Twisted Tapes Research Articles

Experimental study of thermal characteristics of alternatively twisted swirl generator tape in a heat exchanger tube

ABSTRACT The heat transfer capacity of a convectional heat exchanger needs to be increased to minimize size and cost. Inserts are a promising way to enhance heat transfer at a bearable penalty in pressure drop. The objective of this study is to evaluate experimentally the thermal-hydraulic characteristics of a heat exchanger tube inserted with a novel alternatively twisted swirl generator (ATSG) tape. The experimental data has been collected for nine distinct combinations of ATSG tapes, includes the tapes with three twist angles (45°, 60°, and 90°) and three twist ratios (3, 4 and 5) for Reynolds numbers of 4,000 to 20,000. The use of ATSG tapes resulted in a considerable improvement in heat transfer rate compared to simple twisted tapes (TT). Over the range evaluated, heat transfer coefficient, pressure drop and thermal performance factor (TPF) with ATSG tapes in a tube are, respectively, 1.57–1.82, 1.58–2.54, and 1.22–1.46 times to that of simple TT in a tube. The maximum TPF achieved is 1.52 for ATSG tape with twist ratio of 3 and twist angle of 90°. The TPF for any combination of ATSG tapes is greater than one, which signifies that it is an efficient approach.

Modeling and optimizing perforated twisted tape for heat transfer enhancement

Previous studies on twisted tapes based on empirical design may overlook some structures having exceptional performance. To further develop the design flexibility, we propose a parametric modeling method for perforated twisted tapes (PTTs) in conjunction with multi-objective optimization to achieve heat transfer enhancement within the flow channel. This method considers the influence of structures on hydrothermal performance more thoroughly, and accelerates the development process. The control coefficients in the mathematical descriptions of the geometric characteristics expressed by Bernstein–Bézier functions were specified as the design variables. Two types of PTTs, full-width and half-width, were presented based on the variable ranges of width optimization. In the optimization, the observed objectives were the average temperature, root mean square temperature, and friction factor. A three-dimensional computational fluid dynamics model was employed to analyze the heat transfer and flow behaviors under three friction factor weight coefficients (0.1, 0.3, and 0.5) and was validated against experimental data. The numerical results showed that the maximum decrease in the average temperature and root mean square temperature of the heat source could attain 18.58 K (5.46%) and 2.92 K (72.64%), respectively. The friction factor was reduced by a maximum of 3.59 (57.35%) at the weight coefficient of 0.5 compared to 0.1. Furthermore, according to the performance evaluation criterion (PEC), the half-width PTTs generate less flow resistance and exhibit superior overall performance. The proposed method elaborates on the potential design space and provides a framework for the creation of efficient convective heat transfer devices.

Heat transfer and fluid flow of swirling impinging jets ejected from nozzles with different twisted tapes

Heat transfer and fluid flow of swirling impinging jets ejected from nozzles with different twisted tapes

Energy, exergy, and entropy generation analyses of a water-based photovoltaic thermal system, equipped with clockwise counter-clockwise twisted tapes: An indoor experimental study

• Improving the performance of a photovoltaic thermal system with twisted tapes. • Performance analyzing from energy, exergy, and entropy (3E) viewpoints. • Enhancing total efficiency of the photovoltaic thermal system by 68.97% with inserts. Nearly half of the insident solar radiation to the photovoltaic (PV) units will be converted to heat, which leads to a high operating temperature, cell structural damage, and the lifetime reduction. Therefore, an effective cooling method for these units is vital. The present work is the first experimental study on the influence of the twisted tapes (clockwise and counter-clockwise), which are inserted in riser tubes, on the performance of a photovoltaic thermal system from energy, exergy, and entropy generation viewpoints. In the indoor experiments, working fluid (pure water) with various flow rates ranged from 0.019 to 0.036 kg/s passed through the collector, where heat fluxes of 300, 500, 700, and 900 W/m 2 were applied on the surface of photovoltaic units. Thanks to utilizing twisted tape inserts with the flow rate of 0.019 kg/s, the average surface temperature decreased by 1.4, 1.2, 1.7, and 0.6 °C, respectively, under heat fluxes of 900, 700, 500, and 300 W/m 2 . In addition, the overall energy efficiency of the photovoltaic thermal system, using clockwise and counter-clockwise twisted tapes, increased by 7.37 and 68.97%, respectively, compared to that of the conventional photovoltaic thermal system and PV unit. From exergy viewpoint, the photovoltaic thermal system using twisted tapes experienced higher overall efficiency (14.86%) compared to that of the conventional photovoltaic thermal system (13.57%) and PV unit (11.57%). Furthermore, lower entropy generation belonged to the photovoltaic thermal system with twisted tape inserts.

