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This work presents a review of the research recent results concerning the augmentation of hydrodynamic and thermal performance of various twisted tape inserts in heat exchanger tubes. The thermal and hydrodynamic correlations for various twisted tape elements have been summarized. A comparative study of thermal and hydrodynamic performance of numerous twisted elements has also been reported to understand the result of applications of twisted tape inserts in heat exchanger tubes. The literature review found that multiple twisted tapes heat exchanger tube shape enhanced hydrodynamic and thermal performance than other comparable twisted tape inserts heat exchanger tube shapes. The review of twisted tape inserts techniques existing in this paper will be helpful to the investigators working in this field.

Experimental examination is carried out to study the turbulent heat transfer and fluid-flow characteristics in circular heat exchanger tube using combined wing with solid ring twisted tape inserts. A series of experiments has been performed with the range of Reynolds number varied from 3000 to 21000, number of twisted taped inserts, N TT , varied from 1.0 to 4.0 with constant value of other twisted tape parameters such as rings pitch ratio, d R /D T = 1.0, wing pitch ratio, P W /W T = = 3.0, and wing depth ratio, W d /W T = 1.67. Based on the examined, turbulent heat transfer and fluid-flow in wing with combined solid ring twisted tape inserts results are compared with plain circular tube under same operating conditions. The experimental results show that the heat transfer is increased around 5.66 times than plane circular heat exchanger tube. The thermal and hydrodynamic performance parameter based on equal pumping power, η p , was found to be highest for N TT = 3.0. The optimum value of thermal and hydrodynamic performance has been found to be 2.74 for Reynolds mumber of 3000 within the range of the parameters investigated. Multiple wings with solid rings twisted tape inserts have been also shown to be thermally as well as hydraulically better in comparison to other similar twisted tape insert geometries.