The resistance wire of a 1000-W iron is 15 in long and has a diameter of D = 0.08 in. Determine the rate of heat generation in the wire per unit volume in Btu/h•ft3 and the heat flux on the outer surface of the wire in Btu/h•ft2 as a result of this heat generation.


The power consumed by the resistance wire of an iron is given. The heat generation and the heat flux are to be determined.

Assumptions Heat is generated uniformly in the resistance wire.



Analysis A 1000 W iron will convert electrical energy into heat in the wire at a rate of 1000 W. Therefore, the rate of heat generation in a resistance wire is simply equal to the power rating of a resistance heater. Then the rate of heat generation in the wire per unit volume is determined by dividing the total rate of heat generation by the volume of the wire to be



Similarly, heat flux on the outer surface of the wire as a result of this heat generation is determined by dividing the total rate of heat generation by the surface area of the wire to be



Discussion Note that heat generation is expressed per unit volume in Btu/h?ft3 whereas heat flux is expressed per unit surface area in Btu/h?ft2.

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