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    Thermodynamic analysis of combustion processes and pollutants emission using nonlinear optimization approach

    , Article Asia-Pacific Journal of Chemical Engineering ; Volume 7, Issue 1 , AUG , 2012 , Pages 80-85 ; 19322135 (ISSN) Farshchi Tabrizi, F ; Zolfaghari Sharak, A ; Zolfaghari Shahrak, A ; Sharif University of Technology
    2012
    Abstract
    Mathematical formulation and modeling of combustion processes is an important tool in the understanding of this phenomenon. Determination of equilibrium temperature and composition is often the first stage in calculation of combustion characteristics. There are number of different techniques for simulation of combustion process. In this study a basic model has been developed based on the minimization of Gibb's free energy to simulate the combustion processes. A nonlinear mathematical optimization has been developed based on Lagrange multipliers and solved using Quasi-Newton method written in MathCAD environment. The effect of various parameters such as initial temperature, pressure, and... 

    Theoretical and experimental study of cascade solar stills

    , Article Solar Energy ; Volume 90 , April , 2013 , Pages 205-211 ; 0038092X (ISSN) Ziabari, F. B ; Sharak, A. Z ; Moghadam, H ; Tabrizi, F. F ; Sharif University of Technology
    2013
    Abstract
    Most part of Iran is dominated by arid and semi-arid areas due to low annual rainfall. The need for production of fresh water from brackish water is considerably high, especially in dry regions. In this study 1 month daily-based experimental data from a solar still site has been reported. The technical and operational problems of this site which finally contributed to the total cease of the site are described. Then a detailed analysis is investigated on progress of a prototype which constructed in order to solve the site's problems. The results of 1 month of experimental data of the final design showed that the last prototype could be used to solve the current problems of the site. The... 

    Assessment of optimal reaction progress variable characteristics for partially premixed flames

    , Article Combustion Theory and Modelling ; Volume 26, Issue 5 , 2022 , Pages 797-830 ; 13647830 (ISSN) Chitgarha, F ; Ommi, F ; Farshchi, M ; Sharif University of Technology
    Taylor and Francis Ltd  2022
    Abstract
    The reaction progress variable is a crucial concept in the advanced flamelet combustion models. As a controlling variable, a well-defined progress variable must consider the essential features of the combustion process. It is usually a heuristically defined linear combination of some major chemical species mass fractions. However, such a simple definition could lead to inaccurate results for the fuel-rich reactive mixtures or complicated fuels, due to the vast number of chemical species in the combustion process. In this paper, a new method for generating a reaction progress variable is proposed through solving a constrained optimisation problem. The proposed method uses a genetic algorithm... 

    Comparative analysis of the boundary transfer method with other near-wall treatments based on the k-ε turbulence model

    , Article European Journal of Mechanics, B/Fluids ; Vol. 44, issue , 2014 , pp. 22-31 ; ISSN: 09977546 Nazif, H. R ; Basirat Tabrizi, H ; Farhadpour, F. A ; Sharif University of Technology
    2014
    Abstract
    Accurate description of wall-bounded turbulent flows requires a fine grid near walls to fully resolve the boundary layers. We consider a locally simplified transport model using an assumed near-wall viscosity profile to project the wall boundary conditions using the boundary transfer method. Related coefficients are obtained numerically. By choosing a near-wall viscosity profile, we derive an analytic wall function, which significantly reduces the CPU costs. The performance of this wall function is compared to other near-wall treatments proposed in the literature for two frequently used benchmark cases: near-equilibrium channel flow and flow over a backward-facing step with separation and... 

    Geometry effects in Eulerian/Granular simulation of a turbulent FCC riser with a (kg-g)-KTGF model

    , Article International Journal of Chemical Reactor Engineering ; Volume 8 , 2010 ; 15426580 (ISSN) Nazif, H. R ; Basirat Tabrizi, H ; Farhadpour, F. A ; Sharif University of Technology
    2010
    Abstract
    Three-dimensional, transient turbulent particulate flow in an FCC riser is modeled using an Eulerian/Granular approach. The turbulence in the gas phase is described by a modified realizable (kg-g) closure model and the kinetic theory of granular flow (KTGF) is employed for the particulate phase. Separate simulations are conducted for a rectangular and a cylindrical riser with similar dimensions. The model predictions are validated against experimental data of Sommerfeld et al (2002) and also compared with the previously reported LES-KTGF simulations of Hansen et al (2003) for the rectangular riser. The (kg-g)-KTGF model does not perform as well as the LES-KTGF model for the riser with a... 

    Large Eddy Simulation of Supercritical Swirling Flow of Injector in a Combustion Chamber

    , Ph.D. Dissertation Sharif University of Technology (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    In the present thesis, the extensive study of reactive and non-reactive supercritical and transcritical flows has been discussed in shear-axial and swirling forms. Considering the need for combustion models with the application of detailed chemistry for accurate simulation of the field, the Laminar Flamelet Models (LFM) are suitable in order to reduce computational expensive. For this purpose, it is necessary to produce thermodynamic tables specific to real gas conditions for the flamelet model. The tables related to the flamelet model in real gas conditions are extracted from the open source software Cantra. The difference point in the Flamelet tables of real gas and ideal gas is for... 

