Heat Transfer Enhancement With Vortex Generators

2019 ◽  
Author(s):  
Md. Islam ◽  
L. Guangda ◽  
S. Ainane ◽  
S. Bojanampati
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Constant Heat Flux ◽  
Vortex Generators ◽  
Cfd Simulations ◽  
Circular Pattern ◽  
Delta Winglet

Abstract In this research, heat transfer and pressure drop from a tube with vortex generators (VGs) insert are numerically investigated. The effects of heights, attack angles of VGs inside a tube on heat transfer and flow behavior are investigated. CFD simulations, with and without VGs insert, are done for an air flow range (Reynolds numbers 6000 to 33000) and for a constant heat flux on the tube model surface. Four VGs are fitted in a circular pattern on the inner surface of the tube. We studied the characteristics of the delta winglet VGs for different attack angles and blockage ratios. The Nusselt number and friction factor results show the influence of the VGs insert on heat transfer and frictional factor. The maximum Nusselt number increment (Nu/Nu0) was achieved to be 1.75 while the maximum friction factor increment (f/f0) was 3.21. In order to understand the flow behavior and different vortices, path lines released by the VGs surface and details of the vortices are also studied.

Fluid Flow and Heat Transfer Behavior for Turbulent Flows in a Tube With Vortex Generator Pairs for an Efficient Heat Exchanger

2018 ◽  
Author(s):  
Md. Islam ◽  
Z. Chong ◽  
S. Bojanampati
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Turbulent Flows ◽  
Flow Behavior ◽  
Vortex Generator ◽  
Tube Diameter ◽  
Vortex Generators ◽  
Blockage Ratio ◽  
Delta Winglet

Various technologies have been developed to enhance flow mixing and heat transfer in order to develop an efficient compact heat exchanging devices. Vortex generators/turbulent promoters generate the vortices which reduce the boundary layer thickness and introduce the better mixing of the fluid to enhance the heat transfer. In this research experimental investigations have been carried out to study the effect of delta winglet vortex generator pairs on heat transfer and flow behavior. To generate longitudinal vortex flow, two pairs of the delta winglet vortex generators (DWVG) with the length of 10mm and winglet-pitch to tube-diameter ratio (PR = 4.8) are mounted on the inner wall of a circular tube. The DWVG pairs with two different winglet-height to tube-diameter ratios (Blockage ratio, BR = 0.1 and 0.2), three attack angles (α = 10°, 20°, 30°) and three spacings between leading edges (S = 10, 15 and 20mm) are studied. The experiments were conducted with DWVGs pairs for the air flow range of Reynolds numbers 5000–25000. The influence of the DWVGs on heat transfer and pressure drop was investigated in terms of the Nusselt number and friction factor. The experimental results indicate that DWVG pair in a tube results in a considerable enhancement in Nusselt number (Nu) with some pressure penalty. It is found that DWVG increases Nu up to 85% over the smooth tube. It is also observed that Nusselt number increases with Re, blockage ratio and attack angle. Friction factor decreases with Re but increases with blockage ratio, spacing and attack angle. And 30° DWVG pair with S = 20mm, BR = 0.2 gets the highest friction factor. The Highest thermal performance enhancement (TPE) was noticed for α = 10°, S = 20mm, BR = 0.2 for turbulent flows. To obtain qualitative information on the flow behavior and vortex structures, flow was visualized by laser sheet using smoke as a tracer supplied at the entrance of the test section. The generation and development of longitudinal vortices influenced by DWVG pairs were clearly observed.

Delta Winglet Pairs in the Core of a Pipe and its Effect on Heat Transfer and Flow

2019 ◽  
Author(s):  
Md. Islam ◽  
Z. Chong ◽  
Md. Alam
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Friction Factor ◽  
Flow Behavior ◽  
Experimental Results ◽  
Vortex Generators ◽  
Experimental Investigations ◽  
Longitudinal Vortices ◽  
The Core ◽  
Delta Winglet

