Giddings equation

Many evaluations of correlations are available (Elliott and Watts Lugg Marrero and Mason). The differences in accuracy of the correlations are minor, and thus the major concern is ease of calculation. The FuUer-Schettler-Giddings equation is usually the simplest correlation to use and is recommended by Reid et al. 

It is seen that the first term differs from the Giddings equation and now contains the mobile phase velocity to the power of one-half. However, when the first... 

A number of HETP equations were developed other than that of Van Deemter. Giddings developed an alternative form that eliminated the condition predicted by the Van Deemter equation that there was a finite dispersion at zero velocity. However, the Giddings equation reduced to the Van Deemter equation at velocities approaching the optimum velocity. Due to extra-column dispersion, the magnitude of which was originally unknown, experimental data were found not to fit the Van Deemter... 

In summary, it can be said that all the dispersion equations that have been developed will give a good fit to experimental data, but only the Van Deemter equation, the Giddings equation and the Knox equation give positive and real values for the constants in the respective equations. 

The Van Deem ter equation appears to be a special case of the Giddings equation. The form of the Van Deemter equation and, in particular, the individual functions contained in it are well substantiated by experiment. The Knox equation is obtained... 

According to Giddings equation,15 the pressure drop across a packed column (AP/L) may be expressed as ... 

It is seen that the first term differs from that in the Giddings equation, in that it now contains the mobile phase velocity to the power of one half. Nevertheless, again when ul/2 >> E, the first term reduces to a constant similar to the Van Deemter equation. The additional term for the resistance to mass transfer in the mobile phase is an attempt to take into account the... 

This can be examined further by considering the detailed expression for the first term of the Giddings equation. 

The expanded expression for the first term in the Giddings equation (7) is as follows ... 

The ail viscosity can be found in Table 1.2, Appendix I, where we find that the viscosity at 644 K is about 3.1 X 10 5 kg/m s. The Fuller—Schettler—Giddings equation is proposed for the determination of the diffusion coefficient of nonpolar gases in binary mixtures at... 

Figure 6.14 Plot of the axial reduced plate height vs. the reduced mobile phase velocity, (a) Comparison of the results measured by three PFGNMR methods (PFGSE, PFGSTE and APGSTE, with S = 2 ms and A - 22 ms) and best fit of these experimental data (s3rmbols) to the Giddings equation (solid line). The individual contributions to this equation are represented by the dotted lines, (b) Best fit of a subset of these data limited to t/ < 15 to the van Deemter model and extrapolation (B = 1.35, A = 0.14, C = 0.11, n = 0). Reproduced with permission from U. Tallarek, E. Bayer, G. Guiochon, f. Am. Chem. Soc., 120 (1998) 1494 (Fig. 8). (c)1998 American Chemical Society.

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