Reassessment of Computational Tools for the Modelling of Heat Transfer in a Molten UO2 Pool in Natural Convection

2021 ◽  
Author(s):  
Claude Jamond ◽  
Elena Martin-Lopez ◽  
Xue-Nong Chen ◽  
N. Girault ◽  
Pierre Gubernatis ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Natural Convection ◽  
Heat Fluxes ◽  
Fuel Pellet ◽  
Simulation Tools ◽  
Axial Profile ◽  
Radial Heat ◽  
The Stability

Abstract This work, performed within the ESFR-SMART H2020 European project, is part of a larger framework intending to reassess the modelling of heat transfer in molten pools on SCARABEE available experimental results. This paper presents simulation results of the in-pile BF1 test, performed within the SCARABEE program, using ASTEC, SIMMER III and SIMMER V simulation tools as well as comparison with its available experimental data. This program was performed in the 80's in the frame of the Safety Assessment studies of Superphenix sodium-cooled reactor. This test was dedicated to verify the stability of a molten UO2 pool under decay heat conditions within natural convection and the long-term resilience of the peripheral fuel crust. The pool was generated in a stainless steel crucible by a progressive heating (six power plateaus) of a fuel pellet stack. For the benchmark purposes, only the molten pool behavior at the last power plateau (largest pool and highest fuel temperatures) was investigated. Experimental data such as the axial profile of radial heat fluxes and heat transfer from the pool to the surrounding inter-assembly coolant or the peripheral fuel crust thickness were used for the reassessment of the simulation tools. In addition, other variables of interest not measured during the test, such as the radial and axial velocities in the pool, were also benchmarked. Finally, a critical analysis of the correlations and models used in the simulation tools for the BF1 test modelling is also provided in the paper.

Full 3D Conjugate Heat Transfer Simulation and Heat Transfer Coefficient Prediction for the Effusion-Cooled Wall of a Gas Turbine Combustor

2008 ◽  
Author(s):  
Andreas Jeromin ◽  
Christian Eichler ◽  
Berthold Noll ◽  
Manfred Aigner
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Gas Turbine ◽  
Conjugate Heat Transfer ◽  
Solid Wall ◽  
Heat Fluxes ◽  
Computational Domain ◽  
Transfer Coefficients ◽  
Wall Functions ◽  
Numerical Predictions

Numerical predictions of conjugate heat transfer on an effusion cooled flat plate were performed and compared to detailed experimental data. The commercial package CFX® is used as flow solver. The effusion holes in the referenced experiment had an inclination angle of 17 degrees and were distributed in a staggered array of 7 rows. The geometry and boundary conditions in the experiments were derived from modern gas turbine combustors. The computational domain contains a plenum chamber for coolant supply, a solid wall and the main flow duct. Conjugate heat transfer conditions are applied in order to couple the heat fluxes between the fluid region and the solid wall. The fluid domain contains 2.4 million nodes, the solid domain 300,000 nodes. Turbulence modeling is provided by the SST turbulence model which allows the resolution of the laminar sublayer without wall functions. The numerical predictions of velocity and temperature distributions at certain locations show significant differences to the experimental data in velocity and temperature profiles. It is assumed that this behavior is due to inappropriate modeling of turbulence especially in the effusion hole. Nonetheless, the numerically predicted heat transfer coefficients are in good agreement with the experimental data at low blowing ratios.

Experimental Study of Heat Transfer to Supercritical Pressure Water Flowing in a 2×2 Rod Bundle

2014 ◽  
Author(s):  
Han Wang ◽  
Qincheng Bi ◽  
Linchuan Wang ◽  
Haicai Lv ◽  
Laurence K. H. Leung
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Pressure Drop ◽  
Wall Temperature ◽  
Mass Flux ◽  
Heat Fluxes ◽  
Outer Diameter ◽  
Square Channel ◽  
Rod Bundle

