The document numerically investigates a finned-tube heat exchanger with circular, elliptical and rectangular tubes. It models the heat exchanger with 3 or 6 tubes in the configurations and analyzes heat transfer and pressure drop characteristics when air or water vapor flows over the tubes. The results show that modified configurations with mixed tube shapes can increase heat transfer by up to 10% compared to baseline designs, though they also increase pressure drop due to the higher frontal area of some tube shapes.

1. Numerical Investigation of Finned-tube Heat
Exchanger with Circular, Elliptical and
Rectangular Tubes.
Supervised by Submitted by
Dipayan Mondal Md. Hasibul Hasan
Assistant Professor Roll: 1205027
Department of Mechanical Engineering Section: B
Khulna University of Engineering & Technology
Course No. ME 4000

2. Outline
•Introduction
•Objectives
•Theoretical Concepts
•Results
•Conclusion

3. Introduction
• A heat exchanger is a device that internal energy is transferred between two or
more fluids available at different temperature.
• Most of the heat exchanger are separated type that means fluids are separated by a
heat transfer surface and ideally fluids don’t mix with one another.
• Heat exchanger are used for several purpose such as power, transportation,
petroleum, air conditioning, refrigeration, cryogenic, heat recovery, alternate fuels
and other industries.
• Now a days, most common examples are automobile radiator, condenser,
evaporator, air preheater and oil coolers.

4. Objectives
• To design & numerically investigate of a finned tube heat
exchanger.
• To investigate with air and then with water vapor that
flowing over the tube.
• To increase heat transfer co-efficient from the conventional
heat exchanger.
• To reduce pressure drop of the heat exchanger.

5. Theoretical Concepts
Fig 1: Isometric view of finned tube heat exchanger.
• Numerical investigation with
circular, elliptical and
rectangular tubes.
• Plate fin with staggered tube
arrangement.
• Number of tubes considered
3,6.
• Perimeter of all the tube are
same.
• Eccentricity of elliptical tube
is 0.6
• Velocity range 0.5-2.5 m/s
Problem Statement

6. Theoretical Concepts
Fig 2: Schematic configuration of a heat exchanger
• Air flows across the tube
bundle.
• Computational domain is
selected as the space between
two adjacent fin surfaces and
the shaded extended regions
bounded by dashed lines.
• Extensions at entrance 1.5 fin
length, at exit 5 fin lengths,
respectively.
Computational Domain
Assumption
• The flow is assumed to be steady,
laminar and incompressible.
• The fin surface is assumed to be
constant wall temperature.
• Temperature of tube surface also
kept constant.

7. Theoretical Concepts
• Geometry
Designation Schematic Representation Category
N3B1 Baseline-1
N3B2 Baseline-2
N3M1 Modified-1
N3M2 Modified-2
N3M3 Modified-3
N3M4 Modified-4
N3M5 Modified-5
N3M6 Modified-6
• In this present investigation,
there are three type of tube,
so total 3P3=6 combinations
are possible.
• But for 6 rows of tube,
those combinations are
doubled in staggered
arrangement.

8. • The finite volume based CFD code ANSYS
Fluent 16.2 is used.
• Under relaxation factor for pressure
correction is taken as 1 for faster
convergence.
• To obtain improved accuracy of the solution,
second order spatial discretization of
pressure is employed.
• QUICK scheme is used for discretizing
higher-order convective terms in momentum
equation.
• The residual is 10e-6 for continuity and
momentum, whereas for energy equation, it
is taken as10e-8.
Fig 3: Schematic representation of grid.
Theoretical Concepts
Solution Methodology

9. Upstream
Top, bottom, front and back = Symmetry
Inlet = Velocity inlet with temperature
Fin Region
Tube Surface = Wall with temperature
Top and bottom = Wall with temperature
Front and back = Symmetry
Downstream
Front and Back = Symmetry
Top and Bottom = Adiabatic Wall
Outlet= Outflow
Fig. 4. The schematic of the computational domain.
Theoretical Concepts
Boundary Condition

