Rectangular Winglet Pairs Research Articles

Experimental and numerical investigations of tube inserted with novel perforated rectangular V-shape vortex generators

The utilization of punched vortex generators has been established as an effective means to enhance heat transfer in heat exchangers. However, there are few studies on the use of perforated rectangular winglet pairs in heat exchange tubes and the study of perforation parameters based on this approach in the existing literature. In this paper, three parameters, including three height ratios, four perforation indices, and three pitch ratios, are considered experimentally and numerically. In the Reynolds number range of 7454–13,664, the effects of perforated rectangular vortex generator pairs on fluid flow and heat transfer are obtained by scaling parameters such as Nusselt number ratio, friction factor ratio, thermal enhancement factor, field synergy number, entropy generation, and exergy efficiency. The numerical results indicate that the perforation will lead to a reduction in turbulent kinetic energy in the local multi-longitudinal vortices on the rear side of the vortex generator, resulting in a decrease in local heat transfer as well as friction loss. Meanwhile, the pitch of perforated rectangular vortex generator pairs plays a crucial role in heat transfer and friction loss, enabling an increase in the Nusselt number of smooth tubes by 68–257%. Furthermore, the results are proved using the principle of entropy generation and exergy efficiency analysis. As Reynolds number increases, the thermal enhancement factor gradually decreases. Notably, the maximum thermal enhancement factor of 1.43 is achieved when the Reynolds number is equal to 7454, the height ratio is 0.08, the perforation index is 0.18, and the pitch ratio is 1.04.

Improvement of Plate-Fin Heat Exchanger Performance with Assistance of Various Types of Vortex Generator

A 3-dimensional incompressible laminar flow and heat-transfer in a plate-fin heat exchanger (PFHE) where investigated numerically in this article. The influence of mounting a longitudinal vortex generator (LVG) on the offset rectangular-triangular fin (ORT) in the PFHE, on thermal and hydro-dynamic fields are presented. The novelty of this study is by attaching a LVG to an offset strip fin (OSF) surface. The cases of study for the PFHE are established, by using a built-in rectangular winglet pair type RWP longitudinal vortex generator carried out and fitted on this fin to improve the convective heat transfer of the (ORT) fin while minimizing pressure loss. The upper and lower plates are exposed to constant heat flux and the working fluid is air where chosen under a laminar range of RE (600 to 1400). The laminar flow and heat-transfer are governed by continuity, momentum and energy equations. ANSYS FLUENT (2021 R1) is used to get the numerical results, based on the finite volume method. The performance of the VG is assessed for an optimum winglet attack angle (45°), as well as by modifying the geometrical size parameters, namely the height and placement (L) of the RWP LVG. The result shows that the Nusselt number reaches its optimum enhancement values by using a common flow up CFU built-in rectangular winglet pair type RWP VG with a height and entrance length of (h=1.25mm, L=0.5mm), by 22.23% as compared with base case configuration (ORT). Finally, a two more LVG are tested with the optimum conditions of the RWP, which they are a delta winglet pair (DWP) and trapezoidal winglet pair (TWP). In addition, the temperature fields for the primary and secondary flows were shown in contour and streamline diagrams

Perforated concave rectangular winglet pair vortex generators enhance the heat transfer of air flowing through heated tubes inside a channel

A significant increase in the rate heat transfer in a heat exchanger system is made possible by increasing the convection heat-transfer coefficient using a passive method. The addition of vortex generators (VGs) to the fins and tubes of a heat exchanger is currently the most effective passive method. However, the increase in heat was accompanied by an increase in pressure drop. Therefore, in this study, we installed perforated concave rectangular winglet pair vortex generators (PCRWP VGs) on plates in rectangular ducts to increase the heat transfer through the six heated tubes to the air stream by lowering the enhancement in the pressure drop. We attempted to determine the best cost-benefit ratio (CBR) with a fluid flow velocity difference of 0.4–2 m/s at intervals of 0.2 m/s (Reynolds number (Re) of 2143 to 11,763) in the channel. The PCRWP VGs were composed of in-line and staggered configurations. The results showed a lower CBR (3.56) for the in-line configuration than for the staggered configuration. Moreover, the lowest CBR was accompanied by an increase in thermal performance (TEF) of 1.29.

