Taylor Dispersion in a Capillary Tube

Figure 1.180 (a) Mixing in a capillary tube by Taylor dispersion. 

Axial dispersion in packed beds, and Taylor dispersion of a tracer in a capillary tube, are described by the same form of the mass transfer equation. The Taylor dispersion problem, which was formulated in the early 1950s, corresponds to unsteady-state one-dimensional convection and two-dimensional diffusion of a tracer in a straight tube with circular cross section in the laminar flow regime. The microscopic form of the generalized mass transfer equation without chemical reaction is... 

Figure 4.6.8 Measured mean concentration distributions at three positions along a capillary tube. Dashed line is distribution that would be due to convection alone for comparison with curve III. [After Taylor, G.l. 1953. Dispersion of soluble matter in solvent flowing slowly through a tube. Proc. Roy. Soc. A219, 186-203. With permission.]...

Electrospray, also called electrohydrodynamic or electrostatic spray, is an atomization technique in which liquids are dispersed solely by the application of high voltages. A simple electrospray setup is shown in Fig. 4. A liquid flows into a metal capillary tube charged to the kilovolt range and emerges from the tip as a conical meniscus, known as a Taylor cone, due to the intense electric field (Fig. 5). An unstable jet extends continuously from the apex of the cone and disperses into charged droplets further downstream. Electrosprays have been used in industrial... 

G.I. Taylor (1953, 1954) first analyzed the dispersion of one fluid injected into a circular capillary tube in which a second fluid was flowing. He showed that the dispersion could be characterized by an unsteady diffusion process with an effective diffusion coefficient, termed a dispersion coefficient, which is not a physical constant but depends on the flow and its properties. The value of the dispersion coefficient is proportional to the ratio of the axial convection to the radial molecular diffusion that is, it is a measure of the rate at which material will spread out axially in the system. Because of Taylor s contribution to the understanding of the process of miscible dispersion, we shall, as is often done, refer to it as Taylor dispersion. 

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