An experiment has recently been performed at Xi’an Jiaotong University to study the wall temperature and pressure drop at supercritical pressures with upward flow of water inside a 2×2 rod bundle. A fuel-assembly simulator with four heated rods was installed inside a square channel with rounded corner. The outer diameter of each heated rod is 8 mm with an effective heated length of 600 mm. Experimental parameters covered the pressure of 23–28 MPa, mass flux of 350–1000 kg/m2s and heat flux on the rod surface of 200–1000 kW/m2. According to the experimental data, it was found that the circumferential wall temperature distribution of a heated rod is not uniform. The temperature difference between the maximum and the minimum varies with heat flux and/or mass flux. Heat transfer characteristics of supercritical water in bundle were discussed with respect to various heat fluxes. The effect of heat flux on heat transfer in rod bundles is similar with that in tubes or annuli. In addition, flow resistance reflected in the form of pressure loss has also been studied. Experimental results showed that the total pressure drop increases with bulk enthalpy and mass flux. Four heat transfer correlations developed for supercritical pressures water were compared with the present test data. Predictions of Jackson correlation agrees closely with the experimental data.

Natural Convection in a Horizontal Cavity Partially Occupied by a Porous Media Saturated by a Coolant Liquid

2006 ◽  
Author(s):  
Fakhreddine S. Oueslati ◽  
Rachid Bennacer ◽  
Habib Sammouda ◽  
Ali Belghith
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Natural Convection ◽  
Flow Structure ◽  
Boussinesq Approximation ◽  
Density Variation ◽  
Heat Fluxes ◽  
Complex Flow ◽  
Coupled Equations ◽  
Complex Flow Structure

The natural convection is studied in a cavity witch the lower half is filled with a porous media that is saturated with a first fluid (liquid), and the upper is filled with a second fluid (gas). The horizontal borders are heated and cooled by uniform heat fluxes and vertical ones are adiabatic. The formulation of the problem is based on the Darcy-Brinkman model. The density variation is taken into account by the Boussinesq approximation. The system of the coupled equations is resolved by the classic finite volume method. The numerical results show that the variation of the conductivity of the porous media influences strongly the flow structure and the heat transfer as well as in upper that in the lower zones. The effect of conductivity is conditioned by the porosity which plays a very significant roll on the heat transfer. The structures of this flow show that this kind of problem with specific boundary conditions generates a complex flow structure of several contra-rotating two to two cells, in the upper half of the cavity.

Natural Convection in Horizontal Thin-Walled Honeycomb Panels

1973 ◽  
Vol 95 (4) ◽  
pp. 439-444 ◽  
Author(s):  
K. G. T. Hollands
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Fluid Layer ◽  
Convection Heat Transfer ◽  
Correlation Equation ◽  
Wave Number ◽  
Equivalent Wave ◽  
Side Walls ◽  
The Stability ◽  
Rayleigh Numbers

This paper presents an experimental study of the stability of and natural convection heat transfer through a horizontal fluid layer heated from below and constrained internally by a honeycomb. Examination of the types of boundary conditions exacted on the fluid at the cell side-walls has shown that there are three limiting cases: (1) perfectly conducting side-walls; (2) perfectly adiabatic side-walls; and (3) side-walls having zero thickness. Experiments described in this paper approach the latter category. The fluid used is air and the honeycomb used is square-celled. Measured critical Rayleigh numbers are found to be intermediate between those applying to cases (1) and (2), and consistent with an “equivalent wave number” of approximately 0.95 times that for case (1). The measured natural convective heat transfer after instability is found to be significantly less than that predicted by the Malkus-Veronis power integral technique. However, it is found to approach asymptotically the heat transfer which would take place through a similar fluid layer unconstrained by a honeycomb. A general correlation equation for the heat transfer is given.

Can Natural Convection on Smooth Vertical Plates in the Laminar Regime Be Improved by Adding Forward Facing Triangular Roughness Elements?

