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Journal Articles

Macrolayer formation model for prediction of critical heat flux in saturated and subcooled pool boiling

Ono, Ayako; Sakashita, Hiroto*; Yoshida, Hiroyuki

Heat Transfer Engineering, 42(21), p.1775 - 1788, 2021/00

 Times Cited Count:0 Percentile:0.01(Thermodynamics)

In this study, the macrolayer formation model is proposed to predict the critical heat flux in the saturated and subcooled pool boiling based on the macrolayer dryout model. This model concept is based on the results of the previous experiments. In the model, the nucleation site is assumed to distribute based on the Poisson distribution. Combining the proposed macrolayer formation model and macrolayer dryout model, the CHFs up to subcooling 40K were predicted and they are successfully good agreement with the experimental data. Moreover, the concept of the model was confirmed by the numerical simulation using the TPFIT.

Oral presentation

Utilization of GTHTR300 waste heat for district heating and snow melting

Murata, Tetsuya*; Miwa, Shuichiro*; Sakashita, Hiroto*; Mori, Michitsugu*; Kasahara, Seiji; Yan, X.

no journal, , 

Application of a high temperature gas-cooled reactor (HTGR) for snow melting and district heating in Hokkaido was investigated. Concept design of a heat delivery system, modeling of pipes and a heat exchanger, calculation of heat supply amount from HTGR, and determination of location of the HTGRs were carried out. Sapporo and Ishikari were assumed as a heat demand district. To supply the maximum heat demand 435 MW in a year, 2 GTHTR300s, a kind of design of HTGR, were required. Though the distance from the GTHTR300 site and the heat demand district was 40 km, the temperature of the GTHTR300 waste heat was enough for the district heating. Double pipe for the heat transportation from the GTHTR300 to the district was advantageous for less heat loss and smaller excavation area. This system required 9 double pipes and more that 5000 heat exchangers.

Oral presentation

Macrolayer formation model for prediction of critical heat flux in saturated and subcooled pool boiling

Ono, Ayako; Sakashita, Hiroto*

no journal, , 

A macrolayer formation model for saturated and subcooled pool boiling is proposed, which is developed based on the visual observation of boiling behavior. The distribution of nucleation sites is assumed to distribute based on Poisson distribution. The predicted macrolayer thicknesses are used for the prediction of CHFs in saturated and subcooled pool boiling based on the macrolayer dryout model. The combination of the macrolayer dryout model and macrolayer formation model is able to predict the CHF well at least up to subcooling 40K.

Oral presentation

Study on boiling heat transfer characteristics in debris beds

Sakurada, Keishi*; Kawakami, Taira*; Sakashita, Hiroto*; Ono, Ayako; Yoshida, Hiroyuki

no journal, , 

This study measured the dryout heat fluxes for bottom heated debris beds, where small spherical particles were placed on a 75mm diameter heating surface. The data were obtained by varying the particle size in the range of 3 to 10mm, and compared with the predicted results with the one dimensional model proposed by Lipinski.

Oral presentation

Study on boiling heat transfer characteristics in debris beds, 2; Dryout heat flux for bottom and volume heated debris beds

Sakurada, Keishi*; Kawakami, Taira*; Sakashita, Hiroto*; Ono, Ayako; Yoshida, Hiroyuki

no journal, , 

This study measured the dryout heat fluxes on a bottom surface for bottom and volume heated debris beds, where small spherical metal particles were placed on a 75 mm diameter heating surface and internally heated by induction heating. The data were obtained by varying the particle size and the volumetric heated rate, and compared with the available correlations.

Oral presentation

Study on boiling heat transfer characteristics in debris beds, 3; Effects of volumetric heated rate and bed height on critical heat flux

Kawakami, Taira*; Sakurada, Keishi*; Sakashita, Hiroto*; Ono, Ayako; Yoshida, Hiroyuki

no journal, , 

The effect of height and density of accumulated particles on the critical heat flux was investigated on the heating surface, where the particles were accumulated, in order to investigate the cooling process of debris under the severe accident. The thermal-hydraulic behavior on the heating surface was visualized from the backsides of heating surface made of glass.

Oral presentation

Study on boiling heat transfer characteristics in debris beds, 4; Visualization of boiling behaviors on a heating surface

Kawakami, Taira*; Sakashita, Hiroto*; Ono, Ayako; Yoshida, Hiroyuki

no journal, , 

Understanding the boiling heat transfer characteristics in debris beds is indispensable to assess the coolability of molten debris at severe accident. However, the trigger mechanism of the critical heat flux on the bottom heated debris beds has not been fully elucidated. This study performed the visualization measurements using a transparent heating surface on which small particles are accumulated. The boiling behaviors were observed via a total reflection technique, and effects of particle size on dryout and rewetting process of the heating surface were examined.

Oral presentation

Critical heat flux during pool boiling in bottom and volume heated particle bets

Sakashita, Hiroto*; Kawakami, Taira*; Ono, Ayako; Yoshida, Hiroyuki

no journal, , 

This study measured the critical heat flux on a bottom surface for bottom and volume heated particulate beds, where small spherical metal particles were placed on a 75mm diameter heating surface and internally heated by induction heating. The data were obtained by varying the particle size and the volumetric heated rates in the particulate beds. The CHF on the bottom surface decreases with decreasing the particle size and is unaffected by the volumetric heated rates of the particulate beds. The previously proposed CHF correlations, which were derived based on the assumption that the CHF is triggered by hydrodynamic phenomena of liquid and vapor flows through the particulate beds, are not applicable to the CHF for bottom and volume heated particulate beds.

Oral presentation

Study on the boiling mechanism under the high pressure region, 1; Development of the measurement technique to detect the liquid-vapor behavior vicinity of heating surface under the high pressure

Ono, Ayako; Yamaguchi, Manabu*; Sakashita, Hiroto*; Uesawa, Shinichiro; Shibata, Mitsuhiko; Yoshida, Hiroyuki

no journal, , 

The establishment of the evaluation method of the critical heat flux for light water reactors is needed. However, the boiling phenomena under high pressure remain to be clarified. The measurement system based on detecting the electric capacitance has been developed, which detects the liquid-vapor behavior vicinity of the heating surface in order to clarify the mechanism of the critical heat flux under the higher pressure region. In this study, the detail of the measurement system and the result to confirm the validity of the measurement system are reported.

Oral presentation

Development of the simplified boiling model applied for the large scale simulation

Ono, Ayako; Yamashita, Susumu; Sakashita, Hiroto*; Suzuki, Takayuki*; Yoshida, Hiroyuki

no journal, , 

JAEA is implementing a simulation of a two-phase flow in the reactor core by TPFIT and JUPITER which are developed by JAEA based on the surface tracking method. However, it is impossible to simulate a boiling on the heating surface in the large-scale domain by this type of simulation method since the simulation of boiling based on the surface tracking method needs the fine mesh which sufficiently resolves the initiation of boiling. Therefore, JAEA started to develop the simplified boiling model applied for the two-phase flow in the fuel assemblies. In this study, the simulation results of the convection boiling on vertical heating surface and the comparison between the simulation results and experimental results are shown.

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