Prediction of Local and Integral Turbulent Transport Properties for Liquid-Metal Heat Transfer in Equilateral Triangular Rod Arrays

1975 ◽  
Vol 97 (2) ◽  
pp. 238-243 ◽  
Author(s):  
H. Ramm ◽  
K. Johannsen
Keyword(s):  
Heat Transfer ◽  
Liquid Metal ◽  
Transport Properties ◽  
Turbulence Model ◽  
Transfer Problem ◽  
Turbulent Transport ◽  
Three Dimensional ◽  
Theoretical Method ◽  
Eddy Diffusivity ◽  
Thermal Mixing

A theoretical method based on a phenomenological turbulence model has been applied to evaluate turbulent transport properties for liquid-metal heat transfer in bare equilateral triangular rod bundles. Results obtained for local distributions of thermal eddy diffusivity in the various directions are presented in terms of correlations. From a subsequent solution of the three-dimensional heat transfer problem between two characteristic interior subchannels under conditions characteristic for tracer-type mixing experiments, integral thermal mixing coefficients and thermal length scales have been evaluated. Results demonstrate that the basic concept of subchannel analysis treating molecular conduction and turbulent transport independently of each other tends to underestimate intersubchannel transport. The uncertainties which are involved in principal assumptions of the turbulence-model as well as in the available empirical results are discussed in some detail.

A New Model Towards Thermal Mixing and Stratification in Passive Containment

2013 ◽  
Author(s):  
He Zhang ◽  
Fenglei Niu ◽  
Yu Yu ◽  
Peipei Chen
Keyword(s):  
Heat Transfer ◽  
System Analysis ◽  
Cooling System ◽  
Transfer Problem ◽  
Ambient Fluid ◽  
Simulation Code ◽  
Thermal Mixing ◽  
Lumped Parameter ◽  
Passive Safety System ◽  
Transfer Problems

Thermal mixing and stratification often appears in passive containment cooling system (PCCS), which is an important part of passive safety system. So, it is important to accurately predict the temperature and density distributions both for design optimization and accident analysis. However, current major reactor system analysis codes only provide lumped parameter models which can only get very approximate results. The traditional 2-D or 3-D CFD methods require very long simulation time, and it’s not easy to get result. This paper adopts a new simulation code, which can be used to calculate heat transfer problems in large enclosures. The new code simulates the ambient fluid and jets with different models. For the ambient fluid, it uses a one-dimensional model, which is based on the thermal stratification and derived from three conservation equations. While for different jets, the new code contains several jet models to fully simulate the different break types in containment. Now, the new code can only simulate rectangular enclosures, not the cylinder enclosure. So it is meaningful for us to modify the code to simulate the actual containment, then it can be applied to solve the heat transfer problem in PCCS accurately.

Formulation of a Statistical Model of Heat Transfer in Perfused Tissue

1994 ◽  
Vol 116 (4) ◽  
pp. 521-527 ◽  
Author(s):  
J. W. Baish
Keyword(s):  
Heat Transfer ◽  
Heat Transport ◽  
Drug Transport ◽  
Transfer Problem ◽  
Three Dimensional ◽  
Tissue Temperature ◽  
Statistical Interpretation ◽  
Transfer Equations ◽  
Vascular Geometry ◽  
Steady State Heat

A new model of steady-state heat transport in perfused tissue is presented. The key elements of the model are as follows: (1) a physiologically-based algorithm for simulating the geometry of a realistic vascular tree containing all thermally significant vessels in a tissue; (2) a means of solving the conjugate heat transfer problem of convection by the blood coupled to three-dimensional conduction in the extravascular tissue, and (3) a statistical interpretation of the calculated temperature field. This formulation is radically different from the widely used Pennes and Weinbaum-Jiji bio-heat transfer equations that predict a loosely defined local average tissue temperature from a local perfusion rate and a minimal representation of the vascular geometry. Instead, a probability density function for the tissue temperature is predicted, which carries information on the most probable temperature at a point and uncertainty in that temperature due to the proximity of thermally significant blood vessels. A sample implementation illustrates the dependence of the temperature distribution on the flow rate of the blood and the vascular geometry. The results show that the Pennes formulation of the bio-heat transfer equation accurately predicts the mean tissue temperature except when the arteries and veins are in closely spaced pairs. The model is useful for fundamental studies of tissue heat transport, and should extend readily to other forms of tissue transport including oxygen, nutrient, and drug transport.

