A long wire 0.7 mm in diameter with an emissivity of 0.9 is placed in a large quiescent air space at 270 K. If the wire is at 800 K, calculate the net rate of heat loss. Discuss your assumptions.
GIVEN
• Long wire in still air
• Wire diameter (D) = 0.7 mm= 7*10-4 m
• Wire temperature (Ts) = 800 K
• Emissivity (?) = 0.9
• Air temperature (T?) = 270 K FIND
• The net rate of heat loss
ASSUMPTIONS
• The enclosure around the wire behaves as a blackbody enclosure at the temperature of the air
• The natural convection heat transfer coefficient is 18 W/(m2 K)
• Steady state conditions prevail
SKETCH
The total rate of heat loss from the wire is the sum of the convective and radiative losses
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