Heat exchangers are the important engineering systems with wide variety of applications including power plants, nuclear reactors, refrigeration and air-conditioning systems, heat recovery systems, chemical processing and food industries. Helical coil configuration is very effective for heat exchangers and chemical reactors because they can accommodate a large heat transfer area in a small space, with high heat transfer coefficients. This project focus on an increase in the effectiveness of a heat exchanger and analysis of various parameters that affect the effectiveness of a heat exchanger and also deals with the performance analysis of heat exchanger by varying various parameters like number of coils, flow rate and temperature. The results of the helical tube heat exchanger are compared with the straight tube heat exchanger in both parallel and counter flow by varying parameters like temperature, flow rate of cold water and number of turns of helical coil.

1. A
presentation
on
Design and fabrication of helical tube in
coil type heat exchanger
Submitted By
Nehete Hemant Rajendra
Guided By
Er. G. E. Chaudhari

2. INTRODUCTION
A heat exchanger is a device used to heat transfer between two or
more fluids for various application including power plants, nuclear
reactors, refrigeration & air condition system, automotive industries, heat
recovery system, chemical processing and food industries. The various
types of heat transfer enhancement techniques are classified into two
main categories. Active techniques which require external power for heat
transfer augmentation, and passive techniques which not require such
external power for enhancement. One of the passive techniques is the use
of helically coiled tubes. Several papers studied and indicated that helical
coiled tubes are superior to straight tube due to their compactness and
increased heat transfer coefficient .Helical coils are used for various
processes such as heat exchangers because they can accommodate a large
heat transfer area in a small space, with high heat transfer coefficient. The
centrifugal forces are acting on the moving fluid due to the curvature of
the tube results in the development.

3. HELICAL TUBE
Helical tubes are universally used in chemical
reactors, ocean engineering, heat exchangers,
piping system and many other engineering
applications. It has been long recognized that heat
transfer characteristic of helical tubes is much
better than the straight ones because of the
occurrence of secondary fluid flow in planes normal
to the main flow inside the helical structure .Helical
tubes show great performance in heat transfer
enhancement, while the uniform curvature of spiral
structure is inconvenient in pipe installation in heat
exchangers. It has been widely reported in literature
that heat transfer rates in helical coils are higher as
compared to those in straight tubes. Due to the
compact structure and high heat transfer
coefficient, helical coil heat exchangers find
extensive use in industrial applications such as
power generation, nuclear industry, process plants,
heat recovery systems, refrigeration, food industry,
etc.

4. OPERATIONAL FEATURES
 Fully drainable inner and outer coil
 Spiral wound for maximum counter flow efficiency
 Spiral wound for maximum parallel flow efficiency
 Constant fluid velocity
 No dead spots or crevices
 Fluids & slurries
 Highly resistant to thermal and hydraulic shock
MATERIALS
 Copper for inner tube
 Copper for outer tube
 SS316 L for fittings and connectors.

5. OBJECTIVES
 System design and theoretical derivation of dimension of inner tube
, outer tube , number of coils for the desired temperature gradient
 Design and fabrication of Helical tube in tube coil heat exchanger
with closed coil structure..
 Design and fabrication of Test rig for testing of Helical tube in tube
coil heat exchanger
 Testing of Helical tube in tube coil heat exchanger in parallel flow
configuration to determine:
• LMTD
• Capacity ratio
• Effectiveness
 Testing of Helical tube in tube coil heat exchanger in counter flow
configuration to determine:
• LMTD
• Capacity ratio
• Effectiveness

6. COMPONENTS
1. Helical Coil
2. Water Tank
3. Boom (vertical support)
4. Holder Pin

7. DESIGN
• Diameter of inner tube di = 6.4mm
• Diameter of outer tube do =12.5mm
• Length of tube L= 2.7 m
• No. of turns of coil N= 7
• Pitch of coil p= 30
• Outside dia of Coil De= 150
1) Design of coil
Fig: Layout of coil

8. 2) Design of tank
Fig: Layout of tank
Expected volume of tank = Flow in 20 minutes + volume of inner annulus
= 0.1x 20 + 0.5 = 2.5 litre
Considering 1.5 as factor of safety Volume of tank = 3.75 litres. Thus following
dimensions of tank are derived as per volume:

9. Thus net volume of oil stored in tank is 4 litres ie, weight of tank with oil =
2.7 +6.4 =9.10 approximately 10 kg.
Considering compressive failure of tank base:
Stress = Force / Area
= 10 x 9.81 / 17 x 170
=0.003 N/mm2
Thus tank base is safe as the actual stress is far below allowable stress 80
N/mm2 for mild steel.

10. 3) Design of boom
Boom is the vertical structural member that carries the tank on to which
the entire weight of the tank & oil acts . This downward acting load will
cause the buckling of the vertical column boom which is fixed at the
bottom end and has a hinge at its top end.

11. Rankine formula
Pc = a σc
1+ C (L/r)
where, C =1/7500 for steel
L = Effective length = 601 mm
r = radius of gyration = 17.25mm
a= area of cross section = 264 mm2
Selection of boom material
Ref :- PSG Design Data.
For Designation C15 :
Ultimate Tensile Strength = 340
N/mm2
Yield strength = 190 N/mm2
6o = 190/2 =95 N/mm2
Pc= 264 x 95
1+ (601/17.25)/ 7500
Pc =25.22 x103 N
As the Crippling load 25.22 x103 N > Actual load
(100N)
The boom is safe under buckling criterion

12. 4) Design of holder pin
Main holder pin is the pin which holds the heat exchager on to the boom.The
entire weight of panel system 100N is transferred to the boom via this pin
hence it will be subjected to double shear failure
Fs = 100 N
Material selection
For Designation EN9(C45):
Ultimate Tensile strength =600 N/mm2
Yield strength = 380 N/mm2
Shear stress = shear force
Shear area
Pin l diameter at mounting point = 14mm
 shear stress fs act = 100
2(/4 x 142)
fs act = 0.325 N/mm2
As f s act < f s all
Pin is safe under shear load

13. APPLICATIONS
1)They are mainly employed in the field of cryogenics for cryogenic
separation and liquefaction of air, natural gas processing and liquefaction,
production of petrochemicals and large refrigeration systems. The
exchangers that are used for cryogenic air separation and LPG fractionation
are the largest and most complex units of the plate fin type and a single unit
could be of several meters in length. .
2)They are being used mainly in environment control system of the aircraft,
avionics and hydraulic oil cooling and fuel heating.
3) In the automobile sector they are used for making the radiators.

14. The other miscellaneous applications are
1. Fuel cells
2 . Process heat exchangers.
3 . Heat recovery plants.
4 . Pollution control systems
5 . Fuel processing and conditioning plants.
6 . Ethylene and propylene production plants.

15. ADVANTAGES
1. Compactness
2. Effectiveness
3. Temperature control
4. Flexibility
5. True counter flow operation

16. DISADVANTAGES
1. Limited range of temperature and pressure.
2. Difficulty in cleaning of passages, which limits it application to clean and
relatively non- corrosive fluids.
3. Difficulty of repair in case of failure or leakage between passages.
4. Helical tube complicated in design.

17. FUTURE WORK

18. a) Fabrication:
Suitable manufacturing methods will be employed to fabricate the components
and then assemble the test set –up.
b) Experimental analysis:
To check the validity of experimental results with theoretical results as:
1. To carry out comparative study of theoretical and experimental analysis
results to decide the heat exchanger parameter optimization in parallel flow
configuration.
2. To carry out comparative study of theoretical and experimental analysis
results to decide the heat exchanger parameter optimization in counter flow
configuration