Experimental investigation of flow condensation in 'v' shaped minichannel

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Special Issue: 03 | May-2014 | NCRIET-2014, Available @ http://www.ijret.org 699
EXPERIMENTAL INVESTIGATION OF FLOW CONDENSATION IN 'V'
SHAPED MINICHANNEL
Doddeshi B C1
, Vilas Watve2
, Manu S3
, T.N.Krishnaiah4
1
M.Tech 4th
sem, Mechanical Engineering, Adichunchanagiri Institute of Technology, Chickmagalur, Karnataka, India
2
Assistant Professor, Department of Mechanical Engineering, Adichunchanagiri Institute of Technology, chickmagalur,
Karnataka, India
3
Assistant Professor, Department of Mechanical Engineering, Sri Siddhartha Institute of Technology, Tumkur, Karnataka,
India
4
Professor, Department of Mechanical Engineering, Adichunchanagiri Institute of Technology, Chickmagalur,
Karnataka, India
Abstract
The measurement of the condensation heat transfer coefficient inside micro and minichannel is still elusive due to the difficulty in
getting accurate result. investigation was carried in a single 'V' shaped channel having hydraulic diameter of 2mm. the experiment
was carried using steam as an refrigerant and water as an coolant. The test was performed by varying mass flux and vapor quality.
The paper concludes that there is a significant effect of mass flux and vapor quality. As the mass flux and vapor quality increases
there is an increase in the heat transfer coefficient and pressure drop.
Keywords: Condensation, Heat transfer coefficient, Minichannel, 'V' Shape
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1. INTRODUCTION
Micro channel and minichannel are increasingly being used to
achieve high heat transfer rates with compact heat exchangers.
Condensation inside small hydraulic diameter channels finds
applications in heat pipes and compact heat exchangers for
electronic equipment, in automotive condensers, and in
refrigeration applications. The adoption of minichannel also
promotes the reduction of the refrigerant charge, which is
favorable to the use of toxic or flammable refrigerants. Micro
channel and Minichannel phase change may differ from the
conventional channels due to differences in the relative
influence of gravity, shear stress and surface tension.
Kandlikar and Grande is classifies the channel are greater than
3mm are conventional channel, 200µm to 3mm are
minichannel, 10µm to 200µm are micro channel, 1µm to
10µm are transitional micro channel, 0.1µm to 1µm are
transitional nano-channel, less than 0.1µm are nano-channel.
There are a few previous studies on the condensation heat
transfer of refrigerants in small diameter tubes. Zhongyu Guo
& N.K. Anand,[1] carried out experiments on condensation
heat transfer of R-410A in a rectangular Channel. The test
section was 3m long horizontal rectangular brass (63% Cu,
37% Zn by mass) tube 12.7 mm wide and 25.4 mm height.
The results showed average condensation heat transfer
coefficient decreases with a decrease in vapor quality due to
the relative content of liquid phase increases with increasing
condensation.M.K. Dobson & J.C. Chato [2] conducted
experimental investigation of condensation using zeotropic
refrigerants over the wide range of mass flux in horizontal
tubes. The test showed 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. J.R. Baird et al.,[3] investigated local
condensation heat transfer rates in fine passages for HCFC-
123 in a 1.95 mm tube, with wall heat flux 60 kWm-2 at 290
kPa. The results showed that significant effect of mass flux on
the heat transfer coefficient. The heat transfer coefficients
increases with increasing mass flux. Yi-Yie Yan and Tsing-Fa
Lin [4] performed experimentation on condensation heat
transfer and pressure drop of refrigerant R-134a in a small
pipe. The result showed, condensation heat transfer coefficient
rises significantly with the mean vapor quality for lower
saturation temperature. S.N. Sapali and Pradeep A.Patil [5]
conducted 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) are
experimentally investigated. The experiment were conducted
at average saturated condensing temperatures ranging from
35°C to 60°C. The mass fluxes are ranges from 90 and 800 kg
m-2s-1. The experimentally obtained results from both smooth
and micro-fin tubes showed the average heat transfer
coefficients and pressure drop increases with mass flux but
decreases with increasing condensing temperature.
Ravigururajan[6] studied the impact of channel geometry on
two phase flow heat transfer characteristics of refrigerant R-
124 in micro channel heat kexchanger. Chen Fang et al.,[7]