Thermo-fluid performance enhancement of a fin-and-tube heat exchanger by rectangular winglets

In this study, numerical simulations have been performed to investigate the influence of rectangular winglets as Vortex generators for enhancement of thermo-fluid performance in a fin-and-tube type heat exchanger having five staggered rows of tubes. The influence of placement of winglets over different pair of tubes, attack angles of the winglet pair, and their location has been examined under laminar flow conditions for Re ranging 400–1500. For the present analysis rectangular winglet pairs having “common-flow-up” orientation were employed for vortex generation. The effect of placement of different number of rectangular winglet pairs (1–5) has been investigated and the maximum enhancement in thermo-fluid performance was obtained as 27.4% compared to the baseline model (without winglet model). The winglets attack angle (5°, 10°, 15°, 20°, and 25°) were also investigated for best thermo-fluid performance and the optimum attack angle resulted in enhancement up to 33% over the baseline model. The optimum stream-wise and span-wise locations were identified which resulted in enhancement up to 29% and 25%, respectively, over the baseline model. Correlations for the prediction of Nusselt number, friction factor, and enhancement factor have been developed for stream-wise distance, span-wise distance, and attack angle of the winglets.

Overall cooling performance evaluation for film cooling with different winglet pairs vortex generators

Previous studies have shown that the film cooling effectiveness can be improved by using a winglet pair vortex generator upstream or downstream of the film hole, but these studies merely focused on rectangular and delta winglet pairs and the overall performance evaluation has no heat transfer results. In this study, the overall film cooling performance of a cylindrical film hole with four types of winglet vortex generators upstream of the film hole was numerically investigated. The numerical simulation with the realizable k-ε turbulence model was performed by commercial software Fluent, solving steady Reynolds-average Navier-Stokes equations. The film cooling effectiveness with vortex generators is one or more times higher than that without the vortex generators owing to the downwash vortices generated by the vortex generators. The downwash vortices mitigate the negative effect of the counter-rotating vortex pair. There is a competitive mechanism between the downwash vortices and the counter-rotating vortex pair, so the beneficial effect of the vortex generators will weaken with the increase of the blowing ratio. The heat transfer coefficient of film cooling with vortex generators is higher, with a maximum augmentation of 11.45%. The heat transfer distributions of different vortex generator configurations are similar. Results prove that the case with the rectangular winglet pair vortex generator is the optimal configuration since it provides 0.08–0.29 higher net heat flux reduction than the case without the vortex generators.

Comparison of eddy viscosity turbulence models and stereoscopic PIV measurements for a flow past rectangular-winglet pair vortex generator

Vortex generators (VG) are widely used in enhancing the heat transfer coefficients in heat exchangers due to the development of longitudinal and transverse vortices. Therefore, understanding the development of these vortices has a high importance for the design and optimization of heat exchangers. When using numerical simulations, the choice of an appropriate turbulence model that can better predict the flow structure downstream a VG is fundamental. In the present study, three-dimensional numerical simulations, with two different commonly used eddy viscosity turbulence models, are performed for channel flow fitted with rectangular-winglet pairs (RWP) vortex generators. The numerical results are compared to experimental data obtained by stereoscopic particle image velocimetry (SPIV). The shear-stress transport (SST) κ-ω model and the re-normalization-group (RNG) κ-ε model are used for modeling turbulence. Validation is conducted by comparing the flow structure topology and velocity field obtained from numerical simulations to those obtained using the SPIV method. It is found that the SST κ-ω model is better than the RNG κ-ε turbulence model in predicting the flow characteristics downstream the RWP.

