Mixed Convective Heat Transfer Past a Heated Square Porous Cylinder in a Horizontal Channel With Varying Channel Height

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Horng-Wen Wu ◽  
Ren-Hung Wang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Darcy Number ◽  
Convection Flow ◽  
Channel Height ◽  
Porous Cylinder ◽  
Governing Equations ◽  
Height Ratio ◽  
Heated Cylinder ◽  
Laminar Mixed Convection

The laminar mixed convection flow across the porous square cylinder with the heated cylinder bottom at the axis in the channel has been carried out numerically in this paper using a semi-implicit projection finite element method. The governing equations with the Brinkman–Forcheimer-extended Darcy model for the region of square porous cylinder were solved. The parameter studies including Grashof number, Darcy number, and channel-to-cylinder height ratio on heat transfer performance have been explored in detail. The results indicate that the heat transfer is augmented as the Darcy number and channel-to-cylinder height ratio increase. The buoyancy effect on the local Nusselt number is clearer for B/H=0.1 than for B/H=0.3 and B/H=0.5.

Local Heat Transfer Distribution in a Rotating Serpentine Rib-Roughened Flow Passage

1993 ◽  
Vol 115 (3) ◽  
pp. 560-567 ◽  
Author(s):  
N. Zhang ◽  
J. Chiou ◽  
S. Fann ◽  
W.-J. Yang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Performance ◽  
Height Ratio ◽  
Nusselt Numbers ◽  
Rayleigh Numbers ◽  
Rib Roughened

Experiments are performed to determine the local heat transfer performance in a rotating serpentine passage with rib-roughened surfaces. The ribs are placed on the trailing and leading walls in a corresponding posited arrangement with an angle of attack of 90 deg. The rib height-to-hydraulic diameter ratio, e/Dh, is 0.0787 and the rib pitch-to-height ratio, s/e, is 11. The throughflow Reynolds number is varied, typically at 23,000, 47,000, and 70,000 in the passage both at rest and in rotation. In the rotation cases, the rotation number is varied from 0.023 to 0.0594. Results for the rib-roughened serpentine passages are compared with those of smooth ones in the literature. Comparison is also made on results for the rib-roughened passages between the stationary and rotating cases. It is disclosed that a significant enhancement is achieved in the heat transfer in both the stationary and rotating cases resulting from an installation of the ribs. Both the rotation and Rayleigh numbers play important roles in the heat transfer performance on both the trailing and leading walls. Although the Reynolds number strongly influences the Nusselt numbers in the rib-roughened passage of both the stationary and rotating cases, Nuo and Nu, respectively, it has little effect on their ratio Nu/Nuo.

Heat Transfer and Pressure Loss in Rectangular One-Side-Ribbed Channels With Different Aspect Ratios

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Sébastien Kunstmann ◽  
Jens von Wolfersdorf ◽  
Uwe Ruedel
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Gas Turbines ◽  
Pressure Loss ◽  
Rectangular Channel ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Aspect Ratios

An investigation was conducted to assess the thermal performance of W-shaped, 2W-shaped and 4W-shaped ribs in a rectangular channel. The aspect ratios (W/H) were 2:1, 4:1, and 8:1. The ribs were located on one channel wall. The rib height (e) was kept constant with a rib height-to-hydraulic diameter ratio (e/Dh) of 0.02, 0.03, and 0.06. The rib pitch-to-height ratio (P/e) was 10. The Reynolds numbers investigated (Re > 90 000) are typical for combustor liner cooling configurations of gas turbines. Local heat transfer coefficients using the transient thermochromic liquid crystal technique and overall pressure losses were measured. The rib configurations were investigated numerically to visualize the flow pattern in the channel and to support the understanding of the experimental data. The results show that the highest heat transfer enhancement is obtained by rib configurations with a rib section-to-channel height ratio (Wr/H) of 1:1. W-shaped ribs achieve the highest heat transfer enhancement levels in channels with an aspect ratio of 2:1, 2W-shaped ribs in channels with an aspect ratio of 4:1 and 4W-shaped ribs in channels with an aspect ratio of 8:1. Furthermore, the pressure loss increases with increasing complexity of the rib geometry and blockage ratio.

