Winglet Type Vortex Generators Research Articles

Hierarchical Deployment of Vortex Generators for Wake Management in Finned-Tube Heat Exchanger

While developing thermal management systems, volumetric compactness of the heat exchange module is a critical design factor. This three-dimensional computational analysis seeks to boost the thermal compactness of fin-and-tube heat exchangers by employing winglet-type vortex generators. Due to the fact that the thermo-hydraulic performance of vortex generators in such thermal systems is determined by three distinct design parameters, namely the attack angle, spatial location, and geometric aspect ratio, a concurrent parametric analysis of all three design parameters is conducted to gain a thorough understanding. In addition, regression analysis is applied to develop functional correlations that can predict the enhanced thermo-hydraulic performance of the heat exchangers. The improvements in wake-affected heat transfer brought on by the modifications are also specifically explored, along with other aspects of the augmentation mechanism. The highest thermal augmentation over the wake-affected fin is seen as 120%. Based on a thermo-hydraulic tradeoff, the friction factor increases exponentially with the attack angle, and the rate of increase is lowest for 15–30 degree range of attack angle and highest for 45–60 degree range. Certainly, there are multiple locations where winglets can be erected, and heat transfer enhancement by each potential location incurs linearized increase in the friction factor.

Integration of winglet type vortex generators in finned-tube heat exchangers for a sizeable capacity augmentation

Compact size of the heat exchange module is an important design consideration in majority of the thermal management systems. Using winglet type vortex generators, a sizeable improvement in the compactness of a widely used finned-tube array is attempted through this study. Since the degree of thermal augmentation changes with the generators’ position, around the tubes, this 3D comprehensive computational investigation aims to develop phenomenological correlations for the positional optimization, which are applicable over a wide range of operating conditions. Besides, this article is dedicated to understanding different aspects of the augmentation mechanism, including the tube-wake management and the performance improvement caused by the best design(s). Based on a parametric investigation, designs that are best suited for obtaining a sizeable performance augmentation of the system are identified. Furthermore, a critical assessment of the best designs is carried out to evaluate their impact on the heat transfer from wake-affected surfaces, both fins and tubes. It is encouraging to observe that the wake-affected surfaces also experience sizeable thermal augmentation, which increases further with the Reynolds number. While the total fin surface experiences a highest Colburn j-factor augmentation of 53.6%, the wake-affected fin undergoes 205.1% rise. An evident manifestation of the augmented Colburn j-factor is the reformed temperature distribution, which bears lower values all over the fins.

Augmented Performance and Wake Management in Finned Tube Arrays Through Hierarchical Deployment of Toe-Out Winglets

Abstract Downsizing the heat exchanger without compromising its heat exchange capacity is highly desirable for containing the box volume of a thermal management system. This investigation seeks to substantially boost the thermal compactness of a widely used gas-to-liquid heat exchanger, called finned tube arrays. For that purpose, winglet-type vortex generators are adopted. The novelty of the present study lies in the fact that it uses regression analysis to develop thermo-hydraulic functional correlations corresponding to three diverse design parameters of winglet-type vortex generators: the attack angle, the location and the geometric aspect ratio. In addition, enhancement in the wake-affected heat transfer is specifically examined, followed by a proof-of-concept study by making the best design(s) of vortex generators perform under widely varying operating conditions. Based on a thermo-hydraulic assessment of the generators' attack angle, 45-degrees is the limiting value of optimal attack angle. Although multiple winglet locations are found to deliver the desired thermal augmentation, a few locations incur disproportionate flow loss whereas majority locations facilitate linearized thermal augmentation. It is encouraging to find that the relative Colburn j-factor of the modified heat exchanger increases with the Reynolds number, despite the absolute values bearing an inverse correlation. While the highest augmentation in the average Colburn j-factor equals 44.1%, it is 150.1% over the wake-affected fin surface.

Prediction of heat transfer characteristics in a microchannel with vortex generators by machine learning

Abstract Because of the prompt improvements in Micro-Electro-Mechanical Systems, thermal management necessities have altered paying attention to the compactness and high energy consumption of actual electronic devices in industry. In this study, 625 data sets obtained numerically according to the change of five different geometric parameters and Reynolds numbers for delta winglet type vortex generator pairs placed in a microchannel were utilized. Four dissimilar artificial neural network models were established to predict the heat transfer characteristics in a microchannel with innovatively oriented vortex generators in the literature. Friction factor, Nusselt number, and performance evaluation criteria were considered to explore the heat transfer characteristics. Different neuron numbers were determined in the hidden layer of each of the models in which the Levethenberg–Marquardt training algorithm was benefited as the training algorithm. The predicted values were checked against the target data and empirical correlations. The coefficient of determination values calculated for each machine learning model were found to be above 0.99. According to obtained results, the designed artificial neural networks can provide high prediction performance for each data set and have higher prediction accuracy compared to empirical correlations. All data predicted by machine learning models were collected within the range of ±3% deviation bands, whereas the majority of the estimated data by empirical correlations dispersed within ±20% ones. For that reason, a full evaluation of the estimation performance of artificial neural networks versus empirical correlations data is enabled to fill a gap in the literature as one of the uncommon works.

