Serpentine variance

Figure 10. Graph of Variance against Flow Rate for Coiled and Serpentine Tubes...

The flow rate is employed as the independent variable, an alternative to the more usual linear velocity, as the flow rate is defined by the column with which the low dispersion tubing is to be used. It will be shown in due course that the column flow rate is independently defined by the nature of the separation that is to be achieved by the column, It is seen that a similar curve is obtained for the serpentine tube, as that for the coiled tube, but the the maximum value of (H) is reached at a much lower flow rate than that with the coiled tube. Furthermore, the variance remains more or less constant over a wide range of flow rates that encompass those usually employed in normal LC separations. 

A serpentine mixer (Fig. 8.18) can be used to mix two chemicals in a shorter length than happens in a straight channel. Figure 8.19 shows a typical solution for a Reynolds number of 1.0 and Peclet number of 1000. Comparing these data with those for a T-sensor (Fig. 8.17) shows that the total length/width necessary has been reduced from 250 to 19.6 when the variance is 2.6 X 10". ... 

Table 8.4 Variance at different points in a serpentine mixer.

Another aspect of the serpentine mixer is to define how much mixing occurs for a given pressure drop. The flow solution gives the pressure drop and the variance gives the mixing. Table 8.4 shows results at different velocities for the serpentine mixer. 

The curves in Figure 8 clearly demonstrate the relative performance of tubes of different geometry. Although the coiled tube has a high variance, the peak is almost symmetrical, but obviously, the curve from the serpentine form is both better in shape and contributes less variance. Nevertheless, the dispersion is still very large when compared with the dispersion from the small bore column previously discussed. Ipso facto connecting tubes should be made as short as possible whatever their geometric form. 

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