Winglet Vortex Generators Research Articles

Efek Longitudinal Vortex Dihasilkan dari Vortex Generator Jenis Concave Delta dan Rectangular Winglet terhadap Perbaikan Perpindahan Panas: Visualisasi Aliran/Studi Eksperimental

The generation of longitudinal vortex to enhance the rate of heat transfer is a passive method that has been widely considered recently. This consideration is based on improving the energy efficiency and optimum design of a heat exchanger. Therefore, this study is focused on the experimental test and flow visualization of effects of longitudinal vortex generated from concave delta and rectangular winglet vortex generators on the increase of heat transfer rate. This is performed by draining the air inside the channel with variations in velocities ranging from 0.4 m/s - 2 m/s through a rectangular plate mounted with the vortex generators. The attack angle of the flow against the vortex generator is 15°. The flow visualization is performed by firing a laser beam on a cylindrical glass rod at certain locations to capture the longitudinal vortex formed on the cross-section plane. Inlet and outlet air temperatures and wall temperature are measured using the thermocouples. The results show that the longitudinal vortices are formed in the wake region of the vortex generators. By using the concave delta winglet, the heat transfer rate can be increased up to 51% and increased to 85% using the concave rectangular winglet.

Thermo-hydrodynamics Performance Analysis of Fluid Flow through Concave Delta Winglet Vortex Generators by Numerical Simulation

Thermo-hydrodynamics Performance Analysis of Fluid Flow through Concave Delta Winglet Vortex Generators by Numerical Simulation

Thermal performance improvement of a solar air heater fitted with winglet vortex generators

Numerical simulations are carried out to investigate the thermal and flow characteristics of a solar air heater (SAH) embedded with winglet vortex generator (WVG) for the Reynolds number (Re) ranging from 3500 to 16,000. The geometrical parameters of WVG considered are the tip edge ratio (c/a) from 0 to 1 and the angle of attack (α) from 30° to 90°, respectively. Computations are based on the finite volume method coupled with the SIMPLE algorithm. The effects of WVG on the dimensionless parameters, Nusselt number (Nu), friction factor (f), Nusselt number ratio (Nu/Nus), friction factor ratio (f/fs), and thermal enhancement factor (TEF) are discussed. Nu and f increase with the initial increase of α from 30° to 60° and then decrease with a further increase in α. The maximum values of Nu and f appears at α = 60° and c/a = 1. The results show that the WVG with c/a = 0 and α = 30° provides the best TEF in the range from 1.72 to 2.20. The internal flow behavior along with the distribution of the temperature field and streamlines is explored to explain the effect of WVG configurations on heat transfer and friction factor, respectively. The modified WVG affects the flow and temperature fields, which leads to a significant enhancement in the convective heat transfer rate.

THE EFFECT OF VORTEX GENERATOR BASE LENGTH ON THERMAL HYDRAULIC PERFORMANCE ACROSS FIN-AND-TUBE HEAT EXCHANGER

Heat transfer enhancement is believed can be achieved by using vortex generator. In the past decades, many researches have been performed to investigate the effect of various vortex generator geometry and parameters including vortex generator angle of attack and height. However, less study has been conducted to investigate the influence of vortex generator length at different arrangement towards the heat transfer performance across the fin-and-tube heat exchanger (FTHE). Therefore, the effects of different strategy on the rectangular winglet vortex generator (RWVG) base length towards the thermal hydraulic performance across the FTHE were numerically investigated in this study. Two types of RWVG arrangement known as common flow down (CFD) or common flow up (CFU) arrangement were used and placed behind four rows of tube in inline arrangement. Total of 7 cases were investigated including the default RWVG, extended front and extended back for both RWVG in CFD and CFU arrangement together with FTHE without vortex generator which was set as the baseline case. The Reynolds number ranged from 500 to 900. It was found that the size of the wake region behind the RWVG contributed to the additional pressure drop penalty across the FTHE. Meanwhile, different thermal characteristics were found for different base length strategy in CFD and CFU arrangement. For RWVG arranged in CFD and CFU arrangement, the extended back case shows the highest heat transfer enhancement with 5 – 25 % and 5 – 15 % increment compared to the baseline case respectively. Based on JF factor evaluation, default RWVG in CFU arrangement provide better heat transfer enhancement than the pressure drop penalty compared to other RWVG cases with average JF factor value is 0.8. Nonetheless, none of the tested cases shows higher JF factor value than the baseline case.

