Consider the spacecraft heat rejection scheme of Problem 13.27, but under conditions for which surfaces 1 and 2 may not be approximated as blackbodies. (a) For isothermal surfaces of temperature T = 325 K and emissivity ε = 0.7 and a U-section of width W = 25 mm and length L = 125 mm , determine the rate per unit length (normal to the page) at which radiation is transferred from a section to deep space. (b) Explore the effect of the emissivity on the rate of heat rejection, and contrast your results with those for emission exclusively from the base of the section.
Consider the spacecraft heat rejection scheme of Problem 13.27, but under conditions for which surfaces 1 and 2 may not be approximated as blackbodies. (a) For isothermal surfaces of temperature T = 325 K and emissivity ε = 0.7 and a U-section of width W = 25 mm and length L = 125 mm , determine the rate per unit length (normal to the page) at which radiation is transferred from a section to deep space. (b) Explore the effect of the emissivity on the rate of heat rejection, and contrast your results with those for emission exclusively from the base of the section.
Solution Summary: The author explains the rate per unit length at which radiation is transferred from a section to deep space. The expression for heat transfer is given by, cq=s
Consider the spacecraft heat rejection scheme of Problem 13.27, but under conditions for which surfaces 1 and 2 may not be approximated as blackbodies. (a) For isothermal surfaces of temperature
T
=
325
K
and emissivity
ε
=
0.7
and a U-section of width
W
=
25
mm
and length
L
=
125
mm
, determine the rate per unit length (normal to the page) at which radiation is transferred from a section to deep space. (b) Explore the effect of the emissivity on the rate of heat rejection, and contrast your results with those for emission exclusively from the base of the section.
Question #9
A circular ceramic plate that can be modelled as a blackbody is being heated by an electrical
heater. The plate is 30cm in diameter and is situated in a surrounding ambient temperature
of 15°C where the natural convection heat transfer coefficient is 12W/m² K. The efficiency
of the electrical heater to transfer heat to the plate is 80%, the electric power is required
such that the heater needs to keep the surface temperature of the plate at 200°C.
Ambient 15°C Tsurr = 15°C
h = 12 W/m².K
Ceramic plate
-T₂ = 200°C
Welec
(A) Determine the heat emitted from the plate, as a blackbody.
(B) Determine the radiation incident on the plate from the surroundings.
(C) Determine the heat transfer from the plate to the surroundings.
(D) Determine the required electric power.
A thin, disk-shaped silicon wafer of diameter D=20 cm on a production line must be maintained at a temperature of 100 deg C. The wafer loses heat to the room by convection and radiation from its upper surface, while heat is supplied at a constant flux from below. The surrounding air is at 20 deg C, while all surrounding surfaces (which can be treated as blackbodies) can be approximated to be isothermal at a temperature of 15 deg C. The wafer-to-air heat transfer coefficient is 30 W/m2-K and the emissivity of the wafer’s surface (which can be approximated to be gray) is 0.85. How much heat (in W) must be supplied to the wafer?
Radiative heat transfer is intended between the inner surfaces of two very large isothermal parallel metal plates. While the upper plate (designated as plate 1) is a black surface and is the warmer one being maintained at 727 °C the lower plate (plate 2) is a diffuse and gray surface with an emissivity of 0.7 and is kept at 227 °C. Assume that the surface are sufficiently large to form a two-surface enclosure and steady state conditions to exist.
Stefan-Boltzmann constant is given as 5.67 x 10-8 W/m²-K4.
(1) The irradiation (in kW/m²) for the plate (plate 1) is
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