Delta Winglet Type Research Articles

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.

Comparison of Turbulent Flow and Heat Transfer in a Rectangular Channel with Delta Wing and Winglet Type Longitudinal Vortex Generators

Comparison of Turbulent Flow and Heat Transfer in a Rectangular Channel with Delta Wing and Winglet Type Longitudinal Vortex Generators

Heat Transfer Enhancement of Crossflow Air-to-Water Fin-and-Tube Heat Exchanger by Using Delta-Winglet Type Vortex Generators

The aim of this work is to numerically analyse fluid flow and heat transfer characteristics in a crossflow air-to-water fin-and-tube heat exchanger (FTHEX) by implementing two configurations of delta-winglet type vortex generators at the air side: delta-winglet upstream (DWU) and delta-winglet downstream (DWD). The vortex generators are mounted on a fin surface and deployed in a “common flow up” orientation. The effects of attack angles of 15°, 30° and 45° on air-side heat transfer and pressure drop were examined. Since the implementation of the full-size model would involve large numerical resources, the computational domain is simplified by considering a small segment in the direction of water flow. The fully developed temperature and velocity boundary conditions were set at the water inlets. To validate the defined mathematical model and numerical procedure, measurements have been performed on a plain FTHEX. The air side Reynolds number, based on hydraulic diameter, was in the range of 176 ≤ ReDh ≤ 400 and water side Reynolds number, based on inner tube diameter, was constant Redi = 17,065. The results have shown that the highest increase in the Colburn factor j (by 11–27%) and reduction in the air-side thermal resistance fraction (from 78.2–76.9% for ReDh = 176 to 76–72.4% for ReDh = 400) is achieved by using the DWD configuration with attack angle 45°. In addition, the overall heat transfer coefficient is improved by up to 15.7%. The DWD configuration with the attack angle 30° provides the greatest improvement in the heat transfer to pressure loss ratio, 5.2–15.4% over the range of ReDhstudied.

Numerical Analysis of the Thermal-Hydraulic Performance on Circular Channel Using Vortex Generator

Vortex generators are often used in the industrial world because they can improve heat transfer well. Vortex generators make it possible to mix hot and cold fluids to be more optimal than not using them. Therefore, the current study aims to investigate the thermal-hydraulic of each case of a delta-winglet type vortex generator in a circular channel using numerical simulations. This modelling is carried out by varying the angle of the vortex generator type delta-winglet, namely, 90°, 105°, and 120°, which are arranged in a line, and the angle of attack in all cases is 30°. The Reynolds number is set from 4,000 to 12,000 with an interval of 2,000 and using the k-ω turbulent SST model. The working fluid used in this study is water. This fluid was chosen because it has better thermal conductivity than air, even though it has a higher viscosity and results in increased flow resistance. This study found that the highest heat transfer was a deltawinglet vortex generator at 90°, 105°, and 120°. But the delta-winglet, which has the highest heat transfer, will impact the increased flow resistance. Furthermore, the best thermal-hydraulic results were achieved in the case of the delta-winglet vortex generator at an angle of 120° of 2.47.

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%.

3D Simulative Investigation of Heat Transfer Enhancement Using Three Vortex Generator Types Surrounding Tube in Plate Fin Heat Exchanger

Vortex generator is a method to enhancing of heat exchanger performance but still have some disadvantages when the heat transfer performance increase. One of the disadvantage using vortex generator is high pressure drop. This investigation will be compared three type vortex generators to result the overall performance of heat transfer around tube in plate fin heat exchanger. The three types of vortex generator to investigate are rectangular winglet type, delta winglet type, and trapezoidal winglet type in laminar flow. The result showed that using the kind of trapezoidal winglet pair type in the plate fin and tube heat exchanger consist of six rows of round tube with two neighboring fins form a channel better performance than two types vortex generators such as rectangular winglet type and delta winglet type. The heat transfer coefficient when use trapezoidal winglet type was increased almost same with rectangular winglet type and pressure drop was decreased more than delta winglet type.

Heat transfer enhancement of inclined projected winglet pair vortex generators with protrusions

Heat transfer enhancement in parallel plate-fin heat exchanger is examined by performing three-dimensional numerical simulations of longitudinal vortex generators (VG) with protrusions. The turbulence is modeled using the shear-stress transport (SST) κ-ω model and validated with correlations and experimental data at Reynolds number equal to 4600. Hemi-spherical protrusions are inserted downstream two VG configurations: delta winglet type (DWP) and a new VG configuration named inclined projected winglet pair (IPWP), in various locations, leading to the definition of six different configurations. Based on the streamwise distribution of Nusselt number and friction coefficient criteria in addition to vorticity, the local performance is analyzed. Some VGs with protrusions are examined and show better performance relative to VGs standing alone. The present study highlights the different mechanisms involved in the convective heat transfer intensification by generating multiple interacting vortices while adding protrusions with low pressure drop penalty. Finally, it is found that the IPWP with protrusions, set downstream in the middle, bestows the best global performance with about 7.1% heat transfer enhancement compared to DWP configuration.

