Combined CFD and DEM Simulations of Fluid Flow and Heat Transfer in a Pebble Bed Reactor

2011 ◽  
Author(s):  
Xiang Zhao ◽  
Trent Montgomery ◽  
Sijun Zhang
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Discrete Element Method ◽  
Reactor Core ◽  
Turbulence Models ◽  
Discrete Element ◽  
Pebble Bed ◽  
Pebble Bed Reactor ◽  
Packing Structure ◽  
Dem Simulations

This paper presents combined computational fluid dynamics (CFD) and discrete element method (DEM) simulations of fluid flow and relevant heat transfer in the pebble bed reactor core. In the pebble bed reactor core, the coolant passes highly complicated flow channels, which are formed by thousands of pebbles in a random way. The random packing structure of pebbles is crucial to CFD simulations results. The realistic packing structure in an entire pebble bed reactor (PBR) is generated by discrete element method (DEM). While in CFD calculations, selection of the turbulence models have great importance in accuracy and capturing the details of the flow features, in our numerical simulations both large eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) models are employed to investigate the effects of different turbulence models on gas flow field and relevant heat transfer. The calculations indicate the complex flow structure within the voids between the pebbles.

scholarly journals HTR-10 OTTO Cycle Depletion Simulation Using Discrete Element Method Coupled Monte Carlo

2021 ◽  
Vol 2048 (1) ◽  
pp. 012031
Author(s):  
F Putra
Keyword(s):  
Monte Carlo ◽  
Discrete Element Method ◽  
Reactor Core ◽  
Discrete Element ◽  
Calculation Model ◽  
Pebble Bed Reactor ◽  
Digital Version ◽  
Section Data ◽  
Surface Contact ◽  
Element Method

Abstract Pebble bed reactor core contains 27,000 pebbles placed in a random position. Since the pebble insertion relies on gravity, the pebble placement pattern is irregular. Discrete Element Method used to simulate the pebble interaction and pebble movement during HTR-10 operation. Even though pebbles distributed randomly, the random generation of pebble positions used in most research does not mimic the actual pebble position and pebble surface contact. The Discrete Element Method provides a realistic interpretation of the pebble position by considering the pebble surface contact and gravity force. Each pebble coordinates from the Discrete Element Method obtained to construct Monte Carlo geometry of the HTR-10 core realistically. By coupling the DEM simulation with Monte Carlo simulation, it is possible to calculate the depletion while considering the core dynamic characteristic. The OTTO recirculation depletion calculation scheme with steady 10MW power for 368 days was constructed and demonstrated in this work. The DEM coupled Monte Carlo method allow one to track and predict each depleted fuel composition. Although the flux distribution change is slight in every timestep, the relation between flux and depleted U235 and Xe135 composition deserves to be taken into account. The calculation model in this work is comparable with the other calculation, but the timestep adjustment is needed to provide more accurate and representative results. Flux calculation and depletion simulation performed using the OpenMC program with ENDF/B-VIII.0 cross-section data. Please refer to digital version to view graph.

Variant Porosity Pebble Bed Reactor Core Thermal Hydraulic Simulation

2010 ◽  
Author(s):  
Gang Zhao ◽  
Ping Ye ◽  
Toru Obala
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Reactor Core ◽  
Maximum Temperature ◽  
Porous Media Flow ◽  
Pebble Bed ◽  
Pebble Bed Reactor ◽  
Passive Cooling System ◽  
Porosity Model ◽  
Random Porosity

Spherical fuel elements are distributed randomly in the pebble bed reactor core and helium flow through the pebble bed to remove nuclear reaction heat. Pebble bed reactor core is usually treated as a uniform porous media flow in thermal hydraulic research. However the porosity distribution is nonuniform and the porosity near the wall increase sharply. A new random model is developed in this paper to investigate thermal hydraulic characteristics of pebble bed reactor core. Porosity assumption is based on porosity measurement of other research. Porosity simulation is divided into three parts according to the distance from wall. In the center of core, porosity is assumed to obey normal distribution, where average porosity is from the experimental relation based on statistical results. The mean and standard deviation of porosity distribution near the wall will increase because of the wall effect, where the distance from the wall is about three times of fuel ball’s diameter. The third part is zone from three times to five times of ball’s diameter departed from the wall. The wall effect of this zone is between center and the wall zone. Based on above assumption, a random porosity simulation is completed to apply in this research. COMSOL Multiphysics 3.5a software is used in this research. COMSOL Multiphysics are a calculation platform using proven Finite Elements Methods (FEM). In this research, Brinkman equation for porous media flow is applied in the simulation. Non-thermal Balance model is used in local heat transfer research between gas and pebble bed. A geometry model is built to simulate HTR-10. Temperature profile of variant porosity is gained from stationary analysis and comparison with uniform porosity is also discussed in the paper. For transient analysis, four cases simulation is carried out in the research. Case 1 and 2 simulate heat transfer phenomena with forced cooling system and with passive cooling system after reactor shut down. Way-Wigner-curve is used in Case 1 and Case 2 to simulate decay heat in the calculation. Case 3 and Case 4 simulate ATWS phenomena with natural convection and without natural convection system when blower is trip off in normal operation. Simulation results also are compared with some ATWS experiments and some discussion is done in the paper. From the results, it can be seen that random porosity will affect temperature distribution near the wall and make outlet temperature non-uniform greatly. The maximum temperature of variant porosity is much greater than the maximum temperature of uniform porosity at the same condition. Transient analyses of variant model show that passive cooling system can remove residual heat even in accident conditions when the blower trip off whether reactor shut down or not and the analyses results correspond substantially with experimental results. In general, variant porosity should be considered in the thermal hydraulic research of pebble bed reactor core. Variant porosity model can provide good prediction of heat transfer phenomena than uniform porosity model. Especially it can explain some transient analysis results.