scholarly journals Viscous flow over a stretching (shrinking) and porous cylinder of non-uniform radius

2019 ◽  
Vol 11 (9) ◽  
pp. 168781401987984
Author(s):  
Azhar Ali ◽  
Dil Nawaz Khan Marwat ◽  
Saleem Asghar
Keyword(s):  
Heat Transfer ◽  
Current Model ◽  
Axisymmetric Flow ◽  
Complex Problem ◽  
Skin Friction Coefficient ◽  
Porous Cylinder ◽  
Heated Cylinder ◽  
Flow And Heat Transfer ◽  
Uniform Diameter ◽  
Benchmark Solutions

The classical models of viscous flows and heat transfer are reformulated in this article. The physical problem describes flow and heat transfer over a stretching (shrinking) and porous cylinder of non-uniform radius. The mathematical model is presented in the form of new equations and dimensionless parameters by means of reframing techniques. A porous and heated cylinder of a non-uniform diameter is stretched (shrunk) with variable stretching (shrinking) velocities. The governing equations and their physical geometrical perspectives are summarized into simplest boundary value ordinary differential equations. A set of unseen, generalized, and convenient transformations are used to solve the complex problem. The current formulation accumulates all the previous models of axisymmetric flow and heat transfer toward stretching (shrinking) and porous cylinder presented in the literature and prevails over all such models. The current model can be easily transformed into classical simulations for particular values of the parameters. The problem is solved numerically and the results were compared with the benchmark solutions. Velocity, temperature, skin friction coefficient, and Nusselt number profiles are plotted and analyzed for different values of the parameters. Moreover, coupling effects of all parameters are seen on flow and heat transfer characteristics and new results are explored and discussed.

Flow and Heat Transfer Characteristics in Rectangular Channels With Staggered Transverse Ribs on Two Opposite Walls

2007 ◽  
Vol 129 (12) ◽  
pp. 1732-1736 ◽  
Author(s):  
Rong Fung Huang ◽  
Shyy Woei Chang ◽  
Kun-Hung Chen
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Turbulence Intensity ◽  
Flow Characteristics ◽  
Channel Height ◽  
Primary Concern ◽  
Height Ratio ◽  
Nusselt Numbers ◽  
Characteristic Flow ◽  
Rectangular Channels

The flow characteristics and the heat transfer properties of the rectangular channels with staggered transverse ribs on two opposite walls are experimentally studied. The rib height to channel height ratio ranges from 0.15 to 0.61 (rib height to channel hydraulic diameter ratio from 0.09 to 0.38). The pitch to rib height ratio covers from 2.5 to 26. The aspect ratio of the rectangular channel is 4. The flow characteristics are studied in a water channel, while the heat transfer experiments are performed in a wind tunnel. Particle image velocimetry (PIV) is employed to obtain the quantitative flow field characteristics. Fine-wire thermocouples imbedded near the inner surface of the bottom channel wall are used to measure the temperature distributions of the wall and to calculate the local and average Nusselt numbers. Using the PIV measured streamline patterns, various characteristic flow modes, thru flow, oscillating flow, and cell flow, are identified in different regimes of the domain of the rib height to channel height ratio and pitch to rib height ratio. The vorticity, turbulence intensity, and wall shear stress of the cell flow are found to be particularly larger than those of other characteristic flow modes. The measured local and average Nusselt numbers of the cell flow are also particularly higher than those of other characteristic flow modes. The distinctive flow properties are responsible for the drastic increase of the heat transfer due to the enhancement of the momentum, heat, and mass exchanges within the flow field induced by the large values of the vorticity and turbulence intensity. Although the thru flow mode is conventionally used in the ribbed channel for industrial application, the cell flow could become the choice if the heat transfer rate, instead of the pressure loss, is the primary concern.

scholarly journals Numerical Simulation of Transient Free Convection Flow and Heat Transfer in a Porous Medium

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Rajesh Sharma ◽  
Anuar Ishak
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Differential Equations ◽  
Darcy Number ◽  
Convection Flow ◽  
Force Model ◽  
Moving Plate ◽  
Drag Forces ◽  
Flow And Heat Transfer ◽  
Momentum And Heat Transfer

