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Behaviour of metal powders during cold and warm compaction
, Article Powder Metallurgy ; Volume 49, Issue 3 , 2006 , Pages 281-287 ; 00325899 (ISSN) ; Veltl, G ; Sharif University of Technology
2006
Abstract
An instrumented die was used to investigate the behaviour of metal powders during cold (ambient temperature) and warm (up to 140°C) compaction. This instrument enables simultaneous measurement of density, die wall friction coefficient, the triaxial stresses acting on the powder during the course of compaction and ejection pressure. Commercial iron, titanium, aluminium, 316L stainless steel (SS) and aluminium-silicon powders were employed for investigation. The results demonstrated the advantages of powder preheating on the compaction behaviour of metal powders concerning green density, dimensional changes, frictional behaviour, ejection characteristics and compactibiiity. However, the...
3D numerical analysis of velocity profiles of PD, EO and combined PD-EO flows through microchannels
, Article 4th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM2006, Limerick, 19 June 2006 through 21 June 2006 ; Volume 2006 A , 2006 , Pages 209-214 ; 0791847608 (ISBN); 9780791847602 (ISBN) ; Monazami, R ; Salehi, M. A ; Sharif University of Technology
American Society of Mechanical Engineers
2006
Abstract
In this paper, a three-dimensional numerical model is developed to analyze flow characteristics of pressure driven, electroosmotic and combined pressure driven-electroosmotic flows through micro-channels. The governing system of equations consists of the electric-field and flow-field equations. The solution procedure involves three steps. 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 charged fluid is calculated along the...
A novel mechanism for heat transfer enhancement through microchannels using electrokinetic effect
, Article 2005 ASME Summer Heat Transfer Conference, HT 2005, San Francisco, CA, 17 July 2005 through 22 July 2005 ; Volume 3 , 2005 , Pages 949-955 ; 0791847314 (ISBN); 9780791847312 (ISBN) ; Manzari, M. T ; Monazami, R ; Bazargan, V ; Sharif University of Technology
2005
Abstract
In this paper a three-dimensional numerical model is developed in order to study the heat transfer enhancement in rectangular microchannels due to electrokinetic effect. The electrokinetic body force on fluid elements gives some superior convective transport properties to the flow relative to pure pressure driven flow in microchannels. Unlike the conventional parabolic velocity profile of pressure driven laminar flow, the electrokinetic body force transforms the velocity profile to a slug-like flow. Due to sharp velocity gradient near the wall, the convective heat transfer properties of the flow are improved dramatically. Net charge distribution across the channel is obtained by solving the...
Propose and characteristics study of a new actuation method for micropumps, using membrane buckling
, Article 4th ASME Integrated Nanosystems Conference: Design, Synthesis, and Applications, Berkeley, CA, 14 September 2005 through 16 September 2005 ; 2005 , Pages 25-26 ; 0791842088 (ISBN); 9780791842089 (ISBN) ; Ahmadian, M. T ; Salehi, H ; Monazami, R ; Zade, A. Q ; Sharif University of Technology
American Society of Mechanical Engineers
2005
Abstract
In this paper, we present a novel idea on actuation system in micropumps. The prominent goal of this paper is to propose and prove a mechanical actuation system which works in high frequency and has good ability in producing flow and pressure in micro actuation system. As like as other common micropumps, the proposed scheme is consisted of two check valves and an actuation space. The actuation space includes a volume of liquid in a chamber and a cylindrical membrane as the actuator. The main aspect of this idea is employment of buckling as a consequence of incensement of its internal pressure caused by temperature rising in the membrane. Rise of temperature is done by passing a controllable...
