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Experimental and numerical study of the gas-gas separation efficiency in a Ranque-Hilsch vortex tube
, Article Separation and Purification Technology ; Vol. 138, issue , Dec , 2014 , p. 177-185 ; Farhadi, F ; Sharif University of Technology
Abstract
A brass vortextube is used to carry out a series of experiments. The main objective of the present research is to investigate the separation performances of a vortex tube (VT) for a hydrocarbon mixture. Examination is also applied to study the effects of nozzle intakes number and cold fraction on the gas species separation at specific inlet pressure 236.37 kPa in a VT with two gas mixtures (LPG as a hydrocarbon mixture and LPG-N2). A two-dimensional computational fluid dynamic (CFD) model simulation of a VT is presented. CFD code after validation is also applied to investigate the role of cold fraction and nozzle intakes number on the gas species separation. The highly rotating flow field...
Microstructrual evolution of aluminum 6061 alloy through tube channel pressing
, Article Materials Science and Engineering A ; Vol. 615 , 2014 , pp. 139-147 ; ISSN: 09215093 ; Kazeminezhad, M ; Miyamoto, H ; Sharif University of Technology
Abstract
The evolution of microstructure and the mechanical properties of an aluminum 6061 alloy tube subjected to a novel severe plastic deformation process called tube channel pressing were studied. Results show that the tube channel pressing causes an impressive grain refinement and strengthening of the material. As an illustration, mostly ultrafine grained tube (D-=760nm) bearing the yield strength of 352. MPa can be obtained after 5 passes of tube channel pressing. Additionally, the tube channel pressing causes the heterogeneous grain refinement resulting in a bimodal distribution of size of grains after 7th pass. Therefore, it can be inferred that the main microstructure refining mechanism...
Numerical study of the effects of process parameters on tool life in a cold radial forging process
, Article Scientia Iranica ; Vol. 21, issue. 2 , 2014 , p. 339-346 ; Movahhedy, M. R ; Sharif University of Technology
Abstract
Radial forging is an open die forging process used for reducing the diameters of shafts, tubes, stepped shafts and axles, and for creating internal profiles in tubes. Due to very large forging loads, the tool should withstand high stress and wear. Therefore, the success of the forging process depends upon recognition of the die failure factors and optimization of the tool working conditions that enhance tool life. In this study, the effect of process parameters on tool life in the cold radial forging process is investigated using nonlinear three dimensional finite element modeling. Wear and mechanical fatigue are considered as the main modes of tool failure, and a parametric study on the...
Residual stress analysis of the autofrettaged thick-walled tube using nonlinear kinematic hardening
, Article Journal of Pressure Vessel Technology, Transactions of the ASME ; Volume 135, Issue 2 , 2013 ; 00949930 (ISSN) ; Voyiadjis, G ; Hoseini, S. H ; Hosseinian, E ; Sharif University of Technology
2013
Abstract
Recent research indicates that accurate material behavior modeling plays an important role in the estimation of residual stresses in the bore of autofrettaged tubes. In this paper, the material behavior under plastic deformation is considered to be a function of the first stress invariant in addition to the second and the third invariants of the deviatoric stress tensor. The yield surface is assumed to depend on the first stress invariant and the Lode angle parameter which is defined as a function of the second and the third invariants of the deviatoric stress tensor. Furthermore for estimating the unloading behavior, the Chaboche's hardening evolution equation is modified. These...
Experimental analysis of a Ranque-Hilsch vortex tube for optimizing nozzle numbers and diameter
, Article Applied Thermal Engineering ; Volume 61, Issue 2 , 2013 , Pages 500-506 ; 13594311 (ISSN) ; Farhadi, F ; Sharif University of Technology
2013
Abstract
A brass vortex tube with changeable parts is used to obtain the optimum nozzle intake numbers and diameter. The effects of inlet pressure and CF (cold fraction) are also investigated. Results illustrate that increasing the number of nozzles causes a temperature drop and the optimum nozzle diameter corresponds to quarter of vortex tube diameter. The distance between cold end orifice and nozzle intakes is investigated in this work and it is found that for a better performance, this distance should be decreased. A series of experiments conducted to investigate the CF effect on VT performance and an optimum amount for this parameter is found. A two-dimensional computational fluid dynamics...
