Numerical investigation of heat transfer in upward flows of supercritical water in circular tubes and tight fuel rod bundles

2007 ◽  
Vol 237 (4) ◽  
pp. 420-430 ◽  
Author(s):  
Jue Yang ◽  
Yoshiaki Oka ◽  
Yuki Ishiwatari ◽  
Jie Liu ◽  
Jaewoon Yoo
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Supercritical Water ◽  
Rod Bundles ◽  
Circular Tubes ◽  
Fuel Rod

Numerical Study of Turbulent Convective in Upward Flows of Supercritical Water in the Triangular Lattice Fuel Rod Bundle

2014 ◽  
Author(s):  
Mohsen Modirshanechi ◽  
Kamel Hooman ◽  
Iman Ashtiani Abdi ◽  
Pourya Forooghi
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Turbulent Boundary Layer ◽  
Physical Properties ◽  
Supercritical Water ◽  
Triangular Lattice ◽  
Rod Bundles ◽  
Fuel Rod ◽  
Thermo Physical Properties

Convection heat transfer in upward flows of supercritical water in triangular tight fuel rod bundles is numerically investigated by using the commercial CFD code, ANSYS Fluent© 14.5. The fuel rod with an inner diameter of 7.6 mm and the pitch-to-diameter ratio (P/D) of 1.14 is studied for mass flux ranging between 550 and 1050 kg/m2s and heat flux of 560 kW/m2 at pressures of 25 MPa. V2F eddy viscosity turbulence model is used and, to isolate the effect of buoyancy, constant values are used for thermo-physical properties with Boussinesq approximation for the density variation with temperature in the momentum equations. The computed Nusselt number normalized by that of the same Reynolds number with no buoyancy against the buoyancy parameter proposed by Jackson and Hall’s criterion. Mentioned results are compared with V2F turbulence model whereas strong nonmonotonic variation of the thermo-physical properties as function of temperature have been applied to the commercial CFD code using user defined function (UDF) technique. A significant decrease in Nusselt number was observed in the range of 10-6<Grq/Reb3.425Prb0.8<5×10-6 before entering a serious heat transfer deterioration regime. Based on an analysis of the shear-stress distribution in the turbulent boundary layer and the significant variation of the specific heat across the turbulent boundary layer, it is found that the same mechanism that leads to impairment of turbulence production in concentric annular pipes is present in triangular lattice fuel rod bundles at supercritical pressure.

CFD Investigation of Heat Transfer in Supercritical Water-Cooled Flow Through 3×3 Fuel Rod Bundles

2008 ◽  
Author(s):  
Zhi Shang ◽  
Yufeng Yao
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Cross Section ◽  
Supercritical Water ◽  
Wall Temperature ◽  
Mass Flux ◽  
Rod Bundles ◽  
Fuel Rod ◽  
Channel Analysis ◽  
The Cross

CFD investigation of heat transfer in supercritical water-cooled flow through fuel rod bundles has been carried out, using commercial software STAR-CD 4.02 with specific ad hoc user routines for modeling physical property of supercritical water. The configuration considered is a typical core assembly of 3×3 fuel rod (round tube) bundles inside solid square box, as seen in the nuclear reactor. After priori mesh convergence studies, investigations are focused on key characteristics of flow and heat transfer performance, notably the wall temperature distributions, the mass flux and the secondary flow patterns in the cross-section. It is found that the rod wall temperature distributions exhibit highly non-uniform feature near the domain exit with very high wall temperatures: about 625°C observed on the corner rod and about 562.5°C on the border rod, respectively. It is believed that the appearance of the extremely wall temperature may be related to the non-uniform distributions of mass flux in the cross-section of the bundles as the low mass flux co-existing with the high wall temperature. Further analysis of the secondary flow in the cross-section reveals wider spectrum of vortex flow structures, more complicated than previously noted by the sub-channel analysis. To verify the influence of turbulence models on the secondary flow, both linear and non-linear k-ε models are applied and results are quite similar. This finding indicates that the cause of the secondary (cross) flow might not be solely due to the anisotropic property of turbulence as suggested by other researchers. The present 3D CFD study provides more complete database of 3×3 rod bundle flows and will be useful to improve the industry practice of applying the sub-channel analysis.

SCWR Rod Bundle Thermal Analysis by a CFD Code

2008 ◽  
Author(s):  
M. Sharabi ◽  
W. Ambrosini ◽  
N. Forgione ◽  
S. He
Keyword(s):  
Heat Transfer ◽  
Supercritical Water ◽  
Power Distribution ◽  
Transport Model ◽  
Rod Bundles ◽  
Fuel Rod ◽  
Reynolds Stress Transport Model ◽  
Rod Bundle ◽  
Transfer Behavior ◽  
Water Reactors

The present paper describes the results of the application of the FLUENT code in the analysis of rod bundle configurations proposed for high pressure supercritical water reactors. The model considers a 1/8 slice of a rod bundle. The details from CFD calculations offer predictions of the circumferential clad surface temperature and of the effect of axial power distribution on the mass exchange between subchannels and on the maximum surface rod temperature. Geometry and boundary conditions are adopted from a previous work that made use of subchannel programs, allowing for a direct comparison between the two techniques. Both the standard k-ε model and the Reynolds stress transport model are used. Conclusions are drawn about the present capabilities in predicting heat transfer behavior in fuel rod bundles proposed for supercritical water reactors.

