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Semisolid joining of zinc AG40A alloy by partial remelting and mechanical stirring
, Article Semi-Solid Processing of Alloys and Composites 10 - Selected, peer reviewed papers from the 10th International Conference on Semi-Solid Processing of Alloy and Composites, S2P 2008, Aachen, 16 September 2008 through 18 September 2008 ; Volume 141-143 , 2008 , Pages 225-230 ; 10120394 (ISSN); 9771012039401 (ISBN) ; Aashuri, H ; Kokabi, A. H ; Khosravani, A ; Kiani, M ; Foroughi, A ; Sharif University of Technology
Trans Tech Publications Ltd
2008
Abstract
A technique to achieve the globular weld structure using stirring the localized semisolid zone during butt-joining of zinc AG40A (Zamak-3) die cast alloy is reported. Since the semisolid temperature range of this alloy is very narrow, the accurate controlling of weld pool temperature must be considered. By presented process, globular microstructure of the weld zone can be achieved. Moreover the near weld zone would have the globular structure due to semisolid holding. A gas heating system was designed to heat up the nitrogen gas to desired temperature accurately. A heating element was embedded in a castable ceramic block while a stream of gas could pass closely around the hot element length....
Multi-directional co-flow fluidic thrust vectoring intended for a small gas turbine
, Article 2007 AIAA InfoTech at Aerospace Conference, Rohnert Park, CA, 7 May 2007 through 10 May 2007 ; Volume 3 , 2007 , Pages 2278-2286 ; 1563478935 (ISBN); 9781563478932 (ISBN) ; Saghafi, F ; Ghoreyshi, M ; Pilidis, P ; Sharif University of Technology
2007
Abstract
This paper concerns an understanding of thrust vectoring, in the presence of co-flowing secondary air. An experimental and computational study was performed on a circular-shape nozzle, integrated with a Coanda surface, to investigate the feasibility of multi-directional deflection of the engine exhaust gases. The vectoring angle was controlled by the relative blowing momentum of air that was injected tangentially through the slots, surrounding the main nozzle. A state of the art design that uses a small step, just after the main nozzle to turn the flow into eddy, was also employed to enhance the effectiveness of the method. The secondary section was divided into four identical sections for...
Simulation of rarefied micro to nano gas flows using improved slip flow models
, Article 37th AIAA Fluid Dynamics Conference, Miami, FL, 25 June 2007 through 28 June 2007 ; Volume 1 , 2007 , Pages 576-583 ; 1563478978 (ISBN); 9781563478970 (ISBN) ; Rikhtegar, F ; Schneider, G. E ; Sharif University of Technology
2007
Abstract
If the hydrodynamic diameter of a channel is comparable with the mean free path of the gas molecules moving inside the channel, the fluid can no longer be considered to be in thermodynamic equilibrium and a variety of non-continuum or rarefaction effects can occur. To avoid enormous complexity and extensive numerical cost encountered in modeling of nonlinear Boltzmann equations, the Navier-Stokes equations can be solved considering the concepts of slip flow regime and applying slip velocity boundary conditions at the solid walls. The high-order slip models can, in some cases, extend the range of applicability of the Navier-Stokes equations beyond Kn = 0.1, where the accuracy of first-order...
Optimization of ferrous biooxidation rate in a packed bed bioreactor using Taguchi approach
, Article Chemical Engineering and Processing: Process Intensification ; Volume 46, Issue 10 , 2007 , Pages 935-940 ; 02552701 (ISSN) ; Yaghmaei, S ; Jafari, A ; Vossoughi, M ; Ghobadi, Z ; Sharif University of Technology
2007
Abstract
The biological oxidation of ferrous ion by iron-oxidizing bacteria is potentially a useful industrial process for removal of H2S from industrial gases, desulphurization of coal, removal of sulfur dioxide from flue gas, treatment of acid mine drainage and regeneration of an oxidant agent in hydrometallurgical leaching operations. The main purpose of this study was to find optimum values of the process parameters on the ferrous biooxidation rate by immobilization of a native Sulfobacillus species on the surface of low density polyethylene (LDPE) particles in a packed-bed bioreactor using Taguchi method. Five control factors, including temperature, initial pH of feed solution, dilution rate,...
