Results of 4-equation turbulence models in the prediction of heat transfer to supercritical pressure fluids

Investigations and numerical modelling are performed on the heat transfer to CO2 at supercritical pressure under buoyancy affected conditions during heating in a vertical tube with inner diameter of 2 mm. Numerical modelling are carried out using several low Reynolds number (LRN) k-ε models, including the model due to Launder and Sharma (LS), Abe, Kondoh and Nagano (AKN), Myong and Kasagi (MK) models. The numerical results are compared with the corresponding experimental data and the predicted values using the semi-empirical correlation for convection heat transfer of supercritical fluids without deterioration. The abilities of various LRN models to predict the heat transfer to fluids at supercritical pressures under normal and buoyancy affected heat transfer conditions are evaluated. Detailed information related to the flow and turbulence is presented to get better understanding of the mechanism of the heat transfer deterioration due to buoyancy, as well as the different behavior of various LRN turbulence models in responding to the buoyancy effect, which gives clues in future model improvement and development to predict the buoyancy affected heat transfer more precisely and in a broader range of conditions as they come to be used to simulate the flow and heat transfer in various applications such as in the supercritical pressure water-cooled reactor (SCWR) and the supercritical pressure steam generator in the high temperature gas cooled reactor (HTR).

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Computational Fluid Dynamics Prediction of Heat Transfer in Rod Bundles With Water at Supercritical Pressure

Journal of Nuclear Engineering and Radiation Science ◽

10.1115/1.4031201 ◽

2015 ◽

Vol 2 (1) ◽

Cited By ~ 1

Author(s):

Andrea Pucciarelli ◽

Walter Ambrosini

Keyword(s):

Heat Transfer ◽

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Turbulence Models ◽

Supercritical Pressure ◽

Navier Stokes ◽

Rod Bundles ◽

Experimental Conditions ◽

Heat Transfer Deterioration ◽

Spacer Grids

The paper further explores the application of computational fluid dynamics (CFD) codes for the study of the heat-transfer phenomena involved when working with fluids at supercritical pressure; bundle analysis is considered here in particular. As for previous simulations performed by the authors considering heat-transfer deterioration inside heated tubes, this application points out the limited capabilities of the most commonly used Reynolds-averaged Navier–Stokes models when approaching the heat-transfer deterioration phenomenon. It must be noted that some of the considered experimental conditions, which are very close to the pseudocritical temperature, represent at the same time one of the most challenging situations for the CFD codes and a very common situation if supercritical water-cooled reactors (SCWRs) will be developed. Improvements of the currently available turbulence models are then needed. The paper analyzes the most likely causes of the observed insufficient quality of the obtained predictions. In addition to comparing the measured and calculated wall temperature trends, the effect of the presence of the spacer grids on the turbulent flow is considered. Spacers are in fact very important to assure the structural stability of fuel, though they also affect the flow, generally improving the turbulence conditions in their neighborhood and slightly impairing it in the downstream region. A comparison between predictions performed including or not including the spacers is also performed.

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Computational Study of Effect of Increasing Heat Flux on Convective Heat Transfer in Sub Channels of Carbon Dioxide Flow at Pressure above Critical Value

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.772.8 ◽

2015 ◽

Vol 772 ◽

pp. 8-13

Author(s):

Deepak Sharma ◽

Krishna Murari Pandey

Keyword(s):

Heat Transfer ◽

Carbon Dioxide ◽

Heat Flux ◽

Convective Heat Transfer ◽

Convective Heat ◽

Water Oxidation ◽

Computational Study ◽

Flow Simulation ◽

Turbulence Models ◽

Supercritical Pressure

This paper is focused on flow simulation in the sub channel of fuel rod assembly using code ANSYS Fluent 14, which is commercial computational fluid dynamics (CFD) code. Computational simulations are reported on convective heat transfer to carbon dioxide at a pressure of 7.59MPa. Pressure which is used in this simulation are just above the thermodynamic critical pressure value of CO2. These have been carried out using a variable property, elliptic computational formulation incorporating low Reynolds number turbulence models ofk–ε. Firstly, the simulations were compared with the effect of increasing heat flux on heat transfer coefficient. It has been found that the effect of buoyancy on turbulence production and heat transfer in fluids at supercritical pressure can be very significant even under conditions of relatively low buoyancy parameter based on bulk properties. It is clear that new heat transfer correlations are needed to account for such effects on heat transfer to supercritical pressure fluids as they come to be used more and more in new energy systems applications such as, advanced water-cooled nuclear reactors, high pressure water oxidation plant for waste processing.

