2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
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sides, and each channel have eight of parallel port flow,
so the total number of port is 24. In order to investigate
the heat transfer of each side, the local heat transfer
coefficients were examined and presented in Fig. 5.
Fig. 5 shows the variation of the measured heat
transfer coefficient along the test section (Z/L) at water
temperature of 25
˚C ,
volume flow rate of 2 LPm, and for
different heat flux of 10.8-16.1 kW/m
2
(Fig. 5a), 17.6-
21.3 kW/m
2
(Fig. 5b), 18.9-23.4 kW/m
2
(Fig. 5c), and
24.4-30.3 kW/m
2
(Fig. 5d),respectively.
Waterinlet
Wateroutlet
h
left0.0
h
left0.5
h
left1.0
h
middle0.0
h
middle0.5
h
middle1.0
h
right0.0
h
right0.5
h
right1.0
Fig. 4. The local area of the measured heat transfer coefficient along
the test section.
water flow 2 LPM heat flux 10.8-16.1 kW/m 2
X/L
0.0
0.2
0.4
0.6
0.8
1.0
1.2
local heat transfer coefficient (kW/m
2
K)
20
30
40
50
left
middle
right
D h = 1.2 mm , n = 24 channel
T w = 25 o C
(a)
water flow 2 LPM heat flux 17.6-21.3 kW/m 2
X/L
0.0
0.2
0.4
0.6
0.8
1.0
1.2
15
20
25
30
35
40
left
middle
right
D h = 1.2 mm , n = 24 channel
T w = 25 o C
local heat transfer coefficient (kW/m
2
K)
(b)
water flow 2 LPM heat flux 18.9-23.4 kW/m 2
X/L
0.0
0.2
0.4
0.6
0.8
1.0
1.2
10
15
20
25
30
left
middle
right
local heat transfer coefficient (kW/m
2
K)
D h = 1.2 mm , n = 24 channel
T w = 25 o C
(c)
water flow 2 LPM heat flux 24.4-30.3 kW/m 2
X/L
0.0
0.2
0.4
0.6
0.8
1.0
1.2
10
15
20
25
30
left
middle
right
D h = 1.2 mm , n = 24 channel
T w = 25 o C
local heat transfer coefficient (kW/m
2
K)
(d)
Fig. 5. The local heat transfer coefficient for heat flux of (a) 10.8-16.1
kW/m
2
, (b) 17.6-21.3 kW/m
2
, (c) 18.9-23.4 kW/m
2
and (d) 24.4-
30.3.
It is illustrated in Fig. 5 that the heat transfer
coefficient of middle side is found to be the highest for
each z-location compared with the heat transfer
coefficient at the left and the right sides. This is due to the
flow rate of middle side is higher than those of the others
side. This figure also shown that the distribution of heat
transfer coefficient along the test section is h
Z/L=0.05
>
h
Z/L=0.95
> h
Z/L=0.05.
The better heat transfer coefficient at
the inlet of the test section is considered as a result of
more turbulent due to transition region as the same way at
the outlet of the test section.
C. Heat transfer coefficient
In order to investigate the overall performance of the
heat exchanger, average heat transfer coefficients are
required. So, the heat transfer coefficients of water in an
extruded multiport minichannel are examined as an
average value over the entire length. The relevant
parameters such as mass flux, and water temperature for
the average heat transfer coefficient are examined and
discussed. The experiments were conducted by varying
the mass flux while the water temperatures, heat flux of
each condition were kept constant.