Numerical Study and Optimization of Corrugation Height and Angle of Attack of Vortex Generator in the Wavy Fin-and-Tube Heat Exchanger

Wavy fins have been considered as an alternative of the straight fins in compact heat exchangers (CHEs) for better heat transfer performance, which can be augmented by considering vortex generators (VGs). This work is related to numerical investigation and optimization of corrugation height of fin and angle of attack of delta winglet type VGs in a wavy fin-and-tube heat exchanger. For this purpose, three-dimensional (3D) Reynolds-averaged Navier-Stokes analysis and a multi-objective genetic algorithm (MOGA) with surrogate modeling are performed. Numerical simulation is carried out to study the effect of delta winglets with varying the corrugation height of wavy fin in three rows of tubes with staggered tube arrangements. The corrugation height (H) and angle of attack (α) vary from 0.3 mm to 1.8 mm and 15 deg to 75 deg, respectively. Results are illustrated by investigating the flow structures and temperature contours. Results show that increasing the corrugation height of wavy fin and angle of attack of delta winglets enhances the heat transfer performance of heat exchanger while friction factor is also increased. Employing delta winglets has augmented the thermal performance for all corrugation heights and superior effect is observed at a higher corrugation. To achieve a maximum heat transfer enhancement and a minimum pressure drop, the optimal values of these parameters (H and α) are calculated using the Pareto optimal strategy. For this purpose, computational fluid dynamics (CFD) data, a surrogate model (neural network), and a multi-objective GA are combined. Results show that optimal orientation of delta winglets with respect to corrugation height can improve both the thermal and hydraulic performance of the heat exchanger.

A Comprehensive Numerical Study on Thermohydraulic Performance of Fluid Flow in Triangular Ducts with Delta-Winglet Vortex Generators

ABSTRACTTriangular ducts fitted with various kinds of delta-winglet type vortex generators (VGs) are commonly used to achieve compactness and heat transfer enhancement in many industries. Successive locations of VGs on the inner surfaces of the ducts can be arranged in Common Flow Up (CFU) and Common Flow Down (CFD) orientations. In the present numerical study simultaneous effects of orientation and streamwise distance between VGs on triangular fin performance is carried out considering both global and local flow and heat transfer fields. With the configurations considered in this study, a CFD–CFU orientation and a nondimensional streamwise distance of 0.5 is determined as the best configuration. “RNG k-ϵ” turbulence model with “Enhanced wall treatment” option is determined as the best turbulence model to predict the flow fields inside the triangular duct with built-in VGs, for Reynolds number of 5000.

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.

Thermal enhancement of triangular fins based on spanwise distance of vortex generators

In this study, the influence of spanwise positions of vortex generators on the fin performance is determined numerically by considering global and local flow and heat transfer fields. The vortex generators are located on the inclined surfaces of equilateral triangular fins and the spanwise distances between them are altered as much as possible depending on the extents of the triangular duct. “RNG k-ɛ” turbulence model with “Enhanced wall treatment” option is determined as the best turbulence model to predict the flow fields inside the triangular fins with built-in vortex generators, for Reynolds number of 5000. It is found that the best performance is achieved when the spanwise distance between the common flow up and common flow down type vortex generator pairs and the triangular duct base are equal to 0.23 and 1.11 times the vortex generator length, respectively. The optimum spanwise distance between the vortex generators is determined as 0.88 times the vortex generator length. The determined values reinforced the secondary flow interactions including mixing of hot and cold fluids, generation of turbulence, swirling motion of vortices, and interaction of vortices with the main flow. The obtained results are useful in designing triangular heat exchangers with built-in delta-winglet type vortex generators.

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.