Thermo-hydraulic performance investigation of a heat exchanger tube inserted with twisted tapes modified with various twist ratio and alternate axis

This paper presents a numerical investigation on a heat transfer enhancement by using a computational fluid dynamics software. The heat transfer enhancement is implemented by inserting twisted tape into a heat exchanger tube. The twisted tapes with twist ratios of 4, 6 and 8 were modified with alternate axis. The pitch of the twisted tape having the rotation direction such as clockwise and counterclockwise are connected with 90º connection angle. Water is selected as working fluid and turbulent flow condition corresponding to Reynolds number ranging from 5000 to 29000 are considered in the study. The heat exchanger tube is under constant heat flux of 50 kW/m2. Numerical analysis results prove that the use of twisted tape improves thermal performance compared to smooth tube. As the twist ratio increased, the heat transfer performance and the friction loss penalty decreased. Overall results are determined with thermohydraulic performance criteria (THP). The highest THP value is obtained as 1.21 for the tube inserted with the twisted tape which has the twist ratio of 4 and alternate axis between the twist pitches at Reynolds number of 5913

Comparative study on flow and heat transfer characteristics of swirling impingement jet issuing from different nozzles

The flow and heat transfer characteristics of spiral rod (SR), twisted tape (TT), guide vane (GV) and thread grooves (TG) nozzles are compared by numerically and experimentally for swirl angle (θ) = 15°-60° and Reynolds number (Re) = 6000–12000. An experimental system is built to investigate the heat transfer characteristics of the impingement target. The experimental results show that the TG nozzle has the highest Nusselt number (Nu) in the stagnation region, 19.19%−55.98% higher than that of the other three nozzles for Re = 6000, and SR nozzle has the highest Nu except in the central area. In addition, it is shown that the gas chamber pressure of TG nozzle is much smaller than that of the other three nozzles. The numerical method studies the streamlines, turbulent kinetic energy and vortex distribution in the jet space, and the Nu under different θ and Re of the four types of nozzles, which is verified with the experimental results. The numerical results show that SR nozzle has the largest impingement velocity, the best heat transfer effect, and uniformity, and is obviously influenced by θ. With the increase of the impingement spacing of the four types of nozzles, the impingement area enlarges and cooling effect weakens simultaneously. By studying the flow and heat transfer characteristics, a new swirl nozzle design method based on heat transfer, heat uniformity and pressure loss is established.

Heat transfer intensification of turbulent forced convection by inserting discontinuous twisted tapes in a wavy tube; hydrothermal and thermodynamics analysis

The current study presents a numerical investigation on turbulent hydrothermal characteristics in a wavy passage equipped with discontinuous twisted tapes. The working fluid is water and passage walls are kept under constant wall temperature. The effect of Reynolds number (Re = 2500, 4500, 6500, 8500 and 10500), twist angle (TA = 90∘ and 180∘) and inclination angle (IA = 15∘ and 30∘) on velocity fields and streamlines, temperature contours, Nusselt number, friction factor, turbulent kinetic energy (TKE), thermal performance factor (TPF), energy efficiency factor (EEF) and entropy generation rate are evaluated. More uniform temperature and velocity fields can be found as both wavy passage and twisted tape are simultaneously applied. Both heat transfer rate and pumping power rise with increasing Reynolds number, twist and inclination angles. Results reveal that the twisted tape play more remarkable role on Nusselt number and friction factor at lower inclination angle. The best value of EEF is detected 24.6% occurring for passage with IA = 15∘ and TA = 180∘ at Re = 2500. Among all considered cases, those of empty wavy passage with IA = 30∘ at Re = 8500 and 10500 provides negative values of EEF, referring to inefficient cases from energy viewpoint. The contribution of wavy passage and twisted tape on heat transfer enhancement is individually assessed and it is found that the best value of twisted tape involvement on enhanced heat transfer is 79.6% taking place for configuration with IA = 15∘ and TA = 180∘ at Re = 4500. Finally, based on CFD results, passages are examined from thermodynamics viewpoint and it is shown that the second law efficiency growths with increasing twist and inclination angles.

