Efficiency and multi-objective optimization of gas-liquid-phase mass transfer in high-viscosity fluids within heart-shaped microchannels

Abstract

Microchannels are widely utilized in the microchemical industry due to their highly efficient and enhanced mass transfer properties. However, when processing high-viscosity fluids, the flow pressure drop in microchannels significantly increases, posing challenges for system performance. To address this, it is crucial to control both mass transfer and pressure drop in gas-liquid two-phase systems in microchannels under high-viscosity conditions. This study investigates the mass transfer and flow behavior of high-viscosity fluids in heart-shaped microchannels (Advanced Flow Reactor, AFR). Experimental visualization techniques are employed to explore the effects of bubble size distribution, gas content, and pressure drop on the gas-liquid two-phase flow and its mass transfer characteristics in high-viscosity systems. A predictive model for the pressure drop in these heart-shaped microchannels is also developed. Air and high-viscosity glycerol-water solution (viscosity range of 50–320 mPa·s) are selected as the gas-liquid two-phase system. The experimental operating conditions are optimized using the enhanced multi-objective NSGA-II algorithm to identify a set of critical process parameters that balance low pressure drop with high mass transfer coefficient. The results demonstrate that compared to the liquid-phase volumetric mass transfer coefficients (K_la) at the lowest gas-phase flow rate for each viscosity, the increase in K_la is 53 %–122.7 % for viscosities ranging from 50 to 150 mPa·s. This improvement is accompanied by a 70 %–100 % increase in gas-phase flow rate and a corresponding 30 %–58 % rise in pressure drop. Optimization results indicate under ideal experimental conditions, mass transfer efficiency is enhanced, and pressure drop loss is reduced by an average of 53 %, despite a small reduction in the mass transfer coefficient. This suggests that an optimal design can effectively balance mass transfer efficiency with pressure drop reduction, offering practical solutions for high-viscosity gas-liquid two-phase systems. The findings provide a theoretical foundation for optimizing microchannel operating parameters in high-viscosity systems and achieving multi-objective optimization with low pressure drop and high mass transfer efficiency.