EFFECT ON BOILING HEAT TRANSFER OF HORIZONTAL
SMOOTH MICROCHANNEL FOR R-410A AND R-407C
Agus Sunjarianto Pamitran, Kwang-Il Choi
Graduate School, Yosu National University, Yosu 550-749, Korea
Jong-Taek Oh*
Dept. of Refrigeration Engineering, Yosu National University, Yosu 550-749, Korea
Hoo-Kyu Oh
Dept. of Refrigeration and AC Engineering, Pukyong National University, Busan 608-739, Korea
Abstract
An experimental study of boiling heat transfer with refrigerants R-410A and R-407C is presented. The present paper
is focused on pressure drop and boiling heat transfer coefficient of the refrigerants inside a horizontal smooth
microchannel. To evaluate the diameter size effect on pressure and heat transfer characteristics, microchannels with
inner diameters of 1.5mm and 3.0mm and with lengths of 1500mm and 3000mm respectively are used. The pressure
drop increases with mass flux and heat flux for both inner tube diameters and for both the refrigerants. The pressure
drop of R-407C is higher than that of R-410A, but the heat transfer coefficient of R-410A is higher than of R-407C
at the low quality region. The heat transfer coefficient in the tube with an inner diameter of 1.5mm is higher than
that of 3.0mm diameter tube at the low quality region. The comparison of heat transfer coefficient between the result
of this study and the predictions of some previous correlations shows a high percentage of deviation.
Keywords: R-410A, R-407C, pressure drop, heat transfer coefficient, microchannel
Introduction
2.92mm, showed a significant effect of the inner tube
diameter, that is, the slug flow pattern regime occurs
Over the last two decades many studies of heat transfer
over a much larger parameter range, and nucleate
characteristics of refrigerant mixtures have been
boiling mechanisms dominate the heat transfer in the
performed. Processes involving boiling of refrigerant
small diameter tube. Peng and Peterson (1996), by
mixtures in a compact heat exchanger are extensively
using a binary mixture and 0.133mm to 0.367mm
encountered in industry. In order to enhance the
hydraulic diameters, concluded that the transition Re
compact heat exchanger performances, several
(Reynolds number) and the transition range (Recr)
investigations on boiling heat transfer in microchannels
decrease with decreasing microchannel dimensions.
have been reported. Wambsganss et al. (1993), by
Study of boiling heat transfer by using refrigerant
using R-113 in a microchannel with inner diameter of
mixtures has also been presented by Zhang et al.
(1996). They showed that the mass transfer resistance
* Corresponding Author. Tel.: +82-61-659-3273;
fax: +82-61-659-3003, E-mail: ohjt@yosu.ac.kr
near the interface significantly reduces the heat transfer
International Congress of Refrigeration 2003, Washington, D.C.
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coefficient of the mixture, especially in low quality and
low mass flux regions. Jung et al. (1989) concluded
that mass transfer resistance was responsible for the
heat transfer degradation from the ideal value, but for
low vapor-liquid composition difference, mass transfer
becomes negligible in the convective region. But these
proposed studies are only valid for evaporated tube
with moderate inner diameters, namely experimental
data of the boiling characteristics for a microchannel is
limited. Also experimental studies of the effect on
boiling heat transfer of horizontal microchannels is
Fig. 1 Experimental test facility
rarely found. Hence in this study, the effect of pressure
drop and boiling heat transfer coefficient of horizontal
inner tube diameters of 1.5mm and 3.0mm is disclosed.
1. Experimental Apparatus and Methods
1.1 Refrigerant loop
The experimental facility is schematically shown in Fig
1, and consists mainly of a refrigerant pump, mass flow
meter, preheater, evaporator, condenser, subcooler and
Fig. 2 Experimental test section
receiver. Flow rate of the refrigerant is controlled by a
variable A.C output motor controller. The mass flow
lengths of 1500mm and 3000mm, respectively. It was
meter was placed to measure the refrigerant flow rate.
assumed uniformly and constantly heated directly
To control quality at the test section inlet, the preheater
through the tube wall. The rate of input voltage E and
was installed. For evaporation at the test- section, a
current I were adjusted in order to control the input
certain heat flux was conducted from a variable A.C
power to determine the applied heat flux, which was
voltage controller. Subsequently vapor refrigerant from
measured by a standard multimeter.
the evaporator was condensed in the condenser and
The test section was isolated by rubber and foam. The
subcooler, and thence, supplied to the receiver before it
outside tube’s wall temperatures were measured at
was pumped through loop.
every 100 mm axial intervals along the tube’s length
from the start of the heated length at the inlet with two
1.2 Test section
copper-constantan thermocouples oriented to measure
Fig. 2 shows a detail of the test-section. The test-
temperature at the top and bottom side of each interval.
section was made of stainless steel smooth tubes, with
The junctions of copper-constantan thermocouples
inner diameters of 1.5mm and 3.0mm and heated
were attached to the surface and were electrically
International Congress of Refrigeration 2003, Washington, D.C.