Fin-and-tube heat exchanger enhancement with a combined herringbone and vortex generator design

Vortex generators (VGs) are the most commonly investigated enhancement methods in the field of improved heat exchangers. The aim of present work is to study the effect of VGs in a fin-and-tube heat exchanger (FTHE) with herringbone fin shape. The delta winglet VG design with length (s) and height (H) is selected based on previous studies. The investigated VG design is simple and considered realistic from the manufacturing point of view. The combined enhancement with herringbone fin and the VG is evaluated by simulating the conjugate heat transfer and the air flow. The structured mesh is created for both solid and fluid domains to solve the model numerically using a coupled open source solver in OpenFOAM. The influence of flow condition on the performance enhancement is studied by changing the Reynolds number in a range Re=1354–6157. The study showed that VGs not only increase the heat transfer in the herringbone fin but also decrease the pressure drop. The highest and longest investigated VG design is found to perform the best because of its ability to delay the flow detachment from the tube, to feed high kinetic energy flow to the recirculation zone and to create longitudinal vortices in the downstream region from the VG. The fin with VG design s=0.5D and H=0.6Fp enhances the overall performance by 5.23% in comparison to the fin without VG. The results demonstrated the usefulness of VGs for the performance enhancement in connection with a herringbone fin design.

Experimental and numerical study on thermal-hydraulic performance of wing-shaped-tubes-bundle equipped with winglet vortex generators

The present work evaluates, experimentally and numerically, by the aid of commercial code FLUENT 6.3.26, the effects of relative locations (∆X or ∆Y), heights (hw), and span-angle (θ) of winglet-vortex-generators (WVGs) on thermal-hydraulic performance enhancement for down-stream and/or up-stream wing-shaped-tubes bundle heat exchangers for air Re ranging from 1.85 × 103 to 9.7 × 103 while water Re = 5 × 102. hw is set as 5 mm, 7.5 mm and 10 mm. For tube down-stream, θ is set as 0° (Base-line-case) and from 5° to 45° clockwise common-flow up (CFUp) and counterclockwise common-flow down (CFDn) while for tube up-stream it is set as −5°, −10° and −15° CFUp. Results show that the increase of θ counterclockwise-(CFDn) or clockwise-(CFUp) leads to increase the values of Nu number. Using WVGs with (+5 ° ≤ θ ≤ +45°) results in increasing Nu number by about from 34 to 48% comparing with that of base-line-case. The lowest values of drag coefficient (f) for tube down-stream are obtained at +5° CFDn and −15° CFUp with respect to the base-line case. For tube up-stream, Nu number increases by increasing θ from 0° to −5° and the values of Nu number for θ varying from −5° to −15° have no significant changes. (f) increases with hw and has negligible effect on ha. Furthermore, optimization analyses of θ and longitudinal fin (LF) are utilized, in four cases, for finding the optimum combination and maximum efficiency. The highest values of heat transfer parameters such as effectiveness (e), area goodness factor (G) and efficiency index (η) and the lowest values of fluid-flow parameters like (f) and hence the best efficiency, are achieved for −15° CFUp down-stream, (“case 3” of −15° CFUp down-stream and 6 mm LF height) and +5° CFDn down-stream. Correlations of Nu number, (f) and (e) as a function of θ and Re for the studied cases are performed.

