The window of a large vacuum chamber is fabricated from a material of prescribed spectral characteristics. A collimated beam of radiant energy from a solar simulator is incident on the window and has a flux of 3000 W / m 2 . The inside walls of the chamber, which are large compared to the window area, are maintained at 77 K. The outer surface of the window is subjected to surroundings and room air at 25 ∘ C , with a convection heat transfer coefficient of 15 W / m 2 ⋅ k (a) Determine the transmissivity of the window mate- rial to radiation from the solar simulator, which approximates the solar spectral distribution. (b) Assuming that the window is insulated from its chamber mounting arrangement, what steady-state temperature does the window reach? (c) Calculate the net radiation transfer per unit area of the window to the vacuum chamber wall, excluding the transmitted simulated solar flux.
The window of a large vacuum chamber is fabricated from a material of prescribed spectral characteristics. A collimated beam of radiant energy from a solar simulator is incident on the window and has a flux of 3000 W / m 2 . The inside walls of the chamber, which are large compared to the window area, are maintained at 77 K. The outer surface of the window is subjected to surroundings and room air at 25 ∘ C , with a convection heat transfer coefficient of 15 W / m 2 ⋅ k (a) Determine the transmissivity of the window mate- rial to radiation from the solar simulator, which approximates the solar spectral distribution. (b) Assuming that the window is insulated from its chamber mounting arrangement, what steady-state temperature does the window reach? (c) Calculate the net radiation transfer per unit area of the window to the vacuum chamber wall, excluding the transmitted simulated solar flux.
Solution Summary: The graph for the transmissivity and the reflectivity for corresponding wavelength functions is shown as follows:
The window of a large vacuum chamber is fabricated from a material of prescribed spectral characteristics. A collimated beam of radiant energy from a solar simulator is incident on the window and has a flux of
3000
W
/
m
2
. The inside walls of the chamber, which are large compared to the window area, are maintained at 77 K. The outer surface of the window is subjected to surroundings and room air at
25
∘
C
, with a convection heat transfer coefficient of
15
W
/
m
2
⋅
k
(a) Determine the transmissivity of the window mate- rial to radiation from the solar simulator, which approximates the solar spectral distribution.
(b) Assuming that the window is insulated from its chamber mounting arrangement, what steady-state temperature does the window reach?
(c) Calculate the net radiation transfer per unit area of the window to the vacuum chamber wall, excluding the transmitted simulated solar flux.
An enclosure has an inside area of 50 m², and its inside surface is black and is maintained at a constant temperature. A small opening in
the enclosure has an area of 0.03 m². The radiant power emitted from this opening is 52 W. What is the temperature of the interior
enclosure wall, in K? If the interior surface is maintained at this temperature, but is now polished so that its emissivity is 0.15, what will
be the value of the radiant power emitted from the opening, in W?
T, =
grad =
i
K
W
An opaque surface which is insulated at the back side has a total, hemispherical
absorptivity a=0.8 for solar radiation and a total, hemispherical emissivity of e=0.2. A solar
radiation flux of 800 W/m2 is incident on this surface. The surface is exposed to the ambient air at T
300 K and convective heat transfer coefficient is h=15 W/m2 K. Neglect the sky radiation.
• Sketch the heat fluxes received and dissipated by this surface
• Estimate the equilibrium temperature of the surface (assume the surface temperature is higher
than the ambient air temperature).
1.= 300 K, h-15 W/m*K
800 W/m?
a-0.8 , e-0.2
A certain body at 20C is displayed on a top of a building during the night. The body sees nothing but the sky which has an effective temperature of 110K. Determine the heat transfer rate from the body to the sky if the body temperature is maintained at 23C, the surface emissivity of the body is equal to 0.92, and none of the radiation going out of the comes back
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