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Wind tunnel study of the effect zigzag tape on aerodynamics performance of a wind turbine airfoil
, Article Journal of Advanced Research in Fluid Mechanics and Thermal Sciences ; Volume 41, Issue 1 , 2018 , Pages 1-9 ; 22897879 (ISSN) ; Lazim, T.M ; Darbandi, M ; Sharif University of Technology
Penerbit Akademia Baru
2018
Abstract
A wind tunnel study was performed on the FFA-W-3-270 airfoil, which form a segment of a 1.25 MW wind turbine blade, to examine the effect of fixed roughness height and position using a zigzag tape boundary layer trip strip. Tests were conducted at a Reynolds number of 1×106 over a wide range of angles of attack. The zigzag tape, as an artificial roughness device, not only triggers a premature transition in the flow whereby laminar flow regimes change to turbulent, but also increases the momentum thickness of the turbulent boundary layer and change the airfoil camber. The 60° zigzag tape of 0.5 mm and 1 mm height was placed on the suction side of the airfoil at different chord wise locations....
Numerical investigation of rectangular-cut twisted tape insert on performance improvement of heat exchangers
, Article International Journal of Thermal Sciences ; Volume 138 , 2019 , Pages 75-83 ; 12900729 (ISSN) ; Esfahani, J. A ; Sharif University of Technology
Elsevier Masson SAS
2019
Abstract
A numerical analysis has been performed to investigate the flow structure and thermal hydraulic performance of turbulent flow through circular tube equipped with twisted tapes with different cut shapes. The geometries of cuts are rectangular with different cut ratios 0.25
Survey on high-temperature superconducting transformer windings design
, Article Journal of Superconductivity and Novel Magnetism ; Volume 33, Issue 9 , 8 June , 2020 , Pages 2581-2599 ; Ardeshiri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
Springer
2020
Abstract
Utilization of superconducting equipment increases every day due to availability of the HTS tapes with reasonable prices, commercially. Since 1997, many high-temperature superconducting (HTS) transformers have been designed and fabricated. In this paper, all the different developments of HTS transformer windings since 1997 will be reviewed. Additionally, the advantages and disadvantages of the application of the two main winding types (the pancake and the layer) in the HTS transformer will be studied. © 2020, Springer Science+Business Media, LLC, part of Springer Nature
Experimental results and finite-element predictions of the effect of nut geometry, washer and Teflon tape on the fatigue life of bolts
, Article Fatigue and Fracture of Engineering Materials and Structures ; Volume 28, Issue 6 , 2005 , Pages 557-564 ; 8756758X (ISSN) ; Farrahi, G. H ; Hardy, S. J ; Pipelzadeh, M. K ; Habibi, N ; Sharif University of Technology
2005
Abstract
The effect of nut geometry, curved spring washer and a sealing material (Teflon tape) on the fatigue life of M12 and M16 ISO bolts was investigated. This was accompanied by the study of the axial and bending stress distribution in threads by numerical simulation of bolt and nut connections using the finite-element method. The experimental results showed that the highest fatigue life is achieved for a slotted tapered nut. The presence of a spring washer also increases the fatigue life, providing that the correct tightening torque is applied to produce a pretension in the bolt. The use of Teflon tape as a filling material between engaging threads of the bolt and nut is shown to significantly...
Numerical study of turbulent nanofluid heat transfer in a tubular heat exchanger with twin twisted-tape inserts
, Article Journal of Thermal Analysis and Calorimetry ; 2017 , Pages 1-19 ; 13886150 (ISSN) ; Akbari, O. A ; Hassanzadeh Afrouzi, H ; Biglarian, M ; Koveiti, A ; Toghraie, D ; Sharif University of Technology
Abstract
In the present study, the turbulent flow of water/Al2O3 nanofluid in a tubular heat exchanger with two twisted-tape inserts has been numerically investigated in the three-dimensional coordinate. This numerical simulation has been done by using FVM, and all of the equations have been discretized by second-order upwind method. For coupling velocity–pressure equations, SIMPLEC algorithm has been used. The investigated parameters of the present study are Reynolds numbers at the range of 10,000–30,000, the effect of twist ratio of twisted-tape inserts from 2.5 to 4, co-swirl flow and counter-swirl flow of two twisted-tapes inside the tube and volume fractions of nanofluid from 1 to 4%. The...
