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Journal Articles

A note on the representation of rate-of-rise of the thermal stratification interface in reactor plenum

Tokuhiro, Akira; Kimura, Nobuyuki

Journal of Nuclear Science and Technology, -(-), 0 Pages, 2001/00

None

JAEA Reports

Applications of ultrasound technique to flow velocity measurement in water experiment of inter-wrapper flow; Comparison with particle image velocimetry

Kimura, Nobuyuki; ; ; ; Kamide, Hideki; Tokuhiro, Akira; Hishida, Koichi

JNC-TN9400 2000-057, 60 Pages, 2000/05

JNC-TN9400-2000-057.pdf:2.11MB

ln experimental study for the thermohydraulics of fast reactor, a simple experiment with fine measurement has been desired for understanding of phenomena and for verification of computer code rather than mockup experiments of large scale. For such purposes quality of experimental data must be improved. ln the velocity measurement, instantaneous velocity profile will have great advances for the understanding of phenomena and for the verification of computer code. ln this report two methods of the velocity profile measurement are discussed; one is ultrasound Doppler velocimetry (UDV) and the other is particle image velocimetry (PIV). These methods were applied to water experiments. The UDV was applied to pipe flow, planer jet, and the inter-wrapper flow which is seen in the gap region between subassemblies of fast reactor core. Cross check with laser Doppler velocimetly showed proper measurement of the UDV. Problems including the application to sodium experiments are also discussed. The PIV was also applied to the inter-wrapper flow. For the application to complex flow geometry, noise reduction method was developed to improve the measurement accuracy.

JAEA Reports

ExperimentaI study on convective mixing for ThermaI Striping Phenomena; Mixing process among paralleI Triple-Jet and effect or discharged velocity

Kimura, Nobuyuki; Tokuhiro, Akira; Kamide, Hideki

JNC-TN9400 2000-027, 181 Pages, 2000/02

JNC-TN9400-2000-027.pdf:10.28MB

A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing among jets causes thermal fatigue in structural components, is of importance for reactor safety. ln this study, a water experiment was performed using vertical and parallel triple jets, those are cold jet on center and hot jets on both side. The experimental parameter was discharged velocity of the triple-jet and local temperature and velocity were measured by ultrasound Doppler velocimetry and movable thermocouples. The objective is a quantification of the mixing process in the multiple-jet. Under isovelocity condition, the jets oscillated periodically and mixing among thejets was promoted by periodic oscillation. The periodic oscillation was dependent on the Strouhal number based on the discharged velocity. Under non-isovelocity condition, on the other hand, the jets did not oscillate periodically and mixing among the jets progressed more gentle compared with the case under isovelocity condition. The tempwrature fluctuation could be decomposed into coherent and random components using the phase averaging process. The rate of the coherent component in the temperature fluctuation increased and the rate of random component in temperature fluctuation decreased in proportion as the discharged velocity was increased.

Journal Articles

Numerical Study on Mixing of Oscillating Quasi-planar Jets with Low Reynolds number Turbulent Stress and Flux Equation Models

; Tokuhiro, Akira; Kimura, Nobuyuki;

Nuclear Engineering and Design, 202(1), p.77 - 95, 2000/00

 Times Cited Count:37 Percentile:9.33(Nuclear Science & Technology)

None

Journal Articles

Noise reduction techniques for particle image velocimetry; Application to an experimental study on natural convection in a fast reactor core

Kimura, Nobuyuki; ; ; Tokuhiro, Akira; ;

Proceedings of 8th International Conference on Nuclear Engineering (ICONE-8) (CD-ROM), 0 Pages, 2000/00

None

Journal Articles

A Summary of Ultrasonic Thermometer Sodium Test Results for Pipe-flow

; Tokuhiro, Akira; ;

Proceedings of 8th International Conference on Nuclear Engineering (ICONE-8) (CD-ROM), 0 Pages, 2000/00

