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

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Hamdi E. Ahmed ◽  
M. Z. Yusoff
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Volume Fraction ◽  
Vortex Generator ◽  
Attack Angle ◽  
Vortex Generators ◽  
Triangular Channel ◽  
Delta Winglet ◽  
The Heat Transfer Coefficient

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.

Numerical Simulation of a Canadian Well With Several Circumferential Rows of Internal Vortex Generators

2021 ◽  
Author(s):  
Nabil Kharoua ◽  
Hamza Semmari ◽  
Houssem Korichi ◽  
Mehdi Haroun
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Residential Buildings ◽  
Vortex Generators ◽  
Ambient Conditions ◽  
Operational Conditions ◽  
Positive Effects ◽  
The Heat Transfer Coefficient

Abstract Canadian Wells exploit the quasi-stable underground temperature throughout the year for cooling and heating applications. This type of heat exchangers is used in residential buildings, agriculture and industry. Implementing Vortex Generators (VGs) is intended to disturb the thermal and dynamic boundary layers developing in the near-wall regions leading to the increase of the heat transfer coefficient. The present work investigates the positive effects of a sequence of several rows of VGs. The commercial code ANSYS FLUENT was used to perform numerical simulations mimicking the variation of the seasonal operational conditions occurring within one year. The ambient conditions were considered for the city of Constantine located in the east of Algeria at an altitude of 600m over the sea level. Sinusoidal functions of time and depth, were used for the yearly variations of the ground and air temperatures. Parallelepiped VGs were considered in this study. The Reynolds number was in the range Re = 14975–42789. The results illustrated a contrasting effect of the Reynolds number on the heat transfer coefficient and the temperature difference between the inlet and outlet of the Canadian Well. In terms of number of VGs rows, the beneficial heat transfer effects were observed till the fifth row only.

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

2019 ◽  
Vol 130 ◽  
pp. 01027
Author(s):  
Stefan Mardikus ◽  
Petrus Setyo Prabowo ◽  
Vinsensius Tiara Putra ◽  
Made Wicaksana Ekaputra ◽  
Juris Burlakovs
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Pair Type ◽  
Tube Heat Exchanger ◽  
Performance Of Heat Transfer ◽  
Delta Winglet ◽  
The Heat Transfer Coefficient

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.

scholarly journals Heat Transfer Enhancement of Plate-Fin Heat Sinks with Different Types of Winglet Vortex Generators

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5219
Author(s):  
Jin-Cherng Shyu ◽  
Jhao-Siang Jheng
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Heat Sinks ◽  
Vortex Generators ◽  
Airflow Velocity ◽  
Delta Winglet ◽  
The Heat Transfer Coefficient

Because the delta winglet in common-flow-down configuration has been recognized as an excellent type of vortex generators (VGs), this study aims to experimentally and numerically investigate the thermo-hydraulic performance of four different forms of winglet VGs featuring sweptback delta winglets in the channel flow in the range 200 < Re < 1000. Both Nusselt number and friction factor of plate-fin heat sinks having different forms of winglets, including delta winglet pair (DWP), rectangular winglet pair (RWP), swept delta winglet pair (SDWP), and swept trapezoid winglet pair (STWP), were measured in a standard wind tunnel without bypass in this study. Four rows of winglets with in-line arrangement were punched on each 10-mm-long, 0.2-mm-thick copper plate, and a total of 16 pieces of copper plates with spacing of 2 mm were fastened together to achieve the heat sink. The projected area, longitudinal and winglet tip spacing, height and angle of attack of those winglets were fixed. Besides that, three-dimensional numerical simulation was also performed in order to investigate the temperature and fluid flow over the plate-fin. The results showed that the longitudinal, common-flow-down vortices generated by the VGs augmented the heat transfer and pressure drop of the heat sink. At airflow velocity of 5 m/s, the heat transfer coefficient and pressure drop of plain plate-fin heat sink were 50.8 W/m2·K and 18 Pa, respectively, while the heat transfer coefficient and the pressure drop of heat sink having SDWP were 70.4 W/m2·K and 36 Pa, respectively. It was found that SDWP produced the highest thermal enhancement factor (TEF) of 1.28 at Re = 1000, followed by both RWP and STWP of similar TEF in the range 200 < Re < 1000. The TEF of DWP was the lowest and it was rapidly increased with the increase of airflow velocity.

