The Effect of Support Grid Design on Azimuthal Variation in Heat Transfer Coefficient for Rod Bundles

2005 ◽  
Vol 127 (6) ◽  
pp. 598-605 ◽  
Author(s):  
Mary V. Holloway ◽  
Timothy A. Conover ◽  
Heather L. McClusky ◽  
Donald E. Beasley ◽  
Michael E. Conner
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Nuclear Reactor ◽  
Nucleate Boiling ◽  
Complex Flow ◽  
Film Sensor ◽  
Azimuthal Variation ◽  
Fuel Bundle ◽  
Grid Design ◽  
Support Grid

Support grids are an integral part of nuclear reactor fuel bundle design. Features, such as split-vane pairs, are located on the downstream edge of support grids to enhance heat transfer and delay departure from nucleate boiling in the fuel bundle. The complex flow fields created by these features cause spatially varying heat transfer conditions on the surfaces of the rods. Azimuthal variations in heat transfer for three specific support grid designs, a standard grid, split-vane pair grid, and disc grid, are measured in the present study using a heated, thin film sensor. Normalized values of the azimuthal variations in Nusselt number are presented for the support grid designs at axial locations ranging from 2.2 to 36.7 Dh. Two Reynolds numbers, Re=28,000 and Re=42,000 are tested. The peak-to-peak azimuthal variation in normalized Nusselt number is largest just downstream of the support grids and decreases to a minimum value by the end of the grid span. A comparison of the azimuthal heat transfer characteristics between the support grids indicates distinctive results for each type of support grid design tested. The split-vane pair grid exhibits the largest peak-to-peak variation in azimuthal heat transfer of +30% to −15% just downstream of the grid at 2.2 Dh. The disc grid has the most uniform azimuthal heat transfer distribution with a peak-to-peak value of ±4% for all axial locations tested.

Inverse Determination of the Local Heat Transfer Coefficients for Nucleate Boiling on a Horizontal Cylinder

2003 ◽  
Vol 125 (6) ◽  
pp. 1087-1095 ◽  
Author(s):  
H. Louahlia-Gualous ◽  
P. K. Panday ◽  
E. A. Artioukhine
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pool Boiling ◽  
Gradient Methods ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Nucleate Boiling ◽  
Nucleate Pool Boiling ◽  
Transfer Coefficients ◽  
Iterative Regularization

This article treats the local heat transfer for nucleate pool boiling around the cylinder using the inverse heat conduction analysis. The physical model considers a half section of a cylinder with unknown surface temperature and heat flux density. The iterative regularization and the conjugate gradient methods are used for solving the inverse analysis. The local Nusselt number profiles for nucleate pool boiling are presented and analyzed for different electric heat. The mean Nusselt number estimated by IHCP is closed with the measured values. The results of IHCP are compared to those of Cornewell and Houston (1994), Stephan and Abdelsalam (1980) and Memory et al. (1995). The influence of the error of the measured temperatures and the error in placement of the thermocouples are studied.

Computational analysis of convective heat transfer properties of turbulent slot jet impingement

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Anuj Kumar Shukla ◽  
Anupam Dewan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
High Efficiency ◽  
Stokes Equations ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Complex Flow ◽  
Content Type

Purpose Convective heat transfer features of a turbulent slot jet impingement are comprehensively studied using two different computational approaches, namely, URANS (unsteady Reynolds-averaged Navier–Stokes equations) and SAS (scale-adaptive simulation). Turbulent slot jet impingement heat transfer is used where a considerable heat transfer enhancement is required, and computationally, it is a quite challenging flow configuration. Design/methodology/approach Customized OpenFOAM 4.1, an open-access computational fluid dynamics (CFD) code, is used for SAS (SST-SAS k-ω) and URANS (standard k-ε and SST k-ω) computations. A low-Re version of the standard k-ε model is used, and other models are formulated for good wall-refined calculations. Three turbulence models are formulated in OpenFOAM 4.1 with second-order accurate discretization schemes. Findings It is observed that the profiles of the streamwise turbulence are under-predicted at all the streamwise locations by SST k-ω and SST SAS k-ω models, but follow similar trends as in the reported results. The standard k-ε model shows improvements in the predictions of the streamwise turbulence and mean streamwise velocity profiles in the zone of outer wall jet. Computed profiles of Nusselt number by SST k-ω and SST-SAS k-ω models are nearly identical and match well with the reported experimental results. However, the standard k-ε model does not provide a reasonable profile or quantification of the local Nusselt number. Originality/value Hybrid turbulence model is suitable for efficient CFD computations for the complex flow problems. This paper deals with a detailed comparison of the SAS model with URANS and LES for the first time in the literature. A thorough assessment of the computations is performed against the results reported using experimental and large eddy simulations techniques followed by a detailed discussion on flow physics. The present results are beneficial for scientists working with hybrid turbulence models and in industries working with high-efficiency cooling/heating system computations.

