2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 135 -
Fig. 6 shows the variation in the average heat transfer
coefficient with the Reynolds number of water in the
multiport minichannel at electrical power input of 64.5-
72.5 W (Fig. 6a) and 114.1-119 W (Fig.6b) for different
water temperature of 20-30 °C. The results indicate that
the heat transfer coefficients increase according to
increases in Reynolds number, especially at low water
temperature conditions. Furthermore, Fig. 6 also shows
the effect of water temperatures on the heat transfer
coefficient. The results show that the increase in water
temperature has significant effect on the decreasing of
heat transfer coefficient.
Reynolds number
400 600 800 1000 1200 1400 1600 1800 2000 2200
Heat transfer coefficient (kW/m
2
K)
0
1
2
3
4
5
6
water temp 20 o C
water temp 25 o C
water temp 30 o C
Power electricinput 64.5-72.5 W D h = 1.2 mm , n = 24 channel
(a)
Reynolds number
400 600 800 1000 1200 1400 1600 1800 2000 2200
Heat transfer coefficient (kW/m
2
K)
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
water temp 20 o C
water temp 25 o C
water temp 30 o C
Power electric input 114.1-119 W D h = 1.2 mm , n = 24 channel
(b)
Fig. 6. The heat transfer coefficient for the electrical power input of (a)
64.5-72.5 W, and (b) 114.1-119 W.
D. Comparison of experimental data with existing
correlations
Figs. 7 shows comparison between the experimental
heat transfer coefficients and those obtained from the
existing correlations proposed by Disttus-Boelter (1930)
[3], Edward et al.(1979) [4], and Chilton colburn (1933)
[2]. Among the existing correlations, the correlation by
Disttus-Boelter (1930), has a relatively good prediction of
heat transfer coefficient, with a mean deviation +10%.
Reynolds number
600
800
1000
1200
1400
1600
1800
heat transfer coefficient (kW/m
2
K)
2
4
6
8
10
12
14
16
18
20
Experimental data
Disttus-Boelter (1930)
Edwards et.al (1979)
Chilton colburn(1933)
( heat flux 7.5-10.4 kW/m
2
T w = 25 o C )
Fig. 7. Comparison of experimental data with existing correlation.
V. C
ONCLUSIONS
This study presents the experimental investigations of
the heat transfer coefficient of water flowing through the
multiport minichannel. The experimental data have been
performed for a wide range of experimental conditions:
Reynolds number from 450 to 1800, heat fluxes from 6-
35 kW/m
2
, water temperature 20 to 30 °C. The majors
finding of this study are summarized as follows:
1.The cooling capacity is strongly affected with the
Reynolds number and the water temperature. It increases
with increasing the Reynolds number, whereas it
inversely propositional to water temperature.
2.According the local heat transfer coefficient, the
heat transfer coefficient of middle side gave the highest
value when compared with the others. Furthermore, 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.
3.According the effects of the relevant parameters on
the average heat transfer coefficient, the mass flux and
water temperature have more significant on the heat
transfer coefficient over the others term.
4.
From comparisons of the experimental data with the
existing correlations. The Distus-Boelter (1930)
correlation give the best predictions with the mean
deviation of 10%, while the Edward et al. (1979)
correlation is satisfactory predicted all of the data and the
correlation of Chilton colburn(1933) fails to predict.
A
CKNOWLEDGMENT
The authors would like to express their appreciation to
the Graduated School, and the Research and
Development Institute, Thaksin University for providing
financial support for this study.
R
EFERENCES
[1] Adams, T.M., Abdel-Khalik S.I., and Jeter, S.M.,
An
Experimental Investigation of Single-phase Forced
Convection in Microchannels
, Int. J. Heat Mass Transfer,
Vol 41, 1998, pp. 851-857.
[2] Colburn A.P.
Transaction of the AIChE 26,
1933, pp. 174.
