Solar radiation is incident on a 5-m 2 solar absorber plate surface at a rate of 800 W/m2. Ninety-three percent of the solar radiation is absorbed by the absorber plate, while the remaining 7 percent is reflected away. The solar absorber plate has a surface temperature of 40 o C with an emissivity of 0.9 that experiences radiation exchange with the surrounding temperature of − 5 o C . In addition, convective heat transfer occurs between the absorber plate surface and the ambient air of 20 o C with a convection heat transfer coefficient if 7 W/m 2 . K . Determine the efficiency of the solar absorber, which is defined as the ratio of the usable heat collected by the absorber to the incident solar radiation on the absorber.
Solar radiation is incident on a 5-m2 solar absorber plate surface at a rate of 800 W/m2. Ninety-three percent of the solar radiation is absorbed by the absorber plate, while the remaining 7 percent is reflected away. The solar absorber plate has a surface temperature of
40
o
C
with an emissivity of 0.9 that experiences radiation exchange with the surrounding temperature of
−
5
o
C
.
In addition, convective heat transfer occurs between the absorber plate surface and the ambient air of
20
o
C
with a convection heat transfer coefficient if
7 W/m
2
.
K
.
Determine the efficiency of the solar absorber, which is defined as the ratio of the usable heat collected by the absorber to the incident solar radiation on the absorber.
The outer surface of a spacecraft in space has an emissivity of 0.6 and an absorptivity of 0.2 for solar radiation. If solar radiation is incident on the spacecraft at a rate of 1000 W/m2 , determine the surface temperature of the spacecraft when the radiation emitted equals the solar energy absorbed
Consider steady heat transfer between two large parallel plates at constant temperatures T1 = 300 K and T2 = 200 K that are L = 1 cm apart, as shown below. Assuming the surface to be black, determine the rate of heat transfer between the plates per unit surface area assuming the gap between the plates is a) filled with still air with k = 0.0219 W/m°C, b) free flowing air with h = 7.5 W/m2°C, c) evacuated, d) filled with urethane insulation with k = 0.026 W/m°C, and e) filled with superinsulation that has an apparent thermal conductivity k = 0.00002 W/m°C
Consider steady heat transfer between two large parallel plates at constant temperatures T1 = 300 K and T2 = 200 K that are L = 1 cm apart, as shown below. Assuming the surface to be black, determine the rate of heat transfer between the plates per unit surface area assuming the gap between the plates is a) filled with still air with k = 0.0219 W/m°C, b) free flowing air with h = 7.5 W/m2°C, c) evacuated, d) filled with urethane insulation with k = 0.026 W/m°C, and e) filled with superinsulation that has an apparent thermal conductivity k = 0.00002 W/m°C
PLEASE ANSWER LETTER D AND E, THANK YOU
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