The spectral transmissivity of plain and tinted glass can be approximated as follows: plain glass: τ λ = 0.9 0 .3 ≤ λ ≤ 2 .5 μ m Tinted glass: τ λ = 0.9 0 .5 ≤ λ ≤ 1. 5 μ m Outside the specified wavelength ranges, the spectral transmissivity is zero for both glasses. Compare the solar energy that could be transmitted through the glasses. With solar irradiation on the glasses, compare the visible radiant energy that could be transmitted.
The spectral transmissivity of plain and tinted glass can be approximated as follows: plain glass: τ λ = 0.9 0 .3 ≤ λ ≤ 2 .5 μ m Tinted glass: τ λ = 0.9 0 .5 ≤ λ ≤ 1. 5 μ m Outside the specified wavelength ranges, the spectral transmissivity is zero for both glasses. Compare the solar energy that could be transmitted through the glasses. With solar irradiation on the glasses, compare the visible radiant energy that could be transmitted.
Solution Summary: The author compares the solar transmissivity of plain glass and tinted glass.
Outside the specified wavelength ranges, the spectral transmissivity is zero for both glasses. Compare the solar energy that could be transmitted through the glasses. With solar irradiation on the glasses, compare the visible radiant energy that could be transmitted.
A typical car's exterior consists of a thin layer of silica (SiO2) over an opaque painted metal panel.
Silica is transparent in the visible wavelengths but offers high reflectance in the near- to mid-
infrared wavelengths. The plot on the next page depicts the diffuse spectral reflectivity (pa) of the
car's surface:
Spectral reflectivity, P₂
0.8
0.6
0.4
ལ
0.2
0
0.1
1
1
10
Wavelength, λ(μm)
100
If the car's exterior temperature is T₁ = 77°C, determine both the total absorptivity (a) and the total
emissivity (a) of the silica-covered panel. Assume that the Sun's temperature is Tsun = 5800 K.
Spectral hemispherical reflectivity distribution of an opaque surface is shown below. Surface is subjected to the spectral irradiation as shown.
1.0
400
a 0.4
200
5
10 15 20
a (um)
5
10
15
2 (um)
Calculate the total irradiation on the surface in W/m2
Calculate the irradiation absorbed by the surface in W/m2
3250 || 3750 || 4250|| 5000 || 5750|| 6250|| 7500
1050 || 1200
1400|| 1600|| 1750| 1850 || 2000
The spectral transmissivity of a 50 mm thick polymer film is measured over the wavelength range 2.5
um si s 15 μm. The spectral distribution may be approximated as t = 0.8 for 2.5 um sλs 7 μm, t₁ =
0.05 for 7 um < s 13 um, and ta=0.55 for 13 m < s 15 m. Transmissivity data outside the range
cannot be acquired du to limitations associated with the instrumentation. An engineer wishes to
determine the total transmissivity of the film. (a) estimate the maximum possible total transmissivity of
the film associated with irradiation from a blackbody at T = 30°C. (b) Estimate the minimum possible total
transmissivity of the fil associated with irradiation from a blackbody at T = 30°C.
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