Table 3 Numerical/experimental findings of modified tape in the laminar region are summarized

Bhattacharyya et al. [71]

Water

Twisted tape angle = 180 and small twist ratio = TR 18.0

Numerical evaluation

Periodic change of direction of swirl

Heavy collision of the mixed fluids behind the varying location

Lead to mixing of superior quality

Better heat transfer, compared with the typical twisted-tape

Meyer and Abolarin [65]

Water 2.9 < Pr < 6.7

Twisted tape twist ratio = TR 3,4 & 5

Experimental in a circular tube

Flow regimes of laminar, transitional and turbulent

Friction factors increased as the twist ratio decreased

Standard deviation method in which the temperature deviations determined

Bhattacharyya et al. [55]

ethylene glycol Nre = 100–2000

Angular cut wavy tape (angles = 45°)

Experimental in a square channel

Angular cut wavy tape with small wavy ratio significantly better

Useful in designing tubes

Boonloi and Jedsadaratanachai [66]

Fluid

modified-twisted tapes (rectangular holes) TR = 1, 1.5, 2, and 4)

Circular Tube Geometry

The maximum thermal enhancement factor is around 1.39 and 1.31 for the double twisted

Tape and single twisted tape, respectively, at Re = 3000, LR = 0.78, and TR = 1

Salman et al. [67]

SiO2 and TiO2 Nanofluids

Conic Cut Twist Tape TR = 2.93

Experimental in a circular tube

Over the range investigated (Re = 220–1500), the Maximum thermal performance factor of 5.13 is found SiO2 and TiO2 nanofluids of different volume concentration in plain tube give good enhancement in Nusselt number compared to deionized water

Saha and Dutta [9]

Water 2.5 < Pr < 5.18

Short length, Full length, Smoothly varying pitch, Regularly Spaced Twisted tapes

Experimental in a circular tube

Friction and Nu low for short length tape

Short length tape requires small pumping power

Multiple twist and single twist has no difference on thermohydraulic performance

It was observed that twisted tape is effective in laminar flow

Ray and Date [37]

Water 100 < Re < 3000 Pr < 5.0

Full-length twisted tape with width equal to side of duct

Numerical work for square duct

Proposed correlations for friction and Nu

Higher hydrothermal performance for square duct than circular one

Local Nusselt number peaks at crosssections where tape aligned with diagonal of duct

Lokanath and Misal [94]

Water 3.0 < Pr < 6.5 lube oil (Pr = 418)

Twisted tape

Experiment in plate heat exchanger and shell and tube heat exchanger

Large value of overall heat transfer coefficient produced in water-to-water mode with oil-to water mode

Ujhidy et al. [34]

Water

Twisted tape

Experiment in channel

Explained flow structure

Proved existence of secondary flow in tubes with helical static elements

Wang and Sunden [39]

Water 0 < Re < 2000 0.7 < Pr < 3.0

Twisted tape

Experiment in circular tube flow

Both inserts effective in enhancing heat transfer in laminar region compared with turbulent flow

Twisted tape has poor overall efficiency if pressure drop is considered

Suresh Kumar et al. [95]

Water

Twisted tape

Experiment in large-diameter annulus

Observed relatively large values of friction factor

Measured heat transfer in annulus with different configurations of twisted tapes

Saha and Chakraborty [96]

Water 145 < Re < 1480 4.5 < Pr < 5.5

Twisted tape regularly spaced 1.92 < y < 5.0

Experiment in circular tube flow

Larger number of turns may yield improved thermohydraulic performance compared with single turn

Ray and Date [7]

Water

Twisted tape

Numerical study in square duct

Higher Prandtl numbers and lower twist ratios can give good performance

Guo et al. [97]

Water

Center-cleared twisted tape Short width

Numerical study in circular tube

Center-cleared twisted tape is a promising technique for laminar convective heat transfer enhancement

Zhang et al.[93]

water

multiple regularly spaced twisted tapes

Numerical study in circular tube

The simulation results verify the theory of the core flow heat transfer enhancement which leads to the separation of the velocity boundary layer and the temperature boundary layer, and thus enhances the heat transfer greatly while the flow resistance is not increased very much

Kumar et al. [98]

water

Twisted tape

Numerical study in a square ribbed duct with twisted tape

Rib spacing and higher twist ratio for high Prandtl fluids and for low Prandtl fluid rib spacing should be higher and twist ratio should be lower

Liao and Xin [99]

Water,Ethylene glycol, Turbine oil 80 < Re < 50,000

Segmented twisted tape and three dimensional extended surfaces

Experiment in tube flow

In a tube with three-dimensional extended surfaces and twisted tape increases average

Stanton number up to 5.8 times compared with empty smooth tube

Al-Fahed and Chakroun [33]

Oil

Twisted tape with twist ratios 3.6, 5.4,7.1 and microfin

Experiment in single shell and tube heat exchanger

For low twist ratio resulting low pressure drop, tight fit will increase more heat transfer

For high twist it is different

Microfins are not used for laminar

Saha et al. [38]

Fluids with 2.05 < Pr < 5.18

Twisted tape (regularly spaced)

Experiment in circular tube

Pinching of twisted tape gives better results than connecting thin rod for thermohydraulic performance

Reducing tape width gives poor results; larger than zero phase angle not effective

Saha and Bhunia [11]

Servotherm medium oil 45 < Re < 840

Twisted tape (twist ratio 2.5 < y < 10)

Experiment in circular tube

Heat transfer characteristics depend on twist ratio, Re and Pr

Uniform pitch performs better than gradually decreasing pitch