Investigations On Characteristics Of Two-phase Slug Flow In Rectangular Channel

The gas-liquid slug flow is one of the most complex two-phase flow patterns with unsteady intermittent characteristics.This flow pattern is encountered in numerous practical situation,such as power engineering,petrochemical industry and nuclear engineering.Rectangular channels present the characteristics of compact layout and good heat transfer ability,they are widely used in the field of nuclear engineering.It is of great importance to investigate the hydrodynamic characteristics of gas-liquid slug flow in rectangular in engineering design.Non-intrusive flow visualization using a high speed video camera system was applied to study characteristics of slug flow in the narrow rectangular channel under vertical and inclined conditions.The experimental loop was open loop and forced circulation.The experiments were conducted under ambient temperature and pressure,and water and air were used as the test fluids.The five transparent test sections had the diameters of 2.08?15.96 mm,with aspect ratios ranging from 0.025 to 0.228.The gas superficial velocity and liquid superficial velocity ranges were 0.10?2.51 m/s and 0.16?2.62 m/s,respectively,the inclination angle(from the vertical)was 0°,10°,20° and 30?.The effects of geometric size of the channel,the inclination angle on the characteristics of slug flow in rectangular channel were investigated.The experimental data of slug bubble velocity in stagnant liquid,flowing liquid,continues slug flow,and undisturbed slug bubble velocity in continues slug flow in vertical rectangular channel were measured.The average slug bubble velocity and undisturbed slug bubble velocity in continues slug flow in inclined rectangular channel were measured.The effects of gas and liquid flow rates,the geometric size and the inclination angle on the slug bubble velocity were analyzed.The data fitting correlations of the slug bubble velocity were proposed based on the experimental data.The structure of the liquid slug and the mechanism of the slug bubble coalescence were investigated.The dependence of the slug bubble velocity on the liquid slug length ahead of it was measured.The effects of flow pattern in the main flow,the geometric size and the inclination angle on the dependence of the slug bubble velocity on the liquid slug length ahead of it were analyzed.Correlations were proposed based on the experimental data.The statistical characteristics of lengths of slug bubble and liquid slug were investigated.The distributions of lengths of liquid slug and slug bubble were all positively skewed.The effects of gas and liquid flow rates,the geometric size and the inclination angle on the lengths of slug bubble and liquid slug,the slug frequency,the slug bubble occurrence rate and the slip ratio were analyzed.The velocity and thickness of liquid film in the slug flow in the channel III were measured.The effects of gas and liquid flow rates and the inclination angle on the velocity and thickness of liquid film were investigated,correlations were proposed.In the present experiments,Images processing was applied to obtain the local and average interfacial parameters,such as the void fraction,interfacial area concentration(IAC),Sauter mean diameter,in the narrow rectangular channel.Lateral distribution of the local interfacial parameters of the slug bubble region,the liquid slug region and the slug unit were investigated.Axial distribution of the cross-sectional average interfacial parameters of the slug bubble region and the liquid slug region were investigated.The void fraction distribution patterns both in the slug bubble region and the slug unit could be classified into four basic types,i.e.flat distribution,flat distribution non step-index,core peak and core peak non step-index.The void fraction distribution patterns in the liquid slug region could be classified into three basic types,i.e.core peak,middle peak and double peak.The effects of gas and liquid flow rates,the geometric size and the inclination angle on the local and average interfacial parameters were analyzed.The correlations of the average void fraction in narrow rectangular channel under vertical and inclined conditions were proposed based on the experimental data.