Twisted Tape Inserts Research Articles

Numerical study of heat transfer enhancement through a circular tube fitted with and without rectangular cut twisted tape insert

Numerical simulations have been carried out to investigate the heat transfer enhancement in a tube fitted with a rectangular cut twisted tape insert and compare the data with a smooth tube. For this purpose, CFD (Computational Fluid Dynamics) was utilized to simulate the three-dimensional model with appropriate boundary conditions. The numerical results show that the flow field can be adjusted and the thickness of boundary layer can be decreased by inserting the rectangular cut twisted tape insert so that the heat transfer can be enhanced in the tube. Water was used as the working fluid. The results obtained show an increase in Nusselt number as a result of increasing heat transfer rate for the tube provided with rectangular cut twisted tapes than the plain tube. The pressure drop across the tube wall for twisted tape with the rectangular cut is higher than the plain tube. This increase in the rate of heat transfer is due to the introduction of secondary swirl flow (due to twisted tape) along with the primary flow.

Heat Transfer and Pressure Drop Investigations of the Compact Exhaust Heat Exchanger With Twisted Tape Inserts for Automotive Waste Heat Utilization

Abstract Thermoelectric-based waste heat recovery is a competent technique to reduce the exhaust emissions and fuel consumption of automobiles. Thermal and hydraulic characteristics of the exhaust heat exchanger plays a decisive role in the extent of waste heat recovery from the exhaust gas. In this study, the exhaust heat exchanger having twisted tape inserts is proposed to increase the internal heat transfer coefficient. The dimensionless Nusselt number and friction factor were evaluated experimentally for different designs of the twisted tapes. The experiments were performed for the Reynolds number in the range 2300–25000. The considered geometric parameters of the twisted rib explored were the pitch fraction, twist fraction, and slope. The obtained results were compared to reveal the best feasible design of the twisted tape. The maximum net thermohydraulic efficiency factor achieved for the system in the present analysis is 1.93. With the use of twisted tapes, the area of the exhaust heat exchanger can be greatly reduced for the same power output as flat geometry. This would help for the integration of the waste heat recovery with the engine, where the space available is very limited.

Numerical Simulation for Comparative Thermo-Hydraulic Performance of Turbulent Flow in Tubes with Twisted Tape Inserts

This article focused on investigating numerically the effects of key design parameters including tape thickness, tube wall to tape edge clearance and three different perforated shapes cut (circular, triangular and pentagon) on the heat transfer coefficient enhancement in tube with twisted tape inserts. Water was considered as the working fluid under the turbulent flow of Reynolds number (Re) between 12,000 and 22,000, with constant wall temperature of the tubes. It is found that due to the swirling flow and efficient mixing of the fluid, all the tape inserts considered in this study produced better thermalhydraulic performance than the plain tube without an insert. At the same time, tape inserts with small tube wall to tape edge clearance and considerable thickness value is beneficial to reduce the friction factor, consequently enhancing the heat transfer rate. Through the thermal performance factor (TPF) evaluation, the twisted tape with perforated triangular shape cut has an advantage over the pentagon and circular shapes cut with increasing Re. A maximum TPF as high as 1.68 can be obtained for the twisted tape with perforated triangular shape cut under low turbulent Re.

Heat transfer performance of a nanofluid-filled tube with wall corrugations and center-cleared twisted-tape inserts

ABSTRACT We numerically examine the thermal performance of a round tubular heat exchanger featuring a combination of three passive techniques for heat-transfer enhancement: (i) center-cleared twisted-tape inserts, (ii) tube corrugations, and (iii) nanofluids. We consider three geometric tape parameters – the central-clearance width (C), the tape width (W), and the 180° tape pitch (H) – across a range of Reynolds numbers (500 ≤ Re ≤ 1250). For both water and a representative nanofluid (Al2O3-water), increasing W or decreasing C or H is found to increase the heat transfer coefficient at all Re. Switching from water to one of four water-based nanofluids − Al2O3-water, CuO-water, Cu-water, and TiO2-water – is found to improve the heat transfer rate sufficiently to overcome any associated rises in pressure drop, resulting in thermal efficiencies higher than those of water. The highest thermal efficiency coefficient (η = 1.157) occurs with the Cu-water nanofluid at the smallest Re (500), whereas the lowest thermal efficiency coefficient (η = 1.115) occurs with the CuO-water nanofluid at the largest Re (1250). Across the entire Re range, increasing the volume concentration of Al2O3 nanoparticles (from ϕ = 2 to 5%) is found to increase the coefficients of heat transfer and thermal efficiency. This study provides new insight into how the heat transfer capabilities of a tubular heat exchanger can be enhanced by combining center-cleared twisted-tape inserts, tube corrugations and nanofluids.