Thermal-hydraulic performance optimization of inline and staggered fin-tube compact heat exchangers applying longitudinal vortex generators

Optimization is now recognized as essential in the design of modern compact heat exchanger since the augmentation of heat transfer applying longitudinal vortex generator depends on different interacting parameters, such as its streamwise and spanwise locations, and attack and roll angles and shape. For this work, an optimization procedure based on the SIMPLEX method was conducted through a fluid–solid conjugated heat transfer modeling considering a fin-tube compact heat exchanger with two rows of tubes in staggered and inline arrangements, in order to find an optimum configuration of the vortex generators for two objective functions related to Colburn factor (j) and Friction factor (f). Two Reynolds numbers (250 and 650), performing as a function of fin-pitch, were evaluated. Moreover, a simple approach based on trigonometric decomposition to treat the constraints is presented, which allows great flexibility to vortex generators to cover the design space solution. Seven independent input parameters for each vortex generator in optimization procedure were considered, totaling fourteen independent variables. The results indicate that this work-optimized configuration for the vortex generators achieved higher heat transfer augmentation than those in previous works in the open literature, for both objective functions, Reynolds number and tube arrangements, and it is more pronounced for staggered tube arrangement than for inline tube arrangement. Moreover, suitable vortex generator shapes to maximize the objective functions are more similar to rectangular-winglet type than delta-winglet type, and the optimum ratio between the vortex generator height and fin-pitch is 0.6. Although several trends could be defined for the optimum points, optimized configurations of the vortex generators were found to be different for each Reynolds number, tube arrangement and objective functions, indicating strong asymmetry between the vortex generators to achieve higher heat transfer augmentation.

Interaction of counter rotating longitudinal vortices and the effect on fluid flow and heat transfer

The flow with longitudinal vortices is an important phenomenon in fluid dynamics and heat transfer. As the longitudinal vortices can potentially enhance heat transfer with small pressure loss penalty, vortex generators (VGs) which can generate longitudinal vortices are widely used to enhance the heat transfer of compact heat exchanger. In order to obtain a better heat transfer performance, researchers always try to punch lots of VGs out of the fin surface. But the increasing number of VGs is not necessarily linked with the rise in heat transfer performance augmentation. This is because the longitudinal vortices will interact with each other when they meet in the flow channel and the interaction between the longitudinal vortices is always disadvantage for the heat transfer enhancement. In this paper, numerical simulation of the interaction between two counter-rotating longitudinal vortices was carried out for the plate–fin heat exchanger using two rows of delta winglet type vortex generators. The effect of the transversal distance between the two VGs on the interaction of vortices and the effect of such interaction on heat transfer enhancement are studied in detail. New and important understandings about the interaction of counterrotating longitudinal vortices are obtained. The intensity of the longitudinal vortices and the heat transfer performance are sensitive to the interaction between longitudinal vortices. The interaction between counterrotating vortices decreases the average intensity of vortices, but does not necessarily decrease the heat transfer performance of longitudinal vortices. The common flow region formed between the counterrotating longitudinal vortices is beneficial to the heat transfer enhancement though interaction takes place in the common flow region between longitudinal vortices. An optimum arrangement of VGs exists for obtaining the best heat transfer performance. The arrangement of VGs with the transversal distance is zero must be avoided due to the serious interaction between longitudinal vortices.

Heat Transfer and Thermal Resistance Characteristics of Fin with Built-In Interrupted Delta Winglet Type

The heat transfer and fluid flow characteristics of a new type of fin with built-in interrupted delta winglets is studied in this paper by three-dimensional numerical simulation. In order to ensure reliability of numerical model, plate fin with common-flow-up delta winglets is firstly simulated. The comparison of numerical and experimental results shows a maximum deviation of 11.4% within the entire range of Reynolds number. The computational results show that heat transfer capacity and overall performance increase by 35–60% and 19–64%, respectively. The flow field visualization shows that the interrupted delta winglets can produce longitudinal vortices at the rear of delta winglets and reduce the wake zone behind the tube, so the proposed fin can enhance heat transfer accompanied by low pressure loss. The field synergy theory and entransy dissipation extremum principle are employed on analyzing the mechanism of heat transfer enhancement. The results indicate that enhancement heat transfer mechanism of interrupted delta winglets can be explained as the result of the decrease of synergy angle and reduction of the entransy dissipation.

Optimization of winglet-type vortex generator positions and angles in plate-fin compact heat exchanger: Response Surface Methodology and Direct Optimization

