Attack Angle Of Vortex Generators Research Articles

Hydrothermal performance of a wavy minichannel heatsink with longitudinal vortex generators

Wavy channels and vortex generators (VGs) are potential heat transfer enhancement methods, and their combination can provide a remarkable hydrothermal performance. In this study, a water-cooled top and bottom walls sinusoidal wavy minichannel equipped with 14 VGs on each of its side walls is experimentally and numerically investigated. The pressure drops and average base temperatures are recorded for the Reynolds numbers (Re) between 500 and 1300 and the obtained experimental data are employed to validate the numerical conjugate heat transfer model. 3 configurations of the wavy channel with inline VGs and 3 with staggered VGs which differ by the attack angle of VGs are numerically investigated. The hydrothermal performances of the cases are studied and compared with a wavy channel without VGs. The Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF) are utilized to evaluate the hydrothermal performances. The most significant TPF is found to belong to the wavy channel with staggered VGs, periodically titled for 45° in the direction of the first part of the local curve of the wavy walls. Its TPF is found to be in the range of 1.4–1.46, while the TPF of the wavy channel without VGs is in the range of 1.17–1.36 for the studied Re range.

A second law analysis for turbulent convective flow through panel type radiator equipped with vortex generators

An irreversibility analysis is arranged for the turbulent convective flow through the panel type radiator equipped with the vortex generators. Delta wing vortex generators are installed inside the system to disrupt the flow and enhance the heat transfer rate. However, vortex generator may affect the second law efficiency of the system, which should be investigated. The increase in the entropy production restricts the thermodynamic advantages of the vortex generators. The influences of several parameters, including the attack angle of vortex generator β, space between the back edge of vortex generator and hot surface of the panel, d, and Re number, Re, on the velocity and temperature characteristics, entropy production owing to viscous friction and heat transfer, and Be number are studied. The results attained by the present numerical investigation are validated with the data reported in the literature to ensure about the accuracy of the numerical solver. The outcomes revealed that the entropy production owing to viscous friction is increased with increasing the attack angel of vortex generators and space between the back edge of vortex generator and the hot surface of the panel. The larger values of entropy production owing to heat transfer are produced when the vortex generators are placed farther from the hot surface of the panel. Both entropy production owing to viscous friction and heat transfer increase with placing the vortex generators inside the panel. The substrate of high Be number grows along the panel length and occupies most of the panel at the exit section. By the way, the entropy production owing to viscous friction is dominate term at the entrance of the panel owing to the high velocity gradient of the developing flow regions.

사다리꼴 와류발생기의 경사각과 충돌각이 열전달 성능에 미치는 영향에 대한 수치해석

The effect of inclination angle and attack angle on heat transfer enhancement of trapezoidal vortex generator was numerically investigated. The commercial package STAR-CCM+ was utilized to analyze the heat transfer and flow characteristics with various inclination and attack angle of vortex generator. The result shows that the optimum inclination angles are α =30°~40° in terms of the heat transfer and pressure drop. At more than 40° of inclination angle, the transverse vortex is dominant, so that the pressure drop is severe and the heat transfer is reduced. As the attack angle is increased, the transverse vortex is reduced, so that the pressure drop is improved. The optimum attack angle is β =30° because the heat transfer performance is maintained. However, more than 30° of attack angle, the heat transfer is decreasing.

Parameters Optimization of Fin-and-Tube Heat Exchanger with a Novel Vortex Generator Fin by Taguchi Method

In this study, the effects of various vortex generator configurations on the heat transfer and flow friction characteristics are investigated by numerical method. Compared with common-flow-down configuration, the Nusselt numbers of common-flow-up configuration increase by 2.7–2.9% in the range of studied Reynolds number, while the friction factors reduce by 7.8–10.0%. A comparative study of the effects of location of axial dimension, location of spanwise dimension, attack angle, and length and height of vortex generator on fin performance is conducted. The results show that the intensity of heat transfer can be greatly increased with decreasing the location and attack angle of vortex generator, and with increasing height of vortex generator, accompanying with the increase of pressure drop. The Nusselt number and friction factors first increase and then decrease with increasing length of vortex generator. The parameters of the vortex generator fin-and-tube heat exchanger are optimized by the Taguchi method. Sixteen kinds of models are made by compounding levels on each factor, and the heat transfer and flow friction characteristics of each model are analyzed. The results allow us to quantitatively estimate the various parameters affecting heat exchanger performance, and the main factors for optimal design of a heat exchanger are selected. The two optimal conditions are acquired, and the reproducibility of the results is verified by two analytical results.