scholarly journals Numerical Study on the Influence of Vortex Generator Arrangement on Heat Transfer Enhancement of Oil-Cooled Motor

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6870
Author(s):  
Junjie Zhao ◽  
Bin Zhang ◽  
Xiaoli Fu ◽  
Shenglin Yan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Vortex Generator ◽  
Attack Angle ◽  
Vortex Generators ◽  
Dimensionless Number ◽  
Transfer Enhancement ◽  
Enhanced Heat Transfer ◽  
Longitudinal Distance

At present, vortex generators have been extensively used in radiators to improve the overall heat transfer performance. However, there is no research on the effect of vortex generators on the ends of motor coils. Meanwhile, the current research mainly concentrates on the attack angle, shape and size, and lacks a detailed study on the transverse and longitudinal distance and arrangement of vortex generators. In this paper, the improved dimensionless number is used as the key index to evaluate the overall performance of enhanced heat transfer. Firstly, the influence of the attack angle on heat transfer enhancement is discussed through a single pair of rectangular vortex generators, and the results demonstrate that the vortex generator with a 45° attack angle is superior. On this basis, we compare the effects of different longitudinal distances (2 h, 4 h, and 6 h, h meaning the height of vortex generator) on enhanced heat transfer under four distribution modes: Flow-Up (FU), Flow-Down (FU), Flow-Up-Down (FUD), Flow-Down-UP (FDU). Thereafter, the performances of different transverse distances (0.25 h, 0.5 h, and 0.75 h) of the vortex generators are numerically simulated. When comparing the longitudinal distances, FD with a longitudinal distance of 4 h (FD-4h) performs well when the Reynolds number is less than 4000, and FU with a longitudinal distance of 4 h (FU-4h) performs better when the Reynolds number is greater than 4000. Similarly, in the comparison of transverse distances, FD-4h still performs well when the Reynolds number is less than 4000, and FU with a longitudinal distance of 4 h and transverse distance of 0.5 h (FU-4h − 0.5h) is more prominent when the Reynolds number is greater than 4000.

The Simulation Study of Turbulence Models for Conjugate Heat Transfer Analysis of a High Pressure Air-Cooled Gas Turbine

2010 ◽  
Author(s):  
Zhenfeng Wang ◽  
Peigang Yan ◽  
Hongfei Tang ◽  
Hongyan Huang ◽  
Wanjin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbine ◽  
Turbulence Model ◽  
Conjugate Heat Transfer ◽  
Turbulence Models ◽  
Turbulence Characteristic ◽  
The Heat Transfer Coefficient

