Investigation On Measurement Error And Flow Characteristics Of Annular Flow Liquid Film Based On PLIF

For the excellent heat and mass transfer performance,the annular flow is widely used in industry.The measurement of annular flow liquid film is helpful to understand its flow mechanism,which is important to reveal the interaction between gas and liquid phase.Planar laser-induced fluorescence(PLIF)realizes the non-invasive,high temporal and spatial resolution measurement of liquid film.Based on PLIF,the axial and circumferential liquid film of annular flow are measured,and the flow characteristics of vertical downward and horizontal annular flow are analyzed respectively.The accurate measurement of the complex gas-liquid interface of annular flow requires the further development of this method.The sources of distortion when measuring the axial and circumferential liquid film of annular flow are analyzed,and the distortion correction methods of the axial and circumferential liquid film are proposed.The specific work includes the following:1.Based on PLIF,the characteristics of axial liquid film in vertical downward annular flow are investigated.Firstly,the axial liquid film is reconstructed based on cross-correlation.Then the single-wave recognition method based on local minimum is determined and the wave height is extracted.Based on the probability density distribution of wave height,a standard for distinguishing ripples and disturbance waves is proposed.Finally,the flow characteristics are analyzed.2.Based on PLIF,the characteristics of circumferential liquid film of horizontal annular flow are investigated.A liquid film image segmentation method based on color difference and clustering is proposed for the images with noise.The thickness of the circumferential liquid film is extracted,and the asymmetry of the circumferential liquid film distribution is studied.Based on the temporal and spatial distribution of the circumferential liquid film,the relationship between the top liquid film and the bottom liquid film is analyzed.The effect of gas and liquid flow velocity on the circumferential liquid film distribution is also studied.3.For accurate measurement of the complex gas-liquid interface,the investigation is carried out around the distortion of the axial and circumferential liquid film,and the sources of distortion are analyzed.The influence of the measurement angle on the PLIF is studied,and a measurement method that suppresses the total reflection by reducing the measurement angle is proposed.The error of the circumferential liquid film distortion correction method based on optical path analysis is analyzed and optimized.