Experimental Study on Influence of Interfacial Behavior on Jet Surface Fragmentation

2009 ◽  
Author(s):  
Yuta Uchiyama ◽  
Yutaka Abe ◽  
Akiko Kaneko ◽  
Hideki Nariai ◽  
Makoto Yamagishi ◽  
...  
Keyword(s):  
Shear Stress ◽  
Interfacial Behavior ◽  
Interfacial Wave ◽  
Molten Material ◽  
Fragmentation Behavior ◽  
Breakup Length ◽  
Piv Technique ◽  
Jet Breakup ◽  
Local Shear ◽  
Local Shear Stress

For the safety design of the Fast Breeder Reactor (FBR), it is strongly required that the Post Accident Heat Removal (PAHR) is achieved after a hypothetical Core Disruptive Accident (CDA). In the PAHR, it is important that the molten material is fragmented to be solidified by the sodium coolant with high boiling point and thermal conductivity. Furthermore, in order to estimate whether the molten material jet is completely solidified in sodium coolant or not, it is necessary to evaluate the jet breakup length. Although there are many previous studies on the jet breakup length, the tendency of jet breakup length is different for the previous studies. To estimate jet breakup length, it is necessary to understand the interaction between molten core material and coolant. The objective of the present study is to clarify the influence of the interfacial behavior of the jet on the fragmentation behavior on the jet surface. The experiments are conducted to obtain the interfacial behavior and the fragmentation behavior on the jet surface by injecting transparent Fluorinert™ (FC-3283) into water. The jet breakup behavior of the Fluorinert and the fragmentation behavior on the jet surface in pool are observed by using high speed video camera. To clarify the influence of interfacial behavior on jet surface fragmentation, it is necessary to clarify the effect of the internal flow of the jet and the surrounding flow structure on the interfacial behavior. The internal and the external velocity distribution of the jet are obtained by Particle Image Velocimetry (PIV) technique from the visual data. Shear stress is evaluated from the velocity data obtained by PIV technique. Reynolds stress and turbulent energy are also evaluated from the velocity data. As the results, shear stress becomes large along the interfacial wave. The maximum value of shear stress is decreased toward downstream. Reynolds stress becomes large at the jet surface. The vortex around the interfacial wave is observed by PIV measurement. The local shear stress acts on the interfacial wave. It is suggested that the local shear stress on the jet surface causes the fragmentation. From the experimental results, the interaction between the interfacial behavior of the jet and flow structure of the jet and surrounding fluid are discussed. The dominant mechanism of the fragmentation behavior and the influence of local shear stress at the interface on the fragementation are also discussed.

Estimation of Fragmentation on Jet Breakup in Coolant

2012 ◽  
Author(s):  
Taihei Kuroda ◽  
Yutaka Abe ◽  
Akiko Kaneko ◽  
Iwasawa Yuzuru ◽  
Hideki Nariai ◽  
...  
Keyword(s):  
Flow Field ◽  
Tap Water ◽  
Energy Ratio ◽  
Liquid Jet ◽  
Sodium Coolant ◽  
Molten Material ◽  
Colorless Liquid ◽  
Fragmentation Behavior ◽  
Breakup Length ◽  
Jet Breakup