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Simulation of mixed convection heat transfer to carbon dioxide at supercritical pressure

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/095440620421801101 ◽

2004 ◽

Vol 218 (11) ◽

pp. 1281-1296 ◽

Cited By ~ 45

Author(s):

S He ◽

W S Kim ◽

P X Jiang ◽

J D Jackson

Keyword(s):

Heat Transfer ◽

Experimental Data ◽

Carbon Dioxide ◽

Mixed Convection ◽

Convection Heat Transfer ◽

Turbulence Models ◽

Supercritical Pressure ◽

Convection Heat ◽

Computational Simulations ◽

Mixed Convection Heat Transfer

Computational simulations of turbulent mixed convection heat transfer experiments using carbon dioxide at supercritical pressure have been performed by solving the Reynolds averaged transport equations using an elliptic formulation. A number of two-equation low Reynolds number turbulence models have been used and the results have been compared directly with the experimental data. It has been shown that most of the models were to some extent able to reproduce the effects of the very strong influences of buoyancy on heat transfer in these experiments. However, the performance of the models varied significantly from one to another in terms of the predicted onset of such effects.

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Computational Fluid Dynamic Simulations of Heat Transfer From a 2 × 2 Wire-Wrapped Fuel Rod Bundle to Supercritical Pressure Water

Journal of Nuclear Engineering and Radiation Science ◽

10.1115/1.4037747 ◽

2017 ◽

Vol 4 (1) ◽

Cited By ~ 2

Author(s):

Krishna Podila ◽

Yanfei Rao

Keyword(s):

Heat Transfer ◽

Wall Temperature ◽

Cfd Simulation ◽

Fluid Dynamic ◽

Turbulence Models ◽

Supercritical Pressure ◽

Wall Functions ◽

Fuel Rod ◽

Rod Bundle ◽

The Wire

Within the Generation-IV International Forum, Canadian Nuclear Laboratories (CNL) led the conceptual fuel bundle design effort for the Canadian supercritical water cooled reactor (SCWR). The proposed fuel rod assembly for the Canadian SCWR design comprised of 64-elements with spacing between elements maintained using the wire-wrap spacers. Experimental data and correlations are not available for the fuel-assembly concept of the Canadian SCWR. To analyze the thermalhydraulic performance of the new bundle design, CNL is using computational fluid dynamics (CFD) as well as the subchannel approach. Simulations of wire-wrapped bundles can benefit from the increased fidelity and resolution of a CFD approach due to its ability to resolve the boundary layer phenomena. Prior to the application, the CFD tool has been assessed against experimental heat transfer data obtained with bundle subassemblies to identify the appropriate turbulence model to use in the analyses. In the present paper, assessment of CFD predictions was made with the wire-wrapped bundle experiments performed at Xi'an Jiaotong University (XJTU) in China. A three-dimensional CFD study of the fluid flow and heat transfer at supercritical pressures for the rod-bundle geometries was performed with the key parameter being the fuel rod wall temperature. This investigation used Reynolds-averaged Navier–Stokes turbulence models with wall functions to investigate the behavior of flow through the wire-wrapped fuel rod bundles with water subjected to a supercritical pressure of 25 MPa. Along with the selection of turbulence models, CFD results were found to be dependent on the value of turbulent Prandtl number used in simulating the experimental test conditions for the wire-wrapped fuel rod configuration. It was found that the CFD simulation tends to overpredict the fuel wall temperature, and the predicted location of peak temperature differs from the measurement by up to 65 deg.

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