Thermodynamics HW Solutions 221

# Thermodynamics HW Solutions 221 - Chapter 15 Steady Heat...

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Unformatted text preview: Chapter 15 Steady Heat Conduction 3-89E An electrical wire is covered with 0.02-in thick plastic insulation. It is to be determined if the plastic insulation on the wire will increase or decrease heat transfer from the wire. Assumptions 1 Heat transfer from the wire is steady since there is no indication of any change with time. 2 Heat transfer is one-dimensional since there is thermal symmetry about the centerline and no variation in the axial direction. 3 Thermal properties are constant. 4 The thermal contact resistance at the interface is negligible. Properties The thermal conductivity of plastic cover is given to be k = 0.075 Btu/h ⋅ ft ⋅ °F. Analysis The critical radius of plastic insulation is Wire Insulation in) 0615 . ( in 36 . ft 03 . F . Btu/h.ft 5 . 2 F Btu/h.ft. 075 . 2 2 = > = = ° ° = = r h k r cr Since the outer radius of the wire with insulation is smaller than critical radius of insulation, plastic insulation will increase heat transfer from the wire....
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## This note was uploaded on 01/14/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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