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Journal Articles

Experiments on gas entrainment phenomena due to free surface vortex induced by flow passing beside stagnation region

Ezure, Toshiki; Ito, Kei; Tanaka, Masaaki; Ohshima, Hiroyuki; Kameyama, Yuri*

Nuclear Engineering and Design, 350, p.90 - 97, 2019/08

 Times Cited Count:3 Percentile:57.07(Nuclear Science & Technology)

This paper reports the results of an experiment on surface vortex-type gas entrainment, which occurs in a shear flow area where flow passes besides the stagnation region. The relationship between the free surface dimple shape and the velocity distribution around the free surface vortex was simultaneously grasped under several horizontal and suction velocity conditions by a combination of visualization and particle image velocimetry measurements. The circulation and the vertical velocity gradient were also evaluated from the velocity distributions at a plane just below the free surface and the middle plane between the free surface and suction nozzle. Quantitative relationships between the circulation, vertical velocity gradient, and gas core length were obtained in time-trends as fundamental data to develop the evaluation method of gas entrainment. Furthermore, it was confirmed that the evaluation method based on a vortex model was an effective way to evaluate gas entrainment.

Journal Articles

Study on multi-dimensional core cooling behavior of sodium-cooled fast reactors under DRACS operating conditions

Ezure, Toshiki; Onojima, Takamitsu; Tanaka, Masaaki; Kobayashi, Jun; Kurihara, Akikazu; Kameyama, Yuri*

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.3355 - 3363, 2019/08

Steady-state sodium experiments under the operating conditions of a decay heat removal system (DHRS) were carried out as part of the safety enhancement of sodium-cooled fast reactors using the PLANDTL 2 facility, which has 30 heated channels with electric heaters and 25 no-heated channels as the simulated core. In the experiments, a direct reactor auxiliary cooling system (DRACS) with a dipped type direct heat exchanger (DHX) in the upper plenum was used as the DHRS. This paper reports on the preliminary experimental results of the PLANDTL 2 experiments under the DRACS operating conditions without flow in the primary circuit, including the thermal hydraulic interactions between the upper plenum and the core under the DHX operating conditions and the resulting core cooling behavior from the outside of the multiple rows of the fuel assemblies

Journal Articles

Experiments on gas entrainment phenomena due to free surface vortex induced by flow passing beside stagnation region

Ezure, Toshiki; Ito, Kei; Tanaka, Masaaki; Ohshima, Hiroyuki; Kameyama, Yuri*

Proceedings of 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17) (USB Flash Drive), 9 Pages, 2017/09

In the design of sodium cooled fast reactors, cover gas entrainment into sodium coolant (gas entrainment) is one of significant thermal hydraulic issues. This paper describes experimental results on surface vortex type gas entrainment which occurs in a share flow area where flow passes beside the stagnation region. In the experiment, the relationship between the free surface dimple shape and the velocity distribution around the free surface vortex was simultaneously grasped under several horizontal and suction velocity conditions by means of visualization measurement and Particle Image Velocimetry measurement. As the results, quantitative relationships among circulation, vertical velocity gradient and the gas core length were obtained in time-trends as fundamental data to develop the evaluation method of gas entrainment. Furthermore, it was confirmed that the evaluation method based on a vortex model, was an effective way to evaluate gas entrainment.

Journal Articles

Influence of fluid viscosity on vortex cavitation at a suction pipe inlet

Ezure, Toshiki; Ito, Kei; Kameyama, Yuri*; Kamide, Hideki; Kunugi, Tomoaki*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 15(3), p.151 - 158, 2016/09

no abstracts in English

Journal Articles

Experimental measurement of vortex cavitation around a suction pipe inlet

Ezure, Toshiki; Ito, Kei; Kameyama, Yuri*; Kurihara, Akikazu; Kunugi, Tomoaki*

Konsoryu, 30(2), p.189 - 196, 2016/06

Journal Articles

Experimental study on vortex cavitation in scaled upper plenum model of Japan Sodium-cooled Fast Reactor, 1; Evaluation of circulation and vortex cavitation occurrences using vortex model

Ezure, Toshiki; Ito, Kei; Kameyama, Yuri*; Hagiwara, Hiroyuki*; Kamide, Hideki

Proceedings of 9th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-9) (CD-ROM), 7 Pages, 2014/11

JAEA Reports

Study on high cycle thermal fatigue in mixing tee; Evaluation of transfer characteristics of temperature fluctuation from fluid to structure

Kimura, Nobuyuki; Kobayashi, Jun; Kameyama, Yuri*; Nagasawa, Kazuyoshi*; Ezure, Toshiki; Ono, Ayako; Kamide, Hideki

JAEA-Research 2014-009, 104 Pages, 2014/07

JAEA-Research-2014-009.pdf:15.23MB
JAEA-Research-2014-009-appendix(CD-ROM).pdf:17.88MB

In this study, water experiments (WATLON) were carried out to clarify the unsteady behavior of heat transfer under wall jet condition in the mixing tee. In experiments, heat transfer coefficients between fluid and wall in the mixing region were obtained from temperature measurements using thermocouples (movable tree type in fluid and embedded type in wall). To clarify the relation between the local velocity and the wall temperature, those were measured simultaneously by the Particle Image Velocimetry (PIV) and the thermocouple measurement, respectively. Sampling time of the velocity by the PIV and the temperature by the thermocouple were synchronized in the measurement. The experimental results showed that the heat transfer coefficient was from 2 - 6 time larger than the reference value predicted by the Dittus-Boelter correlation in straight pipes and was increased as the local velocity near the wall.