Abstract Vortex generators/turbulent promoters generate the longitudinal vortices which introduce the better mixing of the fluid with fluid circulation and enhance heat transfer. In this research, experimental investigations have been carried out to study the effect of delta winglet vortex generator (DWVG) in the core of the pipe on heat transfer and flow behavior. In this experiment, two pairs of delta winglet vortex generators (DWVG) were printed on the upside and downside of the thin plate using 3D printing technology in a ring and then placed in the core of the pipe to generate longitudinal vortices. Middle plate was very thin. The effect of heights (H = 5mm, 10mm, 15mm and 20mm) of DWVG for 10° angle of attack and 15mm spacing between leading edges of VG pairs on heat transfer and pressure drop was studied. The experiments were conducted for a fully developed turbulent flow of air in the range of Reynolds numbers (Re) 5000–25000. The influence of the DWVGs on heat transfer and pressure drop was investigated in terms of the Nusselt number (Nu) and friction factor (f). The experimental results indicate that DWVG in the core of the tube results in a considerable increase in Nu with some pressure penalty. It is found that DWVG increase Nu considerably only when H is over 10mm. Nu increases with Re and H. Friction factor decreases with Re but increase with H. The thermal performance enhancement (TPE) was noticed decreasing with Re. TPE could be obtain up to 1 only when the height is over 10mm for Re ≤ 7500. The experimental results show that the DWVG in the core of the pipe is not a good option to enhance the heat transfer at a higher Re.

scholarly journals Efek vortex generators terhadap peningkatan perpindahan panas pada aliran melewati heated tubes

2020 ◽  
Vol 9 (2) ◽  
Author(s):  
Yafid Effendi ◽  
Ali Rosyidin
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Rectangular Channel ◽  
Evaluation Criteria ◽  
Vortex Generators ◽  
High Thermal Resistance ◽  
Flow Pressure ◽  
Delta Winglet

In this decade, improving the rate of heat transfer has become a big challenge. The high thermal resistance of the gas side of the heat exchanger has an impact on the low rate of heat transfer. Therefore, an experimental study was carried out aimed at looking at conditions of hot temperature and decreased air flow pressure through a heated tube in a rectangular channel using artificial surfaces, namely the concave delta winglet and delta winglet vortex generators. Concave delta winglet vortex generators (CDW VGs) are installed in-line and staggered with one, and two pairs are arranged in common-flow-down (CFD) in the direction of flow with an angle of attack of 15o. The experimental results show that the best thermal performance is observed in the use of two rows CDW VGs staggered, where the value of performance evaluation criteria (PEC) is 28.88% higher than the use of CDW VGs in-line, DW VGs staggered and DW VGs in-line at the same Reynolds number. At the same Reynolds number, the Nusselt number ratio and the friction factor ratio increased 45.25% and 152.05% respectively, occurring in two rows of CDW VGs staggered compared to other vortex generators.Keywords: vortex generators, heat transfer, Nusselt number, friction factor, PEC

scholarly journals Investigating the impacts of included angles on flow and heat transfer in cross-corrugated triangular ducts with field synergy principle

2013 ◽  
Vol 17 (3) ◽  
pp. 823-832 ◽  
Author(s):  
Zuoyi Chen ◽  
Lizhi Zhang ◽  
Han Song
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Field Synergy ◽  
Field Synergy Principle ◽  
Included Angle ◽  
Flow And Heat Transfer ◽  
Performance Evaluation Criterion ◽  
Vital Effect

Included angles (?) have vital effect on the flow and heat transfer in cross-corrugated triangular ducts. The friction factor and Nusselt number were estimated at different Reynolds numbers from both experiments and simulations. Results show that the flow in the duck with ?=90 has the largest friction factor and Nusselt number. However, the included angle influences the flow and heat transfer in cross-corrugated triangular ducts in different ways. The field synergy principle was used to explore the mechanism of the different impacts of the included angle. Results show that the flow in the cross-corrugated triangular duct with ?=90o has the smallest domain averaged included angle (?m), which implies the best synergy performance. The results of the field synergy principle were also validated by analyzing the performance evaluation criterion and studying the velocity vector and temperature distributions.

