DOI 10.4010/2016.1683
ISSN 2321 3361 © 2016 IJESC
`
Research Article
Volume 6 Issue No. 6
Heat Transfer Analysis of Simultaneously Developing Flow in Two
Isosceles Right Triangular Microchannel Heat Exchanger Using
ANSYS
Avinash Yadav1, Dr. Satyendra Singh2, Ravi Kumar3
M.Tech Scholar1, Associate Professor2, Assistant Professor3
Department of Mechanical Engineering
B.T.K.I.T, Dwarahat Almora, Uttarakhand, India
[email protected], [email protected]
Abstract:
In this work thermal performance of microchannel heat exchanger is performed on single phase liquid flow in microchannel heat
exchanger is analyzed. The result was achieved by solving the continuity and Navier–Stokes equations for the hot and cold fluids
the governing equations are solved in ANSYS FLUENT 16.0. The water is used as working fluid for cold fluid and hot fluid. The
effectiveness, heat transfer rate, friction factor, performance index, and pressure drop along the heat exchanger are calculated under
different values of Reynolds number. The results shows that effectiveness, friction factor, and performance index of microchannel
heat exchanger are decreasing with increasing values of Reynolds number, whereas the pressure drop and heat transfer rate are
increasing as increased in Reynolds number.
Keywords: Microchannel, No-Slip, Reynolds Number, Effectiveness, Performance Index.
Introduction
Microfluidic systems like silicon, glass, quartz are developed
by using of micromachining technology. Microchannels are
part of any such systems. In the last two spans the canvassers
have dedicated countless determinations in mounting
miniaturized microdevices. The application of microchannel
in varieties of field such as electronic cooling, space thermal
management, MEMS devices for chemical and biological
systems, etc. they have need of high heat transfer rate in
small channel. Mehendale et al. [8] gives the criteria’s of
microchannel, conventional channel and meso-chennal but
Kandilkar and Grade [5] slightly modified the and present
earlier channel classification scheme of smallest channel
dimensions. Tuckerman and Pease [13] first time scrutinizes
in microchannel with single phase and two-phase flow and
demonstrated the high heat flux removal capability of up to
800 W/cm2. In the present study different parameters are
investigated such as velocity profiles, effectiveness, pressure
drop, friction factor, heat transfer rate, and performance
index.
Tuckerman and Pease [13] gives a novel idea to invent a
number of design and germinated broad research
determination in the field of microchannel. Hasan et al. [2]
study the axial heat conduction in isosceles right triangular
channel. They showed that different parameters such as
thermal conductivity ratio, Reynolds number, hydraulic
diameter, channel volume, and wall thickness affect the axial
heat conduction rate in a isosceles right triangular channel.
Wu and Little [11] in thier experiments
used the trapezoidal cross-section silicon/glass microchannel
to measure the flow friction by taking gases (N2, H2, Ar)
International Journal of Engineering Science and Computing, June 2016
with different hydraulic diameter as a working fluid in
laminar flow condition and established that experimental
friction factor were large those predicted by the conventional
theory due to channel surface roughness affected the values
of the friction factor.
Harley and Bau [4] dignified the
friction factor using isopropanol as a working fluid in
trapezoidal/rectangular silicon microchannel with 45µm and
65µm hydraulic diameter, they initiate that experimentally
Poiseuille number was higher than the predictable theoretical
value. Choi et al. [12] dignified the friction factor in silica
micro pipes using nitrogen as a functioning fluid with
diverse hydraulic diameter (3,7,10,53,81µm). They
concluded that Poiseuille numbers were lower than the
conventional value for different values of Reynolds.
Hernando et al. [10] experimentally inspected heat transfer
and pressure drop with deionized water in two different
cross-sectional microchannels. The result showed the no heat
transfer incremental seemed as an outcome of small channel
sizes, and result showed moral contract with the common
theory.
Aggarwal et al. [1] analyze the pressure drop in diverging
microchannel heat exchanger with boiling in different
divergence angle and recommended that the existence of
critical angle can reduce the mean pressure drop. Baharami
et al. [7] projected a compact approximate model that could
guess pressure drop in wide variety of channel shapes. They
authenticate this model for square, circular, rectangular,
trapezoidal cross-section by relating with testing data and
exact methodical solution.
Park and Punch [3]
experimentally calculated heat transfer and friction factor of
laminar flow (69 < Re < 800) in rectangular microchannel
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with varying hydraulic diameter between 106-307µm. On
the basis of their work they initiated that, while predictable
hydrodynamic theory for fully-developed flow is relevant for
this range of flow Re, eccentricities were observed in heat
transfer predictions.
