Wing-type Vortex Generators Research Articles

Improvement of an exhaust gas recirculation cooler using discrete ribbed and perforated louvered strip vortex generator

This CFD study represents the improvement of cooling performance of Exhaust Gas Recirculation (EGR) by adding newly designed vortex generators inside the engine space of an automobile. The simulation of EGR cooler model was validated comparing with the available data and a reasonable agreement has been observed. A total of twelve different shapes of proposed wing-type vortex generators were numerically investigated to compare the cooling effect of a single VG in the duct. For all the studies, a forward inclination angle of 135° was considered as it is the best inclination angle to get the highest vorticity. Among all, it was found that kite type wing VG provides the best cooling effect. Later, the VGs were arranged in several array configurations with 5 different pitch distances to find the best pitch distance. With the 3mm pitch distance in an array, among twelve different VGs, Gothic type wing VG showed the best performance in terms of cooling performance and 11% cooling improvement rather than a single placed VG was determined. Vorticity and cooling effect were also compared by changing the inlet velocity of the exhaust gas. A comparative study was carried out to highlight that Gothic type wing VG performed best in lowering the outlet temperature. Gothic type VG is 12% and 4% more effective than the discrete ribbed and perforated louvered strip VGs respectively.

Compound heat transfer enhancement for shell side of double-pipe heat exchanger by helical fins and vortex generators

To improve heat transfer performance of shell side of double-pipe heat exchanger with helical fins on its inner tube, some vortex generators (VGs) were installed along the centerline of the helical channel. Heat transfer performance and pressure drop characteristic of the enhanced heat exchangers were investigated using air as the working fluid and steam as the heating medium. The helical fins were in the annulus and span its full width at different helical pitch. Wing-type VGs (delta or rectangular wing) and winglet-type VGs (delta or rectangular winglet pair) were used to combine with helical fins. The friction factor and Nusselt number can be well correlated by power-law correlations in the Reynolds number range studied. In order to evaluate the thermal performance of the shell side enhanced over the shell side without enhancement, comparisons were made under three constraints: (1) identical mass flow rate, IMF; (2) identical pressure drop, IPD and (3) identical pumping power, IPP. The results show the shell side enhanced by the compound heat transfer enhancement has better performance than the shell side only enhanced by helical fins at shorter helical pitch under the three constraints.

Experimental Study of Heat Transfer Enhancement in Tube in Tube Heat Exchanger using Rectangular Wing Type Vortex Generator

Experimental Study of Heat Transfer Enhancement in Tube in Tube Heat Exchanger using Rectangular Wing Type Vortex Generator

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The efficiency of heat transfer η, i.e., the ratio between heat transfer enhancement and drag increase from a smooth channel, is discussed for the turbulent and laminar flows in a channel with a wing-type vortex generator (VG) installed on the wall. In this report, the effect of Prandtl number Pr on ηis mainly discussed. η decreases slightly in the turbulent flow with Pr while it increases noticeably in the laminar flow. In the laminar flow, since there is no background turbulence in the smooth channel, the fluctuation generated by VG directly enhances the heat transfer, which is greater in high Pr region where the thermal diffusion effect is weakened. In addition, the increase of convective heat transfer near the wall has an important effect on the good efficiency for the laminar flow. The effect of down-flow around VG on η is discussed from the comparison with the numerical results for the channel without the notch hole just under the wing.

Sizing problem for a cross flow heat exchanger with wing-type vortex generator

In the present study, sizing of a single pass cross flow heat exchanger with unmixed fluid streams has been investigated. The heat exchanger is a cross flow heat exchanger. It has overall dimensions of 20 × 20 × 20 cm. Two the most common heat exchanger design problems are the rating and sizing problem. Sizing problems deal with designing an exchanger and determining its physical size to meet the specified heat duty, pressure drops and other considerations. It means the determination of the exchanger construction type, flow arrangement, heat transfer surface geometries and materials, and the physical sizes of an exchanger to meet specified heat transfer and pressure drop. In this study, the physical size (length, width, height, mass flow rates of both fluids and surface areas on each side of the exchanger) are determined. Inputs to the sizing problem are surface geometries, fluid mass flow rates, inlet and outlet fluid temperatures and pressure drop on each side. Dimensions of L a , L b , and L c for the selected surfaces were investigated such that the design meets the heat duty and pressure drops on both sides exactly.