Numerical investigations on fluid flow and heat transfer characteristics of different locations of winglets mounted in fin-tube heat exchangers

A three-dimensional numerical investigation of airflow through heated fin-tube heat exchangers with winglet type vortex generators is performed for both inline and staggered arrangements of circular tubes. Heat transfer augmentation of such heat exchangers strongly depends on the mounting locations of the winglet pair corresponding to tubes. The present numerical study shows the effect of location of rectangular winglet pairs (RWPs) on thermal performance for both the arrangements. Among numerous considered RWP locations, all promising locations of RWPs are identified which give higher heat transfer enhancement with less flow loss. The effects of RWP locations on flow features and heat transfer are demonstrated by streamlines and Nusselt number contours respectively. Estimation of enhancement in heat transfer is achieved by Colburn’s factor and flow loss is quantified from the measured pressure drop. The thermohydraulic effect is analyzed by using the thermal performance factor. Locations of RWPs, which are capable of producing higher thermal performance, have been optimized and found that upstream RWP location, i.e. ΔX = 2.0, ΔY = ±1.25 delivers higher heat transfer enhancement with maximum thermal performance factor value for both arrangements. Evaluation of secondary flow induced by RWPs is achieved by secondary flow intensity and is correlated with heat transfer.

Thermal performance analysis of fin-tube heat exchanger with staggered tube arrangement in presence of rectangular winglet pairs

Longitudinal vortices generated by winglet type vortex generators mounted on fin surface improve fluid mixing with disruption of boundary layer growth, which results in convective heat transfer enhancement. The present study reports the three-dimensional numerical investigation of airflow through heated fin-tube heat exchangers in presence of common flow down configured rectangular winglet pairs (RWPs) for staggered arrangements of circular tubes. It is well known that the thermal performance of a fin-tube heat exchanger is majorly influenced by various locations of winglets corresponding to tube centre. Henceforth, fluid flow and heat transfer characteristics of different possible RWP locations concerning each tube are examined. Further, for higher performance, a search for an effective angle of attack ranging from 15° to 60° is also performed for optimized locations. The effect of different inlet flow conditions is also investigated for Reynolds number ranges from 2000 to 10,000. Thermohydraulic performance is studied by considering Nusselt number, friction factor, secondary flow intensity and thermal performance factor. Irreversibilities due to RWPs are analysed by calculating the entropy generation rate due to viscous and heat transfer effects. Obtained results illustrate that the selection of promising RWP locations plays a vital role in improving thermal performance. The relationship between heat transfer, secondary flow and irreversibility parameters are also reported.

Thermodynamic performance analysis of an inline fin-tube heat exchanger in presence of rectangular winglet pairs

This paper investigates the irreversibilities caused by fluid flowing under the effect of isothermal walls of fin-tube heat exchanger in the presence of longitudinal vortex generators. Inline arrangement of circular tubes with fin-surface mounted rectangular winglet pairs (RWPs) arranged in common flow down configuration are selected for the present three-dimensional numerical study. Initially, thermodynamic performance analysis of different possible RWP locations corresponding to tubes has been examined for a fixed angle of attack. Further, the study is expanded for some specific locations by varying angle of attack ranging from 15° to 60° and flow Reynolds number ranging from 2000 to 4000. Thermodynamic performance of the present system has been evaluated by analyzing the irreversibilities caused due to RWPs and compared with the thermo-hydraulic performance. Thermodynamic analysis is categorized into two parts: the first ‘entropy generation analysis’ and the second ‘exergy analysis’. For entropy generation analysis entropy generation rate, irreversibility distribution ratio and Bejan number are examined. The obtained results indicate that the irreversibility caused by entropy generation in the present system is majorly dominated by the entropy generation rate due to thermal effect. Exergy analysis is studied by calculating the irreversibility rate, exergy destruction number, heat transfer improvement number and exergetic efficiency. The observation of exergetic efficiency variation for different RWP locations demonstrates that the present system with upstream RWP locations delivers higher performance.