Laminar falling film flow of aqueous Li Br solution on a horizontal elliptical tube
, Article International Journal of Fluid Mechanics Research ; Volume 40, Issue 4 , 2013 , Pages 324-343 ; 10642277 (ISSN) ; Saidi, M. H ; Sharif University of Technology
2013
Abstract
Flow hydrodynamics of laminar falling film of aqueous Li Br solution (Li Br - H2O) on a horizontal elliptical tube has been investigated in this research. The film velocity distribution and film thickness, namely, the flow characteristics are determined by solving analytically simultaneous simplified Navier - Stokes equations and continuity equation in polar and Cartesian coordinates. The analysis is based on steady state laminar flow of falling liquid film of Li Br - H2O on a horizontal elliptical tube in polar model and Cartesian model (CM), for cases in which traction on the film surface is considered negligible. Models are compared with each other in three cases of aspect ratios (Ar),...
Experimental investigation on laminar forced convection heat transfer of ferrofluids under an alternating magnetic field
, Article Experimental Thermal and Fluid Science ; Volume 49 , 2013 , Pages 193-200 ; 08941777 (ISSN) ; Dibaei, M. H ; Hakim Sima, A ; Shafii, M. B ; Sharif University of Technology
2013
Abstract
This research study presents an experimental investigation on forced convection heat transfer of an aqueous ferrofluid flow passing through a circular copper tube in the presence of an alternating magnetic field. The flow passes through the tube under a uniform heat flux and laminar flow conditions. The primary objective was to intensify the particle migration and disturbance of the boundary layer by utilizing the magnetic field effect on the nanoparticles for more heat transfer enhancement. Complicated convection regimes caused by interactions between magnetic nanoparticles under various conditions were studied. The process of heat transfer was examined with different volume concentrations...
Investigations of the failure in boilers economizer tubes used in power plants
, Article Journal of Materials Engineering and Performance ; Volume 22, Issue 9 , 2013 , Pages 2691-2697 ; 10599495 (ISSN) ; Mehdipour, M ; Ghorbani, M ; Mohebali, M ; Koohbor, B ; Sharif University of Technology
2013
Abstract
In this study, failure of a high pressure economizer tube of a boiler used in gas-Mazut combined cycle power plants was studied. Failure analysis of the tube was accomplished by taking into account visual inspection, thickness measurement, and hardness testing as well as microstructural observations using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD). Optical microscopy images indicate that there is no phase transformation during service, and ferrite-pearlite remained. The results of XRD also revealed Iron sulfate (FeSO4) and Iron hydroxide sulfate (FeOH(SO4)) phases formed on the steel surface. A considerable amount of Sulfur was also...
Numerical modeling of pulse tube refrigerator and sensitivity analysis of simulation
, Article HVAC and R Research ; Volume 19, Issue 3 , 2013 , Pages 242-256 ; 10789669 (ISSN) ; Saidi, M. H ; Ghahremani, A. R ; Sharif University of Technology
2013
Abstract
In this article a double-inlet pulse-tube refrigerator (DIPTR) is modeled using the nodal analysis technique. The main complexity of the problem is oscillatory and unsteady characteristics of the flow. Solving the flow field in the regenerator section of the system as a porous medium with nonlocal thermal equilibrium is challenging. Governing equations are developed applying mass, energy, and momentum equations to different finite volumes in each component of DIPTR. A numerical code (SharifPTR), with graphical user interface, has been developed to investigate the influence of geometrical and working parameters on performance. The governing equations are a system of boundary value problems....
Severe plastic deformation of 6061 aluminum alloy tube with pre and post heat treatments
, Article Materials Science and Engineering A ; Volume 563 , 2013 , Pages 60-67 ; 09215093 (ISSN) ; Kazeminezhad, M ; Miyamoto, H ; Sharif University of Technology
2013
Abstract
In this work, the 6061 aluminum alloy tubes are severely deformed through a novel method called Tube Channel Pressing (TCP). The ability of this process in improving mechanical properties, grain refinement and microstructural changes of the alloy with different heat treatments before and after TCP process is investigated. Results show that TCP has notable effect on grain refinement and decreases crystallite size of solid solution treated aluminum 6061 material to 52. nm after equivalent strain of 3.09 which is comparable with the measured data from other SPD processes. The strength of the specimens aged before TCP is higher than that of those aged after TCP. The specimens artificially aged...
