A Study of Natural Convection in a Rotating Enclosure

1994 ◽  
Vol 116 (1) ◽  
pp. 136-143 ◽  
Author(s):  
F. J. Hamady ◽  
J. R. Lloyd ◽  
K. T. Yang ◽  
H. Q. Yang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Field ◽  
Laser Sheet ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Fluxes ◽  
Cross Sectional ◽  
Rayleigh Numbers

The local and mean natural convection heat transfer characteristics and flow fields were studied experimentally and numerically in an air-filled, differentially heated enclosure with a cross-sectional aspect ratio of one. The enclosure is rotated above its longitudinal horizontal axis. A Mach-Zehnder interferometer was employed to reveal the entire temperature field, which enable the measurement of the local and mean Nusselt numbers at the hot and cold surfaces. Laser sheet flow visualization was employed to observe the flow field. The result showed that the Coriolis and centrifugal buoyancy forces arising from rotation have a remarkable influence on the local heat transfer when compared with the nonrotating results. Local heat fluxes were obtained as a function of Taylor (Ta≤4×105) and Rayleigh numbers (104<Ra≤3×105), at different angular positions of the enclosure. In addition, a series of interferograms, stream function and isotherm plots demonstrated the strong effect of rotation on the flow field and heat transfer. A correlation of Nusselt number as a function of Taylor and Rayleigh numbers is presented.

Can Natural Convection on Smooth Vertical Plates in the Laminar Regime Be Improved by Adding Forward Facing Triangular Roughness Elements?

2019 ◽  
Author(s):  
Jakob Hærvig ◽  
Anna Lyhne Jensen ◽  
Henrik Sørensen
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Aspect Ratio ◽  
Dead Zone ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Fluxes ◽  
Smooth Surfaces ◽  
Roughness Elements ◽  
Triangular Elements

Abstract Vertical smooth surfaces are commonly used for transferring heat by natural convection. Many studies have tried altering smooth surfaces in various ways to increase heat transfer. Many of these studies fail to increase global heat transfer. The problem commonly reported is dead zones appearing just upstream and downstream obstructions that effectively decrease wall temperature gradients normal to the surface. In this study, we simulate how changes geometry of forward facing triangular roughness elements affect local and global heat transfer for isothermal plates. We change the aspect ratio of the triangular elements from L/h = 5 to L/h = 40 at Grashof numbers of GrL = 8.0 · 104 and GrL = 6.4 · 105. In all cases the flow remains laminar. Even when accounting for the increase in surface area, we keep observing a decrease in global heat transfer compared to the smooth vertical plate. However, the results show by carefully selecting the aspect ratio and pitch distance of the triangular elements based on the Grashof number, the dead zone behind the horizontal part can be eliminated thereby significantly increasing local heat transfer. This observation could help to improve cooling of electronics with high localised heat fluxes.

An Experimental Investigation of Natural Convection With Vertical Cylinders in Mercury

1974 ◽  
Vol 96 (4) ◽  
pp. 455-458 ◽  
Author(s):  
L. E. Wiles ◽  
J. R. Welty
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Natural Convection ◽  
Flat Plate ◽  
Convection Heat Transfer ◽  
Vertical Cylinder ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Flat Plates

An experimental investigation of laminar natural convection heat transfer from a uniformly heated vertical cylinder immersed in an effectively infinite pool of mercury is described. A correlation was developed for the local Nusselt number as a function of local modified Grashof number for each cylinder. A single equation incorporating the diameter-to-length ratio was formulated that satisfied the data for all three cylinders. An expression derived by extrapolation of the results to zero curvature (the flat plate condition) was found to agree favorably with others’ work, both analytical and experimental. The influence of curvature upon the heat transfer was found to be small but significant. It was established that the effective thermal resistance through the boundary layer is less for a cylinder of finite curvature than for a flat plate. Consequently, local heat transfer coefficients for cylinders are larger than those for flat plates operating under identical conditions.

Natural Convection Heat Transfer From a Staggered Vertical Plate Array

1993 ◽  
Vol 115 (4) ◽  
pp. 938-945 ◽  
Author(s):  
G. Tanda
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Vertical Plate ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

An experimental study was performed to evaluate the natural convection heat transfer characteristics of an array of four staggered vertical plates. The thermal input at each plate was the same or differed from plate to plate depending on various heating modes. The effects of the interplate spacing and the plate-to-ambient temperature difference were investigated. The experiments were performed in air. Convective interactions among the plates were identified by examining the per-plate heat transfer coefficients and the local heat transfer coefficients along the vertical sides of plates. Local heat transfer results were obtained by means of the schlieren quantitative technique. Comparison of local heat transfer coefficients along the plate assembly with those of a continuous vertical plate (having the same height) showed enhancements up to a factor of two. Comparison of average heat transfer results with those for a parallel plate channel having the same exchanger size showed only little reductions in heat transfer rate, despite a 28 percent reduction in heat transfer area, with enhancements, in terms of specific heat flux, up to 30 percent.

scholarly journals CFD Calculation of Internal Natural Convection in the Annulus Between Horizontal Concentric Cylinders

2003 ◽  
Author(s):  
Stephen W. Webb ◽  
Nicholas D. Francis ◽  
Michael T. Itamura ◽  
Darryl L. James
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Turbulence Models ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Wall Functions ◽  
Thermally Induced ◽  
Concentric Cylinders ◽  
Commercial Code

Thermally-induced natural convection heat transfer in the annulus between horizontal concentric cylinders has been studied using the commercial code Fluent. The boundary layers are meshed all the way to the wall because forced convection wall functions are not appropriate. Various oneand two-equation turbulence models have been considered. Overall and local heat transfer rates are compared with existing experimental data.