Numerical Analysis of Laminar Forced Convection in Sinusoidal-Wavy-, Rounded-Ellipse-, and Rounded-Vee-Shaped Corrugated-Plate Channels

2010 ◽  
Author(s):  
Dean Ferley ◽  
Scott J. Ormiston
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Numerical Analysis ◽  
Prandtl Number ◽  
Friction Factor ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Ansys Cfx ◽  
Prandtl Numbers ◽  
Laminar Forced Convection

Numerical analysis of steady, two-dimensional, laminar forced convection in corrugated-plate channels is performed using a commercial CFD code: ANSYS CFX. The flow domain consists of six modules in each of three wall corrugations: sinusoidal-wavy-shaped (SWS), rounded-ellipse-shaped (RES), and rounded-vee-shaped (RVS). One ratio of minimum-to-maximum plate spacings and one module length-to-height ratio is considered. Fluid flow and heat transfer are repeating in the modules and the results are examined in a typical module in the fully-developed region for Reynolds numbers in the range of 25 to 300 for Prandtl numbers of 0.7 (air), 2.29 (water), and 34.6 (ethylene glycol). The RES corrugation produced the highest peak value of local Nusselt number as well as the highest friction factor. The SWS corrugation produced the highest average Nusselt number, except at a Prandtl number of 34.6 at higher Reynolds number where the RES corrugation had the highest value. The RVS corrugation had the lowest friction factor for the geometric configuration considered. The highest heat transfer rate per unit pumping power was found at the highest Prandtl number for the RES corrugation.

scholarly journals Experimental investigation of the effect of wave turbulators on heat transfer in pipes

2021 ◽  
pp. 183-183
Author(s):  
Sendogan Karagoz ◽  
Semih Erzincanli ◽  
Orhan Yildirim ◽  
Ilker Firat ◽  
Mehmet Kaya ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Enhancement Factor ◽  
Single Phase ◽  
Reynolds Numbers ◽  
Nusselt Numbers ◽  
Thermal Enhancement ◽  
Enhancement Factors ◽  
Thermal Enhancement Factor

This experimental study deals with the heat transfer and friction effects of sinusoidal part turbulators for single-phase flows occurring in a circular shaped pipe. Turbulators with three different radius values are placed in the pipe to make the flow turbulent. In this way, changes in Nusselt number and friction coefficient are examined. As a result of the experiments made with Reynolds numbers in the range of 6614-20710, the increase rates of the Nusselt numbers of turbulators with 20 mm, 110 mm and 220 mm radius compared to the empty pipe were obtained as 153.49%, 85.36%, and 52.09%, respectively. As a result of the decrease in the radius, there was an increase in the Nusselt number and the friction factor. Parallel to the Nusselt number, the highest friction factor was obtained in the smallest radius turbulator. It was found that the thermal enhancement factors of 110 mm and 220 mm radius turbulators increased by 179.54% and 132.95%, respectively, compared to the 20 mm radius turbulator. Similarly, it was determined that the thermal enhancement factor of the 110 mm radius turbulator increased by 20% compared to the 220 mm radius turbulator.

Heat Transfer and Flow Structure in a Latticework Duct With Different Sidewalls

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Wei Du ◽  
Lei Luo ◽  
Songtao Wang ◽  
Jian Liu ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Flow Structure ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Pressure Side ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Abstract Heat transfer characteristics in a latticework duct with various sidewalls are numerically investigated. The crossing angle is 90 deg and the number of subchannels is eleven on both the pressure side and suction side for each latticework duct. The thickness of the ribs is 8 mm and the distance between adjacent ribs is 24 mm. The investigation is conducted for various Reynolds numbers (11,000 to 55,000) and six different sidewalls. Flow structure, pressure drop, and heat transfer characteristics are analyzed. Results revealed that the sidewall has significant effects on heat transfer and flow structure. The triangle-shaped sidewall provides the highest Nusselt number accompanied by the highest friction factor. The sidewall with a slot shows the lowest friction factor and Nusselt number. An increased slot width decreased the Nusselt number and friction factor simultaneously.