Application of inverse finite element method in tube hydroforming modeling
, Article Applied Mathematical Modelling ; Volume 37, Issue 8 , 2013 , Pages 5913-5926 ; 0307904X (ISSN) ; Shirin, M. B ; Assempour, A ; Sharif University of Technology
2013
Abstract
In tube hydroforming, the inverse finite element method (IFEM) has been used for estimating the initial length of tube, axial feeding and fluid pressure. The already developed IFEM algorithm used in this work is based on the total deformation theory of plasticity. Although the nature of tube hydroforming is three-dimensional deformation, in this paper a modeling technique has been used to perform the computations in two-dimensional space. Therefore, compared with conventional forward finite element methods, the present computations are quite fast with no trial and error process. In addition, the solution provides all the components of strain. Using the forming limit diagram (FLD), the...
Optimization of the angle of attack of delta-winglet vortex generators over a bank of elliptical-tubes heat exchanger
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Volume 8 A , 2013 ; 9780791856345 (ISBN) ; Godazandeh, B ; Ansari, M. H ; Ashjaee, M ; ASME ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2013
Abstract
In order to reach a more efficient and compact heat exchanger, it is essential to optimize the design, having in mind the impact of different geometrical parameters. Many of the previously cited studies in the area of heat transfer enhancement using vortex generators were confined only to defined points in the possible design space. Thus, a multiobjective optimization study is particularly suitable in order to cover this space entirely. A CFD simulation along with Pareto method were used to simulate the air flow and heat transfer and optimize the design parameters. The angle of attack of a pair of delta-winglets mounted behind each tube is varied between β = -90° and ß = +90°. Three...
The strain gradient approach to predict necking in tube hydroforming
, Article Journal of Manufacturing Processes ; Volume 15, Issue 1 , 2013 , Pages 8-13 ; 15266125 (ISSN) ; Abrinia, K ; Assempour, A ; Sharif University of Technology
2013
Abstract
A stress-based forming limit diagram for necking prediction which is based on the strain gradient theory of plasticity in conjunction with the M-K model has been represented and used in tube hydroforming. In this study, the finite element model for bulge forming of straight tube has been constructed and verified with published experimental data. The adaptive simulation technique is based on the ability to detect the onset and growth of defects (e.g., wrinkling, and bursting) and to promptly readjust the loading paths. Thus, a suitable load path has been obtained by applying Adaptive Simulation Method in ANSYS Parametric Design Language (APDL)
Twisted bundle heat exchangers performance evaluation by CFD (CJ12/5054)
, Article International Communications in Heat and Mass Transfer ; Volume 39, Issue 10 , 2012 , Pages 1654-1660 ; 07351933 (ISSN) ; Farhadi, F ; Sharif University of Technology
Abstract
Shell and tube heat exchanger with single twisted tube bundle in five different twist angles, are studied using computational fluid dynamics (CFD) and compared to the conventional shell and tube heat exchanger with single segmental baffles. Effect of shell-side nozzles configurations on heat exchanger performance is studied as well. Heat transfer rate and pressure drop are the main issues investigated in the paper. The results show that, for the same shell-side flow rate, the heat transfer coefficient of heat exchanger with twisted tube bundle is lower than that of the heat exchanger with segmental baffles while shell-side pressure drop of the former is even much lower than that of the...
Experimental study of evaporator surface area influence on a closed loop pulsating heat pipe performance
, Article American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM, 8 July 2012 through 12 July 2012, Rio Grande ; Volume 2 , 2012 , Pages 233-238 ; 08888116 (ISSN) ; 9780791844762 (ISBN) ; Mohammadi, M ; Shafii, M. B ; Sharif University of Technology
Abstract
Pulsating Heat Pipes are an effective mean for heat removal with the potential for a widespread application in electronic packaging. An experimental study a Closed Loop Pulsating Heat Pipe (CLPHP) constructed of copper tubes formed into four meandering turns is presented. Once configured in a vertical orientation the lower portion of the CLPHP comes in contact with a heat source (called the evaporator) from which it will remove heat through the pulsating action of the two-phase mixture contained within the initially evacuated copper tubes eventually transfer the heat to a heat sink (known as the condenser). Heat fluxes can be measured using temperature data gathered from experiments....
