Thermodynamics HW Solutions 578

Thermodynamics HW Solutions 578 - 000 282 521 1 6974 4 1...

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

View Full Document Right Arrow Icon
Chapter 7 External Forced Convection 7-49 A long aluminum wire is cooled by cross air flowing over it. The rate of heat transfer from the wire per meter length when it is first exposed to the air 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 The properties of air at 1 atm and the film temperature of (T s + T )/2 = (370+30)/2 = 200 ° C are (Table A-15) 6974 . 0 Pr /s m 10 455 . 3 C W/m. 03779 . 0 2 5 - = × = ° = υ k 370 ° C Aluminum wire D = 3 mm Analysis The Reynolds number is 0 . 521 /s m 10 455 . 3 m) m/s)(0.003 (6 Re 2 5 = × = = D V V = 6 m/s T = 30 ° C The Nusselt number corresponding this Reynolds number is determined to be () [] () [] 48 . 11
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 000 , 282 . 521 1 6974 . / 4 . 1 ) 6974 . ( ) . 521 ( 62 . 3 . 000 , 282 Re 1 Pr / 4 . 1 Pr Re 62 . 3 . 5 / 4 8 / 5 4 / 1 3 / 2 3 / 1 5 . 5 / 4 8 / 5 4 / 1 3 / 2 3 / 1 5 . = ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + + + = ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + + + = = k hD Nu Then the heat transfer coefficient and the heat transfer rate from the wire per meter length become C . W/m 6 . 144 ) 48 . 11 ( m 003 . C W/m. 03779 . 2 ° = ° = = Nu D k h W 463.4 = C 30)-)(370 m 5 C)(0.00942 . W/m 6 . 144 ( ) ( m 0.009425 = m) m)(1 003 . ( 2 2 2 ° ° = − = = = ∞ T T hA Q DL A s s conv s & ππ 7-33...
View Full Document

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.

Ask a homework question - tutors are online