Development of a surface heat flux model for urban wind simulation using locally mesh-refined lattice Boltzmann method

Onodera, Naoyuki; Idomura, Yasuhiro; Hasegawa, Yuta; Nakayama, Hiromasa

Dai-35-Kai Suchi Ryutai Rikigaku Shimpojiumu Koen Rombunshu (Internet), 3 Pages, 2021/12

A detailed wind simulation is very important for designing smart cities. Since a lot of tall buildings and complex structures make the air flow turbulent in urban cities, large-scale CFD simulations are needed. We develop a GPU-based CFD code based on a Lattice Boltzmann Method (LBM) with a block-based Adaptive Mesh Refinement (AMR) method. In order to reproduce real wind conditions, the wind condition and ground temperature of the mesoscale weather forecasting model are given as boundary conditions. In this research, a surface heat flux model based on the Monin-Obukhov similarity theory was introduced to improve the calculation accuracy. We conducted a detailed wind simulation in Oklahoma City. By executing this computation, wind conditions in the urban area were reproduced with good accuracy.

Critical heat flux prediction for subcooled flow boiling in annulus

Liu, W.

Dai-20-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu, p.391 - 392, 2015/06

Subcooled flow boiling is a boiling that begins and develops even though the mean enthalpy of liquid phase is lower than saturation. This forced convective boiling is one of the most efficient ways for the removal of high heat flux. It is widely used in the high heat flux components such as nuclear reactor cores, accelerator targets and fusion reactor components. The thermal outputs of these systems are restricted by Critical Heat Flux(CHF). Because of the importance of the CHF, lots of researches, including both experimental and mechanistic modelling, have been performed. However, the CHF prediction for rod bundles still remains unsolved. As the first step for the CHF prediction in rod bundles, in this paper, we tried to predict the CHF in annulus, which is the most basic flow geometry simplified from a rod bundle. We performed the CHF prediction by using liquid sublayer dryout model, combined with Nouri single phase velocity distribution correlation for annulus. The results show that the CHF in annulus can be predicted in an accuracy of about 20%.

Effect of cladding surface pre-oxidation on rod coolability under reactivity initiated accident conditions

Sugiyama, Tomoyuki; Fuketa, Toyoshi

Journal of Nuclear Science and Technology, 41(11), p.1083 - 1090, 2004/11

https://doi.org/10.3327/jnst.41.1083

The effect of cladding surface pre-oxidation on the rod coolability under reactivity initiated accidents was investigated. NSRR tests on irradiated fuel rods have shown higher rod coolability than that of fresh rods, which arose from suppressed DNB and early quench at the surface. To identify the dominant factor, possible factors such as pellet cracking and so on, were assessed. The most probable factor, the cladding pre-oxidation, was examined by pulse irradiation tests on fresh rods with three cladding surface conditions, no oxide layer, 1m and 10m-thick oxide layers. Temperature measurements showed increased thresholds for DNB and quench at the pre-oxidized surface, leading to a reduced film boiling duration. The shifts of the critical and minimum heat flux points could be caused by the surface wettability increase. In the present tests, the wettability change was probably dominated by the chemical potential change at the surface due to pre-oxidation. The test results indicate the effects do not depend on the oxide layer thickness, but on the presence of the oxide layer.

Critical power in axially uniformly-heated tight-lattice rod bundles

Kureta, Masatoshi; Akimoto, Hajime

Nihon Kikai Gakkai Rombunshu, B, 69(682), p.1469 - 1476, 2003/06

https://doi.org/10.1299/kikaib.69.1469

no abstracts in English

Study on point of net vapor generation by neutron radiography in subcooled boiling flow along narrow rectangular channels with short heated length

Kureta, Masatoshi; Hibiki, Takashi*; Mishima, Kaichiro*; Akimoto, Hajime

International Journal of Heat and Mass Transfer, 46(7), p.1171 - 1181, 2003/03

https://doi.org/10.1016/S0017-9310(02)00398-8

no abstracts in English

Summary of the 5th Workshop on the Reduced Moderation Water Reactor; March 8, 2002, JAERI, Toaki

Nakano, Yoshihiro; Ishikawa, Nobuyuki; Nakatsuka, Toru; Iwamura, Takamichi

JAERI-Conf 2002-012, 219 Pages, 2002/12

JAERI-Conf-2002-012.pdf:17.4MB

no abstracts in English

Effect of cladding pre-oxidation on rod coolability during reactivity accident conditions

Sugiyama, Tomoyuki; Fuketa, Toyoshi

IAEA-TECDOC-1320, p.102 - 110, 2002/11

http://www-pub.iaea.org/MTCD/Publications/PDF/te_1320_web/attention.pdf

This report discusses effect of cladding surface pre-oxidation on fuel rod coolability during reactivity initiated accident (RIA) conditions. NSRR irradiated fuel experiments had shown cladding surface temperature lower than fresh fuel experiments. One possible speculation for the temperature difference is that oxide layer at the cladding outer surface enhanced heat transfer. To verify the speculation, pulse irradiation tests were performed on fuel rods with three different surface conditions: without oxide layer, with 1m-thick and 10m-thick oxide layer. Transient records of the cladding surface temperature showed the critical heat flux and the minimum heat flux increased for the oxidized fuel rods. These effects depend on presence of the oxide layer, not on the thickness of the layer, because no difference existed between results from 1m and 10m rods.

Fast measurement of ELM heat and particle fluxes, and plasma flow in the scrape-off layer of the JT-60U tokamak

Asakura, Nobuyuki; Sakurai, Shinji; Naito, Osamu; Itami, Kiyoshi; Miura, Yukitoshi; Higashijima, Satoru; Koide, Yoshihiko; Sakamoto, Yoshiteru

Plasma Physics and Controlled Fusion, 44(5A), p.A313 - A321, 2002/05

https://doi.org/10.1088/0741-3335/44/5A/333

no abstracts in English

Study on critical heat flux in narrow rectangular channel with repeated-rib roughness, 1; Experimental facility and preliminary experiments

Kinoshita, Hidetaka; Terada, Atsuhiko*; Kaminaga, Masanori; Hino, Ryutaro

JAERI-Tech 2001-061, 43 Pages, 2001/10

JAERI-Tech-2001-061.pdf:5.21MB

no abstracts in English

Critical heat flux of subcooled boiling in high-heat-load narrow channels

Kureta, Masatoshi; Akimoto, Hajime

Nihon Kikai Gakkai Rombunshu, B, 67(662), p.2550 - 2557, 2001/10

https://doi.org/10.1299/kikaib.67.2550

no abstracts in English