Tatsuya Hazuku

Interfacial area transport of bubbly flow under microgravity environment

Abstract 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 (0.0083–0.022 m/s) and superficial liquid velocity (0.073–0.22 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.

Measuring interfacial waves on film flowing down a vertical plate wall in the entry region using laser focus displacement meters

Abstract Waves on a film flowing down a vertical wall appear in many processes. The resulting interfacial waves show fascinating nonlinear phenomena, including solitary waves and complex disordered patterns. Measurements have often been made of these phenomena using electrical resistance or electrical capacitance methods, optical methods, and laser beam methods. This paper presents a new way of measuring the interfacial waves on a film flowing down a vertical plate wall in an entry region, using two laser focus displacement meters. The purpose of the study was to clarify the effectiveness of the new method for obtaining detailed information on the waves, and to investigate the effect of the entry length on the phenomena. With this method, accurate measurements of film thickness were achieved in real time with a sensitivity of 2 μm and 1 kHz. The error caused by refraction of the laser beam passing through a transparent wall was clarified. The present results for wave velocity and maximum film thickness agreed well with past experimental and theoretical studies. In short entry length conditions, the average measured film thickness and wave velocity agreed with those calculated using Nusselt’s Law, indicating that the flow is laminar even at a high flow rate. As a result of this study, an empirical equation expressing wave frequency in the entry region was formulated.

Simultaneous measuring system for free surface and liquid velocity distributions using PIV and LFD

Abstract In order to predict the free surface phenomena in a pool, the interaction between the liquid flow field and free surface should be evaluated. In this study, we aimed at developing a new three-dimensional measurement system for surface elevation and liquid velocity profiles in pool water using an image-processing technique and a laser focus displacement meter. The purpose of the experiments was to confirm the effectiveness of this new technique for obtaining temporal and spatial information on surface elevation and inclination as well as three-dimensional liquid velocity distribution. We confirmed that the free surface position and inclination were measured by this technique within 0.1 mm and 0.7° deviation. A data set for free surface and three-dimensional liquid velocity distribution was obtained through this study.

Measurement on Liquid Film in Microchannels Using Laser Focus Displacement Meter

This paper presents a new method for measuring the interfacial displacement of a liquid film in microchannels using a laser focus displacement meter (LFD). The purpose of the study is to clarify the effectiveness of the new method for obtaining detailed information concerning interfacial displacement, especially in the case of a thin liquid film, in microchannels and minichannels. To prevent the tube wall signal from disturbing that of the gas–liquid interface, a fluorocarbon tube with a water box was used; the refraction index of this device is the same as that for water. With this method, accurate instantaneous measurements of the interfacial displacement of the liquid film were achieved. The error caused by refraction of the laser beam passing through the acrylic water box and fluorocarbon tube was estimated analytically and experimentally. The formulated analytical equation can estimate the real interface displacement by using the measured displacement in a fluorocarbon tube of 25 μm to 2.0 mm I.D. A preliminary test using fluorocarbon tubes of 1 mm and 2 mm I.D. showed that the corrected interface displacement calculated by the equation agreed with the real displacement to within a 1% margin of error. It was also confirmed that the LFD in the system could measure a liquid film of 0.25 μm at the thinnest. We made simultaneous measurements of the interface in fluorocarbon tubes of 0.5 mm and 1 mm I.D. using the LFD and a high-speed video camera with a microscope. These showed that the LFD could measure the interface of a liquid film with high spatial and temporal resolution during annular, slug, and piston flow regimes. The data also clarified the existence of a thin liquid film of less than 1 μm in thickness in the slug and annular flow regimes.

Interfacial Area Transport of Bubbly Flow Under Microgravity Environment

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.Copyright

Flashing Hammer Phenomenon in Rapid Liquid-Liquid Contact

In a wall crack accident or loss-of-coolant accident (LOCA) in an advanced reactor with water filled containment, high pressure saturated water is discharged from the pressure vessel into the low-pressure, low-temperature water of the containment. The discharged saturated water causes flashing and generates steam. Steam is then condensed by the water in the containment. This paper describes our study of high pressure saturated water that rapidly contacts low-pressure, low-temperature water. The purpose of the study was to clarify the transient phenomena that occur when high pressure saturated water blows down from a pressure vessel into a water filled containment during a wall crack accident or LOCA in an advanced reactor. The experimental results revealed that flashing of high-pressure saturated water and a subsequent water hammer occurred under the specified experimental settings. Pressure peaked when steam generation or flashing occurred at the wall surface and the flashing steam condensed. After the peak, pressure oscillated and reached equilibrium condition in a short time. The pressure oscillation might have been caused by a balancing action between the flashing of high pressure saturated water and condensation of the steam generated by flashing in low-pressure, low-temperature water. To check the results of the experiments, numerical analyses were conducted. The numerical results cleared the mechanism behind flashing hammer phenomenon.Copyright

Interfacial Area Transport of Bubbly Flow in a Small Diameter Pipe Under Microgravity Environment

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.© 2002 ASME