BACCHUS-3D/SP, A Computer Program to Describe Transient Three-Dimensional Single Phase Flow in LMFBR Rod Bundles

A computational fluid dynamic (CFD) model for single phase flow in the three dimensional randomly packed bed with spherical particles has been developed and validated with experimental results. The flow characteristics within this complex geometry are very complicated. In order to obtain insight into the interior and local flow characteristics, Three-dimensional simulation is required. First, we constructed the randomly packed bed with spherical particle, using Discrete Element Method (DEM) based on the integration of Newton’s laws of motion. To validate the DEM simulations the global bed porosity and the radial porosity distribution were compared with empirical correlation from literature. Second, the complex geometrical properties of random packed bed make it difficult to produce a fine mesh. Herein, the bridge method for meshing the particle-particle and particle-wall contact points in the packed bed was applied. The contact zones are modified and then partitioned into several regular parts, so the structure gird was meshed. Finally, the simulation of water flow in the randomly packed bed with a tube-to-particle diameter ratio of 6.325 has been carried out by the commercial CFD code. A comparison with previously published correlations and experimental data shows that the relationship proposed by KTA agree well with the measured pressure drop. Furthermore the results of simulation for distribution of velocity in the bed were analyzed and discussed.

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Experimental and Numerical Investigation of Gravity-Driven Pipe Flow With Cavitation

10th International Conference on Nuclear Engineering, Volume 3 ◽

10.1115/icone10-22026 ◽

2002 ◽

Cited By ~ 4

Author(s):

Tobias Giese ◽

Eckart Laurien ◽

Wolfgang Schwarz

Keyword(s):

Mass Flux ◽

Pipe Flow ◽

Single Phase ◽

Two Phase Flow ◽

Three Dimensional ◽

Phase Flow ◽

Single Phase Flow ◽

Two Phase ◽

One Dimensional ◽

Gravity Driven

Gravity driven pipe flows contain no risk of pump failure and are considered to be reliable even under accident conditions. However, accurate prediction methods are only available for single phase flow. In case of the occurrence of two-phase flow (caused e.g. by boiling or cavitation), a considerable reduction in mass flux can be observed. In this study, an experimental and numerical investigation of gravity driven two-phase pipe flow was performed in order to understand and model such flows. An experiment was conducted to analyse gravity driven flow of water near saturation temperature in a complex pipe consisting of several vertical and horizontal sections. The diameter was 100 mm with a driving height of 13 m between an elevated tank and the pipe outlet. The experiment shows that cavitation leads to formation of steam. The two-phase character of the flow causes a significant reduction of mass flux in comparison to a single phase flow case. The experimental flow rate was reproduced by one dimensional single and two phase flow analysis based on standard one dimensional methods including models for steam formation. The main part of this study consists of a three dimensional CFD analysis of the two phase flow. A three dimensional model for cavitation and recondensation phenomena based on thermal transport processes was developed, implemented and validated against our experimental data. Due to the fact that beside bubbly flow, also the stratified and droplet flow regimes occur, a new approach to model phase interaction terms of the Two-Fluid Model for mass, momentum and energy is presented. Thereby, the transition from one flow regime to another is taken into account. The experimental mass flow rate can be predicted with an accuracy of 10%. The three dimensional analysis of the flow situation demonstrates the influence of pipe elements such as horizontal and vertical sections, bends and valves of the pipe on the mass flux and the steam distribution. The analysis of secondary flows in bends emphases their importance for the steam distribution within the pipe, for the pressure loss and the average mass flux.

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Verification benchmarks for single-phase flow in three-dimensional fractured porous media

Advances in Water Resources ◽

10.1016/j.advwatres.2020.103759 ◽

2021 ◽

Vol 147 ◽

pp. 103759 ◽

Cited By ~ 1

Author(s):

Inga Berre ◽

Wietse M. Boon ◽

Bernd Flemisch ◽

Alessio Fumagalli ◽

Dennis Gläser ◽

...

Keyword(s):

Porous Media ◽

Single Phase ◽

Three Dimensional ◽

Fractured Porous Media ◽

Phase Flow ◽

Single Phase Flow

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Heat-Transfer Augmentation in Rod Bundles Near Grid Spacers

Journal of Heat Transfer ◽

10.1115/1.3245071 ◽

1982 ◽

Vol 104 (1) ◽

pp. 76-81 ◽

Cited By ~ 94

Author(s):

S. C. Yao ◽

L. E. Hochreiter ◽

W. J. Leech

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Critical Heat Flux ◽

Single Phase ◽

Local Heat Transfer ◽

Phase Flow ◽

Single Phase Flow ◽

Rod Bundles ◽

Dispersed Flow ◽

Heat Transfer Augmentation

Heat-transfer augmentation by straight grid spacers in rod bundles is studied for single-phase flow and for post-critical heat flux dispersed flow. The heat transfer effect of swirling grid spacers in single-phase flow is also examined. Governing heat-transfer mechanisms are analyzed, and predictive formulations are established. For single-phase flow, the local heat transfer at a straight spacer and at its upstream or downstream locations are treated separately. The effect of local velocity increasing near swirling spacer is considered. For post critical heat flux (CHF) dispersed flow, the heat transfer by thermal radiation, fin cooling, and vapor convection near the spacer are calculated. The predictions are compared with experimental data with satisfactory agreement.

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