Rectangular Winglet Research Articles

Thermo-hydraulic Characterization of the Smooth Wavy Fin-and-elliptical Tube Heat Exchangers Using New Type Vortex Generators

In the present study, 3D computational analysis was performed to investigate heat transfer and pressure drop characteristics of flow in new Smooth Wavy Fin-and-Elliptical Tube (SWFET) heat exchanger model with new vortex generators. Performance results are presented in terms of non-dimensional parameters, friction factor f and Colburn j factor. Four new types of vortex generators were considered; rectangular trapezoidal winglet (RTW), angle rectangular winglet (ARW), curved angle rectangular winglet (CARW) and Wheeler wishbone (WW). Fluid flow and heat transfer are simulated and the results are compared. The SST k–ω turbulence model is used, with steady-state solvers to calculate pressure drop, flow and temperature fields. The influences of the geometrical factors of mounted vortex generators including attack angles of the winglets (αVG = 15°, 30°, 45°, 60° and 75̊) and width/length aspect ratio (w/l = 0.5,1.0) of the Wheeler wishbones in enhancing the heat transfer performance of a smooth wavy fin heat exchanger with a three-row staggered elliptical tube bundle are investigated. The Reynolds number ranges from 500 to 3000 based on the hydraulic diameter. 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 of the SWFET heat exchanger with winglet VGs in the larger attack angle, was obtained at RTW VGs arrangement. For the SWFET heat exchangers, the WW VGs with width/length aspect ratio of w/l = 0.5 provide the best heat transfer performance.

Effect of Pitch to Height Ratio on Flow Visualization, Heat Transfer, and Thermal Performance in a Round Tube with Upstream RWVG

Fully developed periodic laminar flow and heat transfer in an isothermal wall tube with 45° upstream rectangular winglet vortex generators (RWVG) with closed end are investigated numerically. The fluid flow and heat transfer characteristics are proposed for Reynolds numbers based on the diameter of the tube, Re = 100 to 2000. The RWVGs with an attack angle of 45° are mounted with in-line arrangement on both sides of a plate and the closed tip pointing upstream is inserted in the middle of the tested tube to produce longitudinal vortex flows through the tested section. Effects of different blockage ratios (b/D, BR) and pitch spacing ratios (P/D, PR) on heat transfer, pressure loss, and the thermal enhancement factor (TEF) in the round tube are studied. The results show that the longitudinal vortex flows can induce impinging flows on a tube wall leading to an extreme increase in heat transfer rate over the round tube for all cases. Additionally, the rise in the BR and the reduction of PR result in the increase of both the Nusselt number and friction factor values. The optimum TEF in the range studied is around 2.9 at BR = 0.15, PR = 1, and Re = 2000.

Fluid mixing in a microchannel with longitudinal vortex generators

A heat transfer enhancement technique based on longitudinal vortex generators (LVGs) has been well established for large-scale heat exchangers. Motivated by the success of the LVGs, this paper is intended as an investigation of micromixers based on the T-shaped channel with rectangular winglet pairs (RWPs) mounted on the bottom of the main channel. The RWPs stay with an angle of attack to the main flow direction and generate longitudinal vortices to enhance fluid mixing. The effects of geometrical parameters on the performance of micromixers with micro-scale LVGs are investigated by numerical simulations and the Taguchi method. The validity of numerical simulations is examined by comparing the numerical and experimental results. The results obtained for a wide range of Reynolds numbers show that the mixing efficiency of the micromixer with divergent RWPs is greater than that of the micromixer without RWPs for convection-dominant cases as well as diffusion-dominant cases. A static Taguchi analysis shows that the relative effectiveness of the geometrical parameters can be ranked as: asymmetry index>angle of attack>winglet height>winglet spacing. Based on the relative influence of the geometric parameters, we can obtain an optimal parameter group on the parameter selected range.

