Research On Circumferential Measurement And Characteristics Analysis Of Annular Liquid Film Based On Laser Induced Fluorescence

For the excellent heat and mass transfer performance,the annular flow is widely used in industry.It is applied in the fields of chemical engineering,oil and gas transportation,refrigeration,aerospace and many other fields.The accurate measurement of the annular flow is the basis for studying the flow mechanism of it.Due to its advantages of non-invasion,high temporal and spatial resolution,Laser-induced fluorescence(LIF)has been increasingly employed in the annular flow measurement in recent years.Based on LIF,a method to measure the circumferential film characteristics of the annular flow is proposed,which lays a foundation for studying the circumferential distribution characteristics and the flow mechanism.Aiming at the image distortion caused by the difference on refractive index and the shape of the transparent pipe,a distortion correction method based on LIF optical path analysis is proposed.And the correction method is verified by falling film experiment.Based on the digital image processing technology,the circumferential characteristics of the annular flow are accurately extracted.Finally,based on LIF,the horizontal annular flow is measured.The formation mechanism of the liquid film which is on the top of the pipe is analyzed,and the circumferential distribution model of the horizontal annular liquid film is established.The specific work includes the following:1.Based on the current in-depth study of the annular flow measurement and LIF detection technology in the fields of annular flow detection,the optical path analysis of LIF is carried out to correct the image distortion.The thickness of the falling film is measured based on the distortion correction method.The measurement results are compared with the classical prediction models to verify this method.2.Because the structure of the annular flow is complex and the gas-liquid interface is blurred in the film image,the digital image processing technologies such as color space conversion,time-frequency domain and wavelet domain filtering are combined to suppress the noise and both highlight the annular flow features.Aiming at the segmentation of liquid film images under different flow conditions,both local adaptive and fuzzy clustering image segmentation techniques are proposed to accurately extract the circumferential features of the annular flow.3.Through LIF,the high-precision measurement on the circumferential characteristics of the horizontal annular flow is carried out.Based on the time-frequency domain analysis and cross-correlation theory,the formation of the liquid film near the top of the pipe is studied.The model of circumferential film thickness distribution is established.