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Total 111 records
Development of a novel severe plastic deformation method for tubular materials: Tube Channel Pressing (TCP)
, Article Materials Science and Engineering A ; Volume 528, Issue 15 , June , 2011 , Pages 5066-5072 ; 09215093 (ISSN) ; Kazeminezhad, M ; Sharif University of Technology
2011
Abstract
A new severe plastic deformation (SPD) method entitled Tube Channel Pressing (TCP) is proposed. In this study, the ability of TCP on strength improvement and grain refinement is assessed. This method is based on pressing a tube through a tubular channel die with a neck zone. Utilization of a mandrel fitted inside the tube prevents the crumpling of tube and preserves its initial dimension. Due to the symmetric design, after one pass, the die is rotated upside down and the second pass is applied by pressing the tube in inverse direction. Ultimate strength of a commercial purity aluminum tube after 5 successful passes is improved to 2 times of the initial strength. Analytical calculations and...
Fabrication of copper/aluminum composite tubes by spin-bonding process: Experiments and modeling
, Article International Journal of Advanced Manufacturing Technology ; Volume 54, Issue 9-12 , November , 2011 , Pages 1043-1055 ; 02683768 (ISSN) ; Akbarzadeh, A ; Sharif University of Technology
2011
Abstract
The aim of this work is to produce two layered thin-walled Cu/Al composite tube by the spin-bonding process. The process is utilized to bond the aluminum tube into the copper one at thickness reductions of 20-60% and process temperatures of 25°C, 130°C, and 230°C. The bond strength is measured by T-peeling test, and the bond interfaces are examined by metallography and scanning electron microscopy (SEM). The results show that after a threshold thickness reduction of about 30%, the bond strength increased with the amount of deformation. SEM fractography of the peel surfaces confirms that the copper oxide film is broken in a shear manner during deformation. Severe shear strains applied during...
Bode stability analysis for single wall carbon nanotube interconnects used in 3D-VLSI circuits
, Article World Academy of Science, Engineering and Technology ; Volume 77 , 2011 , Pages 568-571 ; 2010376X (ISSN) ; Faez, R ; Davoodi, B ; Farrokhi, M ; Sharif University of Technology
2011
Abstract
Bode stability analysis based on transmission line modeling (TLM) for single wall carbon nanotube (SWCNT) interconnects used in 3D-VLSI circuits is investigated for the first time. In this analysis, the dependence of the degree of relative stability for SWCNT interconnects on the geometry of each tube has been acquired. It is shown that, increasing the length and diameter of each tube, SWCNT interconnects become more stable
Performance analysis and optimization of high capacity pulse tube refrigerator
, Article Cryogenics ; Volume 51, Issue 4 , 2011 , Pages 173-179 ; 00112275 (ISSN) ; Saidi, M. H ; Jahanbakhshi, R ; Roshanghalb, F ; Sharif University of Technology
2011
Abstract
High capacity pulse tube refrigerator (HCPTR) is a new generation of cryocoolers tailored to provide more than 250 W of cooling power at cryogenic temperatures. The most important characteristics of HCPTR when compared to other types of pulse tube refrigerators are a powerful pressure wave generator, and an accurate design. In this paper the influence of geometrical and operating parameters on the performance of a double inlet pulse tube refrigerator (DIPTR) is studied. The model is validated with the existing experimental data. As a result of this optimization, a new configuration of HCPTR is proposed. This configuration provides 335 W at 80 K cold end temperature with a frequency of 50 Hz...
Microstructure and mechanical properties of an Al-Mg-Si tube processed by severe plastic deformation and subsequent annealing
, Article Materials Science and Engineering A ; Volume 640 , July , 2015 , Pages 42-50 ; 09215093 (ISSN) ; Kazeminezhad, M ; Miyamoto, H ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
This study is aimed to realize evolution of microstructure and mechanical properties of aluminum 6061 alloy tube subjected to Severe Plastic Deformation (SPD) and subsequent annealing. For this purpose, the tube is initially processed by different passes of an SPD process called Tube Channel Pressing (TCP) and then subjected to a subsequent annealing at 473. °K for 2. h. Afterwards, tension test is used for the evaluation of mechanical properties while Electron Back-Scattered Diffraction (EBSD) equipped Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) are utilized for the microstructural characterizations. Results show that the Continuous Static Recrystallization...
