Analysis of Surface Enhancement by a Porous Substrate

1990 ◽  
Vol 112 (3) ◽  
pp. 700-706 ◽  
Author(s):  
Kambiz Vafai ◽  
Sung-Jin Kim
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Fluid Layer ◽  
Composite Layer ◽  
Darcy Number ◽  
Temperature Fields ◽  
External Boundary ◽  
Porous Substrate ◽  
Frictional Drag ◽  
Practical Applications

Convective flow and heat transfer through a composite porous/fluid system have been studied numerically. The composite medium consists of a fluid layer overlaying a porous substrate, which is attached to the surface of the plate. The numerical simulations focus primarily on flows that have the boundary layer characteristics. However, the boundary layer approximation was not used. A general flow model that accounts for the effects of the impermeable boundary and inertia is used to describe the flow inside the porous region. Several important characteristics of the flow and temperature fields in the composite layer are reported. The dependence of these characteristics on the governing parameters such as the Darcy number, the inertia parameter, the Prandtl number, and the ratio of the conductivity of the porous material to that of the fluid is also documented. The results of this investigation point out a number of interesting practical applications such as in frictional drag reduction, and heat transfer retardation or enhancement of an external boundary.

Analysis of Heat Transfer Regulation and Modification Employing Intermittently Emplaced Porous Cavities

1994 ◽  
Vol 116 (3) ◽  
pp. 604-613 ◽  
Author(s):  
K. Vafai ◽  
P. C. Huang
Keyword(s):  
Heat Transfer ◽  
Skin Friction ◽  
External Surface ◽  
Composite Layer ◽  
Darcy Number ◽  
Interactive Effects ◽  
Temperature Fields ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Inertia Parameter

The present work forms a fundamental investigation on the effects of using intermittently porous cavities for regulating and modifying the flow and temperature fields and therefore changing the skin friction and heat transfer characteristics of an external surface. A general flow model that accounts for the effects of the impermeable boundary and inertial effects is used to describe the flow inside the porous region. Solutions of the problem have been carried out using a finite-difference method through the use of a stream function-vorticity transformation. Various interesting characteristics of the flow and temperature fields in the composite layer are analyzed and discussed in detail. The effects of various governing dimensionless parameters, such as the Darcy number, Reynolds number, Prandtl number, the inertia parameter as well as the effects of pertinent geometric parameters are thoroughly explored. Furthermore, the interactive effects of the embedded porous substrates on skin friction and heat transfer characteristics of an external surface are analyzed. The configuration analyzed in this work provides an innovative approach in altering the frictional and heat transfer characteristics of an external surface.

Development of Convective Heat Transfer Near Suddenly Heated, Vertically Aligned Horizontal Wires

1987 ◽  
Vol 109 (4) ◽  
pp. 912-918 ◽  
Author(s):  
J. R. Parsons ◽  
M. L. Arey
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Fluid Layer ◽  
Convective Motion ◽  
Transient Behavior ◽  
Temperature Fields ◽  
Heat Sources ◽  
Transfer Coefficients ◽  
Vertically Aligned ◽  
The Wire

Experiments have been performed which describe the transient development of natural convective flow from both a single and two vertically aligned horizontal cylindrical heat sources. The temperature of the wire heat sources was monitored with a resistance bridge arrangement while the development of the flow field was observed optically with a Mach–Zehnder interferometer. Results for the single wire show that after an initial regime where the wire temperature follows pure conductive response to a motionless fluid, two types of fluid motion will begin. The first is characterized as a local buoyancy, wherein the heated fluid adjacent to the wire begins to rise. The second is the onset of global convective motion, this being governed by the thermal stability of the fluid layer immediately above the cylinder. The interaction of these two motions is dependent on the heating rate and relative heat capacities of the cylinder and fluid, and governs whether the temperature response will exceed the steady value during the transient (overshoot). The two heat source experiments show that the merging of the two developing temperature fields is hydrodynamically stabilizing and thermally insulating. For small spacing-to-diameter ratios, the development of convective motion is delayed and the heat transfer coefficients degraded by the proximity of another heat source. For larger spacings, the transient behavior approaches that of a single isolated cylinder.

scholarly journals Heat transfer in the seabed boundary layer

2021 ◽  
Vol 928 ◽  
Author(s):  
S. Michele ◽  
R. Stuhlmeier ◽  
A.G.L. Borthwick
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Free Surface ◽  
Surface Waves ◽  
Multiple Scales ◽  
Perturbation Expansion ◽  
Phase Speed ◽  
Maximum Heat ◽  
Practical Applications ◽  
Free Surface Waves