Greek Symbol
f
:
:
:
:
µ
:
friction factor
performance index
effectiveness
density
dynamic viscosity
Subscript
h
:
c
:
i
:
o
:
max
:
hot fluid
cold fluid
inlet
outlet
maximum
Dimensionless group
Reynolds number, Re
:
Nomenclature
Notation
x
y
z
h
b
l
v
vin
ch
cc
Dh
Q
m
P
qmax
qactual
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
Meaning
horizontal coordinate, m
vertical coordinate, m
axial coordinate, m
channel height, m
channel width, m
channel length, m
velocity of fluid, m/s
average velocity, m/s
heat capacity of hot fluid, w/k
heat capacity of cold fluid, w/k
hydraulic diameter, m
heat transfer rate, w
mass flow rate, kg/s
pressure, Pa
maximum possible heat transfer rate, w
actual heat transfer rate, w
Problem declaration:
Simulation of full continuity, momentum and
energy equations for unlike fluid flows arises in various
International Journal of Engineering Science and Computing, June 2016
engineering problems. Various different algorithms have
been projected and settled by various investigators.
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The structure shown in Fig. 1 a rectangular channel with a
separating wall between them where, “l” (2 cm) is channel
length, “h” (0.2mm) is height and “b” (0.2mm) base of
channel, “t” (0.005mm) is solid thickness and “z” is
projected distance of thickness. In this figure, the hot fluid
enters the lower channel, the all the data are taken from [6]
while the cold fluid enters the upper channel with a uniform
velocity “v” and uniform temperature “T”. The solid material
of a channel is aluminium. The water is taken as working
fluid for hot and cold fluid. Heat is transported from the hot
fluid to the cold fluid. The physical and geometrical
assumptions are
 The flow is laminar and steady.
 The Knudsen number is small enough so that, the
fluid is a endless medium (no slip).
 The fluids are incompressible, Newtonian with
persistent properties.
 There is no heat transfer to/from the ambient.
 The energy degeneracy is negligible.
 The pressure rise is in axial direction only.
Solid Wall
∆P = ∆Ph + ∆Pc
(5)
Where
∆Ph = (Ph in - Ph out)
(6)
and,
∆Pc = (Pc in – Pc out)
(7)
Once the total pressure drop are determine the friction factor
can be calculated as
(8)
And the performance index of parallel flow microchannel
are calculated as
(9)
Results and Discussion:
The performance effectiveness, heat transfer, pressure drop,
friction factor, performance index in a parallel flow
microchannel heat exchanger in altered circumstances of
Reynolds number have been deliberate. Both hot and cold
fluids are water with stuffs taken based on the ordinary bulk
temperature [6].
In order to verify the precision of the current numerical
model, a evaluation is prepared concerning the results of
present model for rectangular microchannel heat exchanger
and that in literature. Fig. 2 shows comparison present
numerical model and data of Hasan et al. (2014).
Cold Fluid (Hasan et al)
Hot Fluid (Hasan et al)
Seperating Wall (Hasan et al)
Cold Fluid (Fluent)
Hot Fluid (Fluent)
Seperating Wall (Fluent)
Fig. 1 Schematic of parallel flow microchannel
The momentum and energy equations are solved in Ansys
Fluent 16.0. From the simulation various results are calculate
such as effectiveness, Heat transfer rate, Friction Factor,
Performance Index and Pressure drop. The effectiveness for
channel becomes
(1)
Qactual = actual heat transferred in the heat exchanger
Qmax = maximum possible heat transfer in the heat exchanger
Now, actual heat transfer rate in a heat exchanger is given
by:
Q = mh. Cph. (Thi - Tho) = Ch.(Thi – Tho)
(2)
and,
Q = mc. Cpc. (Tco – Tci) = Cc. (Tco – Tci) (3)
Then the effectiveness is
(4)
Once the effectiveness can obtained, the heat transfer rate
can be determined for different value of Reynolds number.
After calculation of heat transfer rate the total pressure drop
are calculated under different Reynolds number flow
condition which is calculated by
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Temperature (˚C)
100
80
60
40
20
0
0
5
10
15
20
Axial distance (mm)
Fig.2 comparison of the temperature distribution for hot
fluids, cold fluids, separating wall for present model and data
of Hasan et al.(2012)
Figure 2 indicates the temperature distribution and the
average percentage error as considered for hot fluid 0.54%,
cold fluid 0.67%, and for separating wall 0.84%. From this
figure it can be realized that, there is a good settlement
among the numerical consequences of present model and
that for Hasan et al. [2].
The effectiveness of rectangular microchannel heat
exchanger is calculated for different values of Reynolds
number (100, 200, 300, and 400) as shown in figure 3.
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Total Pressure Drop, ∆P (Pa)
0.35
Effectiveness, 𝜀
0.3
0.25
0.2
0.15
0.1
0.05
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
0
100
100
200
300
400
200
300
400
Reynolds number, Re
Reynolds number, Re
Heat transfer rate, q(10¯³)
From Fig. 3 the reduction in effectiveness noted with
increasing values of Reynolds number for parallel flow
microchannel heat exchanger. It means Reynolds number is
directly proportional to inlet velocity. For high value of
Reynolds number the inlet velocity would be high and
finally temperature difference decreases. Hence the
effectiveness decreases with increased value of Reynolds
number.
