The document reviews heat transfer enhancement techniques using twisted tape inserts. It discusses heat exchangers and classifications. Twisted tape is described as a passive enhancement method that induces swirl and turbulence to disrupt the thermal boundary layer. Attributes of twisted tape like pitch, twist ratio and shape are examined. Using twisted tape can increase heat transfer rate in a heat exchanger by up to 188% but also increases friction loss. Different tape configurations are evaluated and it is found that optimization of parameters like twist ratio can improve thermal performance.

1. REVIEW ON HEAT TRANSFER
ENHANCEMENT WITH TWISTED TAPE
By
Mr. Shekhar S. Babar
Prof. K. D. Devade
MECHANICAL ENGINEERING
(Indira College of Engineering & Management,Pune)

2. OVERVIEW
 INTRODUCTION
 CLASSIFICATION & APPLICATIONS
 DESIGN CONSIDERATIONS
 MECHANISM OF HEAT TRANSFER
ENHANCEMENT
 NEED FOR HEAT TRANSFER ENHANCEMENT
 ENHANCEMENT TECHNIQUIES
 TWISTED TAPE : A PASSIVE METHOD
 THERMAL CHARACTERISTICS OF HEAT
EXCHANGER WITH TWISTED TAPE
 CONCLUSION
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3. INTRODUCTION
 HEAT EXCHANGER
A heat exchanger is a device that transfers thermal
energy from a high-temperature fluid to a low-
temperature fluid with both fluids moving
through the device. A heat exchanger is a device
that is used to transfer thermal energy (enthalpy)
between two or more fluids, between a solid
surface and a fluid, or between solid particulates
and a fluid, at different temperatures and in
thermal contact. In heat exchangers, there are
usually no external heat and work interactions.
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4. CLASSIFICATION OF HEAT EXCHANGERS
 According to Transfer process
 Indirect contact type
 Direct contact type
 According to Construction
 Tabular Type -Double Pipe, Shell& tube, Spiral tube, Pipe coil
 Plate Type
 Extended surface type
 Regenerative
 According to Flow arrangement
 According to Heat transfer mechanism
 Single phase convection on both side
 Two phase convection on both side
 Single phase convection on one side & two phase on other side
 Process function
 Condenser Evaporator &
 Heaters, Cooler, Chillers
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5. APPLICATIONS OF HEAT EXCHANGERS
 Applications involve heating or cooling of a fluid
stream of concern and evaporation or condensation
of single- or multi component fluid streams.
 In other applications, the objective may be to recover
or reject heat, or sterilize, pasteurize, fractionate,
distill, concentrate, crystallize, or control a process
fluid.
 Heat exchanger for an ocean thermal energy
conversion (OTEC),
 Heat exchangers for process industries, Sugar
factories, diary plants, Chemical industries Heating
and cooling in evaporators,
 Heat exchangers thermal power plants, air-
conditioning equipment, refrigerators, radiators for
space vehicles, automobiles.
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6. DESIGN CONSIDERATIONS
 Resistance to heat transfer should be
minimized
 Contingencies should be anticipated via
safety margins; for example, allowance for
fouling during operation.
 The equipment should be sturdy.
 Cost and material requirements should be
low.
 Corrosion should be avoided.
 Pumping cost should be kept low.
 Space required should be kept low.
 Required weight should be kept low.
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7. NEED FOR HEAT TRANSFER ENHANCEMENT
 To make the equipment compact
 To achieve a high heat transfer rate using minimum
pumping power
 Minimize the cost of energy and material
 A need for miniaturization of a heat exchanger in specific
applications Space, OTEC
 Working fluids of low thermal conductivity (gases and
oils) and desalination plants
 Increase efficiency of process & system.
 Design optimum heat exchanger size
 Transfer required amount of heat with high effectiveness
 Reduce the volume & weight
 For given temperature difference improved HT
 Effective utilization of energy-Minimum operating cost
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8. MECHANISMS OF AUGMENTATION OF HEAT TRANSFER
 Use of a secondary heat transfer surface.
