Use of Regular Rod Arrays to Model Heat Transfer From BWR Fuel Assemblies Inside Transport Casks

2007 ◽  
Author(s):  
Pablo E. Araya ◽  
Miles Greiner
Keyword(s):  
Heat Transfer ◽  
Spent Nuclear Fuel ◽  
Two Dimensional ◽  
Fuel Cladding ◽  
Cfd Simulations ◽  
Fuel Assemblies ◽  
Computational Fluid Dynamics Cfd ◽  
Heat Transfer Effects ◽  
Computational Resources ◽  
Volume Mesh

The current work is a scoping study to determine which heat transfer effects are significant in the fuel/backfill gas region of spent nuclear fuel transport casks. A two-dimensional finite volume mesh that accurately models the geometry of a 7×7 Boiling Water Reactor (BWR) assembly with its channel in a square isothermal enclosure is constructed. The peak cladding temperature is determined using computational fluid dynamics (CFD) simulations for a range of enclosure temperatures, fuel heat generation rates, cladding surface emissivities, and for both nitrogen and helium backfill gases. This work quantifies both the effect of buoyancy induced gas motion in the fuel/backfill gas region and the conditions when it does not significantly affect heat transfer. Future cask design simulations that neglect gas motion will require less computational resources than ones that do not. This work also quantifies the sensitivity of the maximum cladding temperature to fuel cladding emissivity. This helps quantify the uncertainty of temperature predictions if the emissivity is not known. The current CFD technique must be experimentally benchmarked before it may be used with confidence to predict peak cladding temperatures in transport casks. This work indicates that the thermal resistance between a BWR assembly’s channel and the basket walls may be modeled analytically. This will reduce the effort required for benchmark experiments because they will not need to include the channel.

Comparison of DSMC and CFD Models of Heat Transfer in a Rarefied Two-Dimensional Geometry

2018 ◽  
Author(s):  
Dilesh Maharjan ◽  
Mustafa Hadj-Nacer ◽  
Miles Greiner ◽  
Stefan K. Stefanov
Keyword(s):  
Heat Transfer ◽  
Rarefied Gas ◽  
Complex Geometry ◽  
Direct Simulation Monte Carlo ◽  
Accurate Method ◽  
Vacuum Drying ◽  
Helium Pressure ◽  
Two Dimensional ◽  
Dsmc Method ◽  
Cfd Simulations

During vacuum drying of used nuclear fuel (UNF) canisters, helium pressure is reduced to as low as 67 Pa to promote evaporation and removal of remaining water after draining process. At such low pressure, and considering the dimensions of the system, helium is mildly rarefied, which induces a thermal-resistance temperature-jump at gas–solid interfaces that contributes to the increase of cladding temperature. It is important to maintain the temperature of the cladding below roughly 400 °C to avoid radial hydride formation, which may cause cladding embrittlement during transportation and long-term storage. Direct Simulation Monte Carlo (DSMC) method is an accurate method to predict heat transfer and temperature under rarefied condition. However, it is not convenient for complex geometry like a UNF canister. Computational Fluid Dynamics (CFD) simulations are more convenient to apply but their accuracy for rarefied condition are not well established. This work seeks to validate the use of CFD simulations to model heat transfer through rarefied gas in simple two-dimensional geometry by comparing the results to the more accurate DSMC method. The geometry consists of a circular fuel rod centered inside a square cross-section enclosure filled with rarefied helium. The validated CFD model will be used later to accurately estimate the temperature of an UNF canister subjected to vacuum drying condition.

Simulations of Heat Transfer Within the Fuel Assembly/Backfill Gas Region of Transport Packages

2005 ◽  
Author(s):  
Pablo E. Araya Go´mez ◽  
Miles Greiner
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Generation ◽  
Radiation Transport ◽  
Transport Processes ◽  
Two Dimensional ◽  
Measurable Effect ◽  
Fuel Cladding ◽  
Reactor Assembly ◽  
Horizontal Support