Effect of aging treatment on the crushing behavior of aluminum 6061 alloy tube
, Article Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications ; Volume 229, Issue 5 , Feb , 2015 , Pages 389-397 ; 14644207 (ISSN) ; Sharif University of Technology
SAGE Publications Ltd
2015
Abstract
The effect of heat treatment on the axial crushing behavior of thin-walled aluminum 6061 alloy tubes is studied in this work. For this purpose, thin-walled grooved specimens were subjected to different aging heat treatments to obtain different work hardening behaviors. Afterward, quasi-static axial compression tests were achieved to evaluate the crushing behavior. Additionally, a finite element method simulation was employed to determine the distributions of stress, strain, and imposed damage during axial compression. Results show that the optimum energy absorption characteristics can be obtained using moderated strain hardening exponent, ''n''. Low strain hardening exponent results in the...
Microstructure evolutions and mechanical properties of tubular aluminum produced by friction stir back extrusion
, Article Materials and Design ; Volume 65 , January , 2015 , Pages 74-79 ; 02613069 (ISSN) ; Movahedi, M ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
Aluminum tubes were successfully fabricated using a novel process of friction stir back extrusion (FSBE) known as one of the severe plastic deformation (SPD) routes. It was found that this process is capable to form a tube with a significant fine grained structure resulting from dynamic recrystallization phenomenon in the stirred area. Several regions were identified in the formed tube in which various microstructural evolutions occur, i.e. dynamic recrystallized (RX), static RX, and partially static RX zones along with extruded base metal. There was also no considerable change in the hardness and strength values of the formed tube with respect to those of the extruded base metal. However,...
An exact analysis for the hoop elasticity and pressure-induced twist of CNT-nanovessels and CNT-nanopipes
, Article Mechanics of Materials ; Volume 82 , 2015 , Pages 47-62A ; 01676636 (ISSN) ; Shodja, H. M ; Sharif University of Technology
Elsevier
2015
Abstract
Carbon nanotubes (CNTs) with and without end caps may be used for fluid storage and transport, respectively, referred to as CNT-nanovessel and CNT-nanopipe. The determination of the stiffness in the hoop (circumferential) and radial directions, ideal hoop strength, and hoop stress-strain curve of such nanostructures is of particular interest. Due to the proposed viewpoint, a chiral free-standing single-walled CNT (SWCNT) has a natural angle of twist and natural extension along the axis of the tube. For example, for the SWCNT (9,3) with diameter of 0.85 nm and chirality angle of 13.9°, the natural angle of twist per unit length is 1.45×10-3 rad/nm. Previously, only Vercosa et al. (2010) who...
Performance analysis and optimization of high capacity pulse tube refrigerator
, Article ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 12 July 2010 through 14 July 2010 ; Volume 1 , 2010 , Pages 257-263 ; 9780791849156 (ISBN) ; Roshanghalb, F ; Jahanbakhshi, R ; Saidi, M. H ; Kazemzadeh Hannani, S ; Sharif University of Technology
Abstract
High capacity pulse tube refrigerator (HCPTR) is a new generation of cryocoolers tailored to provide more than 250 W of cooling power at cryogenic temperatures. The most important characteristics of HCPTR when compared with other types of pulse tube refrigerators are a powerful pressure wave generator, and an accurate design. In this paper the influence of geometrical and operating parameters on the performance of a double inlet pulse tube refrigerator (DIPTR) is studied. The DIPTR is modeled applying the nodal analysis technique, using mass, momentum and energy conservation equations. The model is able to compute instantaneous flow field throughout the system and calculate cooling capacity...
First and second law analysis of fluid flow in the regenerator of pulse tube refrigerators
, Article 2010 14th International Heat Transfer Conference, IHTC 14, 8 August 2010 through 13 August 2010, Washington, DC ; Volume 4 , 2010 , Pages 247-255 ; 9780791849392 (ISBN) ; Saidi, M. H ; Jafarian, A ; Imanimehr, F ; Asadi, M ; Sharif University of Technology
2010
Abstract
The objective of the present work is to analyze the performance of the regenerator of pulse tube refrigerators. Hydrodynamic and thermal behavior of the regenerator is investigated in this respect. To consider the system performance, a system of conservation equations including two energy equations for the regenerator as a porous media is employed. The present model considers one dimensional periodic unsteady compressible flow in the regenerator. The conservation equations are transformed by implementing the volumetric average scheme. Method of harmonic approximation is employed to derive an analytical solution. To explore the system performance, net energy flow and entropy generation...
