Thermodynamics HW Solutions 782

Thermodynamics HW Solutions 782 - Chapter 9 Natural...

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

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Chapter 9 Natural Convection 9-109 A group of 25 transistors are cooled by attaching them to a square aluminum plate and mounting the plate on the wall of a room. The required size of the plate to limit the surface temperature to 50 C is to be determined. Assumptions 1 Steady operating conditions exist. 2 Air is an ideal gas with constant properties. 3 The local atmospheric pressure is 1 atm. 4 Any heat transfer from the back side of the plate is negligible. Properties The properties of air at 1 atm and the film temperature of ( T s + T )/2 = (50+30)/2 = 40 C are (Table A-15) Transistors, 25 1.5 W = 0.9 T s = 50 C Room 30 C Plate L L 1- 2 5 K 003195 . K ) 273 40 ( 1 1 7255 . Pr /s m 10 702 . 1 C W/m. 02662 . = + = = = = = f T k Analysis The Rayleigh number can be determined in terms of the characteristic length (length of the plate) to be 3 9 2 2 5 3-1 2 2 3 10 571 . 1 ) 7255 . ( ) /s m 10 702 . 1 ( ) )( K 30 50 )( K 003195 . )( m/s 81 . 9 ( Pr )...
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