An investigation of the thermo-hydraulic performance of the smooth wavy fin-and-elliptical tube heat exchangers utilizing new type vortex generators

A three-dimensional CFD numerical simulation is successfully carried out on thermo-hydraulic characteristics of a new smooth wavy fin-and-elliptical tube (SWFET) heat exchanger with three new types of vortex generators (VGs), namely – rectangular trapezoidal winglet (RTW), angle rectangular winglet (ARW) and curved angle rectangular winglet (CARW). Several parameters have been examined in this study. There have a pronounced effect on the thermo-hydraulic performance. In addition the results are analyzed from the viewpoint of the field synergy principle which emphasizes that the reduction of the synergy angle between velocity and fluid temperature gradient is the principal mechanism for enhancement of heat transfer performance. These parameters include: Reynolds number (based on the hydraulic diameter, ReDh=500–3000), geometric shape of VGs, attack angle of VGs (αVG=15–75°), placement of VG pairs (up- or/and downstream), tube ellipticity ratio (e=0.65–1.0) and wavy fin height (H=0.8–1.6mm). The results demonstrate that with increasing Reynolds number and wavy fin height, decreasing the tube ellipticity ratio, the heat transfer performance of the SWFET heat exchanger is enhanced. The SWFET heat exchanger with the advantages of using CARW VGs and RTW VGs at smaller and larger attack angles, respectively, presents good thermo-hydraulic performance enhancement. Finally, new correlations are proposed to estimate the values of the average Nusselt number Nu, friction factor f and synergy angle θ based on the Reynolds number, attack angle of VGs, tube ellipticity ratio and wavy fin height.

3D numerical investigation of flow and heat transfer characteristics in smooth wavy fin-and-elliptical tube heat exchangers using new type vortex generators

3D computational analysis was performed to investigate heat transfer and pressure drop characteristics of flow in SWFET (Smooth Wavy Fin-and-Elliptical Tube) heat exchanger with four new VGs (vortex generators), RTW (rectangular trapezoidal winglet), ARW (angle rectangular winglet), CARW (curved angle rectangular winglet) and WW (Wheeler wishbone). The numerical model was well validated with the available experimental results. Numerical results illustrate that vortex generators can bring about further heat transfer enhancement through careful adjustment of the position with respect to the elliptical tube, type and attack angle of vortex generators. The influences of the geometrical factors including attack angles of the winglets (αVG = 15∘,30∘,45∘,60∘ and 75°) and width/length aspect ratio (w/l = 0.5,1.0) of the Wheeler wishbones on enhancing the heat transfer performance of a smooth wavy fin heat exchanger with a three-row staggered elliptical tube bundle are investigated. A parametric study on the winglet vortex generators indicated that for the small attack angle, CARW vortex generators gives better thermohydraulic performance under the present conditions. The best thermal performance with winglet VGs in larger attack angle, was obtained at RTW VGs arrangement. For the SWFET heat exchangers, the WW VGs with w/l = 0.5 provide the best heat transfer performance.

Impact of Delta-Winglet Pair of Vortex Generators on the Thermal and Hydraulic Performance of a Triangular Channel Using Al2O3–Water Nanofluid

This paper presents the laminar forced convection of Al2O3–water nanofluid in a triangular channel, subjected to a constant and uniform heat flux at the slant walls, using delta-winglet pair (DWP) of vortex generator which is numerically investigated in three dimensions. The governing equations of mass, momentum, and energy are solved using the finite volume method (FVM). The nanofluid properties are estimated as constant and temperature-dependent properties. The nanoparticle concentrations and diameters are in ranges of 1–4% and 25–85 nm, respectively. Different attack angles of vortex generators are examined which are 7 deg, 15 deg, 30 deg, and 45 deg with range of Reynolds number from 100 to 2000. The results show that the heat transfer coefficient is remarkable dependent on the attack angle of vortex generators and the volume fraction of nanoparticles. The heat transfer coefficient increases as the attack angle increases from 7 deg to 30 deg and then diminishes at 45 deg. The heat transfer rate remarkably depends on the nanoparticle concentration and diameter, attack angle of vortex generator and Reynolds number. An increase in the shear stress is found when attack angle, volume fraction, and Reynolds number increase.

Secondary flow intensity determines Nusselt number on the fin surfaces of circle tube bank fin heat exchanger

Secondary flow is the flow on the cross section normal to the main flow. It can greatly enhance the convective heat transfer. Mounting or punching vortex generators (VGs) on heat transfer surface can produce secondary flow. The heat transfer of circle tube bank fin heat exchanger with VGs or without VGs on the fin surface having ten different configurations (different fin spacing, height and attack angle of VGs) was numerically studied. It is found that if a non-dimensional parameter based on the absolute vorticity flux is introduced to specify the intensity of secondary flow, the volume average non-dimensional intensity of secondary flow has one-to-one correlation with Nusselt number for all the cases studied, but there is no such correlation with the friction factor. Considering the pressure drop produced by the shape of VGs, the ratio of cross section area reduction after introducing VGs is introduced to modify the friction factor. At the same fin spacing, both Reynolds number and the volume average non-dimensional intensity of secondary flow have one-to-one correlation with the modified friction factor. These results reveal that secondary flow intensity determines the heat transfer characteristics of the fin surfaces of circle tube bank fin heat exchanger only.