10. • Baseline N3B1 is taken for
consideration. Grid 1 = 264935
node, Grid 2 = 361911 node,
Grid 3 = 498982 node.
• Mesh dependency is checked for
heat transfer co-efficient at
different inlet velocity.
Result
Mesh Dependency
Fig 5: Grid independence results (N=3)

11. Result
Result Validation
• For the fin and tube heat
exchangers with plain fin
configuration, the air side
performance characteristics have
been examined experimentally for
various samples (varying
geometrical parameters) by Wang
and Chi.
• The present results are validated
with the experimental work of
Wang and Chi
Fig 6: Validation results for N=2

12. Normalized Nu number for air N=3
• The result has been presented on Normalized Nu number and friction factor. The results are normalized
(Xi/Xo), where i stands for modified cases and o stands for baseline cases which are conventional heat
exchanger.
a) b) c)
Fig 7:Normalized Nu of air with Re number for various combination N=3 w.r.t N3B1 and N3B2 a), b), c)
0.80
0.85
0.90
0.95
1.00
1.05
1.10
50 100 150 200 250 300 350 400
NormalizedNu
Renolds Number
N3M1&N3B1 N3M1&N3B2
N3M2&N3B1 N3M2&N3B2
0.80
0.85
0.90
0.95
1.00
1.05
1.10
50 100 150 200 250 300 350 400
NormalizedNu
Renolds Number
N3M3&N3B1 N3M3&N3B2
N3M4&N3B1 N3M4&N3B2
0.96
0.98
1.00
1.02
1.04
1.06
1.08
1.10
0 100 200 300 400
NormalizedNu
Renolds Number
N3M5&N3B1 N3M5&N3B2
N3M6&N3B1 N3M6&N3B2

13. Normalized Nu number for air N=6
a) b) c)
Fig 8: Normalized Nu of air with Re number for various combination N=6 w.r.t N6B1 and N6B2 a), b), c)
• In the present study, the hydraulic diameter of circular, elliptical and rectangular tubes are different due to
different in cross section under constant perimeter, hence, Reynolds number based on fin height is used for
representing the results.
0.80
0.85
0.90
0.95
1.00
1.05
50 150 250 350 450
NormalizedNu
Renolds Number
N6M1 & N6B1 N6M1 & N6B2
N6M2 & N6B1 N6M2 & N6B2
0.80
0.85
0.90
0.95
1.00
1.05
50 100 150 200 250 300 350 400
NormalizedNu
Renolds Number
N6M3 & N6B1 N6M3 & N6B2
N6M4 & N6B1 N6M4 & N6B2
0.85
0.90
0.95
1.00
1.05
50 100 150 200 250 300 350 400
NormalizedNu
Renolds Number
N6M5 & N6B1 N6M5 & N6B2
N6M6 & N6B1 N6M6 & N6B2

14. Normalized Nu number for water-vapor N=3
a) b) c)
Fig 9: Normalized Nu of water-vapor with Re number for various combination N=3 w.r.t N3B1 and
N3B2 a), b), c)
• At low inlet velocity natural convection occurs but at high inlet velocity forced convection takes place.
0.80
0.85
0.90
0.95
1.00
1.05
40 90 140 190 240
NormalizedNu
Reynolds Number
N3M1 & N3B1 N3M1 & N3B2
N3M2 & N3B1 N3M2 & N3B2
0.85
0.90
0.95
1.00
1.05
40 90 140 190 240
NormalizedNu
Reynolds Number
N3M3 & N3B1 N3M3 & N3B2
N3M4 & N3B1 N3M4 & N3B2
0.95
0.97
0.99
1.01
1.03
1.05
40 90 140 190 240
NormalizedNu
Reynolds Number
N3M5 & N3B1 N3M5 & N3B2
N3M6 & N3B1 N3M6 & N3B2