2019 ◽  
Author(s):  
Jakob Hærvig ◽  
Anna Lyhne Jensen ◽  
Henrik Sørensen
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Aspect Ratio ◽  
Dead Zone ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Fluxes ◽  
Smooth Surfaces ◽  
Roughness Elements ◽  
Triangular Elements

Abstract Vertical smooth surfaces are commonly used for transferring heat by natural convection. Many studies have tried altering smooth surfaces in various ways to increase heat transfer. Many of these studies fail to increase global heat transfer. The problem commonly reported is dead zones appearing just upstream and downstream obstructions that effectively decrease wall temperature gradients normal to the surface. In this study, we simulate how changes geometry of forward facing triangular roughness elements affect local and global heat transfer for isothermal plates. We change the aspect ratio of the triangular elements from L/h = 5 to L/h = 40 at Grashof numbers of GrL = 8.0 · 104 and GrL = 6.4 · 105. In all cases the flow remains laminar. Even when accounting for the increase in surface area, we keep observing a decrease in global heat transfer compared to the smooth vertical plate. However, the results show by carefully selecting the aspect ratio and pitch distance of the triangular elements based on the Grashof number, the dead zone behind the horizontal part can be eliminated thereby significantly increasing local heat transfer. This observation could help to improve cooling of electronics with high localised heat fluxes.

Stability and Enhancement of Boiling in Microchannels

2011 ◽  
Author(s):  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
High Heat ◽  
Heat Fluxes ◽  
Transfer Enhancement ◽  
The Past ◽  
The Stability ◽  
Saturated Boiling ◽  
Microelectronic Components

During the past 20 years, there has been intense worldwide interest in microchannel heat exchangers, particularly for cooling of microelectronic components. Saturated boiling of the coolant is usually indicated in order to accommodate high heat fluxes and to have uniformity of temperature. However, boiling is accompanied by several instabilities, the most severe of which can sharply limit the maximum, or critical, heat flux. These stability phenomena are reviewed, and recent studies will be discussed. Elevation of the critical heat flux will be discussed within the context of heat transfer enhancement. Means to improve the stability of boiling and the enhancement of boiling heat transfer, in general, are discussed.

Computational Simulation of Turbulent Natural Convection in a Volumetrically Heated Hemispherical Cavity

2014 ◽  
Author(s):  
Camila Braga Vieira ◽  
Bojan Ničeno ◽  
Jian Su
Keyword(s):  
Experimental Data ◽  
Natural Convection ◽  
Nuclear Power ◽  
Computational Simulation ◽  
Numerical Data ◽  
Local Heat Transfer ◽  
Heat Fluxes ◽  
Severe Accident ◽  
Turbulent Heat ◽  
Turbulent Natural Convection

This work presents an analysis of the turbulent natural convection in a volumetrically hemisphere cavity, representing a lower plenum of a Light Water Reactor (LWR) vessel. Considering isothermal top and bottom walls at temperature of 298.5 K and a fluid with Prandtl number (Pr) equal to 8.52, the experiment performed by Asfia et al. [1] was reproduced, so that their experimental data could be used for the validation of the numerical data provided by the present work. Ranging the internal Rayleigh numbers (Rai) from 108 to 3.03 × 1013, numerical simulations were performed using the open-source Computational Fluid Dynamics (CFD) code OpenFOAM (Open Field Operation and Manipulation), making use of the “code-friendly” modification of the turbulence model V2-f, a Reynolds Averaged Navier-Stokes (RANS) based equation model. The calculation of the turbulent heat fluxes was done by the Simple Gradient Diffusion Hypothesis (SGDH), which proved to be adequate for the case considered. Bearing in mind the complexity of the phenomena inside a molten core after a severe accident in a nuclear power plant, some assumptions were done such as the fluid was considered Newtonian, with no-phase change and homogeneous. Numerical correlations of Nusselt number (Nu¯) over the bottom and top walls as function of the Rai were obtained and a good agreement with the experimental data provided by Asfia et al. [1] was reached for the local heat transfer with respect to the angle for the cooled top wall.

