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Optimization of Synthesis Method and Operational Improvement of High Temperature Water-gas Shift Catalyst
, M.Sc. Thesis Sharif University of Technology ; Baghghalha, Morteza (Supervisor) ; Kazemeini, Mohammad (Supervisor) ; Bahmani, Mohsen (Co-Advisor)
Abstract
The water-gas shift reaction, as a vital reaction in industry especially as a source of hydrogen for the manufacture of ammonia, is influential for all of the scientists and researchers in chemical engineering all around the world. In this research, high temperature water-gas shift (HTS) catalysts were investigated in order to study synthesis parameters and improvement of their performance and catalytic activity. The two catalyst categories; non pre-active and pre-active (magnetite-based samples, not requiring a reduction step prior to use) were prepared by co-precipitation method, using chloride, sulfate and nitrate metal (Fe, Cr, Cu) precursors and NaOH as precipitating agent (the aging...
Zero-Sum Flows in Designs and Hypergraphs
, M.Sc. Thesis Sharif University of Technology ; Akbari, Saieed (Supervisor)
Abstract
Let X = fx1; : : : ; xng be the set of vertices of a hypergraph H and E = fe1; : : : ; emg be the set of its edges. The incidence matrix of hypergraph H is an n m and (0; 1)-matrix, N, such that nij = 1 if xi 2 ej and nij = 0, otherwise. A zero-sum flow for H is a vector with non-zero entries that is in the null space of N. A zero-sum k-flow is a flow with non-zero integer entries that absolue value of each entry is at
most k 1. In this thesis we study the existence of zero-sum flows for designs and hypergraphs. Also we consider zero-sum 3-flows in 2-Steiner designs
most k 1. In this thesis we study the existence of zero-sum flows for designs and hypergraphs. Also we consider zero-sum 3-flows in 2-Steiner designs
An Empirical Study of the Relationship between Emergent States and Behavioral Processes of the Board
, M.Sc. Thesis Sharif University of Technology ; Alavi, Babak (Supervisor)
Abstract
In this research study, the reciprocal relationship between Emergent States and Team Processes has been analyzed in boards of directors, by using case study method with semi-structured interview as the method of data collection and thematic analysis as the method of data analysis. This research was conducted on the companies which are active in Information Technology industries, their size is in the range of SMEs, and have passed the early startup stage and an external investor has joined the board. After thematic analysis, narrating each case’s story, and theoretical analysis on each case, the obtained results are demonstrated with discussion on both cases, introducing a theoretical model,...
A hybrid analytical-numerical model for predicting the performance of the Horizontal Ground Heat Exchangers
, Article Geothermics ; Volume 101 , 2022 ; 03756505 (ISSN) ; Hakkaki Fard, A ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
Horizontal Ground Heat Exchangers (HGHE) as a means of exploiting geothermal energy has come to the fore for a few decades. Various analytical and Computational Fluid Dynamics (CFD) methods have been proposed to predict the performance of the HGHEs. The available analytical approaches are fast; however, they are based on various simplifications and assumptions, affecting their accuracy. On the other hand, CFD methods are more accurate, but their computational cost is a burden. Therefore there is an acute need for an accurate and fast method for predicting the long-term performance of HGHEs. To this aim, this study puts forward a novel hybrid analytical-numerical model for predicting the...
Modeling of Heat Transfer and Thermo-Mechanical Contact in Fractured Medium using XFEM Method
, M.Sc. Thesis Sharif University of Technology ; Khoei, Amir Reza (Supervisor)
Abstract
Heat transfer phonomenon is very important in solids and fluids, specially in fractured medium which has a major role in response of domain.In fact the fracture in special conditions can prevent the heat flow and in different conditions can aid the heat flow and conducts it.Propagation of hydraulic fracture by non-isothermal injection in fractured domain is a problem that has many physical phenomena like modeling of porous medium, heat transfer process in medium, discontinuities presence, concevtion of heat process by hydraulic fracture, fracture propagation, interaction of hydraulic fracture with existing fractures, junctions of cracks, contact phenomenon, etc. Therfore, solving this...
