a closed system and large extent of dispersion, the variance, it, is related to the Peclet number by the equation [Pg.72]

In studying the mixing characteristics of chemical reactors, a sharp pulse of a nonreacting tracer is injected into the reactor at time t = 0. The concentration of material in the effluent from the reactor is measured as a function of time c(f). The residence time distribution (RTD) function for the reactor is defined as [Pg.256]

If we design a reactor type for which we have no previous experience we have no idea what its RTD may be. We then have several options. We can (i) solve the detailed hydrodynamic model numerically for the actual reactor geometry, (ii) build a hydro-dynamically similar cold model and perform tracer studies to get the RTD or (iii) try to bracket the reactor performance based on some extreme RTDs. The first approach is costly and very difficult to implement for turbulent flows, the third is not accurate enough which leaves only the second approach as the viable one. Prudent designers of new reactor types will follow it. [Pg.130]

This review did not cover extensively the stochastic approach in reactor modeling and in tracer studies interpretation. Some references were given with respect to the work of Shinnar and coworkers (12,31,55,112). Recently this stochastic approach has been pursued extensively by Fan and coworkers (180-183) and the interested reader is referred to it. A promising model towards a generalized RTD for a reactor was also reported by Glasser and Jackson (184). [Pg.175]

Other reactors and uses of tracers. Tracers are used extensively in all other two-phase (gas-liquid, gas-solid, liquid-solid) and three-phase reactor types (gas-liquid-solid, liquid-liquid-solid). Tracers confined to a single phase are used to determine the RTD of that phase and evaluate its flow pattern. Tracers that can be transported from one phase to another are frequently used for evaluation of various rate parameters and transport coefficients such as mass transfer coefficients, particle effective diffusivity, adsorption rate constants, kinetic rate constants, etc. The interpretation of tracer studies in evaluation of the above parameters is always dependent on the selected model for the system. We do not attempt to review this vast literature but will just cite a few examples as good starting points for the interested reader. [Pg.174]

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