Numerical analysis on heat transfer enhancement of sCO2 in the tube with twisted tape

Supercritical carbon dioxide (sCO2) has the advantages of easy to reach critical conditions, inactive chemical properties and good safety, which can be used as reactor coolant. However, the thermophysical properties of sCO2 change drastically near the pseudo-critical point. The resulting buoyancy and flow acceleration effects may cause local heat transfer deterioration in the coolant channel. Twisted tape is a good structure for heat transfer enhancement in tube. It can enhance turbulence, generate secondary flow, and disturb fluid flow boundary layer and thermal boundary layer, which can effectively mitigate the heat transfer deterioration of sCO2. The numerical analysis of sCO2 heat transfer deterioration and the heat transfer enhancement of twisted tape is presented in the article using ANSYS Fluent. The default turbulent Prandtl number model was modified to improve the calculation of turbulence generation and diffusion. The heat transfer enhancement characteristic of sCO2 with twisted tape under different working conditions was considered, and the effects of geometric characteristics were also discussed. The results indicate that when the flow rate is low and the heat flux is high, adding twisted tape can effectively suppress the heat transfer deterioration by reducing the viscous sublayer thickness and enhancing the turbulence intensity near the wall. The smaller the twist ratio, the more obvious the enhancement of heat transfer.

Investigation of fouling mitigation using stationary and rotating twisted tapes

• Fouling mitigation is achieved using stationary and rotating twisted tapes. • Stationary twisted tapes offer 50% reduction in fouling resistance over plain tube. • Rotating twisted tape offered a maximum of 90% reduction in fouling resistance. • Fouled tube pressure drop is about 2–24% higher than unfouled tube. The fouling phenomenon is one of the critical issues to be solved in industrial heat exchangers, which can adversely affect the size of the heat exchanger, thermofluids performance, and operational lifetime. In this paper, a novel fouling mitigation technique using stationary and rotating twisted tapes is introduced. The particulate fouling phenomenon was experimentally studied using the accelerated fouling test. The aluminum oxide particle was used as a foulant material, and the experiments were performed for different twisted tape pitches (60 mm and 120 mm), flow rates (1.5–5 l min −1 ), and particle sizes (1.2 µm and 6.9 µm). The results showed that within the turbulent flow region, the fouling resistance decreased with an increase in flow rate. Moreover, compared to the plain tubes, a maximum of 68% and 90% reduction in fouling resistance was attained using the rotating twisted tapes for the 1.2 µm and 6.9 µm particle sizes, respectively. Compared to the tube with stationary twisted tape, the rotating twisted tape provided an additional 16% reduction in the fouling resistance for the 1.2 µm particle size. However, for both plain and twisted tape tubes, the pressure drop of the fouled tube is about 2–24% higher than the unfouled tube.

Performance of a heat exchanger with compound inclined circular-rings and twisted tapes

Optimization was done of the aerothermal performance factor ( η ) of a tube into which a combination of inclined circular-rings (ICRs) and twisted-tapes (TTs) were installed. The key contribution of this research is determination of the appropriate ICR and TT sizes to produce the best heat exchanger performance. An ICR's purpose is to produce counter-rotating vortices, whereas the TT's role is to create swirl flow within a tube to improve turbulence and transfer cold fluid from the core region to the heated-wall zone. The influence of circular-ring inclination angle ( α = 30 o , 45 o , 60 o and 90 o ), number of twisted tapes ( H = 2, 4, and 6) and twist ratios ( TR = 1.0, 2.0, and 3.0) on heat transfer and pressure losses were assessed to determine an optimum η condition. The heat transfer and friction factor tend to increase with H values and decreasing TR . The heat transfer of ICRs together with TTs is higher than in a plain tube by up to 128.7% and 155.3%, respectively, while it is better than the transverse circular-ring ( α = 90 o ) and twisted-tape by up to 116.9% and 146.5%, respectively. Furthermore, due to moderate heat transfer and low pressure losses, a maximal η of 1.66 was achieved for α = 30 o , H = 2 and TR = 3.0 within the examined range.