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insulated.
The differential pressure was measured by a bourdon
tube type pressure gauge and differential pressure
transducer at the inlet, middle and outlet of the test
section. To visualize the flow, a sight glass with the
same inner tube diameter as the test section was
installed at the inlet, middle and outlet of the test
Table 1 Experimental conditions
Refrigerants
R-407C, R410A
Test Section
Horizontal smooth
microchannel
Inner Diameter (mm)
1.5, 3.0
Tube Length (mm)
1500, 3000
Mass Flux (kg/m2s)
300 – 600
Heat Flux (kW/m2)
5 – 20
Quality
0.0 – 1.0
Inlet temperature (oC)
10
section.
1.3 Testing procedure
The experimental conditions performed in this test are
shown in tables 1 and 2. It underwent steady-state
conditions. The temperature data were recorded by
using Darwin DAQ32 Plus logger R9.01 program, and
the flow rate data were recorded by Micro Motion
ProLink Software version 2.41.
Table 2 Experimental conditions of the convective
boiling heat transfer test
G[kg/m2s]
q[kW/m2] q[kW/m2]
G[kg/m2s]
300
5, 10,
5
300, 400,
15, 20
500, 600
400
5, 10,
10
300, 400,
15, 20
500, 600
500
5, 10,
15
300, 400,
15, 20
500, 600
600
5, 10,
20
300, 400,
15, 20
500, 600
The local heat transfer coefficients, at position z along
2. Results and Discussion
the length of the test-section, were defined as
h
q
Twi  Ts
(1)
2.1 Effect of inner diameter on pressure drop
Fig. 3 shows the pressure drop of R-410A per unit
where the heat flux q was calculated by
length of the test sections with inner diameters of
Q
q
Do z
(2)
increases with mass flux and heat flux, with increasing
where Q was the electrical input
Q  EI
(3)
The inside tube wall temperature Twi was determined
considering radial thermal conduction through the wall,
D
Q
Twi  Two 
ln o
2kz Di
(4)
The local saturation temperature was calculated from
the measured saturation pressure and quality x for
given
overall
composition.
3.0mm and 1.5mm. The figure shows the pressure drop
The
quality
x
at
measurement locations z were determined based on
pressure drop at the higher mass flux and heat flux. The
pressure drop for the tube with inner diameter of
1.5mm is higher than that of the 3.0mm one, under the
heat flux of 5kW/m2, whereas it has no relation with
the test conditions of under 10kW/m2.
Fig. 4 shows the pressure drop of R-407C per unit
length of the test section, with various mass flux and
heat flux, for both inner diameters. As is shown in the
figure, the pressure drop increases considerably with
increasing mass flux and heat flux, and the increase
thermodynamic properties
x
i  if
i fg
rate of pressure drop in inner diameter of 1.5mm, at the
(5)
condition of similar mass flux and heat flux rate, is
International Congress of Refrigeration 2003, Washington, D.C.
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three times higher than of 3.0mm. Therefore, as
In Fig. 6, the effect of heat flux on pressure drop is
pressure drop increases with decreasing inner diameter,
higher for R-410A than R-407C. Also, it is shown that
we must consider an important factor of pressure drop
pressure drop increases with increasing mass flux and
when designing a heat exchanger using microchannels.
heat flux for both the refrigerants at all mass flux test
The effect of mass flux on pressure drop is more
conditions.
clearly depicted in Fig. 5. Pressure drop increases with
Heat flux, mass flux and inner diameter give different
mass flux and heat flux increase for both refrigerants at
effects on pressure drop. The effect of mass flux and
all heat flux rate test conditions. It is shown that the
inner diameter on pressure drop is higher for R-407C
effect of mass flux on pressure drop of R-407C is
than R-410A, whereas the effect of heat flux is not.
higher than on R-410A.
