Monolith Reactors for Intensified Processing in Green Chemistry - Process Intensification for Green Chemistry - page 179

Figure 6.5 Flow fields within the liquid slugs in the W¼1.5mm tube for (a) L S <D c , 30% v/ v
isopropanol/ water-air mixture, Ca¼0.008, V GS ¼0.384m/ s, V LS ¼0.111m/ s, V B ¼0.576m/ s;
(b) L S >D c , water-air mixture, Ca¼0.0287, V GS ¼0.209m/ s, V LS ¼0.106m/ s, V B ¼0.343m/ s.
Units of velocity are m/ s. Reprinted from Tsoligkas et al # 2007c, with permission from Elsevier.

long slugs the axial velocity component depends upon both the axial position in the tube
andthetubecross-section.ParabolicvelocityprofilesareapproximatedforV max /V b 1.1-1.7.

Significant differences from upflow operation were observed, with upflow recirculation
times being three times faster than downflow, which has implications for the models used
to predict mass transfer and residence time distribution (RTD).

6.3.2.2 Mass-Transfer Processes

A detailed analysis of the mass-transfer steps involved in Taylor flow within the monolith
reactor has been given by Kreutzer et al. [11] and is summarized in this section. The three
mass-transfer modes of steps (1)-(3) may be combined, with the (2) GL and (3) LS steps
considered as resistances in series and as in parallel with respect to (1) GS mass transfer.
For the overall mass transfer, the following expression can be used:

1

1
k GL a GL þ

1
k LS a LS

k OV a ¼ k GS a GS þ (6.2)

The individual mass-transfer coefficients and areas are determined as:
k GS ¼ D
d

(6.3)

41 ð e L Þ

a GS ¼ (6.4)

D C