Heat Transfer for Round Air Jets Flowing Along a Concave Surface

2007 ◽  
Author(s):  
Ryuta Ito ◽  
Kenichiro Takeishi ◽  
Yutaka Oda ◽  
Naoki Yoshida
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Numerical Simulations ◽  
Large Scale ◽  
Concave Surface ◽  
Complex Flow ◽  
Free Jet ◽  
Recirculating Flow ◽  
Air Jets ◽  
Complex Flow Structure

Local Nusselt number distributions for a square array of round air jets impinging on a flat surface and a concave surface were measured in high resolution by naphthalene sublimation techniques. Corresponding numerical simulations using a realizable k-ε model were also conducted to investigate the heat transfer characteristics of the multiple jets and to clarify the complex flow structure. The experiments were conducted for Re = 5000, 10000, and 15000 at the non-dimensional nozzle to plate distance of 3.75. The Nusselt number for both flat and concave surfaces increased as Reynolds number increased from 5000 to 10000. Unexpectedly, experimental results showed the tendency of Nu to be saturated for Re = 15000, while showing a monotonic increase in numerical simulations. Most amount of wall jets from a central impinging jet formed large-scale recirculating flows, which surrounded free jet region of each jet, while some other wall jet were entrained by a small vortical structure near the target wall and merged into large-scale recirculating flow of the neighboring jets.

Optimization Study for Uncertainty Reduction of In-Pile CHF Experiments in TREAT

2020 ◽  
Author(s):  
Seokbin Seo ◽  
Nicholas R. Brown ◽  
Robert J. Armstrong ◽  
Charles P. Folsom ◽  
Colby B. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Energy Deposition ◽  
Nuclear Reactor ◽  
National Laboratory ◽  
Nucleate Boiling ◽  
Surface Heat ◽  
Idaho National Laboratory ◽  
Optimization Study ◽  
Reactor Test

Abstract Reactivity-initiated accidents (RIAs) are one of the postulated incidents that can threaten the operational safety of a nuclear reactor. During a RIA, a rapid increase of energy deposition in the fuel can lead to a departure from nucleate boiling (DNB) occurrence which refers to the point where a drastic decrease in heat transfer capabilities occurs and the surface heat flux exceeds the critical heat flux (CHF). Aiming to understand the fundamentals beneath CHF and to predict it, the Transient Reactor Test (TREAT) facility at the Idaho National Laboratory (INL) is a unique facility that will be used to experimentally investigate the transient CHF under in-pile pool boiling condition. As part of a comprehensive effort to utilize TREAT for this project, this study analyzed the expected uncertainties in the experimental data by identifying the key inputs for the uncertainty in the temperature measurements and quantifying their priorities. The sensitivities of key inputs from neutronics modeling, the clad-to-coolant heat transfer, thermophysical properties of the tube, and coolant conditions were quantified using Sobol sensitivity analysis methods, and the significant effect of the occurrence of the CHF on the sensitivity of input was found.

Parametric Design and Optimization for Impingement Jet Heat Transfer Over Dimpled Topologies

2012 ◽  
Author(s):  
Deepchand Singh Negi ◽  
Arvind Pattamatta
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Parametric Design ◽  
Turbulence Models ◽  
Impinging Jet ◽  
Initial Section ◽  
Geometric Parameters ◽  
Complex Flow ◽  
Target Plate