Modeling convective heat propagation in a fractured domain with x-fem and least square method
, Article ASME 2017 International Mechanical Engineering Congress and Exposition, IMECE 2017, 3 November 2017 through 9 November 2017 ; Volume 8 , 2017 ; 9780791858431 (ISBN) ; Khoei, A. R ; ASME ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2017
Abstract
The main goal of the current study is developing an advanced and robust numerical tool for accurate capturing heat front propagation. In some applications such as impermeable medium, Heat transfer in the surrounding domain of fracture acts just as a conduction process but the heat transfer through the fractures appears as a convection process. From a mathematical point of view, a parabolic partial differential equation (PDE) should be solved in the surrounding domain whereas a hyperbolic PDE should be solved in the domain of fractures. In fact, they have completely different treatments and this is one of the complicated problems in this area. In this paper, the presence of fractures and...
A new method for estimating Score Function Difference (SFD) and its application to Blind Source Separation
, Article 13th European Signal Processing Conference, EUSIPCO 2005, Antalya, 4 September 2005 through 8 September 2005 ; 2005 , Pages 1507-1510 ; 1604238216 (ISBN); 9781604238211 (ISBN) ; Babaie Zadeh, M ; Jutten, C ; Sharif University of Technology
2005
Abstract
Score Function Difference (SFD) is a recently proposed "gradient" for mutual information which can be used in Blind Source Separation algorithms based on minimization of mutual information. To be applied to practical problems, SFD must be estimated from the data samples. In this paper, a new method for estimating SFD is proposed. To compare the performance of this new estimator with other proposed SFD estimation methods, we have applied them in separating linear instantaneous mixtures. It will be seen that our method performs superior to all other methods previously proposed for estimation of SFD
A Mathematical Model to Prediction of the Formation of Microporsities in Aluminium Alloy Cast Parts
, M.Sc. Thesis Sharif University of Technology ; Varahram, Naser (Supervisor) ; Davami, Parviz (Supervisor)
Abstract
Today, application of aluminium alloys in industries is developing. And this is because of some specification of these alloys like high proportion of the Strength per weight. One of the most useful alloys of this alloy group is A356 alloy that contain 7 % Silicon and 0.4 Percent of magnesium, this alloy because of cast ability, heat treat ability specification is use developing in air and automotive industries. But usage of this alloys combined with some difficulties like low fluidity and formation of shrinkage and gas porosities in this alloys. In present work with programmer software Visual Fortran, based on Finite difference method, a simulation model has been developed, can solve heat...
Off-line Arabic/Farsi handwritten word recognition using RBF neural network and genetic algorithm
, Article Proceedings - 2010 IEEE International Conference on Intelligent Computing and Intelligent Systems, ICIS 2010, 29 October 2010 through 31 October 2010, Xiamen ; Volume 3 , 2010 , Pages 352-357 ; 9781424465835 (ISBN) ; Alamdar, F ; Azmi, R ; Haratizadeh, S ; Sharif University of Technology
2010
Abstract
In this paper an off-line ArabiclFarsi handwritten recognition Algorithm on a subset of Farsi name is proposed. In this system, There is no sub-word segmentation phase. Script database includes 3300 images of 30 Farsi common names. The features are wavelet coefficients extracted from smoothed word image profiles in four standard directions. The Centers of competitive layer of RBF neural network have been determined by combining GA and K-Means clustering algorithm. Weights of supervised layer has been trained by using LMS rule and the distances of feature vector of each sample to the centre of RBF network have been computed based on warping function. Experimental results show advantages of...
Qualitative Study of the Dynamic Adsorption Layer by Bubble Rising Method
, M.Sc. Thesis Sharif University of Technology ; Bastani, Dariush (Supervisor) ; Lotfi, marzieh (Co-Advisor)
Abstract
Surface phenomena and dynamic interfacial properties plays a significant role in multiphase gas-liquid & liquid-liquid processes applied in different industrial applications. However, current laboratory equipment and represented methods for dynamic and unsteady state condition caused by motivation of interface of two phases (like rising bubble), in purpose of qualitative investigation of interphase properties are not satisfying enough. Also, common modeling methods are represented with lots of modified assumptions which are not validated properly with experimental results. In current thesis, with development of laboratory tools and applying the “rising bubble method” for investigating the...