Measurement and correlation of vapor-liquid equilibria of the aqueous poly(ethylene glycol) + sodium citrate and poly(ethylene glycol) + potassium citrate systems
, Article Fluid Phase Equilibria ; Volume 262, Issue 1-2 , 2007 , Pages 137-148 ; 03783812 (ISSN) ; Zafarani Moattar, M. T ; Taghikhani, V ; Ghotbi, C ; Sharif University of Technology
Elsevier
2007
Abstract
In this study, water activities for the ternary systems of PEG6000 + sodium citrate (Na3Cit) + H2O and PEG6000 + potassium citrate (K3Cit) + H2O have been measured using an improved isopiestic method over the entire homogeneous mixing range at 298.15 K. From these measurements, values of the vapor pressure of solutions were also determined. The experimental data for the activity of water, collected in this work, were accurately correlated with local composition based models of the NRTL, modified NRTL, Wilson and modified Wilson. The results showed that these models can accurately correlate the water activity data generated in this work. © 2007 Elsevier B.V. All rights reserved
High pressure effects in YBCO and YSCO
, Article Physica Status Solidi C: Conferences ; Volume 1, Issue 7 , 2004 , Pages 1859-1862 ; 16101634 (ISSN) ; Mossalla, B ; Akhavan, M ; Sharif University of Technology
2004
Abstract
Electronic structure calculations for two isofamilies, YBa 2Cu3O7 (YBCO) and YSr2Cu 3O7 (YSCO) high Tc cuprates, have been done for ambient and high pressures (-15 GPa
Mechanical and chemical pressure effects on the AeFe 2 As 2 (Ae = Ba, Sr, Ca) compounds: Density functional theory
, Article Computational Materials Science ; Volume 160 , 2019 , Pages 233-244 ; 09270256 (ISSN) ; Hadipour, H ; Akhavan, M ; Sharif University of Technology
Elsevier B.V
2019
Abstract
We have studied the pressure-induced structural, magnetic and electronic properties of AeFe 2 As 2 (Ae = Ba, Sr, Ca) compounds in the framework of density functional theory within the GGA-PBE method. The effects of chemical pressure generated by Sr and Ca substitutions in BaFe 2 As 2 have been investigated. We have found a magnetic transition at the same primitive unit cell volume, around 81 Å 3 for the (Ba⧹Ca)Fe 2 As 2 compounds, which predicts a magnetic transition pressure of 12 GPa for SrFe 2 As 2 . The structural parameters of FeAs 4 tetrahedra are obtained after ionic relaxation and compared with the existing experimental results. The change of these internal parameters is ascribed to...
The Effect of Pressure on Microstructure and Mechanical Properties of TLP Bonded Dual Phase Steels
, M.Sc. Thesis Sharif University of Technology ; Ekrami, Ali Akbar (Supervisor)
Abstract
Dual Phase ferritic-martensitic steels are kind of high strength low alloy steels (HASLA) which are widely used in industry because of their strength and formability. Since welding of dual phase steels in conventional welding methods causes structural change and Subsequently alters mechanical properties of both weld zone and heat affected zone(HAZ), additional operations which are not commercially viable is needed to achieve a dual phase structure in structurally changed regions. In this study, transient liquid phase (TLP) bonding method is used during dual phasing process in order to preserve dual phase ferritic-martensitic structure and avoid extra heat treatment. Applied pressure during...
The Effect of Pressure on the Coexistence of Superconductivity and Magnetism in RuSr2GdCu2O8 and RuSr2Gd1.4Ce0.6Cu2O10-δ
, Ph.D. Dissertation Sharif University of Technology ; Akhavan, Mohammad (Supervisor)
Abstract
The coexistence of long-range magnetic order and superconductivity in the ruthenocuprate families, Ru1212 and Ru1222 has been studied both theoretically and experimentally. Historically these two different phases are incompatible with each other and in the most previous research reported on the coexistence of these phases, there have been observed separated magnetic and superconducting phases. However in the ruthenocuprate families, there is a single phase with both magnetic and superconducting phase which coexist with each other. It has been determined that superconductivity arises in CuO2 planes, and magnetic orders occur in RuO2. From experimental point of view, we have investigated the...
Modeling the Effect of Pressure on the Shrinkages Distribution
, M.Sc. Thesis Sharif University of Technology ; Davami, Parviz (Supervisor) ; Abachi, Parvin (Supervisor)
Abstract
Due to the shrinkage defects, casting parts is sometimes unusable; as a result, researchers is tackling porosity removal problem, so that they would be able to cast parts in a way that have the least porosity. Nowadays, simulation is used to predict the location of the porosity. The design and the elimination of defects, which leads to additional costs, can reduce the overall costs in the projects.
In this thesis, we focus on shrinkage defects. The main cause of porosity is the drop of pressure. As a matter of fact, the thermal agitation of the molecules is weaker than the strong intermolecular forces that would pull the molecules; therefore, the molten metals’ density will be increased...
In this thesis, we focus on shrinkage defects. The main cause of porosity is the drop of pressure. As a matter of fact, the thermal agitation of the molecules is weaker than the strong intermolecular forces that would pull the molecules; therefore, the molten metals’ density will be increased...