Fast Breeder Reactor (FBR) is designed with safety in mind. However, there is billion to one possibility that a hypothetical Core Disruptive Accident (CDA) occurs. When CDA occurs, the Post Accident Heat Removal (PAHR) must be achieved. In the PAHR, the molten material is required to be fragmented and solidified in sodium coolant. In order to estimate whether the molten material jet is completely solidified in sodium coolant or not, it is significant to estimate jet breakup length. Although, the jet breakup length is influenced with fragmentation behavior, the correlation between them is not clear yet. Therefore, it is strongly required to clarify the mechanism of the fragmentation behavior on the jet surface. The objective of the present study is to estimate fragmentation on jet breakup in coolant experimentally. Tap water and Fluorinert™ (FC-3283) are used as simulated coolant and molten material, respectively. Flourinert is transparent and colorless liquid and its density is higher than water, therefore we can observe internal flow structure of Fluorinert. Fluorinert injected into water, and the jet breakup behavior and the fragmentation behavior of the jet are observed by using high speed video camera. In order to estimate fragmentation on liquid jet, we identified the position of the interface with back lighting technique and also, we conducted velocity measurement with Particle Image Velocimetry (PIV) technique simultaneously. It is observed that interfacial waves of the jet are generated. Waves are pulled with surrounding liquid and grown up. Finally, a fragment is separated as a droplet from front edge of the wave. Also, the vorticity is evaluated from the velocity data in order to investigate influence of the flow field in detail. From the result of calculating vorticity, the high value was estimated when jet was fragmented. It is suggested that fragmentation behavior correlates with the surrounding flow field. And the energy ratio contributing to fragmentation is calculated from velocity field. The energy ratio is important to investigate the amount of the fragmentation on liquid jet. Fragmentation on jet breakup in coolant is estimated.

Experimental Study on Jet Breakup Behavior With Surface Solidification

2010 ◽  
Author(s):  
Takashi Wada ◽  
Yutaka Abe ◽  
Akiko Kaneko ◽  
Yuta Uchiyama ◽  
Hideki Nariai ◽  
...  
Keyword(s):  
Size Distribution ◽  
Reactor Vessel ◽  
Image Processing Technique ◽  
Core Material ◽  
Dominant Factor ◽  
Sodium Coolant ◽  
Molten Material ◽  
Breakup Length ◽  
Jet Breakup ◽  
Median Diameter

For the safety design of the Fast Breeder Reactor (FBR), the Post Accident Heat Removal (PAHR) is required when a hypothetical Core Disruptive Accident (CDA) occurs. In the PAHR, it is strongly required that the molten core material can be cooled down and solidified by the sodium coolant in the reactor vessel. There is high possibility for molten material to be ejected as a liquid jet into sodium coolant in the reactor vessel. In order to estimate whether the molten material jet is completely solidified by sodium coolant or not, it is necessary to understand the interaction between molten core material and coolant such as jet breakup and fragmentation behavior in coolant. The jet breakup behavior is the phenomenon that the front of molten material breaks up in coolant. To clarify the mechanism of jet breakup and fragmentation during the CDA for the FBR, it is necessary to understand the correlation between jet breakup lengths and size distribution of fragments when molten material jet interacting with coolant. The objective of the present study is to clarify the dominant factor of the jet breakup length and the size distribution of fragments experimentally. Molten jet of U-alloy 138 is injected into water as simulated core material and coolant by free-fall. The density ratio of core material and coolant is almost same as that of the real FBR system. The jet breakup behavior as interaction of molten material with coolant is observed with high speed video camera. Front velocity of the molten material jet is estimated by using the image processing technique. It suddenly decreases when the jet fall into the coolant. The jet breakup length estimated from observed images is compared with the breakup theories to understand the effect of experimental parameters for the jet breakup length. The solidified fragments are gathered and classified in size, and the mass in each size is measured. Median diameter is obtained from the mass distribution of the fragments. In comparison with interfacial instabilities, the median diameter of fragments shows the independent of relative velocity. The jet breakup lengths and median diameters compared with existing theories is discussed.

Visual Observation of Fragmentation Behavior on Molten Material Jet Surface in Coolant

2008 ◽  
Author(s):  
Yuta Uchiyama ◽  
Yutaka Abe ◽  
Akiko Fujiwara ◽  
Hideki Nariai ◽  
Eiji Matsuo ◽  
...  
Keyword(s):  
Water Surface ◽  
High Speed ◽  
Internal Flow ◽  
Core Material ◽  
Generation Process ◽  
High Speed Camera ◽  
Sodium Coolant ◽  
Molten Material ◽  
Fragmentation Behavior ◽  
Jet Breakup