Flow optimization in a microchannel with vortex generators using genetic algorithm

• The effect of different geometrical and flow conditions for microchannels with VGs. • Thermal-hydraulic performance of the microchannels with VGs is examined in details. • Response Surface Methodology is adopted for optimization work. • Pareto optimal solution is obtained from Multi-Objective Genetic Algorithm method. • Predictive sensitivity of the empirical correlations proposed for Nu and f is fairly well. In this study, delta winglet-type vortex generators, widely used in conventional macro channels and proven to be effective, are used in microchannels to increase their heat transfer capacities. The effects of vortex generators on heat transfer and pressure loss characteristics are studied numerically for different angles of attack, vortex generator arrangement type, the transverse and longitudinal distance between vortex generators, vortex generator length and height, and different Reynolds numbers. The thermal and hydraulic characteristics are presented as the Nusselt number, the friction factor, and the performance evaluation criteria number ( PEC ) that takes into account the heat transfer enhancement and the corresponding increase in pressure loss. The variation of Nu/Nu 0 , f/f 0 , and PEC are found to be in the range of 1.03–1.87, 1.04–1.8, and 0.92–1.62, respectively. A multi-objective optimization study are performed with the response surface methodology analysis to see how different parameters affect heat transfer and pressure loss and to determine the most optimum design. Besides, local sensitivity analysis study is carried out through the RSM, and water inlet velocity for heat transfer enhancement is found to be the most effective parameter. Among the geometric parameters, vortex generator height is determined as the most effective factor. Finally, practical Nusselt number and friction factor correlations taking many parameters into account are proposed to be able to compare the results of other researchers, and for engineers designing microchannel cooling systems.

Thermo-hydraulic performance and exergy analysis of a fin-and-tube heat exchanger with sinusoidal wavy winglet type vortex generators

The widely used fin-and-tube heat exchangers have a low air-side heat transfer capacity. Enhancing the air-side thermo-hydraulic performance is a key point of the relevant research. Vortex generators have been proven to be one of the most promising techniques to improve the air-side heat transfer capacity of the fin-and-tube heat exchangers. Herein, this paper proposed an original sinusoidal wavy winglet type vortex generator to achieve high heat transfer performance with moderate increased pressure drop penalty. A three-dimensional numerical simulation was conducted to explore the air-side thermo-hydraulic performance with Reynolds number ranging from 1027 to 2054. The longitudinal vortex is generated in the channel so as to enhance the intensify of convective heat transfer. Especially, the wave-shaped vortex generators can produce many local small-scale secondary flows. And it is confirmed that the frontal area of the vortex generator can be effectively extended by such wavy shape and a more intensified disturbance can be caused in the air-side. Furthermore, the effects of the attack angle (α), dimensionless height (Hp) and especially arrange position of the vortex generator were investigated. Additionally, the ranges of the Nusselt number ratio, friction factor ratio and surafece goodness factor in this study are 1.09–1.52, 1.09–2.31, and 1.06–1.24, respectively. Moreover, it is also very crucial to evalute the grade of energy and to explore the irreversible loss druing the heat tranfer process in view of the second law of thermodynamics. And the thermal dissipation can be reduced by up to 5.85% compared with the plain fins from the perspective of exergy analysis.

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.

Nusselt number and friction characteristics of a solar air heater that has a winglet type vortex generator in the absorber surface

The present investigation is based on the experimental analysis of heat transfer distribution and friction features of a solar air heater that has a rough absorbent surface with winglet type vortex generator has been made using liquid crystal thermography technique. The RrGgBb (red, green and blue) colour pattern obtained because of temperature variation which can be visualized by the captured image through a CCD camera. The captured colour pattern can be digitized and decoded it into HIS (Hue, Intensity, and Saturation). For the given winglet rib the roughnesss parameters considered as relative roughnesss pitch (P/e) values of 5 to 12, attack angle (α) of 30° to 75°, relative roughnesss width (W/w) values of 3 to 7 and flowing Reynolds number (Re) varies from 3000 to 22000. The effects of change in roughnesss parameters on heat transfer and friction factor are investigated. The optimum enhancement of heat transfer observed at P/e of 8 while the required friction factor decreases with the increases in relative roughnesss pitch. The presence of a winglet type vortex generator creates additional mixing, as well as a small hole at the winglet tip, produces air jet on the downstream side and enhances the heat transfer coefficient. The observation made for enhancement value of Nusselt number achieves its optimal at W/w of 5 while the friction factor observed to be maximum at W/w of 3 for the considered geometric parameters correspondings to an attack angle (α) of 60°.