Numerical investigation for the heat transfer mechanisms between subchannels of bar rod bundles cooled by liquid sodium

2021 ◽  
Vol 161 ◽  
pp. 108460
Author(s):  
X.A. Wang ◽  
Dalin Zhang ◽  
Mingjun Wang ◽  
Yandong Hou ◽  
Wenxi Tian ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Liquid Sodium ◽  
Rod Bundles ◽  
Transfer Mechanisms

Numerical Analysis of the Flow and Heat Transfer in the Sub-Channel of Supercritical Water Reactor

2013 ◽  
Author(s):  
Ajoy Debbarma ◽  
K. M. Pandey
Keyword(s):  
Heat Transfer ◽  
Fuel Assembly ◽  
Supercritical Water ◽  
High Performance ◽  
Flow Distribution ◽  
Diameter Ratio ◽  
Light Water Reactor ◽  
Water Reactor ◽  
Fuel Rod ◽  
Gap Width

Research activities are ongoing for High performance light water reactor (HPLWR) with square double rows fuel assembly to develop nuclear power plants with the purpose to achieve a high thermal efficiency and to improve their economical competitiveness. However, there is still a big deficiency in understanding and prediction of heat transfer in supercritical fluids. This paper evaluates three-dimensional turbulent flow and convective heat transfer in a single-phase and steady-state sub-channel of HPLWR by using general computational fluid dynamics code, Ansys 14 Fluent. The major concern using supercritical water as work fluid is the heat transfer characteristics due to large variations of thermal properties of supercritical water near pseudo-critical line. In order to ensure the safety of operation in High performance light water reactor (HPLWR), heat transfer deterioration (HTD) must be avoided. Numerical results prove that the RNG k-e model with the enhanced near-wall treatment obtained the most satisfactory prediction and lead to satisfactory simulation results. The HPLWR Square fuel assembly has many square-shaped water rods, Out of four types of sub-channels; three sub-channels SC-1, SC-2 and SC-3 are investigated (adjacent to the side of the moderator flow channels (SC-1) (moderator tube and assembly gap), central sub-channels formed by four fuel rods (SC-2), adjacent to the corner of the moderator tube (SC-3). Since coolant flow distribution in the fuel assembly strongly depends on the gap width between the fuel rod and water rod, fuel rod pitch to diameter ratio 1.1–1.4 with 8mm diameter are considered for simulation. Sub-channel analysis clarifies that coolant flow distribution becomes uniform when the gap width is set to 1.0 mm. was less than 620°C. Effects of various parameters, such as boundary conditions and pitch-to-diameter ratios, on the mixing phenomenon in sub-channels and heat transfer are investigated. The effect of pitch-to-diameter ratio (P/D) on the distributions of surface temperature and heat transfer coefficient (HTC) in a sub-channel, it was found that HTC increases with P/D 1.1 first and then decreases with increasing P/D ratio. Apart from the basic geometry sub-channel, a square sub-channel with a wire-wrapped rod inside has been chosen to investigate the “wire effect”.

Numerical Investigation on the Effect of Transversal Septa on Forced Convection in Circular Tubes

2009 ◽  
Author(s):  
O. Manca ◽  
S. Nardini ◽  
D. Ricci
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Circular Tubes ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Conventional sources of energy have been depleting at an alarming rate, which makes future sustainable development of energy use very difficult. Thus, heat transfer enhancement technology plays an important role and it has been widely applied to many applications as in refrigeration, automotive, process industry, solar energy heater, etc. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by increasing thermal conductivity of the fluid. Another possibility for increasing heat transfer with gas is to employ extended surfaces. In this paper a numerical investigation is carried out on forced convection in circular tubes with septa heated by constant fluxes and characterized by different shapes. When gas flows in a tube, septa with one or more openings can be used as fins. Furthermore, when the openings are arranged to give a spiral motion around the cylinder axis wall-fluid contact area increases. As a consequence the presence of the septa may significantly augment pressure drops. The fluid is air and properties are function of temperature. Septa of the same material of the tube are introduced and several shapes and arrangements are analyzed as well as different Reynolds numbers, baffle spacings and heat fluxes applied on the external surface. The investigation is accomplished by means of the commercial code Fluent. A k-e turbulence model is used with enhanced wall treatment options. Results are presented in terms of temperature and velocity fields, local and average heat transfer coefficients, friction factors and pressure drops for different values of heat flux, Reynolds numbers and baffle spacings. The aim of this study is to find the shape and arrangement of septa such to give high heat transfer coefficients and low pressure drops.

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