AUGMENTATION HEAT TRANSFER IN A CIRCULAR TUBE USING TWISTED - TAPE INSERTS: A REVIEW

: Heat transfer enhancement is the process of increasing the heat-transfer coefficient, which enhances the system's performance. Enhancing heat transfer is a major problem for saving energy and is also beneficial economically. Many passive devices are used inside tubes to improve heat transfer such as twisted tape inserts, rough parts, extended surfaces, additives for liquids wire plugs, etc. This research reviewed one of the most effective passive devices which are twisted tape inserts. Since it has many advantages such as simple fabrication, simple operation, and ease of maintenance. The twisted tape inserts generated swirl flow and vortex inside the tube. Therefore, the internal convective heat transfer process is significantly improved. The current research article provides an overview of different twisting tape inserts that can improve heat transfer rates. By reducing boundary layer thickness near tube walls. Which lead to reduce the size and cost of many industrial applications, including heat exchangers, refrigeration systems, air conditioners, reactors, thermal power plants, spacecraft, and automobiles. A summary of previous experimental and numerical studies is presented as well. The primary results indicated that the twisted tape inserts are demonstrated to be efficient in enhancing heat transfer inside the tube for laminar and turbulent flow. But during a turbulent flow, twisted tapes increased pressure loss more than laminar flow because of flow obstruction.


Introduction
Improving heat transfer has become one of the most important goals in today's engineering business. The cost and size of industrial equipment including heat exchangers, refrigeration systems, air conditioners, and reactors were reduced using heat transfer argumentation techniques. Heat transfer enhancement techniques are generally divided into three categories: active, passive, and compound approaches. The active approach improves heat transfer by using an external source of power. It's indeed actually rather difficult from a design perspective. As a result of the need for external power, it is only somewhat useful. While for Passive methods, there is no external power supplied. A hybrid technique called the compound heat transfer method uses both active and passive mechanisms. That technique is highly difficult and only has a few uses. So, the most common passive method to improve heat transfer in tubes is twisted tapes inserts since twisted tape generated axial flow, which recirculates due to increased fluid mixing and a consequent significant reduction in boundary layer thickness or improved heat transfer in turbulent and laminar flow, disrupting thermal boundary layers and viscous sub layers. Twisted straps can be easily attached to tubular heat exchangers and are very inexpensive Dewan A et al [1] ; Eiamsa-ard S et al. [2] as shown in Fig.1. The purpose of this study was to review the many experimental and analytical studies conducted by researchers on various topics.

Thermal performance Factor (PF)
A frequently employed metric to assess the effectiveness of various heat transfer augmentation ways is the Factor of thermal Performance (PF). It is described as the proportion of increasing heat transfer to increasing skin friction coefficient for a specified Reynolds number, at constant pumping power. = ( ) ( ) 1/3 (1) ⁄ While Nup and FP represent the plain tube values of the Nusselt number and friction factor, respectively Hwang SD et al. [3].