Thermal Performance of a Heated Pipe in the Presence of a Metal Foam and Twisted Tape Inserts

To meet the demand for more efficient ways of cooling and heating, new designs and further development of heat exchangers is essential in industry. The present study focuses on the thermal performance of a circular pipe with two inserts. The first insert consists of a porous medium having a porosity of 0.91, and the second one consists of a single twist solid insert. Different ranges of heating conditions have been applied for different flow rates. Water and titanium dioxide (TiO2) nanofluid 1% vol are the liquid media used for cooling. Laminar flow is assumed for two different Reynolds numbers of 1000 and 2000. The results of the study have shown that the twisted tape insert increases the thermal efficiency of the pipe more than the porous media insert and the plain pipe. In addition, different temperature readings in the cross section of the pipe have indicated that the twisted tape helps mixing up the fluid and provides a constant temperature in the overall volume of the fluid, whereas for the porous media insert and plain pipe the fluid temperature increases in the fluid particles close to the pipe inner surface. TiO2 nanofluid exhibited an enhancement when compared to water for a plain and porous pipe. However, this enhancement was absent when a twisted insert is used.

Heat transfer assessment of turbulent nanofluid flow in a circular pipe fitted with elliptical-cut twisted tape inserts

In the present work, a numerical study is conducted to improve the thermal performance of a circular pipe fitted with the elliptical-cut twisted tape (ECT) inserts in presence of a nanofluid as the working fluid. A comparison between the pipe with and without ECTs in different cases is implemented. This investigation is accomplished for a 3D periodically turbulent flow with constant heat flux on the walls. The effect of inserting the ECTs with different parameters, namely the ratio of short diameter to twisted tape width (WA = a/W = 0.7, 0.8, 0.9) as well as the ratio of long diameter to short diameter of the twisted tape (BA = b/a = 2, 2.5, 3) is examined. In the case of WA = 0.7 and BA = 2 for Reynolds number of 7000, the Nusselt number and thermal efficiency factor (TEF) are maximum with the values about 117.25 and 1.392, which show 6.18% and 6.6% improvement compared to the case with the square-cut twisted tape. Moreover, the Cupric Oxide nanoparticles-enhanced fluid with the nanoparticle concentration ranging from 1 to 4% is used to study the effects of the nanofluid on the heat transfer performance of the different configurations. Based on the results, the highest Nusselt number and TEF occur at the concentration of 4%, which are equal to 177.81 and 1.7637, respectively. Moreover, the TEF for the case with the elliptical-cut twisted tape and nanofluid is 21% higher than the same geometry with water as the working fluid, and 26% higher than the square-cut twisted tape in the presence of water.

Review on Heat Transfer Enhancement by Insert Devices

The scientists revise the heat transfer enhancement techniques time to time to achieve better performance and to obtain optimized designs of heat exchangers. The present study reviews the performance and techniques of heat transfer enhancement using various insert devices such as twisted tape and wire coil insert as well as completely different forms of other inserts like air-foil shape inserts, X-shaped twisted tape inserts, baffles and V-winglets inserts with various types of medium and nanofluids. According to the summary of recent significant researches on the heat transfer enhancement by using different types of inserts and combinations of these inserts with various nanofluids showed that insert can indicatively enhance the heat transfer rate by modifying its geometry or configurations like twist ratio, length ratio, pitch ratio, segmented tape, perforated tape, angle of arrangements and insert quantities and so on which caused a considerable impact on performance characteristics of heat transfer enhancement along with the pressure drop and friction factor. It is revealed through reviewing the related literature that the highest value of equivalence heat transfer enhancement is as maximum as 400%, 300% and 9% for the twisted tape insert with helical tube, the air foil shaped inserts and for the wire coil inserts, respectively when compared with the smooth tube. In the case of baffles in nanofluids, as maximum as 255% equivalence heat transfer enhancement could be achieved when compared with that of baffles without nanofluids.