None

JAEA Reports

A Note on the representation of rate-of-rise of the thermal stratification interface in reactor plenum

Tokuhiro, Akira; Kimura, Nobuyuki

JNC-TN9400 2000-015, 26 Pages, 1999/09

JNC-TN9400-2000-015.pdf:1.43MB

The quantification of the rate-of-rise of the thermal stratification interface, a "thin" vertical zone where the temperature gradient is the steepest, is important in assessing the potential implications of thermally-induced stress problems in liquid-metal cooled reactors. Thermal stratification can likewise occur in confined volumes containing ordinary fluids (Pr$$geq$$1), where there is an input of thermal convective energy. In the prominent case of liquid metal reactors, there have been many studies on quantifying the rate-of-rise of a defined stratification interface, in terms of one or more of the following dimensionless groups, mainly: Richardson (Ri), Reynolds (Re), Grashof (Gr), Rayleigh (Ra) and/or Froude (Fr) numbers. Stratification is also a transient process in the volume in question. In the present work the anthors presents a derivation based on order-of-magnitude analysis (OMA), including an sensible energy balance, that produces a new representation more consistent than p

JAEA Reports

Thermal striping an experiental investigation on mixing of jets; Part III Remaining hydrodynamic results from initial experiments

Tokuhiro, Akira; Kimura, Nobuyuki;

JNC-TN9400 2000-014, 86 Pages, 1999/06

JNC-TN9400-2000-014.pdf:11.72MB

Experiments were performed using the WAJECO facility to investigate the thermohydraulic mixing of multiple jets flowing out of a LMFBR core. Mixing is the root of the thermal striping problem. The multiple jets are typically at different velocities and temperatures and may induce thermal stresses upon components they impinge. In our study we modeled the mixing of three vertical jets, the central at a lower temperature than the two adjacent jets at equal temperatures. The jets are quasi-planar. The parameters were the average exit jet velocities (Uo,av) and the temperature difference between the "cold" and "hot" jets ($$Delta$$Thc=Thot-Tcold). Measurements of the liquid velocity, initially using laser Doppler velocimetry (LDV) and later ultrasound Doppler velocimetry (UDV), for both our reference single-jet and the triple-jet configuration, comprised Phase I of the experiments (up to 1994). Two reports (TN9410 96-181 and TN9410 96-296; in Japanese) reported on the hydraulic and heat tra

Journal Articles

Experimental investigation of a vertical planar jet by ultrasound and laser Doppler velocimetry

Tokuhiro, Akira

Journal of Nuclear Science and Technology, 36(6), p.540 - 548, 1999/06

None

Journal Articles

Journal Articles

Computational Study on Quasi-planar Jets Mixing with Low Reynolds Number Turbulent Stress and Flux Equation Models

; Tokuhiro, Akira; Kimura, Nobuyuki;

Proceedings of 9th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-9), 0 Pages, 1999/00

None

JAEA Reports

A Study on a velocity distribution measurement system applying the ultrasonic technique

Hirabayashi, Masaru; Kobayashi, Jun; Tokuhiro, Akira; Oki, Yoshihisa; ;

PNC-TN9430 98-002, 29 Pages, 1998/01

PNC-TN9430-98-002.pdf:1.25MB

no abstracts in English

Journal Articles

An experimental investigation on Penetration of buouyancy-driven cold liquid into a vertical channel with hot,forced-flow

Tokuhiro, Akira; ; ; Ohshima, Hiroyuki;

Nuclear Engineering and Design, 177, p.91 - 104, 1998/00

 Times Cited Count:2 Percentile:75.67(Nuclear Science & Technology)

None

JAEA Reports

Stirring-indueced vortical motion measured by ultrasound Doppler velocimetry; Initial 2D vector plots

