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Effect of temperature on microstructural evolution and subsequent enhancement of mechanical properties in a backward extruded magnesium alloy
, Article International Journal of Advanced Manufacturing Technology ; 2017 , Pages 1-12 ; 02683768 (ISSN) ; Mirjavadi, S. S ; Salandari Rabori, A ; Sharif University of Technology
Abstract
The capability of backward extrusion (BE) method was assessed to achieve modified structures in AZ80 magnesium alloy. At first, 3D-Deform was employed to simulate the deformation flow through the deformed cup which gives an evidence from the flow behavior of the material. The material was processed via BE method at various temperatures of 250, 350, and 450 °C. Metallographic investigations were conducted in three different regions of the BE-processed cup (wall, bottom, and flow channel). The main feature observed at the wall of the BE cup was the presence of mechanical twins, the frequency of which was reduced by raising the process temperature. The flow localization in the form of shear...
Effect of temperature on microstructural evolution and subsequent enhancement of mechanical properties in a backward extruded magnesium alloy
, Article International Journal of Advanced Manufacturing Technology ; Volume 95, Issue 9-12 , 2018 , Pages 3155-3166 ; 02683768 (ISSN) ; Mirjavadi, S. S ; Salandari-Rabori, A ; Sharif University of Technology
Springer London
2018
Abstract
The capability of backward extrusion (BE) method was assessed to achieve modified structures in AZ80 magnesium alloy. At first, 3D-Deform was employed to simulate the deformation flow through the deformed cup which gives an evidence from the flow behavior of the material. The material was processed via BE method at various temperatures of 250, 350, and 450 °C. Metallographic investigations were conducted in three different regions of the BE-processed cup (wall, bottom, and flow channel). The main feature observed at the wall of the BE cup was the presence of mechanical twins, the frequency of which was reduced by raising the process temperature. The flow localization in the form of shear...
Solution of thermally developing zone in short micro-/nanoscale channels
, Article Journal of Heat Transfer ; Volume 131, Issue 4 , 2009 , Pages 1-15 ; 00221481 (ISSN) ; Vakilipour, S ; Sharif University of Technology
2009
Abstract
We numerically solve the Navier-Stokes equations to study the rarefied gas flow in short micro-and nanoscale channels. The inlet boundary conditions play a critical role in the structure of flow in short channels. Contrary to the classical inlet boundary conditions, which apply uniform velocity and temperature profiles right at the real channel inlet, we apply the same inlet boundary conditions, but at a fictitious position far upstream of the real channel inlet. A constant wall temperature incorporated with suitable temperature jump is applied at the channel walls. Our solutions for both the classical and extended inlet boundary conditions are compared with the results of other available...
Fluid dynamics performance of bio -inspired flow channel design for bipolar plates in PEM fuel cells
, Article 3rd European Fuel Cell Technology and Applications - Piero Lunghi Conference, EFC 2009, 15 December 2009 through 18 December 2009 ; 2009 , Pages 203-204 ; 9788882862114 (ISBN) ; Karimi Moghaddam, G ; Barchiesi C ; Cigolotti V ; Chianella M ; McPhail S ; Lunghi P ; Sharif University of Technology
ENEA
2009
Abstract
This study concentrates on the improvement in the performance of PEM fuel cells through optimization of the channel dimensions and patterns in the velocity and pressure fields in bipolar plates. For design and optimization purposes, a 2D numerical simulation of the flow distribution based on the Nervier-Stokes equations using individual computer code has been done. The outcome of the numerical simulations showed excellent agreement with the experimental results in previous works. Finally numerical simulation has been conducted to investigate the advantages of conventional patterns with inspiration from leaf flow pattern. It was found that both velocity and pressure fields are very uniform in...
Analytical solution of temperature field in micro-Poiseiulle flow with constant wall temperature
, Article 6th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2008, Darmstadt, 23 June 2008 through 25 June 2008 ; Issue PART B , 2008 , Pages 1371-1379 ; 0791848345 (ISBN); 9780791848340 (ISBN) ; Safari Mohsenabad, S ; Vakilipour, S ; ASME ; Sharif University of Technology
2008
Abstract
The analytical study of microchannels has been considered as a preliminary approach to alleviate the difficulties which are normally encountered in numerical and experimental studies. Among the analytical solutions, those with high robustness and low complexities are certainly more attractive. In this work, we present a theoretical approach to predict the temperature field in micro-Poiseuille channel flow with constant wall temperature. The use of power series method simplifies the solution in the current analytical approach. The current analytical derivations are examined for channels with both hot-wall and cold-wall conditions. The current solutions agree well with the numerical solutions...