Thermo-Hydraulic Performance Analysis on the Effects of Truncated Twisted Tape Inserts in a Tube Heat Exchanger

This paper investigates the convective heat transfer in a heat exchanger equipped with twisted tape elements to examine effects of the twisted tape truncation percentage, pitch value, position and Reynolds number using 3D numerical simulation. A symmetric heat flux is applied around the tube as the studied heat exchanger. Based on the influences in both heat transfer enhancement and pressure drop, the performance evaluation criterion (PEC) is utilized. Inserting twisted tape elements and reducing the pitch value significantly augment the Nusselt number, friction coefficient and PEC number compared to the plain tube. For the best case with a Reynolds number of 1000, the average Nusselt number increases by almost 151%, which is the case of fully fitted twisted tape at a pitch value of L/4. Moreover, increasing the twisted tape truncation percentage reduces both heat transfer and pressure drop. Furthermore, the highest heat transfer rate is achieved when the truncated twisted tape is located at the entrance of the tube. Finally, it is concluded that for P = L, L/2, L/3 and L/4, the optimum cases from the viewpoint of energy conservation are twisted tapes with truncation percentages of 75, 50, 50 and 0%, in which the related PEC numbers at a Reynolds number of 1000 are almost equal to 1.08, 1.24, 1.4 and 1.76, respectively.

Numerical Analysis of FLiBe Laminar Convective Heat Transfer Characteristics in Tubes Fitted With Coaxial Cross Twisted Tape Inserts

Molten salts are now widely used as heat transfer fluids in solar thermal plants and molten salt nuclear reactors. In order to explore its heat transfer enhancement method, new coaxial cross twisted tapes (CCTTs) are applied to plain tube with molten salt FLiBe as working fluid, and the characteristics of pressure drop and heat transfer are numerically investigated by the CFD software STAR-CCM+. Simulations are performed in a laminar flow regime where Reynolds number ranges from 100 to 1100, and the velocity, temperature profiles, and enhanced performance evaluation criteria (PEC) are analyzed to investigate the heat transfer performance of FLiBe in the tube fitted with CCTTs and typical twisted tape (TT). Water and lubricating oil are also researched to investigate the effects of fluid thermal-physical properties on the performance of CCTTs. The results show that CCTTs can produce stronger swirl flow and greatly enhance heat transfer. For overall heat transfer performance, the maximum PEC of FLiBe with CCTTs reaches 2.37. The comparison of three different fluids also indicates that CCTTs have better heat transfer performance for higher Prandtl number fluids such as molten salt. The correlations of CCTTs and TT are developed into a unified form for the prediction of friction factors and Nusselt numbers for various Prandtl number fluids.

Heat Transfer of rGO/CO3O4 Hybrid Nanomaterial-Based Nanofluids and Twisted Tape Configurations in a Tube

Abstract The friction factor, thermal performance, and heat transfer are experimentally analyzed for reduced-graphene oxide/cobalt oxide (rGO/CO3O4) hybrid nanomaterial-based nanofluid circulating in a plain tube with and without twisted tape inserts having different pitches. The reduced-graphene oxide/cobalt oxide (rGO/CO3O4) hybrid nanomaterial is prepared using in situ/chemical reduction technique and then characterized with transmission electron microscope, X-ray diffraction, and magnetometry. The experiments were conducted with different values of particle loading (0.05%, 0.1%, and 0.2%) and Reynolds number (2000–2,020,000). Three twisted tape inserts of helixes 285 mm, 190 mm, and 95 mm were used. The nanofluids was produced from the addition of the hybrid nanomaterial to water yield an increase, as compared to the basefluid (water), of the Nusselt number, which is further enhanced by increasing the nanoparticle loading. Therefore, when compared to water, the Nusselt number is enhanced by 25.65%, with no twisted tape and by 79.16% with twisted tape with helix of 95 mm for the nanofluid of 0.2% volume concentration. However, when compared to water, there is a slight friction factor penalty with the 0.2% particle loading of 1.11-times and 1.49-times for the plain tube and for the 95-mm twisted tape helix, respectively. The thermal performance factor gets enhanced by increasing the nanoparticles concentration of the hybrid nanofluids with or without twisted tape inserts, and it is always higher than one. Based on the experimental data, regression equations were developed for the Nusselt number and friction factor.