Optimizing the operation of current differential protection by power differential relay for three phase transformer
, Article 2006 IEEE GCC Conference, GCC 2006, Manama, 20 March 2006 through 22 March 2006 ; 2006 ; 9780780395909 (ISBN) ; Esmi Jahromi, M ; Ranjbar, A. M ; Sharif University of Technology
2006
Abstract
To avoid the needless trip by magnetizing inrush current, the second harmonic component is commonly used for blocking differential relay in power transformers. However, the main problems of the current comparison method are in the very high inrush currents and relatively small fault currents regarding winding short circuits. Also The second harmonic component in fault current is increased in long lines which may blocks the relay operation. This paper describes a method to discriminate internal fault from inrush current and faults with a high second harmonic component by the sum of active power flowing into the transformer from each terminal. The average power is almost negligible for...
Stability Improvement and Protection of Grid-following Bidirectional Three-phase Voltage-sourced Converters under Unbalanced Grid Conditions
, M.Sc. Thesis Sharif University of Technology ; Mokhtari, Hossein (Supervisor) ; Karimi, Houshang (Co-Supervisor)
Abstract
With the increasing expansion of modern DC loads and utilizing energy storage systems along with distributed renewable energy resources, grid-following bidirectional voltage-sourced converters (GFBVSCs) with fast dynamic performance are required. Due to the presence of single-phase loads and asymmetrical short circuit faults, unbalanced grid voltage conditions are available in the distribution system. Under unbalanced conditions, an oscillating component with a frequency of twice the grid angular frequency appears on the DC side. Removing double-frequency ripple in the DC link voltage without third harmonic current injection and reactive power injection to the grid based on the grid codes to...
Synthesis of NiAl-TiC composites from elemental powders by volume combustion method
, Article Materials Science and Technology (United Kingdom) ; Volume 35, Issue 7 , 2019 , Pages 831-838 ; 02670836 (ISSN) ; Minagar, A ; Naseri, G ; Bahmani, A ; Malekan, M ; Sharif University of Technology
Taylor and Francis Ltd
2019
Abstract
NiAl-TiC composites were synthesised by volume combustion (VC) method from elemental powders to improve the mechanical properties and high temperature performance of nickel aluminide. Synthesised specimens with porous nature were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analysis. XRD results showed that NiAl was dominant phase and other phases like Al 3 Ni 2 (in NiAl + 5 wt-% TiC, NiAl + 10 wt-% TiC specimens) and AlNi 3 (in equimolar NiAl-TiC) were present in specimens. Synthesised specimens of NiAl, NiAl + 5 wt-% TiC, NiAl + 10 wt-% TiC, NiAl + 15 wt-% TiC and equimolar NiAl-TiC achieved Vickers...
Solidification of A356 Al alloy: Experimental study and modeling
, Article Kovove Materialy ; Volume 49, Issue 4 , 2011 , Pages 253-258 ; 0023432X (ISSN) ; Mazahery, A ; Bahmani, A ; Davami, P ; Varahram, N ; Sharif University of Technology
2011
Abstract
While it is well recognized that microstructure controls the physical and mechanical properties of a material, the complexity of the microstructure often makes it difficult to be simulated by analytical or numerical techniques. In this paper we present a suitable approach to compute microstructures within a casting using the finite element technique. This technique allows implementing microstructure data from experiments and equations that describe microstructure as function of local solidification parameters. The comparison of this model's predictions with the ones in the literature and also experimental measurements of secondary dendrite arm spacing, average length and diameter of silicon...
