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Experimental Study of Gas-Liquid Mass Transfer in a Rectangular Microchannel by Digital Image Analysis Method


 Study of mass transfer in microchannels is indispensable for the design of microreactors. Gas-phase volume monitoring method has been widely used to study the mass transfer process. When using this method, bubble length was measured in most studies to calculate the bubble volume by assuming a symmetrical bubble shape. Therefore, this method is not suitable for asymmetric bubbles. The present study focuses on the mass transfer of CO2 bubbles in a flat rectangular microchannel by using the method of digital image analysis (DIA), especially for deformed bubbles. The dynamics of gas-liquid flow at different volumetric flow rates were observed by a high-speed recording system. Flow patterns were mapped and scaling laws were given for bubble size and bubble velocity. The results showed that the bubble volume increases as gas flow rate increases, while decreases as liquid flow rate increases. It can be explained by the bubble breakup mechanism. Besides, the bubble velocity increases as gas and liquid flow rates increase. The mass transfer of CO2 from bubbles to liquid slugs was quantitatively characterized by volumetric mass transfer coefficient kLa. The results showed that kLa and kL increase with increasing of superficial gas and liquid velocities. The same tendencies can be found in the literature. Finally, new mass transfer correlations were proposed. Predictions from the correlations showed a good agreement with the experimental data.