(2)
d dx T x L k q k L h iT ,i T s,i
qLh iT ,i T s,i
(3)
q L h o T s ,o T ,o h iT s ,i T ,iT s 4 ,o T s 4ky
Rco,nhvchW 1t2694 K4 W
The resistance to heat transfer by radiation may be obtained by first noting that the cell forms a three-surface enclosure for which the sidewalls are reradiating.
The cell forms an enclosure that may be classified as a horizontal cavity heated from below, and the appropriate form of the Rayleigh number is
R e 1 qR c 1 o R n c 1 d o R n r 1 v a hd c
Example 12.1
The rear window of an automobile is of thickness L=8mm and height H=0.5m and contains fine-meshed heating wires that can induce nearly volumetric heating. Consider steady-state conditions for which the interior surface of the window is exposed to air at 10 ℃, while the exterior surface is exposed to air at -10 ℃ and a very cold sky with an effective temperature of -33 ℃. The air moves in parallel flow over the surface with a velocity of 20m/s. Determine the volumetric heating rate needed maintain the interior window surface at Ts,i=15℃.
