Tadayoshi Matsumoto

New entrainment rate correlation in annular two-phase flow applicable to wide range of flow condition

Abstract Assuming the rate of droplet entrainment is characterized by the ratio of the interfacial shear force to the surface tension force acting on the phase interface, new correlation representing the rate of droplet entrainment in annular-dispersed two-phase flow was developed. Although the correlation is based on the simple assumption, the quasi-equilibrium droplet flow rates measured in many experiments were predicted reasonably well (root mean square error of entrainment fraction was roughly halved comparing with several existing correlations). Its applicability to the non-equilibrium situation was also demonstrated by the numerical calculations using a one-dimensional three-fluid model.

Flow Patterns of Gas-Liquid Two-Phase Flow in Round Tube With Sudden Expansion

Experimental studies were made on the multi-dimensional behavior of upward gas-liquid two-phase flow through the vertical round tube with an axisymmetric sudden expansion, which is one of the typical multi-dimensional channel geometry. The aims of this study are to clarify the multi- dimensional behavior of bubbly or slug flow affected by sudden expansion channel geometry, and to accumulate the experimental data for two-phase flow analysis, which is applicable to predict with appropriate accuracy the multi- dimensional its behavior. The direct observation using high- speed video camera was performed and revealed the multi- dimensional dynamic flow behavior with bubbles and gas-slug affected by the sudden expansion part (20 mm-tube to 50 mm- tube). The characteristic phenomena were observed such as bubble break-up, deformation due to the strong shear of liquid flow, or liquid micro jet penetration through the gas-slug, and so on. From these results, the flow regime map and the flow patterns at the below and above of the sudden expansion part were classified in relation to the bubble diameter. Additionally, the measurement of the void fraction profiles in the tube cross sections of sudden expansion were conducted at the different axial positions. The void fraction was measured using a point- electrode resistivity probe. The void fraction measurements in this study showed in detail that how the two phase flow develops along the direction of the downstream of the sudden expansion. In just above the sudden expansion, the void fraction distribution appeared the wall peak or the core peak in void fraction in the upstream of the sudden expansion. In the downstream of the sudden expansion, the void fraction distribution changes from a saddle shape or power-low shape into finally the saddle shape as the bubbly flow develops along the downstream of the sudden expansion. These experimental data in the sudden expansion of a vertical upward bubbly flow would become benchmark with respect to the multi- dimensional behavior of the two-phase flow analysis.

Gas-Core Turbulence Structure of Annular Flow Passing Through a Throat Section Affected by the Wavy Interface on Liquid Film Flow

Experimental studies were made on the gas-core turbulence structure in vertical upward annular two-phase flow passing through a round tube with a throat section. The gas-core turbulence is affected and modified by the dynamic interaction between gas-core flow and liquid film flow through the wavy interface. The test channel has a throat section, which consist of nozzle, throat and diffuser part, where the cross sectional area of the channel is changed along the flow direction. In the throat section, the flow is in transient state because the flow is accelerated or decelerated along the flow direction as the cross sectional area of the channel is changes. The gas-phase turbulence structure such as the time-averaged velocity profiles and fluctuation velocity profiles were precisely measured by using the constant temperature hot-wire anemometer. For the liquid film flow, the time-averaged film thickness, base-film thickness and interfacial wave height were obtained by using the point electrode resistivity probe. Direct observations for the interfacial waves on liquid film flow such as disturbance waves and ripple were also carried out by using the high-performance camera system to make clear the interfacial wave structure.Copyright

Phase Distribution of Air-Water Bubbly Flow in a Vertical Pipe With an Axisymmetric Sudden Expansion

Experimental studies were made on the multi-dimensional behavior of upward gas-liquid two-phase flow through a vertical pipe with an axisymmetric sudden expansion, which is one of the typical multi-dimensional channel geometries. The aims of this study are to clarify the multi-dimensional behavior of bubbly and slug flow affected by the sudden expansion channel geometry and to accumulate the experimental data for two-phase flow analysis, which is applicable to predict appropriate accuracy the multi-dimensional behavior. In this report, the first, the observation using high-speed video camera was performed and revealed the multi-dimensional dynamic flow behavior with bubbles and gas-slug affected by the sudden expansion point. From these results, the flow regime map at the below and above of the sudden expansion point were classified with bubble diameter. The second, the variation of the phase distribution in the sudden expansion was measured at the different axial positions using a point-electrode resistivity probe for various gas and liquid flow conditions. Thirdly, the cross-sectional averaged void fractions along the flow direction were calculated by using the one-dimensional two-fluid model considering the phase distribution parameter to confirm the applicability of the computations. As a result, they concretely pointed out that some multi-dimensional modeling or modifications for numerical simulation would be needed for more accurate prediction of two-phase flow. Such radial phase distributions in this study are significant for the multi-dimensional two-phase flow analysis.Copyright

Study of the behavior of ephemeral waves in gas-liquid two-phase flow: I. Determination of sub-wave-veins

Time-spatial measurements of liquid holdup distributions along the axis of a tube were carried out over the length of 1325 mm in upward gas-liquid two-phase flow. In order to clarify the characteristics of the behavior of ephemeral waves, a method of determining sub-wave-veins, that is, the traces of ephemeral waves on the time-spatial behavior charts of the interface, was developed. This method was applied to the flow conditions in huge wave flow and annular flow regimes, and the sub-wave-veins in these flow regimes were successfully determined. Time-spatial behavior charts of the interface with determined sub-wave-veins were systematically presented and the characteristics of sub-wave-veins were discussed. Close inspection of the behavior of sub-wave-veins reveals that there are two types of ephemeral waves: one has a shorter life span and the other has a longer life span during which absorption and discharge of small ephemeral waves occurs

Study on behavior of ephemeral wave in gas-liquid two-phase flow: Part 2. Characteristics in flow parameter of ephemeral waves

In order to clarify the behavior of ephemeral waves, flow parameters of ephemeral waves, such as the number and residence zone lengths per unit axial length, mean values and standard deviations of wave velocity, width, and maximum holdup, were determined using a wave-vein analysis in upward huge wave flow and annular flow. The mean values of wave velocities, widths, and maximum holdups of ephemeral waves are compared with those of liquid lumps having main wave-veins, and the differences in the parameters between those liquid lumps are discussed. Furthermore, the parameters of both active ephemeral waves and inactive ephemeral waves are determined, and the characteristics in the flow parameters of two types of ephemeral waves are presented