The coupled momentum and heat transfer in unsteady, incompressible flow along a semi-infinite vertical porous moving plate adjacent to an isotropic porous medium with viscous dissipation effect are investigated. The Darcy-Forchheimer nonlinear drag force model which includes the effects of inertia drag forces is employed. The governing differential equations of the problem are transformed into a system of nondimensional differential equations which are solved numerically by the finite element method (FEM). The non-dimensional velocity and temperature profiles are presented for the influence of Darcy number, Forchheimer number, Grashof number, Eckert number, Prandtl number, plate velocity, and time. The Nusselt number is also evaluated and compared with finite difference method (FDM), which shows excellent agreement.

Combined Mixed Convection and Radiation Heat Transfer in an Obstacle Wall Mounted Lid-driven Cavity

2016 ◽  
Vol 17 (6) ◽  
pp. 277-289 ◽  
Author(s):  
M. Moein Addini ◽  
S. A. Gandjalikhan Nassab
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Gas Flow ◽  
Radiation Heat Transfer ◽  
Simple Algorithm ◽  
Bottom Wall ◽  
Temperature Fields ◽  
Convection Flow ◽  
Driven Cavity ◽  
Laminar Mixed Convection

AbstractThis paper presents a numerical investigation for laminar mixed convection flow of a radiating gas in a lid-driven cavity with a rectangular-shaped obstacle attached on the bottom wall. The vertical walls of the square cavity are assumed to be adiabatic, while other walls of cavity and obstacle are kept at constant temperature. The fluid is treated as a gray, absorbing, emitting and scattering medium. The governing differential equations consisting the continuity, momentum and energy are solved numerically by the computational fluid dynamics techniques to obtain the velocity and temperature fields. Discretized forms of these equations are obtained by the finite volume method and solved using the SIMPLE algorithm. Since the gas is considered as a radiating medium, besides convection and conduction, radiative heat transfer also takes place in the gas flow. For computation of the radiative term in the gas energy equation, the radiative transfer equation is solved numerically by the discrete ordinate method. The streamline and isotherm plots and the distributions of convective, radiative and total Nusselt numbers along the bottom wall of cavity are presented. The effects of Richardson number, obstacle location, radiation–conduction parameter, optical thickness and albedo coefficient on the flow and temperature distributions are carried out. Comparison between the present numerical results with those obtained by other investigators in the cases of conduction–radiation and pure convection systems shows good consistencies.

Heat Transfer and Pressure Loss in Rectangular One-Side-Ribbed Channels With Different Aspect Ratios

2009 ◽  
Author(s):  
Se´bastien Kunstmann ◽  
Jens von Wolfersdorf ◽  
Uwe Ruedel
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Gas Turbines ◽  
Pressure Loss ◽  
Rectangular Channel ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Aspect Ratios

An investigation was conducted to assess the thermal performance of W-shaped, 2W-shaped and 4W-shaped ribs in a rectangular channel. The aspect ratios (W/H) were 2:1, 4:1 and 8:1. The ribs were located on one channel wall. The rib height (e) was kept constant with a rib height-to-hydraulic diameter ratio (e/Dh) of 0.02, 0.03 and 0.06. The rib pitch-to-height ratio (P/e) was 10. The Reynolds numbers investigated (Re>90,000) are typical for combustor liner cooling configurations of gas turbines. Local heat transfer coefficients using the transient thermochromic liquid crystal technique and overall pressure losses were measured. The rib configurations were investigated numerically to visualize the flow pattern in the channel and to support the understanding of the experimental data. The results show that the highest heat transfer enhancement is obtained by rib configurations with a rib section-to-channel height ratio (Wr/H) of 1:1. W-shaped ribs achieve the highest heat transfer enhancement levels in channels with an aspect ratio of 2:1, 2W-shaped ribs in channels with an aspect ratio of 4:1 and 4W-shaped ribs in channels with an aspect ratio of 8:1. Furthermore, the pressure loss increases with increasing complexity of the rib geometry and blockage ratio.

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