Kinetics and mechanisms of nanoparticle formation and growth in vapor phase condensation process
, Article Materials and Design ; Volume 28, Issue 3 , 2007 , Pages 850-856 ; 02613069 (ISSN) ; Ahmadi, R ; Reihani, S. M. S ; Mahdavi, A ; Sharif University of Technology
Elsevier Ltd
2007
Abstract
Design of nanoparticle synthesis by inert-gas condensation process was studied according to the mechanisms and kinetics of nucleation and growth in the vapor phase. The effect of process parameters, e.g., source temperature, evaporation rate, and the inert-gas pressure, on the particle size and particle shape was examined at the example for silver and copper-tin alloy. The synthesized nanopowders had near spherical shape with particle size range from 10 to 60 nm dependent on the processing condition. Scanning and transmission electron microscopy (SEM and TEM) analyses showed that the crystallites are subunits of larger agglomerate particles, and relatively large particles display crystal...
Co-flow fluidic thrust vectoring requirements for longitudinal and lateral trim purposes
, Article AIAA/ASME/SAE/ASEE 42nd Joint Propulsion Conference, Sacramento, CA, 9 July 2006 through 12 July 2006 ; Volume 8 , 2006 , Pages 6283-6292 ; 1563478188 (ISBN); 9781563478185 (ISBN) ; Banazadeh, A ; Sharif University of Technology
2006
Abstract
The feasibility of using fluidic thrust-vectoring system, as a control technique for the longitudinal and lateral trim purpose was investigated in this study. For this purpose, integration of a Co-flow method into the propulsion unit of a conceptual aerial vehicle was assumed. The focus of the research presented was to estimate the required thrust vector angle in order to trim the aerial vehicle in different flight phases. Since the fluidic thrust vectoring requires secondary air flow to deflect the engine exhaust gas, this research also provides an analytical toolset for preliminary sizing of a suitable secondary air supply. It was found that thrust vectoring could be an effective mean of...
Importance of N-P-N junction in H2S sensing process of SnO2-CuO heterostructures: A theoretical macroscopic approach
, Article IEEE Sensors Journal ; Volume 21, Issue 6 , 2021 , Pages 7123-7129 ; 1530437X (ISSN) ; Ghorbani, M ; Mohammadpour, R ; Moosavi, A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2021
Abstract
Metal-oxide gas sensors are widely used for detection of detrimental H2S gas. Among them, SnO2-CuO system has been proved to be an excellent candidate. The previous theoretical 2D thin bilayer model was able to explain some aspects of H2S sensing performance of this promising system. However, experimental researches have indicated that response values for this system are very diverse and various SnO2-CuO multicomponent heterostructures such as rods, wires and particles have much higher response than their thin bilayer counterparts. Understanding the reason behind this differences would help fabrication of optimized sensor element. However, the previous model cannot address this issue mainly...
Investigation of the continuum-rarefied flow and isotope separation using a hybrid CFD-DSMC simulation for UF6 in a gas centrifuge
, Article Annals of Nuclear Energy ; Volume 152 , 2021 ; 03064549 (ISSN) ; Akbar Salehi, A ; Reza Keshtkar, A ; Mahdi Shadman, M ; Hossein Askari, M ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
UF6 gas flow in the total regions of a rotor with the radius of 0.1 m and the length of 1 m in axisymmetric and steady states was simulated using a new hybrid CFD-DSMC method in the OpenFOAM framework. Implicit coupled density-based scheme was performed for CFD method, and Variable Hard Sphere (VHS) and diffuse model were employed in DSMC method. Also, as an initial estimation, the local Knudsen number was applied to determine the interface location between the continuum-rarefied regions (r = 0.0855 m). Then it was modified (r = 0.084 m) to reduce the computational cost. The comparison results of pure CFD and CFD-DSMC methods illustrated that there were large differences between the flow...
Fast and accurate multiscale reduced-order model for prediction of multibreath washout curves of human respiratory system
, Article Industrial and Engineering Chemistry Research ; Volume 60, Issue 10 , 2021 , Pages 4131-4141 ; 08885885 (ISSN) ; Boozarjomehry, R. B ; Sharif University of Technology
American Chemical Society
2021
Abstract
The curve of exhaled inert gas concentration against exhaled volume is called gas washout curve. The slope at the end part of gas washout curve (Sn) is a measure of structural abnormalities. Sn depends on the spatial concentration distribution and dynamic of gas washout, which depends on several mechanisms including asymmetry of airways, nonhomogeneous ventilation, sequential emptying, and gas exchange with blood. Due to a large number of airways in human lungs, using simplified models is inevitable. On the other hand, these simplified models cannot capture some of the mentioned mechanisms and subsequently were not able to predict experimental trend of change in Sn with breath number in...