A large number of experimental and theoretical studies investigating heat transfer of impinging jet and jet arrays exist in the literature. However, there are only a few experimental and numerical studies that consider the heat transfer performance of the impinging jet and jet array over complex impinging surface topologies. In spite of these studies, several other factors concerning the dimpled target plate configuration such as dimple height, diameter, pitch spacing between dimples, and their effects on the heat transfer coefficient have not yet been well apprehended. The purpose of the present study is to address some of these aspects through a detailed computational investigation of 3D impinging jet interaction on dimpled target plates. The initial section of the study is focused on the evaluation of different turbulence models in capturing the complex flow features associated with dimpled topology. These models are validated for Nusselt number against previous experimental data in literature. This is followed by a parametric study in which geometric parameters of the dimpled target plate such as dimple diameter, pitch spacing between dimples and dimple height are varied to understand their role on heat transfer enhancement. The final section of the study deals with the optimization of the above geometric parameters based on three factorial design of parametric space. Results from these designed simulations are used to construct a surrogate model based on response surface analysis and the optimized configuration is determined. The objective functions for optimization include maximizing the average Nusselt number, Nuavg, and minimizing the deviation of maximum Nusselt number, Numax-sd. With respect to the reference configuration there is 12% and 8.58 % increase in the average Nusselt number values for the optimized case corresponding to Reynolds number of 3000 and 8200 respectively. Enhancement in terms of Nusselt number is observed with the dimpled target plate over corresponding non dimpled target plates.

Two-Phase Heat Transfer in a Wall-Driven Cubical Heat Sink

2016 ◽  
Author(s):  
Majid Molki
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Sink ◽  
Volume Fraction ◽  
Turbulent Heat Transfer ◽  
Liquid Volume ◽  
Turbulent Heat ◽  
Fluid Temperature ◽  
Complex Flow ◽  
Liquid Volume Fraction

Turbulent heat transfer for flow of water-air mixture driven by moving walls in a cubical heat sink is investigated. One wall is maintained at an elevated temperature, while the vertical walls are at a low temperature. The cubical enclosure functions as a heat sink using water-air mixture with no phase change. Different arrangements for wall motion are considered, which include 1 to 4 moving walls. As the number of moving walls increases, the flow and heat transfer become more complex. In general, the flow reveals complex and multi-scale structures with an unsteady and evolving nature. The larger structure of the flow is resolved using Large Eddy Simulation, while the sub-grid scales are captured by the dynamic k-equation eddy-viscosity model. The focus of this work is on thermal field and heat transfer as affected by the complex flow field generated by multiple moving walls. The results indicate that the Nusselt number for the heat sink varies from 5202.8 to 7356.1, depending on the number of moving walls. Contours of fluid temperature, liquid volume fraction, local and average values of Nusselt number are among the results presented in this paper.

Numerical Analysis of a Multiple Jet Impingement System

2009 ◽  
Author(s):  
G. Arvind Rao ◽  
Myra Kitron-Belinkov ◽  
Yeshayahou Levy
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Turbulent Regime ◽  
Transfer Coefficients ◽  
Complex Flow

Jet impingement is known to provide higher heat transfer coefficients as compared to other conventional modes of single phase heat transfer. Jet impingement has been a subject of research for a long time. Single jets have been studied extensively for their heat transfer and flow characteristics. However, for practical usage, multiple jets (in the form of arrays) have to be used for increasing the total heat transfer over a given area. Most of the research on multiple impinging jets have focused on evaluating heat transfer correlations for such arrays in the turbulent regime (Re >2500). The focus of the present paper is on experimental investigation of a large array of impinging jets in the low Reynolds number regime (<1000) and subsequently numerically modeling the same array by using existing Computational Fluid Dynamics tools in order to study the physical phenomena within such a complex system. Different turbulence models were used for modeling the fluid flow within these impinging jets and it was found that the SST k-ω model is the most suitable. Results obtained from CFD analysis are in reasonable agreement with experimental values. It was observed that CFD simulations over predicted the Nusselt number and pressure drop when compared to the experimentally obtained values. It was also observed that the decrease in Nusselt number along the streamwise direction of the array was not monotonic. This could be due to the complex flow field resulting from interaction between the crossflow and the impinging jets in the wall jet region. It is anticipated that results obtained from the present work will provide greater insight into the flow behavior and the heat transfer mechanism occurring in multiple impinging jets.