For the safety design of the Fast Breeder Reactor (FBR), it is strongly required that the post accident heat removal (PAHR) is achieved after a postulated core disruptive accident (CDA). In the PAHR, it is important that the molten core material is solidified in sodium coolant which has high boiling point. Thus it is necessary to estimate the jet breakup length which is the distance that the molten core material is solidified in sodium coolant. In the previous studies (Abe et al., 2006), it is observed that the jet is broken up with fragmenting in water coolant by using simulated core material. It is pointed out that the jet breakup behavior is significantly influenced by the fragmentation behavior on the molten material jet surface in the coolant. However, the relation between the jet breakup behavior and fragmentation on the jet surface during a CDA for a FBR is not elucidated in detail yet. The objective of the present study is to elucidate the influence of the internal flow in the jet and fragmentation behavior on the jet breakup behavior. The Fluorinert™ (FC-3283) which is heavier than water and is transparent fluid is used as the simulant material of the core material. It is injected into the water as the coolant. The jet breakup behavior of the Fluorinert™ is observed by high speed camera to obtain the fragmentation behavior on the molten material jet surface in coolant in detail. To be cleared the effect of the internal flow of jet and the surrounding flow structure on the fragmentation behavior, the velocity distribution of internal flow of the jet is measured by PIV (Particle Image Velocimetry) technique with high speed camera. From the obtained images, unstable interfacial wave is confirmed at upstream of the jet surface, and the wave grows along the jet-water surface in the flow direction. The fragments are torn apart at the end of developed wave. By using PIV analysis, the velocity at the center of the jet is fast and it suddenly decreases near the jet surface. This means that the shear force acts on the jet and water surface. From the results of experiment, the correlation between the interfacial behavior of the jet and the generation process of fragments are discussed. In addition, the influence of surface instability of the jet induced by the relative velocity between Fluorinert™ and coolant water on the breakup behavior is also discussed.

Roughness Influence on Turbulent Flow Through Annular Seals

1994 ◽  
Vol 116 (2) ◽  
pp. 321-328 ◽  
Author(s):  
Victor Lucas ◽  
Sterian Danaila ◽  
Olivier Bonneau ◽  
Jean Freˆne
Keyword(s):  
Surface Roughness ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Flow ◽  
Dynamic Characteristics ◽  
Reynolds Equation ◽  
Mixing Length ◽  
Local Shear ◽  
Wall Shear ◽  
Local Shear Stress

This paper deals with an analysis of turbulent flow in annular seals with rough surfaces. In this approach, our objectives are to develop a model of turbulence including surface roughness and to quantify the influence of surface roughness on turbulent flow. In this paper, in order to simplify the analysis, the inertial effects are neglected. These effects will be taken into account in a subsequent work. Consequently, this study is based on the solution of Reynolds equation. Turbulent flow is solved using Prandtl’s turbulent model with Van Driest’s mixing length expression. In Van Driest’s model, the mixing length depends on wall shear stress. However there are many numerical problems in evaluating this wall shear stress. Therefore, the goal of this work has been to use the local shear stress in the Van Driest’s model. This derived from the work of Elrod and Ng concerning Reichardt’s mixing length. The mixing length expression is then modified to introduce roughness effects. Then, the momentum equations are solved to evaluate the circumferential and axial velocity distributions as well as the turbulent viscosity μ1 (Boussinesq’s hypothesis) within the film. The coefficients of turbulence kx and kz, occurring in the generalized Reynolds’ equation, are then calculated as functions of the flow parameters. Reynolds’ equation is solved by using a finite centered difference method. Dynamic characteristics are calculated by exciting the system numerically, with displacement and velocity perturbations. The model of Van Driest using local shear stress and function of roughness has been compared (for smooth seals) to the Elrod and Ng theory. Some numerical results of the static and dynamic characteristics of a rough seal (with the same roughness on the rotor as on the stator) are presented. These results show the influence of roughness on the dynamic behavior of the shaft.

scholarly journals Stress-gradient Coupling in Glacier Flow: IV. Effects of the “T” Term