Optimization of heat exchangers with vortex-generator fin by Taguchi method

A comparative study of effects of attack angle, length of vortex generator, height of vortex generator, fin material, fin thickness, fin pitch and tube pitch on fin performance of vortex-generator fin-and-tube heat exchanger is conducted by numerical method. The parameters of vortex-generator fin-and-tube heat exchangers are optimized by the Taguchi method. Eighteen kinds of models are made by compounding levels on each factor, and the heat transfer and flow characteristics of each model are analyzed. The results show that these six factors (fin pitch, longitudinal tube pitch, transverse tube pitch, length of vortex generator, height of vortex generator, and attack angle of vortex generator) have great influences on the JF-factor. The fin material and fin thickness have trifling effects on the JF-factor. The two optimal conditions (A1B3C3D2E1F2G1H3 and A2B2C2D3E1F2G1H3) are acquired, and the reproducibility of the results is verified by two analytical results.

Tube Transverse Pitch Effect on Heat/Mass Transfer Characteristics of Flat Tube Bank Fin Mounted With Vortex Generators

For one heat exchanger model of three-row flat tube bank fin mounted with vortex generators (VGs), the effect of transversal tube pitch on heat/mass transfer performance was investigated by the experimental method of naphthalene sublimation. For the same arrangement of VGs around the tube, it is found that the larger the transversal tube pitch, the larger the heat transfer enhancement because of less interactions of vortices generated from different VGs. Interaction of vortices decreases the heat transfer enhancement on the fin surfaces with and without VGs for the case with small transversal tube pitch. For isothermal condition, two correlated equations of average Nusselt number and friction factor considering the fin spacing, the attack angle of VG, the height of VG, the ratio of transversal tube pitch, and Reynolds number are reported.

Numerical investigation and analysis of heat transfer enhancement in channel by longitudinal vortex based on field synergy principle

3-D numerical simulations were presented for laminar flow and heat transfer characteristics in a rectangular channel with vortex generators. The effects of Reynolds number (from 800 to 3 000), the attack angle of vortex generator (from 15° to 90°) and the shape of vortex generator were examined. The numerical results were analyzed based on the field synergy principle. It is found that the inherent mechanism of the heat transfer enhancement by longitudinal vortex can be explained by the field synergy principle, that is, the second flow generated by vortex generators results in the reduction of the intersection angle between the velocity and fluid temperature gradient. The longitudinal vortex improves the field synergy of the large downstream region of longitudinal vortex generator (LVG) and the region near (LVG); however, transverse vortex only improves the synergy of the region near vortex generator. Thus, longitudinal vortex can enhance the integral heat transfer of the flow field, while transverse vortex can only enhance the local heat transfer. The synergy angle decreases with the increase of Reynolds number for the channel with LVG to differ from the result obtained from the plain channel, and the triangle winglet performs better than the rectanglar one under the same surface area condition.

Numerical study on laminar convection heat transfer in a rectangular channel with longitudinal vortex generator. Part A: Verification of field synergy principle

This study presents numerical computation results on laminar convection heat transfer in a rectangular channel with a pair of rectangular winglets longitudinal vortex generator punched out from the lower wall of the channel. The effect of the punched holes and the thickness of the rectangular winglet pair to the fluid flow and heat transfer are numerically studied. It is found that the case with punched holes has more heat transfer enhancement in the region near to the vortex generator and lower average flow frictional coefficient compared with the case without punched holes. The thickness of rectangular winglet can cause less heat transfer enhancement in the region near to the vortex generator and almost has no significant effect on the total pressure drop of the channel. The effects of Reynolds number (from 800 to 3000), the attack angle of vortex generator (15°, 30°, 45°, 60° and 90°) were examined. The numerical results were analyzed from the viewpoint of field synergy principle. It was found that the essence of heat transfer enhancement by longitudinal vortex can be explained very well by the field synergy principle, i.e., when the second flow generated by vortex generators results in the reduction of the intersection angle between the velocity and fluid temperature gradient, the heat transfer in the present channels will be enhanced. Longitudinal vortices (LVs) improve the synergy between velocity and temperature field not only in the region near LVG but also in the large downstream region of longitudinal vortex generator. So LVs enable to enhance the global heat transfer of channel. Transverse vortices (TVs) only improve the synergy in the region near VG. So TVs can only enhance the local heat transfer of channel.