Modeling and estimation of unmeasured variables in a wastegate operated turbocharger
, Article Journal of Engineering for Gas Turbines and Power ; Vol. 136, Issue. 5 , 2014 ; ISSN: 07424795 ; Vossoughi, G ; Alasty, A ; Sharif University of Technology
Abstract
Estimation of relevant turbocharger variables is crucial for proper operation and monitoring of turbocharged (TC) engines, which are important in improving fuel economy of vehicles. This paper presents mean-value models developed for estimating gas flow over the turbine and the wastegate (WG), the wastegate position, and the compressor speed in a TC gasoline engine. The turbine is modeled by an isentropic nozzle with a constant area and an effective pressure ratio calculated from the turbine upstream and downstream pressures. Another physically sensible model is developed for estimating either the WG flow or position. Provided the WG position is available, the WG flow is estimated using the...
Temperature and composition effect on CO2 miscibility by interfacial tension measurement
, Article Journal of Chemical and Engineering Data ; Volume 58, Issue 5 , March , 2013 , Pages 1168-1175 ; 00219568 (ISSN) ; Escrochi, M ; Ayatollahi, S ; Sharif University of Technology
2013
Abstract
Crude oil reservoirs have different temperatures, compositions, and pressures, therefore oil recovery performance by CO2 injection varies from one case to another. Furthermore, it is predicted that lower interfacial tension between injected CO2 and reservoir fluid results in more oil recovery. In this study, we investigate the effect of temperature on the equilibrium interfacial tension between CO2 and three different oil fluids at different pressures. Also minimum miscible pressure (MMP) is measured by the vanishing interfacial tension (VIT) technique to determine the temperature effect on the CO2 miscible gas injection. The results on different pure and mixtures of hydrocarbon fluids show...
Toward an equation of state for water inside carbon nanotubes
, Article Journal of Physical Chemistry B ; Volume 116, Issue 16 , April , 2012 , Pages 4943-4951 ; 15206106 (ISSN) ; Parsafar, G. A ; Sharif University of Technology
American Chemical Society
2012
Abstract
Water inside carbon nanotubes as an example of nanoconfined water has gained noticeable attention, in both theoretical and applied aspects. Molecular simulation has played a major role in the studies in this field. Yet, there is a need for systematic study of simulation results and compilation of scientifically reliable predictive relations. Here we present Monte Carlo simulations of water inside carbon nanotubes with different radii. An equation of state which was derived on the basis of the extended Lennard-Jones (12,6,3) as the effective pair potential is chosen for the system of water inside the carbon nanotubes. The equation of state is modified to take the effects of anisotropic...
An experimental and theoretical study of the effects of excess air ratio and waste gate opening pressure threshold on NOx emission and performance in a turbocharged CNG SI engine
, Article International Journal of Engineering, Transactions B: Applications ; Volume 28, Issue 2 , March , 2015 , Pages 251-260 ; 1728-144X (ISSN) ; Benisi, A. H ; Mozafari ; Sharif University of Technology
Materials and Energy Research Center
2015
Abstract
In this research, effects of excess air ratio and waste gate opening pressure threshold on NOx emission and performance in a turbocharged CNG SI engine are studied experimentally at 13-mode ECE-R49 test cycle. The engine power, boost ratio and charge air temperature are investigated experimentally at the cycle for different waste gate pressure thresholds. A code is developed in MATLAB environment for predicting engine performance and NOx and the results are validated with the research experiments. The effects of excess air ratio on the engine indicated power and specific fuel consumption as well as NOx emission are numerically investigated at WOT by the code. NOx emission of WOT is max at...
Modelling the temperature rise effect through high-pressure torsion
, Article Materials Science and Technology (United Kingdom) ; Volume 32, Issue 12 , 2016 , Pages 1218-1222 ; 02670836 (ISSN) ; Kazeminezhad, M ; Sharif University of Technology
Taylor and Francis Ltd
Abstract
An approach composed of the thermodynamics-based dislocation model and the Taylor theory is used to investigate the evolution of microstructure and flow stress during high-pressure torsion (HPT). The incremental temperature rise is considered through the modelling of HPT. The temperature can affect the annihilation of dislocations and thus the dislocation density. The model predicts the dislocation density, sub-grain size and flow stress during HPT. The modelling results are compared with the experimental data and the modelling results without considering the incremental temperature rise. A remarkable agreement is observed between the modelling results with considering the temperature rise...