1986 ◽  
Vol 32 (112) ◽  
pp. 342-349 ◽  
Author(s):  
Barclay Kamb ◽  
Keith A. Echelmeyer
Keyword(s):  
Shear Stress ◽  
Coupling Theory ◽  
Longitudinal Stress ◽  
Longitudinal Flow ◽  
Stress Gradients ◽  
Flow Coupling ◽  
Flow Response ◽  
Longitudinal Variations ◽  
Local Shear ◽  
Local Shear Stress

AbstractThe “T term” in the longitudinal stress-equilibrium equation for glacier mechanics, a double y-integral of ∂2τxy/∂x2 where x is a longitudinal coordinate and y is roughly normal to the ice surface, can be evaluated within the framework of longitudinal flow-coupling theory by linking the local shear stress τxy at any depth to the local shear stress τB at the base, which is determined by the theory. This approach leads to a modified longitudinal flow-coupling equation, in which the modifications deriving from the T term are as follows: 1. The longitudinal coupling length is increased by about 5%. 2. The asymmetry parameter σ is altered by a variable but small amount depending on longitudinal gradients in ice thickness h and surface slope α. 3. There is a significant direct modification of the influence of local h and α on flow, which represents a distinct “driving force” in glacier mechanics, whose origin is in pressure gradients linked to stress gradients of the type ∂τxy/∂x. For longitudinal variations in h, the “T force” varies as d2h/dx2 and results in an in-phase enhancement of the flow response to the variations in h, describable (for sinusoidal variations) by a wavelength-dependent enhancement factor. For longitudinal variations in α, the “force” varies as dα/dx and gives a phase-shifted flow response. Although the “T force” is not negligible, its actual effect on τB and on ice flow proves to be small, because it is attenuated by longitudinal stress coupling. The greatest effect is at shortest wavelengths (λ 2.5h), where the flow response to variations in h does not tend to zero as it would otherwise do because of longitudinal coupling, but instead, because of the effect of the “T force”, tends to a response about 4% of what would occur in the absence of longitudinal coupling. If an effect of this small size can be considered negligible, then the influence of the T term can be disregarded. It is then unnecessary to distinguish in glacier mechanics between two length scales for longitudinal averaging of τb, one over which the T term is negligible and one over which it is not.Longitudinal flow-coupling theory also provides a basis for evaluating the additional datum-state effects of the T term on the flow perturbations Δu that result from perturbations Δh and Δα from a datum state with longitudinal stress gradients. Although there are many small effects at the ~1% level, none of them seems to stand out significantly, and at the 10% level all can be neglected.The foregoing conclusions apply for long wavelengths λh. For short wavelengths (λ h), effects of the T term become important in longitudinal coupling, as will be shown in a later paper in this series.

Comparison of void fraction change and local shear stress fluctuation in channel flow

2018 ◽  
Vol 2018 (0) ◽  
pp. OS3-5
Author(s):  
Hayato NAKAMURA ◽  
Satoshi OGAMI ◽  
Yoshihiko OISHI ◽  
Hideki KAWAI ◽  
Yuichi MURAI
Keyword(s):  
Shear Stress ◽  
Channel Flow ◽  
Void Fraction ◽  
Stress Fluctuation ◽  
Local Shear ◽  
Local Shear Stress

scholarly journals The Brachial Artery Remodels to Maintain Local Shear Stress Despite the Presence of Cardiovascular Risk Factors

2009 ◽  
Vol 29 (4) ◽  
pp. 606-612 ◽  
Author(s):  
William B. Chung ◽  
Naomi M. Hamburg ◽  
Monika Holbrook ◽  
Sherene M. Shenouda ◽  
Mustali M. Dohadwala ◽  
...  
Keyword(s):  
Risk Factors ◽  
Shear Stress ◽  
Cardiovascular Risk ◽  
Cardiovascular Risk Factors ◽  
Brachial Artery ◽  
Local Shear ◽  
Local Shear Stress
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