Effect of Twisting Ratio and Twisting Angle
Researchers have performed numerous experiments on the heat, transfer, and pressure losses characteristics of heat transfer in tape eddy flows to find the best design of tapes, which gives the least amount of friction losses in both laminar and turbulent flow for various twisting strips such as Dhumal AH et al. [ conducted an experimental examination utilizing twisting tapes with a ratio of (5, 7) Nusselt number increases progressively from 920 to 6700, and it is 12-15 percent higher than plain one, due to the increasing swirl degree of flow. For copper pipe with tape inserts and a square-edged intake.
Nutw and Ftw represent the estimated values for the Nusselt number and friction factor for tubes with twisting tape inserts, respectively. He Y et al. [42]; Li P et al. [51] Hollow twisting tapes that cross each other Twisted tape production requires the employment of many tapes.
Piriyarungrod N et al.
[10] Looked at the impact of curved twisted-tapes with four angles of (0.0, 0.3, 0.6, and 0.9) degrees, for four various ratios (3.5, 4.0, and 4.5) on heat transfer. The results that as the taper angle and twist ratio decreased, heat transfer enhancement and friction loss increased, with the tube with a taper angle of 0.9 and the twisting ratio of 3.5 supplying the superior (PF) of 1.05 at Reynolds number of 6000. Tusar M et al. [11] Estimated the impact of the tape twisting of heat transfer strips for airflow through a pipe with constant wall heat flux Reynolds numbers ranging from 3642 to 21857. The study's findings demonstrate that, at lower Reynolds numbers and twist ratios, twisting tapes improve heat transfer. The highest value is approximately 1.16 times at Re-5000, indicating that it is greater than a plain tube. Durga P V and Gupta AVSSKS [12] carried out an experimental investigation of the heat transfer of a Nanofluid inside a twisted tape insert-equipped U-tube heat exchanger. Under various operating conditions with volume fractions from 0.01% to 0.03% and twist ratios (5 -20), the heat-transfer coefficients and related friction factors of the heat exchangers are computed with Reynolds numbers range between 3000 to 30,000. With twisted tape inserts the Nusselt number of tube with 0.03% concentrations of Nano-fluid is increased by 31.28%, while friction factor by 1.23 times when compared with water flow. Sundar LS et al. [13] Fe O3-Oil Nanofluid flow characteristics and heat transmission were evaluated experimentally at the mass flow of (0.04 kg/s -0.208 kg/s), fractions of (0.05% -0.5%), and Prandtl numbers (440 to 2534). Based on the results, the Nusselt number for the 0.5% Nano fluid rate of 0.0416 kg/s and 0.208 kg/s, respectively, is raised by 8.94% and 13.48% compared to the pure fluid. For the rate of 0.208 kg/s and 0.5 vol. % Nanofluid, the friction factor consequence is 1.21 times more than the pure fluid.

Effect of Tape Length and Number
Several researchers Yadav AS [14]; Eiamsa-ard S et al. [15] included conducted studies to determine how the length of the twisted taps affected performance.
Yadav AS [14] Looked into how pressure loss and heat exchange in double-pipe U -bend heat exchangers are affected by half-length twisting tape inserts. Comparing half-length twisted tape inserts to a standard heat exchanger, heat transfer rates are increased by about 40%. Halflength tape inserts outperform simple heat exchangers in terms of heat transfer while the mass flow rate is the same, however smooth tubes outperform half-length twisted tapes when the pressure drops. Standard heat exchangers outperform half-length twisting tape thermally by 1.3 to 1.5 times. A fading swirl turbulent, flow created by short twisted tapes positioned in the test section's entrance with three distinct twisting ratios (3, 4, and 5) was studied analytically and empirically by Eiamsa-ard S, and Seemawute P [15]. The results demonstrate that short tape inserts have inferior thermal performance over the Reynolds number range of (5200-15,300) and at the same twist ratios as full-length tape. Gugulothu SK. [ For the Reynolds number range of 5000 -15000 and cut ratios (0. 6-1. 8), the results indicated an improvement in the thermal performance, Nusselt number due to greater vortex flow in the V-cuts, which disrupts thermal viscous layers more effectively and speeds up heat transfer. Li P et al. [51] unique idea known as the centrally hollow thin twisted tape was examined in laminar flow conditions. When compared to conventional twisted tape, the new type of tape performs overall heat transfer 28.1 percent better. According to the US National Institute of Standards and Technology, the cross-hollow twisted tape is suitable for laminar flow situations. Saysroy A, and Eiamsa-ard S. [52] Simulated three dimension tube flows with square-cutout twisted tapes at constant heat flux-wall. Kumar A et al. [53] Twisted tape was used to evaluate the heat transfer characteristics in a heat exchanger with two pipes. The average Nusselt number index rose by 85% and 34%, respectively, while the pressure decrease is larger for twisted tape with holes. Mashoofi N et al. [54] Used numerical techniques to decrease pressure loss and increase a heat transfer performance factor for axial perforated twisting tape with various hole diameters. Zheng L et al.
[55] examined numerically by using CFX15.0 the influence of dimpled tape on heat transmission of Nanofluid with different constrictions the result indicated that The usage of dimples increases convective heat transfer by 25.53 % when compared to smooth tape, and the maximum rise is 58.96 %. Eiamsa-ard S et al . [56] Investigated different materials: twist ratio, tube dimple angles, and TiO2-water Nano fluid constriction. According to the experimental findings, twisted tapes and dimpled tubes produced higher heat transfer rates than dimpled tubes alone. The results also showed that the dimple angle, twist ratio, and concentration of the TiO2-water Nano fluid had a significant impact on thermo-hydraulic performance. The greatest increase in heat transfer was produced with a dimple angle of 45 degrees. With a declining twist ratio and rising Nano fluid concentration, the Nusselt number increased. The maximum thermo-hydraulic performance of 1.258 over the studied range was attained by using Nano fluid with = 0.15 Saysroy A, and Eiamsa-ard S. [57] Compared numerically the heat transfer and thermal performance of square cut twisted tapes placed into a circular tube to typically twisted tapes inserted into the same tube. The influence of square cut twisted-tape geometries. The primary findings are that when the perforated width-totape width ratio and perforated length-to-tape width ratio decrease, heat transfer and pressure loss increase, whereas the thermal performance factor increases as perforated width-to-tape width ratios increase.
23.86%, for the 0.5% Nano fluid when applying twisted tape inserts of 5. As compared to the basic fluid, the impact of friction factor cost is 1.44 times higher. .

