Fin
- 1. PROPRIETARY MATERIAL. © 2011 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course
preparation. If you are a student using this Manual, you are using it without permission.
3-113
m0942.0)m1)(m03.0( 2
1fin LDA
The efficiency of these circular fins is, from the efficiency curve, Fig. 3-44
3-166 Circular aluminum alloy fins are to be attached to the tubes of a heating system. The increase in heat transfer from the
tubes per unit length as a result of adding fins is to be determined.
Assumptions 1 Steady operating conditions exist. 2 The heat transfer coefficient is constant and uniform over the entire fin
surfaces. 3 Thermal conductivity is constant. 4 Heat transfer by radiation is negligible.
Properties The thermal conductivity of the fins is given to be k = 180 W/m °C.
Analysis In case of no fins, heat transfer from the tube per meter of its length is
no
W537C)25120)(m0942.0)(C.W/m60()( 22
finnofinno TThAQ b
96.0
207.0
m)C)(0.002W/m180(
CW/m60
2
002.0
015.0
2
07.2
0.015
)2/002.0(03.0)2/(
m015.02/)03.006.0(2/)(
fin
o
o2
2/1
2/3
1
2
12
kt
ht
L
kA
h
L
r
tr
DDL
p
c
eat transf from a single fin is
22
finfinmaxfin,finfin
2
TThAQQ b
gle unfinned portion of the tube is
2
1fin sDA
here are 200 fins and thus 200 interfin spacings per meter length of the tube. The total heat transfer from the finned tube is
Therefore, the increase in heat transfer from the tube per meter of its length as a result of the addition of the fins is
Discussion The The overall effectiveness of the finned tube is 5380/537 = 10. That is, the rate of heat transfer from the
steam tube increases by a factor of 10 as a result of adding fins. This explains the widespread use of finned surfaces.
H er
C)25120)(m004624.0)(C.W/m60(96.0
)(
m004624.0)002.0)(03.0(2)015.003.0(22)(2 22
2
2
1
2
2fin trrrA
W3.25
Heat transfer from a sin
W6.1C)25120)(m000283.0)(C.W/m60()( 22
unfinunfin TThAQ b
m000283.0m)m)(0.00303.0(un
T
then determined from
W5380)6.13.25(200)( unfinfinfintotal, QQnQ
W48435375380finnofintotal,increase QQQ