The different turbulence models are adopted to simulate NASA-MarkII high pressure air-cooled gas turbine. The experimental work condition is Run 5411. The paper researches that the effect of different turbulence models for the flow and heat transfer characteristics of turbine. The turbulence models include: the laminar turbulence model, high Reynolds number k-ε turbulence model, low Reynolds number turbulence model (k-ω standard format, k-ω-SST and k-ω-SST-γ-θ) and B-L algebra turbulence model which is adopted by the compiled code. The results show that the different turbulence models can give good flow characteristics results of turbine, but the heat transfer characteristics results are different. Comparing to the experimental results, k-ω-SST-θ-γ turbulence model results are more accurate and can simulate accurately the flow and heat transfer characteristics of turbine with transition flow characteristics. But k-ω-SST-γ-θ turbulence model overestimates the turbulence kinetic energy of blade local region and makes the heat transfer coefficient higher. It causes that local region temperature is higher. The results of B-L algebra turbulence model show that the results of B-L model are accurate besides it has 4% temperature error in the transition region. As to the other turbulence models, the results show that all turbulence models can simulate the temperature distribution on the blade pressure surface except the laminar turbulence model underestimates the heat transfer coefficient of turbulence flow region. On the blade suction surface with transition flow characteristics, high Reynolds number k-ε turbulence model overestimates the heat transfer coefficient and causes the blade surface temperature is high about 90K than the experimental result. Low Reynolds number k-ω standard format and k-ω-SST turbulence models also overestimate the blade surface temperature value. So it can draw a conclusion that the unreasonable choice of turbulence models can cause biggish errors for conjugate heat transfer problem of turbine. The combination of k-ω-SST-γ-θ model and B-L algebra model can get more accurate turbine thermal environment results. In addition, in order to obtain the affect of different turbulence models for gas turbine conjugate heat transfer problem. The different turbulence models are adopted to simulate the different computation mesh domains (First case and Second case). As to each cooling passages, the first case gives the wall heat transfer coefficient of each cooling passages and the second case considers the conjugate heat transfer course between the cooling passages and blade. It can draw a conclusion that the application of heat transfer coefficient on the wall of each cooling passages avoids the accumulative error. So, for the turbine vane geometry models with complex cooling passages or holes, the choice of turbulence models and the analysis of different mesh domains are important. At last, different turbulence characteristic boundary conditions of turbine inner-cooling passages are given and K-ω-SST-γ-θ turbulence model is adopted in order to obtain the effect of turbulence characteristic boundary conditions for the conjugate heat transfer computation results. The results show that the turbulence characteristic boundary conditions of turbine inner-cooling passages have a great effect on the conjugate heat transfer results of high pressure gas turbine.

Experimental Investigation of Air–Water Mist Jet Impingement Cooling Over a Heated Cylinder

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Chunkyraj Khangembam ◽  
Dushyant Singh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Stagnation Point ◽  
Jet Impingement ◽  
Water Mist ◽  
Heated Cylinder ◽  
Air Jet ◽  
The Heat Transfer Coefficient

Experimental investigation on heat transfer mechanism of air–water mist jet impingement cooling on a heated cylinder is presented. The target cylinder was electrically heated and was maintained under the boiling temperature of water. Parametric studies were carried out for four different values of mist loading fractions, Reynolds numbers, and nozzle-to-surface spacings. Reynolds number, Rehyd, defined based on the hydraulic diameter, was varied from 8820 to 17,106; mist loading fraction, f ranges from 0.25% to 1.0%; and nozzle-to-surface spacing, H/d was varied from 30 to 60. The increment in the heat transfer coefficient with respect to air-jet impingement is presented along with variation in the heat transfer coefficient along the axial and circumferential direction. It is observed that the increase in mist loading greatly increases the heat transfer rate. Increment in the heat transfer coefficient at the stagnation point is found to be 185%, 234%, 272%, and 312% for mist loading fraction 0.25%, 0.50%, 0.75%, and 1.0%, respectively. Experimental study shows identical increment in stagnation point heat transfer coefficient with increasing Reynolds number, with lowest Reynolds number yielding highest increment. Stagnation point heat transfer coefficient increased 263%, 259%, 241%, and 241% as compared to air-jet impingement for Reynolds number 8820, 11,493, 14,166, and 17,106, respectively. The increment in the heat transfer coefficient is observed with a decrease in nozzle-to-surface spacing. Stagnation point heat transfer coefficient increased 282%, 248%, 239%, and 232% as compared to air-jet impingement for nozzle-to-surface spacing of 30, 40, 50, and 60, respectively, is obtained from the experimental analysis. Based on the experimental results, a correlation for stagnation point heat transfer coefficient increment is also proposed.