Numerical study of turbulent nanofluid heat transfer in a tubular heat exchanger with twin twisted-tape inserts
, Article Journal of Thermal Analysis and Calorimetry ; Volume 132, Issue 1 , April , 2018 , Pages 741-759 ; 13886150 (ISSN) ; Akbari, O. A ; Hassanzadeh Afrouzi, H ; Biglarian, M ; Koveiti, A ; Toghraie, D ; Sharif University of Technology
Springer Netherlands
2018
Abstract
In the present study, the turbulent flow of water/Al2O3 nanofluid in a tubular heat exchanger with two twisted-tape inserts has been numerically investigated in the three-dimensional coordinate. This numerical simulation has been done by using FVM, and all of the equations have been discretized by second-order upwind method. For coupling velocity–pressure equations, SIMPLEC algorithm has been used. The investigated parameters of the present study are Reynolds numbers at the range of 10,000–30,000, the effect of twist ratio of twisted-tape inserts from 2.5 to 4, co-swirl flow and counter-swirl flow of two twisted-tapes inside the tube and volume fractions of nanofluid from 1 to 4%. The...
Cu-water nanofluid flow and heat transfer in a heat exchanger tube equipped with cross-cut twisted tape
, Article Powder Technology ; Volume 339 , 2018 , Pages 985-994 ; 00325910 (ISSN) ; Esfahani, J. A ; Sharif University of Technology
Elsevier B.V
2018
Abstract
This paper presents a numerical analysis for Cu-water nanofluid flow through a circular duct inserted with cross-cut twisted tape with alternate axis (CCTA). Three dimensional (RNG) k − ϵ turbulence model is applied to simulate this problem. All simulations are performed for plain tube and nine different CCTA geometries in the range of width ratio (b/w) from 0.7 to 0.9, length ratio (s/w) from 2 to 2.5, Reynolds numbers in the range of 5000 to 15,000 and volume fraction of nanoparticles from 0 to 1.5%. The calculated results indicate that the swirl flow created by CCTA is transferred from the tube core to the near wall regions. This results in higher fluid mixing, which enhances heat...
Numerical Study of Passive Heat Transfer Enhancement Methods in Automobile Radiator
, M.Sc. Thesis Sharif University of Technology ; Mousavi, Ali (Supervisor)
Abstract
In this study, a three dimensional model of water-ethylene glycol based aluminum oxide nanofluid in the laminar flow of an automobile radiator has been numerically studied. The passive heat transfer enhancement method of twisted tape insertion in the flat tubes of radiator is used. The effects of different parameters on heat transfer and pressure drop have been investigated. Simulation results show that utilizing twisted tapes is an effective way of enhancing heat transfer in an automobile radiator. Despite the pressure drop penalty of using twisted tapes, the thermal performance factor which is a proper criteria for evaluating the practical use of the twisted tapes and considers the effect...
Geometric optimization of a double pipe heat exchanger with combined vortex generator and twisted tape: A CFD and response surface methodology (RSM) study
, Article Thermal Science and Engineering Progress ; Volume 18 , 2020 ; Amiri, P ; Saffari Pour, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
In this research, a numerical investigation is done on the effect of employing the new combined vortex generators, the twisted tape turbulator and Al2O3-H2O nanofluid as the involved base fluid. Such study is carried out on the behavior of the heat transfer rate and the pressure drop of a double pipe heat exchanger. Accordingly, the response surface methodology (RSM) grounded on the central composite design (CCD) is used for acquiring the optimized geometry of the combined vortex generator and twisted tape turbulator. In order to have the maximum Nusselt number and minimum friction factor, twenty cases with different pitches ratio Pil=0.09-0.18, angles (θ=0-30°) and Reynolds numbers (Re =...
An analytical approach for optimal design of rotor iron for superconducting synchronous machine
, Article IECON Proceedings (Industrial Electronics Conference), 7 November 2011 through 10 November 2011, Melbourne, VIC ; 2011 , Pages 1741-1745 ; 9781612849720 (ISBN) ; Yazdanian, M ; Zolghadri, M. R ; Fardmanesh, M ; Sharif University of Technology
2011
Abstract
Although iron-cored superconducting machine has been recently proposed in many papers for its advantages over conventional air-cored structure such as less cost and less perpendicular magnetic component on HTS tapes it has not been studied analytically yet. This paper analytically investigates a general model for iron-cored superconducting synchronous machine. In this paper, analytical equations for magnetic flux in different regions of machine have been proposed along with an algorithm to solve the equations. The analytical equations will be then used to optimize the thickness of rotor iron in order to maximize the machine power density. Analytical and finite element simulation results will...