Numerical simulation of flow and heat transfer characteristics in wavy fin-and-tube heat exchanger with combined longitudinal vortex generators

The air-side heat transfer and fluid flow characteristics of wavy fin-and-tube heat exchanger punched with combined rectangular winglet pairs (CRWPs) were numerically analyzed. The influences of several main parameters of the CRWP on heat transfer and friction were examined and compared to rectangular winglet pairs (RWP). The numerical results showed that the wavy fin-and-tube heat exchanger has a better heat transfer performance when the winglets punched on the suction side of the wavy fin. For the wavy fin punched with CRWPs, the Nusselt number and friction factor increase with increases of secondary attack angle, accessory winglet length or accessory winglet width. In comparison with RWP, the vortices generated by CRWP are more, larger and stronger. Hence, CRWP can more effectively improve heat transfer and increase friction.

Numerical investigation of turbulent flow and heat transfer in a channel with novel longitudinal vortex generators

A novel combined longitudinal vortex generator (LVG), comprising a rectangular wing mounted with an accessory rectangular wing, is developed and the turbulent flow and heat transfer characteristics are numerically analyzed. The influences of six main parameters of the combined rectangular winglet pair (CRWP) on heat transfer enhancement and fluid flow resistance characteristics in a rectangular channel are examined. The parameters include the location of accessory wing on the main wing and geometric sizes of the accessory wing. The Reynolds number range is from 2000 to 16,000. The numerical results show that in the range of the present study, the increase of the six parameters can result in the increase of heat transfer and pressure drop. Specially, the pressure drop decreases at large value of the distance of accessory wing from the channel bottom. In comparison with RWP, the CRWP generates vortices with larger area and lower core. Furthermore, the accessory wings generate vortices that swirl downward the channel bottom and disturb the boundary layer growth more effectively. Hence the heat transfer is enhanced. The numerical result for the Nusselt number of the channel agrees well with the experimental result, indicating the reliability of the present numerical predictions.

Numerical study of heat transfer enhancement and fluid flow with inline common-flow-down vortex generators in a plate-fin heat exchanger

Three-dimensional numerical simulations are performed on a plate-fin heat exchanger (with triangular fins as inserts between the plates) to evaluate the laminar heat transfer and fluid flow characteristics with longitudinal vortex generators (LVGs). The effect with an inline rectangular winglet pair (RWP) with a common-flow-down (CFD) configuration is studied. The numerical results indicate that the application of inline LVGs effectively enhances the heat transfer of the channel. The heat transfer further increases with the increase in the Reynolds number from 200 to 500 and angle of attack from β = 15° to 22.5°. The computations are also performed to find the best location for the second RWP. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.20414

Analysis of heat transfer and pressure drop for fin-and-tube heat exchangers with rectangular winglet-type vortex generators

In present work, heat transfer enhancement and pressure loss penalty for fin-and-tube heat exchangers with rectangular winglet pairs (RWPs) were numerically investigated in a relatively low Reynolds number flow. The purpose of this study was to explore the fundamental mechanism between the local flow structure and the heat transfer augmentation. The RWPs were placed with a special orientation for the purpose of enhancement of heat transfer. The numerical study involved three-dimensional flow and conjugate heat transfer in the computational domain, which was set up to model the entire flow channel in the air flow direction. The effects of attack angle of RWPs, row-number of RWPs and placement of RWPs on the heat transfer characteristics and flow structure were examined in detail. It was observed that the longitudinal vortices caused by RWPs and the impingement of RWPs-directed flow on the downstream tube were important reasons of heat transfer enhancement for fin-and-tube heat exchangers with RWPs. It was interesting to find that the pressure loss penalty of the fin-and-tube heat exchangers with RWPs can be reduced by altering the placement of the same number of RWPs from inline array to staggered array without reducing the heat transfer enhancement. The results showed that the rectangular winglet pairs (RWPs) can significantly improve the heat transfer performance of the fin-and-tube heat exchangers with a moderate pressure loss penalty.

