scholarly journals Free and forced convection around line sources of heat and heated cylinders in porous media

2001 ◽  
Vol 427 ◽  
pp. 389-409 ◽  
Author(s):  
VADIM N. KURDYUMOV ◽  
AMABLE LIÑÁN
Keyword(s):  
Porous Media ◽  
Free Convection ◽  
Numerical Solution ◽  
Forced Convection ◽  
Line Source ◽  
Free Stream ◽  
Outer Region ◽  
Circular Cylinders ◽  
Stream Velocity ◽  
Wide Range

An analysis is presented for the steady, two-dimensional, free convection around line sources of heat and heated cylinders in unbounded saturated porous media. It is extended to account also for the effects of forced convection. The study is based on the Boussinesq equations, with the velocities calculated using Darcy's law.The analysis begins with the non-dimensional formulation and numerical solution of the problem of pure free convection around a line source of heat. When this analysis is extended to include the effects of forced convection, two parameters appear in the non-dimensional formulation: the non-dimensional value, V∞, of the free-stream velocity and its angle γ of inclination with respect to the vertical. We first describe the asymptotic form of the solution for large and small values of the distance to the source. The far-field description, which is also applicable to the flow around heated cylinders, is needed to facilitate the numerical solution of the problem. It includes a thermal wake, aligned with the free stream, and an outer irrotational flow with a sink and a vortex at the line source. The temperature distribution near the source involves a constant A0(V∞, γ), to be calculated with the numerical solution of the complete problem, which is used in the evaluation of the heat transfer from heated cylinders when the Rayleigh and Péclet numbers are small compared with unity. In this case we find an inner region where heat conduction is dominant, and an outer region where the cylinder appears as a line source of heat. The asymptotic analysis is complemented with the numerical solution of the general problem for circular cylinders with a wide range of Rayleigh numbers and some representative values of V∞ and γ. We give correlations for the Nusselt number in the limiting cases of pure free convection and pure forced convection.

scholarly journals Laminar free convection induced by a line heat source, and heat transfer from wires at small Grashof numbers

1998 ◽  
Vol 362 ◽  
pp. 199-227 ◽  
Author(s):  
AMABLE LIÑÁN ◽  
VADIM N. KURDYUMOV
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Line Source ◽  
Outer Region ◽  
Analytical Description ◽  
Temperature Fields ◽  
Thermal Plume ◽  
Line Heat Source ◽  
First Approximation ◽  
Wide Range

The buoyancy-induced laminar flow and temperature fields associated with a line source of heat in an unbounded environment are described by numerically solving the non-dimensional Boussinesq equations with the appropriate boundary conditions. The solution is given for values of the Prandtl number, the single parameter, ranging from zero to infinity. The far-field form of the solution is well known, including a self-similar thermal plume above the source. The analytical description close to the source involves constants that must be evaluated with the numerical solution.These constants are used when calculating the free convection heat transfer from wires (or cylinders of non-circular shape) at small Grashof numbers. We find two regions in the flow field: an inner region, scaled with the radius of the wire, where the effects of convection can be neglected in first approximation, and an outer region where, also in first approximation, the flow and temperature fields are those due to a line source of heat. The cases of large and small Prandtl numbers are considered separately. There is good agreement between the Nusselt numbers given by the asymptotic analysis and by the numerical analysis, which we carry out for a wide range of Grashof numbers, extending to very small values the range of existing numerical results; there is also agreement with the existing correlations of the experimental results. A correlation expression is proposed for the relation between the Nusselt and Grashof numbers, based on the asymptotic forms of the relation for small and large Grashof numbers.

scholarly journals Numerical study of forced convection heat transfer over three cylinders in staggered arrangement immersed in porous media

2018 ◽  
Vol 22 (1 Part B) ◽  
pp. 467-475 ◽  
Author(s):  
Habib-Olah Sayehvand ◽  
Sakene Yari ◽  
Parsa Basiri
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Forced Convection ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Circular Cylinders ◽  
Convection Heat ◽  
State Equations ◽  
Forced Convection Heat Transfer ◽  
Staggered Arrangement

Staggered arrangement is one of the common configurations in heat exchangers that make better mixing of flow and heat transfer augmentation than other arrangements. In this paper forced convection heat transfer over three isothermal circular cylinders in staggered configuration in isotropic packed bed was investigated. In this work laminar 2-D incompressible steady-state equations of momentum and energy were solved numerically by finite volume method. Simulation was done in three Reynolds numbers of 80, 120, and 200. The results indicate that, using porous medium the Nusselt number enhanced considerably for any of cylinders and it presents thin temperature contours for them. Also is shown that by increasing Reynolds number, the heat transfer increased in both channel but the growth rate of it in porous media is larger. In addition, results of simulation in porous channel show that with increasing Peclet number, heat transfer increased logarithmically.

