Michell and Furzer

Axial Dispersion and the Peclet Number Peclet numbers are measures or deviation from phig flow. They may be calculated from residence time distributions found by tracer tests. Their values in trickle beds are fA to Ve, those of flow of liquid alone at the same Reynolds numbers. A correlation by Michell and Furzer (Chem. Eng. /., 4, 53 [1972]) is... 

Plug-flow assumption Using die Michell and Furzer correlation (eq. (3.417)), the liquid-phase Peclet value is 0.66 and die minimum value of Z/d, evaluated by using the Mears criterion (eq. (3.421)) 4.81, which is much lower that the experimental one, which is 100. Then, condition (c) is satisfied. 

In general. and hsL are known or could be estimated,27-77 98 so this model is a single-parameter (q) model. Michell and Furzer correlated q with the film Reynolds number by the relation... 

Here A is the film thickness. By comparing the variance of the response obtained by this model and the one obtained for an axial dispersion model of the same system, Michell and Furzer derived the following approximate relationship between Peclet number and the parameter q ... 

Figure 3-10 Correlation of the extent of axial mixing in trickle flow (after Michell and Furzer ).

The Otake-Kunugita type of correlation for the Peclet number has also been used by Co and Bibaud.10 Bennett and Goodridge2 and Michell and Furzer.35 Co and Bibaud10 examined trickle-flow air-water systems in 12.7- and 27.94-cm i.d. columns. The columns were packed to 304.8 cm with either 1.27- or 2.54-cm Raschig rings for the RTD measurement. The data were correlated by the following relation ... 

Local liquid flow vizualisation by Michell and Furzer (13)... 

Here, A is the cross-sectional area of fluid flow, V is the interstitial velocity of liquid, and M is the mass of tracer added. Michell and Furzer61 and Furzer and Michell35 claim that an accurate estimation of Ez can be obtained by fitting the experimental RTD with Eq. (3-8) by nonlinear regression techniques. The first and second moments are given by the relations... 

Trickle-bed models assume plug flow for both phases. Thus, it is interesting to evaluate the respective Peclet numbers. The correlations of Michell-Furzer for liquid (eq. (3.417)) and Hochman-Effron for gas (eq. (3.419)) are used and the results are shown in Table 5.15. The Reynolds number for the gas phase is 32.28. 

At this point, it is also important to check the plug-flow assumption, as the models assume plug flow for liquid. Tire coiielation of Michell-Furzer (eq. (3.417)) for the liquid is used and the results ai e shown in Table 5.17. The minimum values of Z d are evaluated by using the Meai s criterion (eq. (3.421)). 

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