Experimental and Numerical Heat Transfer Study of Swirling Air Jet Impingement

Experimental and numerical study has been performed to study effect of swirl on heat transfer. A twisted swirl tape with twist ratio (T. R)=2 is used to generate swirl and effect of parameters like z/d=2 to 8 and Re varying between 3000 to 9000 are studied experimentally. Experiments show heat transfer dependency on Reynolds number. This study is further extended numerically using commercial CFD code ANSYS Fluent for much higher Reynolds number flow up to 20000. It is seen that CFD centerline peak Nu profile matches pretty well with experiments conducted. A relation between peak Nu and Re is established numerically for the conditions mentioned above. Further, effect of multiple swirl jet impingement (two jets separated by distance 1.5D, 2D and 3D) on Peak Nu is explained through CFD studies. CFD results show that jet distance of 1.5D is more effective in achieving higher heat transfer compared to 2D and 3D distances.

Numerical Simulation of the Flow Pattern of Spiral Annular Flow with a Guide Strip by Spiral On-Way.

To study the gas–liquid two-phase spiral annular flow pattern and its conversion law in a horizontal tube with twist tape by spiral on-way, a numerical simulation is carried out using the RNG k-ε model, and the DPM model is adopted as the particle motion model. The research results show that three main flow patterns are obtained, which are spiraling churn flow, spiraling annular flow, and spiraling annular twine flow. The ratio of the liquid-phase to gas-phase velocity VL/VG is the main factor that affects the existence of the gas phase. When VL/VG > 1/2, the flow pattern is a spiral cluster flow; when 1/5 < VL/VG< 1/2, the flow pattern is a spiral annular flow; and when VL/VG < 1/5, the flow pattern is a spiral annular flow. Compared with the flow pattern of the local spiral flow pattern of the short twisted band, it was found that the occurrence conditions of annular flow were postponed and a new flow pattern appeared. The research results of this paper have guiding significance for the pipeline risk management of natural gas hydrates and the engineering application of the full rotation of guide strips.

Machine learning assisted modeling of thermohydraulic correlations for heat exchangers with twisted tape inserts

This article presents the application of machine learning (ML) algorithms in modeling the heat transfer correlations (e.g., Nusselt number and friction factor) for a heat exchanger with twisted tape inserts. The experimental data for the heat exchanger at different Reynolds numbers (Re), twist ratio (t), percentage of perforation (p), and a varied number of twisted tapes (n) were used for the correlation modeling. Three ML algorithms: polynomial regression (PR), random forest (RF), and artificial neural network (ANN) were used in the data-driven surrogate modeling. The hyperparameters of the ML models were carefully optimized to ensure generalizability. The performance parameters (e.g., R2 and mean absolute error (MAE)) of different ML algorithms were analyzed. It was observed that the ANN predictions of heat transfer coefficients outperform the predictions of PR and RF across different test datasets. Based on our analysis we make recommendations for future data-driven modeling efforts of heat transfer correlations and similar studies.

Heat transfer in pipes with twisted tapes: CFD simulations and validation

Inserts are placed inside heat exchangers to promote turbulence and maximize the heat transferred. Twisted tapes enhance heat transfer with minimal pressure drop increase for double pipe heat exchangers. Their design typically relied on experimental correlations, but nowadays CFD software is gaining interest. The choice of the turbulent model is of paramount importance and not addressed in the literature. This research aims to compare the combinations of k-ε, k-ω and RSM as well as their different wall treatments available in Ansys Fluent® and literature experimental data. Different twist ratios and Reynolds numbers are tested. Currently, no research is found in literature comparing different CFD methods for this type of units. The main objective of this research is to find the combination of RANS turbulent model and wall treatment that will most accurately reproduce the global values needed (Nusselt number and friction factor) when designing a heat exchanger with twisted tape inserts. Results show that the selection of the wall treatment is far more relevant than the turbulence model. Simulations have less discrepancy between themselves than the empirical correlations. Best performing models were k-ε Standard with ML wall treatment, which provided an average deviation from correlations ranging between 15 and 18%. K-ω SST models also provided accurate performance when estimating friction factor values with 17 to 20% deviation. Results provide clues for choosing a suitable turbulent model and are useful to minimize the error provided by the models.