Numerical Study of Heat Transfer in a Row of Cylinders by 2D Large Eddy Simulation

2019 ◽  
Author(s):  
Andreas Stengaard Thorstensen ◽  
Andreas Krogh ◽  
Bjørn Christian Dueholm ◽  
Sebastian Bækkel Højte ◽  
Signe Birkebæk Thomasen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Large Eddy Simulation ◽  
Local Time ◽  
Numerical Study ◽  
Heat Transfer Analysis ◽  
Spanwise Direction ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Large Eddy

Abstract Complex flow structures arise as fluids are forced to flow across cylinder rows at moderate Reynolds numbers. In this study a numerical heat transfer analysis of 12 cylinders in an inline configuration is performed using Large Eddy Simulation (LES). The LES is conducted to get a better understanding of changes in the time averaged Nusselt number, 〈Nu〉, and local time averaged Nusselt number, 〈Nuθ〉, for each cylinder in the cylinder row. The simulations are performed at Re = UD/v = 10,000 and Pr = 0.71 with isothermal cylinders and a constant and uniform inflow temperature. The results show that the time averaged Nusselt number increases slightly between the first and second cylinder due to increased turbulent velocity fluctuations. Beyond the second cylinder, the time averaged Nusselt number decreases until it reaches a near constant value after the fifth cylinder. For all 12 cylinders the local time averaged Nusselt number around the surface is highest at the stagnation point. The first cylinder in the row has the same distribution as the reference simulation conducted for a single cylinder. From the second cylinder and onwards a larger part of the overall heat transfer is in the spanwise direction compared to the first- and reference cylinder.

Optimization of the Heat Transfer Rate of Energy Systems of Conductive Bodies Confined to the Center of a Cavity

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Fatma Habbachi ◽  
Fakhreddine S. Oueslati ◽  
Rachid Bennacer ◽  
Afif Elcafsi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Rate ◽  
Temperature Difference ◽  
Transfer Rate ◽  
Numerical Study ◽  
Local Thermal Equilibrium ◽  
Solid Matrix ◽  
Complex Flow ◽  
Flow And Heat Transfer

This paper is a numerical study conducted to investigate the conjugate flow and heat transfer occurring in three-dimensional (3D) natural convection. A cubical enclosure partially filled with porous block (central cubic) and considered in local thermal equilibrium with the fluid. The physical case considered concerns the existence of a horizontal temperature difference across the enclosure, between the left and the right wall, with the other external surfaces being adiabatic. Under these conditions, flow inside the enclosure is generated by the density (temperature) difference across the enclosure and the interaction between the solid porous blocks and the fluid. The Nusselt number on the hot and cold walls is presented to illustrate the overall characteristics of heat transfer consequence of the constrained flow inside the enclosure. The study focuses on the fluid flow and heat transfer evolution versus the dimensionless thickness of the inserted porous layer (0% ≤ η ≤ 100%) and the relative thermal conductivity of the solid matrix to that of the fluid (10−3≤λ̃≤103). The obtained complex flow structure and the corresponding heat transfer (velocity, temperature profiles) are discussed in a steady-state situation. The numerical results are illustrated in terms of isotherms, velocity, streamlines fields, and averaged Nusselt number. Thus, the results of this work can help developing new tools and to optimize the overall heat transfer rate, which is important in many electronic energy components and other energy recovering systems.

Numerical Prediction of Flow and Heat Transfer in a Rectangular Channel With a Built-in Circular Tube

2001 ◽  
Author(s):  
S. Basu ◽  
V. Eswaran ◽  
G. Biswas
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Flow Structure ◽  
Circular Tube ◽  
Rectangular Channel ◽  
Bottom Plate ◽  
Complex Flow ◽  
Flow And Heat Transfer ◽  
Horseshoe Vortices ◽  
Limiting Streamlines

Abstract Numerical investigation of flow and heat transfer in a rectangular duct with a built-in circular tube has been carried out for a Reynolds number of 1000 and blockage ratio of 0.44. Since the heat transfer in the duct is dictated by the flow structure, the present study is directed toward characterization of the flow structure. To this end, the topological theory shows the promise of becoming a powerful tool for the study of the flow structure. Computations show helical vortex tubes in the wake and existence of horseshoe vortices. The w component of velocity is surprisingly large in front and in the near wake of the tube. The limiting streamlines on the tube and the bottom-plate reveal a complex flow field. The separation lines as well as singularity (saddle and nodal) points have been investigated. The iso-Nusselt number contours and the span-averaged Nusselt number in the flow passage shed light on the heat transfer performance in the duct.

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