Heat Transfer Enhancement of Plate-Fin Heat Sinks with Different Types of Winglet Vortex Generators

Because the delta winglet in common-flow-down configuration has been recognized as an excellent type of vortex generators (VGs), this study aims to experimentally and numerically investigate the thermo-hydraulic performance of four different forms of winglet VGs featuring sweptback delta winglets in the channel flow in the range 200 < Re < 1000. Both Nusselt number and friction factor of plate-fin heat sinks having different forms of winglets, including delta winglet pair (DWP), rectangular winglet pair (RWP), swept delta winglet pair (SDWP), and swept trapezoid winglet pair (STWP), were measured in a standard wind tunnel without bypass in this study. Four rows of winglets with in-line arrangement were punched on each 10-mm-long, 0.2-mm-thick copper plate, and a total of 16 pieces of copper plates with spacing of 2 mm were fastened together to achieve the heat sink. The projected area, longitudinal and winglet tip spacing, height and angle of attack of those winglets were fixed. Besides that, three-dimensional numerical simulation was also performed in order to investigate the temperature and fluid flow over the plate-fin. The results showed that the longitudinal, common-flow-down vortices generated by the VGs augmented the heat transfer and pressure drop of the heat sink. At airflow velocity of 5 m/s, the heat transfer coefficient and pressure drop of plain plate-fin heat sink were 50.8 W/m2·K and 18 Pa, respectively, while the heat transfer coefficient and the pressure drop of heat sink having SDWP were 70.4 W/m2·K and 36 Pa, respectively. It was found that SDWP produced the highest thermal enhancement factor (TEF) of 1.28 at Re = 1000, followed by both RWP and STWP of similar TEF in the range 200 < Re < 1000. The TEF of DWP was the lowest and it was rapidly increased with the increase of airflow velocity.

Thermo-hydraulic optimization of a solar air heater duct with non-periodic rows of rectangular winglet pairs

Surrogate-based optimization is employed to maximize the thermo-hydraulic performance of a solar air heater duct with non-periodic rows of rectangular winglet pairs mounted in the absorber plate. The present optimization study encompasses the variation of Reynolds number (5000 and 10,000) and of three geometric parameters for each row of rectangular winglets such as chord of the winglets ranging from 8 mm to 40 mm; height of winglets from 8 mm to 21 mm; and angles of attack from 15° to 45° (Flow-Up) and from −45° to −15° (Flow-Down). The Pareto frontiers show that periodic configurations are suboptimal solutions, i.e., the thermo-hydraulic performance of a solar air heater with rectangular winglet pairs not periodically arranged along the channel outperform the periodic arrangements. The aspect ratios and angles of attack for non-periodic and periodic optimized designs are completely different from each other. Moreover, the optimized solutions for Flow-Down arrangement present higher performance than Flow-Up, and this behavior is independent of the Reynolds number. Complex flow patterns and heat transfer mechanisms of the non-periodic optimized solutions are observed, especially the interactions of corner and main vortices along the duct. The first row of winglet pair play the most important role on pressure penalty and heat transfer enhancement when compared to the other rows of rectangular winglet pairs, mainly on Flow-Up arrangement at Re = 10,000. In general, Flow-Up arrangements create a vortex structure more intense than Flow-Down arrangement.

Experimental analysis by stereo-PIV of the development of streamwise vortices downstream of rectangular winglets

Accurate experimental characterization of longitudinal vortices induced by rectangular winglets is necessary to develop and validate numerical models that can predict these flows. For this aim, an experimental investigation is conducted to examine the characteristics of longitudinal vortices generated downstream rectangular winglets in fully developed turbulent channel flow. A row of rectangular winglet pairs is implemented in a parallel plate flow. Stereoscopic Particle Image Velocimetry (SPIV) is used to harvest three-dimensional (3D) instantaneous velocity fields for a Re = 4400 based on the channel’s hydraulic diameter and mean flow velocity. 3D velocity components, velocity streamlines, topologies of Γ2 function and normalized turbulent kinetic energy downstream the winglets are analyzed. It is shown that the flow properties are disturbed, and a main vortex pair is generated in addition to induced vortices downstream the rectangular winglets. Moreover, this work provides an SPIV benchmark of the complex flow developing downstream rectangular winglet pairs, where this configuration has been widley studied using numerical simulations.