Single phase flow heat transfer characteristics of quad-channel twisted tape inserts in tubes

Heat transfer and pressure drop of turbulent fluid flow were studied numerically and experimentally in a quad-channel with twisted tapes placed in a circular tube under uniform heat flux boundary condition. All the tests were conducted with water as the working fluid where the turbulent flow range of Reynolds numbers were maintained at 4250 to 11000. Quad-channel twisted tapes (QCTT) were manufactured by 3D printer with the material PLA, the lengths of 50 mm, 100 mm, 200 mm with the twist ratio of 4.48. The tapes were identified with their tape/pipe length ratios (TPR) of 0.025, 0.05 and 0.1. Validation of the experimental data was performed by the comparison of the experimental results with the data from the well-known empirical correlations. Alteration of the friction factors and Nusselt numbers with the Reynolds numbers are presented in this paper. The results showed that the Nusselt number and the friction factor increased with the increasing of the length of QCTTs. On the other hand, the performance evaluation criteria (PEC) should be declining with the increase of the lengths of the tapes. The evaluated temperature distributions inside the tested tubes with the inserts were plotted in order to investigate the observed data. Based on the obtained experimental data, the empirical correlations for the Nusselt number within the deviation of ±2% and the friction factor within the deviation of ±5% were developed for the practical usage.

An experimental study on heat transfer enhancement and flow characteristics of a tube with plain, perforated and dimpled twisted tape inserts

In order to increase the performance of a heat exchanger flowing ethylene glycol (EG) and water (W) mixtures, the effects of different twisted tapes on heat transfer and flow characteristics in a heat exchanger tube is experimentally investigated. Material of the twisted tapes and the tube is selected as stainless steel. Three different volumetric ratios of EG and W mixtures are used with the volumetric ratio of (0:100), (20:80) and (40:60). The twisted tapes having twist ratio of 5.88 are perforated and dimpled with pitch ratio of (Pp/y and Pd/y) of 0.25, 0.5 and 1.0. The experiments are conducted under constant heat flux and Reynold number ranging from 5217 to 22,754. The experiments for both the smooth tube and the typical twisted tape inserted tube are validated with the literature. The results indicated that the use of twisted tape inserts enhances the heat transfer performance. Experimental results revealed that novelty dimpled twisted tape insert provides higher heat transfer performance than the others. Adding the ethylene glycol on pure water has not major role on increase in the friction factor. As the amount of ethylene glycol in the mixture increases, thermo hydraulic performance decreases. The best thermo-hydraulic performance results are obtained as 1.42, 1.17 and 1.05 for dimpled twisted tape (Pd/y = 0.25) inserted tube at the lowest Reynolds numbers for the fluids which are (0:100), (20:80) and (40:60), respectively.

Investigation of Overlapped Twisted Tapes Inserted in a Double-Pipe Heat Exchanger Using Two-Phase Nanofluid.

This study investigated the laminar convective heat transfer and fluid flow of Al2O3 nanofluid in a counter flow double-pipe heat exchanger equipped with overlapped twisted tape inserts in both inner and outer tubes. Two models of the same (co-swirling twisted tapes) and opposite (counter-swirling twisted tapes) angular directions for the stationary twisted tapes were considered. The computational fluid dynamic simulations were conducted through varying the design parameters, including the angular direction of twisted tape inserts, nanofluid volume concentration, and Reynolds number. It was found that inserting the overlapped twisted tapes in the heat exchanger significantly increases the thermal performance as well as the friction factor compared with the plain heat exchanger. The results indicate that models of co-swirling twisted tapes and counter-swirling twisted tapes increase the average Nusselt number by almost 35.2–66.2% and 42.1–68.7% over the Reynolds number ranging 250–1000, respectively. To assess the interplay between heat transfer enhancement and pressure loss penalty, the dimensionless number of performance evaluation criterion was calculated for all the captured configurations. Ultimately, the highest value of performance evaluation criterion is equal to 1.40 and 1.26 at inner and outer tubes at the Reynolds number of 1000 and the volume fraction of 3% in the case of counter-swirling twisted tapes model.