A CFD Analysis of Rectangular Winglet Vortex Generators in Heat Exchanger

A good performance of the heat exchanger will support energy efficiency and economic sustainability. One way to improve heat transfer coefficient is to increase turbulent flow by using vortex generators. The addition of vortex generators on heat exchanger will pose wake on the flow field which then reduce the stability of thermal boundary layer and enhance heat transfer coefficient. The effect of winglet vortex generators with the variations of angle of attack (AoA) is studied in this research. Each variation is applied in a single row and three rows of inline configurations. The results show that the addition of vortex generators with 160 o angle of attack and three rows of inline configuration improve heat transfer coefficient as 59% higher than conventional configurations.

Experimental investigation on thermoelectric generator with non-uniform hot-side heat exchanger for waste heat recovery

In typical gas-to-liquid thermoelectric generators for waste heat recovery, the stream-wise gas temperature drop in the hot-side heat exchanger leads to the decrease of power output of the whole system. Denser fins are usually arranged on the downstream of the hot-side heat exchanger to improve the uniformity of temperature field and thus the total power output performance of thermoelectric generators when the steam-wise temperature drop is small, but it is not benificial when the steam-wise temperature drop is large. This work investigates the effect of configuration of winglet vortex generators on the performance of thermoelectric generator system. Three sets of hot-side heat exchangers, including a heat exchanger with smooth channel, a heat exchanger with uniform configuration of winglet vortex generators and a heat exchanger with non-uniform configuration of winglet vortex generators, are tested in a gas-to-liquid thermoelectric generators experimental system. The hot-side Reynolds number ranges from 3000 to 6400 and the hot-side inlet temperature is within 523–553K. The experimental results show that the total and net power output of thermoelectric generator under matched load resistance with uniform heat exchanger can respectively outperform that with smooth heat exchanger by 97.5% and 77.7% in average, whereas that with non-uniform heat exchanger by 189.1% and 177.4% in average. Since the uniform and non-uniform heat exchangers have the same number but different configuration of winglet vortex generators, this kind of active cascade control of heat transfer enhancement elements is proved to be effective in improving the power output of thermoelectric generator system without increasing pumping power.

Application of vortex generators to heat transfer enhancement of a pin-fin heat sink

In this paper, the thermal-fluid characteristics of a pin-fin heat sink with delta winglet vortex generators in a cross flow are investigated experimentally and numerically. The effects of the Reynolds number of the flow, the angle of attack of the vortex generators, the shortest distance between the vortex generators, the distance between each vortex generator and the heat sink, the height of the vortex generators, and the configuration of the vortex generators on the performance of the heat sink are explored. The results show that the thermal resistance decreases as the Reynolds number increases, but that the magnitude of the decrease tends to diminish with increasing Reynolds numbers. By considering the thermal resistance and the pressure difference simultaneously, it was determined that an angle of attack of 30° is a better arrangement for the vortex generators. The thermal resistance produced with the shortest distance between the vortex generators equal to the length of the heat sink is lower than that produced with the shortest distance between the vortex generators greater than the length of the heat sink. The heat transfer of the heat sink is higher when the vortex generators are installed against the middle of the heat sink on both sides of it. Although increasing the height of the vortex generators can enhance the heat transfer, the pressure difference also increases. The thermal resistance of the heat sink with the vortex generators arranged in the common-flow-up configuration is lower than that of the heat sink with the vortex generators arranged in the common-flow-down configuration.

Heat transfer enhancement of internal flow by inserting punched delta winglet vortex generators with various attack angles

Effects of punched delta winglet vortex generator inserts (PDWVGs) on single-phase forced convection heat transfer and friction loss of internal flow were experimentally investigated. The PDWVGs were manufactured by punching directly on aluminum strips with different attack angles (α) of 30°, 50° and 70°. Winglet-pitch ratio (Rp) and a winglet-width ratio (Rb) of PDWVGs were 1.05 and 0.42, respectively. Longitudinal strip and plain tube were also tested for comparison. The experiments were carried out under the conditions of Reynolds number from 5500 to 14500. Experimental results reveal that the PDWVG insert in a tube provided considerably higher heat transfer coefficient than the tube without the insert through pressure loss was also increased. The Nusselt number and friction factor increased with the increasing of α. The heat transfer enhancement by the PDWVGs with α of 30°, 50° and 70° provided higher than the plain tube in the range of 110–131%, 157–188% and 218–264%, respectively. The average friction factors in the inner tube generated by the PDWVGs with α of 30°, 50° and 70° were about 8.80, 10.21 and 11.87 times above the plain tube, respectively. The thermal enhancement factor was in the range of 0.91–1.22 for PDWVGs and 0.88–0.99 for L-S. In addition, the empirical correlations of Nusselt number, friction factor and thermal performance factor for PDWVGs were developed from the experimental results.

