Two-Fluid and Single-Fluid Natural Convection Heat Transfer in an Enclosure

1986 ◽  
Vol 108 (4) ◽  
pp. 848-852 ◽  
Author(s):  
E. M. Sparrow ◽  
L. F. A. Azevedo ◽  
A. T. Prata
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Cross Section ◽  
Convection Heat Transfer ◽  
Immiscible Fluids ◽  
Nusselt Numbers ◽  
Baseline Information ◽  
Vertical Walls ◽  
Predicted Values ◽  
Two Fluid

Natural convection experiments were performed for an enclosure of square cross section containing either a single fluid or two immiscible fluids in a layered configuration. The two vertical walls of the cross section were respectively heated and cooled, while the two horizontal walls were adiabatic. The single-fluid experiments, performed with distilled water and with n-hexadecane paraffin (Pr = 5 and 39.2, respectively), yielded Nusselt numbers whose Rayleigh and Prandtl number dependences were perfectly correlated by a single dimensionless group. These single-fluid results were used as baseline information for the development of methods to predict the heat transfer in two-fluid layered systems. To test the utility of the predictive methods, experiments were carried out for water–hexadecane systems in which the position of the interface separating the liquids was varied parametrically. It was found that the experimentally determined, two-layer Nusselt numbers were in excellent agreement with the predicted values. The prediction methods are not limited to the particular fluids employed here, nor do they require additional experimental data for their application.

An Experimental Study of Natural Convection in a Vertical Cavity With Discrete Heat Sources

1988 ◽  
Vol 110 (3) ◽  
pp. 616-624 ◽  
Author(s):  
M. Keyhani ◽  
V. Prasad ◽  
R. Cox
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Visualization ◽  
Vertical Wall ◽  
Convection Heat Transfer ◽  
Cold Wall ◽  
Onset Of Convection ◽  
Flow Cells ◽  
Nusselt Numbers ◽  
Vertical Cavity

Natural convection heat transfer in a tall vertical cavity (aspect ratio = 16.5), with one isothermal vertical cold wall, and eleven alternately unheated and flush-heated sections of equal height on the opposing vertical wall, is experimentally investigated. The flow visualization pictures for the ethylene glycol–filled cavity reveal a flow pattern consisting of primary, secondary, and tertiary flows. The heat transfer data and the flow visualization photographs indicate that the stratification is the primary factor influencing the temperature of the heated sections. This behavior persists for all the runs where the secondary flow cells cover a large vertical extend of the cavity. Based on the analysis of the photographs it is suggested that the turbulent flow should be expected when the local modified Rayleigh number is in the range of 9.3×1011 to 1.9×1012. It is found that discrete flush-mounted heating in the enclosure results in local Nusselt numbers that are nearly the same as those reported for a wide flush-mounted heater on a vertical plate. This is believed to be due to the fact that the present problem is inherently unstable, and the smallest temperature difference between a heated section and the cold wall results in the onset of convection motion.

Numerical Investigation of Natural Convection Heat Transfer from Square Cylinder in a Vented Enclosure

2011 ◽  
Vol 110-116 ◽  
pp. 4451-4464 ◽  
Author(s):  
Ghalib Y. Kahwaji ◽  
Abbas S. Hussien ◽  
Omar M. Ali
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Cross Section ◽  
Convection Heat Transfer ◽  
Grid Generation ◽  
Flow Patterns ◽  
Horizontal Cylinder ◽  
Natural Convection Heat Transfer ◽  
Computational Domain ◽  
Convection Heat

In the present work, the natural convection heat transfer from horizontal cylinder with square cross section situated in a square enclosure, vented symmetrically from the top and the bottom was investigated numerically. The work investigate the effect of the Ra, enclosure width and opening size of the enclosure on the streamlines, isotherms and heat transfer results. The numerical work included the solution of the governing equations in the vorticity-stream function formulation which were transformed into body fitted coordinate system. The transformations are based initially on algebraic grid generation and elliptic grid generation to map the physical domain between the heated horizontal cylinder and the vented enclosure into a computational domain. A hybrid scheme finite volume based finite difference method was used. The study included the following ranges of the studied variables:- 0 < Ra ≤ 6.5× 105 1.5 ≤ W/H ≤ 4 0.375 < O/H ≤ 4 The numerical results were compared with experimental results, which showed good agreement. The effect of cylinder cross section, Ra, enclosure width, and opening size on the Nu, mass flowrate, flow patterns and isotherms were investigated. The results show that the cylinder cross section has a large influence on the results especially the Nu. The Nu is proportional with Ra and inversely proportional with enclosure width and opening size. The flow patterns and isotherms display the flow and temperature behaviors with changing studied variables. The results show that the starting of natural convection heat transfer depended on the cylinder cross-section, enclosure width and opening size in addition with Ra. In addition, the results display that the hydrodynamic and thermal boundary layer thickness decreases with increasing Ra. Nomenclature