Forced convective heat transfer in parallel flow multilayer microchannels
, Article Journal of Heat Transfer ; Volume 129, Issue 9 , 2007 , Pages 1230-1236 ; 00221481 (ISSN) ; Hajiaghaee Khiabani , R ; Sharif University of Technology
2007
Abstract
In this paper, the effect of increasing the number of layers on improving the thermal performance of microchannel heat sinks is studied. In this way, both numerical and analytical methods are utilized. The analytical method is based on the porous medium assumption. Here, the modified Darcy equation and the energy balance equations are used. The method has led to an analytical expression presenting the average dimensionless temperature field in the multilayer microchannel heat sink. The effects of different parameters such as aspect ratio, porosity, channel width, and the solid properties on the thermal resistance are described. The results for single layer and multilayer heat sinks are...
Analysis of combined pressure-driven electroosmotic flow through square microchannels
, Article Microfluidics and Nanofluidics ; Volume 3, Issue 1 , 2007 , Pages 123-126 ; 16134982 (ISSN) ; Manzari, M. T ; Sharif University of Technology
2007
Abstract
In this paper three-dimensional single-phase liquid flow through microchannels with a square-shaped cross-section driven by simultaneous application of pressure gradient and electroosmotic pumping mechanism is studied. The governing system of equations consists of the electric potential field and flow field equations. The solution procedure involves three steps. First, the net charge distribution on the cross-section of the microchannel is computed by solving two-dimensional Poisson-Boltzmann equation using the finite element method. Then, using the computed fluid's charge distribution, the magnitude of the resulting body force due to interaction of an external electric field with the...
Simulation of an innovative flow-field design based on a bio inspired pattern for PEM fuel cells
, Article Renewable Energy ; Volume 41 , 2012 , Pages 86-95 ; 09601481 (ISSN) ; Arbabi, F ; Moghaddam, G. K ; Sharif University of Technology
2012
Abstract
Proton exchange membrane (PEM) fuel cell performance is directly related to the bipolar plate design and their channels pattern. Power enhancements can be achieved by optimal design of the type, size, or patterns of the channels. It has been realized that the bipolar plate design has significant role on reactant transport as well as water management in a PEM Fuel cell. Present work concentrates on improvements in the fuel cell performance by optimization of flow-field design and channels configurations. A three-dimensional, multi-component numerical model of flow distribution based on Navier-Stokes equations using individual computer code is presented. The simulation results showed excellent...
Investigation the Effect of Different Pattern of Bi-Polar Plates on PEM Fuel Cells Performance
, M.Sc. Thesis Sharif University of Technology ; Roshandel, Ramin (Supervisor) ; Saboohi, Yadollah (Supervisor)
Abstract
Proton exchange membrane (PEM) fuel cell performance is directly related to the flow channel design on bipolar plates. Power gains can be found by varying the type, size, or arrangement of channels. It has been understood that the flow field design has a deterministic role on mass transport and water management, and thus great efforts have been made for the optimal design of flow field such that high and stable cell performance can be achieved. This study concentrates on the improvement in the performance of PEM fuel cells through optimization of the channel dimensions and patterns in the velocity and pressure fields in bipolar plates. For design and optimization purposes, a 2D numerical...
A high-order compact finite-difference lattice Boltzmann method for simulation of steady and unsteady incompressible flows
, Article International Journal for Numerical Methods in Fluids ; Vol. 75, Issue. 10 , 2014 , Pages 713-746 ; ISSN: 02712091 ; Ezzatneshan, E ; Sharif University of Technology
Abstract
A high-order compact finite-difference lattice Boltzmann method (CFDLBM) is proposed and applied to accurately compute steady and unsteady incompressible flows. Herein, the spatial derivatives in the lattice Boltzmann equation are discretized by using the fourth-order compact FD scheme, and the temporal term is discretized with the fourth-order Runge-Kutta scheme to provide an accurate and efficient incompressible flow solver. A high-order spectral-type low-pass compact filter is used to stabilize the numerical solution. An iterative initialization procedure is presented and applied to generate consistent initial conditions for the simulation of unsteady flows. A sensitivity study is also...