A two-dimensional computational model of a spent 7×7 Boiling Water Reactor assembly in a horizontal support basket was developed using the Fluent computational fluid dynamics package. Heat transfer simulations were performed to predict the maximum cladding temperature for assembly heat generation rates between 100 and 600W, uniform basket wall temperatures of 25 and 400°C, and with helium and nitrogen backfill gases. Different sets of simulations modeled conduction/radiation and natural convection/radiation transport across the gas filled regions to assess the importance of different transport processes. Simulations that included natural convection exhibited measurably lower cladding temperatures than those that did not only for nitrogen, at the lower basket wall temperature, and within an intermediate range of heat generation rates. Outside these conditions and for helium, conduction and radiation transport are sufficiently large so that natural convection has no measurable effect. Finally, the maximum cladding temperature is more sensitive to the assumed value of the fuel cladding emissivities when nitrogen is the backfill gas than when helium is used.

Extent, capacity and possibilities of computational fluid dynamics as a design tool for pump intakes: a review

2018 ◽  
Vol 18 (5) ◽  
pp. 1518-1530 ◽  
Author(s):  
Jie Zhang ◽  
Tien Yee
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Three Dimensional ◽  
Design Tool ◽  
Cfd Modeling ◽  
Cfd Simulations ◽  
Pump Station ◽  
Computational Fluid Dynamics Cfd ◽  
Future Direction ◽  
Computational Resources

Abstract Flow near pump intakes is three-dimensional in nature, and is affected by many factors such as the geometry of the intake bay, uniformity of approach flow, critical submergence, placements and operation combinations of pumps and so on. In the last three decades, advancement of numerical techniques coupled with the increase in computational resources made it possible to conduct computational fluid dynamics (CFD) simulations on pump intakes. This article reviews different aspects involved in CFD modeling of pump station intakes, outlines the challenges faced by current CFD modelers, and provides an attempt to forecast future direction of CFD modeling of pump intakes.

scholarly journals NUMERICAL ANALYSIS OF SWIRL INTENSITY IN TURBULENT SWIRLING PIPE FLOWS

2016 ◽  
Vol 78 (5-10) ◽  
Author(s):  
Bahbibi Rahmatullah ◽  
Khairul Fikri Tamrin ◽  
Nadeem Ahmed Sheikh
Keyword(s):  
Turbulent Flow ◽  
Swirling Flow ◽  
Reynolds Stress Model ◽  
Swirling Flows ◽  
Complex Flow ◽  
Cfd Simulations ◽  
Swirl Intensity ◽  
Computational Fluid Dynamics Cfd ◽  
Computational Resources ◽  
And Control

Swirling flows are often observed in nature such as weather systems, cyclones and tornados. A number of applications use swirling nature of flow for enhanced mixing, heat transport and other transport phenomena. Naturally occurring swirls as well as induced swirls are often usually turbulent in nature. Understanding the flow physics of turbulent swirling flow is important for better understanding and control of processes involving swirling flows. With the increase of computational resources and advancements in turbulent flow modelling, it is now possible to simulate highly complex flow structures. Here turbulent swirling flow induced by guide vanes is studied using Computational Fluid Dynamics (CFD) simulations in a two-dimensional axisymmetric channel. The results for the variation of velocity components are compared with the work of an earlier research. The results are initially compared for the evaluation of best discretisation scheme. It was observed that the second-order and third-order schemes produced similar results. To simulate the turbulent flow two equations (k-ε) model and the five equations Reynolds Stress Model (RSM) are used. The comparison of both models with higher order discretisation schemes shows that the standard k-ε model is incapable of predicting the main features of the flow whilst RSM yields result close to the experimental data.

Maximization of Solar Gains of an Air Collector by Simulations

2013 ◽  
Vol 284-287 ◽  
pp. 483-487 ◽  
Author(s):  
Ondrej Sikula ◽  
Vit Merka ◽  
Jiri Hirs ◽  
Josef Plášek
Keyword(s):  
Heat Transfer ◽  
Solar Energy ◽  
Solar Collector ◽  
Cfd Simulations ◽  
Ansys Fluent ◽  
Operation Conditions ◽  
Flow And Heat Transfer ◽  
Solar Air Collector ◽  
Computational Fluid Dynamics Cfd ◽  
The Impact

The paper deals with numerical simulations of the impact of design, shading, positioning and orientation of a solar air collector an efficiency of exploitation of solar energy. The solar collector is used to preheat of an air, which then is supplied into the building. There are various requirements for solar air collectors. We are focused on maximization of solar energy gain by optimizing geometry, orientation and positioning of a solar air collector. To achieve the desired objective was a combination of two methods used. The firs one is Computational Fluid Dynamics (CFD) simulations of flow and heat transfer by convection, conduction and radiation in software ANSYS Fluent. The second one is the numerical simulation of the annual operations of the collector in the software BSim. The result of this work is an optimal design and operation conditions of the air collector.

