Natural Convection in a Horizontal Porous Annulus With a Step Distribution in Permeability

1986 ◽  
Vol 108 (4) ◽  
pp. 889-893 ◽  
Author(s):  
K. Muralidhar ◽  
R. A. Baunchalk ◽  
F. A. Kulacki
Keyword(s):  
Outer Wall ◽  
Constant Heat Flux ◽  
Layer System ◽  
Nusselt Numbers ◽  
Variable Permeability ◽  
Flow And Heat Transfer ◽  
Flux Boundary Conditions ◽  
Uniform Case ◽  
Special Case ◽  
Permeability Problem

A numerical and experimental study of free convective flow and heat transfer in a horizontal annulus containing saturated porous material is reported in the present study. The special case of a step distribution in permeability, resulting in a two-layer system, has been considered. Both isothermal and constant heat flux boundary conditions have been imposed on the inner wall, while the outer wall is kept at a constant temperature. For the case of isothermal boundaries, a simple resistance law gives rise to a model of permeability which collapses the average Nusselt numbers of the variable permeability problem to that of the uniform case. Generally, agreement between experiments and calculation is satisfactory, although under certain circumstances, a systematic divergence of the data is observed. It is deduced in the present work that this is strictly related to non-Darcy effects.

Non-Darcy Natural Convection in a Saturated Horizontal Porous Annulus

1988 ◽  
Vol 110 (1) ◽  
pp. 133-139 ◽  
Author(s):  
K. Muralidhar ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Computational Study ◽  
Viscous Friction ◽  
Fluid Phase ◽  
Outer Wall ◽  
Constant Heat Flux ◽  
Darcy Flow ◽  
Constant Heat ◽  
Nusselt Numbers

A computational study of free convective flow and heat transfer in a saturated porous horizontal annulus is reported. Both isothermal and constant heat flux boundary conditions have been considered on the inner walls while the outer wall is held at a constant temperature. The calculation of the flow field involves consideration of non-Darcy effects, such as inertial and viscous forces, and also the variation of porosity near the walls. While the literature shows that Darcy flow model is inadequate in predicting average Nusselt numbers, the present study examines whether non-Darcy effects, and in particular the presence of the boundary, could play a significant role in explaining this discrepancy. Average Nusselt numbers have been obtained for Rayleigh–Darcy numbers from 20 to 4000 for the case of isothermal boundaries, and 20 to 20,000 for the case of constant heat flux on the inner wall. Radius ratio has been varied from 1.1 to 3. Over this range of parameters, inertia and viscous friction in the fluid phase have been found to produce a small effect on the Darcy flow. The effect of including variable porosity near a boundary is seen to produce channeling near the wall which in turn substantially increases the heat transfer coefficient.

A Numerical Study of Heat Transfer and Flow Structure in Channels With Miniature V Rib-Dimple Hybrid Structure on One Wall

2018 ◽  
Author(s):  
Peng Zhang ◽  
Yu Rao ◽  
Yanlin Li
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Hybrid Structure ◽  
Transfer Enhancement ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Flow Mixing

This paper presents a numerical study on turbulent flow and heat transfer in the channels with a novel hybrid cooling structure with miniature V-shaped ribs and dimples on one wall. The heat transfer characteristics, pressure loss and turbulent flow structures in the channels with the rib-dimples with three different rib heights of 0.6 mm, 1.0 mm and 1.5 mm are obtained for the Reynolds numbers ranging from 18,700 to 60,000 by numerical simulations, which are also compared with counterpart of a pure dimpled and pure V ribbed channel. The results show that the overall Nusselt numbers of the V rib-dimple channel with the rib height of 1.5 mm is up to 70% higher than that of the channels with pure dimples. The numerical simulations show that the arrangement of the miniature V rib upstream each dimple induces complex secondary flow near the wall and generates downwashing vortices, which intensifies the flow mixing and turbulent kinetic energy in the dimple, resulting in significant improvement in heat transfer enhancement and uniformness.

scholarly journals Nusselt number evaluation for combined radiative and convective heat transfer in flow of gaseous products from combustion

2013 ◽  
Vol 17 (4) ◽  
pp. 1093-1106 ◽  
Author(s):  
Soraya Trabelsi ◽  
Wissem Lakhal ◽  
Ezeddine Sediki ◽  
Mahmoud Moussa
Keyword(s):  
Heat Transfer ◽  
Radiation Effects ◽  
Combustion Products ◽  
Radiative Properties ◽  
Inlet Temperature ◽  
Gaseous Products ◽  
Nusselt Numbers ◽  
Coupled Heat Transfer ◽  
Flow And Heat Transfer ◽  
Fluid Properties

Combined convection and radiation in simultaneously developing laminar flow and heat transfer is numerically considered with a discrete-direction method. Coupled heat transfer in absorbing emitting but not scattering gases is presented in some cases of practical situations such as combustion of natural gas, propane and heavy fuel. Numerical calculations are performed to evaluate the thermal radiation effects on heat transfer through combustion products flowing inside circular ducts. The radiative properties of the flowing gases are modeled by using the absorption distribution function (ADF) model. The fluid is a mixture of carbon dioxide, water vapor, and nitrogen. The flow and energy balance equations are solved simultaneously with temperature dependent fluid properties. The bulk mean temperature variations and Nusselt numbers are shown for a uniform inlet temperature. Total, radiative and convective mean Nusselt numbers and their axial evolution for different gas mixtures produced by combustion with oxygen are explored.