    Simulation of detonation initiation in straight and baffled channels

    , Article Scientia Iranica ; Volume 11, Issue 1-2 , 2004 , Pages 37-49 ; 10263098 (ISSN) Farshchi, M ; Hossainpour, S ; Sharif University of Technology
    Sharif University of Technology  2004
    Abstract
    Euler conservation equations, ideal gas state equations and simplified chemical kinetics models were used to simulate two-dimensional straight and baffled shock tubes. In a straight channel, detonation waves were initiated by a strong shock wave and allowed to travel down the channel to reach a CJ wave condition. It has been shown that a two-step reaction, kinetics model with an induction time delay, resulted in a physically plausible transient solution. The one-step kinetics model solution is only valid at the limit of a steady state CJ wave condition and should not be used for transient problems. The two-step kinetics model was then used to simulate a detonation initiation in a baffled... 

    Numerical Investigation of Laminar Premixed Flame Response to Acoustic Excitation

    , M.Sc. Thesis Sharif University of Technology Behzadi, Milad (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    Flame Response to acoustic excitation which plays an important role in combustion chamber stability state may be found through numerical simulation. A finite volume code of higher order accuracy developed for compressible flows was adopted. Species equations along with a single-step irreversible reaction model were added to this non-reacting program. Changes were also made to the energy equation. Premixed methane/air flame in tubes was studied and the same problem was solved with FLUENT software. It was found that whether the Lewis number is considered constant or temperature dependent has a strong effect on flame structure and shape and that using mean values for gas properties yields out... 

    Unsteady Analysis of a Slinger Combustion Chamber by the Chemical Reactor Network Model

    , M.Sc. Thesis Sharif University of Technology Soroush, Fariborz (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    Up to early seventies, Gas turbine combustor design was very time consuming and costly process including trial and errors through test rigs. Over the time analytical-experimental relationships take place as one of the key rules in the design processes. With the increasing power of computer calculations, computational fluid dynamics find its way in the procedure. Obtaining a deeper understanding of flow conditions and geometry inside the chamber, a great reduction in production time and cost of revisions to rigs and samples were achieved. Finding a precise prediction of polluting elements like NOx (less than 10 ppm) after many run hours and enormous computing resources, CFD methods must... 

    Experimental Study of Low Swirl Burners Interferences

    , M.Sc. Thesis Sharif University of Technology Shahsavari, Mohammad (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    One of the problems associated with lean premixed combustion is their stability. Low swirl flame is a modern technology for reducing NOx emissions and increasing stability.In this thesis, first, the effect of geometric parameters on the flame stability was investigated. This study was carried out in high fuel and oxidizer mixture flow rate. Having find, the most stable burner, two other burners with the same geometrical parameters were built. Stability of these three burners were analyzed. Second, they were located in a ring together in three different relative positions. In each configuration stability and NOx emissions of the burners were determined.The study shows that NOx and CO... 

    Numerical Study of Accelerating Flame and Flame-Sound Interaction in Tubes

    , M.Sc. Thesis Sharif University of Technology Jafari, Samira (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    Numerical study of the interaction mechanism of the premixed flame and the acoustic field is performed in this work. The geometry similar to those used in experiments, is a two-dimensional tube in which flame travels form open end towards the closed end. The numerical study is done using PPM method. Results show that the shape and speed of laminar flame is strongly affected by the induced acoustic field. Stronger interaction is observed in the closed-end tube with no slip boundary conditions. The effect of the Lewis number on the interaction mechanism is also investigated. Premixed flame- accelerated flame – interaction of flame and acoustic field  

    Experimental Study of Flame Stability on a Reheat System

    , M.Sc. Thesis Sharif University of Technology Nozari, Hadi (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    In conventional afterburning systems, the burnt products of the primary combustion enter the afterburning zone, where the fuel is injected and the mixture is ignited to form a flame which is stabilized by a flameholder.
    The present experimental study focuses on concepts of afterburning and flame stability in a reheat system. For this purpose an afterburner setup is designed and manufactured. The setup comprises of two main regions; the preheating region and the reheat zone. Fuel used in preheater is LPG while jet fuel is injected in reheat zone. Through the tests the key parameters which are adjusted to be in similar ranges as the conventional afterburners are the oxygen amount of the... 

    Investigations on Stability of Premixed Flames in Turbine Engines

    , Ph.D. Dissertation Sharif University of Technology Riazi, Rouzbeh (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    This thesis is a complementary experimental and theoretical investigation on stability of premixed flames and a study of combustion instability and combustion dynamics in a swirl-stabilized combustor, aiming to understand the fundamental mechanisms responsible for combustion oscillations in gas turbine combustors. Theoretical investigations on acoustic modeling of a simple combustor and a study on kinematic response of premixed flames to flow perturbations have been discussed in the first part of this work. In another part of thesis, experimental studies on the response of premixed flames to acoustic perturbations have been performed. In addition, experimental investigations on combustion... 