Figure 4 spectacles the heat transfer rate with diverse values
of Reynolds number. The variation is taken for parallel flow.
The different values of Reynolds are 100, 200, 300, and 400.
From Fig. 4 it can be seen that with increasing Reynolds
number the heat transfer rate is increasing. The variations of
both actual and maximum possible heat transfer are linear.
This difference is increasing with increased value Reynolds
number. Re = 100 has minimum heat transfer difference and
Re = 400 has maximum heat transfer difference.
2
q_max
q_actual
Friction Factor
Fig. 3 Variation of effectiveness with different values of
Reynolds number
Fig. 5 Variation for pressure drop with axial distance for
Reynolds number
Figure 5 spectacles the disparity of pressure drop with axial
distance for different values of Reynolds number. This
variation is taken for cold channel of Parallel flow with Re
100, 200, 300, and 400. From the figure it can be illustrated
that at Reynolds 400 the maximum amount of pressure drop
occur and at Reynolds 100 the minimum pressure drop
accounted.
The variations in friction factor are investigated for different
values of Reynolds number as shown in figure 6.
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
100
200
300
400
Reynolds Number, Re
1.5
1
0.5
0
100
200
300
400
Reynolds number, Re
Fig. 4 variation for heat transfer rate with different values of
Reynolds number
Fig. 6 Variation of friction factor for different values of
Reynolds number
From Figure it can be realized that friction factor is reducing
with amplified values of Reynolds number. Re = 100 has
maximum friction factor and Re = 400 has minimum friction
factor. The variation of friction factor is nonlinear.
Fig. 7 shows the disparity of performance index with
Reynolds number. Performance index displays the relation
among the thermal and hydrodynamic performance. This
deviation is taken for parallel flow with different values of
Reynolds number taken are 100, 200, 300, and 400.
Reynolds number should be less to get the minimum heat
transfer difference. This minimum heat transfer difference
leads to high effectiveness.
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Performance index, 𝜂 = 𝜀/∆P
0.012
6.
Kothandaraman,C.P., Subramanyan, S., Heat and Mass
Transfer Data Book. New Age International (P) Ltd.,
Publishers (2014).
7.
M. Bahrami, M.M. Yovanovich, J.R. Culham, (2006)
Pressure drop of fully developed laminar flow in
microchannels of arbitrary cross-section, J. Fluids Eng.
128, 1036-1044.
8.
Mehendale, S.S., Jacobi A.M. and Ahah, R.K., (2000),
“Fluid Flow and Heat Transfer at Micro and MesoScales with Application to Heat Exchanger Design”,
Appl. Mech. Rev. 53, 175–193.
9.
M. Thirumaleshwar, Fundamental of Heat and Mass
Transfer, Pearson 2006.
0.01
0.008
0.006
0.004
0.002
0
100
200
300
400
Reynolds number, Re
Fig. 7 Variation of performance index
From figure it can be understood that the performance index
is decreasing with increased value of Reynolds number. Re =
100 has maximum performance index and Re = 400 has
minimum. This occurs due to the cumulative value of
pressure drop and falling value of effectiveness with
increased value of Reynolds number.
Conclusion
The rectangular microchannel heat exchanger is investigated
numerically with No-slip flow heat transfer. Thermal and
hydrodynamic performance of microchannel is investigated
with different parameters. The microchannel heat exchanger
with aluminium material has found better effectiveness.
Effectiveness is decreasing with increased value of Reynolds
number due to the higher inlet velocity. Pressure drop
increases with increased value of Reynolds number for
parallel flow channel. Heat transfer rate also increases with
increased value of Reynolds number in the microchannel
heat exchanger and the performance index drops with
increased value of Reynolds number. Performance index
signifies the overall performance of microchannel heat
exchanger unit.
10. N. García-Hernando, A. Acosta-Iborra, U. Ruiz-Rivas,
M. Izquierdo, (2009) Experimental investigation of
fluid flow and heat transfer in a single-phase liquid
flow micro-heat exchanger, Int. J. Heat Mass Transf.
52, 5433-5446.
11. P.Y. Wu, W.A. Little, (1983) Measurement of friction
factor for flow of gases in very fine channels used for
micro-miniature
Joule-Thompson
refrigerators,
Cryogenics 24(8) 273-277.
12. S.B. Choi, R.F. Barron, R.O. Warrington, (1991) Fluid
flow and heat transfer in microtubes, in:
Micromechanical Sensors, Actuators and Systems,
ASME DSC, vol. 32, Atlanta, GA, pp. 123–134.
13. Tuckerman, D.B. and Pease, R.F., (1981) “High
performance heat sinking for VLSI”, IEEE electron
device letter 2, 126–129.
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