| In recent years,with the continuous development of miniaturized and intelligent equipment,micro-chemical technology has been widely concerned by scholars and enterprises.Compared with the conventional pipeline,the gas-liquid two-phase flow in the microchannel reactor is more complex and changeable.The measurement technology has some limitations in the microscale measurement,resulting in differences of measurement results.Therefore,it is an urgent need for new measurement techniques to accurately obtain the gas-liquid two-phase flow characteristics in the microchannels.The flow characteristics of air-water,glycerol aqueous solution-air,and ethanol aqueous solution-air two-phase system were studied using electrical resistance tomography(ERT)in a circular microchannel with an inner diameter of 1 mm.The effect of liquid properties(surface tension and viscosity)and gas/liquid superficial velocities on the flow pattern,gas holdup,and friction pressure drop were disccussed.The gas holdup obtained by ERT technique and the flow pattern information obtained by the eigenvalue extraction method were compared and analyzed with high-speed camera technology’s results,classic models and correlations in the literature.In the air-water two-phase flow system,five flow patterns of bubble flow,bubbly-cap flow,slug flow,elongated slug flow,and unstable slug flow were observed,which were better than those of Zhang,Mishima,and Ishii in literatures.The accuracy rate of identification of the flow pattern by the eigenvalue extraction method from ERT data was 90.8%.And the bubble generation mechanism under different flow patterns was proposed.In addition,the ERT technology can also reproduce the 3D flow of the gas-liquid two-phase flow in the microchannel.The gas holdup of the system was obtained through analysis.Its value was in good agreement with the calculated value of the Mishima and Hibiki’s correlation,but it was slightly lower than that of the high-speed camera technology’s results.The average error was 8.5%,which verifies the accuracy of ERT technology.With the increase of liquid viscosity and the decrease of the surface tension,in addition to the above flow patterns,bubble flow and bubble-slug flow with smaller equivalent diameters were also observed.The ERT technology used the method of eigenvalue extraction to identify the average flow pattern with over 84% of the accuracy rate.The results showed that the effect of liquid surface tension on the transition line of flow pattern is great.With the decrease of the surface tension,the flow pattern transition could occur earlier,while the effect of viscosity on the transition line of the flow pattern is not significant.At the same time,the gas holdup of the system will also decrease to some extent.By comparing the results of high-speed camera technology and ERT technology,it was found that the overall average error of the glycerol aqueous solution(5-25wt%)-air system was 15.19%,and that of the ethanol aqueous solution(5-25wt%)-air system was 22.75%.According to the experimental data,the correlation of gas holdup within the experimental range was proposed.In addition,the friction pressure drop gradient increased with the increase of the superficial gas velocities,the superficial liquid velocities and the liquid viscosity,and increased with the decrease of the liquid surface tension,which was in good agreement with the literature values and verified the reliability of data in the microchannels.It also provides a new measurement method for the study of the gas-liquid two-phase flow characteristics in the microchannels. |
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