Long-lived and unstable modes of Brownian suspensions in microchannels
, Article Journal of Fluid Mechanics ; Volume 701 , 2012 , Pages 407-418 ; 00221120 (ISSN) ; Jalali, M. A ; Sharif University of Technology
2012
Abstract
We investigate the stability of the pressure-driven, low-Reynolds-number flow of Brownian suspensions with spherical particles in microchannels. We find two general families of stable/unstable modes: (i) degenerate modes with symmetric and antisymmetric patterns; (ii) single modes that are either symmetric or antisymmetric. The concentration profiles of degenerate modes have strong peaks near the channel walls, while single modes diminish there. Once excited, both families would be detectable through high-speed imaging. We find that unstable modes occur in concentrated suspensions whose velocity profiles are sufficiently flattened near the channel centreline. The patterns of growing unstable...
An innovative three dimensional numerical model for bipolar plates to enhance the efficiency of PEM fuel cells
, Article ASME 2012 10th International Conference on Fuel Cell Science, Engineering and Technology Collocated with the ASME 2012 6th International Conference on Energy Sustainability, FUELCELL 2012, 23 July 2012 through 26 July 2012 ; July , 2012 , Pages 351-360 ; 9780791844823 (ISBN) ; Roshandel, R ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2012
Abstract
The efficiency of proton exchange membrane (PEM) fuel cell is straightly correlated to the bipolar plate design and fluid channel arrangements. Higher produced energy can be attained by optimal design of type, size, or patterns of the channels. Previous researches showed that the bipolar plate channel design has a considerable effect on reactant distribution uniformity as well as humidity control in PEM fuel cells. This paper concentrates on enhancements in the fuel cell performance by optimization of bipolar plate design and channels configurations. A numerical model of flow distribution based on Navier-Stokes equations using individual computer code is presented. The results gained from...
Local scour at open-channel junctions
, Article Journal of Hydraulic Research ; Volume 48, Issue 4 , Sep , 2010 , Pages 538-542 ; 00221686 (ISSN) ; Jabbari Sahebari, A ; Sharif University of Technology
2010
Abstract
High bed-shear stress resulting from secondary flows and velocity increase at a channel junction cause local erosion and deposition in natural rivers and earth-lined channels. Herein, the scour patterns at the junction of two loose bed channels were studied under clear-water conditions. The main dimensionless variables are the angle between the two approach flow branches, the discharge and width ratios of the tributary to the downstream channel branches, and the ratio of the mean downstream velocity to the threshold velocity. The results indicate that the position of the maximum scour depth temporally moves to the outer wall and upstream to the main channel, as affected by the dimensionless...
Effect of a standing baffle on the flow structure in a rectangular open channel
, Article Journal of Hydraulic Research ; Volume 48, Issue 3 , Jun , 2010 , Pages 400-404 ; 00221686 (ISSN) ; Takeda, Y ; Firoozabadi, B ; Sharif University of Technology
2010
Abstract
The effect of an intermediate standing baffle on the flow structure in a rectangular open channel has been investigated by a three-dimensional acoustic Doppler velocimeter. Investigation of time-averaged velocity profiles at different streamwise positions reveals that the approach flow is fully developed upstream of the baffle. By analysing the space-averaged power spectra of streamwise velocity, a peak structure was observed in the upstream baffle region. Downstream of the baffle this peak structure has been alleviated by the baffle. The same analysis for the vertical component indicates the existence of a peak structure both up- and downstream of the baffle. Consequently, a baffle affects...
Determination of discharge coefficient of triangular labyrinth side weirs with one and two cycles using the nonlinear PLS method
, Article Sustainable Hydraulics in the Era of Global Change - Proceedings of the 4th European Congress of the International Association of Hydroenvironment engineering and Research, IAHR 2016, 27 July 2016 through 29 July 2016 ; 2016 , Pages 653-657 ; 9781138029774 (ISBN) ; Parvaneh, A ; Kabiri Samani, A ; Sharif University of Technology
CRC Press/Balkema
2016
Abstract
Side weirs are hydraulic control structures widely used in irrigation, drainage networks and waste water treatment plants. These structures can be used for adjusting and diverting of flow with minimum energy loss. In spite of many studies were carried out on rectangular side weirs, the studies on oblique and labyrinth side weirs are scarce. In this study, based on the experimental data from more than 210 laboratory tests and through using the multivariable nonlinear partial least square (PLS) method, two nonlinear equations are presented for discharge coefficient CM of triangular labyrinth side weirs with one and two cycles. The obtained empirical equations relating CM with the relevant...