Heat Transfer of Springs in Oblique Crossflows

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Daniel B. Biggs ◽  
Christopher B. Churchill ◽  
John A. Shaw
Keyword(s):  
Heat Transfer ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Experimental Program ◽  
Convection Heat ◽  
Computational Tool ◽  
Cfd Simulations ◽  
Nonmonotonic Dependence ◽  
Computational Fluid Dynamics Cfd ◽  
Good Agreement

An experimental program is presented of heated tension springs in an external crossflow over a range of laminar Reynolds numbers, spring stretch ratios, and angles of attack. Extensive measurements of the forced convection heat transfer of helical wire within a wind tunnel reveal an interesting nonmonotonic dependence on angle of attack. Computational fluid dynamics (CFD) simulations, showing good agreement with the experimental data, are used to explore the behavior and gain a better understanding of the observed trends. A dimensionless correlation is developed that well captures the experimental and CFD data and can be used as an efficient computational tool in broader applications.

Thermal Simulations of Thermocouple Tips in Hot Jets

2014 ◽  
Vol 6 (4) ◽  
Author(s):  
Sassan Etemad
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Measurement Accuracy ◽  
Reynolds Numbers ◽  
Cfd Simulations ◽  
Hot Gas ◽  
Gas Jets ◽  
Spherical Bead ◽  
Computational Fluid Dynamics Cfd ◽  
Thermal Simulations

Computational fluid dynamics (CFD) simulations have been carried out for the turbulent convective heat transfer, conduction and radiation for metal thermocouple tips, accommodated in hot gas jets to study the measurement accuracy of the thermocouples. The study covers several thermocouple sizes, jet temperatures, and Reynolds numbers. The spherical bead, representing the tip, becomes so hot that it radiates some heat to the colder surrounding surfaces. This phenomenon is responsible for a gap between the jet temperature and the bead temperature. The mentioned temperature difference is significant. It grows both with bead size and gas temperatures but decreases with the Reynolds number.

Computational Fluid Dynamics Simulation of Flow-Mixing and Heat Transfer in 4 × 4 Rod Bundle With a Twist-Vane Spacer Grid

2019 ◽  
Vol 5 (4) ◽  
Author(s):  
Ganesh Lal Kumawat ◽  
Anuj Kumar Kansal ◽  
Naresh Kumar Maheshwari ◽  
Avaneesh Sharma
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Atomic Energy ◽  
Cfd Simulations ◽  
Spacer Grid ◽  
Fuel Rod ◽  
Rod Bundle ◽  
Flow Mixing ◽  
Computational Fluid Dynamics Cfd

The clearance between fuel rods is maintained by spacer grid or helical wire wrap. Thermal-hydraulic characteristics inside fuel rod bundle are strongly influenced by the spacer grid geometry and the bundle pitch-to-diameter (P/D) ratio. This includes the maximum fuel temperature, critical heat flux, as well as pressure drop through the fuel bundle. An understanding of the detailed structure of flow mixing and heat transfer in a fuel rod bundle geometry is therefore an important aspect of reactor core design, both in terms of the reactor's safe and reliable operation, and with regard to optimum power extraction. In this study, computational fluid dynamics (CFD) simulations are performed to investigate isothermal turbulent flow mixing and heat transfer behavior in 4 × 4 rod bundle with twist-vane spacer grid with P/D ratio of 1.35. This work is carried out under International Atomic Energy Agency (IAEA) co-ordinated research project titled as “Application of Computational Fluid Dynamics (CFD) Codes for Nuclear Power Plant Design.” CFD simulations are performed using open source CFD code OpenFOAM. Numerical results are compared with experimental data from Korea Atomic Energy Research Institute (KAERI) and found to be in good agreement.

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