Unformatted text preview: 1 Heat transfer is steady since there is no change with time. 2 Heat transfer is onedimensional since there is thermal symmetry about the center line and no change in the axial direction. 3 Thermal conductivity is constant. 4 Heat generation in the heater is uniform. Properties The thermal conductivity is given to be k = 4.5 Btu/h ⋅ ft ⋅ °F. Analysis The resistance heater converts electric energy into heat at a rate of 3 kW. The rate of heat generation per unit volume of the wire is 3 8 2 2 wire Btu/h.ft 10 933 . 2 ft) (1 ft) 12 / 04 . ( Btu/h) 14 . 3412 3 ( × = × = = = L r Q V Q g o gen gen & & & Then the temperature difference between the centerline and the surface becomes F 181.0 ° = ° × = = Δ F) Btu/h.ft. 5 . 4 ( 4 ft) 12 / 04 . )( Btu/h.ft 10 933 . 2 ( 4 2 3 8 2 max k r g T o & 251...
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 Fall '10
 Dr.DanielArenas
 Thermodynamics, Mass, Heat, Heat Transfer, Thermal conductivity, resistance heater

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