Chebyshev collocation spectral lattice boltzmann method in generalized curvilinear coordinates
, Article Computers and Fluids ; Volume 146 , 2017 , Pages 154-173 ; 00457930 (ISSN) ; Hajihassanpour, M ; Sharif University of Technology
Abstract
In this work, the Chebyshev collocation spectral lattice Boltzmann method is implemented in the generalized curvilinear coordinates to provide an accurate and efficient low-speed LB-based flow solver to be capable of handling curved geometries with non-uniform grids. The low-speed form of the D2Q9 and D3Q19 lattice Boltzmann equations is transformed into the generalized curvilinear coordinates and then the spatial derivatives in the resulting equations are discretized by using the Chebyshev collocation spectral method and the temporal term is discretized with the fourth-order Runge–Kutta scheme to provide an accurate and efficient low-speed flow solver. All boundary conditions are...
High-order weighted essentially nonoscillatory finite-difference formulation of the lattice boltzmann method in generalized curvilinear coordinates
, Article Physical Review E ; Volume 95, Issue 2 , 2017 ; 24700045 (ISSN) ; Saadat, M. H ; Taheri, S ; Sharif University of Technology
Abstract
In this work, a high-order weighted essentially nonoscillatory (WENO) finite-difference lattice Boltzmann method (WENOLBM) is developed and assessed for an accurate simulation of incompressible flows. To handle curved geometries with nonuniform grids, the incompressible form of the discrete Boltzmann equation with the Bhatnagar-Gross-Krook (BGK) approximation is transformed into the generalized curvilinear coordinates and the spatial derivatives of the resulting lattice Boltzmann equation in the computational plane are solved using the fifth-order WENO scheme. The first-order implicit-explicit Runge-Kutta scheme and also the fourth-order Runge-Kutta explicit time integrating scheme are...
Simulation of three-dimensional incompressible flows in generalized curvilinear coordinates using a high-order compact finite-difference lattice Boltzmann method
, Article International Journal for Numerical Methods in Fluids ; 2018 ; 02712091 (ISSN) ; Hejranfar, K ; Sharif University of Technology
John Wiley and Sons Ltd
2018
Abstract
In the present study, a high-order compact finite-difference lattice Boltzmann method is applied for accurately computing 3-D incompressible flows in the generalized curvilinear coordinates to handle practical and realistic geometries with curved boundaries and nonuniform grids. The incompressible form of the 3-D nineteen discrete velocity lattice Boltzmann method is transformed into the generalized curvilinear coordinates. Herein, a fourth-order compact finite-difference scheme and a fourth-order Runge-Kutta scheme are used for the discretization of the spatial derivatives and the temporal term, respectively, in the resulting 3-D nineteen discrete velocity lattice Boltzmann equation to...
Application of the homotopy method for analytical solution of non-Newtonian channel flows
, Article Physica Scripta ; Volume 79, Issue 6 , 2009 ; 00318949 (ISSN) ; Kharazmi, S ; Farjami, Y ; Sharif University of Technology
2009
Abstract
This paper presents the homotopy series solution of the Navier-Stokes and energy equations for non-Newtonian flows. Three different problems, Couette flow, Poiseuille flow and Couette-Poiseuille flow have been investigated. For all three cases, the nonlinear momentum and energy equations have been solved using the homotopy method and analytical approximations for the velocity and the temperature distribution have been obtained. The current results agree well with those obtained by the homotopy perturbation method derived by Siddiqui et al (2008 Chaos Solitons Fractals36 182-92). In addition to providing analytical solutions, this paper draws attention to interesting physical phenomena...
Constitutive equations for micropolar hyper-elastic materials
, Article International Journal of Solids and Structures ; Volume 46, Issue 14-15 , 2009 , Pages 2765-2773 ; 00207683 (ISSN) ; Naghdabadi, R ; Sohrabpour, S ; Sharif University of Technology
2009
Abstract
In this paper, the concept of hyper-elasticity in the micropolar continuum theory is investigated. The restrictions on the fourth-order elasticity tensors are investigated. Using the representation theorems, a general form of constitutive equations for micropolar hyper-elastic isotropic materials is presented. As some special cases, generalizations of the neo-Hookean and Mooney-Rivlin type materials to the micropolar continuum theory are presented. The generalized constitutive equations reduce to those of the microplar linear elasticity theory when the deformations are infinitesimal. Also, Updated Lagrangian finite element formulations for the micropolar hyper-elastic materials are...