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4.2. Perhitungan Data
Berikut contoh perhitungan untuk spesimen 1 dan spesimen 5 Data spesimen dan seksi uji:
Panjang seksi uji L
t
= 250 mm = 0,25 m
Tinggi sirip H = 75 mm
= 0,075 m Panjang sisi-sisi sirip segiempat
= 12,7 mm x 12,7 mm = 0,0127 m x 0,0127 m
Panjang spesimen L = 200 mm
= 0,2 m Lebar spesimen W
b
= 150 mm = 0,15 m
Contoh perhitungan 1.
Spesimen 1
S
x
D = 2,95; S
y
D = 1,97
pada kecepatan aliran udara 0,5 ms Data hasil pengujian:
Tegangan heater = V
h
= 31 V T
in, rata-rata
=
in
T
= 26,1
o
C = 299,1 K Arus heater =
I
h
= 2,14 A T
out,, rata-rata
=
out
T
= 35,5
o
C = 308,5 K Tegangan fan =
V
f
= 102 V T
base, rata-rata
=
b
T
= 60,1
o
C = 333,1 K Arus fan =
I
f
= 1,2 A Beda ketinggian fluida manometer =
∆h = 1,2 mm • Pumping power
ϕ
cos I
V P
f f
fan
. .
=
= 102 V x 1,2 A x 0,8 = 97,92 W
• Temperatur film
2
out in
f
T T
T +
=
2 K
308,5 1
, 99
2 +
= K
8 ,
303 =
• Properti udara ρ
299,1K
= 1,1655994 kgm
3
tabel Incropera
2 4
10 ]
2 10
7 ,
7 8185
, 9
[ x
T T
x x
C
out in
p
+ +
=
−
commit to user
2 4
10 ]
8 ,
303 10
7 ,
7 8185
, 9
[ x
x x
−
+ =
kg.K J
2426 ,
5 100
=
3 2
10 ]
2 10
495 ,
7 7415
, 3
[
− −
+ +
= x
T T
x x
k
out in
3 2
10 ]
8 ,
303 10
495 ,
7 7415
, 3
[
− −
+ =
x x
x
m.K W
0,02651131 =
6 2
10 ]
2 10
483 ,
4 9934
, 4
[
− −
+ +
= x
T T
x x
out in
µ
6 2
10 ]
8 ,
303 10
483 ,
4 9934
, 4
[
− −
+ =
x x
x
m.s kg
8613754 0,00001
=
• Luas penampang melintang saluran udara
b
W H
A .
= m
0,15 x
m 0,075
=
2
m 0,01125
= • Luas total permukaan perpindahan panas
A
s
= W
b
.L + 2a+b.H.N
f
– a.b.N
f
25 m
0,016129 -
25 x
075 ,
0127 ,
0127 ,
2 m
0,2 x
m 0,15
2
x x
m m
+ +
=
2
m 21
0,1 =
• Diameter hidrolik saluran udara P
A D
h
4 =
b b
W H
W H
+ =
2 .
. 4
m 0,15
m 0,075
x 2
m 0,15
x m
0,075 x
4 +
= m
0,1 =
• Laju aliran panas dari heater ϕ
cos .
I .
V Q
h h
elect
=
1 x
A 14
, 2
x V
31 =
66,34Watt =
commit to user
• Laju aliran massa udara
V A
m .
.
ρ
=
s m
0,5 x
m 01125
, x
m kg
1655994 ,
1
2 3
=
s kg
0,00655 =
• Laju perpindahan panas konveksi
in out
p conv
T T
C m
Q −
= .
.
K 299,1
308,5 x
kg.K J
426 1005,2
x s
kg 0,006554
− =
W 93
, 61
= • Heat losses yang terjadi pada seksi uji
100 x
Q Q
Q Q
conv conv
elect loss
− =
100 x
W 93
, 61
W 93
, 61
66,34W −
= 12
, 7
= • Koefisien perpindahan panas konveksi rata - rata
[ ]
2 .
. .
in out
b s
in out
p a
T T
T A
T T
C m
h +
− −
=
[ ]
2 K
1 ,
99 2
5 ,
08 3
K 1
, 33
3 x
m 121
, K
1 ,
99 2
5 ,
08 3
kg.K J
2426 ,
005 1
x s
kg 006554
,
2
+ −
− =
.K m
W 468
, 17
2
= • Bilangan Nusselt
¾ Duct Nusselt number
k D
h Nu
h a
. =
m.K W
0,02651131 m
0,1 x
.K m
W 468
, 17
2 2
= 89
, 65
= • Bilangan Reynolds
¾ Duct Reynolds number
commit to user
µ ρ
h
D V
Re .
. =
m.s kg
54 0000186127
, m
0,1 x
s m
0,5 x
m kg
1655994 ,
1
2 3
= 19
, 3131
= • Penurunan tekanan
h g
P .
. ρ
= ∆
m 0012
, s
m 81
, 9
m kg
800
2 3
x x
= Pa
42 ,
9 =
• Faktor gesekan
⎥ ⎥
⎦ ⎤
⎢ ⎢
⎣ ⎡
⎟⎟ ⎠
⎞ ⎜⎜
⎝ ⎛
⎟⎟ ⎠
⎞ ⎜⎜
⎝ ⎛
∆ =
2
2
V ρ
D L
P f
h t
⎥ ⎥
⎦ ⎤
⎢ ⎢
⎣ ⎡
⎟⎟ ⎠
⎞ ⎜⎜
⎝ ⎛
⎟⎟ ⎠
⎞ ⎜⎜
⎝ ⎛
= 2
s m
5 ,
m kg
1655994 ,
1 m
1 ,
m 25
, Pa
9,42
2 3
x 86
, 25
= 2.
