Sharif Digital Repository

Knowledge of the properties of aerosols is of great importance in aerosol science. To gain a better understanding of particle properties, behaviors and dynamics, measurement capabilities are crucial and inevitable. The most critical steps in the aerosol size measurements based on electrical techniques are the processes of particle charging and neutralizing. Corona discharge is a paramount method among all aerosol charging methods because of highest concentration of produced ions, which is essential for the efficient particle charging, based on diffusion and field charging mechanisms. The only known method, which could be applied to provide required conditions for these two charging... 

Corrosion is a main problem for oil and gas industries at refineries and petrochemical process. Presence of sulfur compounds in crude oil and creation a corrosive environment for steel structure, caused failure and unfortunate damages. H2S which present at cracking and sweetening process in sour feed obtain hydrogen atoms that can diffuse into steel structure which involve with its instruments and consequent to hydrogen damage .distribution and storage of these sour environments can be done by high strength low alloy steel (HSLA).Electrochemical hydrogen permeation test were performed to measure the hydrogen permeation current through A106/GR B pipeline steel in the electrolytes simulating... 

The fundamental goal of communication networks is to transfer messages across the network between the nodes. Often, maximizing the information flow which is limited by connectivity of the network could be interesting. The concept of connectivity is divided into edge and vertex connectivity. If our focus were on the vertex-connectivity, connected dominating sets (CDS) could be a valuable tool. Obtaining (fractionally) vertex-disjoint connected dominating sets which are called fractional CDS packing presents a backbone to get an information flow matching the size of connectivity. In this thesis, we will present a distributed algorithm that is given a communication network with n nodes and... 

The modern science of networks helps us to have a better understanding of complex systems. Networked systems can be found everywhere and many systems can be represented by a complex network. A networked structure consists of a number of nodes and links connecting to them. Networks’ ability in information propagation is one of their amazing features that have attracted lots of scholars to work on. It has potential applications in many fields ranging from marketing to biology, epidemiology and sociology. Information propagation studies how information such as computer viruses, contagion, rumor, or new product’s interest propagates over a network. Percolation theory and various epidemic models... 

Nanomachines are molecules inspired by natural molecular machines and are able to move and transport at the nanoscale. Due to the advancement of nanotechnology, the need to move materials and energy on a small scale is necessary more than ever. Nanocars are artificial molecular machines with chassis, axles, and wheels designed for nanoscale transport at materials’ surfaces. Understanding the dependence of surface dynamics of nanocars on the substrate’s physico-chemical properties is critical to the design of the transport properties of such man-made nanoscale devices. Among the multitude of potential substrates for the nanotransporters, graphene exhibits intrinsic ripples on its surface,... 

Thermal penetration is one of the separation methods. In this process, due to the temperature difference, the concentration gradient in one of the gas or liquid phases in the resulting system and the relative separation of the components is possible. The column used for this work is the Classius-Dickel column. This column consists of two vertical plates, one warm and the other cold, spaced a short distance apart. Due to the temperature gradient, the gradient is deliberately created, which creates a concentration gradient in the column, so that the light component accumulates at the top of the column and the heavy component at the bottom of the column. The difference in concentration between... 

This study consists of two parts: steady state calculations and neutron noise calculations in the frequency domain for two rectangular and hexagonal geometries. In the steady state calculation, the neutron diffusion and its adjoint equations are approximated by two-dimensional coordinates in two-group energy and are solved using the average current nodal expansion method. Then, by considering the node size in the dimensions of a fuel assembly, different orders of flux expansion are investigated. For verification purposes, the calculations have been performed by power iteration method for two test problems of BIBLIS-2D and IAEA-2D. For rectangular geometry with increasing flux expansion order... 

Lithium ion battery is one of the innovative and emerging technologies in energy sector that has played a major role in electricity supply security by integration of renewable energy technologies in electrical grid, implementation of electrical transportation system and de-carbonation of the both sectors in recent years. On the other hand, the formation of the potential market of technology as one of the functions of the technological innovation system plays an essential role in creation and advancement of innovation in the energy sector. Therefore, in this thesis, the development of lithium ion battery technology in Iran has been investigated from the perspective of the technology market in... 

Conventional MRI has been used to diagnose different types of brain injuries. However these methods have generally failed to diagnose mild types of injury. We are working on the specification of mild traumatic brain injury, using diffusion MRI data, based on a multi compartment simulation of white matter tissue. This effort is essential for better understanding of underlying tissue micro-structure changes in patients with trauma. Some studies have been used in similar data fitting approaches in order to estimate axon diameter distribution. Specifically, a comparative study between different Compartment Models has shown that “ActiveAx” model has the best agreement with underlying tissue... 

Magnetic resonance imaging is one of non-invasive methods to measure the hemodynamic and morphologic parameters of tissues, especially brain tissues. Hemodynamic parameters monitoring in brain tissue is of significant importance in many majors such as detection of tumor occurrence, brain abnormalities, and track of treatment procedures. Blood is a suspension, comprised of plasma, red blood cells, white blood cells, platelet, etc. Plasma is a Newtonian fluid which is composed of proteins and has a constant viscosity in body temperature. Rheological properties of blood are highly dependent on mechanical and rheological properties of its cells and this dependence is multiplied in narrow vessels... 

