Thermodynamics HW Solutions 725

Thermodynamics HW Solutions 725 - Chapter 9 Natural...

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Unformatted text preview: Chapter 9 Natural Convection 9-32 A fluid flows through a pipe in calm ambient air. The pipe is heated electrically. The thickness of the insulation needed to reduce the losses by 85% and the money saved during 10-h are to be determined. Assumptions 1 Steady operating conditions exist. 2 Air is an ideal gas with constant properties. 3 The local atmospheric pressure is 1 atm. Properties Insulation will drop the outer surface temperature to a value close to the ambient temperature, and possible below it because of the very low sky temperature for radiation heat loss. For convenience, we use the properties of air at 1 atm and 5 ° C (the anticipated film temperature) (Table A-15), 1- 2 5 K 003597 . K ) 273 5 ( 1 1 7350 . Pr /s m 10 382 . 1 C W/m. 02401 . = + = = = × = ° = − f T k β υ Asphalt L = 100 m D + 2 t ins 25 ° C Insulation ε = 0.1 T sky = -30 ° C T ∞ = 0 ° C Analysis The rate of heat loss in the previous problem was obtained to be 29,094 W. Noting that insulation will cut down obtained to be 29,094 W....
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This note was uploaded on 01/24/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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