Local Heat Transfer Characteristics in Simulated Electronic Modules

When heat is released by forced convection from electronic modules in a narrow printed circuit board channel, complex flow phenomena—such as stagnation and acceleration on the front surface, separation and reattachment on the top surface, wake or cavity flow near the rear surface—affect the heat transfer characteristics. The purpose of this study is to investigate how these flow conditions influence the local heat transfer from electronic modules. Experiments are performed on a three-dimensional array of hexahedral elements as well as on a two-dimensional array of rectangular elements. Naphthalene sublimation technique is employed to measure three-dimensional local mass transfer, and the mass transfer data are converted to their counterparts of the heat transfer process using the analogy equation between heat and mass transfer. Module location and streamwise module spacing are varied, and the effect of vortex generators on heat transfer enhancement is also examined. Dramatic change of local heat transfer coefficients is found on each surface of the module, and three-dimensional modules have a little higher heat transfer value than two-dimensional modules because of bypass flow. Longitudinal vortices formed by vortex generator enhance the mixing of fluids and thereby heat transfer, and the rectangular wing type vortex generator is found to be more effective than the delta wing type vortex generator.

Heat Transfer Enhancement and Pressure Loss in the Channel with a Vortex Generator

Using the time-space averaged momentum and energy equations obtained in the preceding report, a theoretical relation was derived to estimate the drag increase and the heat-transfer enhancement in the channel with a turbulence promoter. The investigation of the relation and the results of DNS for the channel with a wing-type vortex generator (VG) show that the heat-transfer efficiency η (i. e., the ratio of the heat transfer enhancement to the drag increase from the smooth channel) is larger when VG is installed in the laminar flow than in the turbulent flow from the following reasons. (I) The large pressure drag on VG in the turbulent flow decreases η. (II) The change of velocity distribution from the laminar parabolic one increases the convective heat transfer near the wall. This effect raises η without the penalty of drag increase.

Vortical structure and heat transfer enhancement in the wake behind a wing-type vortex generator in drag-reducing surfactant flow

Vortical structure and heat transfer enhancement in the wake behind a wing-type vortex generator in drag-reducing surfactant flow

Flow visualization of a longitudinal vortex in drag-reducing surfactant flow

Vortical structures behind a wing-type vortex generator (WVG) immersed in a drag-reducing flow were visualized with a fluorescence dye illuminated with a planer laser sheet to investigate the enhancement mechanism of heat transfer on the WVG-installed target wall. Particle image velocimetry (PIV) system was also used to measure the flow velocity profiles. Both the flow visualization and the velocity measurement revealed that small amounts of surfactant, Cetyl-Trimethyl-Ammonium-Chloride/ Sodium Salicylate (CTAC/NaSal), added in water changed drastically the flow patterns together with the wall heat transfer distributions due to the reduction of momentum exchange in the vortical flows behind WVG.

Flow visualization of longitudinal vortices induced by an inclined impinging jet in a crossflow—effective cooling of high temperature gas turbine blades

One of the most fundamental principles to improve the energy conversion efficiency is to raise the working temperature of a gas turbine. In order to realize high temperature gas turbines, development of effective cooling system of turbine blades is indispensable. The attention was paid to the utilization of longitudinal vortices to enhance the heat transfer from the inner surfaces of turbine blades. Effectiveness of longitudinal vortices in enhancing wall heat transfer were already confirmed for the case of a disturbed flat plate boundary layer with the insertion of a wing-type vortex generator (WVG) attached to a large-eddy-break-up (LEBU) plate. Pressure loss due to a form drag of the WVG, however, was not small. Then, longitudinal vortices generated by an inclined jet (VG jet) into crossflow have been examined to apply for effective cooling of gas turbine blades. Flow visualization and heat transfer experiments were conducted for a duct flow including longitudinal vortices without the insertion of any body in addition to a conventional impinging jet with crossflow. It was experimentally demonstrated that jet impingement is effective for heat transfer augmentation even in the case with crossflow, and that the longitudinal vortices have been confirmed to be generated by the insertion of the VG jet. The generated vortices are expected to effectively enhance the heat transfer from the inner surface of the blades of a gas turbine.

