Yoshinori Hirose

Experimental Study on Contact Angle of Water Droplet in High-Temperature Condition

In recent decades, a number of reports have pointed out the importance of the influence of wall wettability on gas-liquid two-phase flow with a gas-liquid or liquid-gas phase change. However, very limited experimental data can be obtained about the wall surface wettability in BWRs high-temperature condition, or in the range from 250 to 300°C. From this point of view, we conducted an experimental study of surface wettability of droplet using a pressure vessel, we measured contact angles of water droplet under various ambient pressures (7.7, 14 and 15 MPa), atmospheric gases (nitrogen and argon), and test plate materials (aluminum, stainless 304, Zircaloy). In addition, experimental correlation was derived based on energy balance. The data obtained in this study will provide more accurate assessment of heat transfer in subchannels of BWRs.Copyright

Measurement of Solid‐Liquid Two‐Phase Flow Using a New Robust Normal‐Line Hough Transform Method

In this paper, we derive a technique for the measurement of the solid particle phase in a solid‐liquid two‐phase flow. The proposed method consists of a two‐step algorithm for the localization of particles. In the first step, we devise a Normal‐line Hough Transform method (NHT) and utilize it to detect the centre of the particles in the stereo images. In the second step, we validate the existence of the particle position extracted using NHT by comparing with a labeling parameter space that yield using image labeling technique, and this improves the robustness to noise and the precision remarkably. The proposed method provides a high detection rate with particularly low level of false positives, and an evident amelioration in time‐consuming as well. We also present extensive experimental results to illustrate the efficiency of the proposed approach.

Effect of Gravity on Axial Development of Vertical Bubbly Flow

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 = 5, 20, 40 and 60) under various flow conditions of superficial gas velocity (0.00823–0.0303 m/s) and superficial liquid velocity (0.138–0.915 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 rigorous transfer mechanisms in two-phase flow under microgravity environment.Copyright

Axial Development of Gas-Liquid Two-Phase Flow in Mini-Channels

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 1.02 and 0.55 mm-diameter pipes. 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 0.475 m/s to 4.89 m/s and from 0.980% to 28.6%, 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-channels.Copyright