Peak Height and Channel Geometry

The coiled tube has so far been the most frequent geometric form of the FIA microreactor. However, it is useful to review all channel geometries (Fig. 2.8). These are straight tube (A), coiled tube (5), mixing chamber (C), single-bead string reactor (D), 3-D or knitted reactor (E)y and imprinted meander (cf. microconduits Section 4.12) or combinations of these geometries. 

The function of these reactors is to increase the intensity of radial mixingy by which the parabolic velocity profile in the axial direction, formed when the sample zone is injected into a laminar flow of carrier stream, is reduced. Thus, (a) the reagent becomes more readily mixed with the sample, and (b) the axial dispersion of the sample zone is reduced. 

Relaxation of the laminar profile in the radial direction is best achieved by creating a local turbulence whereby the direction of flow is suddenly changed. In this way the elements of fluid that are lagging because they are close to the walls of the channel are moved into the rapidly advancing 

In a straight tube of uniform diameter (Fig. 2.SA), the parabolic profile (Fig. 3.4) formed by laminar flow remains undisturbed up to a flow velocity not normally reached in a typical FIA system, and since the radial diffusion occurring in the time frame oif an FIA experiment is not sufficient to offset the axial dispersion initially formed during sample injection, an asymmetrical peak is recorded (Figs. 2.4a and 2.10a). 

T as Vm/Q and by defining t /2 as the time span during which any C decreases by one-half, 

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