A new design for floating offshore platforms
, Article Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE ; Volume 1 , 2012 , Pages 529-537 ; 9780791844885 (ISBN) ; England, G. L ; Moradkhan, E ; Valikhani, A. R ; Bahadori, M. R ; Sharif University of Technology
2012
Abstract
While for shallow waters the use of old offshore jackets still seems efficient and justifiable, for deep and ultra-deep waters such platforms cannot be used. During the past few decades the old generation of fixed offshore platforms was succeeded by the new floating platforms and new designs such as FPSOs. A new family of floating offshore platforms has been developed. These should be able to respond to size, weight and space for operating equipment, i.e. they can be constructed to have a wide range of load-bearing capacities. Use is made of the old concept of Life Saving Tubes, which in their simplest form can be a toroidal shaped tyre inner tube. The Torus-shaped idea can be further...
Deformation behavior of 6061 aluminum alloy through tube channel pressing: Severe plastic deformation
, Article Journal of Materials Engineering and Performance ; Volume 21, Issue 10 , 2012 , Pages 2099-2105 ; 10599495 (ISSN) ; Kazeminezhad, M ; Sharif University of Technology
Springer
2012
Abstract
The deformation behavior of solid solution-treated AA6061 tubes in a novel severe plastic deformation process named Tube Channel Pressing has been assessed. In order to do so, an analysis based on the finite element method and dislocation density model is utilized, and microhardness measurement is carried out to verify the trends of analysis results. By comparing FEM results with experimental data, the optimized geometrical parameters controlling the deformation behavior of the tube in tube channel pressing are determined to obtain the best strain homogeneity and minimum dimensional changes in tube
Residual stress analyses of re-autofrettaged thick-walled tubes
, Article International Journal of Pressure Vessels and Piping ; Volume 98 , 2012 , Pages 57-64 ; 03080161 (ISSN) ; Voyiadjis, G. Z ; Hoseini, S. H ; Hosseinian, E ; Sharif University of Technology
Elsevier
2012
Abstract
In this paper the effect of the re-autofrettage process on the residual stress distribution at the wall of a thick-walled tube is considered. For accurate material behavior modeling, it is assumed that the yield surface is a function of all the stress invariants. Also for estimating the behavior of the material under loading-unloading process, a modified Chaboche's hardening model is applied. For evaluation of this unloading behavior model a series of loading-unloading tests are conducted on specimens that are made of the high strength steel, DIN1.6959. In addition the finite element simulations are implemented to simulate the re-autofrettage process and to estimate the residual stresses....
Computation on new deformation routes of tube channel pressing considering back pressure and friction effects
, Article Computational Materials Science ; Volume 59 , June , 2012 , Pages 174-181 ; 09270256 (ISSN) ; Kazeminezhad, M ; Sharif University of Technology
2012
Abstract
Three deformation routes for recently invented severe plastic deformation (SPD) method named tube channel pressing (TCP) have been introduced in this paper. The effects of routes, back pressure and friction have been investigated on deformation behavior of commercially pure (CP) aluminum tubes. Utilizing finite element analysis provides a broader understanding of these effects through different deformation routes. Due to the large values of strains accumulated in TCP, modified Estrin-Tóth-Molinari-Brechet (METMB) constitutive model has been employed in finite element analysis program to consider a realistic flow stress of the material in TCP. Employing experimental procedures confirms the...
Determination of strain field and heterogeneity in radial forging of tube using finite element method and microhardness test
, Article Materials and Design ; Volume 38 , June , 2012 , Pages 147-153 ; 02641275 (ISSN) ; Saidi, P ; Karimi Taheri, A ; Hossein Zadeh, M ; Sharif University of Technology
2012
Abstract
Utilizing the Finite Element Method (FEM), the strain field in the radial forging process of tube is calculated at different process conditions and compared with the experimental results achieved using the microhardness test. The effect of various process parameters such as friction, axial feed, back push and front pull forces and die angles on the strain field are investigated. Using the results of the analysis, it is shown that the deformation inhomogeneity, introduced by an Inhomogeneity Factor (IF), is maximum in the inner zone of tube, while the minimum and the maximum effective strains are appeared at the inner zone of tube and about the core of the tube thickness, respectively. Also,...