We present a theoretical model of the temperature distribution in the boundary layer region close to the seabed. Using a perturbation expansion, multiple scales and similarity variables, we show how free-surface waves enhance heat transfer between seawater and a seabed with a solid, horizontal, smooth surface. Maximum heat exchange occurs at a fixed frequency depending on ocean depth, and does not increase monotonically with the length and phase speed of propagating free-surface waves. Close agreement is found between predictions by the analytical model and a finite-difference scheme. It is found that free-surface waves can substantially affect the spatial evolution of temperature in the seabed boundary layer. This suggests a need to extend existing models that neglect the effects of a wave field, especially in view of practical applications in engineering and oceanography.

Non-Darcian Boundary Layer Flow and Forced Convective Heat Transfer Over a Flat Plate in a Fluid-Saturated Porous Medium

1990 ◽  
Vol 112 (1) ◽  
pp. 157-162 ◽  
Author(s):  
A. Nakayama ◽  
T. Kokudai ◽  
H. Koyama
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Porous Medium ◽  
Flat Plate ◽  
Similarity Solution ◽  
Temperature Fields ◽  
Solid Boundary ◽  
Local Similarity ◽  
Viscous Term ◽  
Inertia Term

The local similarity solution procedure was successfully adopted to investigate non-Darcian flow and heat transfer through a boundary layer developed over a horizontal flat plate in a highly porous medium. The full boundary layer equations, which consider the effects of convective inertia, solid boundary, and porous inertia in addition to the Darcy flow resistance, were solved using novel transformed variables deduced from a scale analysis. The results from this local similarity solution are found to be in good agreement with those obtained from a finite difference method. The effects of the convective inertia term, boundary viscous term, and porous inertia term on the velocity and temperature fields were examined in detail. Furthermore, useful asymptotic expressions for the local Nusselt number were derived in consideration of possible physical limiting conditions.

scholarly journals Series solutions for the flow in the vicinity of the equator of an MHD boundary-layer over a porous rotating sphere with heat transfer

2014 ◽  
Vol 18 (suppl.2) ◽  
pp. 527-537 ◽  
Author(s):  
Mohammad Rashidi ◽  
Navid Mehr
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Temperature Fields ◽  
Strength Parameter ◽  
Shear Stresses ◽  
Surface Shear ◽  
Rotating Sphere ◽  
Mhd Boundary Layer ◽  
Magnetic Strength ◽  
Blowing Parameter

In this paper, an analytical method (DTM-Pad?) is employed to solve the flow and heat transfer near the equator of an MHD boundary-layer over a porous rotating sphere. This method is used to give solutions of nonlinear ordinary differential equations with boundary conditions at infinity. The velocity components in all directions (meridional, rotational and radial) and temperature fields are derived. The obtained results are verified with the results of numerical solution. A very good agreement can be observed between them. The effect of involved parameters such as magnetic strength parameter, rotation number, suction/blowing parameter and Prandtl number on the all-different types of velocity components, temperature field and surface shear stresses in meridional and rotational directions, infinite radial velocity and rate of heat transfer is checked and discussed.

Flows in Rotating Cylinders With a Porous Lining

2007 ◽  
Author(s):  
M. Subotic ◽  
F. C. Lai
Keyword(s):  
Porous Layer ◽  
Stokes Equations ◽  
Fluid Layer ◽  
Outer Cylinder ◽  
Tangential Velocity ◽  
Darcy Number ◽  
Temperature Fields ◽  
Rotating Cylinders ◽  
Press Fit ◽  
Porous Sleeve

Flow and temperature fields in an annulus between two rotating cylinders have been examined in this study. While the outer cylinder is stationary, the inner cylinder is rotating with a constant angular speed. A homogeneous and isotropic porous layer is press-fit to the inner surface of the outer cylinder. The porous sleeve is saturated with the fluid that fills the annulus. The Brinkman-extended Darcy equations are used to model the flow in the porous layer while Navier-Stokes equations are used for the fluid layer. The conditions applied at the interface between the porous and fluid layers are the continuity of temperature, heat flux, tangential velocity and shear stress. Analytical solutions have been attempted. Through these solutions, the effects of Darcy number, Brinkman number, and porous sleeve thickness on the velocity profile and temperature distribution are studied.

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