Pressure drop increases with increasing mass flux and
Figure 3 Effect of tube diameter on pressure drop at
Figure 5 Effect of mass flux on pressure drop at
different mass flux and heat flux for R-410A
Figure 4 Effect of tube diameter on pressure drop at
different mass flux and heat flux for R-407C
various heat fluxes for 3.0mm Di
Figure 6 Effect of heat flux on pressure drop at
various mass fluxes for 3.0mm Di.
International Congress of Refrigeration 2003, Washington, D.C.
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heat flux for both inner tube diameters. The pressure
coefficient, at test conditions of constant heat flux and
drop is much more decreased with inner diameter size
inner diameter of 3.0mm. The figure shows that the
decrease for R-407C, in other words the effect of inner
effect of mass flux on heat transfer of R-407C is higher
diameter on pressure drop is higher for R-407C.
than on R-410A. The heat transfer coefficient increases
with increasing mass flux for R-407C at all test
2.2 Effect of heat flux and mass flux on heat
conditions. For R-410A, the higher mass flux does not
transfer coefficient
always mean there is a higher heat transfer coefficient,
At the low quality region under test conditions of
but it depends on heat flux and inner diameter. The
varying heat flux and constant mass flux for similar
effect of mass flux on the heat transfer coefficient, in
inner diameters, it is shown that the higher heat flux
the case of comparison of both refrigerants at the same
yields to the higher heat transfer coefficients for both
test condition, is somewhat similar as the effect of heat
refrigerants, whereas at the high quality region, the heat
flux on heat transfer coefficient. Namely, the heat
transfer coefficient shows a different trend. Fig. 7
transfer coefficient of R-407C is lower than of R-410A
shows the effect of heat flux on the heat transfer
at the low quality region, as is depicted in Fig. 8. The
coefficient for the tube with an inner diameter of
maximum value of the heat transfer coefficient, which
1.5mm. The figure shows that the heat transfer
is the dry out point, under all test conditions, appears
coefficient of R-410A is higher than of R-407C. The
earlier for R-410A; this being similar to the trend with
maximum value of the heat transfer coefficient, which
the effect of heat flux on the heat transfer coefficient,
is the dry out point, at all test conditions appears earlier
as cited above.
for R-410A. The figure shows that the effect of heat
flux on the heat transfer coefficient of R-410A is higher
2.3 Effect of inner diameter on heat transfer
than on R-407C, especially before the dry out point.
coefficient
Fig. 8 shows the effect of mass flux on the heat transfer
Fig. 9 shows the effect of inner diameter on the heat
Figure 7 Effect of heat flux on heat transfer coefficient
at constant mass flux for 1.5mm Di.
Figure 8 Effect of mass flux on heat transfer
coefficient at constant heat flux for 3.0mm Di.
International Congress of Refrigeration 2003, Washington, D.C.
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Fig. 10 shows the effect of inner diameter on heat
transfer coefficient, under test condition of a constant
mass flux of 300kg/m2s and heat flux of 15kW/m2, for
R-407C. As shown in the figure, the heat transfer
coefficient increases with increasing quality for both
inner tube diameters. The difference of the heat transfer
coefficient, between inner diameter of 3.0mm and
1.5mm, is small at the start of evaporation, but after a
quality of 0.2, the heat transfer coefficient of the tube
with an inner diameter of 1.5mm is higher than for
Figure 9 Effect of inner diameter on heat transfer
coefficient at constant mass flux of
300kg/m2s and heat flux of 10kW/m2 for R410A
3.0mm, and at a quality of 0.7 the difference reaches
more than 50%. The heat transfer coefficient of both
inner diameters decreases rapidly by dry out, at a high
quality of more than 0.7.
2.4 Heat transfer coefficient comparison with
previous correlations
The heat transfer coefficient in this study, in a quality
range of 0.0 to 0.9, is compared with the predicted heat
transfer coefficient of Chen (1963a), Gungor-Winterton
(1986) and Jung et al. (1989) correlations. All
comparisons show high deviation, in both tubes with
diameters of 3.0mm and 1.5mm. Fig. 11 and 12 depict
the R-407C heat transfer coefficient of the present
Figure 10 Effect of inner diameter on heat transfer
coefficient at constant mass flux of
300kg/m2s and heat flux of 15kW/m2 for R407C.
study against the predicted one of the GungorWinterton correlation, in tubes of 3.0mm and 1.5mm
inner diameter, respectively. The figures show that the
transfer coefficient for constant mass flux of 300kg/m2s
predicted heat transfer coefficient with the smaller
and heat flux of 10kW/m2 for R-410A. As shown in the
inner diameter is higher than of the larger one, this
figure, the increase of the local heat transfer coefficient
for both inner diameters is low with increasing quality
in the range of qualities from 0.0 to 0.5, but the heat
transfer coefficient in the tube with an inner diameter
of 1.5mm increases by about 40% higher than in that of
the 3.0mm one, till dry out occurs at a quality of 0.7.
occurring for both refrigerants.