Journal Articles

Effects of fluid viscosity on occurrence behavior of vortex cavitation; Vortex structures and occurrence condition

Ezure, Toshiki; Ito, Kei; Kimura, Nobuyuki; Onojima, Takamitsu; Kamide, Hideki; Kameyama, Yuri*

Proceedings of 15th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-15) (USB Flash Drive), 12 Pages, 2013/05

An experimental study on vortex cavitation was carried out in a cylindrical water tank to clarify how the viscosity of fluid influences on vortex cavitation occurrences. Vertical and horizontal velocity distributions were obtained under several experimental conditions, where the kinematic viscosity of water and the velocity of suction flow were varied as parameters. As the results, the flow patterns and the vortex structures, such as the circulation around the vortex, were grasped. And also, the acceleration behavior of vortex from the bottom of tank towards the intake of suction nozzle was clarified. Then, the occurrence map of vortex cavitation was also improved by using the present experimental data.

Oral presentation

Study on cavitation due to sub-surface vortex at intake of hot-leg pipe in sodium cooled fast reactor, 5; Measurement of circulation around hot leg pipe intake in complicated geometry

Ezure, Toshiki; Ito, Kei; Kameyama, Yuri*; Kamide, Hideki

no journal, , 

Velocity measurements based on Particle Image Velocimetry were carried out in 1/22 scaled water model of sodium-cooled fast reactor to grasp velocity distributions around hot leg pipes. Circulation around sub-surface vortex was evaluated as an indicator of vortex strength using measured velocity distributions. As the results, it is confirmed the circulation normalized by the mean hot leg velocity was nearly constant and dose not depends on the variation of kinematic viscosity.

Oral presentation

Evaluation of pressure decrease at vortex center from velocity distribution around vortex cavitation

Ezure, Toshiki; Ito, Kei; Kameyama, Yuri*; Kamide, Hideki; Kunugi, Tomoaki*

no journal, , 

In this study, fundamental behavior of vortex cavitation was studied in cylindrical tank geometry related to establishment of an evaluation method of vortex cavitation in sodium-cooled fast reactors. Velocity distribution around vortex, which causes cavitation, was quantitatively grasped by means of Particle Image Velocimetry. Pressure drop at vortex center was also evaluated based on Burgers vortex model and compare to occurrence behavior of vortex cavitation.

Oral presentation

Study on cavitation due to sub-surface vortex at intake of hot-leg pipe in sodium cooled fast reactor, 8; Evaluation of vortex cavitation considering turbulent viscosity

Ezure, Toshiki; Ito, Kei; Kameyama, Yuri*; Kurihara, Akikazu; Kunugi, Tomoaki*

no journal, , 

no abstracts in English

Oral presentation

Development of evaluation method for vortex cavitation onset behavior in sodium-cooled fast reactor

Ezure, Toshiki; Ito, Kei; Kameyama, Yuri*; Kurihara, Akikazu; Kunugi, Tomoaki*

no journal, , 

In order to provide knowledge about applicability of vortex model based evaluation method to vortex cavitation in sodium-cooled fast reactor, the evaluation method was applied to experimental results in a small-scaled water model of advanced SFR. Furthermore, to improve the evaluation accuracy of the pressure decrease, an empirical modification of evaluation formula was proposed based on experimental results obtained in another simple geometry. As the results, time-trends of pressure decrease at a vortex center in typical cases showed fluctuation in time. Occurrences of vortex cavitation, which showed intermittent behavior, concentrated at maximal points of the time-trends of pressure decrease. In other words, the qualitative onset behavior of vortex cavitation in the small model was captured successfully by the current evaluation formula. More importantly, the modified formula could evaluate the onset behavior of vortex cavitation successfully also in quantitative aspects.

Oral presentation

Study on gas entrainment in sodium cooled fast reactors, 11; Applicability of vortex model based evaluation on vortex type gas entrainment

Ezure, Toshiki; Ito, Kei*; Kameyama, Yuri*; Tanaka, Masaaki; Kurihara, Akikazu; Ohshima, Hiroyuki

no journal, , 

In order to establish an evaluation method of gas entrainment, gas entrainment experiments were performed in shearing flow geometry. Velocity distribution and vortex dimple depth were grasped simultaneously by means of PIV and visualization measurements. The vortex dimple depth was also evaluated by applying the measured velocity distribution to a vortex model. Then, the evaluated vortex dimple depth was compared with the experimental result. As the results, it was shown that vortex model based evaluation provided the appropriate results while having a certain conservativeness.

Oral presentation

Study on decay heat removal in sodium-cooled fast reactors; In-vessel cooling characteristics by direct heat exchanger

Ezure, Toshiki; Onojima, Takamitsu; Tanaka, Masaaki; Kameyama, Yuri*

no journal, , 

As a part of safety enhancement of sodium-cooled fast reactors, experiments was carried out using PLANDTL-2 facility to grasp the core cooling behavior only relying on the natural circulation inside the vessel using dipped-type DHX. As the result, temperature distributions in the core were quantitatively grasped under a situation where cold coolant from DHX penetrated the core. Furthermore, it was observed that temperature distribution at the middle height of core became flat due to the flow redistribution among heating channels resulting from the buoyancy balance between channels.

15 (Records 1-15 displayed on this page)
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