Fast and accurate multiscale reduced-order model for prediction of multibreath washout curves of human respiratory system
, Article Industrial and Engineering Chemistry Research ; Volume 60, Issue 10 , 2021 , Pages 4131-4141 ; 08885885 (ISSN) ; Boozarjomehry, R. B ; Sharif University of Technology
American Chemical Society
2021
Abstract
The curve of exhaled inert gas concentration against exhaled volume is called gas washout curve. The slope at the end part of gas washout curve (Sn) is a measure of structural abnormalities. Sn depends on the spatial concentration distribution and dynamic of gas washout, which depends on several mechanisms including asymmetry of airways, nonhomogeneous ventilation, sequential emptying, and gas exchange with blood. Due to a large number of airways in human lungs, using simplified models is inevitable. On the other hand, these simplified models cannot capture some of the mentioned mechanisms and subsequently were not able to predict experimental trend of change in Sn with breath number in...
Methane conversion to hydrogen and higher hydrocarbons by double pulsed glow discharge
, Article Plasma Chemistry and Plasma Processing ; Volume 25, Issue 1 , 2005 , Pages 19-29 ; 02724324 (ISSN) ; Matin, N. S ; Sharif University of Technology
2005
Abstract
Pulsed atmospheric glow plasma, sustained by corona discharge, was utilized to convert methane. Analysis by gas chromatography showed that hydrogen and C2-products are the main constituents of outlet mixture while C 2+-products with small concentrations were also detected. The chemical energy efficiency turned out to be about 9% for the best result obtained by this type of reactor. It has been shown that more improvement of energy efficiency is possible by increasing ' the pulse repetition rate
Optimal pipe diameter sizing in a tree-structured gas network: A case study
, Article International Journal of Industrial and Systems Engineering ; Volume 12, Issue 3 , 2012 , Pages 346-368 ; 17485037 (ISSN) ; Mahdavi, I ; Mahdavi Amiri, N ; Sharif University of Technology
2012
Abstract
We design an optimal pipe diameter sizing in a tree-structured natural gas network. Design of pipeline, facility and equipment systems are necessary tasks to configure an optimal natural gas network. A mixed-integer programming model is formulated to minimise the total cost in the network. The aim is to optimise pipe diameter sizes so that the location-allocation cost is minimised. Pipeline systems in natural gas network must be designed based on gas flow rate, length of pipe, gas maximum drop pressure allowance and gas maximum velocity allowance. We use information based on relationship among gas flow rates and pipe diameter sizes considering gas pressure and velocity restrictions. We apply...
Energy and exergy analyses of an integrated gas turbine thermoacoustic engine
, Article Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy ; Volume 225, Issue 4 , June , 2011 , Pages 389-402 ; 09576509 (ISSN) ; Ghorbanian, K ; Gholamrezaei, M ; Sharif University of Technology
2011
Abstract
In this article, an attempt is made to utilize the exhaust gases of a small gas turbine to augment power output through the employment of a thermoacoustic system. A simple gas turbine cycle is selected as the base cycle and it is assumed that the thermoacoustic system is powered only by the waste heat of the base gas turbine. A comprehensive cycle analysis of the integrated gas turbine thermoacoustic engine (IGTTE) is carried out from an energy and exergy point of view. Exergy efficiency and internal exergy efficiency are calculated for the different components of the base gas turbine engine as well as the IGTTE. Value and exergy flow diagrams are used to investigate the possible...
Novel manufacturing process of nanoparticle/Al composite filler metals of tungsten inert gas welding by accumulative roll bonding
, Article Materials Science and Engineering A ; Volume 648 , 2015 , Pages 47-50 ; 09215093 (ISSN) ; Noei Aghaei, V ; Dabiri, A. R ; Amirkhanlou, S ; Akhavan, S ; Fattahi, Y ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
In the present work, accumulative roll bonding (ARB) was used as an effective method for manufacturing nanoparticle/Al composite filler metals of tungsten inert gas (TIG) welding. After welding, the distribution of ceramic nanoparticles and mechanical properties of welds were investigated. By applying ARB, ceramic nanoparticles were uniformly dispersed in the composite filler metals. Consequently, the welds produced by these filler metals had a uniform dispersion of ceramic nanoparticles in their compositions. The test results showed that the yield strength of welds was greatly increased when using the nanoparticle/Al composite filler metals. The improvement in the yield strength was...
Torque data on non-isothermal rarefied Cylindrical Couette flow
, Article Vacuum ; Volume 121 , November , 2015 , Pages 56-63 ; 0042207X (ISSN) ; Javadi, K ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
Abstract The torque exerted on the walls of a micro cylindrical Couette gas flow is studied using Direct Simulation Monte Carlo (DSMC) method and analytical solutions. An analytical solution for temperature filed under specified wall heat flux condition is proposed using a previously introduced power-law (PL) wall-scaling approach. The results of cylindrical Couette flow under specified wall heat flux condition are compared with those of isothermal flow. The effects of rarefaction, compressibility, tangential momentum accommodation coefficient (TMAC) and gas-surface heat exchange on the torque values are investigated for slip to free molecular flow regimes. The results indicate that the...
