Sharif Digital Repository

In this work a generalized non-equilibrium model of three-phase flow in porous media including gravity as well as capillary terms is developed and used for analysis of Riemann’s problem in several three-phase systems. The proposed model uses the extension of Barenblatt model to three-phase systems considering dynamic effects in both relative permeability and capillary pressure functions. We compare the solution of the Riemann’s problem when non-equilibrium effects are included. While equilibrium formulation develops unstable oscillatory solution in the elliptic region, non-equilibrium solution is smooth and stable. The proposed non-equilibrium model is validated by the experimental data of... 

In this thesis, a field effect transistor (FET) using armchair graphene nanoribbon as the channel is simulated, and the effects of changing nanoribbon width and length, as well as adding defects, are also studied. To obtain the Hamiltonian matrix and the energy band structure of graphene nanoribbon, tight binding method is used in which the first and third neighbor approximation is considered. Also, to maximize accuracy, we also considered the edge bond reconstruction. To obtain the transport characteristics of the transistor, such as the transmission coefficient and the density of states (DOS), Poisson and Schrodinger equations are solved self-consistently. We used the nonequilibrium... 

In this thesis, we simulate and investigate two transistors which both have tunneling FET (TFET) structure but the channel in the first one is graphene nanoribbon (GNR) and in the second one is a monolayer of phosphorene (PML). To describe the quantum systems of the transistors, we use the tight binding method and its models for the channel materials. In case of the PML TFET, based on the behavior of the phosphorene nanoribbon in different widths, we obtain a proper amount for the width to model the infinite-width channel. To extract the channel quantum transport, the Schrodinger-Poisson equations are self-consistently solved. In the next step, we simulate the GNR TFET and present the... 

In this thesis, a field-effect transistor using armchair bilayer grapheme nanoribbon as channel material in simulated. In first, electronic property of bilayer graphene and bilayer graphene nanoribbons using tight binding are studied. Transport properties of transistor, sush as transsmition and density of carriers, are studied by self-consistently solving poisson equation and Non-Equilibrium Green’s Function. Finally, I-V characteristics of the transistor can be obtained using the Landauer formula.
Also, effect of Stone-Wales defect on bandstructure and transmission of armchair bilayer grapheme nanoribbon is investigated. This defect increases energy gap and broadens egergy bands in... 

Forced convection in a parallel plate channel filled by porous medium, with walls held at constant heat flux is investigated. A criterion for employing a local Thermal Equilibrium assumption between solid matrix and fluid in a porous channel is developed. Darcy-Brinkman-Forchheimer momentum equation is solved by Homotopy perturbation method. The energy equation for solid and fluid phases employing Local Thermal Non Equilibrium (LTNE) assumption is solved for fully developed and thermally developing forced convection. The analysis leads to an expression for fluid and solid temperatures and also the local Nusselt number. The effect of pertinent parameters such as the Darcy number, the Inertia... 

Pulse tube refrigerator due to the relatively high efficiency, high reliability of linear compressor and the absence of moving parts in the cold area is known as one of the best options to generate up to one kW of cooling power at temperatures from 4 to 123 K. More recently, the use of the device at a temperature of about 150 K, makes use of it even outside of cryogenic temperature. The most important part of the device is regenerator, so understanding the nature of the flow and interaction of gas and solid network in the retrievers is necessary. In this study, Inertance pulse tube refrigerator (IPTR) is simulated using Ansys Fluent in two different conditions. In the first condition the... 

This paper numerically studies the convection heat transfer enhancement of a developing two dimensional laminar flow in a pipe partially filled with porous materials. One of the most important effects of the systems with porous materials in them, is that they can improve some heat transfer components if they be used in a proper way. This study has been performed under both local thermal equilibrium (LTE) and local thermal non-equilibrium (LTNE) conditions. Two energy equations are used in non-thermal equilibrium condition between fluid and porous material. Darcy-Brinkman-Forchheimer model is used to model the flow inside the porous medium. The effects of different parameters such as, Darcy... 

In the early days of quantum mechanics it seemed that, this theory is presented to describe atoms and molecules. As the time went on, by distinguishing different applications of quantum mechanics a question raised in scientists minds. Is it possible to see strange quantum effects in every day life. In this regard several attempt have been made to see such properties. One of these phenomena is observing interference effects for Fulleren molecules. In this thesis we investigate different properties of a macroscopic quantum system in different situations. We showed that an asymmetric double well potential, which is a macroscopic quantum system in interaction with environment violates... 

One of the critical challenges in droplet based micro- and nanofluidic devices is handling the droplet breakup such that a controllable droplet size is produced. The experimental and numerical investigations at the microscale indicate that the droplet size can be well controlled by T junction geometries. In the present study we use non-equilibrium molecular dynamics (NEMD) simulations to investigate this phenomenon at the nanoscale. In order to generalize the study the Lennard-Jones type potential between the fluids and the walls have been considered and the strength and the effective range of the potential are changed to consider a wide variety of materials. Our results reveal that the... 

The fact that materials and crack behave differently under different temperatures, brings a need for further investigation in this field. Recent studies regarding this behavior are mainly based on molecular dynamic method. While this method garuntee a highpercicion, the computational costs of this method can be high when dealing with crack propagation problem. Taking advantage of multiscale methods allows us to overcome this challenge by reducing the calculation time while providing acceptable results. In this research a multi-scale method capable of considering thermal effects has been developed. A concurrent model is created by using theory of elasticity for continuum part and taking... 

