Norihiro Fukamachi

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.

Axial Development of Vertical Upward Bubbly Flow in a Minipipe

Accurate prediction of the interfacial area concentration is essential to successful development of the interfacial transfer terms in the two-fluid model. Mechanistic modeling of the interfacial area concentration entirely relies on accurate local flow measurements over extensive flow conditions and channel geometries. From this point of view, accurate measurements of flow parameters such as void fraction, interfacial area concentration, gas velocity, bubble Sauter mean diameter, and bubble number density were performed by the image processing method at five axial locations in vertical upward bubbly flows using a 1.02 mm-diameter pipe. The frictional pressure loss was also measured by a differential pressure cell. In the experiment, the superficial liquid velocity and the void fraction ranged from 1.02 m/s to 4.89 m/s and from 0.980% to 24.6%, respectively. The obtained data give near complete information on the time-averaged local hydrodynamic parameters of two-phase flow. These data can be used for the development of reliable constitutive relations which reflect the true transfer mechanisms in two-phase flow. As the first step to understand the flow characteristics in mini-channels, the applicability of the existing drift-flux model, interfacial area correlation, and frictional pressure correlation was examined by the data obtained in the mini-channel.Copyright

Measurement of Interfacial Displacement of a 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 micro- and mini-channels. To prevent the tube wall signal from disturbing that of the gas-liquid interface, a fluorocarbon tube with water box was used ; the refraction index of this device is same as that for water. With this method, accurate instantaneous measurements of 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 using measured displacement in a fluorocarbon tube of 25μm to 2.0 mm I.D. A preliminary test using fluorocarbon tubes of 1 and 2 mm I.D. showed that the corrected interface displacement calculated by the equation agreed with real displacement 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 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 less than 1 pm in thickness in slug and annular flow regions.

Experimental study on axial development of bubbly flow under normal- and micro-gravity environment

In view of the great importance of two geometrical parameters such as void fraction and interfacial area concentration to the accurate two-phase flow analysis at microgravity conditions, axial developments of flow parameters such as void fraction, interfacial area concentration, bubble Sauter mean diameter, and bubble number density were measured by image-processing in bubbly flow at microgravity and low liquid Reynolds number conditions where the gravity effect on the flow parameters were pronounced. Negligible bubble breakup was observed because of weak turbulence under tested flow conditions. 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.

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