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studied the influence of film thickness and cross-sectional
geometry on hydrophilic micro channel condensation. The
investigation result showed, a smaller channel yields higher
condensation heat transfer efficiency than a larger channel.
Baird et al.,[3] conducted an experimental investigation on
condensation of HCFC-123 and R11 in tubes with diameters
of 0.92 and 1.95 mm for a range of mass velocities (70–
600kgm-2s-1), heat fluxes (15–110 kWm-2) and pressures
(1.2-4.1bar). Wu et al., [8] carried an experimental
investigation on heat transfer and flow friction during steam
condensation in trapezoidal silicon micro channels with
diameters of 77.5, 93.0, and 128.5�m. experimental results
showed that the condensation Nusselt number increases with
an increase in the Re, Co (condensation number), and �h/�.
Cavallini et al. [9] measured the heat transfer coefficient for
condensation of R134a and R410a inside multi-port
minichannel having a hydraulic diameter of 1.4 mm. The heat
transfer coefficient was found as high as 16,000Wm-2K -1.
The result showed that, condensation heat transfer will be
enhanced with decreasing hydraulic diameter. The
experimental investigation was carried out in a single 'V'
shaped channel in order to determine and find the effect of
experimental flow condensation heat transfer coefficient and
pressure drop.
2. FABRICATION OF MINICHANNEL TEST
SECTION
Aluminium bar of cross sections (150mm X 50mm) is
fabricated for triangular minichannel of hydraulic diameter
2mm and length of 96mm with single channel were cut on the
rectangular block as shown in Fig-1.
Fig -1: Shows the refrigerant and coolant side of channel cross
section
The top of the mini channel was covered with the cover plate.
Two cover plates(Acrylic glass) are provided with the two
drilled holes of the inlet and outlet for the working fluid and
coolant. The channel and cover plate are joined and tightened
by using bolt and nuts in order to reduce leakage of refrigerant
and coolant side. The entire shape of the test specimen was
machined by C.N.C milling machine.
Table 1: Specifications of the test specimen
Channel geometry
Width Depth Hydraulic diameter Length
3mm 1.5mm 2mm 96mm
3. EXPERIMENTAL SETUP
The experimentation involves two cycles, refrigerant cycle
and coolant cycle. In the refrigerant cycle it consists of pump,
digital pressure gauge, and thermocouples. In this refrigerant
cycle, the two major components are arranged in series as
shown in Fig-2..they are preheater and minichannel condenser.
Fig -2: Experimental setup and flow diagram
This experimentation was conducted using steam as an
refrigerant and water as an 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 minichannel. The

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booster pumps are used to circulate the refrigerant and coolant
through the test line. The generated vapor is condensed in the
test section. The five thermocouples are inserted between the
refrigerant and the coolant side as shown in Fig-2. The
intensive and extensive properties like temperature, pressure
and flow rate are measured at various points during testing.
The condensate from the condenser was measured.
4. OPERATING PARAMETERS
Table -1: Operating Conditions
Sl
No
Saturation
temperature(°C)
Saturation
pressure(bar)
Mass
flow
rate
of
steam
Mass
flow
rate of
coolant
Inlet
vapor
Quality
(Xi)
(g/s)
1 100 1.0123 0.8 1 0.2
2 0.6 0.4
3 0.4 0.6
0.8
5. DATA REDUCTION
The inlet vapor quality to the test section is determined by
energy balance in the heat sink.
𝑚 𝑠 𝑕𝑓 + 𝑄 𝑎 = 𝑚 𝑠 (𝑕𝑓 + 𝑥 𝑜 𝑕𝑓𝑔 )
Where,
hf is inlet enthalpy of the water in to the sink
hfg is the latent heat of vaporization
Qa= I*V is the heat to the heater
The experimental Heat transfer coefficient (h) is given by:
h=𝑄𝑐/ 𝑇𝑠 − 𝑇𝑤 𝐴
Where,
Qc= heat removed by refrigerant in W
A= Area of surface in m2
= (a* L) 2
a= Depth of the channel in m
L= Length of the channel in m
Heat absorbed by cooling water (Q c) is given by:
𝑄𝑐 = 𝑚 𝑐 𝑐 𝑝(𝑇𝑐𝑜 − 𝑇𝑐𝑖 )
Where,
mc= Mass flow rate of coolant in kg/s
Cp= specific heat of coolant in kj/kg °c
Tco= outlet temperature of coolant in °c
Tci= Inlet temperature of coolant in °c
6. RESULT AND DISCUSSIONS
6.1 Effect of Wall Temperature along the Channel
Length
Fig-3 (a)
Fig-3 (b)
30 40 50 60 70 80 90 100
70
75
80
85
90
95
WallTemperature(
0
C)
Axial Distance (mm)
G=355.55 kgm
-2
s
-1
G=266.66 kgm
-2
s
-1
G=177.77 kgm
-2
s
-1
xi
=0.2
30 40 50 60 70 80 90 100
80
82
84
86
88
90
92
94
WallTempaperature(
0
C)
Axial Distance (mm)
G=355 Kg/m
2
s
G=266 Kg/m
2
s
G=177 Kg/m
2
s
X=0.4

