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Zhang, H.*; Umehara, Yutaro*; Horiguchi, Naoki; Yoshida, Hiroyuki; Eto, Atsuro*; Mori, Shoji*
Energy, 335, p.138090_1 - 138090_18, 2025/10
Times Cited Count：0 Percentile：0.00(Thermodynamics)Nuclear power is a key low-carbon energy source for a carbon-neutral future. In boiling water reactors (BWRs), steam-water annular flow near fuel rods is crucial for reactor safety, but its high-temperature, high-pressure conditions (285
C, 7 MPa) make direct measurement challenges. To address this, we used an HFC134a-ethanol system at lower conditions (40C, 0.7 MPa) to simulate BWR annular flow. Using a high-speed camera and the constant electric current method, we analyzed liquid-film characteristics, wave velocity and frequency. We also examined surface tension and interfacial shear stress effects. Furthermore, we proposed a new correlation for base film thickness.
Zhang, H.*; Umehara, Yutaro*; Horiguchi, Naoki; Yoshida, Hiroyuki; Mori, Shoji*
Proceedings of 12th International Conference of Fluid Flow, Heat and Mass Transfer (FFHMT 2025), P. 222_1, 2025/07
In the past decades, the liquid film characteristics of annular flow, such as film thickness and wave height, have been studied extensively. However, most of experimental data and analyses available in previous studies are limited to the air-water annular flows under near-atmospheric conditions. Thus, the variation in surface tension and gas-liquid density ratio is also limited, and their effects on the characteristics of annular flow are not well-understood. The objective of this study is to clarify the effect of surface tension and gas-liquid density ratio on the wave height and interfacial shear stress in annular flows. We conducted experiments for gas-liquid annular flows and measured the time-varying liquid film thickness. Using water and ethanol as working liquids, whereas nitrogen and HFC134a gas as working gases, we varied the surface tension range from 30.7 to 67.4 mN/m and density ratio range from 27 to 434. The accuracy of sensors for the measurement using the conductance probe method is 
5%. By post-processing for the measurement data, liquid film thicknesses (base, average, and maximum film thickness) and wave height were estimated. As the experimental results, the data of both the maximum film thickness and the height of disturbance wave converged on a single curve when they plotted for the interfacial shear stress. The reason was considered that the shape of the disturbance wave is decided by the balance between the surface tension and the interfacial shear stress. With additional analysis based on a potential method, a direct relationship between the height of disturbance wave and interfacial shear stress was clarified. These findings enhance the understanding of annular flow dynamics and contribute to improving the two-phase flow modelling.
Zhang, H.*; Umehara, Yutaro*; Yoshida, Hiroyuki; Mori, Shoji*
International Journal of Heat and Mass Transfer, 218, p.124750_1 - 124750_11, 2024/01
Times Cited Count：15 Percentile：79.71(Thermodynamics)Zhang, H.*; Umehara, Yutaro*; Yoshida, Hiroyuki; Mori, Shoji*
International Journal of Heat and Mass Transfer, 211, p.124253_1 - 124253_13, 2023/09
Times Cited Count：14 Percentile：77.61(Thermodynamics)Mori, Shoji*; Zhang, H.*; Umehara, Yutaro*; Horiguchi, Naoki; Yoshida, Hiroyuki
no journal, ,
To ensure nuclear safety, understanding of liquid film behavior of annular flow like flow near fuel rods in BWRs is important. It is hard to experimentally obtain thin liquid behavior in BWRs because of technical limits under the high pressure and temperature, 7MPa and 285C, and to understand the behavior sufficiently. Therefore, in this study, liquid film behavior under the actual condition was reproduced using ethanol-HFC134a system at 0.7MPa and 40C such as a university laboratory, which has almost same physical properties with the actual water-vapor system. In addition, the liquid film behavior was measured using the constant electric current method, and the measurable range and accuracy of the method were examined.
Abe, Yutaka*; Nishi, Yoshihisa*; Iwaki, Chikako*; Umehara, Yutaro*; Horiguchi, Naoki; Sonoda, Hiroki*
no journal, ,
Human resource development is an important issue in the nuclear field, and it is extremely important to transfer the know-how of veteran researchers who have accumulated over many years in the research field to the younger generation. In the field of reactor safety research in particular, the research environment has been changing in recent years, as it has become more difficult to conduct research using large experimental equipment, and many young researchers are finding the difficulty. This session will provide a forum in the form of a "round-table discussion" to discuss what veteran researchers want to tell young researchers and what young researchers want to ask veteran researchers. Through the panel discussion, communication between veteran researchers and young researchers about the future in the field will be promoted.
Zhang, H.*; Mori, Shoji*; Umehara, Yutaro*; Horiguchi, Naoki; Yoshida, Hiroyuki
no journal, ,
To ensure nuclear safety, understanding of liquid film behavior of annular flow like flow near fuel rods in BWRs is important. It is hard to experimentally obtain thin liquid behavior in BWRs because of technical limits under the high pressure and temperature, 7MPa and 285C, and to understand the behavior sufficiently. Therefore, in this study, liquid film behavior under the actual condition was reproduced using ethanol HFC134a system at 0.7MPa and 40C such as a university laboratory, which has almost same physical properties with the actual water-vapor system. In addition, the liquid film behavior was measured using the constant electric current method, and we considered the effects of pipe diameter on file flow behavior based on measured results.
Yomogida, Takumi; Murakami, Yohei*; Umehara, Yutaro*
no journal, ,
At the International Affairs Committee's planning session for 2025 Fall Meeting of the Atomic Energy Society of Japan, we report on activities conducted at the Institut de Physique du Globe de Paris during a stay facilitated by the Study Abroad Program in JAEA and discuss strategies to promote overseas activities among young researchers.
Zhang, H.*; Umehara, Yutaro*; Mori, Shoji*; Horiguchi, Naoki; Yoshida, Hiroyuki
no journal, ,
Due to the operating conditions of BWRs (285C and 7 MPa), the direct visualization and detailed liquid film measurement of steam-water annular flow in BWRs have been highly challenging. This study addresses this limitation by developing a novel HFC134a-ethanol annular flow system at lower temperature and pressure (40C and 0.7 MPa), simulating the steam-water annular flow under BWR conditions. The experiments of HFC134a-ethanol upward annular flow were conducted in a 5 mm inner diameter tube using the constant electric current method, and we obtained the flow characteristics including base, average, and maximum film thickness and the height of disturbance wave.