Discrete Element Method–Based Investigations of Granular Flow in a Pebble Bed Reactor

2017 ◽  
Vol 199 (1) ◽  
pp. 47-66
Author(s):  
Vaibhav Khane ◽  
Mahmoud M. Taha ◽  
Gary E. Mueller ◽  
Muthanna H. Al-Dahhan
Keyword(s):  
Discrete Element Method ◽  
Granular Flow ◽  
Discrete Element ◽  
Pebble Bed ◽  
Pebble Bed Reactor ◽  
Element Method

Multiphase Flow and Heat Transfer in Pebble Bed Reactor Core

2021 ◽  
Author(s):  
Shengyao Jiang ◽  
Jiyuan Tu ◽  
Xingtuan Yang ◽  
Nan Gui
Keyword(s):  
Heat Transfer ◽  
Multiphase Flow ◽  
Reactor Core ◽  
Pebble Bed ◽  
Pebble Bed Reactor ◽  
Flow And Heat Transfer

scholarly journals Effect of pebble size and bed dimension on the distribution of voidages in pebble bed reactor

2017 ◽  
Vol 10 (3) ◽  
pp. 99-108 ◽  
Author(s):  
Yin Xiong ◽  
Ge Liang ◽  
Gui Nan ◽  
Yang Xingtuan ◽  
Tu Jiyuan ◽  
...  
Keyword(s):  
Particle Size ◽  
Discrete Element Method ◽  
Economic Efficiency ◽  
Discrete Element ◽  
Inherent Safety ◽  
Wall Effects ◽  
Pebble Bed ◽  
Pebble Bed Reactor ◽  
Tsinghua University ◽  
2D And 3D

The HTR-10 built at Tsinghua University is an advanced pebble bed reactor because of its inherent safety and economic efficiency. It is fundamental to explore the voidage of the pebble bed. The existing experimental bed is limited in depth and contains mono-size pebbles. The effects of pebble size and bed dimension of voidage distribution are still not well known. In this work, the discrete element method is used to simulate the static packing of pebbles of three sizes in 2D and 3D pebble beds under the same load. The effects of bed dimension and pebble size on voidage distribution are analyzed. The results are useful for better understanding of the voidage distribution of pebble bed reactor and the effects of bed dimension and particle size as well as the wall effects.

Simulation of Heat Transfer in Moving Granular Material by the Discrete Element Method With Special Emphasis on Inner Particle Heat Transfer

2009 ◽  
Author(s):  
S. Rickelt ◽  
H. Kruggel-Emden ◽  
S. Wirtz ◽  
V. Scherer
Keyword(s):  
Heat Transfer ◽  
Discrete Element Method ◽  
Discrete Element ◽  
Temperature Model ◽  
Contact Heat ◽  
Radial Temperature ◽  
Dem Simulations ◽  
Contact Heat Transfer ◽  
Granular Assemblies ◽  
Element Method

Physical processes involving static or dynamic granular assemblies are best modeled on the particle scale by Discrete Element Methods (DEM) rather than continuum approaches. Due to the high computational effort of DEM simulations, present studies assume the inner particle temperature to be spatially uniform and neglect the inner particle heat transfer. For this reason the Radial Temperature Model was introduced [1, 2] It assumes radial temperature distributions within the particles and is based on an analytical solution of the heat conduction equation in a spherical particle. The scope of this paper is to present the further development of the Radial Temperature Model that allows to simulate granular systems of particles of different sizes and materials, enabling the use of DEM in various applications. The contact heat transfer is modeled making additional material-specific data unnecessary. It is shown that a very good accuracy for the contact heat transfer between different spherical particles is achieved for binary contacts. DEM simulations were performed using the Radial Temperature Model and uniform particle temperatures, respectively. The results demonstrate that the Radial Temperature Model that has been developed and incorporated in the Discrete Element Method allows for an improved calculation of the transient thermal behavior of granular assemblies even for large numbers of particles.

Development of Local Heat Transfer and Pressure Drop Models for Pebble Bed High Temperature Gas-Cooled Reactor Cores

2008 ◽  
Author(s):  
Brian McLaughlin ◽  
Matthew Worsley ◽  
Richard Stainsby ◽  
Andrew Grief ◽  
Ana Dennier ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Pebble Bed ◽  
Ansys Fluent ◽  
Pebble Bed Reactor ◽  
Rans Turbulence Models

This paper describes pressure drop and heat transfer coefficient predictions for a typical coolant flow within the core of a pebble bed reactor (PBR) by examining a representative group of pebbles remote from the reflector region. The three-dimensional steady state flow and heat transfer predictions utilized in this work are obtained from a computational fluid dynamics (CFD) model created in the commercial software ANSYS FLUENT™. This work utilizes three RANS turbulence models and the Chilton-Colburn analogy for heat transfer. A methodology is included in this paper for creating a quality unstructured mesh with prismatic surface layers on a random arrangement of touching pebbles. The results of the model are validated by comparing them with the correlations of the German KTA rules for a PBR.

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