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Yadav [14] Experimental Turbulent utube oil mass flow rate 4,8,12,18,24,30 Half-length twisted tape y/w=7 (2-piece) When compared to a simple heat exchanger, half-length twisted tape inserts enhance the heat transfer coefficient by 40%, and smooth tube heat transfer performance is superior to half-length twisted tape based on unit pressure drop. Plain heat exchangers' thermal performance exceeds half-length twisted tape by 1.3-1.5 times.

Re=5200-15300 Water
Short-tape (STT) y/w=3, 4, 5 The full-length tape ones with y/w=4 and 5 gave higher TPF, because of the large improvement in heat transmission compared to the rise in friction factor. . 12 Gugulothu When dual twisted tapes are inserted, the increase in heat transfer is greater than when single twisted tapes are inserted. At low Reynolds numbers, the highest improvement of heat transfers by inserting single and dual inserts is 290 and 595 percent, respectively.

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Eiamsa-Experimental Re=6000-Helically tape ard et al. [20] 20000 Air H-T y/W= 2, 2.5, 3 for helical pitch ratios p=1, 1.5 , 2 The TPF of 1.29 is obtained by using the tape with the highest twisting ratio of 3 and helical pitch ratio of 2. The V-cut TT in the corrugated tube is greater than that of the conventional TT (from 1.15 to 1.40) and empty corrugated tube (from 1.50 to 2.2) in the experiments. 24 Kumar The average heat transfer coefficient has increased by 82% compared with the bare tape. Similarly the average pressure drop for the holed twisted tape they are 8.7%, 9.1%, and 10.02% for 1 mm, 3 mm, and 5 mm holes respectively higher than the normal twisted tape.

Conclusions
Twisted tape produces swirling flow, increasing turbulence and mixing inside the tube. This is the main influencing factor for increasing heat transfer. Twisting inserts are beneficial for enhancing heat transfer in Nanofluids with high viscosity, however, it has been discovered that they are more effective in laminar and transitional flow. It suggests that these more efficient techniques can increase heat transfer while keeping constant pumping in a laminar flow regime. However, due to flow obstruction in turbulent flow, twisted tapes increased pressure loss more than in laminar flow; as a result, the thermal Performance Factor decreased with increasing Reynolds number, while pressure drop increased with twisting tapes. The smaller twisting ratios enhance heat transfer more than larger ones. Tape inserts with surface modifications like wings, cuts, baffles and dimples, and others, have better thermalhydraulic performance than ordinary twisting tapes. In addition, the employment of twisted tapes with Nanofluids has been proven to be quite effective. However, an additional future study in this field will be highly essential in creating this technology and obtaining more broad useful connections.

Author Contribution Statement
All authors contributed to writing and editing this manuscript. Author Ibrahim S. proposed the research problem and Author Naji Z. developed the introduction and the manuscript pattern. All authors discussed the results and contributed to the final manuscript.