Thermodynamics HW Solutions 769

Thermodynamics HW Solutions 769 - room s o combined cond i...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 9 Natural Convection 8 2 2 5 3 -1 2 2 3 2 1 10 412 . 1 ) 7342 . 0 ( ) /s m 10 409 . 1 ( ) m 357 . 0 )( K ) 4 ( 20 )[ K 003559 . 0 )( m/s 81 . 9 ( Pr ) ( × = × = = υ β c L T T g Ra 43 . 29 ) 10 412 . 1 ( 27 . 0 27 . 0 4 / 1 8 4 / 1 = × = = Ra Nu C . W/m 998 . 1 ) 43 . 29 ( m 357 . 0 C W/m. 02424 . 0 2 ° = ° = = Nu L k h c i Using the thermal resistance network, the rate of heat loss through the skylight is determined to be W 115 C . W/m 898 . 6 1 C W/m. 78 . 0 m 005 . 0 C . W/m 998 . 1 1 C )] 10 ( 20 )[ m 5 . 2 ( 1 1 ) ( 2 2 2 glass , , , , , = ° + ° + ° ° = + + = + + = h k t h T T A R R R T T Q glass i out room s o combined glas cond i conv o i s skylight Using the same heat transfer coefficients for simplicity, the rate of heat loss through the roof in the case of R-5.34 construction is determined to be W 36 . 5 C . W/m 898 . 6 1 C/W . m 34 . 5 C . W/m 998 . 1 1 C )] 10 ( 20 )[ m 5 . 2 ( 1 1 ) ( 2 2 2 2 , , , , = ° + ° + ° ° = + + = + + = h R h T T A R R R T T Q glass i out
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: room s o combined cond i conv o i s roof & Therefore, a house loses 115/5.36 21 times more heat through the skylights than it does through an insulated wall of the same size. Using Newtons law of cooling, the glass temperature corresponding to a heat transfer rate of 115 W is calculated to be 3.3 C, which is sufficiently close to the assumed value of -4 C. Therefore, there is no need to repeat the calculations. 9-92...
View Full Document

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.

Ask a homework question - tutors are online