Color-based image processing to measure local temperature distributions by wide-band liquid crystal thermography

This study presents a color-image-processing procedure for non-intrusive local temperature measurements by thermochromic liquid crystals (TLCs). The image evaluation software is completely independent of the color detection and acquisition hardware. This allows to use a wide variety of hardware solutions. An easy reproducible calibration of camera and light source is presented. The dependence of the detected hue values on intensity is investigated and further the hueversus temperature relation is studied. Sprayable TLC formulations and TLC-coated polyester sheets are studied and compared with regard to their signal-to-noise ratio and the dependence of their hue values on illumination and viewing angle. Furthermore, a method to investigate the hue resolution is presented. The relation between the resolution of hue values and the illumination intensity and its influence on signal noise is discussed for the first time for TLC applications. Different techniques of signal noise reduction are implemented in the image processing system. Their effects on the signal noise level are discussed. As an example the two dimensional temperature distribution caused by wing-type vortex generators in a channel flow is given.

Vortex Generators for Compact Heat Exchangers

Compact heat exchangers are characterized by high heat duties per unit volume and high heat transfer coefficients. This implies small hydraulic diameters, low Reynolds numbers and fins. Emphasis is placed on wing-type vortex generators (WVG). They can be used as fins or to modify fins and are easily incorporated into heat exchangers. Different WVGs are evaluated experimentally and numerically with regard to heat transfer enhancement and pressure loss. Detailed data are presented for flow structure, local and global heat transfer and pressure losses. The high potential of WVGs for compact heat exchangers is shown. Comparison of WVG-fins with offset-strip fins and louvered fins shows the advantages of WVGs. Examples of fin-tube heat exchanger elements indicate the large saving potential inherent in WVGs. Because of the many geometrical parameters of WVGs, many possibilities for improvements and incorporation into heat exchangers exist. Examples of fin-tube and fin-plate heat exchanger elements with and without WVGs are given.

Comparison of Wing-Type Vortex Generators for Heat Transfer Enhancement in Channel Flows

Longitudinal vortices can be generated in a channel flow by punching or mounting small triangular or rectangular pieces on the channel wall. Depending on their forms, these vortex generators (VG) are called delta wing, rectangular wing, pair of delta winglets, and pair of rectangular winglets. The heat transfer enhancement and the flow losses incurred by these four basic forms of VGs have been measured and compared in the Reynolds number range of 2000 to 9000 and for angles of attack between 30 and 90 deg. Local heat transfer coefficients on the wall have been measured by liquid crystal thermography. Results show that winglets perform better than wings and a pair of delta winglets can enhance heat transfer by 46 percent at Re=2000 to 120 percent at Re=8000 over the heat transfer on a plate.

Wing-type vortex generators for fin-and-tube heat exchangers

The effect of wing-type vortex generators on heat transfer and pressure drop of a fin-and-tube heat exchanger element was investigated. Local heat transfer was measured by liquid crystal thermography on the fin in the Reynolds number range of 600–2700. Flow losses were estimated from the measured pressure drop of an element. Delta winglets were used as vortex generators. Four fin-and-tube configurations were tested, an inline and a staggered arrangement, each with plain fins and with fins with a pair of vortex generators behind each tube. For the inline tube arrangement the vortex generators increase the heat transfer by 55–65% with a corresponding increase of 20–45% in the apparent friction factor. Results indicate that the vortex generators have the potential to reduce considerably the size and mass of heat exchangers for a given heat load.

Heat transfer in a channel with built-in wing-type vortex generators

An extension of earlier work is made in the present paper to determine numerically the structure of flow and heat transfer characteristics in a rectangular channel with a built-in delta wing protruding from the bottom wall. The predictions are made through the numerical solution of complete Navier-Stokes and energy equations. Augmentation of heat transfer between the flowing fluid and channel wall is seen. The effect of a punched hole, beneath the wing-type vortex generator, on the heat transfer and skin friction characteristics has been determined. The influence of the vortex generator's angle of attack and Reynolds number on heat transfer and skin friction is determined. The combined spanwise average Nusselt number showed increases as large as 34% even at the exit of a long channel at an angle of attack of 26°.

Heat transfer enhancement in fin‐plate heat exchangers by wing type vortex generators

AbstractHeat transfer and fluid mechanical data were computed for laminar channel flows containing strong longitudinal vortex pairs. The strong vortices are generated by thin delta wings and delta winglet pairs of low aspect ratios and large angles of attack. These wings are attached to the channel walls. The data show that longitudinal vortices cause high local peaks in heat transfer and marked increases in the overall channel heat transfer. These increases occur over a wide region of channel wall, compared to the vortex generating wing area. The results are of special interest for compact heat exchangers. The heat transfer enhancement allows a considerable reduction in the heat transfer area which, in turn, reduces the manufacturing and operating costs.