Study On The Influence Of The Wettability Of The Inner Wall Of The Serpentine Microchannel On The Kinetic Mass Transfer Of Gas-liquid Two Phases

In a microchannel reactor,the gas-liquid two-phase flow process is influenced by multiple factors such as channel geometry,fluid properties,surface characteristics,etc.These factors are crucial for fluid mechanics,mass transfer,and reactions.Among them,the wall hydrophilicity of microchannels also plays an important role in the flow and mass transfer processes of gas-liquid Taylor systems.This study used a high-speed camera on a confocal microscope to track the evolution of CO₂ bubbles in a serpentine microchannel and investigated the effects of wall wettability on the gas-liquid two-phase flow and mass transfer dynamics in pure water-CO₂ and MEA solution-CO₂ systems.The surface wettability of PMMA microchannels was regulated by using air plasma and surface chemical grafting modification techniques with methacryloyloxyethyl sulfonic betaine（SBMA）as the grafting monomer.Three microchannels with contact angles of 10°,40°,and 70°were obtained by changing the plasma treatment time and UV irradiation time.After ultrasonic treatment for 30 minutes,the wall wettability of the modified microchannels remained stable,indicating that a stable wettability wall can be obtained by this modification method.A gas-liquid unit model was constructed to study the dynamic mass transfer between the gas and liquid phases in Taylor flow.Based on this unit model,parameters such as bubble surface area,bubble volume,specific interfacial area,and overall volumetric mass transfer coefficient of the liquid phase were calculated.In the pure water-CO₂ system,the bubble length increased with decreasing contact angle.The bubble shrinkage process was divided into three stages:a fast linear decrease stage,a moderate exponential decrease stage,and a slow linear decrease stage.The overall volumetric mass transfer coefficient（k_La）of the liquid phase and the specific interfacial area（a）both increased with increasing contact angle.With an increasing contact angle,the decrease in leak flow was unfavorable for mass transfer,but the increase in bubble velocity was beneficial.Ultimately,the positive effect of bubble velocity on mass transfer was greater than the negative effect of leak flow.Considering the effects of contact angle and non-ideal mixing in the continuous phase on mass transfer,a model was proposed to predict the dynamic mass transfer coefficient of gas-liquid systems,which showed good predictive performance.In the MEA-CO₂ system,the absorption process of CO₂ belongs to chemical absorption,and the formula for calculating the equilibrium concentration of CO₂ was derived based on Henry’s law.The length of the bubble decreased with increasing contact angle,and the initial bubble length in this system was significantly smaller than that in the pure water system.Under the same operating conditions,the k_La in this system was significantly greater than that in the CO₂-pure water system.The k_L value in the 70°contact angle channel was significantly greater than that in the 10°contact angle channel.The increase in a value with increasing contact angle was mainly due to an increase in the frequency of bubble generation and a decrease in the length of individual bubbles under the same gas and liquid flow rate,resulting in an increase in specific interfacial area.