Utilization of air injection together with spring wire and twisted tape to enhance performance of vertical tube with downward stream

ABSTRACT Present investigation, provides thermal and exergetic evaluations of downward gas–liquid two-phase flow within a vertical tube, which equipped two types of turbulators (spring wire and twisted tape). The vertical tube was put under fixed value of heat flux, which was provided via flexible wire heaters that were wrapped around the tube. The volume fraction varied between the values of 0.11 and 0.77. For each type of turbulators three different twist ratios of 2.2, 4.4, and 6.6 were considered to check the effect of twist ratio. Findings revealed that the maximum value of the Nu number, observed in the tube with Spring wire turbulator was 17% more than that in the tube with a Twisted tape turbulator. Also, it was found that the minimum value of the C.B.R factor was about 0.81 which was associated with Twisted tape that had the twist ratio of 4.4. Furthermore, the ratio between the maximum value of exergy efficiency associated with Spring wire turbulator and Twisted tape turbulator was about 1.11.

Experimental study on thermo‐hydraulic performance of metal foam twisted tape in a double pipe heat exchanger

AbstractA recent study compared experimentally the hydraulic and thermal activity of twisted tape inserts for two types, metal foam twisted tape (MFTT) and traditional twisted tape (TTT), in a double pipe heat exchanger. The investigation goal of the innovatively designed MFTT is to enhance the heat transfer process, which provides a higher thermal enhancement factor over those of TTT under the same conditions. Heat transfer activity in terms of Nusselt number (Nu) and Nusselt number ratio (Nu/Nuo) as the heat exchanger equipped with the proposed MFTT and TTT inserts with various tape‐twist ratios (y/W = 3.6, 5.2, and 6.8) are considered over various values of Reynolds numbers (16,300 &lt; Re &lt; 32,500). The results reveal an improvement in heat transfer rate with both MFTT and TTT and this improvement is proportional inversely to the twisted ratio, but the MFTT showed the highest value of heat transfer compared to TTT and clear tube. Also, the Nu of MFTT augments averaged about 175%–230% compared to the TTT depending on the twist ratio and about 275% and 500% over that of the clear tube. At a twist ratio of 3.6, the heat transfer coefficient is recorded at 37% and 45% for MFTT and TTT models, respectively, with an increase in Re. However, friction factor (f) increases about 35% for MFTT with decreasing in twist ratio (from 6.8 to 3.6). The effectiveness of the proposed MFTT in the range of Re used is found to be about 12%, 15%, and 18% higher than those induced by TTT at twisted tape ratio (y/w = 3.6, 5.2, and 6.8), respectively.

Performance boost of a helical heat absorber by utilization of twisted tape turbulator, an experimental investigation

Present investigation, experimentally probes the influence of utilization of twisted tape turbulator inside a helical tube. Twisted tapes mix the flow and enhance the heat transfer rate. The pitch of twisted tape was considered as variant parameter. Tube was considered to be under constant heat flux. Also, Re number was within the range of 6000–32000 which denotes that flow was the turbulent flow regime. Various parameters including Nu number, friction factor and entropy generation were evaluated. Furthermore, performance evaluation criteria based on first law and second law of thermodynamics together with economic performance parameters were evaluated. The results revealed that by the increment of water flow rate and the decrement of twist pitch the Nu number would face a rise of 66% in comparison with the smooth helical tube. Also, it was found that the application of twisted tape has more effect on frictional entropy generation rather than thermal entropy generation. Finally, the results indicated that the maximum value of ηc was about 1.59 ×10−7 ($/J) which presented up to 2.7 times enhancing in the financial beneficial of the helical tube.

