Gas-liquid, Liquid-liquid Mass Transfer And Liquid Heat Transfer Characteristics In Microchannels

The characteristics of mass and heat transfer in microchannels are a highlight point of micro-chemical technology. Previous reports of mass transfer in microchannels were mainly focused on gas-liquid and liquid-liquid two-phase, while for heat transfer in microchannels concentrated on single phase flow. So far no report was found about the mass transfer of gas-liquid-solid and gas-liquid-liquid three-phase flow and the liquid-solid heat transfer in microchannels.This thesis investigated the mass transfer characteristics of gas-liquid and liquid-liquid two-phase flow in a single microchannel with the diameter of 400μm.The effects of superficial gas velocity, superficial liquid velocity, liquid surface tension and liquid viscosity on the volumetric mass transfer coefficients were systematically studied. And the mass transfer characteristics of gas-liquid-solid and gas-liquid-liquid three-phase flow were prelimimarily studied in the microchannel. In the experiment of gas-liquid and gas-liquid-solid mass transfer study, the adopted liquid phase was Na₂SO₃-CoSO₄ aqueous solution, or the solution of Na₂SO₃ -CoSO₄-CMC and Na₂SO₃ -CoSO₄-CTAB; the gas phase was air and the solid phase was micron CaCO₃,BaSO₄ and Fe₂O₃, or nanometer TiO₂ and SiO₂ particles. In the experiment of liquid-liquid and gas-liquid-liquid mass transfer, the liquid phase was deionized water and kerosene (the solute was benzoic acid), the gas phase was nitrogen. Experimental results reffected that within theΦ400μm microchannel the gas-liquid and liquid-liquid volumetric mass transfer coefficients were two orders of magnitude larger than those of conventional equipments. Surface and interfacial properties (liquid surface tension and liquid viscosity) significantly influenced the mass transfer of microchannels. The introducing particles did not intensify gas-liquid mass transfer, but even decreased the volumetric mass transfer coefficients dramatically, and introducing gas phase intensified liquid-liquid mass transfer remarkably. Morever, several flow patterns of liquid-liquid two-phase flow in theΦ400μm single microchannel, such as parallel flow, annular flow, churn flow and slug flow, were recorded through high-speed photography, so did two flow patterns of gas-liquid-liquid three-phase flow, i.e., tri-annular flow and slug-tri-annular flow.Additionally, the convective heat transfer characteristics of liquid single-phase and liquid-solid two-phase flow were investigated in theΦ400μm microchannel. Effects of mass flux, liquid surface tension, liquid viscosity and solid particles on the overall heat transfer coefficients were studied systematically. The adopted liquid phase was deionized water, the solid particles was the single size dispersed nano- SiO2. The results indicated that the convective heat transfer coefficients in theΦ400μm microchannel were much larger than those of conventional equipments. Surface and interfacial properties (liquid surface tension and liquid viscosity) dramatically affected the heat transfer in the microchannel. The single size dispersed nano-SiO2 increased overall heat transfer coefficients dramatically.