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 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.

scholarly journals Uniform versus Nonuniform Axial Power Distribution in Rod Bundle CHF Experiments

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Baowen Yang ◽  
Jianqiang Shan ◽  
Junli Gou ◽  
Hui Zhang ◽  
Aiguo Liu ◽  
...  
Keyword(s):  
Power Distribution ◽  
Fundamental Difference ◽  
Heat Fluxes ◽  
Correction Factors ◽  
Light Water Reactors ◽  
Rod Bundles ◽  
Light Water ◽  
Driving Mechanisms ◽  
Rod Bundle ◽  
Water Reactors

Rod bundle experiments with axially uniform and nonuniform heat fluxes are examined to explore the potential limitations of using uniform rod bundle CHF data for CHF correlation development of light water reactors with nonuniform axial power distribution (APD). The case of upstream burnout is presented as an example of unique phenomena associated with nonuniform rod bundle CHF experiments. It is a result from combined effect of axial nonuniform power shape and different interchannel mixing mechanisms. In addition, several key parameters are investigated with respect to their potential impacts on the thermal-hydraulic behaviors between rod bundles with uniform and nonuniform APDs. This type of misrepresentation cannot be amended or compensated through the use of correction factors due to the lack of critical information in the uniform rod bundle CHF testing as well as the fundamental difference in the underlining driving mechanisms. Other potential issues involved with the use of uniform rod bundle CHF data for nonuniform APD system applications also present strong evidence concerning the limitations and inadequacy of using uniform rod bundle CHF data for the correlation, prediction, and design limit calculation for safety analysis.

Modeling of the Effect of Parallel Rib-Type Roughness on Local, Single-Phase Heat Transfer in Rod Bundles by CFD: Part 1—Flow Resistance

2010 ◽  
Author(s):  
Leo Carrilho ◽  
Jamil Khan
Keyword(s):  
Heat Transfer ◽  
Flow Resistance ◽  
Experimental Testing ◽  
Model Parameters ◽  
Light Water Reactors ◽  
Rod Bundles ◽  
Roughness Effects ◽  
Fuel Rod ◽  
Computational Fluid Dynamics Cfd ◽  
Water Reactors

The applicability of artificial roughness in light-water reactors is investigated for the purpose of heat transfer improvement in fuel rod bundles. Since the roughening technique has a significant impact on friction losses, the investigation is divided in two distinct steps: flow resistance and convective heat transfer. The present paper deals with roughness effects on flow resistance. The technique consists of a multiplicity of small elements distributed on the surface of the simulated fuel rod. A parallel rib-type roughness is selected for this work for simplicity and since it has been extensively investigated in the past. Locally flow resistance is simulated using Computational Fluid Dynamics, CFD, in smooth and in rough rod bundles downstream of support grids with and without flow-enhancing features (vanes). This investigation is performed with basis on experimental testing. With model parameters established, various candidate roughness designs can evaluated for minimum flow resistance.

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.

A Blind, Numerical Benchmark Study on Supercritical Water Heat Transfer Experiments in a 7-Rod Bundle

2016 ◽  
Vol 2 (2) ◽  
Author(s):  
M. Rohde ◽  
J. W. R. Peeters ◽  
A. Pucciarelli ◽  
A. Kiss ◽  
Y. F. Rao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Supercritical Water ◽  
Real Life ◽  
Predictive Ability ◽  
Test Facility ◽  
Test Case ◽  
Significant Deterioration ◽  
Rod Bundle ◽  
Sst Turbulence Model ◽  
Water Reactors

Heat transfer in supercritical water reactors (SCWRs) shows a complex behavior, especially when the temperatures of the water are near the pseudocritical value. For example, a significant deterioration of heat transfer may occur, resulting in unacceptably high cladding temperatures. The underlying physics and thermodynamics behind this behavior are not well understood yet. To assist the worldwide development in SCWRs, it is therefore of paramount importance to assess the limits and capabilities of currently available models, despite the fact that most of these models were not meant to describe supercritical heat transfer (SCHT). For this reason, the Gen-IV International Forum initiated the present blind, numerical benchmark, primarily aiming to show the predictive ability of currently available models when applied to a real-life application with flow conditions that resemble those of an SCWR. This paper describes the outcomes of ten independent numerical investigations and their comparison with wall temperatures measured at different positions in a 7-rod bundle with spacer grids in a supercritical water test facility at JAEA. The wall temperatures were not known beforehand to guarantee the blindness of the study. A number of models have been used, ranging from a one-dimensional (1-D) analytical approach with heat transfer correlations to a RANS simulation with the SST turbulence model on a mesh consisting of 62 million cells. None of the numerical simulations accurately predicted the wall temperature for the test case in which deterioration of heat transfer occurred. Furthermore, the predictive capabilities of the subchannel analysis were found to be comparable to those of more laborious approaches. It has been concluded that predictions of SCHT in rod bundles with the help of currently available numerical tools and models should be treated with caution.

Heat Transfer to Supercritical Water in Vertical Annular Channel and 3-Rod Bundle

2009 ◽  
Author(s):  
V. G. Razumovskiy ◽  
Eu. N. Pis’mennyy ◽  
A. Eu. Koloskov ◽  
I. L. Pioro
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Supercritical Water ◽  
Annular Channel ◽  
Heat Fluxes ◽  
Inlet Temperature ◽  
Outlet Temperature ◽  
Rod Bundle ◽  
Temperature Regimes ◽  
Outside Diameter

The results of heat transfer to supercritical water flowing upward in a vertical annular channel (1-rod channel) and tight 3-rod bundle consisting of the tubes of 5.2-mm outside diameter and 485-mm heated length are presented. The heat-transfer data were obtained at pressures of 22.5, 24.5, and 27.5 MPa, mass flux within the range from 800 to 3000 kg/m2·s, inlet temperature from 125 to 352°C, outlet temperature up to 372°C and heat flux up to 4.6 MW/m2 (heat flux rate up to 2.5 kJ/kg). Temperature regimes of the annular channel and 3-rod bundle were stable and easily reproducible within the whole range of the mass and heat fluxes, even when a deteriorated heat transfer took place. The data resulted from the study could be applicable for a reference estimation of heat transfer in future designs of fuel bundles.

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