Spesimen tanpa sirip pada pumping power = 97,92 W Data hasil pengujian:
Tegangan heater = V
h
= 19 V T
in, rata-rata
=
in
T
= 25,9
o
C = 298,9 K Arus heater =
I
h
= 0,76 A T
out,, rata-rata
=
out
T
= 27,4
o
C = 300,4 K Tegangan fan =
V
f
= 102 V T
base, rata-rata
=
b
T
= 60,3
o
C = 333,3 K Arus fan =
I
f
= 1,2 A Beda tekanan ketinggian fluida manometer = h = 0,4 mm
• Temperatur film
2
out in
f
T T
T +
=
2 K
4 ,
300 9
, 98
2 +
= = 299,65 K
commit to user
• Properti udara ρ
298,9K
= 1,16650326 kgm
3
tabel Incropera
2 4
10 ]
2 10
7 ,
7 8185
, 9
[ x
T T
x x
C
out in
p
+ +
=
−
2 4
10 ]
65 ,
299 10
7 ,
7 8185
, 9
[ x
x x
−
+ =
kg.K J
923 ,
004 1
=
3 2
10 ]
2 10
495 ,
7 7415
, 3
[
− −
+ +
= x
T T
x x
k
out in
3 2
10 ]
65 ,
299 10
495 ,
7 7415
, 3
[
− −
+ =
x x
x
m.K W
026200267 ,
=
6 2
10 ]
2 10
483 ,
4 9934
, 4
[
− −
+ +
= x
T T
x x
out in
µ
6 2
10 ]
65 ,
299 10
483 ,
4 9934
, 4
[
− −
+ =
x x
x
m.s kg
84267 0,00001
=
• Luas penampang melintang saluran udara
b
W H
A .
= m
0,15 .
m 0,075
=
2
m 0,01125
= • Luas total permukaan perpindahan panas
b s
W L
A .
= m
0,15 x
m 0,2
=
2
m 0,03
= • Diameter hidrolik saluran udara
P A
D
h
4 =
b b
W H
W H
+ =
2 .
. 4
m 0,15
m 0,075
x 2
m 0,15
x m
0,075 x
4 +
= m
0,1 =
• Laju aliran panas dari heater
commit to user
ϕ
cos .
I .
V Q
h h
elect
= 1
x A
76 ,
x V
19 =
W 44
, 14
= • Laju aliran massa udara
V A
m .
.
ρ
=
s m
68 ,
x m
01125 ,
x m
kg 1,16650326
2 3
=
s kg
0,00892375 =
• Perpindahan panas konveksi
in out
p conv
T T
C m
Q −
= .
.
K 298,9
- 300,4
x kg.K
J 1004,923
x s
kg 892375
0,00 =
W 45
, 13
= • Heat loss yang terjadi
100 x
Q Q
Q Q
conv conv
elect loss
− =
100 x
3,45W 1
W 45
, 13
4,44W 1
− =
36 ,
7 =
• Koefisien perpindahan panas konveksi rata - rata
[ ]
2 .
. .
in out
b s
in out
p s
T T
T A
T T
C m
h +
− −
=
[ ]
2 K
298,9 4
, 00
3 K
3 ,
33 3
x m
0,03 K
9 ,
98 2
4 ,
00 3
kg.K J
923 ,
004 1
x s
kg 0,0089
2
+ −
− =
.K m
W 289
, 13
2
= • Bilangan Reynolds
¾ Duct Reynolds number µ
ρ
h
D V
Re .
. =
commit to user
m.s kg
0000184267 ,
m 0,1
x s
m 0,68
x m
kg 16650326
, 1
2 3
= 744
, 4304
= • Bilangan Nusselt
¾ Duct Nusselt number
k D
h Nu
h s
. =
m.K 7W
0,02620026 m
0,1 x
.K m
W 3,289
1
2 2
= =
50,72 • Penurunan tekanan
h g
P .
. ρ
= ∆
m 0004
, s
m 81
, 9
m kg
800
2 3
x x
= Pa
1392 ,
3 =
• Faktor gesekan
⎥ ⎥
⎦ ⎤
⎢ ⎢
⎣ ⎡
⎟ ⎟
⎠ ⎞
⎜ ⎜
⎝ ⎛
⎟⎟ ⎠
⎞ ⎜⎜
⎝ ⎛
= 2
∆
2
V ρ
D L
P f
h t
⎥ ⎥
⎦ ⎤
⎢ ⎢
⎣ ⎡
⎟ ⎟
⎠ ⎞
⎜ ⎜
⎝ ⎛
⎟⎟ ⎠
⎞ ⎜⎜
⎝ ⎛
= 2
s m
68 ,
m kg
16650326 ,
1 m
1 ,
m 25
, 3,1392Pa
2 3
x 6559
, 4
= • Unjuk kerja termal pada pin-fin array
p s
a
h h
= η
.K m
W 289
, 13
.K m
W 468
, 17
2 2
=
31447 ,
1 =
commit to user
55
4.3 Analisis Data 4.3.1. Pengaruh Bilangan Reynolds dan Jarak Antar Titik Pusat Sirip
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