CFD simulation of subcooled boiling flow in PWR 5 ⨯ 5 rod bundle

Kerntechnik ◽  
2021 ◽  
Vol 86 (1) ◽  
pp. 24-32
Author(s):  
B. Ren ◽  
Y. Dang ◽  
F. J. Gan ◽  
P. Yang
Keyword(s):  
Void Fraction ◽  
Cfd Simulation ◽  
Phase Distribution ◽  
Flow Boiling ◽  
Fluid Model ◽  
Three Dimensional ◽  
Spacer Grid ◽  
Pressurized Water ◽  
Rod Bundle ◽  
Boiling Flow

Abstract This paper describes the computational fluid dynamics (CFD) methodology to simulate the boiling flow in a typical Pressurized Water Reactor (PWR) 5 ⨯ 5 rod bundle. The method includes the Eulerian-Eulerian two-fluid model coupled with the improved wall heat partitioning model. The NUPEC PWR Subchannel and Bundle Test (PSBT) International Benchmark are used for validation. The simulated surface averaged void fraction agree well with the experimental data, which indicate the promising application of the present method for modeling the boiling flow in the fuel rod bundle. The main emphasis of current research has been given to the analysis of the phase distribution around and downstream the spacer grid, the effect of the spacer grid structure, including the mixing vanes, the springs and the dimples on the void fraction distribution is investigated. The findings can contribute to a better understanding of three dimensional flow boiling characteristics and can be used to assist in optimizing the spacer grid.

A Mechanistic Model for Predicting Subcooled Boiling Flow

2003 ◽  
Author(s):  
G. H. Yeoh ◽  
J. Y. Tu
Keyword(s):  
Void Fraction ◽  
Liquid Velocity ◽  
Fluid Model ◽  
Mechanistic Model ◽  
Three Dimensional ◽  
Annular Channel ◽  
Heat Fluxes ◽  
Group Model ◽  
Subcooled Boiling ◽  
Boiling Flow

Population balance equations combined with a three-dimensional two-fluid model are employed to predict subcooled boiling flow at low pressure in a vertical annular channel. The MUSIG (MUltiple-SIze-Group) model implemented in CFX4.4 is extended to account for the wall nucleation and condensation in the subcooled boiling regime. Comparison of model predictions against local measurements is made for the void fraction, bubble Sauter diameter and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcoolings. Good agreement is achieved with the local radial void fraction, bubble Sauter diameter and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapor velocity. Work is in progress to circumvent the deficiency of the extended MUSIG model by the consideration of an algebraic slip model to account for bubble separation.

Numerical Simulation of Boiling Two-Phase Flow in Tight-Lattice Rod Bundle by 3-Dimensional Two-Fluid Model Code ACE-3D

2008 ◽  
Author(s):  
Hiroyuki Yoshida ◽  
Takeharu Misawa ◽  
Kazuyuki Takase
Keyword(s):  
Void Fraction ◽  
Lift Force ◽  
Fluid Model ◽  
Phase Flow ◽  
Two Phase ◽  
Rod Bundle ◽  
Fraction Distribution ◽  
Two Fluid Model ◽  
Tight Lattice ◽  
Two Fluid

Two-fluid model can simulate two phase flow less computational cost than inter-face tracking method and particle interaction method. Therefore, two-fluid model is useful for thermal hydraulic analysis in large-scale domain such as a rod bundle. Japan Atomic Energy Agency (JAEA) develops three dimensional two-fluid model analysis code ACE-3D, which adopts boundary fitted coordinate system in order to simulate complex shape channel flow. In this paper, boiling two-phase flow analysis in a tight lattice rod bundle is performed by ACE-3D code. The parallel computation using 126CPUs is applied to this analysis. In the results, the void fraction, which distributes in outermost region of rod bundle, is lower than that in center region of rod bundle. At height z = 0.5 m, void fraction in the gap region is higher in comparison with that in center region of the subchannel. However, at height of z = 1.1m, higher void fraction distribution exists in center region of the subchannel in comparison with the gap region. The tendency of void fraction to concentrate in the gap region at vicinity of boiling starting point, and to move into subchannel as water goes through rod bundle, is qualitatively agreement with the measurement results by neutron radiography. To evaluate effects of two-phase flow model used in ACE-3D code, numerical simulation of boiling two-phase in tight lattice rod bundle with no lift force model (neglecting lift force acting on bubbles) is also performed. From the comparison of numerical results, it is concluded that the effects of lift force model are not so large on overall void fraction distribution in tight lattice rod bundle. However, higher void fraction distribution in center region of the subchannel was not observed in this simulation. It is concluded that the lift force model is important for local void fraction distribution in rod bundles.

