Laminar Natural Convection in an Air-Filled Square Cavity With Partitions on the Top Wall

2009 ◽  
Author(s):  
Wenjiang Wu ◽  
Chan Y. Ching
Keyword(s):  
Boundary Layer ◽  
Natural Convection ◽  
Thermal Effect ◽  
Rear Surface ◽  
Vertical Wall ◽  
Square Cavity ◽  
Recirculating Flow ◽  
Vertical Walls ◽  
Laminar Natural Convection ◽  
Temperature And Flow Fields

The laminar natural convection in an air-filled square cavity with a partition on the top wall was experimentally investigated. Temperature measurements and flow visualizations were performed for cases with heated and cooled vertical walls (corresponding to a global Grashof number GrH of approximately 1.3 × 108) and non-dimensional top wall temperatures θT of 0.56 (insulated) to 2.3. Experiments were performed with an aluminum partition with non-dimensional height HP/H of 0.0625 and 0.125 attached to the top wall at x/H = 0.1, 0.2, 0.4 and 0.6. The blockage effect and/or the thermal effect of the partition resulted in changes to the temperature and flow fields, but were mainly limited to the vicinity of the partition. The partition on the heated top wall resulted in a recirculating flow between the partition and the heated vertical wall. For a given partition height, the structure of this recirculating flow was dependent on the partition location and θT. A thermal boundary layer developed along the rear surface of the partition due to the thermal effect of the partition. The ambient temperature outside the boundary layer and Nu near the corner region were affected by the partition height due to the changes in the recirculating flow and due to the thermal effect on the rear surface of the partition.

The Effect of Partitions on the Laminar Natural Convection in a Square Cavity

2008 ◽  
Author(s):  
Wenjiang Wu ◽  
Chan Y. Ching
Keyword(s):  
Boundary Layer ◽  
Natural Convection ◽  
Secondary Flow ◽  
Rear Surface ◽  
Vertical Wall ◽  
Convection Flow ◽  
Square Cavity ◽  
Flow Circulation ◽  
Laminar Natural Convection ◽  
Layer Flow

The effect of a partition on the laminar natural convection flow in an air-filled square cavity driven by a temperature difference across the vertical walls was investigated experimentally. Two partitions with non-dimensional heights of 0.0625 and 0.125 was attached either to the upper half of the heated vertical wall or the top wall at different locations. The experiments were performed for a global Grashof number of approximately 1.24×108 and non-dimensional top wall temperatures of approximately 0.48 to 2.28. At the higher top wall temperatures, a secondary flow circulation region formed between the partition attached to the top wall and the heated vertical wall of the cavity. This secondary flow circulation region was sensitive to the location and height of the partition, in addition to the top wall temperature of the cavity. The secondary flow circulation region moved the location where the upward boundary layer flow along the heated vertical wall turned over to be further away from the top wall, than in the cavity without the partition. A thermal boundary layer was observed to move along the rear surface of the partition attached to the top wall. In the region close to the top wall, the partitions caused the non-dimensional temperature outside of the boundary layer and the local Nusselt number along the heated vertical wall to be different from that in the cavity without the partition. There were no significant effects of the partition on the flow and heat transfer characteristics in the lower half of the cavity.

The Effect of the Top Wall Temperature on the Laminar Natural Convection in Rectangular Cavities With Different Aspect Ratios

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
Wenjiang Wu ◽  
Chan Y. Ching
Keyword(s):  
Natural Convection ◽  
Aspect Ratio ◽  
Wall Temperature ◽  
Vertical Wall ◽  
Flow Region ◽  
Temperature Profiles ◽  
Aspect Ratios ◽  
Vertical Walls ◽  
C And N ◽  
Laminar Natural Convection

The effect of the top wall temperature on the laminar natural convection in air-filled rectangular cavities driven by a temperature difference across the vertical walls was investigated for three different aspect ratios of 0.5, 1.0, and 2.0. The temperature distributions along the heated vertical wall were measured, and the flow patterns in the cavities were visualized. The experiments were performed for a global Grashof number of approximately 1.8×108 and nondimensional top wall temperatures from 0.52 (insulated) to 1.42. As the top wall was heated, the flow separated from the top wall with an undulating flow region in the corner of the cavity, which resulted in a nonuniformity in the temperature profiles in this region. The location and extent of the undulation in the flow are primarily determined by the top wall temperature and nearly independent of the aspect ratio of the cavity. The local Nusselt number was correlated with the local Rayleigh number for all three cavities in the form of Nu=C⋅Ran, but the values of the constants C and n changed with the aspect ratio.