Tokuhiro, Akira; Kobayashi, Jun

PNC-TN9410 97-059, 59 Pages, 1997/04

PNC-TN9410-97-059.pdf:2.78MB

An experimental investigation on stirring-induced vortical motion of a liquid was conducted in a cylindrical container measuring 280mm diameter $$times$$ 280mm height. The test medium was water and a magnetic stirrer located at the bottom on the container (centered) induced the flow. The motion can be generally described as rotationally induced vortex motion, which is of relevance to gas entrainment concerns, from the free surface of pool-type LMFBR. The objective of the investigation were two-fold: (1)to demonstrate that a two dimensional (2D) velocity field, using ultrasound Doppler velocimetry and a multiple number of ultrasound transducers (TDXs), could be measured and (2)to evaluate the content of the measured velocity information with respect to understanding the relevant vortex dynamics. Our results show that our first objective was fulfilled; that is, using 6 orthogonally situated TDXs to measure the V$$_{r}$$ and V$$_{z}$$ components of the flow field, a 2D vector field plot of a segment of the meridional plane was generated and shown to change with the rate of induced flow (rotation rate). However, because the number of TDXs used (6)were small, the coarse resolution of the velocity field limits the amount of velocity information. Therefore traditional data presentation methods to evaluate average and fluctuating quantities under steady and stepwise viewed transient conditions, are indispensible for data analysis. The measurement method holds promise as a useful tool in thermohydraulics as the number of TDXs is increased and therefore the spatial resolution. Some of these possibilities are described in this report.

Journal Articles

An experimental investigation on thermal striping, 1; Mixing of a vertical cooled jet with two adjacent heated jets as measured by ultrasound Doppler velocimetry

Tokuhiro, Akira; ; Kimura, Nobuyuki

Proceedings of 8th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-8), Vo.3, p.1712 - 1723, 1997/00

None

Journal Articles

An Experimental investigation thermal striping, 2; Heat transferand transfer and temperature measurement results

Kimura, Nobuyuki; Tokuhiro, Akira;

Vol.3,pp1724$$sim$$1734, p.1724 - 1734, 1997/00

None

JAEA Reports

Experimental study for thermal striping phenomena of parallel triple-jet; Effects of the difference between hot jets and cold jet in discharged temperature and velocity on convective mixing

Kimura, Nobuyuki; Tokuhiro, Akira; Miyakoshi, Hiroyuki

PNC-TN9410 96-296, 136 Pages, 1996/10

PNC-TN9410-96-296.pdf:9.21MB

Elucidation on thermal hydraulic behavior of Thermal Striping is of importance for a reactor safety, which is arisen form exit temperature difference of fuel subassemblies. Since its temperature fluctuation may cause thermal cycle fatigue on upper internal structure (UIS). A series of experiments was performed using the Thermal Striping water test facility in order to investigate the mixing phenomena on three vertical jets with exit velocity and temperature differences. The parameters were the velocity and temperature of the jets at discharge nozzles. The local velocities were measured by Ultrasound Velocity Profile (UVP) monitor and Laser Doppler Anemometry (LDA), and temperature distributions were measured by thermocouples. This report mainly examined the experimental results of temperature measurements. There is a typical region where the gradient of the temperature variation in the triple-jet is 2$$sim$$3 times larger than that in a single-jet: that is the Convective Mixing region. This region is independent of the discharged temperature difference. While the region is dependent on the discharged velocity difference, e.g. this region spreads with larger velocity difference among the jets. For isovelocity discharge conditions, non-dimensional temperature fields are almost independent of discharged temperature differences within Convective Mixing region. Consequently, the effect of temperature difference is negligible compared to that of velocity difference on the flow field. There are remarkable frequencies of 2$$sim$$5 Hz in temperature fluctuation due to a oscillation of the central jet (cold jet) for this condition. While, for non-isovelocity discharge condition, there are no remarkable frequencies. Hence, it is clear that there is the region where a large thermal fatigue is imposed by Thermal Striping against structures of Fast Reactor. It is suggested that the structures have to be placed outside of Convective Mixing region. Also, it is considered that ...