Nusselt number and friction factor correlation of solar air heater having winglet type vortex generator over absorber plate

The experimentation has been done using the winglet type vortex generator as a roughness element above the absorber surface of a solar air heater (SAH) system. Different geometry-based roughness parameters have been considered such as relative roughness pitch (Pi/e) value of 5–12, relative roughness width (Ww/w) value of 3–7, angle of attack (α) value of 300-750 and the flowing fluid Reynolds number diversified between 3000 and 22,000 respectively and its effect on Nusselt number (Nuu) and friction factor (fr1) were studied. In order to achieve its optimum condition, the Nusselt number (Nuu) and friction factor (fr1) are analyzed for the roughness parameters to obtain the best overall performance and the required values are compared with the smooth type duct under similar flowing condition. Using regression analysis, correlations have been expanded for Nusselt number (Nuu) and friction component (fr1) in terms of Reynolds number (Re) and with different parametric condition which is considered to be satisfactory when compared with the experimental results.

Thermal-hydraulic performance and optimization of attack angle of delta winglets in plain and wavy finned-tube heat exchangers

This work is related to numerical investigation and optimization of the attack angle of delta winglet type vortex generators in plain and wavy finned-tube heat exchangers. For this purpose, three-dimensional numerical simulation data and a multi-objective genetic algorithm with Artificial neural network are employed. The heat exchanger models considered in this study are three rows of tubes in staggered arrangement. The angle of attack (α) of delta winglets and Reynolds number varies from 15° to 75° and 500 to 1300, respectively. Results are illustrated by investigating the flow structures and local heat transfer coefficient. Results show that compared to plain fins, wavy fins enhance the heat transfer performance of the heat exchanger due to constant disruption of thermal boundary. Applying delta winglets on the plain and wavy fins further increased the heat transfer by energizing flow in the wake of tubes while friction factor is also increased. To achieve a maximum heat transfer enhancement and a minimum pressure drop, the optimal angle of attack for varying Reynolds numbers are calculated using the Pareto optimal strategy. For this purpose, CFD data, artificial neural network and a multi-objective genetic algorithm are combined. Results show that compared to the corresponding smooth fins, heat transfer per unit volume (Qv) and pumping power per unit volume (Pv) performances of delta winglets in wavy finned-tube heat exchanger has increased up to 12.5% and 7.41%, respectively. Similarly, for plain finned-tube heat exchangers, the maximum increase in Qv is 14.7% while Pv is increased by 6.93%.

Heat Transfer Enhancement and Pressure Drop Performance for Fin and Tube Compact Heat Exchangers with Radiantly Arranged Rectangular Winglet-Type Vortex Generators

In this paper, heat transfer enhancement has been numerically investigated for fin and tube compact heat exchangers with radiantly arranged rectangular winglets and has been compared with the existing structures. In the proposed structure, there are total 12 winglets, 3 on each tube arranged radiantly with an attack angle of 60ï‚° each. Investigation has been carried out on low Reynolds number from 400-800 heat transfer is compared with other structures without winglet as baseline arrangement, prevailing rectangular winglet arrangement and wavy down rectangular winglet arrangement. The simulation results show that the radiantly arranged winglet that guides the fluid from main flow to the wall creates collision and leads to turbulence behind the tube. It is found that newly proposed structure with radiantly arranged winglets has the highest heat transfer rate, as compared to the existing structures and this can replace the previous structures. The heat transfer characteristics and flow structures are numerically investigated in ANSYS.