Numerical analysis to predict the optimum configuration of fin and tube heat exchanger with rectangular vortex generators for enhanced thermohydraulic performance

The current numerical study has explored the effect of incorporation of rectangular winglets with circular, flat and oval tubes on the performance of compact heat exchangers. Rectangular winglet pairs are mounted behind the tubes at a span angle of 5° to obtain the enhanced performance. The obtained results show that fin and oval tube heat exchanger (FOTHE) having rectangular winglet pairs (RWPs) provides the higher thermal-hydraulic performance compared to the other configurations, on the basis of area goodness factor (j/f) and heat transfer rate per unit fan power consumption (Q/Pf). MOORA method also incorporated to obtain the performance ranking of the considered configurations of compact heat exchangers. The optimal configuration i.e. finned tube heat exchanger having oval tubes with rectangular winglet pairs, provides an increment of 13.84% and 9.99% in the heat transfer coefficient of air (h) at Re = 400 and Re = 900 respectively, compared to the baseline case. Moreover, an appreciable reduction of 26.61% and 29.79% in the pressure drop (∆p), compared to the baseline case, is obtained at Re = 400 and Re = 900 respectively.

Numerical investigation to predict optimum attack angle combination of longitudinal vortex generators in compact heat exchangers for thermo-hydraulic heightened performance

The current 3-D numerical analysis explores the effect of combinations of rectangular winglet pairs (RWPs) having different attack angles (i.e. 5°, 15° and 25°) along a row of the tube array, on the performance of the fin and tube heat exchanger (FTHE). The considered airside Reynolds number Re ranges from 500 to 900. In total, six combinations of three attack angle vortex generators (VGs) have been numerically analysed namely 5°-15°-25°, 5°-25°-15°, 15°-5°-25°, 15°-25°-5°, 25°-5°-15° and 25°-15°-5°. The performance of the FTHE is represented by area goodness factor. The performance rankings of the FTHEs are also obtained by the MOORA method. Finally, 5°-25°-15° case provides the best thermal hydraulic performance for which heat transfer coefficient (h) is increased by 68.20% at Re = 500 and 81.78% at Re = 900, with a significant pressure drop penalty.

Numerical Analysis of Thermofluid Performance of Fin-and-Tube Heat Transfer Surface Using Rectangular Winglets

AbstractThis paper numerically investigates the heat transfer enhancement using rectangular winglet pairs in a fin-and-tube type heat transfer surface having five inline rows of tubes. The influence of number of winglets, attack angles of the winglets, and their location has been analyzed under laminar flow conditions with Reynolds number ranging 400–1500. To account for the combined effect of heat transfer enhancement and pressure drop penalty, an enhancement factor is also discussed by changing the winglet pair's number and location. The numerical results show that pressure drop can be reduced significantly by placing the winglet more toward the exit of the flow channel. Streamwise distance and spanwise distance of the winglet pairs have been investigated for maximum enhancement factor. The numerically obtained results show that the winglets number and their placement at different locations have a major influence on enhancement factor. The results show that both the heat transfer and the pressure drop increase with an increase in attack angle of the winglets and best angle for the highest enhancement factor has been found out. Correlations have been developed for streamwise distance, spanwise distance, and angle of attack for different range of Reynolds numbers.

Thermal-Hydraulic Performance Enhancement by the Combination of Rectangular Winglet Pair and V-Shaped Dimples

Abstract This paper presents numerical study on heat transfer enhancement due to the combination of rectangular winglet pair with V-dimples in an array-type arrangement. Array of rectangular winglet pairs results in heat transfer enhancement, however, at a cost of significant pressure drop, resulting in reduced thermal-hydraulic performance (THP). On the other hand, dimples are associated with lower heat transfer enhancement levels at relatively lower pumping power penalty. To this end, a combination of rectangular winglet pair and V-shaped dimples has been studied in this paper, where the arrangements were intended to achieve enhanced thermal-hydraulic performance. Three different configurations, namely, rectangular winglet pair, rectangular winglet pair with one V-dimple between two consecutive winglets, and rectangular winglet pair with two V-dimples packed in a pitch, are studied here. The variation of heat transfer enhancement, pressure drop gain, and THP with respect to winglet-to-winglet (S) spacing variation for rectangular winglet pair and rectangular winglet pair with one V-dimple configuration is presented at a Reynolds number of 25,000. The THP of the rectangular winglet pair configuration decreases up to S/H equal to 2.5 and then increases (H: channel height). For rectangular winglet pair with one V-dimple, three values of winglet-to-dimple (P) spacings are analyzed. For fixed S/H, the highest P/H configuration provided highest heat transfer enhancement and THP. Among the three configurations studied, rectangular winglet pair with two V-dimples resulted in the highest thermal-hydraulic performance.

