Thermodynamics HW Solutions 631

Thermodynamics HW Solutions 631 - Chapter 7 External Forced...

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Chapter 7 External Forced Convection 7-101 A spherical tank filled with liquid nitrogen is exposed to winds. The rate of evaporation of the liquid nitrogen due to heat transfer from the air is to be determined for three cases. Assumptions 1 Steady operating conditions exist. 2 Radiation effects are negligible. 3 Air is an ideal gas with constant properties. 4 The pressure of air is 1 atm. Properties The properties of air at 1 atm pressure and the free stream temperature of 20 ° C are (Table A-15) 7309 . 0 Pr kg/m.s 10 023 . 5 kg/m.s 10 825 . 1 /s m 10 516 . 1 C W/m. 02514 . 0 6 C 196 @ , 5 2 5 - = × = × = × = ° = ° s k μ υ Analysis ( a ) When there is no insulation, D = D i = 4 m, and the Reynolds number is [] 6 2 5 10 932 . 2 /s m 10 516 . 1 m) (4 m/s 1000/3600) (40 Re × = × × = υ = D V The Nusselt number is determined from [] [] 2333 10 023 . 5 10 825 . 1 ) 7309 . 0 ( ) 10 932 . 2 ( 06 . 0 ) 10 932 . 2 ( 4 . 0 2 Pr Re 06 . 0 Re 4 . 0 2 4 / 1 6 5 4 . 0 3 / 2 6
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