 Disruption of the unenhanced fluid velocity.
 Disruption of the laminar sub layer in the turbulent boundary layer.
 Introducing secondary flows.
 Promoting boundary-layer separation. .
 Enhancing effective thermal conductivity of the fluid under static conditions
 Enhancing effective thermal conductivity of the fluid under dynamic
 Delaying the boundary layer development.
 Thermal dispersion
 Increasing the order of the fluid molecules.
 Redistribution of the flow.
 Modification of radiative property of the convective medium.
 Increasing the difference between the surface and fluid temperatures.
 Increasing fluid flow rate passively.
 Increasing the thermal conductivity of the solid phase using special
Nanotechnology fabrications
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9. HEAT TRANSFER ENHANCEMENT TECHNIQUES
 Active method: external power input for the
enhancement of heat transfer
 pulsation by cams and reciprocating plungers
 magnetic field to disturb seeded light particles in a
flowing stream,
 fluid vibration, jet impingement ,Suction
 Passive method: surface or geometrical modifications
to the flow channel by incorporating inserts or
additional devices
 Inserts, Rough surfaces, Coiled / Twisted tape
 Baffles, Extended surface additives,
 Compound method: When any two or more
techniques employed simultaneously
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10. ACTIVE METHODS
 Mechanical Aids:
 Surface vibration:
 Fluid vibration:
 Electrostatic fields:
 Injection
 Suction:
 Jet impingement:
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11. PASSIVE METHODS
 Treated Surfaces:.
 Rough surfaces:
 Extended surfaces:
 Displaced enhancement devices:.
 Swirl flow devices:
 Coiled tubes:.
 Surface tension devices:
 Additives for liquids:
 Additives for gases:
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12. WHY PASSIVE TECHNIQUES?
 These techniques generally use simple surface or
geometrical modifications to the flow channel by
incorporating inserts or additional devices
 It does not need any external power input.
 Insert manufacturing process is simple and these
techniques can be easily employed in an existing heat
exchanger.
 Passive insert configuration can be selected According to
the heat exchanger working condition
 It can be used in design of compact heat exchangers.
 It is not only applicable in heat exchanger but also in solar
air heater and cooling of electronic components (heat
sink).
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13. TWISTED TAPE
 TWISTED TAPE :A PASSIVE
METHOD
 Inserts refer to the
additional arrangements
made as an obstacle to
fluid flow so as to
augment heat transfer.
 Twisted tapes are the
metallic strips twisted
with some suitable
techniques with desired
shape and dimension,
inserted in the flow.
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14. TYPES OF TWISTED TAPES
 Plain Twisted Tape
 Full length twisted tape
 Varying length twisted tape
 Short length TT
 Regularly spaced twisted tapes
 Tape with attached baffles
 Slotted tapes and tapes with holes
 Tapes with dimpled surface modifications
 Serrated twisted tape
 Edge fold twisted tape
 Oblique teeth Twisted tape
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15. TYPES OF TWISTED TAPES
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16. ATTRIBUTES OF TWISTED TAPE
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 Width (W)
 Thickness (δ)
 Pitch (y)
 Twist ratio (Y)= y/W
 Clearance
ratio(CR)=D/W
 Depth ratio(DR)=d/W
 Width ratio(WR)=w/W
 Wing depth ratio
 Perforated diameter
ratio
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17. THERMAL CHARACTERISTICS OF HEAT EXCHANGER
WITH TWISTED TAPE
 TT induce swirl into bulk flow-disrupting boundary layer at tube
surface due to repeated changes in surface geometries, TT
induce turbulence & superimpose vortex motion results thinner
boundary layer
 Effect of TT on Thermal Characteristics of Heat exchangers like
Thermo hydraulic performance, Thermal performance factor, Nu,
Friction factor
 Effect of Twist ratio-TT with Twist ratio-5,7 increases the Heat
transfer rate about 188%-159% than plain tube
 Smaller the TR larger is the Heat transfer but penalty of greater
friction factor & Pressure drop
