Natural Convection in an Inclined Rectangular Cavity With Different Thermal Boundary Conditions at the Top Plate

1988 ◽  
Vol 110 (2) ◽  
pp. 350-357 ◽  
Author(s):  
T. G. Karayiannis ◽  
J. D. Tarasuk
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boundary Conditions ◽  
Forced Convection ◽  
Rectangular Cavity ◽  
Forced Flow ◽  
Cold Plate ◽  
Transfer Rates ◽  
Average Heat ◽  
Thermal Boundary Conditions

Natural convection inside a rectangular cavity with different temperature boundary conditions on the cold top plate was studied using a Mach-Zehnder interferometer for θ = 15, 45, and 60 deg to the horizontal. At θ = 60 deg coupling with external forced convection and non-coupled heat transfer from a cavity with an isothermal top plate was studied. In all experiments the bottom hot plate was isothermal. The Rayleigh number Ra was varied from subcritical to 6×105 and the cavity aspect ratio ARx, from 6.68 to 33.4. The Reynolds number of the external forced flow Redh was constant and approximately equal to 5.8×104. It was found that for Ra ≲ 3×104 the differing thermal boundary conditions at the top plate did not affect the local or average heat transfer rates from the cavity. For Ra ≳ 3×104 coupling at the top plate compared to the non-coupled case resulted not only in a reduction in the variation of the local heat transfer rates at the cold plate, but also in a significant reduction in the variation of the average transfer rates from hot and cold plates of the cavity. Forced convection at the top plate as compared to natural convection resulted only in a small reduction in the heat transfer coefficient at the cold plate. Correlation equations for coupled and noncoupled average heat transfer rates are presented.

Three-Dimensional Natural Convection From Vertical Heated Plates With Adjoining Cool Surfaces

1992 ◽  
Vol 114 (1) ◽  
pp. 115-120 ◽  
Author(s):  
B. W. Webb ◽  
T. L. Bergman
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Control Volume ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Uniform Heat Flux ◽  
Infrared Thermal Imaging ◽  
Transfer Rates ◽  
Thermal Boundary Conditions

Natural convection in an enclosure with a uniform heat flux on two vertical surfaces and constant temperature at the adjoining walls has been investigated both experimentally and theoretically. The thermal boundary conditions and enclosure geometry render the buoyancy-induced flow and heat transfer inherently three dimensional. The experimental measurements include temperature distributions of the isoflux walls obtained using an infrared thermal imaging technique, while the three-dimensional equations governing conservation of mass, momentum, and energy were solved using a control volume-based finite difference scheme. Measurements and predictions are in good agreement and the model predictions reveal strongly three-dimensional flow in the enclosure, as well as high local heat transfer rates at the edges of the isoflux wall. Predicted average heat transfer rates were correlated over a range of the relevant dimensionless parameters.

Effects of Thermal Boundary Conditions on Entropy Generation During Natural Convection in a Differentially Heated Square Cavity

2010 ◽  
Author(s):  
Ram Satish Kaluri ◽  
Tanmay Basak ◽  
A. R. Balakrishnan
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boundary Conditions ◽  
Entropy Generation ◽  
Bottom Wall ◽  
Convection Flow ◽  
Uniform Heating ◽  
Square Cavity ◽  
Fluid Friction ◽  
Thermal Boundary Conditions

Natural convection is a widely occurring phenomena which has important applications in material processing, energy storage devices, electronic cooling, building ventilation etc. The concept of ‘entropy generation minimization’, which is a thermodynamic approach for optimization, may be very useful in designing efficient thermal systems. In the current study, entropy generation in steady laminar natural convection flow in a square cavity is studied with following isothermal boundary conditions: (1) Bottom wall is uniformly heated (2) Bottom wall is sinusoidally heated. The side walls are maintained cold and the top wall is maintained adiabatic. The thermal boundary condition in non-uniform heating case (case 2) is such that the dimensionless average temperature of the bottom wall is equal to that of uniform heating case (case 1). The prime objective of this work is to investigate the influence of uniform and non-uniform heating on entropy generation. The governing mass, momentum and energy equations are solved using Galerkin finite element method. Streamlines, isotherms, contour maps of entropy generation due to heat transfer and fluid friction are studied for Pr = 0.01 (molten metals) and 7 (water) in range of Ra = 103–105. Detailed analysis on the effect of uniform and non-uniform thermal boundary conditions on entropy generation due to heat transfer and fluid friction has been presented. Also, the average Bejan’s number which indicates the relative dominance of entropy generation due to heat transfer or fluid friction and the total entropy generation are studied for each case.

Three-Dimensional Natural Convection in a Vertical Porous Layer With a Hexagonal Honeycomb Core

1992 ◽  
Vol 114 (4) ◽  
pp. 924-927 ◽  
Author(s):  
Y. Asako ◽  
H. Nakamura ◽  
Y. Yamaguchi ◽  
M. Faghri
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boundary Conditions ◽  
Porous Layer ◽  
Numerical Solutions ◽  
Transfer Problem ◽  
Three Dimensional ◽  
Temperature Fields ◽  
Honeycomb Core ◽  
Thermal Boundary Conditions

Numerical solutions are obtained for a three-dimensional natural convection heat transfer problem in a vertical porous layer with a hexagonal honeycomb core. The porous layer is assumed to be long and wide such that the velocity and temperature fields repeat themselves in successive enclosures. The natural convection problem is solved for only one honeycomb enclosure with periodic thermal boundary conditions. The porous layer is assumed to be homogeneous and isotropic and the flow is obtained by using the Darcian model. The numerical methodology is based on an algebraic coordinate transformation technique, which maps the hexagonal cross section onto a rectangle. The transformed governing equations are solved with the SIMPLE algorithm. The calculations are performed for the Darcy–Rayleigh number in the range of 10 to 103 and for eight values of the aspect ratio (H/L = 0.25, 0.333, 0.5, 0.7, 1, 1.4, 2, and 5). Two types of thermal boundary condition for the honeycomb core wall are considered: conduction and adiabatic honeycomb core wall thermal boundary conditions. The results are presented in the form of average and local heat transfer coefficients and are compared with the corresponding values for two and three-dimensional rectangular enclosures.

Effect of Thermal Boundary Conditions on Natural Convection in Vertical and Inclined Air Layers

1982 ◽  
Vol 104 (3) ◽  
pp. 515-520 ◽  
Author(s):  
S. M. ElSherbiny ◽  
K. G. T. Hollands ◽  
G. D. Raithby
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boundary Conditions ◽  
Thermal Conditions ◽  
Wall Region ◽  
Flat Plates ◽  
Total Heat Transfer ◽  
Thermal Boundary Conditions ◽  
Air Layers ◽  
The Impact

Measurements of the heat transfer by natural convection across vertical and inclined air layers are reported. The air layer is bounded by two parallel isothermal flat plates and around the edges by a low thermal conductivity wall of thickness B. A critical wall thickness Bc was determined by solving the two-dimensional conduction equation in the bounding wall region: for B>Bc the convective heat transfer should be insensitive to B. Measurements are reported for air layers with B>Bc and an aspect ratio of 5. They cover a range in Rayleigh number from 103 to 108, and a range in orientation from horizontal to vertical. The effect of the emissivity of the bounding wall on the heat transfer across the air layer was evaluated from measurements obtained respectively with a low and a high value of the wall emissivity. The paper proposes terminology required to define the thermal conditions, and discusses the impact of these boundary conditions on the total heat transfer.

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