Determination of optimum winglet height of longitudinal vortex generators for the best thermo-hydraulic performance of compact heat exchangers

The effect of winglet height on the thermal-hydraulic performance of finned tube heat exchanger (FTHE) is investigated numerically. The rectangular winglet pairs (RWPs) having 5° attack angle are placed in common flow up (CFU) manner adjacent to the tubes for analysis. The air-side performance evaluation has been done based on the area goodness factor (j/f). The working fluid (air) is considered as incompressible fluid. Additionally, MOORA (multi objective optimization on the basis of ratio analysis) method is employed to get the best performance order of various configurations by taking Nusselt number (Nu) and area goodness factor (j/f) as beneficial attributes and friction factor (f) as a non-beneficial attribute having equal significances. The present study reveals that the rectangular vortex generators having 60 % of the channel height provides the better thermal hydraulic performance compared to the other considered cases.

Freeform winglet design of fin-and-tube heat exchangers guided by topology optimization

This paper presents a novel winglet design of a fin-and-tube heat exchanger, and its performance regarding heat transfer enhancement is numerically investigated. In this study, the fin pattern is designed considering the shape, arrangement, and number of the winglets, because a higher degree of freedom for the structural design results in further improvement of the performance. To obtain promising features for the winglet design, topology optimization is applied in a simplified model that incorporates key factors of the physical phenomena. The optimization problem is formulated as a maximization problem of the heat extraction by the winglets in a two-dimensional simplified model under lowered Reynolds number flows. The optimized configurations are evaluated via three-dimensional high-fidelity analyses to obtain a promising design candidate. A manufacturable fin pattern is then designed from the promising candidate. The results indicate that the gradually curved winglets along the flow can enhance the heat transfer at a moderate pressure loss. The proposed fin demonstrates up to 16.0% improvement in the quality factor j/f compared with a fin with rectangular winglet pairs.

Heat Transfer Enhancement with Considering Pressure Loss Penalty of Airflow through Heated Plate Mounted by Perforated Concave Rectangular Winglet Vortex Generators

The use of longitudinal vortex generator results in decreased hydrodynamic flow performance by increasing pressure drop values. The purpose of this research is to obtain the improvement of heat transfer with pressure drop as low as possible. In order to achieve this purpose, experiment was performed on perforated concave rectangular winglet pair vortex generators (CRWP VGs). The test results show that the CRWP VGs without hole increase thermal performance by 24.02% up to 129.75% against baseline (without using any vortex generators) and by 12,21% up to 19,41% against rectangular winglet pair vortex generator (RWP VG). The pressure drop value for the CRWP VGs case increased by more than 10 times against the baseline case and increased by almost 100% against RWP VGs case. By using the perforated CRWP VGs, pressure drop value can be reduced by 15.07% to 72.73% followed by a slight decrease in thermal performance of 5.50% to 5.73% against the CRWP VGs without hole. Based on the evaluation using London goodness factor criteria, perforated CRWP VGs is better than the CRWP VGs without hole.

Heat Transfer Enhancement in a Heat Exchanger Tube with 45° Rectangular-Winglet Pairs

An experimental investigation on thermal characteristics in a heat exchanger equipped with 45° rectangular winglet pairs (RWP) is conducted using air flowing in a constant heat flux tube with Reynolds number (Re) in a range of 5,200 to 23,000. Parameters of RWP included three relative height or blockage ratios (BR = 0.06, 0.08 and 0.1) and two pitch-spacing ratios (PR = 1.0 and 2.0). The heat transfer and the pressure drop in the test tube are displayed in the form of Nusselt number (Nu) and friction factor (f), respectively. The investigation shows that Nu and f values of the tube with RWP insert are, respectively, in the range of about 1.55−3.2 and 3.76−6.44 times above the plain tube alone, depending on the operating condition. The maximum thermal performance for using the RWP is found to be 1.7 at the lowest Re.