Releasing radioactive materials in atmosphere and their damages on human health via emitting radioactivity, show the necessity of investigations on their behavior. To simulate behavior of radioactive materials in atmosphere, we use Gaussian plume model. Gaussian model as a mathematical tool can simulate diffusion of Gaseous matters. This model also can be employed for radioactive materials. Radioactive materials vanish by decaying and can be produced via decaying of their mothers! Therefore, later effect must be considered in the Gaussian model via a factor. Many factors like wind speed and weather conditions also are involved in diffusion of radioactive materials. By considering all of... 

Numerical analysis method improvement is a topic of interest among all engineering disciplines. Regarding the fact that our ability to predict the behavior of a physical system is often limited by our computational resources, the efficiency of the employed numerical method is an important factor in the degree of approximation used in modeling. One of the recent numerical methods is the Cell Method (CM), which is also known as the Direct Discrete Method (DDM). This method combines some features of a variety of methods, especially finite volume and finite element, and gains some insight from the graph theory used in network analysis. The result is a method in which the set of equations which... 

In the present study, the effect of the diffuser inlet-to-nozzle exit area ratio (A_d/A_e ) on the gradual starting performance of a second throat exhaust diffuser has been investigated experimentally. Experiments have been carried out with four conical nozzles with different expansion ratios and considering two approaches of gradual increase and gradual decrease of nozzle chamber pressure by a high-pressure air tank. Investigations show that at high area ratios before starting the diffuser, oscillations in the pressure of the test chamber are created due to the instability of the flow at the diffuser inlet. By frequency analysis of the vacuum chamber pressure, it is observed that as A_d/A_e... 

The aim of this study was to investigate the response of counter flow flames to acoustic excitations numerically. For this purpose, the one-dimensional and two-dimensional laminar counter flow flames are numerically simulated. Cantera is used to simulate the flame in one dimension. In order to consider the counter flow flame as one-dimensional, limiting assumptions are needed, and coding is also required to stimulate the flame acoustically. As a result, a two-dimensional field can be used to simulate a counter flow flame and its acoustic stimulation. This study used Ansys Fluent software to simulate a two-dimensional counterflow flame. Cold solutions without acoustic excitation are first... 

In this study, using a non-interference experimental method, the chemical luminosity of CH* in co-flow diffusion flames with soot and using natural gas hydrocarbon in a laminar flow regime has been investigated. In addition to experimental research, in current research, numerical simulation has been used to extract information such as temperature field, mass fraction of species, and flow structure and comparison and validation with experimental results. Numerical simulation has been used to simulate the mechanism of CH* species formation. Two different mechanisms have been used. In addition, the Soot simulation model from the Moss-Brookes model and radiation heat transfer mechanism... 

The primary purpose of the present thesis is to provide the feasibility of experimental determination of Counterflow flames dynamic response to acoustic excitations. Following this cause, an excitable counterflow burner test platform was designed, fabricated, implemented, and finally validated. The rich scientific literature associated with counterflow burners, the simple structure of the flame, conceivability of numerical simulation analysis in one, two, or three dimensions, the simplicity of structure among fundamental flames which are correspondingly in resemblance with industrial flames and finally the ability of universalization of scientific result to industrial flames are the reasons... 

Often in a vacuum test facility, a supersonic exhaust diffuser uses the energy of the outflow from the nozzle to create and maintain a vacuum condition in the engine test chamber. In this system, the temperature of the motor exhaust gas, which directly hits the diffuser walls, is much higher than the tolerance of the metal body of the diffuser. The purpose of this research is to design a cooling system for thermal protection of diffuser walls of a vacuum simulator using a water-jacket tool. At the beginning of this study, the effective parameters in the design of the water-jacket cooling system were identified. Then, a new algorithm to design and optimize the water-jacket cooling system was... 

In this study, an Experimental investigation of plasma-assisted combustion using a DBD actuator has been performed. This actuator ionizes the fluid flow by producing asymmetric and cold plasma. Ionizing the flow of fuel or air in the combustion chamber reduces the combustion time scale. The test chamber consists of two coaxial quartz tubes that fuel passes through the central tube and the air pass through the side tube. In the case of fuel (natural gas) ionization, one rod as the electrode passes through the center tube, and the second electrode closes in a loop around the inner tube. One annular electrode is closed around the central tube during air ionization, and the second electrode is... 

CDA and NACA65 airfoils, originally designed for aircraft engine applications so do not have the best possible performance for heavy-duty industrial gas turbines and should be optimized according to the operating conditions and requirements of these turbines. For example, due to the high mass flow in industrial gas turbines, the first rows of the compressor deal with the distribution of critical velocities and sound level, while in the middle and end rows of the flow, the flow is subsonic. In designing these airfoils, two parameters of wide performance drop and range should be considered. Since the diffusion of the suction surface causes a drop, the design of new airfoils should start with... 

In this study, the performance of the Moss-Brooks semi-empirical model in estimating soot for six different diffusion flames with methane, ethylene, and kerosene fuels in laminar and turbulent regimes has been investigated. The results show that the model with the default constants in the laminar ethylene flame has relatively acceptable performance, but in the turbulent ethylene flame as well as the laminar and turbulent flames of methane, has a significant error. In this regard, inspired by past research and performing sensitivity analysis, the constants of oxidation and coagulation sub-models were reviewed and Improved. The results of soot volume fraction were evaluated for values of 0.015...