LES Analysis of Flow and Heat Transfer in a Rib-Roughened Duct in Clockwise and Anti-Clockwise Rotation Regimes

2017 ◽  
Author(s):  
Alessandro Salvagni ◽  
Domenico Borello
Keyword(s):  
Heat Transfer ◽  
Constant Heat Flux ◽  
Rectangular Duct ◽  
Clockwise Rotation ◽  
Constant Heat ◽  
Flow And Heat Transfer ◽  
Axis Parallel ◽  
Secondary Motion ◽  
Heat Transfer Effects ◽  
Insight Into

We report on an LES study of effects of stabilising/destabilising rotation on heat transfer over a ribbed surface in a rectangular duct at Re = 15000. The duct bottom wall, ribbed by flow-normal, equally-spaced square-sectioned ribs, was uniformly heated (except for the ribs) by a constant heat flux. The duct was rotated with angular velocity corresponding to the rotation number of 0.3, around an axis parallel to the ribs in counter-clockwise (clockwise) direction, thus destabilising (stabilising) the ribbed-wall adjacent flow. These well-resolved LES gave some new insight into the rotation effects on flow and heat transfer providing information that are not easily accessible by experiments. An attempt was made to identify the heat transfer effects due to the rotation-induced modifications of the secondary motion.

scholarly journals Effect of Rayleigh Number on Internal Eccentricity in a Heated Horizontal Elliptical Cylinder to its Coaxial Square Enclosure

2020 ◽  
Vol 25 (3) ◽  
pp. 17-29
Author(s):  
Abdelkrim Bouras ◽  
Djedid Taloub ◽  
Zied Driss
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Outer Cylinder ◽  
Boussinesq Approximation ◽  
Square Enclosure ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Commercial Code ◽  
Volume Method ◽  
Rayleigh Numbers

AbstractThis paper deals with numerical investigation of a natural convective flow in a horizontal annular space between a heated square inner cylinder and a cold elliptical outer cylinder with a Newtonian fluid. Uniform temperatures are imposed along walls of the enclosure. The governing equations of the problem were solved numerically by the commercial code Fluent, based on the finite volume method and the Boussinesq approximation. The effects of Geometry Ratio GR and Rayleigh numbers on fluid flow and heat transfer performance are investigated. The Rayleigh number is varied from 103 to 106. Throughout the study the relevant results are presented in terms of isotherms, and streamlines. From the results, we found that the increase in the Geometry Ratio B leads to an increase of the heat transfer coefficient. The heat transfer rate in the annulus is translated in terms of the average Nusselt numbers along the enclosure’s sides. Tecplot 7 program was used to plot the curves which cleared these relations and isotherms and streamlines which illustrate the behavior of air through the channel and its variation with other parameters. The results for the streamlines, isotherms, local and average Nusselt numbers average Nusselt numbers are compared with previous works and show good agreement.

scholarly journals Simulation of Nanofluid Flow in a Micro-Heat Sink With Corrugated Walls Considering the Effect of Nanoparticle Diameter on Heat Sink Efficiency

2021 ◽  
Vol 9 ◽  
Author(s):  
Yacine Khetib ◽  
Hala M. Abo-Dief ◽  
Abdullah K. Alanazi ◽  
Goshtasp Cheraghian ◽  
S. Mohammad Sajadi ◽  
...  
Keyword(s):  
Heat Sink ◽  
Figure Of Merit ◽  
Reynolds Numbers ◽  
Constant Heat Flux ◽  
Maximum Temperature ◽  
Nanofluid Flow ◽  
Numerical Work ◽  
Volume Percentage ◽  
Flow And Heat Transfer ◽  
20 Nm

In this numerical work, the cooling performance of water–Al2O3 nanofluid (NF) in a novel microchannel heat sink with wavy walls (WMH-S) is investigated. The focus of this article is on the effect of NP diameter on the cooling efficiency of the heat sink. The heat sink has four inlets and four outlets, and it receives a constant heat flux from the bottom. CATIA and CAMSOL software were used to design the model and simulate the NF flow and heat transfer, respectively. The effects of the Reynolds number (Re) and volume percentage of nanoparticles (Fi) on the outcomes are investigated. One of the most significant results of this work was the reduction in the maximum and average temperatures of the H-S by increasing both the Re and Fi. In addition, the lowest Tmax and pumping power belong to the state of low NP diameter and higher Fi. The addition of nanoparticles reduces the heat sink maximum temperature by 3.8 and 2.5% at the Reynolds numbers of 300 and 1800, respectively. Furthermore, the highest figure of merit (FOM) was approximately 1.25, which occurred at Re=1800 and Fi = 5%. Eventually, it was revealed that the best performance of the WMH-S was observed in the case of Re=807.87, volume percentage of 0.0437%, and NP diameter of 20 nm.

