Heat transfer coefficient modeling for downward saturated boiling flows in vertical pipes

Wada, Yuki; Shibamoto, Yasuteru; Hibiki, Takashi*

International Journal of Heat and Mass Transfer, 249, p.127219_1 - 127219_16, 2025/10

https://doi.org/10.1016/j.ijheatmasstransfer.2025.127219

Sharp surface tension model with pressure discontinuity and refined curvature for multiphase particle methods

Wang, Z.; Matsumoto, Toshinori; Shibamoto, Yasuteru; Duan, G.*

Journal of Computational Physics, 537, p.114072_1 - 114072_29, 2025/09

https://doi.org/10.1016/j.jcp.2025.114072

Experimental study on the rewetting velocity on dry out surface due to stepwise boundary condition changes

Satou, Akira; Wada, Yuki; Shibamoto, Yasuteru

Nuclear Engineering and Design, 437, p.114020_1 - 114020_14, 2025/06

https://doi.org/10.1016/j.nucengdes.2025.114020

Post-boiling transition (post-BT) heat transfer is essential for analyzing the duration of surface dryout and peak cladding temperature during abnormal transients and accidents in light water reactors. The rewetting phenomenon is very important for evaluating the dryout duration. However, due to the lack of an experimental database on rewetting velocities under high flow and heat flux conditions, sufficient data for model development and validation do not exist. Therefore, a database on rewetting velocities caused by stepwise boundary condition changes under a wide range and multiple combination of thermal-hydraulic conditions was obtained using a single-tube experimental apparatus. Based on this database and the characteristics of rewetting velocities obtained, an experimental correlation for rewetting velocity was proposed. This correlation predicts the rewetting velocity accurately by taking the change in the mass flux of the liquid or gas phase with stepwise transients as a parameter. This suggested that the change in the mass flux of the gas or liquid phase near the liquid film front has a strong influence on the rewetting under extremely high mass flux conditions compared to the reflooding process.

CFD applications to pressurized thermal shock-related phenomena (Contract research, Translated document)

Okagaki, Yuria; Hibiki, Takashi*; Shibamoto, Yasuteru

JAEA-Review 2024-047, 58 Pages, 2025/02

JAEA-Review-2024-047.pdf:2.22MB

In PWR accident scenarios, the injection of water from the ECCS (ECC injection) might result in thermal stratification in the case of the insufficient mixing of cold and hot water and induce a PTS, affecting the RPV integrity. Therefore, PTS is a vital research issue in reactor safety, and its analysis is essential for evaluating the integrity of RPVs, which determines the reactor life. The PTS analysis comprises a coupled analysis between thermal-hydraulic and structural analysis. Especially in the thermal-hydraulic approach, reliable CFD simulations should play a vital role in the future because predicting the temperature gradient of the RPV wall requires data on the transient temperature distribution of the DC. This study reviewed from the viewpoint of the turbulence models most affecting PTS analysis based on papers published since 2010 on single- and two-phase flow CFD simulation for the experiment on PTS performed in the ROCOM, Transient TOPFLOW, UPTF, and LSTF.

Free outflow from the end of a horizontal circular pipe related to flow from the PWR cold leg to the downcomer

Satou, Akira; Hibiki, Takashi*; Ikeda, Ryo; Shibamoto, Yasuteru

Progress in Nuclear Energy, 180, p.105593_1 - 105593_11, 2025/02

https://doi.org/10.1016/j.pnucene.2024.105593

During a loss-of-coolant accident in a pressurized water reactor (PWR), there is a risk that pressurized thermal shock (PTS) may occur on the internal wall of the reactor pressure vessel (RPV) due to the flow of emergency core cooling (ECC) water injected into the cold leg that flows into the downcomer. PTS is caused by the rapid cooling of the downcomer wall by the ECC water and is strongly influenced by the temperature of the ECC water, the collision position and velocity of the water jet on the wall, the velocity of the liquid film on the wall, the thickness of the liquid film, and the spread of the downward flow. Therefore, the flow of ECC water discharging from the cold leg to the downcomer may strongly impact PTS events. To help understand this flow phenomenon, we reviewed studies on free outflow from a circular pipe. Experimental findings on the classification of flow conditions, transition conditions between flow conditions, end depth ratio, free surface profile of flow in the circular pipe, and shape of the nappe flowing out from the pipe have been obtained in a form that is almost consistent with each other. In contrast, when considering the flow from the cold leg to the downcomer, it is necessary to deal with the flow field in a specific situation, such as the flow into a narrow gap rather than a free space, the existence of rounded corners at the outlet of the circular pipe, and the influence of steam flow flowing from the core to the cold leg. However, few previous studies consider these factors, so we summarized them as knowledge that needs to be accumulated in the future.

Opposing mixed convection heat transfer for turbulent single-phase flows (Contract research, Translated document)

Motegi, Kosuke; Shibamoto, Yasuteru; Hibiki, Takashi*; Tsukamoto, Naofumi*; Kaneko, Junichi*

JAEA-Review 2024-039, 45 Pages, 2024/09

JAEA-Review-2024-039.pdf:2.23MB

Several heat transfer correlations have been reported related to single-phase opposing flow; however, these correlations are based on experiments conducted in various channel geometries, working fluids, and thermal flow parameter ranges. Therefore, establishing a guideline for deciding which correlation should be selected based on its range of applicability and extrapolation performance is important. This study reviewed the existing heat transfer correlations for turbulent opposing-flow mixed convection. Furthermore, the authors evaluated the predictive performance of each correlation by comparing them with the experimental data obtained under various experimental conditions. The Jackson and Fewster, Churchill, and Swanson and Catton correlations can accurately predict all the experimental data. The authors confirmed that heat transfer correlations using the hydraulic-equivalent diameter as a characteristic length can be used for predictions regardless of channel-geometry differences. Furthermore, correlations described based on nondimensional dominant parameters can be used for predictions regardless of the differences in working fluids.

Boundary layer measurements for validating CFD condensation model and analysis based on heat and mass transfer analogy in laminar flow condition

Soma, Shu; Ishigaki, Masahiro*; Abe, Satoshi; Shibamoto, Yasuteru

Nuclear Engineering and Technology, 56(7), p.2524 - 2533, 2024/07

https://doi.org/10.1016/j.net.2024.02.011

CFD applications to pressurized thermal shock-related phenomena

Okagaki, Yuria; Hibiki, Takashi*; Shibamoto, Yasuteru

International Journal of Energy Research, 2024, p.5114542_1 - 5114542_37, 2024/04

https://doi.org/10.1155/2024/5114542

Critical heat flux for downward flows in vertical round pipes

Hirose, Yoshiyasu; Shibamoto, Yasuteru; Hibiki, Takashi*

Progress in Nuclear Energy, 168, p.105027_1 - 105027_17, 2024/03

https://doi.org/10.1016/j.pnucene.2023.105027

Application of analytical wall functions to CFD analysis of condensation flow

Soma, Shu; Ishigaki, Masahiro*; Abe, Satoshi; Shibamoto, Yasuteru

Nuclear Engineering and Design, 416, p.112754_1 - 112754_18, 2024/01

https://doi.org/10.1016/j.nucengdes.2023.112754