(551e) Gas-Liquid Mass Transfer in Slug Flow through Narrow Channels

This paper will present experimental findings of a systematic study carried out to determine the mass transfer performance of slug flow in narrow channels. The influence of liquid viscosity on mass transfer rate will be highlighted by developing an empirical correlation based on average velocity of flow, length of unit cell, void fraction and channel diameter. This data is being currently used by the process intensification research group at Clarkson to develop and evaluate the performance of several intensified reactors using hydraulic path lengths in the range of 500 to 1000 microns.

Background

A uniform continuous flow of gas bubbles separated by liquid slugs is called slug flow. This flow generates a thin liquid film around the gas bubble. High interfacial surface area, low pressure drop and uniformity of distribution of flow are some of the important characteristics of slug flow. Experimental studies[1] were carried out to calculate mass transfer rates from air to water in slug flow through narrow channels. The limitation of the developed correlation is its applicability to air-water system only. Limited experimental work has been reported in public domain regarding gas-liquid mass transfer in slug flow through narrow channels with liquids of higher viscosities (>1 cP). Therefore the objective is to study in detail the gas-liquid mass transfer in slug flow through narrow channels where fluids such as glycerol and sucrose solutions will be used. This study will help to predict gas-liquid mass transfer rates in slug flow applications where fluids of higher viscosities will be used. This limitation has hindered the progress of narrow channel reactors in gas liquid mass transfer activities involving removal of monomers from pre-polymers which have significantly higher viscosities than water.

Description of the research

An experimental setup to obtain mass transfer data for air-water system has been developed. A high speed camera is used to measure the bubble velocity and void fraction of slug flow in narrow channels. Based on the initial experiments[2], the dependence of mass transfer rate on superficial gas velocity and the length of unit cell were found to be same as predicted by Vandu et al. The setup developed for air-water system has been used to study the influence of fluid properties such as viscosity on mass transfer rates. Mass transfer rates obtained experimentally have been used to develop empirical correlations. An empirical correlation is being developed using our experimental results. This correlation will include variables such as: 1) average velocity of the flow, 2) length of unit cell, 3) void fraction and 4) channel diameter.

References

1. Vandu, C. O. Liu, H. and Krishna, R. ?Mass transfer from Taylor bubbles rising in single capillaries? Chemical Engineering Science, 60, 6430-6437, (2005)

2. ?Process Intensification: Mass transfer characterization of slug flow in narrow channel reactor?, presented at the Annual meeting of AIChE , Cincinnati, Ohio, November, (2005).