Augmentation of Heat Transfer by Creation of Streamwise Longitudinal Vortices Using Vortex Generators

This paper summarizes the current state of the art related to improvement of the heat exchanger surfaces using streamwise longitudinal vortices. Primarily, the improvements related to fin-tube cross-flow heat exchangers and the plate-fin heat exchangers have been addressed. Protrusions in certain forms, such as delta wings or winglet pairs, act as vortex generators, which can enhance the rate of heat transfer from the heat-exchanger surfaces that may be flat or louvered. The strategically placed vortex generators create longitudinal vortices, which disrupt the growth of the thermal boundary layer, promote mixing between fluid layers, and hence lead to augmentation in heat transfer. The flow fields are dominated by swirling motion associated with modest pressure penalty. Heat transfer is augmented substantially for all the proposed configurations of the longitudinal vortex generators, such as delta wings, rectangular winglet pairs, and delta winglet pairs, with varying degree of pressure penalty. Both computational and experimental investigations on flow and heat transfer in the heat exchanger passages with built-in vortex generators are revisited and summarized.

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.

Numerical Simulation of Performance Augmentation in a Plate Fin Heat Exchanger Using Winglet Type Vortex Generators

A detailed evaluation of the performance parameters in the laminar flow regime with regard to the enhancement of heat transfer using winglet type vortex generators has been accomplished in this study. Three dimensional numerical studies of flow structure and laminar convectionheat transfer are performed in a plate fin heat exchanger with longitudinal vortex generators (LVGs) in present paper. The Effects of common flow up and common flow down pairs of vortices produced by LVGs with two different shapes of the winglets, a pair of rectangular winglet (RWP) and a pair of delta winglet (DWP), are studied at various Reynolds numbers. The results show that effect of LVGs could effectively enhance the heat transfer of the heat exchanger. According to the non-dimensional defined parameter for evaluation of performance, (Num/Num,0)/(f/f0), the channel with DWP shows better overall performance than RWP. The common flow down configuration of DWP shows a better overall performance at Reynolds numbers lower than 720 and common flow up configuration of DWP shows a better overall performance at Reynolds numbers more than 720; also, the common flow down configuration shows a better overall performance than the common flow up configuration for RWP.

Numerical Simulation of Flow and Heat Transfer Characteristics in Rectangular Channel with Novel Longitudinal Vortex Generators

A novel combined longitudinal vortex generator, comprising a rectangular wing mounted with an accessory rectangular wing, was introduced and the turbulent flow and heat transfer characteristics of a rectangular channel with rectangular winglet pair and combined winglet pair were numerically analyzed. The effects of six parameters were examined. The results show that in the range of the present study, the increase of the six parameters can result in the increase of heat transfer and pressure drop. Specially, the pressure drop decrease at large value of the distance of accessory wing from the channel bottom. The effect of the main attack angle of the combined winglet pair is somewhat different to that of the rectangular winglet pair. The heating plate temperature of the channel with combined winglet pair is lower than that of the channel with rectangular winglet pair, and hence the heat transfer is enhanced.

Numerical Simulation of Flow and Heat Transfer Characteristics in Rectangular Channel with Novel Longitudinal Vortex Generators

A novel combined longitudinal vortex generator, comprising a rectangular wing mounted with an accessory rectangular wing, was introduced and the turbulent flow and heat transfer characteristics of a rectangular channel with rectangular winglet pair and combined winglet pair were numerically analyzed. The effects of six parameters were examined. The results show that in the range of the present study, the increase of the six parameters can result in the increase of heat transfer and pressure drop. Specially, the pressure drop decrease at large value of the distance of accessory wing from the channel bottom. The effect of the main attack angle of the combined winglet pair is somewhat different to that of the rectangular winglet pair. The heating plate temperature of the channel with combined winglet pair is lower than that of the channel with rectangular winglet pair, and hence the heat transfer is enhanced.