A novel spin-bonding process for manufacturing multilayered clad tubes
, Article Journal of Materials Processing Technology ; Volume 210, Issue 3 , 2010 , Pages 510-517 ; 09240136 (ISSN) ; Akbarzadeh, A ; Sharif University of Technology
2010
Abstract
Utilizing the so-called tube spinning, a cold-bonding process entitled as "spin-bonding" is developed to produce seamless thin-walled clad tubes and cylinders. By this method, two layers of AA 1050 tubes were successfully bonded together to form a clad tube at room temperature. Based on mechanical aspects of the tube spinning process, the mechanism of spin-bonding is explained in two stages: surface preparation before occurrence of a stable bond and bond strengthening thereafter. The effects of process temperature, thickness reduction, feed rate and roller attack angle as the parameters of tube spinning on the bond strength are studied. It is shown that the bond strength increases by...
Microstructural and failure analysis of welded primary reformer furnace tube made of HP-Nb micro alloyed heat resistant steel
, Article Engineering Failure Analysis ; Volume 68 , 2016 , Pages 32-51 ; 13506307 (ISSN) ; Karimi Taheri, A ; Jalilvand, S ; Habibi, A ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
In this paper, the failure of the reformer furnace tube, made of HP-Nb micro alloyed heat resistant steel is investigated. The failure was due to a longitudinal crack developing in the circumferential weld joint close to the outlet end of the tube, where the mean wall temperature had reached the highest value during service. According to the temperature records during the period of 7 years of being in service, the tube had experienced temperatures higher than the tubes designed temperature. This situation besides the occurrence of several sudden shutdowns caused the mechanical properties degradation.Macroscopic and microscopic examinations revealed that the failure had occurred due to the...
Examination of a novel solar still equipped with evacuated tube collectors and thermoelectric modules
, Article Desalination ; Volume 382 , 2016 , Pages 21-27 ; 00119164 (ISSN) ; Shahmohamadi, M ; Faegh, M ; Sadrhosseini, H ; Sharif University of Technology
Elsevier
2016
Abstract
In this article, a novel solar still which is equipped with thermoelectric modules to utilize the heat of vapor condensation is experimentally investigated. The use of thermoelectric modules as devices for generating electricity from the temperature difference between two environments (hot vapor steam and cold ambient air) as well as taking outstanding advantages of evacuated tubes as collectors with high performances in adverse climatic conditions, led to utilizing of the energy dissipated due to vapor condensation and a considerable increase in the performance of the system. The effect of using the generated electricity to operate a small propeller fan for inducing forced convection was...
A high power high voltage short pulse width pulse generator using direct drive method in application of modulating-cathode tubes drive
, Article IEEE International Symposium on Industrial Electronics, 5 July 2009 through 8 July 2009 ; 2009 , Pages 2097-2102 ; 9781424443499 (ISBN) ; Sadriyeh, S. M. R ; Mohammadi, A ; Maghsoudlou, B ; Mokhtari, H ; Alizadeh, H. R ; Shams Mousavi, S. M ; Sharif University of Technology
Abstract
The power supply of microwave tubes has high voltage and the possibility of produce high power pulse, which called in modulator. In this work, the results of design, construction and characterization of a direct drive pulse modulator for driving high power short pulse-width magnetron are reported. The sub-assemblies of modulator are; a primary high voltage supply, a switch bank with drivers and snubber circuits, a filament circuit, a digital control circuit with sensors and finally a pulse transformer. This paper is concerned with introduction and presentation of experimental evaluation of a new drive method for high power high voltage modulating-cathode microwave tubes. ©2009 IEEE
An analytical approach in prediction of necking and suitable load path in tube hydroforming by using the strain gradient
, Article SAE Technical Papers, 20 April 2009 through 20 April 2009, Detroit, MI ; 2009 ; Masoumi, E ; Safikhani, A. R ; Hashemi, R ; Abrinia, K ; Sharif University of Technology
Abstract
A theoretical forming limit stress diagram (FLSD) for necking prediction which is based on the strain gradient theory of plasticity in conjunction with the M-K approach was represented and used in tube hydroforming. This approach introduces an internal length scale into conventional constitutive equations and takes into account the effects of deformation inhomogeneity and material softening. The nonlinear second order ordinary differential equation of the thickness of tube has been solved by collocation method. It has been shown that this method overcomes the imperfection sensitivity encountered in the conventional M-K method. The predicted FLSD has been compared with published experimental...