The effect of shape of winglet vortex generator on the thermal–hydrodynamic performance of a circular tube bank fin heat exchanger

In real application, the shape of the vortex generator has great influence on the heat transfer and flow resistance characteristics of tube bank fin heat exchanger. Therefore, the effect of the shape of the vortex generator on heat transfer performance of such heat exchanger should be considered. In this paper, the effect of three different shaped vortex generators (i.e. delta winglet, rectangular winglet and trapezoid winglet) on heat transfer intensity and secondary flow intensity of a circular tube bank fin heat exchanger was numerically studied. The results show that with increasing Re, overall average Nu and the non-dimensional secondary flow intensity Se m increase however friction factor f decreases. A corresponding relationship can be found between Nu and Se m, which indicates that the secondary flow intensity determines the heat transfer intensity in the fin-side channel of circular tube bank fin heat exchanger with different shaped vortex generators on the fin surfaces. Under the identical pumping power constrain, the optimal shape of the vortex generators is the delta winglet vortex generators for the studied cases.

Flow Visualization of Flat and Curved Trapezoidal Winglet Vortex Generator in Fin-and-Tube Channel in Inline Arrangement

In this study, a flow visualization experiment using the dye injection technique was conducted. Visual observation of the flow characteristics across the scaled up fin-and-tube heat exchanger (FTHE) channel model with and without trapezoidal winglet vortex generator (TWVG) were presented. Four cases of FTHE channel in inline tube arrangement were examined with TWVG at different geometries and arrangements, as well as a case without the vortex generator. The two TWVG geometries used in this study were a flat trapezoidal winglet (FTW) and a curved trapezoidal winglet (CTW) either arranged in common flow up (CFU) or common flow down (CFD) compositions. The Reynolds number (Re) used ranged from 500 to 2500. It was found that with the introduction of TWVG in the FTHE channel, the wake region size behind tubes reduced compared to the baseline case. However, the formation of an additional wake region behind the TWVG was also observed.

Experimental investigation of heat transfer and friction factor characteristics of solar air heater using wavy delta winglets

Abstract In the present work experimental investigation on the heat transfer and friction characteristics of a solar air heater duct roughened with wavy-up delta winglet vortex generators placed on absorber plate having a uniform wall heat flux is carried out. Reynolds number in the present study is taken in the range 4000–17,300 based on the hydraulic diameter of the channel. The investigated parameters of wavy delta winglets are no of waves (ϕ): 3, 5, 7 and relative longitudinal pitch (P/H): 3, 4, 5 and 6, respectively at single angle of attack (α): 60°. The comparison of the staggered and inline arrangement reveals that the inline arrangement produces the higher Nusselt Number. The maximum Nusselt number enhancement was found to be 223% over the flat plate using a relative longitudinal pitch of 3 with five wave winglets at Reynolds number of 4000 with an increase in friction factor by 10.3 times. The thermohydraulic performance obtained for the configuration was 2.09.