Comparison of Various RANS Models for Impinging Round Jet Cooling From a Cylinder

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Ketan Atulkumar Ganatra ◽  
Dushyant Singh
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Turbulence Model ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Target Surface ◽  
Point Of View ◽  
Nozzle Diameter ◽  
Round Jet

The numerical analysis for the round jet impingement over a circular cylinder has been carried out. The v2f turbulence model is used for the numerical analysis and compared with the two equation turbulence models from the fluid flow and the heat transfer point of view. Further, the numerical results for the heat transfer with original and modified v2f turbulence model are compared with the experimental results. The nozzle is placed orthogonally to the target surface (heated cylindrical surface). The flow is assumed as the steady, incompressible, three-dimensional and turbulent. The spacing between the nozzle exit and the target surface ranges from 4 to 15 times the nozzle diameter. The Reynolds number based on the nozzle diameter ranges from 23,000 to 38,800. From the heat transfer results, the modified v2f turbulence model is better as compared to the other turbulence models. The modified v2f turbulence model has the least error for the numerical Nusselt number at the stagnation point and wall jet region.

J0550404 Predictions for turbulent thermal mixing and heat transfer in Tjunction channel flow via turbulence model

2015 ◽  
Vol 2015 (0) ◽  
pp. _J0550404--_J0550404-
Author(s):  
Kenji TSUTSUI ◽  
Hirofumi HATTORI ◽  
Tomoya HOURA ◽  
Masato TAGAWA
Keyword(s):  
Heat Transfer ◽  
Channel Flow ◽  
Turbulence Model ◽  
Thermal Mixing

scholarly journals Prediction of Heat and Mass Transfer in a Rotating Ribbed Coolant Passage With a 180 Degree Turn

1998 ◽  
Author(s):  
David L. Rigby
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Boundary Condition ◽  
Turbulence Model ◽  
Heat Mass Transfer ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Wall Boundary Condition ◽  
Wall Boundary

Numerical results are presented for flow in a rotating internal passage with a 180 degree turn and ribbed walls. Reynolds numbers ranging from 5200 to 7900, and Rotation numbers of 0.0 and 0.24 were considered. The straight sections of the channel have a square cross section, with square ribs spaced one hydraulic diameter (D) apart on two opposite sides. The ribs have a height of 0.1D and are not staggered from one side to the other. The full three dimensional Reynolds Averaged Navier-Stokes equations are solved combined with the Wilcox k-ω turbulence model. By solving an additional equation for mass transfer, it is possible to isolate the effect of buoyancy in the presence of rotation. That is, heat transfer induced buoyancy effects can be eliminated as in naphthalene sublimation experiments. Heat transfer, mass transfer and flow field results are presented with favorable agreement with available experimental data. It is shown that numerically predicting the reattachment between ribs is essential to achieving an accurate prediction of heat/mass transfer. For the low Reynolds numbers considered, the standard turbulence model did not produce reattachment between ribs. By modifying the wall boundary condition on ω, the turbulent specific dissipation rate, much better agreement with the flow structure and heat/mass transfer was achieved. It is beyond the scope of the present work to make a general recommendation on the ω wall boundary condition. However, the present results suggest that the ω boundary condition should take into account the proximity to abrupt changes in geometry.

Three-Dimensional Natural Convection in a Vertical Porous Layer With a Hexagonal Honeycomb Core

1992 ◽  
Vol 114 (4) ◽  
pp. 924-927 ◽  
Author(s):  
Y. Asako ◽  
H. Nakamura ◽  
Y. Yamaguchi ◽  
M. Faghri
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boundary Conditions ◽  
Porous Layer ◽  
Numerical Solutions ◽  
Transfer Problem ◽  
Three Dimensional ◽  
Temperature Fields ◽  
Honeycomb Core ◽  
Thermal Boundary Conditions