Experimental investigations of thermal and flow characteristics of curved trapezoidal winglet type vortex generators

The performance of a pair of new vortex generators – curved trapezoidal winglet (CTW) has been experimentally investigated and compared with traditional vortex generators – rectangular winglet, trapezoidal winglet and delta winglet using dimensionless factors – j / j 0 , f / f 0 and R = ( j / j 0 )/( f / f 0 ). The results showed that delta winglet pair is the best in laminar and transitional flow region, while curved trapezoidal winglet pair (CTWP) has the best thermohydraulic performance in fully turbulent region due to the streamlined configuration and then the low pressure drop, which indicates the advantages of using this kind of vortex generators for heat transfer enhancement. Parametric study on CTWP showed that smaller attack angle ( β = 0° = and 15°), larger curvature ( b / a = 1/2) and larger angle of inclination ( α = 20°) gives better thermohydraulic performance under the present conditions. An appropriate spacing between the leading edges of a pair of CTW VG should be considered for different flow regions. In addition, double rows of CTWP do not show better thermohydraulic performance due to the larger pressure drop and the spacing between the two rows of CTWP should also be optimized. ► New VG-curved trapezoidal winglet has high thermohydraulic performance particularly for turbulent region. ► Curved trapezoidal winglet has low flow resistance due to the streamlined configuration. ► For present conditions, smaller attack angle, larger curvature and angle of inclination give better performance. ► Appropriate spacing between the leading edges of the new VG pair is important for overall performance.

Numerical study on a slit fin-and-tube heat exchanger with longitudinal vortex generators

A 3-D numerical simulation is performed on laminar heat transfer and flow characteristics of a slit fin-and-tube heat exchanger with longitudinal vortex generators. Heat transfer enhancement of the novel slit fin mechanism is investigated by examining the effect of the strips and the longitudinal vortices. The structure of the slit fin is optimized and analyzed with field synergy principle. The result coincides with the guideline ‘front coarse and rear dense’. The heat transfer and fluid flow characteristics of the slit fin-and-tube heat exchanger with longitudinal vortex generators are compared with that of the heat exchanger with X-shape arrangement slit fin and heat exchanger with rectangular winglet longitudinal vortex generators. It is found that the Colburn j-factor and friction factor f of the novel heat exchanger with the novel slit fin is in between them under the same Reynolds number, and the factor j/( f 1/3) of the novel heat exchanger increased by 15.8% and 4.2%, respectively.

Numerical Investigation of Flow and Heat Transfer over a flat plate using Curved Rectangular Winglet Vortex Generators

Numerical Investigation of Flow and Heat Transfer over a flat plate using Curved Rectangular Winglet Vortex Generators

Heat transfer augmentation in a plate-fin heat exchanger using a rectangular winglet

RCAM Labs, SMU, Dallas, U.S.AThis study presents numerical computation results on laminar convection heattransfer in a plate-fin heat exchanger, with triangular fins between the plates of aplate-fin heat exchanger. The rectangular winglet type vortex generator is mounted onthese triangular fins. The performance of the vortex generator is evaluated for varyingangles of attack of the winglet i.e., 20, 26, and 37° and Reynolds number 100, 150,and 200. The computations are also performed by varying the geometrical size andlocation of the winglet. The complete Navier–Stokes equation and the energy equationare solved by the (Marker and Cell) MAC algorithm using the staggered grid arrange-ment. The constant wall temperature thermal boundary conditions are considered. Airis taken as the working fluid. The heat transfer enhancement is seen by introducingthe vortex generator. Numerical results show that the average Nusselt number in-creases with an increase in the angle of attack and Reynolds number. For the samearea of the LVG, the increase in length of the LVG brings more heat transferenhancement than increasing the height. The increase in heat transfer comes with amoderate pressure drop penalty. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res,39(8), 590–610, 2010; Published online 20 September 2010 in Wiley Online Library(wileyonlinelibrary.com). DOI 10.1002/htj.20318

Three-Dimensional Numerical Study of Flow and Heat Transfer Enhancement Using Vortex Generators in Fin-and-Tube Heat Exchangers

