50
Radiation A
Radiation B
Radiation C
No Radiation
10
1
0.5
5
6
7
10
10
10
Rayleigh Number
Figure 30. Nusselt and Rayleigh number plot for the 4-in. pipe in the
1-ft 1-ft enclosure (numerical data).
50
Radiation A
Radiation B
Radiation C
10
5
4
5
6
10
10
10
Rayleigh Number
Figure 31. Nusselt and Rayleigh number plot for the insulated 4-in.
pipe in the 1-ft 1-ft enclosure (numerical data).
Radiation A, Pipe or insulation surface 0.9, inside insulation surface 0.9
Radiation B, Pipe or insulation surface 0.9, inside insulation surface 0.6
Radiation C, Pipe or insulation surface 0.5, inside insulation surface 0.9.
Significant differences are seen for each different radiation condition.
In Figure 30, the convection data alone (no radiation condition) do not all coin-
cide on one line as expected. This is thought to be due to errors associated with
too coarse a mesh, or for other unidentified reasons.
Figure 34 shows the data for the 1.27-ft 1.27-ft and the 2-ft 2-ft enclosures.
The 1.27-ft 1.27-ft enclosure had a 4-in. pipe with two inches of insulation. This
resulted in nearly the same effective gap as the 2-in. insulated pipe in the 1-ft 1-
ft enclosure. The meager amount of data obtained with two pipes is also shown
on the plot. The effective gap in this case was obtained using the total area of the
two insulated pipes to determine an effective interior radius.
37
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