16-51 Consider a person whose exposed surface area is 1.7 m², emissivity is 0.5, and surface temperature is 32°C. Determine the rate of heat loss from that person by radiation in a large room having walls at a temperature of (a) 300 K and (b) 280 K. Answers: (a) 26.7 W, (b) 121 W 16-52 Consider a sealed 20-cm-high electronic box whose base dimensions are 50 cm x 50 cm placed in a vacuum chamber. The emissivity of the outer surface of the box is 0.95. If the electronic components in the box dissipate a total of 120 W of power and the outer surface temperature of the box is not to exceed 55°C, determine the temperature at which the surrounding surfaces must be kept if this box is to be cooled by radiation alone. Assume the heat transfer from the bottom surface of the box to the stand to be negligible. 50 cm 120 W ε = 0.95 T = 55°C S 20 cm Stand 50 cm Electronic box

16-51 Consider a person whose exposed surface area is 1.7 m², emissivity is 0.5, and surface temperature is 32°C. Determine the rate of heat loss from that person by radiation in a large room having walls at a temperature of (a) 300 K and (b) 280 K. Answers: (a) 26.7 W, (b) 121 W 16-52 Consider a sealed 20-cm-high electronic box whose base dimensions are 50 cm x 50 cm placed in a vacuum chamber. The emissivity of the outer surface of the box is 0.95. If the electronic components in the box dissipate a total of 120 W of power and the outer surface temperature of the box is not to exceed 55°C, determine the temperature at which the surrounding surfaces must be kept if this box is to be cooled by radiation alone. Assume the heat transfer from the bottom surface of the box to the stand to be negligible. 50 cm 120 W ε = 0.95 T = 55°C S 20 cm Stand 50 cm Electronic box

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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Concept explainers

Conduction and Convection

When energy travels from one object to another it is said to have undergone heat transfer. Heat transfer is nothing but the transfer of thermal energy or internal energy from one thing to another, like e.g., when a vessel with water, kept on top of a burner, heats up because of the flame underneath it.

Question

16-51 Consider a person whose exposed surface area is
1.7 m², emissivity is 0.5, and surface temperature is 32°C.
Determine the rate of heat loss from that person by radiation
in a large room having walls at a temperature of (a) 300 K and
(b) 280 K. Answers: (a) 26.7 W, (b) 121 W
16-52 Consider a sealed 20-cm-high electronic box whose
base dimensions are 50 cm x 50 cm placed in a vacuum
chamber. The emissivity of the outer surface of the box is 0.95.
If the electronic components in the box dissipate a total of
120 W of power and the outer surface temperature of the box
is not to exceed 55°C, determine the temperature at which the
surrounding surfaces must be kept if this box is to be cooled
by radiation alone. Assume the heat transfer from the bottom
surface of the box to the stand to be negligible.
50 cm
120 W
ε = 0.95
T = 55°C
20 cm
Stand
FIGURE P16-52
50 cm
Electronic
box

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