A mathematical model for prediction of microporosity in aluminum alloy A356
, Article International Journal of Advanced Manufacturing Technology ; Volume 64, Issue 9-12 , April , 2013 , Pages 1313-1321 ; 02683768 (ISSN) ; Hatami, N ; Varahram, N ; Davami, P ; Shabani, M. O ; Sharif University of Technology
2013
Abstract
In the present work, a mathematical model was developed based on finite difference method to predict the microporosity distribution in A356 aluminum alloy casting. Heat, mass, and gas conservation equations were solved in this model. Moreover, Darcy's equation was considered in the mushy zone. Results show that the distribution and concentration of microporosities in cast parts vary with both cooling rate and initial gas content. Simulation results were compared with experimental data where proportionally good agreement with experimental results was found. Finally, a complex cast part was simulated presenting the ability of the model to predict the porosities in industrial cast parts
Evaluation of "brand image" Impact on Purchase Intention while Shopping for Cellular Phones in an Online Setting. A study
, M.Sc. Thesis Sharif University of Technology ; Sheikhzadeh, Mehdi (Supervisor) ; Ekhlasi, Amir (Supervisor)
Abstract
Marketing channels are a set of organizations which because of having access to target market and communication with consumers play an effective role in consumer buying process and offering goods and services.The main purpose of this thesis is to investigate consumer buying process in online stores, as a marketing channel. In order to meet the objective and investigate customer’s attitude, the focus is on brand image whose three main components are: store brand image, product brand image, and product specifications. The three components collectively influence customer purchase intention. To have a holistic understanding of purchase process, the value of transaction is defined as a mediator...
Effects of hydrogen level and cooling rate on ultimate tensile strength of Al A319 alloy
, Article Russian Journal of Non-Ferrous Metals ; Vol. 55, issue. 4 , July , 2014 , p. 365-370 ; 10678212 ; Eisaabadi, G. B ; Davami, P ; Varahram, N ; Shabani, M. O ; Sharif University of Technology
2014
Abstract
The present study investigated the effects of initial Hydrogen level and cooling rate on ultimate tensile strength of commercial Al-A319 alloys. Three hydrogen levels (0.01, 0.2, and 0.41 mL/100 grams of melt) and five cooling rate were studied. Total of 45 tensile test bars was prepared (three hydrogen levels × five cooling rate × three repeats). The UTS of the samples was determined though uniaxial tension tests. Furthermore, the microstructures of the samples were studied by standard metallographic technique and image analysis software. Finally the relationship between UTS and microstructurai features—SDAS and fraction of porosity (Fp%)—of the alloys was investigated.Results of tensile...
Fabrication of novel chitosan-g-PNVCL/ZIF-8 composite nanofibers for adsorption of Cr(VI), As(V) and phenol in a single and ternary systems
, Article Carbohydrate Polymers ; Volume 224 , 2019 ; 01448617 (ISSN) ; Koushkbaghi, S ; Darabi, M ; ZabihiSahebi, A ; Askari, A ; Irani, M ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
The chitosan-grafted-poly(N-vinylcaprolactam) (chitosan-g-PNVCL) nanofibers were synthesized via electrospinning method. ZIF-8 metal-organic frameworks nanoparticles were incorporated into the nanofibers for adsorption of Cr(VI), As(V) and phenol from water. The BET, FTIR, XRD and SEM analysis were carrfried out to obtain the characteristics of nanofibers. The optimum parameters of ZIF-8 content, pH, contact time, adsorbent dosage, and initial concentration of adsorbates on the Cr(VI), As(V) and phenol removal were studied. The reusability of synthesized nanofibers for five sorption-desorption cycles was also examined. The maximum experimental adsorption capacity of the...
Sole versus dual-sourcing under order dependent lead-times and prices [electronic resource]
, Article Computers And Operations Research, Published in: Elsevier Journals ; Volume 36, Issue 12, December 2009, Pages 3272–3280 ; Eshghi, Kourosh ; Sharif University of Technology
Abstract
In this paper, we consider a dual-sourcing model with constant demand and stochastic lead times. Two suppliers may be different in terms of purchasing prices and lead-time parameters. The ordering takes place when the inventory level depletes to a reorder level, and the order is split among two suppliers. Unlike previous works in the order splitting literature, the supply lead time between vendor and buyer as well as unit purchasing prices is considered to be order quantity dependent. The proposed model finds out the optimal reorder point, order quantity and splitting proportion, using a solution procedure. Numerical results show that neglecting the relationship between ordering batch size...