Effect of non-uniform magnetic field on heat transfer of swirling ferrofluid flow inside tube with twisted tapes
, Article Chemical Engineering and Processing: Process Intensification ; Volume 117 , 2017 , Pages 70-79 ; 02552701 (ISSN) ; Hariri, S ; Barzegar Gerdroodbary, M ; Yeganeh, R ; Sharif University of Technology
Abstract
In this article, a three-dimensional numerical simulation is performed to investigate the effect of magnetic field on the heat transfer of ferrofluid inside a tube which is equipped with twisted tape. This work comprehensively focused on the flow feature and temperature distribution of ferrofluid in presence of non-uniform magnetic field while ferrofluid swirled inside a tube with twisted tape. In this study, it is assumed that the ferrofluid is single phase and laminar and constant heat flux is applied on the outside of the tube. The magnetic field is established by wire in parallel direction with the axis of the tube. The base fluid is water with 0.86 Vol% Nano particles (Fe3O4). The...
Pool boiling heat transfer enhancement by twisted-tape fins
, Article Applied Thermal Engineering ; Volume 135 , 2018 , Pages 170-177 ; 13594311 (ISSN) ; Najm Barzanji, Z ; Hakkaki Fard, A ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
The boiling phenomena in a quiescent fluid is the nucleate pool boiling which has attracted much interest in the thermal management studies. This paper investigates the effect of the installed Twisted Tape Fins (TTFs) on the heat transfer from a surface with a temperature above the water saturation point to a coil condenser. Four different arrangements of TTFs (1, 3, 5, and 9 TTFs) are fabricated and their boiling performance in distilled water at atmospheric pressure is experimentally tested. It was observed that the increase in the boiling heat transfer coefficient of the plate with nine TTFs compared to that of the plain one is 15.5%. Furthermore, the effect of TTFs heights on the heat...
Performance intensification of turbulent flow through heat exchanger tube using double V-cut twisted tape inserts
, Article Chemical Engineering and Processing - Process Intensification ; Volume 141 , 2019 ; 02552701 (ISSN) ; Esfahani, J. A ; Sharif University of Technology
Elsevier B.V
2019
Abstract
This paper aims to present a numerical model for heat transfer intensification in a heat exchanger tube equipped with novel double V-cut twisted tape. The effects of different cut ratios (0.6 < b/c<1.8)on the turbulent flow characteristics and thermal performance of the system are investigated over the Reynolds number range from 5000 to 15,000. The accuracy of (RNG)k-ε turbulence model used in the present study is validated by comparing with experimental results. The tube equipped with double V-cut twisted tape shows improved thermal performance in comparison with conventional twisted tape. This improvement is due to the additional vortex flow induced by the V-cuts which leads to more...
Sensitivity analysis of a heat exchanger tube fitted with cross-cut twisted tape with alternate axis
, Article Journal of Heat Transfer ; Volume 141, Issue 4 , 2019 ; 00221481 (ISSN) ; Esfahani, J. A ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2019
Abstract
Numerical simulations are used to analyze the thermal performance of turbulent flow inside heat exchanger tube fitted with cross-cut twisted tape with alternate axis (CCTA). The design parameters include the Reynolds number (5000 < Re < 15; 000), cross-cut width ratio (0:7 < b=D < 0:9), cross-cut length ratio (2 < s=D < 2:5), and twist ratio (2 < y=D < 4). The objective functions are the Nusselt number ratio (Nu=Nus), the friction factor ratio (f =fs), and the thermal performance (g). Response surface method (RSM) is used to construct second-order polynomial correlations as functions of design parameters. The regression analysis shows that heat transfer ratio decreased with increasing both...
Heat transfer intensification of turbulent forced convection by inserting discontinuous twisted tapes in a wavy tube; hydrothermal and thermodynamics analysis
, Article Chemical Engineering and Processing - Process Intensification ; Volume 181 , 2022 ; 02552701 (ISSN) ; Sadrhosseini, H ; Kazemzadeh Hannani, S ; Sharif University of Technology
Elsevier B.V
2022
Abstract
The current study presents a numerical investigation on turbulent hydrothermal characteristics in a wavy passage equipped with discontinuous twisted tapes. The working fluid is water and passage walls are kept under constant wall temperature. The effect of Reynolds number (Re = 2500, 4500, 6500, 8500 and 10500), twist angle (TA = 90∘ and 180∘) and inclination angle (IA = 15∘ and 30∘) on velocity fields and streamlines, temperature contours, Nusselt number, friction factor, turbulent kinetic energy (TKE), thermal performance factor (TPF), energy efficiency factor (EEF) and entropy generation rate are evaluated. More uniform temperature and velocity fields can be found as both wavy passage and...