scholarly journals A Review on the Control Parameters of Natural Convection in Different Shaped Cavities with and without Nanofluid

Processes ◽  
2020 ◽  
Vol 8 (9) ◽  
pp. 1011 ◽  
Author(s):  
Sara Rostami ◽  
Saeed Aghakhani ◽  
Ahmad Hajatzadeh Pordanjani ◽  
Masoud Afrand ◽  
Goshtasp Cheraghian ◽  
...  
Keyword(s):  
Porous Media ◽  
Natural Convection ◽  
Free Convection ◽  
Forced Convection ◽  
Opposite Effect ◽  
Fluid Velocity ◽  
Experimental Studies ◽  
Effective Parameters ◽  
Magnetic Forces ◽  
Numerical Studies

Natural convection in cavities is an interesting subject for many researchers. Especially, in recent years, the number of articles written in this regard has grown enormously. This work provides a review of recent natural convection studies. At first, experimental studies were reviewed and, then, numerical studies were examined. Then, the articles were classified based on effective parameters. In each section, numerical studies were examined the parameters added to the cavity such as magnetic forces, fin, porous media and cavity angles. Moreover, studies on non-rectangular cavities were investigated. Free convection in enclosures depends more on the fluid velocity relative to the forced convection, leading to the opposite effect of some parameters that should essentially enhance rate of heat transfer. Nanoparticle addition, magnetic fields, fins, and porous media may increase forced convection. However, they can reduce free convection due to the reduction in fluid velocity. Thus, these parameters need more precision and sometimes need the optimization of effective parameters.

scholarly journals Concept Tests for a New Wire Flying Vehicle Designed to Achieve High Horizontal Resolution Profiling in Deep Water

2011 ◽  
Vol 28 (12) ◽  
pp. 1657-1671 ◽  
Author(s):  
Chris Roman ◽  
Dave Hebert
Keyword(s):  
Water Column ◽  
Deep Water ◽  
Free Stream ◽  
Horizontal Resolution ◽  
Vehicle Body ◽  
Scale Model ◽  
Stream Velocity ◽  
Wide Range ◽  
High Horizontal Resolution ◽  
Ship Speed

Abstract Efficiently profiling the water column to achieve both high vertical and horizontal resolution from a moving vessel in deep water is difficult. Current solutions, such as CTD tow-yos, moving vessel profilers, and undulating tow bodies, are limited by ship speed or water depth. As a consequence, it is difficult to obtain oceanographic sections with sufficient resolution to identify many relevant scales over the deeper sections of the water column. This paper presents a new concept for a profiling vehicle that slides up and down a towed wire in a controlled manner using the lift created by wing foils. The wings provide a novel low-power method of propulsion along the cable by using the free stream velocity of the wire moving through the water in similar fashion to a sailboat sailing up wind. Scale model tests show a wide range of achievable profiling glide slopes for tow cable angles between vertical and 45°, and effective isolation of cable strum vibration from the towed vehicle body. The concept is not depth limited and will offer two-dimensional resolution that meets or exceeds current undulating tow bodies over the full water column. Additionally, this system could be used simultaneously with many other deep towed instrument packages to produce complementary datasets.

An Empirical Formula for Stagnation Point Velocity Gradient for Spheres and Circular Cylinders in Hypersonic Flow

1965 ◽  
Vol 69 (654) ◽  
pp. 407-408 ◽  
Author(s):  
D. R. Topham
Keyword(s):  
Stagnation Point ◽  
Velocity Gradient ◽  
Stream Flow ◽  
Free Stream ◽  
Circular Cylinders ◽  
Stream Velocity ◽  
Flow Properties ◽  
Transfer Rates ◽  
Point Velocity ◽  
Image Position

When stagnation heat transfer rates are expressed in terms of free stream flow properties, the following combination of terms is found to occur: —where ps pressure at the stagnation pointp∞free stream pressureU∞free stream velocityDnose diameterßstagnation point velocity gradient.

scholarly journals Turbulence Intensity, Length Scale, and Heat Transfer Around Stagnation Line of Cylinder and Model Blade

1999 ◽  
Author(s):  
V. P. Maslov ◽  
B. I. Mineev ◽  
K. N. Pichkov ◽  
A. N. Secundov ◽  
A. N. Vorobiev ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Turbulence Models ◽  
Leading Edge ◽  
Circular Cylinders ◽  
Length Scale ◽  
Stagnation Line ◽  
Free Stream Turbulence ◽  
Wide Range

A hot-wire technique was used to measure turbulence characteristics in the vicinity of the stagnation line of circular cylinders and a turbine blade model (a chord length of 1 metre). Heat transfer intensity at the stagnation line of the cylinders was also measured by on-surface probes. The experiments were carried out in a wide range of the Reynolds number based on the blade leading edge/cylinder diameter, D (Re = 2.103–2.106) and integral length scale of free-stream turbulence, Le (Le = 0.1–10D) at two values of free stream turbulence intensity, Tu (Tu = 0.02 and 0.10). Along with the experimental data results of the 2D RANS computations are presented of the flow and heat transfer at the circular cylinder with the use of two turbulence models: a two-equation, k-ω SST, model of Menter, and a new two-equation, ν1-L, model developed in the course of the present study.