An Experimental Study of Natural Convection Heat Transfer in Concentric and Eccentric Horizontal Cylindrical Annuli

1978 ◽  
Vol 100 (4) ◽  
pp. 635-640 ◽  
Author(s):  
T. H. Kuehn ◽  
R. J. Goldstein
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Laminar Convection

An experimental study has been conducted to determine the influence of eccentricity and Rayleigh number on natural convection heat transfer through a fluid bounded by two horizontal isothermal cylinders. Eccentricity of the inner cylinder substantially alters the local heat transfer on both cylinders, but the overall heat transfer coefficients change by less than 10 percent over the range of eccentricities investigated. Heat transfer results using the concentric geometry are given for Rayleigh numbers from 2.2 × 102 to 7.7 × 107 which includes regions of conduction, laminar convection, and partially turbulent convection.

An Approximate Analysis for Convective Heat Transfer on Thermally Nonuniform Surfaces

1990 ◽  
Vol 112 (4) ◽  
pp. 952-958 ◽  
Author(s):  
S. H. Park ◽  
C. L. Tien
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Mixed Convection ◽  
Numerical Solutions ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Similarity Solutions ◽  
Heat Fluxes ◽  
Superposition Method ◽  
Nonuniform Surfaces

This paper presents a new, simple, but powerful technique for nonsimilar natural and assisting mixed convection heat transfer problems in which thermal boundary conditions are specified arbitrarily even with step discontinuities. Temperature and velocity fields for natural convection over thermally nonuniform surfaces are formulated in terms of equivalent Grashof numbers defined by the superposition of surface heat fluxes and velocities obtained from similarity analyses for isoflux or isothermal surfaces. A local heat transfer rate for assisting mixed convection over thermally nonuniform surfaces is approximated using Nusselt numbers for pure forced and pure natural convection over such surfaces, which are obtained by the superposition method. Comparisons with existing similarity solutions, experimental results, and numerical solutions validate the use of this simple superposition method in many practical situations such as cooling configurations in electronic and manufacturing equipment.

Numerical Simulation of Natural Convection in Concentric and Eccentric Horizontal Cylindrical Annuli

1982 ◽  
Vol 104 (4) ◽  
pp. 624-630 ◽  
Author(s):  
C. H. Cho ◽  
K. S. Chang ◽  
K. H. Park
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Circular Cylinders ◽  
Maximum Deviation ◽  
Radial Temperature ◽  
Concentric Cylinders ◽  
Eccentric Annuli

Natural convection heat transfer in concentric and eccentric annuli made of two isothermal horizontal circular cylinders is numerically investigated for Rayleigh numbers less than 5.0 × 104 which is based on the difference of radii. Bipolar coordinates are used for eccentric annuli, and it is found that for very small eccentricity the overall thermal behavior of the annuli exhibits that of the exactly concentric cylinders. The maximum deviation of the local heat-transfer coefficient of the cylinder walls remains, for example, for ε = 0.01, Ri/R0 = 0.3846 and RaL = 1.0 × 104, within a meager 5 percent. The parametric effect on the heat-transfer characteristics is discussed with respect to the diameter ratio for concentric cylinders, and eccentricity and azimuthal angular location of the inner cylinder for eccentric annuli. Output is displayed in terms of streamlines, isothermal contours, radial temperature distribution and equivalent thermal conductivities. Convection patterns are explained in detail.

Entropy generation optimization for MHD natural convection of a nanofluid in porous media-filled enclosure with active parts and viscous dissipation

2017 ◽  
Vol 27 (2) ◽  
pp. 379-399 ◽  
Author(s):  
M.A. Mansour ◽  
Sameh Elsayed Ahmed ◽  
Ali J. Chamkha
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Viscous Dissipation ◽  
Entropy Generation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Convection Flow ◽  
Negative Effects ◽  
Content Type ◽  
Volume Method

Purpose This paper aims to investigate the entropy generation due to magnetohydrodynamic natural convection flow and heat transfer in a porous enclosure filled with Cu-water nanofluid in the presence of viscous dissipation effect. The left and right walls of the cavity are thermally insulated. There are heated and cold parts, and these are placed on the bottom and top wall, respectively, whereas the remaining parts are thermally insulated. Design/methodology/approach The finite volume method is used to solve the dimensionless partial differential equations governing the problem. A comparison with previously published woks is presented and is found to be in an excellent agreement. Findings The minimization of entropy generation and local heat transfer according to different values of the governing parameters are presented in details. It is found that the presence of magnetic field has negative effects on the local entropy generation because of heat transfer and the local total entropy generation. Also, the increase in the heated part length leads to a decrease in the local Nusselt number. Originality/value This problem is original, as it has not been considered previously.

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