Study On Interfacial Behavior Of Annular Flow In Narrow Rectangular Channel

Annular flow,as one of the most typical gas-liquid two-phase flow patterns,exists in engineering fields such as nuclear power generation,phase change heat transfer,air conditioning and refrigeration,and petrochemical industry.Accurately understanding the interface behavior of annular flow can provide more accurate information on its formation reasons,which supports the modeling and parameter prediction of annular flow.It is of great significance for the smooth operation,reasonable regulation,and safety control of systems with annular flow.This study mainly focuses on the gas-liquid interface behavior of vertically rising annular flow in narrow rectangular channels,analyzes the characteristics of high-speed photography dynamic images in the experiment,and divides the interface morphology of different features through image processing systems.The parameters observed in the experiment mainly include gas-liquid phase flow rate signal,experimental section pressure difference signal,as well as parameters such as annular flow liquid film thickness,wave frequency,and wave velocity.Combining nonlinear analysis methods such as wavelet analysis,multi-scale entropy method,and power spectrum method to conduct in-depth analysis and discussion on the dynamic characteristics of annular flow.Based on the analysis of dynamic characteristics,the formation mechanism of wavy interfaces is obtained,and based on this,predictions of parameters such as disturbance wave velocity,liquid film thickness,and wall shear force for annular flow are given.The experimental results show that the annular flow with liquid phase downcomer contains two regions.According to the reversal discriminant,the reversal phenomenon of the liquid film is proved.Six interface shapes were obtained by dividing the interface of the completely ascending annular flow,and the characteristics of the corresponding interface behavior under different gas-liquid phase conditions were elaborated.In the experiment,the wavelet analysis method was used to analyze the pressure parameters.The results showed that the high-frequency components d3 and d4 were widely distributed,but the signal characteristics were not obvious.However,the energy distribution was concentrated in the intermediate frequency component d5 frequency band and the approximate frequency band a frequency band,and the signal analysis at different scales showed a "bimodal" feature.The results of multi-scale entropy analysis method indicate that as the gas flow rate increases,the entropy value of each interface behavior decreases.In addition,there are always two dominant interface forms in the annular flow under each gas-liquid working condition.At low gas phase flow rates,banded disturbance waves and banded entrainment waves are the main interface forms.As the gas phase flow rate increases,banded disturbance waves and banded crushing waves gradually become the main waveforms.The power spectrum analysis method was used to analyze the liquid film signal,and the results also showed a "double peak" shape.The low-frequency region had a large amount of energy,while the high-frequency region had a lower energy,with a large frequency proportion range and uniform distribution.The increase in gas flow rate tends to distribute energy into higher frequency waves,with a decreasing trend in peak values.However,the increase in liquid flow rate has no significant impact on frequency,and the proportion of energy increases.This study focuses on the correlation between wall shear force,annular flow liquid film thickness,and channel disturbance wave velocity.The analysis results show that shear force varies with the square of channel disturbance wave velocity.Regarding the results of channel disturbance wave velocity,the correlation of Ju can effectively predict the velocity of disturbance waves.Based on the characteristics of the wavy interface,this study considers the disturbance wave velocity,gas core density,and liquid phase density,and provides a wall shear stress relationship formula.The calculation results are all within the error range of ±20%.