Thermal performance in a modified header solar water heating system using salt hydrate technology with twisted tape insert

In this study, the thermal performance of a solar water heater while using Epsom salt as a phase change material and the temperature maintenance in water are explained in detail. Here the Epsom salt (Magnesium Sulfate hepta hydrate form) acts as an energy-storing medium that is used as mixed with water. Generally, the solar water heating system maintains water temperature at an optimum level at day time and very less in the night time when there is no radiation. When using Epsom salt, mixing with water, the Epsom content absorbs heat and it keeps the heat with itself for a long time. So the heat remains in the water at night time too. Therefore a constant rate of temperature is maintained in water during day and night time. Besides, with the insertion of HT (Helix Twist) is used to excel in the heat transfer rate between water and tube by increasing the swirl effect of water. The circulation of water is carried out by the Thermosyphon effect. The results confirmed that this proposed solar water heater provides higher efficiency up to 92%, which is higher than the conventional SWH efficiency of 82%. The average Nusselt number is 18% greater than the conventional one. Apart from efficiency enhancement, the addition of Epsom salt provides some health benefits like pain relief, reduction of insulin resistance in the body with an increase in magnesium, and Sulfate content and for plants by supplying the used water. It is most important that it is advisable to use the water for bathing purposes only.

Augmentation of Heat Transfer of High Prandtl Number Fe3O4/vacuum pump oil nanofluids flow in a tube with twisted tape inserts in laminar flow

The heat transfer coefficient and friction factor of Fe3O4/vacuum pump oil nanofluids flowing in a tube with twisted tape inserts were analyzed experimentally. The experiments were conducted for different mass flow rates (0.04 kg/s to 0.208 kg/s), volume concentrations (0.05% to 0.5%), Prandtl numbers (440 to 2534), Graetz numbers (500 to 3000) and twisted tape inserts (H/D = 5, 10 and 15). Results reveal that the Nusselt number is enhanced by 8.94% and 13.48% for the 0.5% nanofluid for the mass flow rates of 0.0416 kg/s and 0.208 kg/s, respectively, relative to the base fluid. For the mass flow rate of 0.208 kg/s with 0.5 vol. % nanofluid, the friction factor penalty is 1.21-times compared to the base fluid. By using twisted tape insert of H/D = 5, the Nusselt number is further enhanced by 23.86% and 39.53% for the 0.5% nanofluid for mass flow rates of 0.0416 kg/s and 0.208 kg/s, respectively, relative to the base fluid. For the twisted tape insert of H/D = 5 with mass flow rate of 0.208 kg/s and 0.5 vol. % nanofluid, the friction factor penalty is 1.44-times compared to the base fluid. New Nusselt number and friction factor correlations are proposed.

Numerical study of circumferential temperature difference reduction at the absorber tube of parabolic trough direct steam generation collector by inserting a twisted tape in superheated region

The present numerical simulation investigates the influence of a twisted tape inserts on circumferential temperature difference reduction and heat transfer enhancement in the absorber tube of parabolic trough collector. The effect of twisted tape geometrical parameters and the Reynolds number on the circumferential temperature difference, Nusselt number, friction factor and thermal performance factor is analyzed. Superheated steam is used as the heat transfer fluid. In present investigation, the Reynolds number is considered in the range of 104 ≤ Re ≤ 9.79×105; clearance ratio and twist ratio are varied in the range of 0–0.5 and 2.5–10, respectively. For the considered range of these parameters, Nusselt number increases 1.0–1.7 times and friction factor increases in the range of 1.8–4.1 times. Therefore, the maximum thermal performance factor under identical pumping power is in the range of 0.85–1.1.Twisted tape with minimum twist ratio and zero clearance provides higher Nusselt number and friction factor due to strong generated swirl flow and increased fluid hydraulic path length. According to the numerical results, the maximum circumferential temperature difference decreases about 10–45% which will significantly reduce thermal stresses in the absorber tube.

