The Gas-Liquid Two-Phase Flow And Mass Transfer In Parallel Microchannels

Microchannels have drawn worldwide attentions due to the excellent massand heat transfer performances, while the scale-up of microchannels is anessential issue in order to achieve required throughput for industrial application.A high-speed camera was used to visualize and investigate the gas-liquidtwo-phase flow pattern, flow distribution, void fraction and mass transferprocess in different gas-liquid distribution structure (internal distribution,external distribution, branching) parallel microchannels.Gas-liquid flow pattern without chemical reaction in different structureparallel microchannels and gas-liquid flow pattern accompanied by chemicalreaction in branching parallel microchannels were observed. Flow regimetransition lines were obtained according to the flow regime map.The relative deviation and the relative standard deviation were adopted toreflect the non-uniformity of two-phase distribution in parallel microchannels.In the three internal distribution parallel microchannels with differentdistributor angle (60°,90°,120°), the non-uniformity of bubble length in branchchannels increased with the increase of distributor angle, liquid flow rate andviscosity; the non-uniformity of bubble velocity in branch channels decreasedwith the increase of distributor angle, liquid viscosity. However it increased upto a maximum and then gradually decreased with the increase of liquid flowrate.For gas-liquid two-phase flow without chemical reaction, the void fractiondecreased with the increase of liquid flow rate and viscosity, and the decrease ofgas phase flow rate. For gas-liquid two-phase flow accompanied by chemicalreaction, the void fraction of whole parallel microchannels decreased with theincrease of chemical reaction rate.Photogrammetry was used to calculate the liquid side volumetric masstransfer coefficient of CO2chemical absorption into monoethanolamine (MEA)aqueous solutions in branching parallel microchannels. The result wascompared with traditional reactors. With the increase of gas flow rate and liquidflow rate, the volumetric mass transfer coefficient increased up to a certainvalue and then remained stable. For smaller gas flow rate, the liquid-phase volumetric mass transfer coefficient decreased with the increase of chemicalreaction rate. But for higher gas flow rate, the liquid-phase volumetric masstransfer coefficient increased with the increase of chemical reaction rate.The study is helpful for the optimization of the parallel microchannelsstructure and control of operation condition in order to realize the uniformtwo-phase distribution and excellent mass transfer performance.