Numerical study of thermal and flow characteristics for a fin-and-tube heat exchanger with arc winglet type vortex generators

Vortex generator can effectively enhance the heat transfer performance on the fin surface by introducing the secondary flow and intensifying the mixing of fluid. In this study, four new types of arc-winglet vortex generator (VG) are proposed and the three-dimensional CFD numerical simulation was employed to investigate the fluid flow and heat transfer characteristics. The results indicate that compared with the conventional rectangular-winglet VG, the two types of plane arc VGs provide a significant improvement on the size of secondary flow behind the tubes and all the wake region size of the fins with the four types of arc-winglet VGs decreased to some extent, especially for the two types of curved arc VGs. The heat transfer enhancement of the fin with curved arc VGs is mainly completed by guiding more fluid to flow into the previous wake region and then scour the downstream tubes directly. In addition, compared with the rectangular-winglet VGs, the Nusselt number averagely increases by 11.5% for the equal-perimeter arc VGs fin, 19.9% for the curved equal-area arc VGs fin, and 35.9% for the curved equal-perimeter arc VGs fin. Although the equal-perimeter arc VG and the curved equal-perimeter arc VG have the same geometry size, the Nusselt number of the fin with the former one averagely increases by 22.2% while the pressure drop only increases by 13.5%.

Thermal performance in solar air heater with perforated-winglet-type vortex generator

An experimental and numerical study of turbulent convective heat transfer in a solar air heater duct with winglet-type vortex generators (WVGs) placed on the absorber plate is presented. Air as the test fluid enters the duct having a uniform wall heat-flux applied on the upper wall or the absorber plate with Reynolds number from 4100 to 25,500. Two types of WVGs are introduced: rectangular (RWVG) and trapezoidal (TWVG) WVGs, in order to create multiple vortex flows along the duct. The WVG parameters in the present study include two relative height (BR = e/H = 0.2 and 0.48), three longitudinal pitch ratios (PR = Pl/H = 1, 1.5 and 2) and a single attack angle, α = 30°. The experimental result reveals that the RWVG with BR = 0.48 and PR = 1 provides the highest heat transfer and friction factor at about 7.1 and 109.5 times above the flat duct, respectively while the TWVG with BR = 0.2 and PR = 1.5 yields the maximum thermal performance around 1.84. Then, to improve the performance by reducing the substantial pressure loss, both the WVGs with BR = 0.48 and PR = 1.5 are modified to be perforated rectangular and trapezoidal winglet-type vortex generators (P-RWVG and P-TWVG) with four different punched hole/pore diameters (d = 1, 3, 5 and 7 mm) on their central area. The investigation indicates that among the perforated WVGs, the P-RWVG at d = 1 mm yields the highest heat transfer and friction factor up to 6.78 and 84.32 times higher than the smooth duct but the best thermal performance of about 2.01 is found for the P-TWVG with d = 5 mm. To explore the flow and heat transfer pattern, a 3D numerical flow simulation is performed and validated with available measurements where both the numerical and measured results are in good agreement.

EFFECT OF FLOW STRUCTURE ON HEAT TRANSFER IN COMPACT HEAT EXCHANGER BY USING FINITE THICKNESS WINGLET AT ACUTE ANGLE

Longitudinal vortex generation is a well-known passive technique for thinning the thermal boundary layer and hence enhancing the heat transfer, but its performance while considering the thickness is essentially unknown. In this study, a single triangular shaped winglet type vortex generator having finite thickness is analyzed in a plate fin heat exchanger with triangular inserts as secondary fins. The vortex generators are mounted on bottom and top plates of the heat exchanger and triangular inserts forms a channel, each representing the symmetry for the gas-side element of the compact heat exchanger. Heat transfer and pressure drop is computed to determine the effectiveness of the vortex generator while varying its thickness, size, and angle of attack under confined laminar flow condition. In addition the winglet is tilted from vertical at an angle known as acute angle and it was found to produce two longitudinal vortices which better did the thinning of boundary layer. It is shown that adding thickness to triangular winglet and mounting at ψ = 45°, augment heat transfer along the channel wall as high as 19.7% with a corresponding increase of 7.8% in pressure loss.

Numerical Study of Heat Transfer Enhancement in Solar Air Heater Duct Fitted with Delta Winglets

The paper brings Numerical study of thermal performance of solar air heater channel in which delta winglet type vortex generators with and without holes punched on it are attached. Delta winglet type vortex generators having holes punched onto it are fitted in an array having 5 pair in one row, having 3 such rows starting at the entry of test section. With pitch of 60mm.Deltawinglet pair have an attack angle of 30 degrees, with height of winglet equal to half of duct height The study is carried out for Reynolds’s No in the range of 5000 to 25000 by changing airflow rate.in the test section with its upper channel wall provided with a uniform heat flux. Results are then compared with that of duct mounted with delta winglet without holes. Thermal performance is evaluated by analyzing both friction factor and Nussult’s number using R L Webb’s correlation for surfaces with roughness. Numerical simulation is done using Ansys fluent software. Analysis findings says that use of winglets brings enhancement in the heat transfer and thus increases the thermal performance. Arrangement of winglets also influences the performance. Improvements in design and performance can be brought by using winglets with different attack angles and span length.