Augmentation of heat transfer has been an important research topic for many years. Although many heat transfer enhancement techniques have been proposed over the years, few researches deal with thermal optimization considering vortex generators (VG). This work is related to optimization of VG position and angles in a fin-tube compact heat exchanger using the Genetic Algorithm (GA). Two approaches were evaluated: Response Surface Methodology (RSM) applying Neural Networking method, and Direct Optimization (DO). Numerical analyses based on the finite-volume methodology was performed to analyze heat transfer and pressure drop of a fin-tube heat exchanger with two row of tubes in staggered tube arrangement applying two delta winglet type longitudinal vortex generators with aspect ratio 2. Turbulent flow simulation was performed for Reynolds number 1400 (based on fin pitch). Four vortex generator parameters which impact heat exchanger performance were analyzed: longitudinal vortex generator position in x–y directions, attack angle (θ) and roll angle (φ). The present work is the first to study the influence of VG roll angle on heat transfer enhancement. Therefore, eight independent input parameters were considered, four VG parameters for each tube. Four performance evaluation criteria (PEC) based on Colburn factor (j) and Friction factor (f) were chosen as objective function. The optimized VG configurations led to heat transfer enhancement rates higher than reported in the literature. Direct Optimization reported better results than Response Surface Methodology for all objective functions. Important flow interactions were found between vortices generated by VG1 and VG2, which influenced the results of Colburn factor (j) and Friction factor (f). The best results for each objective functions were achieved when VG1 was not symmetrical to VG2. Regarding global pressure drop, VG1 does not contribute to its mitigation, whereas VG2 is very important to flow separation delay in tube 2. The main contribution of VG1 is to increase the heat transfer rate, whereas VG2 increases the heat transfer rate and decreases the pressure drop. Roll angle has a strong influence on friction factor (f), especially for VG1.

Experimental Investigation on Turbulent Convection in Solar Air Heater Channel Fitted with Delta Winglet Vortex Generator

The paper presents an experimental study on the heat transfer and flow friction characteristics in a solar air heater channel fitted with delta-winglet type vortex generators (DWs). The experiments are conducted by varying the airflow rate for Reynolds number in the range of 5000 to 24000 in the test section with a uniform heat-flux applied on the upper channel wall. Firstly, the DW pairs are mounted only at the entrance of the lower wall of the test channel (called DW-E) to create multiple vortex flows at the entry. The effect of two transverse pitches (RP = Pt/H = 1 and 2) at three attack angles (α = 30°, 45° and 60°) of the DW-E with its relative height, b/H = 0.5 (half height of channel) is examined. Secondly, the 30° DWs with three different relative heights (b/H = 0.3, 0.4 and 0.5) are placed on the upper wall only (absorber plate, called DW-A) of the test channel. The experimental result reveals that in the first case, the 60° DW-E at RP = 1 provides the highest heat transfer and friction factor while the 30° DW-E at RP = 1 performs overall better than the others. In the second case, the 30° DW-A at b/H = 0.5 yields the highest heat transfer and friction factor but the best thermal performance is found at b/H = 0.4.

Enhancement of Heat Transfer Using Delta-Winglet Type Vortex Generators with a Common-Flow-up Arrangement

Simulations of a coolant air flowing in a heat exchanger with delta-winglet type vortex generators in common-flow-up configuration have been performed to unveil the salient heat transfer characteristics. The heat exchanger is approximated as a periodic rectangular channel with heated walls and a pair of built-in tubes near the inlet and outlet. The heat transfer characteristics of the heat exchangers with vortex generators near the inlet, outlet, and both inlet and outlet have been compared. The Navier-Stokes equations together with the energy equation are solved employing unstructured finite volume method. The simulations reveal a significant enhancement in heat transfer because of the strong swirling motion originating from the streamwise longitudinal vortices behind the pair of delta winglets. The spiraling flow entrains air into the core and causes intermixing of the fluid layers to disrupt the growth of the thermal boundary layer. A parametric study on the angles of attack identifies the conditions under which enhancement in heat transfer can lead to significant miniaturization of the heat exchangers. The analysis also reveals interesting flow structures behind the winglets and correlates them to the mechanism of heat transfer.

Application of Combined Enhanced Techniques for Design of Highly Efficient Air Heat Transfer Surface

In order to reduce the size and cost of heat exchangers, an air-side wavy fin-and-tube heat transfer surface with three-row tubes needs to be replaced by two-row tubes with some appropriate enhancing techniques. The major purpose of the present paper is to search for such new structure by numerical simulation. First, longitudinal vortex generators of Delta-winglet type are tried. The influence of number and of arrangement of the winglets on the performance of the heat transfer surface is studied in detail. The numerical results show that the fin with two winglets aligned spanwise in the front and rear of each tube (Fin W6) has higher heat transfer capability than other enhanced structures with vortex generators, but it still unable to meet the heat transfer requirement. Then a combination design of the longitudinal vortex generator with slotted protruding parallel strips is proposed and different variations of their arrangement are tried. Finally we come to such a combination (C3), which is based on Fin W6 with additional eight protruding strips situated at five positions (grouped by 1, 2, 2, 2, and 1) along the flow direction. Fin C3 can satisfy the requirements for heat transfer rate of the original wavy fin of three-row tubes with a mild increase in pressure drop, and its volume and material reduce to about 67% of the original one.