Experimental study on the breakup of liquid jet discharged from a nozzle with sudden contraction

Sun, G.*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Uchibori, Akihiro; Okano, Yasushi

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 8 Pages, 2023/05

When liquid sodium leaks as a liquid jet from piping in a sodium-cooled fast reactor, the jet impinges with structures to produce splashing droplets which can cause significant combustion. According to previous studies on circular nozzles, the amount of splash is affected by the state of the jet at the moment of impingement. In the present work, a nozzle with a sudden contraction in the cross-sectional area was designed to reproduce a supposed pipe leakage, and the breakup behavior of jet discharged from this nozzle was observed. The result shows that the breakup of jet was accelerated until the jet transformed into a particularly stable state when the jet velocity exceeded a certain value. Once the jet has transformed, it will not turn back unless turning down the flow rate to a very low value. The stable jet after the transformation has a longer breakup length than that before the transformation in the same flow rate.

Toward mechanistic evaluation of critical heat flux in nuclear reactors, 2; Recent studies and future challenges toward mechanistic and reliable CHF evaluation

Okawa, Tomio*; Mori, Shoji*; Liu, W.*; Ose, Yasuo*; Yoshida, Hiroyuki; Ono, Ayako

Nihon Genshiryoku Gakkai-Shi ATOMO, 63(12), p.820 - 824, 2021/12

https://doi.org/10.3327/jaesjb.63.12_820

The evaluation method of the critical heat flux based on the mechanism is needed for the efficient design and development of fuel in reactors and the appropriate safety evaluation. In this paper, the current researches relating to the mechanism of the critical heat flux are reviewed, and the issue to be considered in the future are discussed.

Experimental study on secondary droplets produced during liquid jet impingement onto a horizon solid surface

Zhan, Y.*; Kuwata, Yusuke*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi

Experimental Thermal and Fluid Science, 120, p.110249_1 - 110249_12, 2021/01

https://doi.org/10.1016/j.expthermflusci.2020.110249

Droplet generation during liquid jet impingement onto a horizontal plate

Zhan, Y.*; Oya, Naoki*; Enoki, Koji*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi

Experimental Thermal and Fluid Science, 98, p.86 - 94, 2018/11

https://doi.org/10.1016/j.expthermflusci.2018.05.022

Splash during liquid jet impingement onto a horizontal plate

Zhan, Y.*; Oya, Naoki*; Enoki, Koji*; Okawa, Tomio*; Ohno, Shuji; Aoyagi, Mitsuhiro; Takata, Takashi

Proceedings of 25th International Conference on Nuclear Engineering (ICONE-25) (CD-ROM), 6 Pages, 2017/07

It is important to set the amount of sodium droplet mechanistically for appropriate numerical evaluations of sodium leak and fire behavior in a sodium-cooled fast reactor plant. In the present work, fundamental experiments are performed to measure the splash ratio during the vertical water jet impact onto a horizontal wall. It is shown that the splash ratio can be correlated well as a function of the impact Weber number and dimensionless impact frequency.

Experimental study on splashing during liquid jet impingement onto a liquid film

Yi, Z.*; Oya, Naoki*; Enoki, Koji*; Okawa, Tomio*; Ohno, Shuji; Aoyagi, Mitsuhiro

Proceedings of 24th International Conference on Nuclear Engineering (ICONE-24) (DVD-ROM), 7 Pages, 2016/06

https://doi.org/10.1115/ICONE24-60033

It is important to set the amount of sodium droplet mechanistically for appropriate numerical evaluations of sodium leak and fire behavior in a sodium-cooled fast reactor plant. In the present work, fundamental experiments were performed to measure the splash ratio during the vertical water jet impact onto a horizontal wall. It was shown that the splash ratio can be correlated well as a function of the impact Weber number and the Strouhal number of the droplets impinging the liquid film.

Study on droplet generation of the surface collision jet

Oya, Naoki*; Okawa, Tomio*; Enoki, Koji*; Ohno, Shuji; Aoyagi, Mitsuhiro

no journal, , 

It is important to set the diameter of leakage sodium droplet mechanistically for appropriate numerical evaluations of sodium leak and fire behavior in a sodium-cooled fast reactor plant. We performed a fundamental experiment with water in order to clarify mechanism of droplet generation in this study. Impinging water jet on a flat plate was tested for various cases of jet velocity, nozzle diameter and nozzle height. The impinging behavior was visualized by using a high-speed video camera. We measured the amount of generated droplet and the maximum droplet diameter. Observed jet flow was categorized into following three modes: drop mode which is droplet state flow, jet mode which is straight flow and lump mode which is partially constricted flow. The amount of generated droplet had a strong correlation with the impact frequency. Larger droplet diameter was observed for the drop and lump modes.

Splashing droplets during liquid jet collision onto solid surface

Zhan, Y.*; Kuwata, Yusuke*; Maruyama, Kiyotaka*; Enoki, Koji*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi

no journal, , 

This study aims improvement of safety analysis for sodium fire accidents in sodium-cooled fast reactors. In the experiment, splashing droplets are investigated by observation of liquid jet collision onto a solid surface.

Development of Mechanistic Prediction Method of DNB Heat Flux Based on Two-Phase Flow CFD, 8; Numerical analysis of vapor mass formation under forced convective boiling

Ono, Ayako; Okawa, Tomio*

no journal, , 

We are developing a new prediction method for a departure from nucleate boiling (DNB) in the fuel assemblies, contributing to the design and safety evaluation for the new-generation reactors. In our project, we consider that the formation of a large vapor mass on the heating surface is the first trigger of the DNB. Therefore, we decided to predict the heat flux to form the large vapor mass by combining two-phase flow CFD and the large vapor mass formation model based on the mechanism. This method enables us to predict the DNB heat flux conservatively. In this study, we developed a simple numerical analysis method that simulates the generation, growth, motion, and coalescence of bubbles in order to predict the large bubble formation. We will report the basis of the models in the simple numerical analysis method and the results of the preliminary analysis.

Numerical simulation of breakup characteristics of sodium liquid jet

Sun, G.*; Yamashita, Susumu; Okawa, Tomio*; Yoshida, Hiroyuki

no journal, , 

When coolant leak occurs in sodium-cooled fast reactors, liquid sodium jet ejected from damaged piping can impact solid surfaces such as floors, generating splashing droplets. These droplets significantly increase the contact area between sodium and atmosphere, thereby intensifying combustion reactions. The quantity and size of splashing droplets, which influence the contact area, depend on the state of the jet during impact. Therefore, understanding the falling behavior of the jet is crucial. In this study, the breakup characteristics were analyzed to investigate the applicability of the numerical fluid dynamics simulation code JUPITER to the falling behavior of liquid sodium jets. The simulation results were similar to the extrapolated values from the empirical equations obtained from the experimental results with alternative fluids. Prospects for applying JUPITER to the analysis of sodium jet falling behavior were obtained.