Numerical Study of Bubble Coalescence and Breakup in the Reactor Fuel Channel with a Vaned Grid

Cong, Tenglong; Zhang, Xiang

doi:10.3390/en11010256

Cited by 6 publications

(2 citation statements)

References 16 publications

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“…The coefficient C L changes its sign at a bubble diameter of d = 5.8 mm for our conditions. It was previously shown that this expression of the lift force can be sufficiently used for predictions of bubbly flows in complex geometrical conditions, as example in fuel columns with grid spacers [34]. C TD = 0.1 is the coefficient of turbulent diffusion [23].…”

Section: Interface Forcesmentioning

confidence: 99%

Experimental and Numerical Study of the Flow and Heat Transfer in a Bubbly Turbulent Flow in a Pipe with Sudden Expansion

2019

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The flow patterns and heat transfer of a downstream bubbly flow in a sudden pipe expansion are experimentally and numerically studied. Measurements of the bubble size were performed using shadow photography. Fluid phase velocities were measured using a PIV system. The numerical model was employed the Eulerian approach. The set of RANS equations was used for modelling two-phase bubbly flows. The turbulence of the carrier liquid phase was predicted using the Reynolds stress model. The peak of axial and radial fluctuations of the carrier fluid (liquid) velocity in the bubbly flow is observed in the shear layer. The addition of air bubbles resulted in a significant increase in the heat transfer rate (up to 300%). The main enhancement in heat transfer is observed after the point of flow reattachment.Energies 2019, 12, 2735 2 of 18 regime. Gas concentration increased immediately after the cross-section of the flow separation. Measurements by [7] were performed in an upward, vertical flow of a liquid (water) and CO 2 bubbles. The distribution of the mean carrier fluid velocity was strongly dependent on the bubbles' diameter. A review of the literature for two-phase flow in sudden expansions and contractions was performed in [8]. Wang et al. [8] have found that none of the existing eight correlations can accurately predict the experimental database. Most of these correlations greatly overpredicted the results for mini test sections. Some of the correlations also underpredicted the data for large test sections.There are only a few papers that consider the numerical modeling of isothermal bubbly flows in a pipe with sudden expansion [9,10]. Krepper et al. [9] presented a mathematical model for polydisperse flow in a vertical pipe with sudden expansion. The numerical predictions for bubbly pipe flow with an obstacle demonstrated very difficult nature of such flows [9]. The Eulerian model was developed to simulate bubbly flows in a pipe with sudden expansion in [10]. Predictions were carried out using the CFD commercial package STAR-CCM+. The developed model was validated against measurements of Bel Fdhila [11]. The eddy-viscosity k−ε model showed poor reproduction of the bubbly flow structure because it disregarded much of the information on fluid flow turbulence. The Second-Moment Closure and LES methods captured the main characteristic turbulent length-scales responsible for the diffusion of the bubble gas phase, and moreover, these methods predicted the flow patterns and bubble distributions across the pipe section [10].Recently published numerical works [12,13] investigated heat transfer in bubbly flows without an abrupt pipe or channel expansion. These studies showed the significant influence of bubble diameter and gas volumetric flow rate ratios on the flow patterns and heat transfer. Heat transfer in bubbly flow increased up to three times that of one-phase fluid flow. The liquid turbulence was modeled using an isotropic k−ε model [12]. The DNS of bubbly flow with heat transfer was performed [13]. The numerical [14...

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Section: Interface Forcesmentioning

confidence: 99%

Experimental and Numerical Study of the Flow and Heat Transfer in a Bubbly Turbulent Flow in a Pipe with Sudden Expansion

2019

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“…The number of investigations into the flow and mixing mechanisms is limited, probably due to difficulties encountered in obtaining meaningful experimental measurements. Bubble coalescence and breakup are the main phenomena for gas-liquid fluid flow inside the devices [25]. Recently, Falzone et al [26] concluded four main mechanisms leading to bubble breakup, which were turbulent fluctuation, macroscopic shear stress, turbulent shear stress and interfacial slip.…”

Section: Introductionmentioning

confidence: 99%

Experimental and Numerical Study on Flow Resistance and Bubble Transport in a Helical Static Mixer

2020

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Flow resistance and bubble transport in a helical static mixer were studied experimentally and numerically. The inline mixer increases the volume fraction of gas in liquids by breaking bubbles into smaller sizes with a micrometer size in the flow experiments. The gas–liquid flow was simulated by a combination of computational fluid dynamics and Taylor expansion methods of moments. The friction factor of the helical static mixer is much smaller than that of the Kenics static mixers. The pressure drop increases with the Reynolds number, and the increment is larger when the Reynolds number is higher. The equidistant pressure drop increases with the argument of Reynolds number, and increases when the pitch decreases from upstream to downstream. The energy expenditure increases significantly when the variable-pitch coefficient is too small. The bubble geometric mean diameter decreases and the geometric standard deviation increases when the gas–liquid fluid flows through the mixer. The variable pitch structure enhances the bubble breakup effectively. The change of the bubble size decreases with the argument of the Reynolds number. The effect of the mixer has a limitation on breaking the bubbles.

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Multi-scale Multiphase Flow Gas–Liquid–Solid Interfacial Equation Based on Thermodynamic and Mathematical Approach

Yonemoto

Kunugi

2022

The Surface Wettability Effect on Phase Change

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Numerical Study of Bubble Coalescence and Breakup in the Reactor Fuel Channel with a Vaned Grid

Cited by 6 publications

References 16 publications

Experimental and Numerical Study of the Flow and Heat Transfer in a Bubbly Turbulent Flow in a Pipe with Sudden Expansion

Experimental and Numerical Study of the Flow and Heat Transfer in a Bubbly Turbulent Flow in a Pipe with Sudden Expansion

Experimental and Numerical Study on Flow Resistance and Bubble Transport in a Helical Static Mixer

Multi-scale Multiphase Flow Gas–Liquid–Solid Interfacial Equation Based on Thermodynamic and Mathematical Approach

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