Comparison between the heat transfer coefficient of
this study and of the predicted one by the Jung et al.
correlation, in tubes with inner diameters of 3.0mm and
1.5mm for R-410A, is depicted in Figs. 13 and 14,
respectively. High deviation is clearly shown in the
figures, and the deviation in the tube with an inner
International Congress of Refrigeration 2003, Washington, D.C.
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Figure 11 Comparison between experimental and
predicted heat transfer coefficient of
Gungor-Winterton correlation with 3.0mm
Di for R-407C.
Figure 13 Comparison between experimental and
predicted heat transfer coefficient of Jung et
al. correlation with inner diameter of
3.0mm for R-410A.
Figure 12 Comparison between experimental and
predicted heat transfer coefficient of
Gungor-Winterton correlation with 1.5mm
Di for R-407C
Figure 14 Comparison between experimental and
predicted heat transfer coefficient of Jung et
al. correlation with inner diameter of
1.5mm for R-410A.
Table 3 Percentage of deviation of heat transfer coefficient comparison between the previous
present data
Previous Correlations
Inner tube
Refrigerant
Chen
Gungor-Winterton
diameter (mm)
M
A
M
A
3.0
34.86
-22.49
39.09
37.29
R-410A
1.5
98.71
73.13
175.67
172.71
3.0
48.34
-6.12
63.08
57.02
R-407C
1.5
67.84
51.03
145.57
145.57
M  Mean Deviation 
1 n h pred  hexp 100
1 n h pred  hexp 100
, A  Average Deviation  

n 1
hexp
n 1
hexp
International Congress of Refrigeration 2003, Washington, D.C.
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correlation and the
Jung et al.
M
A
71.84
52.66
251.73
243.60
70.17
68.51
183.08
181.64
diameter of 1.5mm is higher than for 3.0mm.
The comparison of the heat transfer coefficient
Table 3 shows the comparisons for the percent
between this study and the predicted of correlations of
deviation. It is clear that the deviation of the smaller
Chen, Gungor-Winterton and Jung et al. shows high
inner diameter is higher than for the bigger one, and the
deviation both in tube diameters of 3.0mm and 1.5mm.
deviation of R-407C is higher than of R-410A. The
The predicted heat transfer coefficient with inner
predicted heat transfer coefficient of the Chen
diameter of 1.5mm is higher than of 3.0mm, for both
correlation is better than of the others. The high
the refrigerants. The deviation of R-407C is higher than
deviation shows that the previous correlations are over-
R-410A. The high deviation shows the necessity to
predicting for both refrigerants inside the small
develop a new correlation for this purpose.
diameter tube, therefore it is needed to develop a new
correlation for this purpose.
Acknowledgements-The authors wish to acknowledge
that this wok was supported by the Ministry of
Concluding Remarks
Maritime Affairs & Fisheries of Korea (KMI Grant
No.20010144) and Reitechnology Co.
The effects of inner diameter on pressure drop and the
References
boiling heat transfer coefficient of R-410A and R-407C
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1.
increase of either both mass flux and heat flux, in both
inner diameters of 1.5mm and 3.0mm. Pressure drop of
R-407C is higher than of R-410A, in the same
experimental condition. Under test conditions of
2.
constant mass flux and heat flux, the increasing of
pressure drop of R-407C with inner diameter of 1.5mm
is three times higher than that of 3.0mm. The effect of
3.
inner diameter on pressure drop, by using working
fluid of R-407C, is higher than of R-410A.
The heat transfer coefficients with inner diameter of
4.
1.5mm increase over 40% higher than those of 3.0mm
for R-410A. In test with R-407C under experimental
5.
condition of constant mass flux and heat flux, the heat
transfer coefficients with inner diameter of 1.5mm
increase by about 50% higher than of 3.0mm, at a
6.
quality of 0.7. The heat transfer coefficient of R-410A
is higher than R-407C at the low quality region. Dry
out occurs earlier on R-410A in both the inner
diameters.
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International Congress of Refrigeration 2003, Washington, D.C.
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