Genetic Algorithm Integrated Fuzzy AHP-VIKOR Approach for the Investigation of W-Cut Insert Heat Exchanger for Cooling of Dielectric Fluid Used in Ultra-High Voltage Transformer

This study proposes a novel W-cut twisted tape to evaluate and enhance the effectiveness of novel grooved tube heat exchanger. The experimental investigations are carried out with W-cut inserts, which possess two main control factors, namely, twist tape ratio (y = 3.5 to 6.5) and width tape ratio (WR = 0.43 to 0.6). The investigation results prove that in all cases the energy transmission and friction factor of W-cut insert along with the first law and second law efficiency are considerably higher than the conventional tube arrangement. The empirical model equations for friction factor, performance enhancement ratio, Nusselt number, and rational efficiency are developed, and they show good affinity with experimental data. Since the abovementioned factors have conflicting terms, it is essential to select the proper operating configuration of the heat exchanger in order to increase the thermal energy transfer rate with reduced consumption of pumping energy. The multi-objective genetic algorithm (GA) tool is used to identify the optimum operating conditions. Further, the hybrid multi-criteria decision-making model, FAHP-VIKOR, is applied to select the perfect model from the set of non-dominated solution. The ranking of alternatives is as follows: A4 &gt; A11 &gt; A2 &gt; A9 &gt; A21 &gt; A17 &gt; A1 &gt; A24 &gt; A11 &gt; A23 &gt; A7 &gt; A18 &gt; A13 &gt; A10 &gt; A20 &gt; A5 &gt; A19 &gt; A14 &gt; A16 &gt; A22 &gt; A25 &gt; A6 &gt; A15 &gt; A3 &gt; A8. The optimized configuration of W-cut insert is compared with the former inserts, and the optimal configuration exhibits supreme performance than other inserts.

Experimental performance enhancement of a flat plate solar collector using straight and twisted flow inserts.

The thermal performance of a flat plate solar collector (FPSC) is limited minimum due to higher heat loss of the collector and poor heat exchange with the heat transfer fluid. The current study investigates the effect of single-slit twisted tape (TT), double-slit TT, and double-slit straight tape passive-insert devices on enhancing the heat transfer of the FPSC at a constant water flow of 0.025kg/s. Double-slit inserts have a higher heat transfer area and reduced hydraulic diameter than conventional single-slit TT inserts. The double-slit TT insert creates more fluid mixing and turbulence in the flow than a single-slit TT. The convective heat transfer coefficient for double-slit TT, single-slit TT, and the double-slit straight insert is 47.7%, 26.9%, and 8.7% higher than FPSC with the plain absorber. Double-slit TT inserts are observed with improved energy and exergy efficiency by 23.9% and 46.2% compared to conventional collectors without a flow insert. The average energy efficiency of FPSC without inserts is 48.2%, whereas the double-slit TT is 66.5%. The pressure drop is higher for the collector with inserts than for the collector without inserts, which leads to a little more pump power. Thus, passive inserts help to augment heat transfer in the FPSC.

Numerical investigation of the flow and heat transfer of Al2O3/water nanofluid in a tube equipped with stationary and self-rotating twisted tapes

In this study, the rotating twisted tape and its effect on fluid flow and heat transfer as well as Performance Evaluation Criterion (PEC) in a tube under constant heat flux is investigated. The twisted tapes are examined in two rotating and stationary cases, namely four geometric cases of Plain Tube (PT), tube equipped with Stationary Twisted Tape (STT), tube equipped with Rotating Twisted Tape- Clockwise (RTT-C) and the tube is equipped with Rotating Twisted Tape-Counterclockwise (RTT-CC). The used nanofluid is Al2O3/water nanofluid in volume fraction of nanoparticles 0, 1, 2, and 3% and is considered as Newtonian, and two-phase mixture method is used to simulate the nanofluid. The flow regime in this study is laminar and the Reynolds numbers are 250, 500, 750, 1000, and heat flux of 5000 W/m2 is applied to the wall of the tube. The height of the twisted tape is 90% of the height of the channel and they act as thermal insulation and are only responsible for creating the secondary flow. The results show that increasing the Reynolds number increases Nuave and increases the pumping power, and by using nanoparticles and changing the volume fraction of nanoparticles from 0 to 3%, heat transfer, pumping power, and pressure drop are increased.