CFD Simulation of PWR Subchannel Void Distribution Benchmark

2010 ◽  
Author(s):  
Wang-Kee In ◽  
Chang-Hwan Shin ◽  
Tae-Hyun Chun
Keyword(s):  
Void Fraction ◽  
Cfd Simulation ◽  
Fluid Model ◽  
Small Diameter ◽  
Operating Conditions ◽  
Heated Wall ◽  
Bubble Generation ◽  
Void Distribution ◽  
Wide Range ◽  
Two Fluid Model

A CFD study was performed to simulate the steady-state void distribution benchmark based on the NUPEC PWR Subchannel and Bundle Tests (PSBT). The void distribution benchmark provides measured void fraction data over a wide range of geometrical and operating conditions in a single subchannel and fuel bundle. This CFD study simulated the boiling flow in a single subchannel. A CFD code was used to predict the void distribution inside the single subchannel. The multiphase flow model used in this CFD analysis was a two-fluid model in which liquid (water) and vapor (steam) were considered as continuous and dispersed fluids, respectively. A wall boiling model was also employed to simulate bubble generation on a heated wall surface. The CFD prediction with a small diameter of vapor bubble shows a higher void fraction near the heated wall and a migration of void in the subchannel gap region. A measured CT image of void distribution indicated a locally higher void fraction near the heated wall for the test conditions of a subchannel averaged void fraction of less than about 20%. The CFD simulation predicted a subchannel averaged void fraction and fluid density which agree well with the measured ones for a low void condition.

scholarly journals Experimental Study of Pressure Loss in a 5 × 5–Rod Bundle With the Mixing Vane Spacer Grid

2021 ◽  
Vol 9 ◽  
Author(s):  
Wenhai Qu ◽  
Weiyi Yao ◽  
Jinbiao Xiong ◽  
Xu Cheng
Keyword(s):  
Pressure Loss ◽  
Lateral Pressure ◽  
Reynolds Numbers ◽  
Wall Friction ◽  
Geometrical Parameters ◽  
Strong Correlations ◽  
Pressurized Water Reactor ◽  
Spacer Grid ◽  
Pressurized Water ◽  
Rod Bundle

Axial and lateral pressure loss in a 5 × 5 rod–bundle with a split-type mixing vane spacer grid was experimentally measured using differential pressure transmitters at different sub-channel Reynolds numbers (Re) and orienting angles. The geometrical parameters of the 5 × 5–rod bundle are as follows: they have the same diameter (D = 9.5 mm) and pitch (p = 12.6 mm) as those of real fuel rods of a typical pressurized water reactor (PWR), with a sub-channel hydraulic diameter (Dh) of 11.78 mm. The characteristics and resistance models of pressure loss are discussed. The main axial pressure loss is caused by the spacer grid, and the spacer grid generates additional wall friction pressure loss downstream of the spacer grid. The lateral pressure loss shows strong correlations with orienting angles and distance from the spacer grid. The lateral pressure loss shows a sudden burst in the mixing vanes region and a slight augmentation at z = 3Dh. After 3Dh, the lateral pressure loss decays in an exponential way with distance from the spacer grid, and it becomes constant quickly at z = 20Dh.

