Detection Of Characteristic Parameters Of Liquid Film Based On Conductance And Optical Attenuation Technology

Annular flow is a widely used multiphase flow pattern in engineering,which is mainly applied to petroleum,chemical,nuclear and other fields.Annular flow is composed of the liquid film and the gas core.Its mass and heat transfer performance depends on the liquid film.The characteristic parameters of the liquid film affect the properties of the annular flow.The main characteristic parameters of liquid film include liquid film thickness,wave velocity and wave frequency.In this paper,experimental technology,signal processing,theoretical analysis and other aspects of research were carried out around the characteristic parameters of liquid film.The main parts are as follows:Firstly,the circumferential liquid film of horizontal annular flow under atmospheric pressure was studied by conductance method.Through simulation and experiment,different sensors and different power supply excitation were compared.Considering the requirements of the circumferential measurement,the experimental was carried out using double parallel conductance probe and high frequency sine wave excitation.The circumferential liquid film was tested at the superficial gas flow rate of 15-35m/s and the superficial liquid flow rate of 0.1-0.4m/s.The results show that the thickness of the liquid film at the bottom decreases obviously with the increase of the gas flow rate,and the circumferential liquid film tends to be uniform.The circumferential thickness increases with the increase of the liquid flow rate,and the liquid film at the bottom tends to be saturated at the highest liquid flow rate,with the liquid film at the lower half circle tending to be uniform.Secondly,the local liquid film in horizontal and vertical pipes under high pressure was studied by optical attenuation method.This method detected the liquid film thickness according to the attenuation of near infrared light through the liquid film,due to the absorption of the medium.Based on the optical path analysis,according to the different error sources in the detection process,the device and experimental improvement scheme were designed to reduce the error.The experimental results under different pressures show that the variation of liquid film in vertical tube is similar to that in horizontal tube.And the effect of pressure is similar to that of gas velocity,which will reduce the thickness of liquid film,but the effect of pressure is weaker than that of gas velocity.Finally,Based on the experimental data of dynamic liquid film,the spatial distribution and development of wave velocity,wave frequency of annular flow were studied.The wave velocity and frequency in the horizontal pipe decrease with the increase of circumferential angle.The wave form of liquid film varies at different circumferential locations.The large amplitude disturbance wave only exists in the lower half of the cycle and has continuity.The wave velocity and wave frequency increase with the increase of pressure,but the effect of pressure is also weaker than that of gas velocity.When the liquid velocity in a horizontal tube increases,the wave frequency doesn't increase with the increasing of wave velocity.The large amplitude wave of the liquid film at the bottom has a tendency to spatially.Similar phenomena hasn't been observed in the thin liquid film of vertical tube.According to the experimental data,the prediction models for the disturbance wave frequency in horizontal and vertical annular flow are designed respectively.The errors of these models are about 10%.