Natural Convection Patterns in Right-Angled Triangular Cavities with Heated Vertical Sides and Cooled Hypotenuses

2005 ◽  
Vol 127 (10) ◽  
pp. 1181-1186 ◽  
Author(s):  
El Hassan Ridouane ◽  
Antonio Campo ◽  
Jane Y. Chang
Keyword(s):  
Natural Convection ◽  
Vertical Wall ◽  
Ambient Air ◽  
Correlation Equation ◽  
Apex Angle ◽  
Cross Sectional ◽  
Vertical Walls ◽  
Laminar Natural Convection ◽  
Convection Patterns ◽  
Volume Method

The present investigation deals with the numerical computation of laminar natural convection in a gamma of right-angled triangular cavities filled with air. The vertical walls are heated and the inclined walls are cooled while the upper connecting walls are insulated from the ambient air. The defining apex angle α is located at the lower vertex formed between the vertical and inclined walls. This unique kind of cavity may find application in the miniaturization of electronic packaging severely constrained by space and/or weight. The finite volume method is used to perform the computational analysis encompassing a collection of apex angles α compressed in the interval that extends from 5° to 63°. The height-based Rayleigh number, being unaffected by the apex angle α, ranges from a low 103 to a high 106. Numerical results are reported for the velocity field, the temperature field and the mean convective coefficient along the heated vertical wall. Overall, the matching between the numerically predicted temperatures and the experimental measurements of air at different elevations inside a slim cavity is of ordinary quality. For purposes of engineering design, a Nu¯H correlation equation was constructed and also a figure-of-merit ratio between the Nu¯H and the cross sectional area A of the cavity was proposed.

The Effect of the Top Wall Temperature on the Laminar Natural Convection in Rectangular Cavities With Different Aspect Ratios

2007 ◽  
Author(s):  
Wenjiang Wu ◽  
Chan Y. Ching
Keyword(s):  
Natural Convection ◽  
Aspect Ratio ◽  
Wall Temperature ◽  
Vertical Wall ◽  
Flow Region ◽  
Temperature Profiles ◽  
Aspect Ratios ◽  
Vertical Walls ◽  
C And N ◽  
Laminar Natural Convection

The effect of the top wall temperature on the laminar natural convection in air-filled rectangular cavities driven by a temperature difference across the vertical walls was investigated for three different aspect ratios of 0.5, 1.0 and 2.0. The temperature distributions along the heated vertical wall were measured and the flow patterns in the cavities were visualized. The experiments were performed for a global Grashof number of approximately 1.8×108 and non-dimensional top wall temperatures from 0.52 (insulated) to 1.42. As the top wall was heated, the flow separated from the top wall with an undulated flow region in the corner of the cavity, which resulted in a non-uniformity in the temperature profiles in this region. The location and extent of the undulation in the flow is primarily determined by the top wall temperature, and nearly independent of the aspect ratio of the cavity. The local Nusselt number was correlated to the local Rayleigh number for all three cavities in the form of Nu = C · Ran, but the values of the constants C and n changed with the aspect ratio.

Laminar Natural Convection Heat Transfer in a Differentially Heated Square Cavity Due to a Thin Fin on the Hot Wall

2003 ◽  
Vol 125 (4) ◽  
pp. 624-634 ◽  
Author(s):  
Xundan Shi ◽  
J. M. Khodadadi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Computational Study ◽  
Convection Heat Transfer ◽  
Square Cavity ◽  
Left Wall ◽  
Flow Modification ◽  
Laminar Natural Convection ◽  
Rayleigh Numbers ◽  
Blockage Effect

A finite-volume-based computational study of steady laminar natural convection (using Boussinesq approximation) within a differentially heated square cavity due to the presence of a single thin fin is presented. Attachment of highly conductive thin fins with lengths equal to 20, 35 and 50 percent of the side, positioned at 7 locations on the hot left wall were examined for Ra=104,105,106, and 107 and Pr=0.707 (total of 84 cases). Placing a fin on the hot left wall generally alters the clockwise rotating vortex that is established due to buoyancy-induced convection. Two competing mechanisms that are responsible for flow and thermal modifications are identified. One is due to the blockage effect of the fin, whereas the other is due to extra heating of the fluid that is accommodated by the fin. The degree of flow modification due to blockage is enhanced by increasing the length of the fin. Under certain conditions, smaller vortices are formed between the fin and the top insulated wall. Viewing the minimum value of the stream function field as a measure of the strength of flow modification, it is shown that for high Rayleigh numbers the flow field is enhanced regardless of the fin’s length and position. This suggests that the extra heating mechanism outweighs the blockage effect for high Rayleigh numbers. By introducing a fin, the heat transfer capacity on the anchoring wall is always degraded, however heat transfer on the cold wall without the fin can be promoted for high Rayleigh numbers and with the fins placed closer to the insulated walls. A correlation among the mean Nu, Ra, fin’s length and its position is proposed.

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