Research On Characteristics Of Upward Annular Flow Based On Laser-induced Fluorescence

The upward annular flow is an important flow pattern of gas-liquid two-phase flow,which has the typical characteristics of annular flow.Due to the high gas-liquid two-phase flow rate of the upward annular flow and the thin liquid film,the flow process in the annular flow is accompanied by power consumption and mass transfer heat transfer,which are widely found in the fields of chemical industry,energy,foundry,refrigeration,and aerospace.Therefore,the accurate acquisition of upward annular flow characteristic parameters is of great significance for both actual production and fluid theory research.Laser-induced fluorescence(LIF)is a non-invasive,high spatial-temporal multiphase flow diagnostic technique.Based on the laser-induced fluorescence technique,the error analysis of the longitudinal liquid film optical distortion correction measurement method is carried out.Based on this method,the influence of the U-bend that widely used in industrial applications on the distribution and development of the upward annular liquid film was investigated,and the influence distance was analyzed.In addition,the spatial-temporal structure of the upward annular flow liquid film was analyzed under different liquid-phase apparent flow rates with different liquid surface tension to explore the influence of surface tension on it.The specific work is as follows:1.Based on the analysis of the existing annular fluid film measurement technique,the non-invasive measurement of the annular flow liquid film was carried out by laser-induced fluorescence technique.And based on the liquid film optical distortion correction model established by analyzing the principle of liquid film imaging,considering the influence of factors such as pipe material,laser incident position and pipe thickness on the measurement of liquid film parameters,the error analysis is carried out to get a better distortion correction result.2.Laser-induced fluorescence technique was used to measure the upward annular flow longitudinal liquid film at different distances from the U-bend,and the image was extracted by digital image processing.And the measurement was compared with relevant classical prediction models.3.For the gas-liquid two-phase annular flow,the laser-induced fluorescence technique was used to measure the upward annular flow longitudinal liquid film at different gas-liquid phase flow rates under normal and low surface tension liquid phase conditions.The characteristics of liquid film were analyzed by time-frequency analysis and the spatial-temporal structure of the liquid film.The characteristics of liquid film thickness,disturbance wave characteristics and flow mechanism were studied and analyzed under low surface tension liquid phase conditions.