Thermodynamics HW Solutions 574

Thermodynamics HW Solutions 574 - Chapter 7 External Forced...

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Chapter 7 External Forced Convection 7-46 The wind is blowing across the wire of a transmission line. The surface temperature of the wire is to be determined. Assumptions 1 Steady operating conditions exist. 2 Radiation effects are negligible. 3 Air is an ideal gas with constant properties. 4 The local atmospheric pressure is 1 atm. Properties We assume the film temperature to be 10 ° C. The properties of air at this temperature are (Table A-15) 7336 . 0 Pr /s m 10 426 . 1 C W/m. 02439 . 0 kg/m 246 . 1 2 5 - 3 = × = ° = = υ ρ k Analysis The Reynolds number is [ ] 4674 /s m 10 426 . 1 m) (0.006 m/s 0/3600) 100 (40 Re 2 5 = × × = = D V The Nusselt number corresponding this Reynolds number is determined to be () [] 0 . 36 000 , 282 4674 1 7336 . 0 / 4 . 0 1 ) 7336 . 0 ( ) 4674 ( 62 . 0 3 . 0 000 , 282 Re 1 Pr / 4 . 0 1 Pr Re 62 . 0 3 . 0 5 / 4 8 / 5 4 / 1 3 / 2 3 / 1 5 . 0 5 / 4 8 / 5 4 / 1 3 / 2 3 / 1 5 . 0 = + + + = + + +
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