Tracer component

All the indices discussed until now are shown in Table 3.2, and the quantitative relationships among the indices are clarified. When one component in the multi-component mixing is treated as the tracer, that is, when the components other than the tracer component are treated without discrimination,... 

Unsteady state diffusion in monodisperse porous solids using a Wicke-Kallenbach cell have shown that non-equimolal diffusion fluxes can induce total pressure gradients which require a non-isobaric model to interpret the data. The values obtained from this analysis are then suitable for use in predicting effectiveness factors. There is evidence that adsorption of the non-tracer component can have a considerable influence on the diffusional flux of the tracer and hence on the estimation of the effective diffusion coefficient. For the simple porous structures used in these tests, it is shown that a consistent definition of the effective diffusion coefficient can be obtained which applies to both the steady and unsteady state and so can be used as a basis of examining the more complex bimodal pore size distributions found in many catalysts. 

The basic equations are derived from a mass balance of a tracer component as follows ... 

Tflp, Tflq Average particle weight of two components p kg X Concentration of tracer component —... 

The coefficient n (or 22) s defined by applying Eq. IV.9 to a three-component system in which the third component is tracer component 1 (or 2) present in vanishingly small quantity. 

The balance contains just two adjustable hydrodynamic parameters, tl l and PeL. The Peclet number is estimated from the separate impulse experiments carried out with the inert tracer (NaCl), while the quantity Tl l is estimated from the kinetic experiments in order to ensure a correct description of the reactor dynamics. The flow pattern of the reactor is characterised by separate impulse experiments with an inert tracer component injecting the tracer at the reactor inlet and measuring in this case the conductivity response at the outlet of the reactor with a conductivity cell operated at atmospheric pressure. In order to get a proper conductivity response, water was employed as the liquid phase. The liquid and hydrogen flow rates should be the same as in the hydrogenation experiments and the liquid hold up was evaluated by weighing the reactor. Some results from the tracer experiments are given in Figure 8.12. 

The first two unenclosed iron-enrichment studies were carried out in 1993 and 1995 in the Equatorial Pacific. In both, nanomolar concentrations of iron were induced in the surface layer by release of iron sulfate, the patches being labeled by SFg addition. The SEg(initial addition of iron, the tracer component was then used as a guide to keep track of the affected patch of ocean. Sampling could be reliably categorized as in or out the patch, even after all the measurable iron had disappeared from solution. In the second study, the main experiment included reseeding the patch with iron, but not tracer, twice after the initial release. Important secondary aims of the tracer component of the experiments have been the study of mixing rates both horizontally in the mixed layer, and vertically across the thermocline. 

Figure 36.3 Concentration profiles after a pulse of tracer component for a gas mixture flowing through an empty tube at a constant volumetric flow rate for two different tube diameters.

Obviously the residence time distribution has consequences for the conversion of a chemical reaction taking place in the fluid, since conversions generally increase with time. A distribution of residence times will generally reduce the conversion (except for reactions of zero order, or of a negative order). The residence time distribution is a physical characteristic of a continuous flow reactor, so that it can be determined by physical measurements. Consider a vessel and a fluid flow passing through it at a constant flow rate, from an entrance to an exit port. The flow conditions in the vessel are not known. By injecting a tracer component into... 

X, number concentration of tracer particles in the i sampling cell (n/N) K number of samples containing tracer components (-)... 

By using a short oligomer as the small-molecule solvent, one can effectively study polymer polymer solvent mixtures in which the two polymers and the small-molecule solvent are chemically identical, differing only in that the tracer component has been given a fluorescent or other tag and may or may not have the same molecular weight as the matrix polymer. This approach eliminates solubility limit issues, permitting determination of Ds from dilute solution to the melt. Applications of this approach are shown in Figure 8.28. The filled points correspond to work of Smith, et al. (45), while the open points reflect experiments by Tead and Kramer(46). 

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