Establishment of reasonable 2-D model to investigate heat transfer and flow characteristics by using scale model of vessel cooling system for HTTR

Takada, Shoji; Ngarayana, I. W.*; Nakatsuru, Yukihiro*; Terada, Atsuhiko; Murakami, Kenta*; Sawa, Kazuhiro*

Mechanical Engineering Journal (Internet), 7(3), p.19-00536_1 - 19-00536_12, 2020/06

https://doi.org/10.1299/mej.19-00536

In this study reasonable 2D model was established by using FLUENT for start-up of analysis and evaluation of heat transfer flow characteristics in 1/6 scale model of VCS for HTTR. By setting up pressure vessel temperature around 200C about relatively high ratio of heat transfer via natural convection in total heat removal around 20-30%, which is useful for code to experiment benchmark in the aspect to confirm accuracy to predict temperature distribution of components which is heated up by natural convection flow. The numerical results of upper head of pressure vessel by the --SST intermittency transition model, which can adequately reproduce the separation, re-adhesion and transition, reproduced the test results including temperature distribution well in contrast to those by the - model in both cases that helium gas is evacuated or filled in the pressure vessel. It was emerged that any local hot spot did not appear on the top of upper head of pressure vessel where natural convection flow of air is separated in both cases. In addition, the plume of high temperature helium gas generated by the heating of heater was well mixed in the upper head and uniformly heated the inner surface of upper head without generating hot spots.

Local-scale high-resolution atmospheric dispersion model using large-eddy simulation; LOHDIM-LES

Nakayama, Hiromasa; Nagai, Haruyasu

JAEA-Data/Code 2015-026, 37 Pages, 2016/03

JAEA-Data-Code-2015-026.pdf:2.48MB

We developed LOcal-scale High-resolution atmospheric DIspersion Model using Large-Eddy Simulation (LOHDIM-LES). This dispersion model is designed based on LES which is effective to reproduce unsteady behaviors of turbulent flows and plume dispersion. The basic equations are the continuity equation, the Navier-Stokes equation, and the scalar conservation equation. Buildings and local terrain variability are resolved by high-resolution grids with of a few meters and these turbulent effects are represented by immersed boundary method. In simulating atmospheric turbulence, boundary layer flows are generated by a recycling turbulent inflow technique in a driver region set up at the upstream of the main analysis region. This turbulent inflow data are imposed at the inlet of the main analysis region. By this approach, the LOHDIM-LES can provide detailed information on wind velocities and plume concentration in the investigated area.

Numerical study of zonal flow dynamics and electron transport in electron temperature gradient driven turbulence

Li, J.; Kishimoto, Yasuaki

Physics of Plasmas, 11(4), p.1493 - 1510, 2004/04

https://doi.org/10.1063/1.1669397

The electron temperature gradient (ETG) driven turbulence in tokamak core plasmas is numerically investigated based on three-dimensional gyrofluid model with adiabatic ion response. Attentions are focused on the zonal flow dynamics in ETG fluctuations and the resultant electron heat transport. A high electron energy confinement mode is found in the weak magnetic shear regime, which is closely relevant with self-organization behavior of turbulence through the enhanced zonal flow dynamics rather than the weak shear stabilization of ETG fluctuations. It is demonstrated that the weak shear is favorable for the enhancement of zonal flows in ETG turbulence.

Interaction between small-scale zonal flows and large-scale turbulence; A Theory for ion transport intermittency in tokamak plasmas

Li, J.; Kishimoto, Yasuaki

Physical Review Letters, 89(11), p.115002_1 - 115002_4, 2002/09

https://doi.org/10.1103/PhysRevLett.89.115002

Interaction between small-scale zonal flows and large-scale turbulence is investigated. The key mechanism is identified as radially non-local mode coupling. Fluctuating energy can be non-locally transferred from the unstable longer to stable or damped shorter wavelength region, so that turbulence spectrum is seriously deformed and deviated from the nonlinear power law structure. Three-dimensional gyro-fluid ion temperature gradient (ITG) turbulence simulations show that an ion transport bursting behavior is consistently linked to the spectral deformity with the causal role of ITG-generated zonal flows in tokamak plasmas.

Model development for bubble turbulent diffusion and bubble diameter in large vertical pipes

Onuki, Akira; Akimoto, Hajime

Journal of Nuclear Science and Technology, 38(12), p.1074 - 1080, 2001/12

https://doi.org/10.3327/jnst.38.1074

Multi-dimensional analyses have been expected recently with expanding computation resources for gas-liquid two-phase flow analyses of advanced nuclear systems such as passive safety systems and natural-circulation-type reactors. However, the applicability of previous constitutive equations for multi-dimensional analyses has not been fully investigated especially for the effects of flow path scale because the equations have been assessed for small-scale experiments. In this study, we analyzed the scale effects by the multi-dimensional two-fluid model code using data in 38 mm and 200 mm diameter pipes. We clarified a key-parameter to model the scale effects and developed models for the effects on phase distribution. The scale effects can be classified by the relative relationship between bubble diameter db and turbulent length scale lT. Bubble-induced turbulence is increased under that db is smaller than lT and bubble coalescence is predominated rather than breakup under that lT is about three times larger than db and under higher void fraction. Based on these findings, we established new models for bubble turbulent diffusion and bubble diameter. The applicability was promising through assessments against the 38 mm and 200 mm pipes under different flow rates and against a database for developing flow along 480 mm pipe.

Analysis of steam-blanket effect in PCCS with horizontal heat exchanger

Onuki, Akira; Nakamura, Hideo; Anoda, Yoshinari

Dai-7-Kai Doryoku Enerugi Gijutsu Shimpojiumu Koen Rombunshu (00-11), p.258 - 263, 2000/00

no abstracts in English

Experimental study on scale effect of flow path against phase distribution of bubbly flow in a vertical pipe

Onuki, Akira; *; Akimoto, Hajime

Konsoryu Shimpojiumu '98 Koen Rombunshu, p.221 - 222, 1998/00

no abstracts in English

Prediction of phase distribution under bubbly flow in a large vertical pipe by multidimensional two-fluid model

Onuki, Akira; Akimoto, Hajime

Proc. of 3rd Int. Conf. on Multiphase Flow (ICMF'98), p.1 - 6, 1998/00

no abstracts in English

Prediction of developing bubbly flow along a large vertical pipe by multidimensional two-fluid model; Development of multidimensional two-fluid model code and analysis under a low velocity

Onuki, Akira; Kamo, Hideki*;

Proceedings of Japan-US Seminar on Two-Phase Flow Dynamics, 0, p.75 - 82, 1996/00

no abstracts in English

Deposition of aerosol particles in turbulent pipe flow; The Deposition in a bent pipe

Matsui, Hiroshi

Earozoru Kenkyu, 8(2), p.139 - 152, 1993/00

http://ci.nii.ac.jp/naid/130000649454

no abstracts in English