Approximate Solution to a Class of Transient Forced Convection Problems

1977 ◽  
Vol 99 (4) ◽  
pp. 567-574 ◽  
Author(s):  
J. Sucec
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Surface Temperature ◽  
Forced Convection ◽  
Free Stream ◽  
The Body ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Response Curves ◽  
Constant Property

Approximate solutions using integral methods and the method of characteristics are found for the case of laminar, low speed, constant property, two-dimensional planar boundary layer type flow over a body which is initially at the constant temperature of the fluid passing over it and then, suddenly, has its surface temperature changed to a new constant value or has a constant heat flux imposed at the surface. The free stream velocity is variable with position along the body and the entire velocity field is assumed to be in the steady state. Response curves for surface heat flux or of surface temperature as a function of position and time are presented for power law variations of free stream velocity (the “wedge” type flows) and also for one particular nonsimilar (nonwedge) case. The relative ease with which the nonsimilar cases can be handled is thought to make the approach, advanced herein, a useful tool for the engineer to attack other nonsimilar cases. It was also found that the use of an “equivalent” wedge variable gives reasonably satisfactory results for the nonsimilar case chosen. Hence the application of the equivalent wedge methods is valid for transient forced convection problems just as it is, as is well known, for steady-state forced convection.

An Experimental Study on Heat Transfer Around Two Side-by-Side Closely Arranged Circular Cylinders

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Takayuki Tsutsui
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Free Stream ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Circular Cylinders ◽  
Stream Velocity ◽  
Heat Transfer Characteristics ◽  
Minimum Drag ◽  
Coefficient Condition

The present paper describes heat transfer around two side-by-side closely arranged circular cylinders. The flows around two circular cylinders in a side-by-side arrangement can be classified into three flow patterns according to the gap between the two cylinders. The heat transfer characteristics of the cylinders in each flow regime were experimentally investigated. The diameter of the circular cylinders was 40 mm and the gap between the two cylinders varied from 4 mm to 40 mm. The free stream velocity ranged from 4 m/s to 24 m/s, resulting in Reynolds nos. ranging from 1.1×104 to 6.2×104. The local heat transfer coefficient of both cylinders was measured. The overall Nusselt no. of the two cylinders was found to be minimum at G/D(=gap/diameter)=0.4, which is the minimum drag coefficient condition of the two cylinders, too.

The turbulent wake of two side-by-side circular cylinders

2002 ◽  
Vol 458 ◽  
pp. 303-332 ◽  
Author(s):  
Y. ZHOU ◽  
H. J. ZHANG ◽  
M. W. YIU
Keyword(s):  
Free Stream ◽  
Vortex Structures ◽  
Heat Fluxes ◽  
Temperature Fields ◽  
Circular Cylinders ◽  
Coherent Motion ◽  
Stream Velocity ◽  
Single Vortex ◽  
Significant Difference ◽  
Vorticity Flux

This work is an experimental study of the turbulent vortex structures, and heat and momentum transport in the wake of two side-by-side circular cylinders. The spacing T between the cylinder axes was varied from 1.5d to 3d (d is the cylinder diameter). Both cylinders were slightly heated. A movable three-wire probe measured the velocity and temperature fluctuations, and an X-wire provided a phase reference. Measurements were conducted at x/d = 10, 20 and 40 at a Reynolds number of 5800 (based on d and the free-stream velocity U∞). At T/d = 1.5, the phase-averaged velocity and temperature fields display a single vortex street. The two rows of vortices exhibit a significant difference in the maximum vorticity, size and lateral distance from the flow centreline. As T/d is increased to 3.0, the flow is totally different. Two antiphase streets occur initially. They are less stable, with vortices weakening faster, than the street at T/d = 1.5. By x/d = 40, one street only is identifiable. Effective vorticity flux density indicates that, while the outer vortex nearer to the free stream interacts largely with the adjacent oppositely signed inner vortices located near the flow centreline, the inner vortex interacts with the cross-stream inner vortices as well as with adjacent outer vortices. As a result, vorticity associated with the inner vortex is annihilated quicker than that associated with the outer vortex, leading to the early disappearance of inner vortices and formation of a single street. The contribution of the coherent motion of various Reynolds-averaged quantities such as the momentum and heat fluxes has also been quantified and discussed in conjunction with the vortex structures of the flow and temperature fields.

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