The flow and mass transfer characteristics of CO 2 absorption in different liquid phases in a microchannel were studied by numerical simulation. The mixture gas phase contained 5 vol% CO 2 and 95 vol% N 2 , and the different liquid phases were water, ethanol solution, 0.2 M monoethanolamine solution, and 0.2 M NaOH solution, respectively. Based on the permeation theory, the distribution of velocity and concentration in the slug flow was obtained by local simulation of flow and mass transfer coupling and was described in depth. The influence of contact time and bubble velocity on the mass transfer of the whole bubble was highlighted. The volumetric mass transfer coefficient on the bubble cap and liquid film, CO 2 absorption rate, and enhancement factor were calculated and analyzed. The results showed that the volumetric mass transfer coefficients of chemical absorption were 3 to 10 times that of physical absorption and the CO 2 was absorbed more completely in chemical absorption. The new empirical correlations for predicting the mass transfer coefficient of the liquid phase were proposed respectively in physical absorption and chemical absorption, which were compared with the empirical formulas in the literature. The volumetric mass transfer coefficients obtained by predictive correlations are in good agreement with those obtained by simulation in this paper. This work made a basic prediction for CO 2 absorption in microchannel and provides a foundation for later experimental research.

No abstract

Heat transfer and flow characteristics under air-water Taylor flow in a square microchannel with T-junction were investigated in this work. Different hydraulic diameters of models were discussed numerically by VOF method. Flow patterns such as bubbly flow, slug flow, annular flow and churn flow were identified by both numerical simulation and experimental methods. Simulation results including bubble formation process, bubble length, bubble velocity, void fraction and heat transfer fit well with literature data. The pressure differential of two sides in gas phase played an important role in bubble development. The gas and liquid superficial velocities were found to have a significant impact on bubble behavior. And the higher liquid viscosity would promote higher bubble velocity, also enhance heat transfer, but weaken the void fraction. The results showed a tiny but not ignorable effect of geometric dimensioning on bubble and liquid slug lengths. An appropriate correlation was proposed to estimate bubble length, and the deviation was −10 ~ + 15 %. By using moving frame of reference technique, the internal circulations inside the moving slugs were displayed more clearly.