Characteristics Of Gas-liquid Flow In Annulus Microchannels

In the traditional microchannel reactor,the catalyst is usually coated on the inner surface of the microchannel.However,the coating quality is difficult to control,and the catalyst regeneration is not easy.In order to solve these problems of coating and regeneration,this paper proposes to apply catalyst to the outer surface of the heat exchange inner tube.Micro-size annulus is constructed between the outer tube and the inner tube providing a space for chemical reaction.Annulus microchannels with annulus size of 0.5,1.0,1.5,2.0,and 2.5mm were machined from quartz glass,plexiglass,and stainless steel.High-speed camera is used to record the flow patterns of single-liquid and gas-liquid flows,to explore the effects of annulus size,outer diameter of annulus,internal structures,fluid properties,and placements.The flow patterns are also simulated with FLUENT and compared to the experimental results.In the single-phase experiment and simulated,the change of the annulus size,pressure drop and friction coefficient are investigated.The high-speed camera observes that the critical Reynolds number is different in these annulus sizes.The critical Reynolds number starts to be smaller than the traditional value at?=1.5mm,and is stable at Re_cr=1500-1600 at??1.0mm.At the same time,both experiments and simulations show that the wall slip is prominent reducing friction coefficient and the friction coefficient and the Reynolds number product in the annulus microchannel.In the gas-liquid experiment and simulated,the flow pattern changes of nitrogen and water are investigated in different annulus sizes.Gas dispersion can be achieved by increasing the liquid phase flow rate,reducing the annulus size or outer diameter,strengthening the wall hydrophilicity and placing vertically.However,the vertical direction enhances the buoyancy and reduces the residence time of the gas.The internal component has a significant effect on the dispersion of gas and the breaking of large bubbles.The effect of viscosity is more prominent than surface tension,the greater viscosity,the better gas dispersion and the smaller bubble size.