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Design and fabrication of helical tube in coil type heat exchanger

Design and fabrication of helical tube in coil type heat exchanger

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.

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.

Helical Tube
Helical Tube 
Operational Features :
  1. Fully drain-able inner and outer coil.
  2. Spiral wound for maximum counter flow efficiency.
  3. Spiral wound for maximum parallel flow efficiency.
  4. Constant fluid velocity.
  5. No dead spots or crevices.
  6. Fluids and slurries.
  7. Highly resistant to thermal and hydraulic  shock.
Material Used For Exchanger 
  • Copper for inner tube
  • Copper for outer tube
  • SS316 L for fittings and connectors.
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.
Components:
  1. Helical Coil.
  2. Water Tank.
  3. Boom (vertical support).
  4. Holder Pin.
Design Of Coil:
  1. Diameter of inner tube di = 6.4 mm
  2. Diameter of outer tube do =12.5 mm
  3. Length of tube L= 2.7 m
  4. No. of turns of coil N= 7
  5. Pitch of coil p= 30
  6. Outside dia of Coil De= 150.
Design and fabrication of helical tube in coil type heat exchanger
Design and fabrication of helical tube in coil type heat exchanger
Application:

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.

Other Applications :
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.

Advantages Of Heat Exchanger:
1. Compactness
2. Effectiveness
3. Temperature control
4. Flexibility
5. True counter flow operation.

Disadvantages Of Heat Exchanger:
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.

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