Numerical Study of Flow and Heat Transfer in Rectangular Channel With Periodic Longitudinal Vortex Generators Under Pulsating Flow

2012 ◽  
Author(s):  
Lin Tian ◽  
Wei Bai ◽  
Shanhu Xue ◽  
Zipeng Huang ◽  
Qiuwang Wang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Small Scale ◽  
Inlet Velocity ◽  
Flow And Heat Transfer

The unsteady turbulent flow and heat transfer in rectangular channel with periodic longitudinal vortex generators on up and bottom walls are investigated by standardized k-ε two equation turbulent model combined with standardized wall function which has been validated by steady experimental data. Influence of varying frequency and amplitude of inlet velocity varying by sine function on heat transfer and friction factor are discussed. It is found that parameters such as Tout, Tf, Tw, Nusselt number and the friction factor f vary with time periodically, phase difference occurred compared with inlet velocity. Pulsating frequency has little impact on time averaged Nusselt number. However, when amplitude increases from 0.2us to 0.8us, the heat transfer rate is augmented by about 4%. Furthermore, a critical frequency has been captured when amplitude equals to 0.8us for the channel studied. The current study will deepen understanding of unsteady flow in plate fuel assembly, which can be used in small-scale reactors.

Numerical Study of Flow and Heat Transfer Enhancement by Using Delta Winglets in a Triangular Wavy Fin-and-Tube Heat Exchanger

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Liting Tian ◽  
Yaling He ◽  
Pan Chu ◽  
Wenquan Tao
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Heat Exchanger ◽  
Friction Factor ◽  
Numerical Study ◽  
Attack Angle ◽  
Geometrical Parameters ◽  
Tube Heat Exchanger ◽  
Delta Winglet

In this paper, three-dimensional numerical simulations with renormalization-group (RNG) k-ε model are performed for the air-side heat transfer and fluid flow characteristics of wavy fin-and-tube heat exchanger with delta winglet vortex generators. The Reynolds number based on the tube outside diameter varies from 500 to 5000. The effects of different geometrical parameters with varying attack angle of delta winglet (β=30 deg, β=45 deg, and β=60 deg), tube row number (2–4), and wavy angle of the fin (θ=0–20 deg) are examined. The numerical results show that each delta winglet generates a downstream main vortex and a corner vortex. The longitudinal vortices are disrupted by the downstream wavy trough and only propagate a short distance along the main flow direction but the vortices greatly enhance the heat transfer in the wake region behind the tube. Nusselt number and friction factor both increase with the increase in the attack angle β, and the case of β=30 deg has the maximum value of j/f. The effects of the tube row number on Nusselt number and friction factor are very small, and the heat transfer and fluid flow become fully developed very quickly. The case of θ=5 deg has the minimum value of Nusselt number, while friction factor always increases with the increase in wavy angle. The application of delta winglet enhances the heat transfer performance of the wavy fin-and-tube heat exchanger with modest pressure drop penalty.

scholarly journals Numerical Investigation of Heat Transfer Enhancement in a Rectangular Heated Pipe for Turbulent Nanofluid

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Hooman Yarmand ◽  
Samira Gharehkhani ◽  
Salim Newaz Kazi ◽  
Emad Sadeghinezhad ◽  
Mohammad Reza Safaei
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Volume Fraction ◽  
Rectangular Channel ◽  
Thermal Characteristics ◽  
Reynolds Numbers ◽  
Constant Heat Flux ◽  
Energy Equations ◽  
Volume Method ◽  
Good Agreement

Thermal characteristics of turbulent nanofluid flow in a rectangular pipe have been investigated numerically. The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The symmetrical rectangular channel is heated at the top and bottom at a constant heat flux while the sides walls are insulated. Four different types of nanoparticles Al2O3, ZnO, CuO, and SiO2at different volume fractions of nanofluids in the range of 1% to 5% are considered in the present investigation. In this paper, effect of different Reynolds numbers in the range of 5000 < Re < 25000 on heat transfer characteristics of nanofluids flowing through the channel is investigated. The numerical results indicate that SiO2-water has the highest Nusselt number compared to other nanofluids while it has the lowest heat transfer coefficient due to low thermal conductivity. The Nusselt number increases with the increase of the Reynolds number and the volume fraction of nanoparticles. The results of simulation show a good agreement with the existing experimental correlations.

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