scholarly journals Nusselt numbers for Poiseuille flow over isoflux parallel ridges accounting for meniscus curvature

2016 ◽  
Vol 811 ◽  
pp. 315-349 ◽  
Author(s):  
Toby L. Kirk ◽  
Marc Hodes ◽  
Demetrios T. Papageorgiou
Keyword(s):  
Nusselt Number ◽  
Poiseuille Flow ◽  
Numerical Solutions ◽  
Surface Deformation ◽  
Slip Length ◽  
Constant Heat Flux ◽  
Flux Boundary Condition ◽  
Nusselt Numbers ◽  
Dual Series Equations ◽  
Hydrodynamic Slip

We investigate forced convection in a parallel-plate-geometry microchannel with superhydrophobic walls consisting of a periodic array of ridges aligned parallel to the direction of a Poiseuille flow. In the dewetted (Cassie) state, the liquid contacts the channel walls only at the tips of the ridges, where we apply a constant-heat-flux boundary condition. The subsequent hydrodynamic and thermal problems within the liquid are then analysed accounting for curvature of the liquid–gas interface (meniscus) using boundary perturbation, assuming a small deflection from flat. The effects of this surface deformation on both the effective hydrodynamic slip length and the Nusselt number are computed analytically in the form of eigenfunction expansions, reducing the problem to a set of dual series equations for the expansion coefficients which must, in general, be solved numerically. The Nusselt number quantifies the convective heat transfer, the results for which are completely captured in a single figure, presented as a function of channel geometry at each order in the perturbation. Asymptotic solutions for channel heights large compared with the ridge period are compared with numerical solutions of the dual series equations. The asymptotic slip length expressions are shown to consist of only two terms, with all other terms exponentially small. As a result, these expressions are accurate even for heights as low as half the ridge period, and hence are useful for engineering applications.

Heat Transfer in a “Cover-Plate” Preswirl Rotating-Disk System

1999 ◽  
Vol 121 (2) ◽  
pp. 249-256 ◽  
Author(s):  
R. Pilbrow ◽  
H. Karabay ◽  
M. Wilson ◽  
J. M. Owen
Keyword(s):  
Heat Transfer ◽  
Rotating Disk ◽  
Reynolds Numbers ◽  
Turbine Disk ◽  
Cover Plate ◽  
Blade Cooling ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Cooling Air ◽  
Plate System

In most gas turbines, blade-cooling air is supplied from stationary preswirl nozzles that swirl the air in the direction of rotation of the turbine disk. In the “cover-plate” system, the preswirl nozzles are located radially inward of the blade-cooling holes in the disk, and the swirling airflows radially outward in the cavity between the disk and a cover-plate attached to it. In this combined computational and experimental paper, an axisymmetric elliptic solver, incorporating the Launder–Sharma and the Morse low-Reynolds-number k–ε turbulence models, is used to compute the flow and heat transfer. The computed Nusselt numbers for the heated “turbine disk” are compared with measured values obtained from a rotating-disk rig. Comparisons are presented, for a wide range of coolant flow rates, for rotational Reynolds numbers in the range 0.5 X 106 to 1.5 X 106, and for 0.9 < βp < 3.1, where βp is the preswirl ratio (or ratio of the tangential component of velocity of the cooling air at inlet to the system to that of the disk). Agreement between the computed and measured Nusselt numbers is reasonably good, particularly at the larger Reynolds numbers. A simplified numerical simulation is also conducted to show the effect of the swirl ratio and the other flow parameters on the flow and heat transfer in the cover-plate system.

Natural Convection in a Non-Uniformly Heated Vertical Annular Cavity

2017 ◽  
Vol 377 ◽  
pp. 189-199 ◽  
Author(s):  
M. Sankar ◽  
S. Kiran ◽  
G.K. Ramesh ◽  
Oluwole Daniel Makinde
Keyword(s):  
Natural Convection ◽  
Boundary Conditions ◽  
Outer Wall ◽  
Uniform Heating ◽  
Cylindrical Wall ◽  
Thermal Boundary Conditions ◽  
Nusselt Numbers ◽  
Implicit Finite Difference Scheme ◽  
Implicit Finite Difference ◽  
Model Equations

Natural convection from the linearly heated inner and/or outer walls of a vertical annular cavity has been numerically investigated. The bottom wall is uniformly heated and top cylindrical wall is thermally insulated. In this analysis, we considered two different thermal boundary conditions, namely case (I) and case (II) to understand the effect of non-uniform heating of inner and/or outer walls on the convective flow and subsequently the local and global heat transfer rate. For case (I), the inner and outer walls are heated linearly, while the linearly heated inner wall and cooled outer wall is considered in case (II). An implicit finite difference scheme is applied to solve the model equations of the problem. The numerical simulations in terms of streamlines and isotherms, local and global Nusselt numbers are presented to illustrate the effects of Rayleigh number and non-uniform thermal boundary conditions for a fixed Prandtl number of Pr = 0.7.

Sign in / Sign up

Export Citation Format

Share Document