Experimental investigation of flow condensation heat transfer in rectangular minichann

1. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM -2014
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
17 – 19, July 2014, Mysore, Karnataka, India
AND TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 5, Issue 9, September (2014), pp. 251-258
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IJMET
© I A E M E
EXPERIMENTAL INVESTIGATION OF FLOW CONDENSATION HEAT
TRANSFER IN RECTANGULAR MINICHANNEL
DODDESHI B C1, VILAS WATVE2, MANU S3, Dr. SANJEEVAMURTHY4
1M.Tech 4th sem, Mechanical Engineering, Adichunchanagiri Institute of Technology, Chickmagalur, India
2Assistant Professor, Department of Mechanical Engineering, Adichunchanagiri Institute of Technology,
Chickmagalur, India
3Assistant Professor, Department of Mechanical Engineering, Sri Siddhartha Institute of Technology, Tumkur, India
4Professor, Department of Mechanical Engineering, Sri Siddhartha Institute of Technology, Tumkur, Karnataka, India
ABSTRACT
Condensation heat transfer coefficients and pressure drops in horizontal rectangular minichannel was measured
using the specially designed aluminium test section with hydraulic diameter of 2mm. The data are reported for steam is a
refrigerant and water as a coolant. The experimental investigation was carried out mass flux range of 88.89 kg/m2s to
177.78 kg/m2s, vapour quality ranges from 20-80% and a saturation temperature of 100°C. The mass flux and vapour
quality were determined to have significant effects on condensation process and also determined to effect of wall
temperature along the channel length, effect of mass flux on pressure drop. The experimental data of condensation heat
transfer coefficients are compared with existing correlation.
Keywords: Condensation, Heat transfer coefficient, Minichannel, Rectangular channel.
1. INTRODUCTION
Minichannel heat exchangers are extensively used in modern heat exchangers of automotive air conditioning
systems as a condenser. The hydraulic diameter of the minichannel heat exchangers are within the range of 200μm to
3mm. Minichannel heat exchangers provide a higher heat transfer performance as compared to conventional heat
exchangers. As a result of its performance, new applications such as those in the field of residential and electronic device
cooling are a important growing issue. However, in spite of their potential usage and present interest, thermal and flow
characteristic behaviours in these minichannel are not well understood, and limited studies have been performed. Hence,
determination of the condensation heat transfer coefficient and the pressure drop across minichannel is of great attention.
In this study, experimentally determine the condensation heat transfer coefficients and pressure drops in rectangular
single minichannel with hydraulic diameter of 2mm. The test was carried out using steam is a refrigerant and water as a
coolant in the horizontal rectangular channel and of saturation temperature 100°C.The effect of wall temperature along
the channel length, effect of vapour quality and mass flux on flow condensation, effect of mass flux on pressure drop
were calculated.
There are a few previous studies on the condensation heat transfer of refrigerants and the effect of mass flux on
pressure drop inside a rectangular minichannel was experimentally investigated. Jeong Seob Shin Moo Hwan Kim [1]
experimentally studied flow condensation heat transfer inside circular and rectangular minichannel. The results showed
the influence of mass flux and vapour quality for all the test sections. The condensation Nusselt numbers increased with
increasing vapour quality and mass flux due to the increase of higher vapour shear force. Also, the Nusselt number
became more sensitive to the mass flux as the average vapour quality increased. M.J. Wilsona et al., [2] experimentally

2. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
investigated the condensation in horizontal smooth and micro finned copper tubes having a diameter of 9 mm, were
successively flattened in order to determine changes in flow field characteristics as a round tube is altered into a flattened
tube profile. Refrigerants R134a and R410A was investigated mass flux range of 75 to 400 kg m-2 s-1 and a quality ranges
from 10–80%. The experimental results showed, increasing mass flux and vapour quality increases the heat transfer
coefficients due to the flattened tube may alter the flow field in a manner that increases the heat transfer without
changing the flow field configuration.
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J.R.Thome et al., [3] investigated condensation in horizontal tubes, the simulation was developed to predict the
trend. The trend was based on heat transfer coefficient as a function of vapour quality and mass velocity. The results
showed, at the lowest flow rate of 30 kg m-2 s-1 the flow was in the stratified regime from inlet to outlet and the heat
transfer coefficient falls off slowly with decreasing vapor quality due to surface tension. Zhongyu Guo N. K. Anand,
[4] experimentally studied condensation for R-410A in a Rectangular channel. A two-phase loop to measure the
condensation heat transfer coefficient was designed, built, and calibrated. The test section was 3 m long horizontal
rectangular brass (63% Cu, 37% Zn by mass) tube 12.7 mm wide and 25.4 mm high. The results showed that average
condensation heat transfer coefficient decreases with a decrease in vapour quality due to the liquid phase increases with
increasing condensation M. M. Rahman, et al., [5] experimentally investigated condensation heat transfer enhancement
through inner grooved copper tubes in a heat exchanger. Experiment was conducted at mass flux variations of 200 to 600
kg/m2 and the vapor qualities ranged from 90% at the inlet to 20% at the outlet and R-22 was used as the working fluid.
The result showed that, condensation heat transfer coefficient and pressure drop are found to be increased as the mass
flux is increased due to increasing in flow mean velocity. S.N. Sapali and Pradeep A.Patil [6] experimentally investigated
two phase heat transfer coefficients and pressure drops of R-404A for different condensing temperatures in a smooth
(8.56 mm ID) and micro-fin tube (8.96 mm ID). The experiment was performed at average saturated condensing
temperatures ranging from 35°C to 60°C. The mass fluxes are at a range of 90 and 800 kg m-2s-1. The experimental
results showed that, the average heat transfer coefficients and pressure drop increases with mass flux but decreases with
increasing condensing temperature.
Todd M. Bandhauer and Akhil Agarwal Srinivas Garimella [7] developed a model for predicting heat transfer
during condensation of refrigerant R134a in horizontal micro channel was presented. The result showed that, the heat
transfer coefficient increases with increasing vapour quality and mass flux due to increase of shear stress and thin liquid
film that reduces the thermal resistance. Melanie Derby et al., [8] experimentally investigated condensation heat transfer
of R134a in 1mm square, triangular, and semi-circular mini-channels. The results showed, for all three test sections heat
transfer coefficients increased with increasing mass flux and vapour quality due to experimental uncertainties or an effect
of the relative magnitude of surface tension, shear, and gravity forces. A.S. Dalkilic, S. Wongwises [9] conducted an
experiment to investigate the condensation on zeotropic refrigerants over the wide range of mass flux in horizontal tubes.
The results showed that, heat transfer coefficient increases with increasing in the mass flux and quality in annular flow
due to increased shear stress and thinner liquid film than in other flow regimes. Al-Hajeri et al., [10] investigated the heat
transfer performance during condensation of R-134a inside helicoidal tubes. The refrigerant side heat transfer coefficient
and overall heat transfer coefficient decrease as the saturation temperature increases due to surface tension effect.
Gil Goss júnior et al., [11] performed experiments on heat transfer coefficient and pressure drop during
condensation of R-134a inside parallel micro channels. The heat transfer coefficient is independent of the mass velocity.
The dependence of heat transfer coefficient on the vapor quality is not clear for vapor quality greater than 0.6. It is
important to note that, the fluid pressure is directly proportional to the mass velocity and the heat transfer coefficient
increases with the rise in pressure, and the opposite occurs due to the effect of mass flow rate. Somchai wongwises,
Maitree polsongkram [12] the two phase heat transfer coefficient and pressure drop of pure HFC-134a condensing inside
a smooth helically coiled concentric tube in tube heat exchanger are experimentally investigated. The experimental result
showed that, pressure drop is increased with increasing vapour quality and mass flux due to increase of mass flux will
increase the vapour velocity. Hence, the shear stress at the interface of the vapour and liquid film increases as a result
pressure drop increases.
2. FABRICATION OF MINICHANNEL CONDENSER
A aluminum bar of cross section (150mm X 50mm) is fabricated for single rectangular minichannel of hydraulic
diameter 2mm and length of 96mm was cut on top and bottom sides of the rectangular block as shown in Fig.1(a), (b).
The top and bottom of the rectangular block was covered with the help of cover plates. Two cover plates are provided
with two drilled holes for the inlet and outlet of the working fluid and coolant. The channel plate and cover plate is
tightened by using bolt and nuts. The entire shape of the test specimen was machined by C.N.C milling machine.

3. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
253
(a) Rectangular channel for
refrigerant side
(b) Rectangular channel for
coolant side
Fig.1: (a), (b): Fabrications of rectangular channel test section
Table 1: Specification of the test specimen
Rectangular channel geometry
Width Depth Hydraulic
diameter
Length
3mm 1.5mm 2mm 96mm
3. EXPERIMENTAL SETUP
Fig.2: Experimental Setup
The experimentation involves two cycles they are refrigerant cycle and coolant cycle. The refrigerant cycle
consists of pump, digital pressure gauge and thermocouple. In this refrigerant cycle, two major components are arranged
in series as shown in Fig.2 and they are preheater and minichannel condenser. The experimentation was carried out using
steam is a refrigerant and water as a coolant in the condenser. The preheater is completely insulated with the glass wool.
Fig.2 shows the test line assembled for the experimental investigation of flow condensation in single rectangular
minichannel. The booster pumps are used to circulate the refrigerant and coolant through the test line. The generated
vapour is condensed in the test section. The five thermocouples are inserted between the refrigerant and the coolant side
in the test section as shown in Fig.2. The properties like temperature, pressure and flow rate are measured at various
points during testing. Finally the condensate from the condenser was measured using the chemical burette.

4. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
254
4. OPERATING PARAMETERS
Table 2: Operating Conditions
Sl.N
o
Saturati
on
tempera
ture
(°C)
Saturation
pressure
(bar)
Mass
flow
rate of
water
Mass
flow
rate
of
coola
nt
Inlet
Vapour
quality
g/s
1
100 1.01325
0.8
1
0.2/0.4/
0.6/0.8
2 0.6
0.2/0.4/
0.6/0.8
3 0.4
0.2/0.4/
0.6/0.8
5. DATA REDUCTION
The total heat input to the preheater is given by.

5. (1)
Where,
m- Mass flow rate of the water (kg/sec)
hfg - latent heat of vaporization (kJ/kg)
Cp - Specific heat of water (kJ/kg °C)
Tsat - Saturated temperature of water (°C)
Tinlet - Inlet cold water temperature (°C)
- Dryness fraction
Heat absorbed by cooling water (Q c) is given by;

6. (2)
Where,
mc - Mass flow rate of coolant (kg/s)
Cp - Specific heat of cooling water (kJ/kg °C)
Tco - Outlet coolant temperature (°C)
Tci - Inlet coolant temperature (°C)
Heat transfer coefficient is given by;
h=

7. ! (3)
Where,
Qc- Heat absorbed by coolant (W)
Ts - Saturated temperature of water (°C)
Twavg - Average wall temperature (°C)
A - Surface area of the channel (m2)
= (w + 2 a) × L
w - Width of the channel (m)
a - Depth of the channel (m)
L - Length of the channel (m)

8. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
6.1 Effect of inlet vapour quality on heat transfer coefficient
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6. RESULT AND DISCUSSIONS
Fig.3: Effect of mass flux and inlet vapour quality on heat transfer coefficient
Fig.3 shows the effect of mass flux and inlet vapour quality on the heat transfer coefficient for a given
condensation temperature of 100°C. In rectangular channel cross section, heat transfer coefficient increased with a
increase in vapour quality due to the increase in shear stress at the wall surface and thinning of the liquid film that
decreases the thermal resistance and also heat transfer coefficient increased with the increasing mass flux due to an
increase in flow mean velocity.
6.2 Effect of wall temperature along the channel length for Rectangular cross section
(a) (b)
(c) (d)
Fig.4: (a), (b), (c), (d): Effect of wall temperature along the rectangular channel length for varying mass flux

9. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
256
Fig.4 (a), (b), (c), (d) shows the variation of wall temperature along length of the rectangular channel. From the
initial observation of the result, it clearly indicates there is a decrease in the trend of the wall temperature along the
channel length. In addition to that it is evident from the Fig.4 the highest wall temperatures was found at highest mass
flux of 177.78 kgm-2s-1. This trend was observed for all the vapour quality. This is due to the low temperature gradient on
the coolant side and increase in the Reynolds number. This increase in the Reynolds number is due to increase in the
mass velocity of refrigerant.
6.3 Effect of mass flux on pressure drop for Rectangular channel
Fig.5: Effect of mass flux on the pressure drop for rectangular channel
The effect of mass flux on the frictional pressure drops during the condensation as shown in Fig.5. The Fig.5
represents the relationship between the frictional pressure drop and the averaged inlet vapour quality at a fixed saturation
temperature of 100°C. The two phase frictional pressure drop is obtained by subtracting pressure at the inlet and outlet
manifold of the channel. It can be seen that frictional pressure drop is increased with increasing vapour quality due to
higher velocity of vapour flow causes more shear stress at the interface of the vapour and liquid film as a result pressure
drop increases.
6.4 Comparison with correlation
Fig.6: Comparison with condensation correlation for rectangular channel
From the Fig.6 it is observed that experimental data are compared with the existing condensation correlation
Chato (1962) developed for both the mini and macro scale. The correlations serve as tools for general comparison;
specific comparisons are not possible as the following correlations were developed for uniformly cooled circular and non
circular tubes. The correlation developed by the Chato (1962) was best predicted with the obtained experimental data.
7. CONCLUSION
The flow condensation heat transfer coefficient can be measured in horizontal single rectangular channel test
specimen with hydraulic diameter of 2mm. The test was carried by varying mass flux 88.88 kg/m2s, 133.33 kg/m2s and
177.78 kg/m2s and vapour quality ranges from 0.2 to 0.8 at a fixed saturation temperature of 100 °C. The experimental

10. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
result was obtained, as the mass flux and vapours quality increases there is an increase in condensation heat transfer
coefficient and pressure drop. And the obtained experimental data was best predicted with the existing correlation.
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ACKNOWLEDGEMENT
Am appreciate Mr. VILAS WATVE, Assistant professor in AIT, chickmagalur and Mr. MANU S, Assistant
professor in SSIT, Tumkur for providing me them valuable guidance and my greatfull parents for their support.
NOMENCLATURE
m-Meter
w-Watt
Tsat - Saturation temperature
mc- Mass flow rate of coolant in (kg/s)
Cp- Specific heat of coolant in (kJ/kg °c)
Tco and Tci -Outlet and inlet temperature of coolant in (°c)
Re-Reynolds number
Co-Condensation number
Dh-Hydraulic diameter (m)
hf - Inlet enthalpy of the water in to the sink(kJ/kg)
hfg -Latent heat of vaporization(kJ/kg)
Qa=I*V is the heat to the heater (w)
Qc-Heat removed by refrigerant in (w)
A- Area of surface in (m2)
a- Depth of the channel in (m)
L- Length of the channel in (m)
8. REFERENCES
Book
[1] Jeong Seob Shin Moo Hwan Kim, “An Experimental Study of Flow Condensation Heat Transfer Inside
Circular and Rectangular Mini-Channels”, Heat Transfer Engineering, Vol. 26:3, 2005, pp. 36-44.
Journal paper
[2] M.J. Wilsona, T.A. Newella, J.C. Chatoa, C.A. Infante Ferreira, “Refrigerant charge, pressure drop, and
condensation heat transfer in flattened tubes”, International Journal of Refrigeration Vol.26, 2003, pp. 442–451.
[3] J.R.Thome,J.ElHajal, A. Cavallini, “Condensation in horizontal tubes, part 2: new heat transfer model based on
flow regimes”, International Journal of Heat and Mass Transfer Vol.46, 2003, pp.3365–3387.
Research paper
[4] Zhongyu Guo N. K. Anand, “Condensation of R-410A in a Rectangular Channel”, HVACR Research,
Vol.5:2, 1999, pp. 97-122.
International conference paper
[5] M. M. Rahman, Malaysia Y. M. Ling, Malaysia G.W.Soon, Malaysia, “An Experimental Investigation of
Condensation and Evaporation Heat Transfer of R-22 inside Internally Grooved Copper Tubes”, ICCBT-F-(04),
2008, pp.35-48.
Journal Paper
[6] S.N. Sapali, Pradeep a.Patil, “two-phase condensation heat transfer coefficients and pressure drops of R-404a for
different condensing temperatures in a smooth and micro-fin tube”, International Journal of Engineering Science
and Technology Vol.1(2), 2009, pp.43-58.
[7] Todd M. Bandhauer, Akhil Agarwal Srinivas Garimella, “Measurement and Modeling of Condensation Heat
Transfer Coefficients in Circular Microchannels”. http://www.asme.org/terms/Terms_Use.cfm.2006.

11. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
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[8] Melanie Derby, Hee Joon Lee , Yoav Peles , Michael K. Jensen, “Experimentally investigated Condensation heat
transfer in square, triangular, and semi-circular mini-channels”, International Journal of Heat and Mass Transfer
Vol.55, 2012, pp 187–197.
[9] A.S. Dalkilic, S. Wongwises, Intensive literature review of condensation inside smooth and enhanced tubes,
International Journal of Heat and Mass Transfer Vol.52, 2009, pp. 3409–3426.
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[10] M.H. Al-Hajeri, A.M. Koluib, M. Mosaad and S. Al-Kulaib Heat transfer performance during condensation of
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of R-134a inside parallel micro channels”, Proceedings of the ASME/JSME 2011 8th Thermal Engineering Joint
Conference AJTEC2011 March 13-17, 2011, Honolulu, Hawaii, USA.
Books
[12] Somchai Wongwises , Maitree polsongkram, Condensation heat transfer and pressure drop of HFC-134a in a
helically coiled concentric tube-in-tube heat exchanger, Fluid Mechanics, Thermal Engineering and Multiphase
Flow Research Lab.(FUTURE), Department of Mechanical Engineering, King Mongkut's University of
technology Thonburi, Bangmod, Bangkok 10140, Thailand.