Kotohiko Sekoguchi

Phase distribution for air-water two-phase flow in annuli.

環状流路内を垂直に上昇する空気-水系二相流の相分布に関する調査を行った。実験には半径比の異なる3種類の環状流路を用いた。まず,環状流路における流動様式について述べ,次いで,断面内ボイド率分布を提示し,流路幅が及ぼす影響について論ずる。調査の対象とした流動様式は気泡流,スラグ流,フロス流およびフロス流領域に近い環状流である。最後に断面平均ボイド率の整理式を導出した結果について報告する。

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

Effects of System Pressure on Flow Regime Transitions in Vertical Upward Gas-Liquid Two-Phase Flow.

The purpose of this study is to investigate the pressure effects on the flow regime transitions in vertical gas-liquid two-phase flow. The following five flow conditions were tested to examine the effects of system pressure; the flow conditions in the transitional area in which the plug flow changes to huge wave flow; the flow conditions of the central gas core in the tube; the flow conditions in the area where the liquid slug disappears; the flow conditions in the transitional area in which the bubble flow changes to plug flow; and the flow conditions in the transitional area in which the time averaged wall shear stress changes from the negative to the positive value. New correlations to predict the flow conditions for the five above-mentioned flow conditions are presented. System pressures tested, range from 0.3 to 20 MPa.

Statistical evaluation of liquid phase distributions in gas-liquid two-phase flow. Froth flow and huge wave regimes.

A statistical method is proposed to express the characteristics in interface on various sizes of liquid lumps appearing both in froth flow and huge wave regimes. According to cross-sectional mean liquid holdup traces, the interfacial structures were assumed fundamentally to consist of base wave and liquid slug or huge wave. The determining procedures of the shape factors and probability density of wave crests for these liquid lumps are explained. In addition, typical examples of applying this method into air-water two-phase upward flow in a 18.0 mm inside diameter tube are presented.

Gas-liquid Two-phase Flow in Double-Tubes-Annular-Passage with Flow Obstruction : 1st Report, Effect of Flow Obstruction on Minimum Film Thickness)

The effect of a flow obstruction was experimentally investigated on the minimum thickness of a water film formed on the outer surface of the inner tube of concentric double tubes, through an annular cross section of which air-water two-phase mixture flows vertically upward. The flow patterns concerned are slug, froth and annular flows. Two kinds of obstructions were used in this experiment ; one is a ring type obstruction and the other is a thin circular tube type spacer. The liquid film thickness is drastically decreased by the existence of a flow obstruction, i.e., to about 40 μm. The film thinning process and the dependency of film thickness upon flow patterns are found to be quite similar to those on the inner wall of a single circular tube with an obstruction . Furthermore, an increase in minimum film thickness near an obstruction is observed resulting from the existence of an upstream obstruction.