Natural Convection and Conduction in Massive Wall Solar Collectors With Honeycomb and Without Vents

1995 ◽  
Vol 117 (3) ◽  
pp. 173-180 ◽  
Author(s):  
E. K. Lakhal ◽  
E. Bilgen ◽  
P. Vasseur
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Aspect Ratio ◽  
Solar Collector ◽  
Constant Heat Flux ◽  
Honeycomb Structure ◽  
Constant Heat ◽  
Nusselt Numbers ◽  
Fin Thickness ◽  
Steady Heat

Steady heat transfer by natural convection and conduction is numerically studied in passive solar collector systems consisting of a massive wall with honeycomb structure and without vents. The boundary conditions are constant heat flux on the wall and fins, isothermal on the vertical bounding sides, and adiabatic on the horizontal sides. The governing parameters are the Rayleigh number (106 ≤ Ra ≤ 5 × 109), the aspect ratio of the enclosures (0.4 ≤ A = H′/L′ ≤ 1.4), the dimensionless lengths of the fins (0 ≤ B = l′/Ll′ ≤ 1), the aspect ratio of the microcavities (0.05 ≤ C = h′/L′ ≤ 1), the wall thickness (0.008 ≤ w = w′/L′ ≤ 0.033). The fin thickness (e = e′/H′ = 0.06) and the Prandtl number (Pr = 0.72) were constant, and the conductivity ratio was variable (10−4 ≤ kr ≤ 5 × 106). Local and average Nusselt numbers along the long sides are calculated as a function of various parameters. Streamlines and isotherms are produced. Effects of various parameters on the heat transfer are examined and heat transfer correlations are derived.

Heat Transfer in Turbulent Pipe Flow With Optically Thin Radiation

1969 ◽  
Vol 91 (3) ◽  
pp. 330-335 ◽  
Author(s):  
C. S. Landram ◽  
R. Greif ◽  
I. S. Habib
Keyword(s):  
Heat Transfer ◽  
Circular Tube ◽  
Constant Heat Flux ◽  
Turbulent Pipe Flow ◽  
Radiation Problem ◽  
Constant Heat ◽  
Nusselt Numbers ◽  
Fully Developed Turbulent Flow ◽  
Good Agreement

The problem considered is the determination of the heat transfer in fully developed turbulent flow of a radiating optically thin gas in a circular tube. The radiation problem is formulated in terms of the Planck mean and the modified Planck mean coefficients and the temperature profiles and Nusselt numbers have been determined. It is shown that the simple constant shear, constant heat flux formulation yields results that are in very good agreement with more complex calculations.

Natural Convection in Shallow, Horizontal Air Layers Encountered in Electronic Cooling

1995 ◽  
Vol 117 (4) ◽  
pp. 307-316 ◽  
Author(s):  
Elias Papanicolaou ◽  
Sridhar Gopalakrishna
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Constant Heat Flux ◽  
Bottom Surface ◽  
Multiple Sources ◽  
Critical Dimensions ◽  
Convection Regime ◽  
Air Layers

A numerical study of natural convection induced in a horizontal, enclosed air layer due to a discrete, constant heat flux source at the bottom surface is carried out in this paper. The nature of the transition from conduction to a cellular convection regime for this discrete-heating case is characterized. Multiple sources are also considered and the results are compared to those for a single source. The governing equations of continuity, momentum, and energy conservation are formulated for a two-dimensional layer. The important parameters are the overall aspect ratio (length/height of the layer), the ratio of source length to total length, and the Rayleigh number. The effect of varying these parameters is investigated, and heat transfer correlations are derived, for both single and multiple sources, in the form Nus ∝ C (Ra)c>, where Nus is the Nusselt number averaged over each source. The value of C is found to depend strongly on the aspect ratio and the source size. Based on the heat transfer results, the tendency of each geometric configuration to fully attain transition to the convection regime is evaluated. This can provide guidelines for maintaining certain critical dimensions that best exploit natural convection effects, in systems where fan-driven cooling is not available.

Natural Convection Local Heat Transfer on Constant-Heat-Flux Inclined Surfaces

1969 ◽  
Vol 91 (4) ◽  
pp. 511-516 ◽  
Author(s):  
G. C. Vliet
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Plate Theory ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Transfer Data ◽  
Inclined Surfaces

Experimental local heat transfer data are presented for natural convection on constant-heat-flux inclined surfaces using water and air. The data extend to Grz* Pr = 1016, cover angles from the vertical to 30 deg with the horizontal, and include the laminar, transition, and turbulent regimes. In the laminar regime the data correlate well with vertical plate theory when the gravitational component parallel to the surface is used. Transition is strongly affected by inclination, the transition Grz* Pr decreasing from near 1013 for vertical surfaces to approximately 108 for a surface at 30 deg to the horizontal. The turbulent local heat transfer data correlate using the actual gravity rather than the parallel component, and indicates a change in the Grz* Pr exponent from near 0 22 for a vertical surface to approximately 1/4 as the inclination decreases. The turbulent data can be correlated quite well by Nuz = 0.30(Grz* Pr)0.24.

Experimental Study of Heat Transfer in Pulsation Flow in a Rectangular Duct

2012 ◽  
Author(s):  
H. Shokouhmand ◽  
M. Safarifard ◽  
S. M. Emami
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Test Section ◽  
Maximum Velocity ◽  
Constant Heat Flux ◽  
Heat Transfer Characteristics ◽  
Constant Heat ◽  
Nusselt Numbers ◽  
Flow Through ◽  
Minimum Velocity

An experimental study was performed to investigate the heat transfer characteristics of the pulsation flow through a rectangular air duct with aspect ratio of 10. The test section was designed to have a constant heat flux. For pulsating flows, the surface temperatures, the temperature of air at the inlet and at the outlet of the test section, maximum velocity and minimum velocity of air in the test section and the frequencies of pulsation flow were measured and averaged local Nusselt numbers and averaged Nusselt numbers were calculated. The effect of pulsation amplitudes and pulsation frequencies on heat transfer were analyzed.

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