Dispersion of solutes

There are several mechanisms responsible for the dispersion of solute as it travels through the column ... 

The changes in optical rotation and the anomalous dispersion of solutions of /-malic acid in solution are due to the presence of two tautomeric forms in dynamic equilibrium. 

Dispersion of solute bands in cells of different dimensions have also been experimentally measured by Scott and Simpson, (II) but with concentric... 

The abscissa is actually the Reynolds number based on local displacement thickness. In this case, only the local solution is predominant at early times. This component also disperses and decays, as can be seen from the solution at t = 100. The observed single peak at t = 0 that is due to the local solution disperses into multiple peaks- as can be noted for all subsequent times. This dispersion of solution is due to the presence of upstream prop>-agating modes and the presence of multiple harmonics for the downstream propagating modes. The adjective upstream here is to be understood with respect to the local condition of the disturbance field. More details about this dispersion mechanism and tracking of the upstream propagating modes were first discussed in Sengupta et al. (1999) and will be discussed again in the next subsection. 

Dispersion of solute bands in cells of different dimensions have also been experimentally measured by Scott and Simpson, (11) but with concentric inlet and outlet tubes, their data, although pertinent to some types of detectors, (for example conductivity detectors) are not applicable to optical detectors where inlet and outlet tubes can not be axially oriented. 

The poblem stated above is sufficiently complex that a closed-form analytical solution in the time domain has not been found. For most purposes, the details of the radial distribution of solute are unimportant, and a description of the longitudinal dispersion of solute in terms of a local mean concentration (that is, radially averaged) will suffice. The most mathematically convenient mean concentration is an area-averaged concentration, defined as... 

Because the driving force of the flow is distributed along the wall of the capillary, the flow profile is nearly flat or pluglike, contrasting the laminar or parabolic flow generated by a pressure-driven system caused by shear forces at the wall. A flat flow profile is beneficial because it does not contribute to the dispersion of solute zones. The magnitude and direction of the EOF can be impacted by the type of electrolyte used, the pH, the ionic strength, the use of additives (e.g.. 

Our main concern here is to present the mass transfer enhancement in several rate-controlled separation processes and how they are affected by the flow instabilities. These processes include membrane processes of reverse osmosis, ultra/microfiltration, gas permeation, and chromatography. In the following section, the different types of flow instabilities are classified and discussed. The axial dispersion in curved tubes is also discussed to understand the dispersion in the biological systems and radial mass transport in the chromatographic columns. Several experimental and theoretical studies have been reported on dispersion of solute in curved and coiled tubes under various laminar Newtonian and non-Newtonian flow conditions. The prior literature on dispersion in the laminar flow of Newtonian and non-Newtonian fluids through... 

Erdogan, M.E. Chatwin, P.C. The effect of curvature and buoyancy on the laminar dispersion of solute in a horizontal tube. J. Fluid Mech. 1967, 294, 465-484. 

Elution of the SPE column also is similar to sorption in that the analytes move in a series of platelike equilibrations down the column, depending on the k (column equilibrium constant) of the solute in the elution solvent. Therefore, the amount of solvent needed to elute the analyte also is affected by the number of plates. That is, the more theoretical plates that an SPE column contains, the smaller the volume that is required to elute the analyte. This is because the column with more plates has less dispersion of solute during the elution step and less elution solvent is needed. Obviously, as the mass of packing material increases, more solvent would be required for elution. 

Figure 2.1 illustrates one of the many possible feedback scenarios. For example, climate changes, mechanical compaction, or heat transport can cause or change ground-water flow. Groundwater flow brings about advection and dispersion of solutes. Mass fluxes across spatial domains cause changes of chemical concentrations, and perturb chemical equilibrium or a chemical steady state, which leads to chemical reactions. 

To obtain a model of practical utility which still emphasizes the important characteristics of the RCFE 1n the high Pe limit, it is desirable to substitute a dispersion equation Involving the transverse average concentration for Equation 1. The y-dependent velocities are replaced by their transverse averages and the convective dispersion of solute associated with the crescent phenomenon is lumped into a lateral dispersion coefficient, K, which simplifies the analysis considerably and allows analytical solution of the governing equation,... 

Hydrodynamic dispersion of solute slugs in a straight conduit occurs due to nonuniformities in the fluid velocity across the channel cross section. On microfluidic devices, such solutal... 

Hydrodynamic Dispersion, Fig. 9 Effect of bowing on the dispersion of solute slugs in rectangular channels... 

Taylor, G. I., Dispersion of solute matter in solvent flowing through a tube, Proc. Roy. Soc. bond., A291 186-203, 1953. 

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