Numerical study of the laminar flow and heat transfer characteristics in a tube inserting a twisted tape having parallelogram winglet vortex generators

The usage of wings or/and winglets vortex generators (VGs) could provide excellent heat transfer performance with a minimal increase in pressure loss comparing with other VGs in a wide range of Reynolds number. For classical twisted tape, the contact area between twisted tape and working fluid is large, which would result in high friction drag. Motivated by this fact, a newly designed twisted tape having parallelogram winglet VGs (PWVGs) is proposed to enhance heat transfer. This twisted tape with winglet VGs is formed by cutting at the edge of the straight tape with parallelogram shape to produce a parallelogram winglet as twisting around its longitudinal axis. The laminar fluid flow and conjugate heat transfer characteristics in a circular tube inserting the twisted tape with PWVGs were analyzed using numerical method under uniform wall temperature condition, and four different attack angle α (α=27.64°, 21.44°, 17.44° and 14.67°) and four different axial spacing St (St=0.83D, 1.0D, 1.25D and 1.67D). The results show that (1) the newly designed twisted tape has two ways to generate secondary flow, including secondary flow generated by the twisted base tape and extra secondary flow generated by PWVGs; (2) the combination of twisted base tape and PWVGs has evident effects on the local flow and heat transfer characteristics; (3) compared with the reference empty tube, the twisted tape with PWVGs can effectively enhance heat transfer under identical pumping power condition, for studied case of α=17.44°, St/D=1.25 and Re ranging from 50 to 600, the average Nusselt number and friction factor are increased by 76.4–190.9% and 179.9–289.1%, respectively, and the corresponding thermal performance factor ranges from 1.25 to 1.85; and (4) as Re ranges from 50 to 600, the helical angle α of PWVGs is a very important parameter in design of the modified twisted tape, and when α is large and St is small the heat transfer performance of the twisted tape with PWVGs is better.

Effect of geometric size of curved delta winglet vortex generators and tube pitch on heat transfer characteristics of fin-tube heat exchanger

Vortex generator has received extensive attention and was widely applied for heat transfer enhancement. In order to further improve the heat transfer performance of compact heat exchanger, curved delta winglet vortex generators with different geometric sizes are experimentally studied for circular tube-and-fin heat exchanger in this paper. A total of 15 samples of circular tube-fin exchanger with three fin pitches, two tube pitches and two sizes of curved delta winglet vortex generators with different base length are carried out to find their effect on heat transfer and pressure losing. Colburn factor and friction factor are used to evaluate the performance of circular tube-and-fin heat exchanger with different parameters. The results showed that smaller vortex generator which locates close to the tube has the advantageous to heat transfer enhancement for flow with low Re and the larger vortex generator is more conducive to heat transfer enhancement for flow with large Re. The change of fin pitch has less effect on Colburn factor while friction factor is obviously affected by the change of fin pitch. Decreasing the tube pitch is beneficial to the heat transfer at the cost of increasing pressure loss and the overall heat performance increases when fin pitch is 2.3mm.

Numerical Heat Transfer Study of Turbulent Tube Flow through Winglet-pairs

A numerical investigation on heat transfer behaviors in a constant heat-fluxed round tube inserted with winglet vortex generators is conducted. Air as the working medium flows through the tube for Reynolds numbers (Re) between 4000 and 20,000. The effect of using the rectangular-winglet tape (RWT) on heat transfer characteristics in the tube is numerically examined. For comparison purpose, the trapezoidal-winglet tape (TWT) and delta-winglet tape (DWT) are also offered. The RWT parameters in this work include four relative winglet-to-tube heights or blockage ratios (BR=b/D= 0.1, 0.15, 0.2, and 0.25) while the TWT and DWT are only at BR= 0.2. All the winglet pairs are at a single attack angle (α= 45°) and pitch ratio (p/D=PR=4). The numerical results show that the Nusselt number (Nu) and friction factor (f) of the tube inserts are enhanced with increasing BR values. The Nu for the inserted tube is about 1.8-2.7 times above that for the smooth tube while the f is around 4.5-11 times higher. For the studied BR ranges, the highest thermal performance is 1.48 for the RWT with BR= 0.1 at lower Reynolds number.

