Effect of Gravity on Axial Development of Vertical Bubbly Flow

In relation to the development of the interfacial area transport equation, axial developments of one-dimensional void fraction, bubble number density, interfacial area concentration, and Sauter mean diameter of adiabatic nitrogen-water bubbly flows in a 9 mm-diameter pipe were measured by using an image-processing method under microgravity environment. The flow measurements were performed at four axial locations (axial distance from the inlet normalized by the pipe diameter = 7, 30, 45 and 60) under various flow conditions of superficial gas velocity (0.0083 m/s ∼ 0.022 m/s) and superficial liquid velocity (0.073 m/s ∼ 0.22 m/s). The interfacial area transport mechanism under microgravity environment was discussed in detail based on the obtained data and the visual observation. These data can be used for the development of reliable constitutive relations which reflect the true transfer mechanisms in two-phase flow under microgravity environment.

Interfacial area transport of bubbly flow under microgravity environment

In relation to the development of the interfacial area transport equation, axial developments of void fraction profile, bubble number density, interfacial area concentration and Sauter mean diameter of adiabatic nitrogen-water bubbly flows in a 9 mm-diameter pipe were measured by using a stereo image-processing method under normal- and micro-gravity environment. The flow measurements were performed at four axial locations (axial distance from the inlet normalized by the pipe diameter, z/D = 5, 20, 40 and 60) at various flow conditions of superficial gas velocity (0.00823-0.0303 m/s) and superficial liquid velocity (0.147-0.907 m/s). The effect of gravity on radial distribution of bubbles and axial developments of two-phase flow parameter was discussed in detail based on the obtained data and the visual observation.

In pursuit of the development of the interfacial area transport equation, the axial development of void fraction profile, bubble number density, interfacial area concentration and Sauter mean diameter of adiabatic nitrogen-water bubbly flows in a 9 mm-diameter pipe were measured in normal and microgravity environments using stereo image-processing. The flow measurements were performed at four axial locations (axial distance from the inlet normalized by the pipe diameter, z/D = 5.0, 20, 40 and 60) at various flow conditions of superficial gas velocity (0.00823–0.0303 m/s) and superficial liquid velocity (0.147–0.907 m/s). The effect of gravity on the radial distribution of bubbles and the axial development of two-phase flow parameters is discussed in detail based on the measured data and the visual observation.

In relation to the development of the interfacial area transport equation, axial developments of void fraction profile, interfacial area concentration and Sauter mean diameter of adiabatic nitrogen-water bubbly flows in a 9 mm-diameter pipe were measured by using a stereo image-processing method at normal-and micro-gravity conditions. The flow measurements were performed at four axial locations (axial distance from the inlet normalized by the pipe diameter, z/D=5, 20, 40 and 60) at various flow conditions of superficial gas velocity (0.008 40-0.029 8 m/s) and superficial liquid velocity (0.138-0.914 m/s). The effect of gravity on radial distribution of bubbles and the axial developments of two-phase flow parameter was discussed in detail based on the obtained data and the visual observation.

This study aims at the measurements of the axial developments of flow parameters such as void fraction profile, interfacial area concentration and Sauter mean diameter of adiabatic nitrogen-water bubbly flows in a 9 mm-diameter pipe by using a stereo image-processing method at normal- and micro-gravity conditions. The flow measurements were performed at four axial locations (axial distance from the inlet normalized by the pipe diameter, z/D = 5, 20, 40 and 60) at various flow conditions of superficial gas velocity (0.00840–0.0298 m/s) and superficial liquid velocity (0.138–0.914 m/s). The effect of gravity on radial distribution of bubbles and the axial developments of two-phase flow parameter was discussed in detail based on the obtained data and the visual observation.

In relation to the development of the interfacial area transport equation, a precise database of the axial development of void fraction profile, interfacial area concentration and Sauter mean bubble diameter in an adiabatic nitrogen-water bubbly flow in a 9 mm-diameter pipe was constructed for normal and microgravity conditions using stereo image-processing. The flow measurements were performed at four axial locations (axial distance from the inlet normalized by the pipe diameter, z/D = 5, 20, 40 and 60) and with various flows: superficial gas velocity of 0.00840–0.0298 m/s, and superficial liquid velocity of 0.138–0.914 m/s. The effect of gravity on radial distribution of bubbles and the axial development of two-phase flow parameters is discussed in detail based on the obtained database and visual observation.

Effect of inlet gas and liquid velocity profiles on one-group interfacial area transport equation in a vertical large rectangular channel

In relation to the development of the interfacial area transport equation, this study focused on modeling of the interfacial area transport mechanism of vertical adiabatic air-water bubbly flows in a relatively small diameter pipe where the bubble size-to-pipe diameter ratio was relatively high and the radial motion of bubbles was restricted by the presence of the pipe wall. The sink term of the interfacial area concentration was modeled by considering wake en-trainment as a possible bubble coalescence mechanism, whereas the source term was neglected by assuming negligibly small bubble breakup for low liquid velocity conditions based on visual observation. One-dimensional interfacial area transport equation with the derived sink term was evaluated by using five datasets of vertical adiabatic air-water bubbly flows measured in a 9.0mm-diameter pipe (superficial gas velocity: 0.013–0.052 m/s, superficial liquid velocity: 0.58–1.0m/s). The modeled interfacial area transport equation could reproduce the proper trend of the axial interfacial area transport and predict the measured interfacial area concentrations within an average relative deviation of 1±11.1%. It was recognized that the present model would be promising for predicting the interfacial area transport of the examined bubbly flows.