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.

scholarly journals Numerical analysis of heat transfer enhancement with the use of γ-Al2O3/water nanofluid and longitudinal ribs in a curved duct

2012 ◽  
Vol 16 (2) ◽  
pp. 469-480 ◽  
Author(s):  
Hosseinali Soltanipour ◽  
Parisa Choupani ◽  
Iraj Mirzaee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Base Fluid ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Transfer Enhancement ◽  
Dean Number ◽  
Particle Volume ◽  
The Heat Transfer Coefficient

This paper presents a numerical investigation of heat transfer augmentation using internal longitudinal ribs and ?-Al2O3/ water nanofluid in a stationary curved square duct. The flow is assumed 3D, steady, laminar, and incompressible with constant properties. Computations have been done by solving Navier-Stokes and energy equations utilizing finite volume method. Water has been selected as the base fluid and thermo- physical properties of ?- Al2o3/ water nanofluid have been calculated using available correlations in the literature. The effects of Dean number, rib size and particle volume fraction on the heat transfer coefficient and pressure drop have been examined. Results show that nanoparticles can increase the heat transfer coefficient considerably. For any fixed Dean number, relative heat transfer rate (The ratio of the heat transfer coefficient in case the of ?- Al2o3/ water nanofluid to the base fluid) increases as the particle volume fraction increases; however, the addition of nanoparticle to the base fluid is more useful for low Dean numbers. In the case of water flow, results indicate that the ratio of heat transfer rate of ribbed duct to smooth duct is nearly independent of Dean number. Noticeable heat transfer enhancement, compared to water flow in smooth duct, can be achieved when ?-Al2O3/ water nanofluid is used as the working fluid in ribbed duct.

Heat Transfer Augmentation and Flow Visualization With Delta Winglets in a Tube: A Numerical Approach

2020 ◽  
Author(s):  
Md. Islam ◽  
Liang Guangda ◽  
Md. Mahbub Alam
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Thermal Performance ◽  
Performance Enhancement ◽  
Swirling Flow ◽  
Circular Tube ◽  
Vortex Generator ◽  
Attack Angle ◽  
Maximum Enhancement ◽  
Longitudinal Vortices

Abstract In this research, heat transfer and pressure penalty from a circular tube with delta winglets insert are numerically investigated through Computational Fluid Dynamics (CFD) methodology. Numerical analysis with and without vortex generators (VGs) insert in a tube are done for a turbulent air flow, Reynolds number ranging from 6000 to 33000, under constant heat flux condition on the circular tube model surface. In our current research, we employed the shear stress transport (SST) k-omega model. The Nusselt number and friction factor results show the influence of the VGs insert on thermal performance. Effects of different winglet attack angles and blockage ratios on thermal performance enhancement were examined. Thermal performance is enhanced 5.1–30.7% using winglets in a tube. It is observed that small blockage ratio, B = 0.1 performed better than its counterpart of 0.2 and 0.3 for all the Reynolds number and for the same attack angle. The attack angle β = 15° and 30° showed better thermal performance enhancement at lower Re while at higher Re, β = 15° showed better performance. The maximum enhancement obtained for β = 30° and B = 0.1. Winglet vortex generator could create swirling flow when attack angle is 0 or 15°. When attack angle is increased, both swirling flow and longitudinal vortices appeared. At attack angle of 45°, large longitudinal vortices was found.

scholarly journals CFD-Entropy generation analysis of refrigerant-based nanofluids flow in a tube

2020 ◽  
Vol 307 ◽  
pp. 01038
Author(s):  
Mohammed Zohud ◽  
Ahmed Ouadha ◽  
Redouane Benzeguir
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Entropy Generation ◽  
Constant Heat Flux ◽  
Flux Boundary Condition ◽  
Flow Heat ◽  
Heat Flux Boundary Condition ◽  
The Heat Transfer Coefficient

The present paper aims to numerically investigate the flow, heat transfer and entropy generation of some hydrocarbon based nanorefrigerants flowing in a circular tube subject to constant heat flux boundary condition. Numerical tests have been performed for 4 types of nanoparticles, namely Al2O3, CuO, SiO2, and ZnO with a diameter equal to 30 nm and a volume concentration of φ = 5%. These nanoparticles are dispersed in some hydrocarbon-based refrigerants, namely tetrafluoroethane (R134a), propane (R290), butane (R600), isobutane (R600a) and propylene (R1270). Computations have been performed for Reynolds number ranging from 600 to 2200. The numerical results in terms of the average heat transfer coefficient of pure refrigerants have been compared to values obtained using correlations from the literature. The results show that the increase of the Reynolds number increases the heat transfer coefficient and decreases the total entropy generation.

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