Stability And Distribution Of Gas-liquid Flows In Microchannels

Microchannel technology is one of the significant methods to realize the safety control and intensified transferring for chemical process.To achieve the desired results of transfer and reaction,the micron channel structure is used to come true the precise control of flow behavior.In order to ensure the controllability and operability features of multiphase flow in microchannel,this dissertation investigated the gas-liquid flow characteristics in microchannel and multi-channel distribution rule at different operating conditions,fluids and channel lengths.Then the corresponding theoretical model and criterion were built to describe and predict the stability of flow behavior.This dissertation aims at providing experimental results and theoretical foundations for the operability in microchannel technology industrial application.In the experimental part,the CCD high speed camera and multi-point optical fiber detection system were utilized to detect and collect data of gas-liquid flow behaviors in microchannel.The former can realize batch of image information by self-programming and the latter can efficiently collect data with the advantages of high accuracy and high response.For the start-up process,a pressure sensor at gas inlet was used to identify this unfavorable process and the start-up process with gas pressure boundary condition was simulated using CFD.The experimental research on bubble uniformity of slug flow,stability of gas-liquid flow and the distribution rule of multi-channel were carried with wide operating conditions(gas 0.2~50 m L/min,liquid 0.05~20 m L/min),various liquids(deionized water,ethanol,glucose solution and kerosene)and different channel structures and sizes.Besides,the variation coefficient and Kolmogorov entropy were used to evaluate uniformity of distribution and stability of flow behavior.The experimental results shown that unsteady flows appeared in regimes of bubbly flow and slug-stratified flow.The most part of slug flow exhibited a steady state flow and the uniformity of bubbles increased with the increase of the Capillary number.Besides,the high flow rate was benefit to achieve uniform distribution in multi-channel,and to generate stable slug flow.In the theoretical model part,a pressure model was established to quantize pressure variations and to predict the uniformity of bubble size for slug flow.A quasi-parabolic equation derived from the definition of Kolmogorov entropy and the analysis of unstable flow reasons was proposed to describe complex two-phase flow behaviors and predict operational ranges.Considering the mass conservation,momentum conservation and the disturbance among channels,a two-phase flow distribution rule model was built to predict the distribution results.These models can effectively predict flow behaviors and distribution results of gas-liquid flow in microchannel,as well as determine the operating ranges with a steady flow,which providing operational guidelines for industrial application of microchannel.