The Gas-liquid Two-phase Flow And Mass Transfer Accompanied By Chemical Reaction In Microchannels

Gas-liquid two-phase mass transfer processes are widely encountered inindustrial applications. Microchannels have drawn worldwide attentions dueto the excellent mass and heat transfer performance. The study on gas-liquidtwo-phase flow and the mass transfer process accompanied by chemicalreaction is necessary due to lacking related reports. By using a high speedcamera and pressure transducers, the effects of operating conditions, suchas gas and liquid flow rates, chemical reaction rate and aspect ratio on flowregime, void fraction, pressure drop and mass transfer process, wereinvestigated experimentally.For gas-liquid two-phase flow accompanied by chemical reaction,slug-bubble flow, slug flow, slug-annular flow and annular flow wereobserved. Flow regime transition lines were obtained according to draftflow regime map, and compared with the transition lines in literature.Transition equations were proposed to predict two-phase flow pattern inmicrochannels accompanied by the chemical reaction. The predicted valuesagreed well with experimental data.Void fraction was calculated by pixel method. Results showed that, theincrease of gas phase flow rate and the decrease of liquid phase flow rate,chemical reaction rate and aspect ratio, could lead to an increase of voidfraction. A semi-theoretical predicting model for void fraction wasproposed, with a good predicting performance.Pressures at the inlet and outlet of the microchannels were measured bypressure transducers, and then the pressure drops were obtained. With theincrease of gas and liquid phase flow rates, chemical reaction rate andaspect ratio, the pressure drops increased. Subsequently, predicting modelswere proposed separately based on the separated model and physical model.Results showed that the modified physical model has better predictingperformance than the separated model.Photogrammetry was adopted to calculate the liquid side volumetricmass transfer coefficient kLa, liquid side mass transfer coefficient kL, and specific surface area a. Results showed that, before the critical ratio, kLa, kL,and a increased with the increasing ratio of gas to liquid phase flow rate, aswell as kLa,kLand a decreased with increasing chemical reaction rate. Afterthe critical ratio, kLa, kL, and a reached up to a constant, kLa and kLincreased while a decreased with increasing chemical reaction rate. Withinthe range of experiment, kLa, kL, and a increased with increasing aspectratio. A few models were proposed to predict kLa for gas-liquid two-phaseflow accompanied by chemical reaction, based on Jepsen’s model,dimensionless parameter groups correlation and Higbie’s unsteady-statepenetration theory separately. The predicting model based on Higbie’sunsteady-state penetration theory has the best predicting performance thanother.