Energy absorption in plastic expansion of circular metal tubes
, Article Computational Plasticity X - Fundamentals and Applications, 2 September 2009 through 4 September 2009, Barcelona ; 2009 ; 9788496736696 (ISBN) ; Salehghaffari, S ; Sharif University of Technology
Abstract
This paper investigates a new method of dissipating energy in which a rigid tube is driven into the deformable tube under axial compression. Since there is a specific clearance between the rigid and deformable tubes, the deformable tube is expanded during axial compression, and the impact energy is absorbed by plastic expansion of deformable tube and frictional energy between deformable and rigid tubes. Quasi-static axial compression tests with different values of friction coefficient between rigid and deformable tubes are performed. Theoretical formulation with consideration of strain hardening effect is presented to predict the mean crushing load. Theoretical and experimental studies show...
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...
Failure analysis of bolt connections in fired heater of a petrochemical unit
, Article Engineering Failure Analysis ; Volume 92 , 2018 , Pages 327-342 ; 13506307 (ISSN) ; Chamani, M ; Reza Kashyzadeh, K ; Mostafazade, A ; Mahmoudi, A. H ; Afshin, H ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
The main function of a fired heater in a petrochemical site is to produce supersaturated steam. Due to extremely difficult working conditions and high temperatures, there is a very high probability of failures in different parts of a fired heater. In the fired heater under study, tube guides are frequently damaged due to malfunctions and fractures in bolt connections. To investigate the nature of such fractures, Computational Fluid Dynamics (CFD), Finite Element (FE) method, Charpy impact test and fractography were used. To obtain the temperature of various components of the fired heater, a CFD analysis was carried out by considering the combustion process and modeling the central and side...
Numerical investigation of the effects of fin shape, antifreeze and nanoparticles on the performance of compact finned-tube heat exchangers for automobile radiator
, Article Applied Thermal Engineering ; Volume 133 , 2018 , Pages 248-260 ; 13594311 (ISSN) ; Mostafazade Abolmaali, A ; Afshin, H ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
In this paper, heat transfer and pressure drop of air in the radiator of an internal combustion engine automobile were investigated. First, three types of fins including louvered, triangular vortex generator and rectangular vortex generator were modeled and their performance were compared with a plain fin. Effects of adding antifreeze in volume ratios of 40, 50 and 60% on the performance of louvered and rectangular vortex generator fins were investigated. Finally, the effects of adding copper oxide and aluminum oxide nanoparticles on the heat transfer improvement of louvered and rectangular vortex generator fins were simulated. The results demonstrated that louvered fin had the highest heat...
An experimental evaluation of copper, steel and polypropylene tubes in solar water heaters with thermosyphonic flow
, Article Applied Solar Energy (English translation of Geliotekhnika) ; Volume 45, Issue 1 , 2009 , Pages 65-69 ; 0003701X (ISSN) ; Razavi, J ; Sadeghi, A ; Javaheri, A ; Sharif University of Technology
2009
Abstract
In this paper we report experimental results for the performance and rate of heat transfer in copper tubes in solar water heaters with thermosyphonic flow in continuation of experimental data reported in previous publications (Solar Energy, 2003, vol. 74, pp. 441-445, and Energy Sources, 1997, vol. 19, pp. 147-152). We also show a comparison between performances of three kinds of tubes: copper, polypropylene and steel under similar conditions. An analytical relation for calculation of rate of heat transfer in copper tubes is also presented in terms of Nusselt versus Reynolds and Prantdl numbers. A comparison of experimental data showed that performance of copper tubes is slightly better than...