Transient testing techniques using tracers

Consider the illustration of Fig. 5. A system with closed boundaries and a constant flow rate through its single inlet and outlet connections is disturbed by a forcing function, or pulse, of tracer, CA it), a time-varying outlet concentration of tracer, Ca o Ct), is observed. A tracer is any material which behaves in an identical manner to the process fluid flowing through the system but which displays some property which enables it to be differentiated from that fluid such properties could be colour, electrical conductivity, or radioactivity for instance. 

For simple tracer experiments, the trace species should be conserved in the sense that the amount eventually eluted from the system is the same as the quantity entering this means, for instance, that the tracer 

The purpose of tracer experiments is to extract information about the system in a chemical reaction engineering context, it is the mixing within the system which is of interest, as represented by the system residence time distribution. Because flow mixing is an inherently linear process, the exact form of the RTD which is recovered from a tracer response experiment should be independent both of the amount of tracer used in the test and also of the particular functional form in which the tracer was 

Writing an unsteady state mass balance on the tracer 

Taking deviation variables (see Appendix 2) and Laplace transforming (see Appendix 1) allows to be defined by 

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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. 

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