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Tokuhiro, Akira; Kobayashi, Jun
PNC TN9410 97-059, 59 Pages, 1997/04
An experimental investigation on stirring-induced vortical motion of a liquid was conducted in a cylindrical container measuring 280mm diameter 
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
and V
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.
Kimura, Nobuyuki; Tokuhiro, Akira; Miyakoshi, Hiroyuki
PNC TN9410 96-296, 136 Pages, 1996/10
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
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 25 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 ...
Tokuhiro, Akira; Hishida, Koichi; Oki, Yoshihisa
PNC TN9410 96-275, 59 Pages, 1996/10
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 (
) distributions were made. The results indicate that for counter-current flow (U
sim$0.245 m/s) of water in a square channel (100 mm) with a single air bubble of ...
Tokuhiro, Akira; Kobayashi, Jun
PNC TN9410 96-068, 51 Pages, 1996/05
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 ...