Study of the densification of a nanostructured composite powder. part 1: effect of compaction pressure and reinforcement addition
, Article Materials Science and Engineering A ; Volume 486, Issue 1-2 , 2008 , Pages 580-584 ; 09215093 (ISSN) ; Farnoush, H ; Salahi, E ; Pourazrang, K ; Sharif University of Technology
2008
Abstract
The compressibility behavior of Al-AlN nanostructured composite powder with different amount of reinforcement content was studied. The composite powder was synthesized by blending and high-energy milling process for 25 h. Williamson-Hall method was applied to determine the crystallite size after milling process. To investigate the role of reinforcement particles in consolidation of composite powders, monolithic aluminum powder was examined. Samples were made at different pressures and relationships were established between the compaction pressure and the density of the compacts. The modified Heckel equation was used to assume the pressure effect on yield strength and then was compared with...
Study of the VAPEX process in fractured physical systems using different solvent mixtures
, Article Oil and Gas Science and Technology ; Volume 63, Issue 2 , 2008 , Pages 219-227 ; 12944475 (ISSN) ; Kharrat, R ; Vossoughi, S ; Ghotbi, C ; Sharif University of Technology
2008
Abstract
In this work, the vapour extraction (VAPEX) process is studied experimentally in a rectangular physical model at moderate-high pressure. The solvent was either pure propane or a mixture of propane/ methane with different compositions. The solvent and carrier gas were totally mixed before injection, so that a solvent with the desired composition flowed through the injector during experiments, and the solvent mixture was in thermodynamic equilibrium before injection into VAPEX cell. Effects of pressure and composition of solvent were studied. Results showed that at a fixed pressure, the process is more effective with pure solvent compared to the use of solvent mixtures. The main feature of...
Experimental study of forced convection heat transfer from a cam shaped tube in cross flows
, Article International Journal of Heat and Mass Transfer ; Volume 50, Issue 13-14 , 2007 , Pages 2605-2611 ; 00179310 (ISSN) ; Lavasani, A. M ; Sharif University of Technology
2007
Abstract
An experimental investigation has been conducted to clarify forced convection heat transfer characteristic and flow behavior of an isothermal cam shaped tube in cross flow. The range of angle of attack and Reynolds number based on an equivalent circular tube are within 0° < α < 180° and 1.5 × 104 < Reeq < 2.7 × 104, respectively. The results show that the mean heat transfer coefficient is a maximum at about α = 90° over the whole range of the Reynolds numbers. It is found that thermal hydraulic performance of the cam shaped tube is larger than that of a circular tube with the same surface area except for α = 90° and 120°. Furthermore, the effect of the diameter of the cam shaped tube upon...
Gas permeability measurement in polyethylene and its copolymer films
, Article Materials and Design ; Volume 28, Issue 9 , 2007 , Pages 2528-2532 ; 02613069 (ISSN) ; Razavi, J ; Mousavi, S. A ; Sharif University of Technology
Elsevier Ltd
2007
Abstract
In this research, low density polyethylene (LDPE) and poly(ethylene-co-vinyl acetate) (EVA) were used as polymeric materials. The methods used to produce LDPE and EVA was film blowing and thermal-dry phase inversion. The amount of permeability, diffusivity and solubility of O2 and CO2 through above polymers were obtained and also the effect of temperature, pressure and film thickness for LDPE was measured. To study film cross-section morphology in EVA, scanning electron microscopy (SEM) was applied. The results showed that the amount of permeability and solubility were decreased by increasing film thickness but diffusivity was increased. However, by increasing temperature, permeability,...
Buckling of cracked cylindrical thin shells under combined internal pressure and axial compression
, Article Thin-Walled Structures ; Volume 44, Issue 2 , 2006 , Pages 141-151 ; 02638231 (ISSN) ; Estekanchi, H. E ; Sharif University of Technology
2006
Abstract
Linear eigenvalue analysis of cracked cylindrical shells under combined internal pressure and axial compression is carried out to study the effect of crack type, size and orientation on the buckling behavior of cylindrical thin shells. Two types of crack are considered; through crack and thumbnail crack. Our calculations indicate that depending on the crack type, length, orientation and the internal pressure, local buckling may precede the global buckling of the cylindrical shell. The internal pressure, in general, increases the buckling load associated with the global buckling mode of the cylindrical shells. In contrast, the effect of internal pressure on buckling loads associated with the...