Thermodynamics HW Solutions 786

Thermodynamics HW Solutions 786 - 122 10 443 5 15 15 3 1 8...

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Chapter 9 Natural Convection Assumptions 1 Steady operating conditions exist. 2 Air is an ideal gas with constant properties. 3 The local atmospheric pressure is 1 atm. Properties The properties of air at 1 atm and the film temperature of ( T s + T )/2 = (42+15)/2 = 28.5 ° C are (Table A-15) 1 - 2 5 K 003317 . 0 K ) 273 5 . 28 ( 1 1 7286 . 0 Pr /s m 10 594 . 1 C W/m. 02577 . 0 = + = = = × = ° = f T k β υ Analysis The characteristic length in this case is determined from Insulation Air T = 15 ° C T sky = -30 ° C Solar collector T s =42 ° C ε = 0.9 L = 1.5 m m 6 . 0 m) 6 + m 2(1.5 ) m 6 )( m 5 . 1 ( = = = p A L s c Then, 8 2 2 5 3 -1 2 2 3 10 443 . 5 ) 7286 . 0 ( ) /s m 10 594 . 1 ( ) m 6 . 0 )( K 15 42 )( K 003317 . 0 )( m/s 81 . 9 ( Pr ) ( × = × = = c s L T T g Ra 5
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Unformatted text preview: . 122 ) 10 443 . 5 ( 15 . 15 . 3 / 1 8 3 / 1 = × = = Ra Nu 2 2 m 9 ) m 6 )( m 5 . 1 ( C . W/m 26 . 5 ) 5 . 122 ( m 6 . C W/m. 02577 . = = ° = ° = = s c A Nu L k h and W 1278 = ° − ° = − = ∞ C ) 15 42 )( m 9 )( C . W/m 26 . 5 ( ) ( 2 2 T T hA Q s s conv & Heat transfer rate by radiation is W 2920 = + − − + × = − = − ] ) K 273 30 ( ) K 273 42 )[( .K W/m 10 67 . 5 )( m 9 )( 9 . ( ) ( 4 4 4 2 8 2 4 4 s surr s rad T T A Q σε & 9-110...
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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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