The Relationship between Microstructure, Properties and Processing in Bimodal Polyethylene with Medium Density Used in Drip Irrigation Tapes
, M.Sc. Thesis Sharif University of Technology ; Pircheraghi, Gholamreza (Supervisor)
Abstract
In recent years, Jam Petrochemical has produced and designed irrigation tape polyethylene grades but because these grades don’t have sufficient melt strength during high-speed processing, it hasn’t been welcomed by manufacturers. Therefore, in first step of this study we tried to characterize the specimens by using referenced grade and by taking advantages of thermal, rheological and mechanical analysis. We observed that main difference between jam petrochemical grades and referenced grade is related to type and content of comonomer and also long chain branches. Based on the obtained results, the ideal molecular structure of irrigation tape grade, include chains with bimodal distribution...
Heat transfer of swirling impinging jets ejected from Nozzles with twisted tapes utilizing CFD technique
, Article Case Studies in Thermal Engineering ; Volume 6 , September , 2015 , Pages 104-115 ; 2214157X (ISSN) ; Mokhtari, M ; Haghshenasfard, M ; Barzegar Gerdroodbary, M ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
This research investigated the forced convection heat transfer by using the swirling impinging jets. This study focused on nozzles, which equipped with twisted tapes via a numerical approach. The computational domain created by utilizing the fully structured meshes, which had very high quality from the viewpoint of aspect ratio and skewness. The numerical simulations were performed at four different jet-to-plate distances (L/D) of 2, 4, 6 and 8, four Reynolds numbers of 4000, 8000, 12,000 and 16,000, and also four different twist ratios (y/w) of 3, 4, 5 and 6. The mesh-independent tests were conducted based upon the average Nusselt number. The obtained results revealed good agreement with...
Design of sliding mode and model reference adaptive control strategies for multivariable tape transport mechanism: a performance comparison
, Article Microsystem Technologies ; Volume 22, Issue 2 , 2016 , Pages 419-431 ; 09467076 (ISSN) ; Moradian, H ; Moradi, H ; Sharif University of Technology
Springer Verlag
Abstract
This paper presents sliding mode control and model reference adaptive control strategies for the tape transport mechanism. A nonlinear multivariable MIMO model of the process, consisting of take-up and supply reel servos for tape tension control and capstan servo for speed control is considered. The sliding mode control is applied for the nonlinear dynamic model of the process, while the model reference adaptive control deals with the linearized one. Moreover, in order to associate with the realistic model of system, design of controllers is accomplished with respect to parametric uncertainties. It is shown that both control strategies can guarantee asymptotic stability of the closed-loop...
Effects of molecular structure on thermal, rheological and mechanical properties of drip irrigation PE tapes
, Article Journal of Polymer Research ; Volume 29, Issue 10 , 2022 ; 10229760 (ISSN) ; Pircheraghi, G ; Houshmandmoayed, S ; Sharif University of Technology
Springer Science and Business Media B.V
2022
Abstract
Considering the microstructure-processing-properties relationship, the attempt was made to distinguish the main structural features of drip irrigation tape grades. In this regards, two different commercial polyethylene grades using for irrigation tape application (DB and MD samples) with various microstructural features were fully characterized by means of thermal, rheological and mechanical measurements and microscopic observations. A set of DSC techniques revealed that DB sample has faster crystallization kinetic probably due to its high crystallizable segments in chains and broad molecular weight distribution. It was found, the type of co-monomer used in DB sample is 1-hexene and in MD...
Robust regulation and tracking system design for multivariable control of the tape transport mechanism
, Article Microsystem Technologies ; Vol. 18, Issue. 5 , 2012 , pp. 557-573 ; ISSN: 09467076 ; Bakhtiari-Nejad, F ; Alasty, A ; Sharif University of Technology
Abstract
Tape mechanisms must be able to transport the tape with a constant velocity for achieving high rate of data transfer. In this paper, a multivariable model of tape transport mechanism including the take-up and supply reel servos for tape tension control and capstan servo for speed control is considered. To achieve desired performance,pole-placement approach based on general canonical control form (GCCF) is used. Instead of using expensive tension sensors, an observer is designed. A regulator system is developed for disturbance rejection; and a modified integral control is designed for perfect tracking of desired setpoints in tape speed and tensions. Since the real dynamic model associates...