An Experimental Investigation of Natural Convection From an Isothermal Horizontal Plate

1989 ◽  
Vol 111 (4) ◽  
pp. 904-908 ◽  
Author(s):  
A. M. Clausing ◽  
J. J. Berton
Keyword(s):  
Experimental Investigation ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Richardson Number ◽  
Horizontal Plate ◽  
Convection Regime ◽  
Variable Property ◽  
Nusselt Number Correlation ◽  
Gas Medium ◽  
Large Rayleigh Number

An investigation of natural convection from a heated, upward-facing, square, horizontal plate to a surrounding gas medium is described in this paper. The results of the experimental investigation provide an improved correlation for the natural convection regime by accounting for variable property effects and extend the applicable Rayleigh number (Ra) range of the correlation over previous research. The large Rayleigh number regime is emphasized. The value of the Richardson number (Ri) at which combined convection influences become important is also determined. The ratio of the plate wall temperature Tw to the ambient temperature T∞ is incorporated into the Nusselt number correlation in order to account for variable property influences. A cryogenic heat transfer tunnel, with test section temperatures that are varied between 80 K and 310 K, is used to help deduce the influences of the relevant parameters. The ranges of the dimensionless parameters investigated are 2 × 108 < Ra < 2 × 1011 and 1 < Tw/T∞ < 3.1.

Natural Convection From Isothermal Cubical Cavities With a Variety of Side-Facing Apertures

1987 ◽  
Vol 109 (2) ◽  
pp. 407-412 ◽  
Author(s):  
A. M. Clausing ◽  
J. M. Waldvogel ◽  
L. D. Lister
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Radiative Heat ◽  
Side Wall ◽  
Large Temperature ◽  
Key Variables ◽  
Cryogenic Wind Tunnel ◽  
Large Rayleigh Number

An experimental investigation of heat transfer by natural convection from a smooth, isothermal cubic cavity with a variety of side-facing apertures is described in this paper. The study was motivated by the desire to predict the convective loss from large solar thermal-electric receivers and to understand the mechanisms which control this loss. Hence, emphasis is placed on the large Rayleigh number, Ra, regime with large ratios of the cavity wall temperature Tw to the ambient temperature T∞. A cryogenic wind tunnel with test section temperatures which are varied between 80 K and 310 K is used to facilitate deduction of the influences of the relevant parameters and to obtain large temperature ratios without masking the results by radiative heat transfer. A 0.4-m cubic cavity, which is mounted in the side wall of this tunnel, is used. The area of the aperture Aa and its location are key variables in this study. The data which are presented cover the ranges: 1 < Tw/T∞ < 3, L2/18 ≤ Aa ≤ L2, and 3 × 107 < Ra < 3 × 1010.

Natural Convection in Horizontal Porous Layers: Effects of Darcy and Prandtl Numbers

1989 ◽  
Vol 111 (4) ◽  
pp. 926-935 ◽  
Author(s):  
N. Kladias ◽  
V. Prasad
Keyword(s):  
Porous Medium ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Prandtl Number ◽  
Numerical Solutions ◽  
Fluid Layer ◽  
Darcy Number ◽  
Solid Particles ◽  
Convection Regime ◽  
Porous Layers

Natural convection in horizontal porous layers heated from below is studied by employing a formulation based on the Brinkman–Forchheimer–extended Darcy equation of motion. The numerical solutions show that the convective flow is initiated at lower fluid Rayleigh number Raf than that predicted by the linear stability analysis for the Darcy flow model. The effect is considerable, particularly at a Darcy number Da greater than 10−4. On the other hand, an increase in the thermal conductivity of solid particles has a stabilizing effect. Also, the Rayleigh number Raf required for the onset of convection increases as the fluid Prandtl number is decreased. In the stable convection regime, the heat transfer rate increases with the Rayleigh number, the Prandtl number, the Darcy number, and the ratio of the solid and fluid thermal conductivities. However, there exists an asymptotic convection regime where the porous media solutions are independent of the permeability of the porous matrix or Darcy number. In this regime, the temperature and flow fields are very similar to those obtained for a fluid layer heated from below. Indeed, the Nusselt numbers for a porous medium with kf = ks match with the fluid results. The effect of Prandtl number is observed to be significant for Prf < 10, and is strengthened with an increase in Raf, Da, and ks/kf. An interesting effect, that a porous medium can transport more energy than the saturating fluid alone, is also revealed.

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