On the solar receiver thermal enhancement by using the dimple combined with delta winglet vortex generator

In this study, effects of dimples and their arrangement on the flow structure, heat transfer and friction factor in a solar receiver heated channel with delta-winglet vortex generators (DWVGs) are numerically studied. The dimples are placed either in an inline or a staggered layout. A smooth channel with pure dimples and a smooth channel with pure DWVGs are studied, in which the smooth channel with DWVGs is considered as baseline. The Reynolds number is ranging from 4000 to 40,000. Results of the flow structure, heat plate Nu number, friction factor, temperature and turbulent kinetic energy (TKE) are included. The results show that the adoption of dimples significantly impacts the flow structure by interacting with the vortex which is generated by the DWVGs. A small part of the vortex moves downward and impinges on the inline arranged dimpled surface, which is beneficial for the heat transfer enhancement. However, for the staggered arrangement of dimples, the vortex flow is lifted upward before it impinges on the dimple surface. In this case, the inline arrangement dimples provides the best mixing and the highest heat transfer performance. The heat transfer is augmented by 36.23% while the friction factor is increased by 36.29% compared to the Baseline, respectively. The thermal performance analysis indicates that the use of dimples increases the thermal performance by 28.50%. It is also found that the adoption of inline dimples contributes to the optimal thermal performance and mixing of the cold and hot fluid.

An inverse study to design the optimal shape and position for delta winglet vortex generators of pin-fin heat sinks

A three-dimensional inverse design problem is examined in this study using a general purpose commercial code CFD-ACE+ and the Levenberg-Marquardt Method (LMM) to estimate the optimal position and shape for delta winglet vortex generators of pin-fin heat sinks for best cooling performance. The algorithm is based on the minimization of the average temperature on the base plate of heat sinks and then try to obtain the optimal design variables for vortex generators of pin-fin heat sinks. The delta winglet vortex generators are utilized on a pin-fin heat sink to estimate the optimal design when the inlet velocities of air al to Re = 10,000, 15,000 and 20,000, respectively. Finally, the heat sink and vortex generator modules are carried on the experimental verification. The results indicate that with the designed optimal vortex generators the cooling performance is indeed better than that with the original design vortex generators and the temperature distributions on the base plate are very similar between the experimental and numerical data.

Heat transfer enhancement of a heat source located in a wake zone using rectangular vortex generators

This study investigated experimentally the effect of rectangular winglet vortex generators on thermal performance of square flat heat source near a wake region. Rectangular winglets were fixed on the base board with common inflow orientation to direct the flow toward the core of stagnation zone. The proposed configuration causes significant flow acceleration that enhances heat transfer from near-wake heat source surfaces besides the generated large-scale turbulence vortices. Over Reynolds number range of 4200⩽ReL⩽12,300, vortex generators with height ratio (b/B) of 3/4–3/2 and length ratio (a/S) of 1/3–2/3 at attack angle of α=45° exhibit better thermal performance. Downstream and spanwise distances of x=(1/3–2/3)S and y=(2/10–3/10)L have the largest heat transfer enhancement, respectively. The heat transfer was augmented such NuL of the downstream heat source exceeds NuL of single heat source by values reach 9.1% at ReL=4676 with applying vortex generator strategy. For physical situation of two rows, NuL of the downstream heat source with installing rectangular winglets vortex generators can be enhanced by 14.5% within 4676⩽ReL⩽12,929 at X=10/50, Y=10/50 and α=45°. An insignificant increase in the friction factor of 9.7% over 12,135⩽ReDh⩽34,305 was noticed.

Numerical study of heat transfer enhancement by rectangular winglet vortex generator pair in a channel

A numerical simulation was performed to investigate the effects of longitudinal vortices on the heat transfer enhancement of a laminar flow in a rectangle duct mounted with rectangular winglet pair on the bottom wall. The studied Reynolds number which was defined using the hydraulic diameter twice the channel height ranges from 500 to 7000. The comparisons of the fluid flow and heat transfer characteristics for the cases with and without rectangular winglet pair were carried out. The effects of the height and attack angle of vortex generator pair on the heat transfer performance were investigated. The results show that mounting rectangular winglet pair on the bottom wall of the channel can significantly enhance heat transfer. The distributions of secondary flow on the cross sections are consistent with the distributions of Nu and J for different attack angles. The maximum heat transfer performance is obtained when the attack angle is 29° due to the maximum value of secondary flow generated by rectangular winglet pair.