Heat Transfer Enhancement in Solar Air Heater Duct Fitted With Punched Hole Delta Winglets

This paper investigates the thermal performance of solar air heater fitted with delta winglet type vortex generators with holes punched on it by experimental and numerical analysis. Delta winglet type vortex generators having holes punched onto it are fitted in a duct of size 400*300*30mm.it is placed in duct in 3 different configurations, as an array having 5 pair in one row. Delta winglet pair has an attack angle of 30degree, with height of winglet equal to half of duct height. The study is done for Reynolds's no in the range of 9000 to 25000. Thermal performance is evaluated by analyzing both friction factor and Nussult's number using Webb's correlation for surface roughness. Numerical simulation is done using Ansys fluent. Experimental and numerical results are then compared. Results shows that heat transfer enhancement of about 20-150% can be achieved by using punched hole delta winglet.

Numerical simulation on performances of plane and curved winglet type vortex generator pairs with punched holes

Thermal and flow characteristics of plane and curved vortex generators (VGs) with and without punched holes on their surfaces are investigated and the corresponding mechanism of heat transfer is analyzed. 3-D numerical simulations are carried out in a channel flow fitted with a pair of VGs to the bottom wall with Re varying from 700 to 26,500. The heat transfer enhancement and pressure loss are examined using the dimensionless parameters Num/Num0, f/f0 and R=(Num/Num0)/(f/f0). The results show that VGs with punched holes present higher heat transfer enhancement and lower flow resistance than those without holes and the value of R is increased by 9.8–15% under the present conditions. Further parametric study suggests that the ratio of hole area to the VG area should be optimized to achieve better heat transfer enhancement. And punching holes at a lower position and close to the leading edge gives better thermal–hydraulic performance. The mechanism of heat transfer enhancement is explored with the help of field synergy principle (FSP) and secondary flow theory. Take the delta winglet pair (DWP) for example, the area – average synergy angle θs between velocity vector and temperature gradient of the cross section along flow direction first increases sharply to a peak of 85.7° before the VGs, After that, it declines dramatically to 81.8° and then climbs back and stabilizes around 89°. Correspondingly, the Num/Num0 shows the opposite trend to θs. It is confirmed that the maximum value of heat transfer augmentation is achieved at the minimum synergy angle, which indicates that the mechanism of heat transfer enhancement can be well explained by FSP.

Development of parametric space for the vortex generator location for improving thermal compactness of an existing inline fin and tube heat exchanger

Heat transfer augmentation due to the intentional generation of longitudinal vortices in a fin-and-tube heat exchanger strongly depends on the location of the generators. This combined experimental and numerical study in the Reynolds number range from 1415 to 7075 is a step forward in the direction of product development. It is aimed at first determining the parametric space for the locations of delta winglet type vortex generators (DVG) which are effective for heat transfer augmentation. Thereafter the locations suitable for maximum augmentation are found. This comprehensive investigation considers the delta winglets attacking the oncoming flow over a wide range of angles ranging from 15° to 60°. It is recognized that the winglet location suitable for maximum augmentation can be defined in two ways, one that delivers maximum enhancement while ignoring the increase in flow loss and the other that incurs justifiable increase in the flow loss. A study of the flow structure reveals that the wake of each tube of an inline fin and tube heat exchanger occupies almost the entire intervening space between the two consecutive tubes. This makes the wetted fin area thermally under-productive due to poor heat transfer coefficients. Augmenting heat transfer in the tube wake is very important for the compact design of such heat exchangers. It is observed that well positioned winglets are effective in reducing the ovality of the isotherms. Such a change is a manifestation of more effective and homogeneous heat transfer from the fin.

Numerical investigation for finding the appropriate design parameters of a fin-and-tube heat exchanger with delta-winglet vortex generators

A numerical simulation is performed to investigate the heat transfer and pressure drop characteristics of three-row inline tube bundles as a part of a heat exchanger (Re = 1000, Pr = 4.29). To enhance heat transfer, two pairs of delta winglet-type vortex generators (VGs) installed beside the first row and between the first and second rows of the tube bundles. The diameter of the second row of the tubes is chosen smaller than those of the first and third. A comprehensive study on the effects of various geometrical parameters such as transverse and longitudinal positions of VGs, length and height of VGs and angle of attack of the delta winglets is performed to augment heat transfer. Based on this study the best values of these design parameters are determined. The results showed that the best model increases the convective heat transfer ratio and thermal performance factor about 59 and 43 %, respectively, in compare with the geometry without VG.