This preview shows page 1. Sign up to view the full content.
Chapter 8
Internal Forced Convection
841
Flow of hot air through uninsulated square ducts of a heating system in the attic is considered. The
exit temperature and the rate of heat loss are to be determined.
Assumptions
1
Steady operating conditions exist.
2
The inner surfaces of the duct are smooth.
3
Air is an
ideal gas with constant properties.
4
The pressure of air is 1 atm.
Properties
We assume the bulk mean temperature for air to be 80
°
C since the mean temperature of air at
the inlet will drop somewhat as a result of heat loss through the duct whose surface is at a lower
temperature. The properties of air at 1 atm and this temperature are (Table A15)
7154
.
0
Pr
C
J/kg.
1008
/s
m
10
097
.
2
C
W/m.
02953
.
0
kg/m
9994
.
0
2
5

3
=
°
=
×
=
°
=
=
p
C
k
υ
ρ
Air
85
°
C
0.1 m
3
/min
10 m
70
°
C
T
e
Analysis
The characteristic length that is the hydraulic diameter,
the mean velocity of air, and the Reynolds number are
D
A
P
a
a
a
h
c
===
=
4
4
4
015
2
.
m
m/s
444
.
4
m)
15
.
0
(
/s
m
10
.
0
This is the end of the preview. Sign up
to
access the rest of the 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.
 Fall '10
 Dr.DanielArenas
 Thermodynamics, Convection, Force, Mass, Heat

Click to edit the document details