15. Normalized Nu number for water-vapor N=6
a) b) c)
Fig 10:Normalized Nu of water-vapor with Re number for various combination N=6 w.r.t N6B1 and
N6B2 a), b), c)
• This is due to at lower velocities, the wake region of circular tube (baseline-1) is higher as
compared with elliptical tube (modified case-1) for a fixed inlet velocity.
• The higher in heat transfer rate of circular tube over elliptical tube is also observed.
0.75
0.80
0.85
0.90
0.95
1.00
1.05
40 90 140 190 240
NormalizedNu
Reynolds Number
N6M1 & N6B1 N6M1 & N6B2
N6M2 & N6B1 N6M2 & N6B2
0.80
0.85
0.90
0.95
1.00
1.05
40 90 140 190 240
NormalizedNu
Reynolds Number
N6M3 & N6B1 N6M3 & N6B2
N6M4 & N6B1 N6M4 & N6B2
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
40 90 140 190 240
NormalizedNu
Reynols Number
N6M5 & N6B1 N6M5 & N6B2
N6M6 & N6B1 N6M6 & N6B2

16. Friction factor for air N=3
a) b) c)
Fig 11: Normalized friction factor of air with Re number for various combination N=3 w.r.t N3B1 and N3B2 a), b), c)
• The modified cases have higher frictional resistance values as compared with heat exchanger with
elliptical tubes alone. This is due to the increased frontal area of circular tube in modified cases leads to
higher pressure drop.
0.50
0.60
0.70
0.80
0.90
1.00
1.10
1.20
50 100 150 200 250 300 350 400
NormalizedFrictionFactor
Reynolds Number
N3M1&N3B1 N3M1&N3B2
N3M2&N3B1 N3M2&N3B2
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
50 100 150 200 250 300 350
NormalizedFrictionFactor
Reynolds Number
N3M3&N3B1 N3M3&N3B2
N3M4&N3B1 N3M4&N3B2
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
50 100 150 200 250 300 350
NormalizedFrictionFactor
Reynolds Number
N3M5&N3B1 N3M5&N3B2
N3M6&N3B1 N3M6&N3B2

17. Friction factor for air N=6
a) b) c)
Fig 12: Normalized friction factor of air with Re number for various combination N=6 w.r.t N6B1 and N6B2 a), b), c)
0.70
0.75
0.80
0.85
0.90
0.95
1.00
50 100 150 200 250 300 350 400
NormalizedFrictionFactor
Reynolds Number
N6M1 & N6B1 N6M1 & N6B2
N6M2 & N6B1 N6M2 & N6B2
0.75
0.80
0.85
0.90
0.95
1.00
1.05
50 100 150 200 250 300 350 400
NormalizedFrictionFactor
Reynolds Number
N6M3 & N6B1 N6M3 & N6B2
N6M4 & N6B1 N6M4 & N6B2
0.83
0.88
0.93
0.98
1.03
1.08
50 100 150 200 250 300 350 400
NormalizedFrictionFactor
Reynolds Number
N6M5 & N6B1 N6M5 & N6B2
N6M6 & N6B1 N6M6 & N6B2

18. Friction factor for water-vapor N=3
a) b) c)
Fig 13: Normalized friction factor of water-vapor with Re number for various combination N=3 w.r.t N3B1 and
N3B2 a), b), c)
0.60
0.70
0.80
0.90
1.00
1.10
1.20
40 90 140 190 240
NormalizedFrictionFactor
Reynolds Number
N3M1 & N3B1 N3M1 & N3B2
N3M2 & N3B1 N3M2 & N3B2
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
40 90 140 190 240
NormalizedFrictionFactor
Reynolds Number
N3M3 & N3B1 N3M3 & N3B2
N3M4 & N3B1 N3M4 & N3B2
0.75
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
40 90 140 190 240
NormalizedFrictionFactor
Reynolds Number
N3M5 & N3B1 N3M5 & N3B2
N3M6 & N3B1 N3M6 & N3B2

