Characterization of flow maldistribution using inlet-outlet tracer techniques: An application of internal residence time distributions

Abstract The internal residence time distribution (RTD) φ(t) (Buffham, B.A., 1983, Chem. Engng Commun.22, 105–107) is shown to be a useful function for the characterization of the flow patterns of a steady-state flow system, especially one with internal flow maldistribution. The relationship between φ(t) and the more familiar external RTD E(t) is rederived in a way which illustrates the physical significance of this new distribution function. Since the internal RTD provides an inventory of eventual residence times performed on molecules inside the vessel, it describes internal flow velocities more directly than E(t), even though both are measured using identical tracer response techniques and hence contain the same intrinsic information. Quantitative, physically based definitions of relative stagnancy and bypassing based on φ(t) are proposed. Next, the utility of the internal RTD in the interpretation of tracer response curves is demonstrated using both theoretical mathematical models and measured tracer results in maldistributed flow fields. Finally, the holdback, which may be expressed in terms of F(t) and Φ(t)—the cumulative internal RTD—is proposed as an alternative single parameter to estimate isothermal reactor yield for first-order reactions.