Thermodynamics HW Solutions 752

Thermodynamics HW Solutions 752 - 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 9-79 A circuit board is cooled by a fan that blows air upwards. The average temperature on the surface of the circuit board is to be determined for two cases. Assumptions 1 Steady operating conditions exist. 2 Air is an ideal gas with constant properties. 3 The atmospheric pressure at that location is 1 atm. Air T ∞ = 35 ° C V ∞ = 0.5 m/s PCB, T s 100 × 0.05 W L = 12 cm Properties The properties of air at 1 atm and 1 atm and the anticipated film temperature of ( T s + T ∞ )/2 = (60+35)/2 = 47.5 ° C are (Table A-15) 1- 2 5 K 00312 . K ) 273 5 . 47 ( 1 1 7235 . Pr /s m 10 774 . 1 C W/m. 02717 . = + = = = × = ° = − f T k β υ Analysis We assume the surface temperature to be 60 ° C. We will check this assumption later on and repeat calculations with a better assumption, if necessary. The characteristic length in this case is the length of the board in the flow (vertical) direction, L c = L = 0.12 m. Then the Reynolds number becomes 3383 /s m 10 774...
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