In relation to the development of the interfacial area transport equation, this study focused on modeling of the interfacial area transport mechanism of vertical adiabatic air-water bubbly flows in a relatively small diameter pipe where the bubble size-to-pipe diameter ratio was relatively high and the radial motion of bubbles was restricted by the presence of the pipe wall. The sink term of the interfacial area concentration was modeled by considering wake en-trainment as a possible bubble coalescence mechanism, whereas the source term was neglected by assuming negligibly small bubble breakup for low liquid velocity conditions based on visual observation. One-dimensional interfacial area transport equation with the derived sink term was evaluated by using five datasets of vertical adiabatic air-water bubbly flows measured in a 9.0mm-diameter pipe (superficial gas velocity: 0.013–0.052 m/s, superficial liquid velocity: 0.58–1.0m/s). The modeled interfacial area transport equation could reproduce the proper trend of the axial interfacial area transport and predict the measured interfacial area concentrations within an average relative deviation of 1±11.1%. It was recognized that the present model would be promising for predicting the interfacial area transport of the examined bubbly flows.

Axial developments of one-dimensional void fraction, bubble number density, interfacial area concentration, and Sauter mean diameter of adiabatic nitrogen-water bubbly flows in a 9-mm-diameter pipe were measured under a microgravity environment using an image-processing method. The interfacial area transport mechanism was determined based on visual observation. Marked bubble coalescence occurred when fast-moving bubbles near the channel center overtook and swept up slower-moving bubbles in the vicinity of the channel wall (velocity profile entrainment). Negligible bubble breakup was observed because of weak turbulence under tested flow conditions. Axial changes of measured interfacial area concentrations were compared with the interfacial area transport equation considering the bubble expansion and wake entrainment as observed under a normal gravity environment. The velocity profile entrainment effect under microgravity was likely to be comparable to the wake entrainment effect under normal gravity in the tested flow conditions. This apparently led to insignificant differences between measured interfacial area concentrations and those predicted by the interfacial area transport equation with the wake entrainment model under normal gravity. Possible bubble coalescence mechanisms would differ, however, between normal gravity and microgravity conditions.

Local flow measurements were performed for vertical upward bubbly flows in a 9 mm-diameter pipe at normal- and micro-gravity conditions. A stereo image-processing method was used for measuring void fraction profile, interfacial area concentration and Sauter mean diameter. The flow measurements were performed at four axial locations (axial distance from the inlet normalized by the pipe diameter, z/D=5, 20, 40 and 60) at various flow conditions of superficial gas velocity (0.00840-0.0298 m/s) and superficial liquid velocity (0.138-0.914 m/s). By taking into account the normalized parameters on void peak fraction and void peak intensity in pipe cross-section, the phase distribution pattern was quantitatively-classified into three patterns : a wall peak, a core peak and an intermediate peak. The phase distribution pattern maps were newly presented for vertical upward bubbly flows at normal-and micro-gravity conditions.

Interfacial area transport due to shear collision of bubbly flow in small-diameter pipes

The axial development of the void fraction, interfacial area concentration and Sauter mean bubble diameter profiles of adiabatic air-water bubbly flows in 5.0 and 3.0 mm-diameter pipes were measured using a stereo image processing method under two gravity conditions, vertical upward (normal gravity) and microgravity. The flow measurements were performed at four axial locations. The axial distances from the pipe inlet (z) normalized by the pipe diameter (D) were z/D = 5.5, 34, 72 and 110 for 5.0 mm-diameter pipe and z/D = 15, 62, 120 and 188 for 3.0 mm-diameter pipe. Data were collected for superficial gas and liquid velocities respectively in the ranges of 0.00434–0.0500 m/s and 0.205–0.754 m/s. The effect of gravity on the radial distribution of bubbles and the axial development of two-phase flow parameters is discussed in detail, based on the obtained database. The phase distributions in pipe cross-sections were classified into 3 basic patterns: core peak, intermediate peak and wall peak distributions, based on two normalized parameters: a normalized void peak position and a normalized void peak intensity. Phase distribution pattern maps under normal and microgravity conditions were generated for bubbly flows in 5.0 and 3.0 mm-diameter pipes. The data obtained in the current experiment are expected to contribute to the benchmarking of CFD simulation of void fraction and interfacial area concentration distribution patterns in forced convective pipe flow under microgravity conditions.

In relation to the development of the interfacial area transport equation, a precise database of the axial development of void fraction profile, interfacial area concentration and Sauter mean bubble diameter in an adiabatic nitrogen-water bubbly flow in a 5 mm-diameter mini pipe was constructed for normal and microgravity conditions using stereo image-processing. The flow measurements were performed at four axial locations (axial distance from the inlet normalized by the pipe diameter, z/D = 5.5, 34, 72 and 110) and with various flows: superficial gas velocity of 0.00434–0.0420 m/s, and superficial liquid velocity of 0.239–0.949 m/s. The effect of gravity on radial distribution of bubbles and the axial development of two-phase flow parameters is discussed in detail based on the obtained database and visual observation.