Consider the flat−plate solar collector of Problem 9.98. The absorber plate has a coating for which ε 1 = 0.96 , and the cover plate has an emissivity of ε 2 = 0.92 . With respect to radiation exchange, both plates may be approximated as diffuse, gray surfaces. (a) For (he conditions of Problem 9.98. what is the rate of heat transfer by free convection from the absorber plate and the net rate of radiation exchange between the plates? (b) The temperature of the absorber plate varies according to the how rate of the working fluid routed through the coiled tube. With all other parameters remaining as prescribed, compute and plot the free convection and radiant heat rates as a t unction of the absorber plate temperature for 50 ≤ T 1 ≤ 100 ° C .
Consider the flat−plate solar collector of Problem 9.98. The absorber plate has a coating for which ε 1 = 0.96 , and the cover plate has an emissivity of ε 2 = 0.92 . With respect to radiation exchange, both plates may be approximated as diffuse, gray surfaces. (a) For (he conditions of Problem 9.98. what is the rate of heat transfer by free convection from the absorber plate and the net rate of radiation exchange between the plates? (b) The temperature of the absorber plate varies according to the how rate of the working fluid routed through the coiled tube. With all other parameters remaining as prescribed, compute and plot the free convection and radiant heat rates as a t unction of the absorber plate temperature for 50 ≤ T 1 ≤ 100 ° C .
Solution Summary: The author explains the rate of heat transfer by free convection and radiation.
Consider the flat−plate solar collector of Problem 9.98. The absorber plate has a coating for which
ε
1
=
0.96
, and the cover plate has an emissivity of
ε
2
=
0.92
. With respect to radiation exchange, both plates may be approximated as diffuse, gray surfaces. (a) For (he conditions of Problem 9.98. what is the rate of heat transfer by free convection from the absorber plate and the net rate of radiation exchange between the plates? (b) The temperature of the absorber plate varies according to the how rate of the working fluid routed through the coiled tube. With all other parameters remaining as prescribed, compute and plot the free convection and radiant heat rates as a t unction of the absorber plate temperature for
50
≤
T
1
≤
100
°
C
.
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.
Pravinbhai
Two concentric spheres of diameter Di = 0.7 mand D2 = 1.2 mare separated by an air space and have surface temperatures
of T = 400 K and T, = 300 K.
(a) If the surfaces are black, what is the net rate of radiation exchange between the spheres, in W?
৭12 =
w
(b) What is the net rate of radiation exchange between the surfaces if they are diffuse and gray with ɛi = 0.5 and e2 = 0.05, in
W?
12
(c) What is the net rate of radiation exchange if D2 is increased to 20 m, with e2 = 0.05, e1 = 0.5, and Di = 0.7 m, in W?
912 = i
(d) What is the net rate of radiation exchange if the larger sphere behaves as a black body (e2 = 1.0) and with e = 0.5, D2 =
20 m, and D1 = 0.7 m, in W?
w
912 =
Physical Properties Mathematical Functions
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