Numerical Investigation of Ventilation Air Methane Catalytic Combustion in Circular Straight and Helical Coil Channels with Twisted Tape Insert in Catalytic-Monolith Reactors

In a catalytic combustion of ventilation air methane, one of the key factors determining the reactor performance is the geometry of the reactor. It should be designed to provide maximum energy conversion at minimum catalyst usage and operating cost. This numerical study is conducted to investigate the catalytic combustion of ventilation air methane from a gassy underground mine in a circular straight and helical reactor channel with twisted tape insert. A three-dimensional computational fluid dynamics model which considers conservation of mass, momentum, energy, and species together with chemical reactions, and constitutive relations for species properties and reactions kinetics was developed and validated against the previously published data. The effect of several key factors affecting the catalytic combustion performance such as inlet Reynolds number, twisted tape ratio, and reactor length are evaluated to obtain the optimum reactor parameters. For evaluation purpose, the reaction performance of the studied reactors will be compared to the straight reactor without twisted tape which is set as a baseline. The results give a firm confirmation on the superior performance of the reactors with twisted tape insert as compared to those without. In addition, it is found that helical reactors generate higher net power as compared to their respective straight reactor counterpart despite having lower FoM due to larger catalyst area. Interestingly, the higher twisting ratio offers better performance in terms of net power as well as FoM. Overall, the results highlight the potential of twisted tape insert application in catalytic combustion.

Numerical and experimental thermal performance with entropy generation analysis on tube with helical screw tape inserts at number of strips in turbulent flow

In the heat exchangers, twisted tape insert is a technique to enhance heat transfer. In this paper, the experimental and numerical investigations are arranged to analyze thermal performance with entropy generation analysis on single and double strip helical screw tape inserts. The finite volume method is used with shear stress transport K-ω model to analyze fluid flow in tube with inserts. The Nusselt number attained enhancement with double strip as compared to single strip helical screw inserts at decreased values of twist ratio and increased values of Reynolds number. However, the Nusselt number attained maximum enhancement of 112% with double strip helical screw insert than plain tube at 4000 of Reynolds number (Re). The common correlations for Nusselt number and friction factor are generated with respect to Reynolds number, number of the strips and twist ratio. Entropy generation analysis is also performed. The thermal performance factor attained its enhancement with double strip than single strip helical screw inserts at twist ratio of 2.5 and 3; whereas, double strip helical screw insert attained maximum value of 1.5 at twist ratio of 2.5 and Reynolds number of 16000. The double strip helical screw inserts are suitable for miniaturization of heat exchanger.

EXPERIMENTAL INVESTIGATIONS TO STUDY THE INFLUENCE OF TWISTED TAPE INSERT ON HEAT TRANSFER EQUIPMENTS – AN EXTENSIVE REVIEW

Heat transfer augmentation with compact and effective manner are the recent developments of the heat exchangers. Considering cost reduction, simplicity, compact size etc were the parameters considered for the design and development of heat exchangers. Use of passive techniques like creating fins, rough surface on the flow path, wire coil inserts, generation of swirl on the flow path and mounting inserts like blocks, winglets and twisted tapes were the impressive methods of heat transfer intensification in heat exchanger design. Twisted tape is the technique that supports to enhance the heat transfer in heat exchanging devices. Many investigators involved on the experimentation to enhance the rate of heat transfer employing twisted tapes by varying the twisted tape geometry , twisted tape shape and the size of the duct etc. This extensive review emphases on the argumentation of heat transfer by twisted tape insert with varying twisted tape geometry, is discussed and disclosed in detail. This review revealed the outcomes of the literatures reported for the past decade.

Numerical Study of Heat Transfer Enhancement of Turbulent Flow Using Twisted Tape Insert Fitted with Hemispherical Extruded Surface

Heat transfer enhancement of heat exchangers is an important matter of concern to achieve more effective thermal energy conversion systems. The use of modified twisted tape (TT) inserts as passive technique of heat transfer augmentation are effective way to improve heat transfer. In this study, a numerical analysis is performed to investigate the heat transfer performance enhancement and flow behavior in a circular pipe using TT insert fitted with a hemispherical extruded surface (HES). The study is carried out for the turbulent flow regime (4000�Re�10000) at a twist ratio of 4.0 using ANSYS FLUENT. A flow domain is designed and mathematically modeled applying boundary conditions and using governing equations for turbulent model. The plain tube data is validated with established correlations. The achieved numerical results reveal that for TT fitted with HES leads to increment in heat transfer rate up to 69.4 compared to plain tube due to effective swirl flow and better mixing caused by the insert. Corresponding increase in friction factor is found relative to plain tube. The impact on the thermal performance factor has obtained a maximum of 1.24 at constant pumping power for Reynold number 4000. © 2020 International Information and Engineering Technology Association. All rights reserved.