Thermodynamics HW Solutions 626

Thermodynamics HW Solutions 626 - 7282 . ( ) 10 304 . 1 (...

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Chapter 7 External Forced Convection 7-96 A spherical tank used to store iced water is subjected to winds. The rate of heat transfer to the iced water and the amount of ice that melts during a 24-h period are to be determined. Assumptions 1 Steady operating conditions exist. 2 Thermal resistance of the tank is negligible. 3 Radiation effects are negligible. 4 Air is an ideal gas with constant properties. 5 The pressure of air is 1 atm. Properties The properties of air at 1 atm pressure and the free stream temperature of 30 ° C are (Table A-15) 7282 . 0 Pr kg/m.s 10 729 . 1 kg/m.s 10 872 . 1 /s m 10 608 . 1 C W/m. 02588 . 0 5 C 0 @ , 5 2 5 - = × = × = × = ° = ° s k μ υ Analysis ( a ) The Reynolds number is [] 6 2 5 10 304 . 1 /s m 10 608 . 1 m) (3.02 m/s 1000/3600) (25 Re × = × × = υ = D V 1 cm Iced water D i = 3 m 0 ° C Q T s = 0 ° C V = 25 km/h T = 30 ° C The Nusselt number corresponding to this Reynolds number is determined from [] [] 1056 10 729 . 1 10 872 . 1 )
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Unformatted text preview: 7282 . ( ) 10 304 . 1 ( 06 . ) 10 304 . 1 ( 4 . 2 Pr Re 06 . Re 4 . 2 4 / 1 5 5 4 . 3 / 2 6 5 . 6 4 / 1 4 . 3 / 2 5 . = + + = + + = = s k hD Nu and C . W/m 05 . 9 ) 1056 ( m 02 . 3 C W/m. 02588 . 2 = = = Nu D k h The rate of heat transfer to the iced water is W 7779 = = = = C ) 30 ( ] m) (3.02 C)[ . W/m 05 . 9 ( ) )( ( ) ( 2 2 2 T T D h T T hA Q s s s & ( b ) The amount of heat transfer during a 24-hour period is kJ 079 , 672 s) 3600 kJ/s)(24 779 . 7 ( = = = t Q Q & Then the amount of ice that melts during this period becomes kg 2014 = = = = kJ/kg 7 . 333 kJ 079 , 672 if if h Q m mh Q 7-81...
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This note was uploaded on 01/22/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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