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Fig-3 (c)
Fig-3 (d)
Fig-3 a,b,c,d:Shows the variation of wall temperature along
the channel length for different inlet vapor quality
The Fig-3.a, b, c, d shows the variation of wall temperature
along the length of the channel. From the initial observation of
the result it is clearly indicates there is an decrease in the trend
of the wall temperature along the length in addition to that it is
evident from the figures the highest wall temperature was
highest mass flux of 355.55kgm-2s-1. This trend was
observed for all the vapor 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.
6.2 Effect of Mass Flux and Inlet Vapor Quality
From the Fig-4 observe that variation of heat transfer
coefficient with mass flux and inlet vapor quality. In the
annular flow, the condensation heat transfer coefficient
increases with increasing mass flux and vapor quality due to
an increase in shear stress at the wall and the thinning of the
liquid film that decreases the thermal (conduction) resistance.
Fig-4: Shows variation of inlet vapor quality on heat transfer
coefficient
6.3 Effect of Mass Flux on Pressure Drop
Fig-5: Effect of mass flux on pressure drop
The effect of mass flux on the pressure drop of condensation
as shown in Fig-5. This graph(Fig-5) indicates the relationship
between the pressure drop and the averaged inlet vapor quality
at a fixed saturation temperature of 100 °C. The two phase
pressure drop is obtained by subtracting pressure at the inlet
30 40 50 60 70 80 90 100
80
82
84
86
88
90
92
94
Walltemperature(
0
C)
Axial Distance (mm)
G=355.55 kgm
-2
s
-1
G=266.66 kgm
-2
s
-1
G=177.77 kgm
-2
s
-1
xi
=0.8
0.2 0.3 0.4 0.5 0.6 0.7 0.8
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
PrssureDrop(bar)
Inlet Vapor Quality (Xi
)
G=177.7778 Kg/m
2
s
G=266.6667 Kg/m
2
s
G=355.5556 Kg/m
2
s
30 40 50 60 70 80 90 100
80
82
84
86
88
90
92
94 G=355 Kg/m
2
s
G=266 Kg/m
2
s
G=177 Kg/m
2
s
WallTemperature(
0
C)
Axial Distance (mm)
X=0.6
0.2 0.3 0.4 0.5 0.6 0.7 0.8
4
8
12
16
20
24
HeatTransfercoefficent(kW/m
2O
C)
Inlet Vapour Quality
G-355.55 Kgm
-2
s
-1
G=266.66 Kgm
-2
s
-1
G=177.77 Kgm
-2
s
-1
0.0 0.2 0.4 0.6 0.8
4
8
12
16
20
24

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and outlet manifold of the channel. It can be seen that pressure
drop is increased with increasing vapor quality due to higher
velocity of vapor flow causes more shear stress at the
interface of the vapor and liquid film.
7. CONCLUSIONS
The triangular channel with hydraulic diameter of 2mm was
tested. the tests was carried by varying mass flux of 177.77,
266.66 and 355.55 kg/m2s & vapor quality ranges from 0.2 to
0.8 at a fixed saturation temperature of 100°C.The result
showed, as the mass flux and vapor quality increases there is
an increase in condensation heat transfer coefficient and
pressure drop.
NOMENCLATURE
m-Meter
w-Watt
Tsat - Saturation temperature
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)
mc- Mass flow rate of coolant in (kg/s)
Cp- Specific heat of coolant in (kJ/kg °c)
Tco-Outlet temperature of coolant in (°c)
Tci-Inlet temperature of coolant in (°c)
ACKNOWLEDGEMENTS
Am appreciate the support of Mr. VILAS WATVE, Assistant
professor in AIT,chickmagalur and Mr. MANU S, Assistant
professor in SSIT, Tumkur for providing me to them valuable
guidance.
REFERENCES
[1]. Zhongyu Guo & N. K. Anand, “Condensation of R-410A
in a Rectangular Channel”, HVAC&R Research, Vol.5:2,
1999, pp. 97-122. 1
[2]. M.K. Dobson, J.C. Chato ,“Condensation in smooth
horizontal tubes”, Journal of Heat Transfer Trans. ASME
,1998, pp.193–213. 2
[3]. J.R.Baird,D.F.Fletcher,B.S.Haynes,“Local condensation
heat transfer rates in fine passages”, International Journal of
Heat and Mass Transfer Vol.46, 2003, pp. 4453–4466. 3
[4]. Yi-Yie Yan, Tsing-Fa Lin, “Condensation heat transfer
and pressure drop of refrigerantR-134a in a small pipe”,
International Journal of Heat and Mass Transfer Vol.42, 1999,
pp.697-708. 4
[5]. 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”,
2009. 5
[6]. S. Ravigururajan, “Impact of Channel Geometry on Two
Phase Flow Heat Transfer Characteristics of Refrigerants in
Micro channel Heat Exchangers”, ASME J. Heat Transfer,
Vol. 120,1998, pp. 485–491. 6
[7]. Chen Fang , Milnes David, Fu-min Wang, Kenneth E.
Goodson, “Influence of film thickness and cross-sectional
geometry on hydrophilic micro channel condensation”,
International Journal of Multiphase Flow Vol.36, 2010, pp.
608–619. 7
[8]. H. Wu, X. Wu, J. Qu, and M. Yu, “Condensation heat
transfer and flow friction in silicon micro channels,” Journal
of Micromechanics and Micro engineering, Vol. 18, 2008, no.
11, Article ID 115024. 9
[9]. A. Cavallini , D. Del Col, L. Doretti, M. Matkovic, L.
Rossetto, C. Zilio, "Two-phase frictional pressure gradient of
R236ea, R134a and R410A inside multi-port mini-channels",
Experimental Thermal and Fluid Science Vol.29, (2005), p.p.
861–870. 10

Experimental investigation of flow condensation in 'v' shaped minichannel

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Experimental investigation of flow condensation in 'v' shaped minichannel