Numerical solutions are obtained for a three-dimensional natural convection heat transfer problem in a vertical porous layer with a hexagonal honeycomb core. The porous layer is assumed to be long and wide such that the velocity and temperature fields repeat themselves in successive enclosures. The natural convection problem is solved for only one honeycomb enclosure with periodic thermal boundary conditions. The porous layer is assumed to be homogeneous and isotropic and the flow is obtained by using the Darcian model. The numerical methodology is based on an algebraic coordinate transformation technique, which maps the hexagonal cross section onto a rectangle. The transformed governing equations are solved with the SIMPLE algorithm. The calculations are performed for the Darcy–Rayleigh number in the range of 10 to 103 and for eight values of the aspect ratio (H/L = 0.25, 0.333, 0.5, 0.7, 1, 1.4, 2, and 5). Two types of thermal boundary condition for the honeycomb core wall are considered: conduction and adiabatic honeycomb core wall thermal boundary conditions. The results are presented in the form of average and local heat transfer coefficients and are compared with the corresponding values for two and three-dimensional rectangular enclosures.

Condensation on Coherent Turbulent Jets: Part II—A Theoretical Study

1989 ◽  
Vol 111 (4) ◽  
pp. 1075-1082 ◽  
Author(s):  
S. Kim ◽  
A. F. Mills
Keyword(s):  
Ad Hoc ◽  
Numerical Solutions ◽  
Transfer Problem ◽  
Turbulent Transport ◽  
Turbulent Jets ◽  
Eddy Diffusivity ◽  
Liquid Jets ◽  
Laminar Jets ◽  
Boussinesq Hypothesis ◽  
Order Of Magnitude

Condensation on coherent turbulent liquid jets was investigated theoretically. The governing conservation equations were obtained using an order of magnitude analysis, and were solved numerically using a finite difference method. The Boussinesq hypothesis was invoked to model turbulent transport. Various eddy diffusivity models, of varying degrees of complexity, were evaluated through comparison with experimental data, and shortcomings noted. An ad hoc model, which allows for axial decay of turbulence by viscosity, and radial decay by both surface tension and viscosity, is shown to be in reasonable agreement with experiment. Numerical solutions were also obtained for laminar jets, and are essentially exact; these solutions are used to give some insight into the nature of the jet heat transfer problem.

Effects of 3-D Local Unsteadiness on Heat Transfer Prediction in Turbulated Passages

2003 ◽  
Author(s):  
Pamela A. McDowell ◽  
William D. York ◽  
D. Keith Walters ◽  
James H. Leylek
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulence Model ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Successful Outcome ◽  
Small Scale ◽  
Cross Sectional ◽  
Fully Implicit

A newly developed unsteady turbulence model was used to predict heat transfer in a turbulated passage typical of turbine airfoil cooling applications. Comparison of fullyconverged computational solutions to experimental measurements reveal that accurate prediction of heat transfer coefficient requires the effects of local small-scale unsteadiness to be captured. Validation was accomplished through comparison of the time- and area-averaged Nusselt number on the passage wall between adjacent ribs with experimental data from the open literature. The straight channel had a square cross-sectional area with multiple rows of staggered and rounded-edge ribs on opposite walls that were orthogonal to the flow. Simulations were run for Reynolds numbers of 5500, 16500, and 25000. Computational solutions were obtained on a multi-block, multi-topology, unstructured, and adaptive grid, using a pressure-correction based, fully-implicit Navier-Stokes solver. The computational results include two-dimensional (2-D) and three-dimensional (3-D) steady and unsteady simulations with viscous sublayers resolved (y+ ≤ 1) on all the walls in every case. Turbulence closure was obtained using a new turbulence model developed in-house for the unsteady simulations, and a realizable k-ε turbulence model was used for the steady simulations. The results obtained from the unsteady simulations show greatly improved agreement with the experimental data, especially at realistically high Reynolds numbers. The key 3-D physics mechanisms responsible for the successful outcome include: (1) shear layer roll-up over the turbulators; (2) recirculation zones both upstream and downstream of the rib faces; and (3) reattachment regions between each rib pair. Results from the unsteady case are superior to those of the steady because they capture the aforementioned mechanisms, and therefore more accurately predict the heat transfer.

Sign in / Sign up

Export Citation Format

Share Document