In this paper, a three-dimensional numerical investigation was performed for heat transfer characteristics and flow structure of full scale fin-and-tube heat exchangers with rectangular winglet pair (RWP). For the Reynolds number ranging from 500 to 880, the baseline configuration (without RWP) is compared with three enhanced configurations (with RWP): inline-1RWP case, inline-3RWP case, and inline-7RWP case. It was found that the air-side heat transfer coefficient improved by 28.1–43.9%, 71.3–87.6%, and 98.9–131% for the three enhanced configurations, with an associated pressure drop penalty increase of 11.3–25.1%, 54.4–72%, and 88.8–121.4%, respectively. An overall performance comparison was conducted by using the London area goodness factor. It is revealed that among the three enhanced configurations, the inline-1RWP case obtains the best overall performance, and the inline-3RWP case is better than the inline-7RWP case. The numerical results were also analyzed on the basis of the field synergy principle to provide fundamental understanding of the relation between local flow structure and heat transfer augmentation. It was confirmed that the reduction in the average intersection angle between the velocity vector and the temperature gradient was one of the essential factors influencing heat transfer enhancement. The analysis also provides guidelines for where the enhancement technique is highly needed.

A numerical study of the effect on flow structure and heat transfer of a rectangular winglet pair in a plate fin heat exchanger

Longitudinal vortices have a great capability of disrupting the growth of boundary layers and bring about the heat transfer enhancement between the fluid and its neighbouring surface. The potential of a winglet pair type vortex generator for the heat transfer enhancement in a plate fin heat exchanger, with triangular fins as inserts, is numerically evaluated in this article. The rectangular winglet pair is mounted on the triangular fins. The numerical computations are performed by solving an unsteady, three-dimensional Navier—Stokes equation, and an energy equation by using the modified MAC method. Air is taken as the working fluid. This study shows the flow structure and the performance of the winglet pair in improving the heat transfer. The computations are performed at Re=200 and placing the winglet at an angle of attack, β=20°. The results show that the heat transfer is increased by 13 per cent, even at the exit, with the winglet pair. The heat transfer enhancement with a winglet pair for different Re=200—500 and Pr=0.71 and for varying heights of the winglet pair is also predicted.

Numerical study of fluid flow and heat transfer in a flat-plate channel with longitudinal vortex generators by applying field synergy principle analysis

Three dimensional numerical simulations are performed on laminar heat transfer and fluid flow characteristics of a flat-plate channel with longitudinal vortex generators (LVGs). The effects of two different shaped LVGs, rectangular winglet pair (RWP) and delta winglet pair (DWP) with two different configurations, common-flow-down (CFD) and common-flow-up (CFU), are studied. The numerical results indicate that the application of LVGs effectively enhances heat transfer of the channel. According to the performance evaluation parameter, ( Nu/ Nu 0)/( f/ f 0), the channel with DWP has better overall performance than RWP; the CFD and CFU configurations of DWP have almost the same overall performance; the CFD configuration has a better overall performance than the CFU configuration for RWP. The basic mechanism of heat transfer enhancement by LVGs can be well described by the field synergy principle.

EFFECT OF VORTEX GENERATORS ON A FRICTION FACTOR IN AN EQUILATERAL TRIANGULAR DUCT

The main objective of this study is to determine the effect of vortex generators on a friction factor for fully developed flow of a fluid such as air. Longitudinal vortices can be generated in a channel flow by punching or mounting protrusions in the channel wall. Such vortex generators (VGs) can be classified into delta wing, rectangular wing, pair of delta-winglet and pair of rectangular winglet. These longitudinal vortices disrupt the growth of the boundary layer and lead to enhance the heat transfer rate between the working fluid and the conductor channel wall, but this enhancement is associated with increasing in a pressure gradient along the axial length of the channel. So, the friction factor for fully developed air flow in an equilateral triangular duct is investigated experimentally with Reynolds number ranging from (31,000) to (53,000) and the size of the generators was kept constant for three cases which are single, double, and triple pairs of delta–winglet type of vortex generators embedded in the turbulent boundary layer for attack angle of generator of (30, 40, and 50 ) degree. The results show that the friction factor increases by about (43.5 %) when the angle of attack is varied from (30 deg) to (50 deg) for the triple pairs case compared with the base case (without VG).