RTD of Multiphase Flow in Microchannels

Because of the laminar flow in microchaimels and the smalt diffusion coefficient in the order of 10 m s , narrow RTD in straight chaimels at low Re-numbers are not easy to obtain. As the radial diffusion time is long, high axial dispersion is particularly important at short residence times. 

In the presented study, liquid segments are separated by gas bubbles. But the liquid wets the channel wall and forms a small film, which allows communication between the segments and, as a consequence, enables axial dispersion. 

The influence of wall film on the RTD in segmented flow was studied in detail by Kuhn et al. [23]. The authors used microreactors with a square section of 0.4 X 0.4 mm and a length of 750 mm. The walls of the silicon-based microdevices were modified by growing a thin silicon oxide layer to get a hydrophilic surface 

The resulting o-numbers estimated by curve fitting was found to be Bo = 300 18 for the hydrophihc channels and o = 520 33 for the hydrophobic channels. 

The results confirm the beneficial use of segmented flow for realizing plug flow behavior in microstructured reactors. Narrow RTD can be obtained even for short residence times, allowing high performance and product yields for fast chemical reactions. 

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