19. Friction factor for water-vapor N=6
a)
b) c)
Fig 14: Normalized friction factor of water-vapor with Re number for various combination N=6 w.r.t N6B1 and N6B2 a), b), c)
0.75
0.80
0.85
0.90
0.95
1.00
40 90 140 190 240
NormalizedFrictionFactor
Reynolds Number
N6M1 & N6B1 N6M1 & N6B2
N6M2 & N6B1 N6M2 & N6B2
0.80
0.85
0.90
0.95
1.00
1.05
40 90 140 190 240
NormalizedFrictionFactor
Reynolds Number
N6M3 & N6B1 N6M3 & N6B2
N6M4 & N6B1 N6M4 & N6B2
0.85
0.87
0.89
0.91
0.93
0.95
0.97
0.99
1.01
1.03
1.05
40 90 140 190 240
NormalizedFrictionFactor
Reynolds Number
N6M5 & N6B1 N6M5 & N6B2
N6M6 & N6B1 N6M6 & N6B2

20. Temperature contour of air for various combination when N=3
Fig 15: Temperature contour of air a) N3B1 at 0.5 m/s b) N3B1 at 2.5m/s c) N3M3 at 0.5 m/s d) N3M3 at 2.5 m/s
a) c)
b) d)

21. Temperature contour of water-vapor for various combination
when N=3
Fig 16: Temperature contour of water-vapor a) N3B1 at 0.5 m/s b) N3B1 at 2.5m/s c) N3M3 at 0.5 m/s d) N3M3 at 2.5 m/s
a)
b)
c)
d)

22. Temperature contour of air for various combination when N=6
Fig 15: Temperature contour of air a) N6B1 at 0.5 m/s b) N6B1 at 2.5m/s c) N6M3 at 0.5 m/s d) N6M3 at 2.5 m/s
a)
b)
c)
d)

23. Temperature contour of water-vapor for various combination
when N=6
Fig 16: Temperature contour of water-vapor a) N6B1 at 0.5 m/s b) N6B1 at 2.5m/s c) N6M3 at 0.5 m/s d) N6M3 at 2.5 m/s
a)
b)
c)
d)

24. Pressure Contour for air when N=3
Fig 17: Pressure contour of air a) N3B1 at 0.5 m/s b) N3B1 at 2.5m/s c) N3M3 at 0.5 m/s d) N3M3 at 2.5 m/s
a)
b)
c)
d)

25. Pressure Contour for water-vapor when N=3
Fig 18: Pressure contour of water-vapor a) N3B1 at 0.5 m/s b) N3B1 at 2.5m/s c) N3M3 at 0.5 m/s d) N3M3 at 2.5 m/s
a)
b)
c)
d)

26. Pressure Contour for air when N=6
Fig 19: Pressure contour of air a) N6B1 at 0.5 m/s b) N6B1 at 2.5m/s c) N6M3 at 0.5 m/s d) N6M3 at 2.5 m/s
a)
b)
c)
d)

27. Pressure Contour for water-vapor when
N=6
Fig 20: Pressure contour of water-vapor a) N6B1 at 0.5 m/s b) N6B1 at 2.5m/s c) N6M3 at 0.5 m/s d) N6M3 at 2.5 m/s
a)
b)
c)
d)

28. Conclusion
• The heat transfer enhancement is being quite good of air for geometry N3M2 and N3M5 than
the grouped elliptical tubes in case of three rows of tube.
• On the other hand for six rows tube N6M3 and N6M6 has performed better than the grouped
circular tube.
• In case of water-vapor, the heat exchanger with geometry N3M1 and N3M2 has been
performed quite better than both circular and elliptical tubes.
• The frictional resistance of air for geometry N3M1 and N3M3 when compared with grouped
circular tube. N3M3 has also performed better than conventional elliptical tube.
• For six rows of tube, N6M5 acts better than circular tube and N6M6 also performs better than
elliptical tubes alone.
• The frictional resistance for water-vapor N3M1 N3M3 and N3M4 all has performed better than
grouped circular and elliptical tubes.