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Journal Articles

Effects of nozzle orifice shape on jet breakup and splashing during liquid jet impact onto a horizontal plate

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

Experimental Thermal and Fluid Science, 151, p.111095_1 - 111095_15, 2024/02

Journal Articles

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.

Journal Articles

Experiment study on the effect of nozzle shape on liquid jet breakup

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

Proceedings of 29th International Conference on Nuclear Engineering (ICONE 29) (Internet), 6 Pages, 2022/08

When a liquid sodium leakage accident occurs in a sodium-cooled fast reactor, the injected sodium collides with structures to produce splashing droplets, which can result in a violent combustion. According to previous studies on circular nozzles, the amount of splash is affected by the state of the jet at the moment of impact. However, the outlet shape of damaged area is hardly to be circular; and meanwhile it influences the flow pattern of jet a lot. Considering about this, in the present work, high-speed cameras were used to observe the jet discharged from oval nozzles vertically downward to investigate the falling process of the jet. The result shows that surface wave appears on the jet and within a certain range of flow velocity it can be observed obviously, meanwhile accelerate the breakup of jet.

Journal Articles

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$$Sigma$$, 63(12), p.820 - 824, 2021/12

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.

Journal Articles

Droplet generation during spray impact onto a downward-facing solid surface

Zhan, Y.*; Sun, G.*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi

Experimental Thermal and Fluid Science, 126, p.110402_1 - 110402_8, 2021/08

 Times Cited Count:5 Percentile:61.49(Thermodynamics)

Journal Articles

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

 Times Cited Count:5 Percentile:73.29(Thermodynamics)

Journal Articles

Effects of surface tension and viscosity on liquid jet breakup

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

Experimental Thermal and Fluid Science, 112, p.109953_1 - 109953_8, 2020/04

 Times Cited Count:9 Percentile:71.8(Thermodynamics)

Journal Articles

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

 Times Cited Count:11 Percentile:65.34(Thermodynamics)

Journal Articles

A Study on splashing during liquid jet impingement onto a horizontal plate

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

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 10 Pages, 2018/10

This study aims improvement of safety analysis for sodium fire accidents in sodium-cooled fast reactors. In the experiment, effect of viscosity on liquid jet impact on solid surface was studied.

Journal Articles

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.

Journal Articles

Production of droplets during liquid jet impingement onto a flat plate

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

Proceedings of 10th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-10) (USB Flash Drive), 7 Pages, 2016/11

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, the Strouhal number and the Ohnesorge number of the droplets impinging the liquid film.

Journal Articles

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

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.

Oral presentation

Study on droplet generation at the time of a water jet, the liquid film collision

Oya, Naoki*; Okawa, Tomio*; 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 means of 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. Both the amount of generated droplet and the maximum droplet diameter increased in the following order: jet, drop and lump modes.

Oral presentation

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.

Oral presentation

Splashing during liquid jet impact onto a horizontal wall

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

no journal, , 

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 rate of splashing during the vertical water jet impact onto a horizontal wall. It was found that the splashing rate is negligibly small when the water jet is continuous at the impact point. Whilst, the splashing rate increased rapidly with an increase in the jet velocity when the jet was broken into droplets at the impact point. Therefore, when the fall height is longer than the breakup length, it was suggested that the dimensionless splashing rate scaled by the liquid jet flow rate can be expressed as a function of the modified Weber number of the primary droplets impacting the target. A semi-empirical method to estimate the splashing rate during liquid jet impact onto a horizontal wall was proposed based on linear stability theory.

Oral presentation

Study on surface collision of the liquid jet

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

no journal, , 

This study aimed at improvement of sodium fire analysis method for coolant leakage in sodium-cooled fast reactor. A semi-empirical method to estimate the splashing rate during liquid jet impact onto a horizontal wall was proposed based on consideration of splashing mechanism.

Oral presentation

Droplet generation during liquid jet collision onto solid surface

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

no journal, , 

This study aims improvement of safety analysis for sodium fire accidents in sodium-cooled fast reactors. In the experiment, droplets were generated by collision of downward liquid jet onto a horizontal solid surface. We studied the mechanism of droplet generation and the empirical correlation of droplet amount.

Oral presentation

Splashing droplets during liquid jet collision onto solid surface

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

no journal, , 

This study aims improvement of safety analysis for sodium fire accidents in sodium-cooled fast reactors. In the experiment, droplets were generated by collision of downward liquid jet onto a horizontal solid surface. We studied the mechanism of droplet generation and the empirical correlation of droplet amount.

Oral presentation

Study on splashing phenomenon of liquid jet collision

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

no journal, , 

This study aims improvement of safety analysis for sodium fire accidents in sodium-cooled fast reactors. In the experiment, droplets were generated by collision of downward liquid jet onto a horizontal solid surface. We studied the mechanism of droplet generation and the empirical correlation of droplet amount.

Oral presentation

Effect of viscosity on liquid jet impact on solid surface

Kuwata, Yusuke*; Zhan, Y.*; 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, effect of viscosity on liquid jet impact on solid surface was studied.

28 (Records 1-20 displayed on this page)