Effects of Various Parameters on Supercritical-Pressure Heat Transfer and Limits for Heat Transfer Correlations Obtained in Vertical Bare Tubes

2017 ◽  
Author(s):  
Hakim Maloufi ◽  
Hanqing Xie ◽  
Andrew Zopf ◽  
William Anderson ◽  
Christian Langevin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Nuclear Power ◽  
Nuclear Reactor ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Wide Range ◽  
Heat Transfer Correlations ◽  
Bare Tube

Currently, there is a number of Generation-IV SuperCritical Water-cooled nuclear-Reactor (SCWR) concepts under development worldwide. These high temperature and pressure reactors will have significantly higher operating parameters compared to those of current water-cooled nuclear-power reactors (i.e., “steam” pressures of about 25 MPa and “steam” outlet temperatures up to 625 °C). Additionally, SCWRs will have a simplified flow circuit in which steam generators, steam dryers, steam separators, etc. will be eliminated, as the steam will be flowing directly to a steam turbine. In support of developing SCWRs studies are being conducted on heat transfer at SuperCritical Pressures (SCPs). Currently, there are very few experimental datasets for heat transfer at SCPs in power-reactor fuel bundles to a coolant (water) available in open literature. Therefore, for preliminary calculations, heat-transfer correlations developed with bare-tube data can be used as a conservative approach. Selected empirical heat-transfer correlations, based on experimentally obtained datasets, have been put forward to calculate Heat Transfer Coefficients (HTCs) in forced convective in various fluids, including water at SCPs. The Mokry et al. correlation (2011) has shown a good fit for experimental data at supercritical conditions within a wide range of operating conditions in Normal and Improved Heat-Transfer (NHT and IHT) regimes. However, it is known that a Deteriorated Heat-Transfer (DHT) regime appears in bare tubes earlier than that in bundle flow geometries. Therefore, it is important to know if bare-tube heat-transfer correlations for SCW can predict HTCs at heat fluxes beyond those defined as starting of DHT regime in bare tubes. The Mokry et al. (2011) correlation fits the best SCW experimental data for HTCs and inner wall temperature for bare tubes at SCPs within the NHT and IHT regimes. However, this correlation might have problems with convergence of iterations at heat fluxes above 1000 kW/m2.

Development and Comparison of a Heat-Transfer Correlation for Supercritical Refrigerants

2017 ◽  
Author(s):  
Nicholas Tarsitano ◽  
Khalil Sidawi ◽  
Igor Pioro
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Fluxes ◽  
Critical Parameters ◽  
Future Research ◽  
Supercritical Conditions ◽  
Wide Range ◽  
Heat Transfer Correlations ◽  
R 134A ◽  
Correlation Accuracy

The objective of this paper is to act as a collection of multiple different heat-transfer correlations and to check their accuracy when compared to experimental data obtained in supercritical-pressure refrigerants (R-22 and R-134a). This paper is also intended to collect as much relevant data of heat transfer in supercritical refrigerants as possible for future research. The experimental data have been retrieved from graphs within a wide range of operating parameters. This study is in support of potential use of supercritical refrigerants as modeling fluids instead of supercritical water. The use of refrigerants as modelling fluids instead of water will allow to decrease costs and technical difficulties during experiments at supercritical pressures and widen operating ranges, because the critical parameters of refrigerants are significantly lower than those of water. The research was completed by collecting graphed data from several different experimental series using both R-22 and R-134a data. The advantage of comparing different refrigerants for determining correlation accuracy is to increase the predictability for other potential experiments using refrigerants. All data are taken from bare-tube experiments to produce a relative baseline for heat-transfer characteristics. These experiments have been performed within the following range: Inner tube diameter ranging between 4.4 mm to 13 mm, pressure ranging between 4.3 MPa to 5.5 MPa, and at a number of various mass and heat fluxes. Sixteen potential heat-transfer correlations have been selected and used in this assessment. The correlation by Watts and Chou [1] and Cheng et al. [2] were shown to have the lowest root-mean-square error. Other correlations with the reasonable accuracy include Mokry et al. [3] and Swenson et al. [4] correlations. However, it was decided to develop a new correlation based on these refrigerant data in an attempt to increase the prediction accuracy. Therefore, based on the Mokry et al. [3] correlation a modified correlation was developed, which generalized the experimental Freon data with higher accuracy than the know correlations. This correlation is intended to create a basis for further study on the use of refrigerants as modeling fluids. While Freon has similar properties to water at supercritical conditions, the different molecular properties causes factors to affect each fluid differently. For refrigerants at supercritical conditions, the factors that seem to have the most effect are the dynamic viscosity and density of a fluid.

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