Experimental investigation on bubble characteristics entrained by surface vortex

Ezure, Toshiki; Kimura, Nobutada; Miyakoshi, Hiroyuki; Kamide, Hideki

doi:10.1016/j.nucengdes.2010.09.021

Cited by 22 publications

(9 citation statements)

References 11 publications

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“…imposition of a tangential inlet) was selected by Moriya [14] and Monji et al [15] to study the velocity distribution around the vortex. Some experimental tests were carried out by Kimura et al [16]- [18] to study the free vortex occurrence under specific conditions (e.g. in the Japanese Sodium Fast Reactor -JSFR): the authors developed a scaled down partial model of the JSFR to understand the main factors and mechanisms related to the GE within this geometry.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of free surface vortices and definition of gas entrainment occurrence maps

Caruso

Cristofano

Nobili

et al. 2014

J. Phys.: Conf. Ser.

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Abstract. For the future development of Generation IV nuclear reactors, both safety and economic targets have to be achieved. In order to increase, at the same time, the power density generation and the safety features, a huge R&D effort is still required. Referring especially to Liquid Metal Cooled Fast Reactors, much attention is placed on Gas Entrainment (GE) phenomena, which could cause unlikely positive reactivity insertion accident. The GETS experimental facility (Gas Entrainment Test Section), especially aimed at studying the free surface vortices occurrence, has been built in the thermal-hydraulics laboratory of the DIAEE. The main purpose of this facility is to identify the most important parameters affecting the whirlpools formation and evolution. Experimental tests and preliminary observations have been performed. Different vortex behaviours related to different experimental conditions have been identified and presented in the present paper. 2D occurrence maps as function of different dimensionless groups (Reynolds, Froude and Weber numbers and H* = H/d ratio) have been defined. In the present paper, the results of a first experimental campaign, carried out with tap water, are discussed.

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Section: Introductionmentioning

confidence: 99%

Experimental investigation of free surface vortices and definition of gas entrainment occurrence maps

Caruso

Cristofano

Nobili

et al. 2014

J. Phys.: Conf. Ser.

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“…The gas entrainment may cause safety and operational problems and, for this reason, becomes an essential issue in SFR safety analyses [13][14][15][16]. This issue has been intensively investigated by the Japan Atomic Energy Agency (JAEA) and its institutional partners [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. The problems associated with gas entrainments in SFRs are: changes in reactivity when the gas reaches the core [11,14,18,[31][32][33], burnout of the fuel pin due to the trap of large bubbles [31], thermal stresses in the reactor structure [32,33], pump cavitation and fluctuations in pump discharge [14,33], reduction in the heat transfer efficiency [11,33], disturbance in the prompt detection of fission products leakage from failed fuel pins [34], disturbance of electromagnetic sensors used for shutdown systems [34], and trouble with acoustic or ultrasonic instrumentation such as boiling noise detector [31,32,34].…”

Section: Introductionmentioning

confidence: 99%

Modeling of the Free-Surface Vortex-Driven Bubble Entrainment into Water

Putra

Lucas

2020

Water

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The recently developed GENTOP (Generalized Two Phase Flow) concept, which is based on the multifield Euler‒Euler approach, was applied to model a free-surface vortex—a flow situation that is relevant for hydraulic intake. A new bubble entrainment model has been developed and implemented in the concept. In general, satisfactory agreement with the experimental data can be achieved. However, the gas entrainment can be significantly affected by several parameters or models used in the CFD (Computational Fluid Dynamics) simulation. The scale of curvature correction C s c a l e in the turbulence model, the coefficient in the entrainment model C e n t , and the assigned bubble size to be entrained have a significant influence on the gas entrainment rate. The gas entrainment increases with higher C s c a l e values, which can be attributed to the stronger rotation captured by the simulation. A smaller bubble size gives higher gas entrainment, while a larger bubble size leads to a smaller entrainment. The results also show that the gas entrainment can be controlled by adjusting the entrainment coefficient C e n t . Based on the modeling framework presented in this paper, further improvement of the physical modeling of the entrainment process should be done.

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“…Then, to study intermittent gas entrainment, new analytical experimental facilities have been designed so as to isolate the key mechanism of turbulent shear flows combined with flow suction, e.g. Ezure et al, 2011, Kimura et al, 2009and Cristofano et al, 2014. These new design experiments are based on open channel flows.…”

Section: Introductionmentioning

confidence: 99%

Experimental study of gas entrainment from surface swirl

Moudjed

Excoffon

Riva

et al. 2016

Nuclear Engineering and Design

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Gas entrainment from surface swirls is characterized using water experiments. A free surface shear flow is generated in an open channel flow. A suction nozzle is set at the bottom of the test section to induce a downward flow and provoke gas entrainment. An important originality of these experiments is the possibility to change the inlet condition so as to generate different turbulent shear flows. This is done by adding obstacles of different sizes and shapes at the end of a flat plate separating the inlet flow from a "stagnant" water area. Velocity fields and profiles, measured with the PIV technique, are provided to describe the inlet conditions corresponding to various geometries and flow rates. Gas entrainment mapping are established from direct observations of the different flow configurations. These new results show that the threshold for the suction velocities required to entrain gas are similar for the configurations with small obstacles and the flat plate configuration triggering a standard shear flow. Increasing the size of the obstacles promotes gas entrainment and reduces the threshold values of the suction velocity to trigger gas entrainment. Shadowgraphy with image processing is used to present new results characterizing the geometrical properties of surface swirls and the quantity of gas entrained. Inlet configurations with obstacles generate larger surface swirls which move upstream from the suction nozzle centre whereas they are situated downstream with the flat plate configuration. Moreover, dimensionless power laws are found to be good approximations for the surface swirl width and the quantity of gas entrained. In addition to provide new insights about gas entrainment in analytical configurations relevant to Sodium cooled fast nuclear reactor, these results should provide different test cases for the validation of MCFD codes, e.g. TRIO-U, NEPTUNE-CFD.

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Experimental investigation on bubble characteristics entrained by surface vortex

Cited by 22 publications

References 11 publications

Experimental investigation of free surface vortices and definition of gas entrainment occurrence maps

Experimental investigation of free surface vortices and definition of gas entrainment occurrence maps

Modeling of the Free-Surface Vortex-Driven Bubble Entrainment into Water

Experimental study of gas entrainment from surface swirl

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