JAEA Reports

Implementation of a Particle Image Velocimetry (PIV) system; An example application of PIV to wake-flows behind objects

Tokuhiro, Akira; Hishida, Koichi; Oki, Yoshihisa

PNC-TN9410 96-275, 59 Pages, 1996/10

PNC-TN9410-96-275.pdf:1.66MB

Particle Image Velocimetry (PIV) describes a velocity measurement technique for gas and liquid flows whereby, as the name implies, movement of tracer particles in motion with the flow are recorded as images. The particles are framr-to-frame "tracked by one of several correlation techniques from which a 2D vector field can be generated. A 3D vector field is also possible. The measurement method takes advantage of current computer, CCD camera and laser light technologies for its image processing needs. A laser light sheet is typically used to illuminate the tracer particles in the flow field of interest and when implemented accentuates the constrast between the particle and the transparent medium. One can also apply Laser Induced Fluorescence (LIF) in order to further distinguish the tracer particles, the transparent, continuous medium and any light reflecting surfaces in the flow field such as the interface of a gas bubble rising in a liquid. It is also possible to deduce the temperature field from LIF images. In the present work an introduction to PIV is given by way of an example. The selected flow configuration is that of wake-flow behind a bubble and its solid equivalent. By solid equivalent we mean a solid model with approximately the equivalent bubble breadth and volume. This two-component, two-phase flow aptly demonstrates the applicability of PIV to spatio-temporal flows. Use was additionally made of an Infrared Shadow Technique (IST) in order to capture the unlit image (shadow) of the bubble or solid within the flow field. By triggering both the laser and infrared light sources with the CCD camera, the shape of the object as well as the flow field was simultaneously recorded. Besides the 2D vector field, calculations of the vorticity, Reynolds stress and turbulent kinetic energy ($$tke$$) distributions were made. The results indicate that for counter-current flow (U$$_{avg}$$sim$0.245 m/s) of water in a square channel (100 mm) with a single air bubble of ...

JAEA Reports

Order of Magunitude Analysis of stratified natural convection and mixed convection penetration flow of cold liquid into a vertical channel with hot,forced flow

Tokuhiro, Akira; Kobayashi, Jun

PNC-TN9410 96-068, 51 Pages, 1996/05

PNC-TN9410-96-068.pdf:1.35MB

In the thermal-hydraulic analysis of nuclear reactors and other energy-related systems, the proper scaling of simulation experiments and separate effect studies, is first determined by the identification of the relevant dimensionless group(s) and then by the reproduction in magnitude of the range. While most experiments contain some idealizations in geometry so that well-known dimensionless groups can be easily identified, the non-ideal nature of any given experiment may appear for instance, in the presentation of data using the selected dimensionless numbers. If this is the case, a reconsideration of the Scale Analysis or Order of Magnitude Analysis (OMA) may reveal slight modifications to classic results that originate from ideal cases. The present work summarizes OMA by way of example; that is, a reconsideration of the stratified natural convection problem from which a stratified Nusselt number is introduced. Two data sets are presented in support of the described modification. This is then followed by an experimental investigation on penetration of cold liquid into a modeled subassembly channel under mixed convection, from the hot plenum of a protypicaI FBR design. The penetration phenomenon occurs under certain natural circulation conditions during the operation of the DRACS (direct reactor auxilialy cooling system) for decay heat removal and can influence the natural circulation head that determines the core flow rate and consequently the core cooling rate. In the present experiment, a simplified test section simulating the upper plenum and a subassembly channel was constructed wherein both temperature and velocity measurements were made to investigate the penetration of cold water into a vertical channel with upward flowing hot water. Upon comparing temperature and velocily data we found an overall similarity in their respective spatio-temporal distributions as expected. The data suggested correlations describing the onset of flow penetration and ...

Journal Articles

None

Tokuhiro, Akira; Hishida, Koichi; *

CD-LOM ISB, , 

None

23 (Records 1-20 displayed on this page)