Consider the steam pipe of Example 1.2. The facilitiesmanager wants you to recommend methods for reducing the heat loss to the room, and two options are proposed. The first option would restrict air movementaround the outer surface of the pipe and thereby reducethe convection coefficient by a factor of two. The second option would coat the outer surface of the pipe witha low emissivity ( ∈ = 0.4 ) paint. (a) Which of the foregoing options would you recommend? (b) To prepare for a presentation of your recommendation to management, generate a graph of the heatloss q ′ as a function of the convection coefficient for 2 ≤ h ≤ 20 W/m 2 ⋅ K and emissivities of 0.2, 0.4, and 0.8. Comment on the relative efficacy ofreducing heat losses associated with convection andradiation.
Consider the steam pipe of Example 1.2. The facilitiesmanager wants you to recommend methods for reducing the heat loss to the room, and two options are proposed. The first option would restrict air movementaround the outer surface of the pipe and thereby reducethe convection coefficient by a factor of two. The second option would coat the outer surface of the pipe witha low emissivity ( ∈ = 0.4 ) paint. (a) Which of the foregoing options would you recommend? (b) To prepare for a presentation of your recommendation to management, generate a graph of the heatloss q ′ as a function of the convection coefficient for 2 ≤ h ≤ 20 W/m 2 ⋅ K and emissivities of 0.2, 0.4, and 0.8. Comment on the relative efficacy ofreducing heat losses associated with convection andradiation.
Solution Summary: The author explains the recommended method of reducing heat transfer coefficient to reduce the heat loss to the room.
Consider the steam pipe of Example 1.2. The facilitiesmanager wants you to recommend methods for reducing the heat loss to the room, and two options are proposed. The first option would restrict air movementaround the outer surface of the pipe and thereby reducethe convection coefficient by a factor of two. The second option would coat the outer surface of the pipe witha low emissivity
(
∈
=
0.4
)
paint. (a) Which of the foregoing options would you recommend? (b) To prepare for a presentation of your recommendation to management, generate a graph of the heatloss
q
′
as a function of the convection coefficient for
2
≤
h
≤
20
W/m
2
⋅
K
and emissivities of 0.2, 0.4, and 0.8. Comment on the relative efficacy ofreducing heat losses associated with convection andradiation.
A spherical interplanetary probe of 0.5-m diameter contains electronics that dissipate 150 W. If the probe surface has an emissivity of 0.8 and the probe does not receive radiation from other surfaces, as, for example, from the sun, what is its surface temperature?
A plate (0.5 m * 0.5 m) is inclined at an angle of 30°. The top surface of the plate is well insulated. Estimate the rate of heat loss from the plate when the bottom surface is maintained at 60°C and the surrounding atmospheric quiescent air is at 0°C.
The small horizontal metal tube with an OD of 0.05 m, 0.1 m long, and with a surface temperature of 25 C is in a very large furnace enclosure with firebrick walls and the surrounding air at 500 C. The emissivity of the metal tube is 0.6. Calculate the net heat transfer to the tube by radiation in Watts.
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