Thermalization or the approach to thermal equilibrium in isolated many-body quantum systems is a fundamental problem in quantum statistical physics. There are various quantum systems, whose properties can be described on the basis of statistical mechanics, but there are also systems in which the thermal equilibrium is not realized.Those, that are integrable or systems that exhibit many-body localization (MBL) due to strong disorder, represent non-thermalized phase. Recent theoretical studies have revealed that integrability and the existence of a static disorder are not necessary conditions for the violation of thermalization, while there are translationally invariant and non-integrable... 

Methane conversion into higher hydrocarbons has been investigated by non-thermal plasma. The most important advantages of utilizing this type of plasma are atmospheric pressure and ambient temperature of the operating system. In order to prepare non-thermal plasma, a spark discharge reactor has been used with the main prospect of acetylene production. Other components such as hydrogen, ethylene and ethane are also formed in the process as by-products. By optimizing the affecting parameters on methane conversion and products selectivity, maximum methane conversion of 83.2% is obtained. Acetylene yield varies between 25%-63% with input gas flow rate, voltage, frequency and discharge volume.... 

In the present research, we have applied reverse non-equilibrium molecular dynamics (RNEMD) to investigate the thermal conductivity (λ) of carbon nanotube (CNT) bundles, CNT-polyamide (PA) nanocomposites, and nanoconfined PA in the vicinity of graphene layers. First, transversal heat transport in CNT bundles with and without intertube chemical bonds are examined. It is found that the transversal λ of samples with cross linkers can surprisingly increase ~9 times than that of neat CNT bundles (0.26 W m-1K-1). According to the simulation results, key parameters are overlapping vibrational density of state (DOS) profiles between the atoms forming the bridging units, cross linker in the direction... 

Non-equilibrium systems refer to systems in which, unlike equilibrium systems, the initial condition plays an important role. Conventional methods in quantum field theory cannot be used to study these systems because they do not necessarily have a convergent perturbative expansion.In this thesis, we first briefly introduce the Ising model and fermions in the lattice gauge theory. We then introduce the two-particle irreducible (2PI) method as a tool to investigate nonequilibrium systems. Finally, using this method, we reformulate the Ising model for a system out of equilibrium  

Genetically the equilibrium and nonequilibrium collective properties of the electron system depend upon the strength of interaction between electrons, and of course between electrons and other degrees of freedom such as phonons. One of the collective states is the so-called exciton, a bound state of electron and hole in narrow-band semiconductors. The bound states give rise to absorption peaks below the gap in optical conductivity measurements.Excitonic insulator is an interesting phase of matter where the ground state is characterized by a coherent ondensation of exciton, much like the condensation of Cooper pairs in superconductors. Despite being introduced and theorized more than five... 

In recent years, the incidence rate of liver cancer has increased sharply and nowadays liver cancer is known as the second leading cause of cancer death in the world. Surgical resection is usually used to treat malignant hepatic tumors. However, in some cases, surgical resection is not possible because of some reasons, such as tumor size and location. In these cases, other minimally invasive ablation methods such as radio-frequency ablation, microwave ablation, and high intensity focused ultrasound (HIFU) can be used. HIFU has some advantages such as noninvasiveness, high penetration depth, and low cost in comparison to the other ablation techniques such as radiofrequency ablation. In HIFU... 

In this study, a fully coupled thermo-hydro-mechanical model for modeling Enhanced geothermal systems (EGS) is introduced using the extended finite method for numerical solution. Enhanced geothermal systems are fractured porous media that in addition to the solid phase usually consist of one or more fluids. Heat extraction from Enhanced geothermal systems involves several Multiphysics coupling processes, including the seepage flow through the fractured porous media, the thermal exchange between the working fluid and the matrix, and the deformation of fractured porous media. modeling of these processes is complex and has several parameters. Therefore, a thermal-hydraulic-mechanical (THM)... 

The primary objective of this study entails the examination of the impact of lubricants intended for implementation in the compaction process of nano-powders, intending to mitigate friction at the nano scale during compaction. Molecular dynamics modeling is employed to scrutinize this phenomenon and derive the friction parameters within the framework of equations derived from continuum mechanics, based on data acquired from the nanoscale investigations. The manufacturing procedure of metallic components from metal powder compaction necessitates the application of immense pressures, thereby engendering notable friction between the powder particles and the confines of the mold. Consequently,... 

In this thesis, the transmission characteristics of a vertical tunneling transistors based on graphene-hBN-MoSe2 heterostructure is studied. We first obtain the tight-binding parameters required for Hamiltonian matrix and bandstructure calculations using density functional theory results. Once we have the tight-binding parameters, Hamiltonian and coupling matrices are calculated both of size 326×326. We then proceed to calulate the density of stated for source and drain contacts using the aforementioned matrices and nonequilibrium Green’s function(NEGF) formalism. We can then calculate the quantum capacitances of source and drain and acquire source/drain potentials using a capacitive circuit... 

Major parts of Iran's oil reservoirs are fractured carbonates, which need time to produce oil due to their much lower permeability than sandstone reservoirs. Molecular diffusion mechanism is an efficient mechanism in oil recovery from fractured reservoirs under gas injection conditions. The main subject of this work is to investigate the role of molecular diffusion mechanism in the non-equilibrium gas injection project and its role in increasing the oil recovery rate in two southern fractured reservoirs located in the west of Iran, taking into account the capillary pressure, as well as the change of interfacial tension closely miscible conditions is also investigated through simulation. The...