    Design, Fabrication and Control of Swarm Robots

    , M.Sc. Thesis Sharif University of Technology Farshchi, Mehdi (Author) ; Meghdari, Ali (Supervisor)
    Abstract
    Swarm robotics is a new approach to the coordination of large numbers of relatively simple robots. The approach takes its inspiration from the system level functioning of social insects which demonstrate three desired characteristics for multi-robot systems: robustness, flexibility and scalability. This research describes development of an autonomous miniature mobile robot for swarm robotics research and education. Several common platforms were studied and this prototype was designed. Wireless communication was selected to transmit robot’s messages. The design of this testbed aims for enhancing the sensing capability of the robotic agents, overcoming the constraints led by lack of... 

    Numerical Analysis of an Afterburner Combustion Stability

    , M.Sc. Thesis Sharif University of Technology Rezaei, Vahid (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    Inlet flow of afterburners comes from the burnt products of the primary combustion chamber. The fuel is injected and the mixture is ignited to form a flame which is stabilized behind a flameholder in the afterburner. Flame stability stems from wake (recirculation zone) of flameholder. With the aid of high residence time of flow behind the flameholder reactants get the time to catch activation energy. Some parameters like oxygen content, mass flow rate, inlet temperature, and nozzle area ratio play an important role in afterburner combustion efficiency and flame stability. In this study we focused on afterburner combustion stability in GE J85-21 engine. This engine will be in service through... 

    Numerical Simulation of A Vortex Cooled Combustion Chamber

    , M.Sc. Thesis Sharif University of Technology Azardar, Milad (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    The aim of the present research is to investigate the combustion chamber cooling with vortex method in presence of kerosene and liquid oxygen as propellants. For this purpose, a part of oxidizer is entered into the cylindrical combustion chamber tangentially (from bottem of the chamber), and creates a vortex flow (outer vortex). With motion of created outer vortex along the wall and eventually hit its top wall (the head of the chamber), secondary vortex (inner vortex) occurs along the center line, with a downward direction (opposite to the primary vortex). The fuel and other part of the oxidizer injection is also carried in the head of chamber, so by mixing the fuel and oxidizer that happens... 

    Large Eddy Simulation of Excited Jet Flow

    , Ph.D. Dissertation Sharif University of Technology Ghadimi, Masoud (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    Excited jet flow has many physical and industrial applications, e.g. in aeroacoustics and the combustion instability. Analysis of this type of flow needs an accurate simulation of flow dynamics. This work presents the large eddy simulation of this type of flow. The numerical method used in the large eddy simulation must have low numerical dissipation and high order of accuracy. Compact methods which satisfy these requirements and have high resolution of frequency, are favorable ones for the large eddy simulation. A fourth-order compact finite volume method which had been developed in the MSc thesis of the author is extended and completed in the present work. This extension includes the... 

    Numerical Simulation of Cellular Structure of Detonation Wave and Evaluation of Linear Instability Analysis

    , Ph.D. Dissertation Sharif University of Technology Barkhordari, Alireza (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    Experimental studies of regular cell structure of a weak detonation wave in a gaseous mixture of hydrogen and oxygen diluted with argon have shown that for a constant initial thermodynamic condition, the final cell size differs by repeating the tests. The question is that if these different final cell sizes for a constant initial condition are because of test errors, or the experiments would lead to a domain of solution in the form of different final cell sizes? Therefore, the aim of this study is to investigate, numerically, the evolution process and domain of variation of cellular structure of a weak detonation, and their dependency to unstable wavelengths obtained from linear instability... 

    Numerical Study of Spray Formation in Slinger Injection

    , M.Sc. Thesis Sharif University of Technology Karimi, Hamed (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    In this M.S. dissertation numerical study of slinger fuel distributer has been studied. This type of atomizer has been used in mini turbojets like Teledyne CAE.
    The main purpose of this work was obtaining spray structure of slinger atomizers. This goal was achieved by implementing a UDF code in FLUENT® software to model the primary atomization that include variation of fluid from exit of slinger disk bores till formation of primary droplet. In FLUENT® the DPM method and its ability to utilizing Lagrangian approaches have been used. The result of this model is validated by the data from experimental test that can be found in Articles. This is the first time that spray structure of slinger... 

    Detail Design of a Supercritical Injection Tester, Based on Numerical Simulation of the Spray Structures under Supercritical Conditions

    , M.Sc. Thesis Sharif University of Technology Pourmahmoud, Ataollah (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    Based on the results of a cryogenic swirl flow numerical simulation under supercritical conditions, a global injection tester has been designed. For numerical simulation of the injection process by using ANSYS FLUENT as the CFD solver, the full 3D flowfield has been meshed by a fully structure manner. k-ω(SST) has been used as the turbulence model which has been captured many of the swirl cryogenic flow structures in the both steady and unsteady conditions. Also, the modified Soave-Redlich-Kwong EOS has been accommodated in a broad range of supercritical pressures for estimating state functions, thermodynamic properties and transport properties. The results show that increasing ambient...