Study of Mixing Characteristics Over a Spacer Grid With Sloping Channels Based on Numerical Simulations in a PWR 5×5 Rod Bundle Using CFD Codes

2013 ◽  
Author(s):  
Xi Chen ◽  
Hong Zhang
Keyword(s):  
Numerical Simulations ◽  
Safety Margin ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Spacer Grid ◽  
Pressurized Water ◽  
Spacer Grids ◽  
Rod Bundle ◽  
Commercial Code ◽  
Water Reactors

Spacer grids are important components of fuel assemblies for Pressurized Water Reactors (PWR). The presence of spacer grid promotes local heat transfer adjacent to the rod wall downstream by inducing swirl and cross flows within and between sub-channels to increase thermal hydraulic safety margin. Recent years, Computational Fluid Dynamics (CFD) methodologies are widely adopted to designs of spacer grids. This paper presents results of numerical simulations with commercial code CFX 12.0 in a PWR 5 × 5 rod bundle including a spacer grid with sloping channels. Based on a combined mesh generation approach of structured and unstructured mesh, distributions of velocity fields, temperature and pressure fields downstream the spacer grid were analyzed. The results indicate that cross flows caused by the spacer grid are uniform in circumference inducing no thermal hydraulic deterioration, but mass exchange between central hot fluid and external cold fluid appears insufficient for the new style grid.

scholarly journals CFD investigation of sub-cooled boiling flow using a mechanistic wall heat partitioning approach with Wet-Steam properties

2018 ◽  
Vol 10 (4) ◽  
pp. 239-258 ◽  
Author(s):  
M Promtong ◽  
SCP Cheung ◽  
GH Yeoh ◽  
S Vahaji ◽  
J Tu
Keyword(s):  
Void Fraction ◽  
Flow Boiling ◽  
Force Balance ◽  
Heated Wall ◽  
Working Fluid ◽  
Group Model ◽  
Wet Steam ◽  
Bubble Interactions ◽  
Boiling Flow ◽  
Heat Partitioning

In this paper, the mechanistic wall heat partitioning approach was used to capture the complex heat and mass transfer in sub-cooled boiling flows. In order to accommodate the changes of local variables to be relevant to the physical properties of sub-cooled fluids, the Wet-Steam (IAPWS-IF97) is used as the working fluid. Currently, the approach is evaluated based on the bubble sliding along the wall before lifting-off, which is usually found in the flow boiling situations. In the simulation, the closure mechanistic models, including the fractal analysis, the force balance and the mechanistic frequency, were coupled with the Eulerian–Eulerian two-fluid framework, while the Shear Stress Transport model was used as a turbulent modelling closure. The Multiple Size Group model was introduced to handle the bubble interactions and predict the bubble size distribution. Moreover, the effect of adopting the sub-cooled liquid properties into the modelling was investigated and compared with the experiments over a wide range of flow conditions. Specifically, the predicted void fraction and the sub-cooling temperature near the heated wall were precisely compared with the cases of using the constant-property liquid. Overall, the satisfactory agreements were found between the experiments and the predictions of the liquid temperature, void fraction, interfacial area concentration, Sauter mean diameter and bubble and liquid velocities with the exception of the case of high heat and mass fluxes. To enhance the current prediction accuracy for a situation of having a high superheating temperature, more bubble interactions on the boiling wall, such as merging of the bubbles while sliding, need to be considered. Furthermore, to assess the model capability, this mechanistic approach will be introduced to elucidate the sub-cooled boiling flow in situations of using different fluids in the near future.

scholarly journals CFD SIMULATION OF UPWARD SUBCOOLED BOILING FLOW OF FREON R12

2016 ◽  
Vol 4 ◽  
pp. 73
Author(s):  
Tomas Romsy ◽  
Pavel Zacha
Keyword(s):  
Cfd Simulation ◽  
Flow Boiling ◽  
Heat Removal ◽  
Industrial Applications ◽  
Test Facility ◽  
Water Mixture ◽  
Ansys Fluent ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Boiling Flow

Subcooled flow boiling under forced convection occurs in many industrial applications of purpose to maximize heat removal from the heat source by the very large heat transfer coefficient. This work deals with CFD simulations of the subcooled flow boiling of refrigerant R12 solved by code ANSYS FLUENT r16. The main objective of this paper is verification of used numerical settings on relevant experiments performed on DEBORA test facility. Also comparisons with previously provided simulation on NRI Rez are presented. Data outputs from this work are basis to subsequent calculations of steam-water mixture cooling of Pb-Li eutectic.

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