Simulation of 3D freely bubbling gas-solid fluidized beds using various drag models: TFM approach
, Article Chemical Engineering Research and Design ; Volume 100 , 2015 , Pages 377-390 ; 02638762 (ISSN) ; Molaei Dehkordi, A ; Sharif University of Technology
Institution of Chemical Engineers
2015
Abstract
In this article, 3D modeling and simulation of bubbling fluidized beds has been conducted using various drag models, and the model predictions were validated against reported experimental data and 2D simulation results. In this regard, different drag models reported in the literature including Gidaspow, Syamlal-O'Brien, Hill-Koch-Ladd, and Wen-Yu were applied. A standard Two-Fluid Model (TFM) closed by the Kinetic Theory of Granular Flows (KTGF) was used to simulate bubbling gas-solid fluidized beds. Excellent agreements between the simulation results and experimental data, concerning bed expansion ratio, gas volume fraction, and time-averaged particles velocity, were found over a wide range...
Fabrication of gas ionization sensor using carbon nanotube arrays grown on porous silicon substrate
, Article Sensors and Actuators, A: Physical ; Volume 162, Issue 1 , 2010 , Pages 24-28 ; 09244247 (ISSN) ; Iraji Zad, A ; Razi, F ; Mortazavi, S. Z ; Sharif University of Technology
2010
Abstract
We fabricated gas sensors based on field ionization from multiwalled carbon nanotube (MWCNT) arrays grown on porous silicon templates. MWCNTs were grown through thermal chemical vapor deposition. We measured breakdown voltages, discharge and pre-discharge currents of the device for various gases in different concentrations. Our gas ionization sensors (GIS) presented good sensitivity, selectivity and short response time. The GISs based on porous substrates showed higher discharge current and good mechanical stability in comparison to those which were fabricated on polished silicon substrates. Additionally, we applied a high electric field to align CNTs. This increased the pre-breakdown...
Exergic, economic and environmental impacts of natural gas and diesel in operation of combined cycle power plants
, Article Energy Conversion and Management ; Volume 109 , 2016 , Pages 103-112 ; 01968904 (ISSN) ; Joda, F ; Bozorgmehry Boozarjomehry, R ; Sharif University of Technology
Elsevier Ltd
Abstract
Combined cycle power plants (CCPPs) play an important role in electricity production throughout the world. Their energy efficiency is relatively high and their production rates of greenhouse gases are considerably low. In a country like Iran with huge oil and gas resources, most CCPP's use natural gas as primary fuel and diesel as secondary fuel. In this study, effect of using diesel instead of natural gas for a selected power plant will be investigated in terms of exergy, economic and environmental impacts. The environmental evaluation is performed using life cycle assessment (LCA). In the second step, the operation of the plant will be optimized using exergy and economic objective...
The simulations of flow and heat over microscale sensors in supersonic rarefied gas flows using DSMC
, Article ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer, 4 January 2016 through 6 January 2016 ; Volume 2 , 2016 ; 9780791849668 (ISBN) ; Mosayebi, G ; Sharif University of Technology
American Society of Mechanical Engineers
Abstract
As the use of MEMS-based devices and systems are continuously increasing, the understanding of their correct characteristics becomes so serious for the related researches. In this study, the supersonic rarefied gas flow over microscale hotwires is investigated using the Direct Simulation Monte Carlo (DSMC) method. Indeed, the DSMC has been accepted as a powerful method to study the rarefied gas flow especially in transitional regime. Therefore, it can be considered as a reliable method to investigate the rarefied supersonic flow over microscale objects including the microscale hotwires. In this work, we study the effective parameters, which affect the performance of these sensors at constant...
On the importance of gel rigidity and coverage in a smart water shutoff treatment in gas wells
, Article Journal of Natural Gas Science and Engineering ; Volume 31 , 2016 , Pages 808-818 ; 18755100 (ISSN) ; Escrochi, M ; Riazi, M ; Ayatollahi, S ; Sharif University of Technology
Abstract
This paper addresses a conceptual study on different aspects of a novel smart treatment method for a relatively new challenge of saline water production from low permeability lenses of high flow gas wells. Selective sealing of such lenses along with minor effect on gas productivity usually faces practical difficulties due to the inherent permeability contrast. Engineered application of salt sensitive gellan biopolymer through a smart treatment scenario that includes a protective gas flow proved its ability for treating such challenge. This paper investigates the importance of the gel rigidity and its coverage in the smart treatment scenario through considering the brine salinity and the...