 Small TR give rise to more Nu, Friction Factor & Enhancement
efficiency at high Re
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18. THERMAL CHARACTERISTICS OF HEAT EXCHANGER WITH TWISTED TAPE
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Effect of parallel rectangular wing
TT are cut at the edge of tape in straight line
at every pitch length & each cut bend in
450
 It is observed that increase in wing depth
ratio increases heat transfer rate &
Friction factor as well as maximum
thermal performance
 For Wing depth ratio 0.1,0.2,0.3 HTR
increases 78%,91%,100% than plain
tube
 Thermal performance Factor is about
1.36 for Wing depth ratio 0.3
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19. THERMAL CHARACTERISTICS OF HEAT EXCHANGER WITH
TWISTED TAPE
Effect of Varying width Twisted Tape
 Enhancement is due to the centrifugal forces resulting
the spiral motion of fluid
 Increasing the width of TT results in increase in Nu
hence the heat transfer rate as well as Friction factor
 For Three TT with different width 26,22,18 mm
enhancement of HT is 48%,40% & 35% than plain
tube & Friction factor rise of 18%,17%15% than plain
tube
 Overall enhancement ratio is 1.62,1.39,1.22
 22mm gives better results with 60% material saving
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20. THERMAL CHARACTERISTICS OF HEAT EXCHANGER WITH
TWISTED TAPE
Effect of single, Twin & Triple TT
 When Number of TT increases HTR increases also
increases Friction factor
 Thermal performance factor better for the Twin&
Triple TT than Single TT
 HTR increases 2.5,3,3.5 times more than plain tube
Effect of Half length TT
 HTR increases 40% than plain tube
 On the basis of equal mass flow rate HT performance
is better than Plain tube but on unit pressure drop
basis plain tube is better than half length TT
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21. THERMAL CHARACTERISTICS OF HEAT EXCHANGER WITH
TWISTED TAPE
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Effect of Perforated TT with parallel wing
 Wing induce extra turbulence near tube
wall & efficiently disrupt thermal
boundary layer
 Hole existing along a core tube diminish
pressure loss within the tube, stream
behaves in between axial & swirl flow.
 Wing depth ratio (w/W) increases
higher turbulence intensity & better
mixing fluid near tube wall hence
higher HTR & greater Friction factor,
Higher Thermal performance factor
 Perforated diameter ratio(d/W) larger
the flow become axial flow lose swirl
intensity between tape & surface wall
 HTR , Friction factor, Thermal
performance factor increases with
decreases in Perforated diameter ratio 21

22. THERMAL CHARACTERISTICS OF HEAT EXCHANGER WITH TWISTED
TAPE
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Effect of Peripherally cut Twisted tape
 TT modified by Peripheral cutting in order to
generate additional turbulence in vicinity of
tube wall
 HT, Nu, Friction factor as well as Thermal
performance factor associated by PCTT
found increased with increasing Tape depth
ratio(d/W) & decreasing width ratio (w/W)
Effect of dimpled tube with TT
 Increase of Nu due to both Turbulence
(dimpled tube) & Swirl flow (TT) higher
reduction of boundary layer thickness &
increase of resultant velocity
 HTR & Friction factor increases with
decreasing both Pitch ratio & Twist ratio
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23. CONCLUSION
Twisted tape is commonly used heat transfer enhancement
tool in heat exchanger because its manufacturing process
is simple and these can be easily employed in an existing
heat exchanger. Study of influence different types Twisted
Tapes with different attributes e.g. Twist Ratio, Pitch,
Depth ratio etc & different configuration on Thermal
characteristics of heat exchangers like Heat transfer rate,
friction factor, Thermal performance ratio etc., reveals that
heat exchanger employed with Twisted tape always gives
the enhanced heat transfer with penalty of appreciable
rise in friction & Pressure drop hence selection of the
optimum Twisted Tape for the required working
conditions gives scope for the future work. Future work
may be extended to Change the tape material from
Aluminium to Copper & employing Compound
enhancement techniques.
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