Effect of Surface Radiation on Conjugate Natural Convection in a Square Enclosure with a Tube at Different Locations

2013 ◽  
Vol 281 ◽  
pp. 190-196 ◽  
Author(s):  
Jian Sheng Wang ◽  
Yong Xu
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Performance ◽  
Convection Heat Transfer ◽  
Surface Radiation ◽  
Square Enclosure ◽  
Conjugate Natural Convection ◽  
Different Temperatures ◽  
Vertical Walls ◽  
Effect Of Surface

The conjugate natural convection heat transfer with and without the interaction of the surface radiation in a square enclosure was carried out by numerical simulation. The vertical walls of the square enclosure were heated with different temperatures, and the others were adiabatic. A circular tube was inserted into the square enclosure. It was observed that varied location of the tube center can lead to different motion and heat transfer intensities. In addition, surface radiation reduces the convective heat transfer in the square enclosure compared to the pure natural convection case and enhances the overall heat transfer performance.

Experimental Investigation of Natural Convection in Partitioned Enclosures

1982 ◽  
Vol 104 (3) ◽  
pp. 527-532 ◽  
Author(s):  
S. M. Bajorek ◽  
J. R. Lloyd
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Core Region ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
The Core ◽  
Different Temperatures ◽  
Vertical Walls ◽  
Good Agreement

Natural convection heat transfer within a two-dimensional, partitioned enclosure of aspect ratio 1 was investigated experimentally using a Mach-Zehnder interferometer. The vertical walls were maintained isothermal at different temperatures, while the horizontal walls and the partitions were insulated. Local and average heat-transfer coefficients were determined for the air and carbon dioxide filled enclosures both with and without partitions for Grashof numbers between 1.7×105 and 3.0×106. Good agreement was found between the results in the present study for the nonpartitioned enclosure and those previously published. The partitions were found to significantly influence the convective heat transfer. Observations of the interferometric fringes indicated that the core region is unsteady, with the unsteadiness occasionally affecting the flow along the vertical isothermal walls, beginning at Grashof numbers as low as 5×105.

Laminar Natural Convection From Isothermal Vertical Cylinders: Revisting a Classical Subject

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Jerod C. Day ◽  
Matthew K. Zemler ◽  
Matthew J. Traum ◽  
Sandra K. S. Boetcher
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Vertical Cylinder ◽  
Vertical Surface ◽  
Nusselt Numbers ◽  
Recent Interest ◽  
Laminar Natural Convection ◽  
Vertical Cylinders ◽  
Classical Subject

Although an extensively studied classical subject, laminar natural convection heat transfer from the vertical surface of a cylinder has generated some recent interest in the literature. In this investigation, numerical experiments are performed to determine average Nusselt numbers for isothermal vertical cylinders (102<RaL<109,0.1<L/D<10, and Pr = 0.7) situated on an adiabatic surface in a quiescent ambient environment. Average Nusselt numbers for various cases will be presented and compared with commonly used correlations. Using Nusselt numbers for isothermal tops to approximate Nusselt numbers for heated tops will also be examined. Furthermore, the limit for which the heat transfer results for a vertical flat plate may be used as an approximation for the heat transfer from a vertical cylinder will be investigated.

Natural Convection Heat Transfer From Horizontal Rectangular Ducts

2006 ◽  
Vol 129 (9) ◽  
pp. 1195-1202 ◽  
Author(s):  
Mohamed E. Ali
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Aspect Ratios ◽  
Rayleigh Numbers

Experimental investigations have been reported on steady state natural convection from the outer surface of horizontal ducts in air. Five ducts have been used with aspect ratios (Γ=duct height/duct width) of 2, 1, and 0.5. The ducts are heated using internal constant heat flux heating elements. The temperatures along the surface and peripheral directions of the duct wall are measured. Longitudinal (circumference averaged) heat transfer coefficients along the side of each duct are obtained for laminar and transition regimes of natural convection heat transfer. Total overall averaged heat transfer coefficients are also obtained. Longitudinal (circumference averaged) Nusselt numbers are evaluated and correlated using the modified Rayleigh numbers for transition regime using the axial distance as a characteristic length. Furthermore, total overall averaged Nusselt numbers are correlated with the modified Rayleigh numbers, the aspect ratio, and area ratio for the laminar and transition regimes. The longitudinal or total averaged heat transfer coefficients are observed to decrease in the laminar region and to increase in the transition region. Laminar regimes are obtained only at very small heat fluxes, otherwise, transitions are observed.

Sign in / Sign up

Export Citation Format

Share Document