Sharif Digital Repository

Depending on the geometry and nozzle pressure, increasing the ratio of the diffuser inlet area to the nozzle outlet area can lead to instability in the high-altitude simulator vacuum chamber startup process. This instability results in the formation of harmonic pressure oscillations throughout the diffuser and the vacuum chamber. In this study, a scaled down second throat diffuser with compressed air has been utilized. The performance of the diffuser has been investigated using four conical nozzles with different expansion ratios to simulate instability at area ratios of 1.27, 1.91, 4.1, and 7.81 with rapid nozzle pressure rise. Experiments were conducted by measuring wall pressures along... 

The adsorption equilibria of carbon dioxide, methane, and nitrogen on pelletized cation-exchanged faujasite zeolite (with alkali, alkaline earth, and transition metal ions) have been investigated by a volumetric apparatus. The standard instrumental analytical techniques, including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) coupled with energy dispersive X-ray spectroscopy (EDX), and atomic absorption spectroscopy (AAS) were utilized to characterize binder-free modified zeolites. The EDX spectra and AAS results revealed that the ion-exchange was successfully achieved with expected tendencies. The results indicate that the type of cation present in the zeolite... 

Molecular diffusion of gases in crude oils plays a crucial role in several oil recovery processes especially in cold-based production process. Nowadays, heavy oil is a considerable part of the world hydrocarbon reservoirs and its importance increases as the ordinary oil reserves decrease. The main obstacle in heavy oil production is its low mobility (i.e. high viscosity). This difficulty can be easily solved by injecting gas solvent in these reservoirs. However, experimental data concerning CO2 diffusivity in heavy oils due to the tedious nature of diffusivity measurements are relatively rare in the open literature. In this work, a comprehensive experimental investigation of the effective... 

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... 

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,... 

The progress in the design of nano-scale machines over the past decade has motivated researchers to study the concept of nano-communications. Inspired by biological systems,diffusion-based molecular communication (MC) systems have been proposed as a potential solution for communication in nano-networks where molecules are used as information carriers.Nano-networks are envisioned to facilitate revolutionary applications in areas such as biological engineering, healthcare, and environmental monitoring. In recent years, there has been a significant amount of work on various aspects of MC systems, including transmitter and receiver design, multiple access protocols, and network layer issues.... 

Air and sound pollution in metropolises is a problem vexing every class of citizens, rich and poor. Extensive research has been carried out in recent decades resulting in strict and ever-expanding environmental regulations for automotive and other polluting industries to reduce emissions. Unfortunately, despite significant progress in emission reduction technologies, growth in population along with the number of vehicles on city roads, has intensified related health problems of citizens. As a result, a recent trend has been started around the world with the goal of development and wide-spread use of zero emission vehicles like electric vehicles in metropolises. One variety of electric... 

Modern technology is accompanied by miniaturized devices. With increasing the use of micro satellites and micro airial vehicles (MAVs), finding new power-generating resources is inevitable. Batteries were always an option however high efficiency, long life-span and environmental consideration have encouraged the researches to focus on micro combustion. On the other hand, hydrocarbon fuel contains about 100 times more energy per unit mass than lithium-ion batteries. Micro combustion is defined as a combustion which is occurred bellow quenching distance and old literatures were uncertain about occurrence of such combustion. In this paper we present the fundamental concepts of micro combustion... 

Transient liquid phase (TLP) bonding of Al2024-T6 alloy, using gallium interlayer, has been investigated. Bonding experiments were carried out using two basic methods; Conventional and Temperature gradient TLP bonding. Optimum values of isothermal solidification temperature and time, pressure, surface roughness, heating rate and homogenizing conditions were determined in conventional TLP bonding experiments. Aluminum oxide layer was not removed before TLP bonding to prevent gallium attack.this layer is crashed during bonding. Al2O3 particles are not soluble in the liquid and are pushed into liquid by solidification front progression. These particles are accumulated in grain boundaries and in... 

Traffic flow modeling on different levels was always the topic of many studies. In this regard, many researchers have tried to eliminate traffic problems by developing precise models. Therefore, in this study and in its two major parts, we developed two models: one macroscopic and one microscopic. Like previous studies, the main purpose here was the development of traffic flow models that have better precision and give more information about the mechanism behind the traffic phenomena. Our focus was on the free spaces in front of drivers which were considered in a macroscopic traffic flow model and resulting microscopic traffic flow model.First part, addresses the first-order extension of the... 

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, transient diffusion of drug into the intervertebral disc is considered. The amount of Diffused drug from the blood into the intervertebral disc of dog is measured and concentration of drug is calculated for each region of the intervertebral disc including nucleus pulpous, inner annulus fibroses and outer annulus fibroses. Using finite element method, it is shown that the amount of drug diffusion into the intervertebral disc is affected by some parameters such as the type of drug, dose if drug and endplate calcification. This research is done in two parts: In first part, diffusion of drug (sulphate) into the dog intervertebral disc is investigated to compare the obtained... 

Supported Ionic Liquid Membranes (SILMs) are fabricated by saturating the pores of a porous support with ionic liquids. To assess the performance of SILMS, it is necessary to obtain data about the properties of ionic liquids such as diffusivity, solubility, and etc. To accomplish this task, in this project the permeability and diffusivity of CO2 and CH4 through three immidazolium-based ionic liquids: [bmim][PF6], [hmim][Tf2N], and "1-methyl-3-(3- tri methoxi silil propyl) imidazolium bis (tri fluoro methyl solphonyl)" , in the temperature range between 27-45 ℃ and pressures within 10-50 kPa, are measured. It is shown in data validation section that the results of this study are in good... 

In this project, we are willing to analyze and design a subsonic wind tunnel WT configuration for the Aerospace Engineering Department in Sharif University of Technology. This WT will be an open-circuit "suck down" type, whose entry is open to the atmosphere (laboratory) and three axial fans downstream of its test section. In addition to three parallel fans, we are expected to design two simultaneous small and large size test sections for it. The small and large sections would have an area about 1.4 and 4 m2and maintain a maximum air velocity of 100 and 50 m/s, respectively. So, our design is faced with two main complexities. In one hand, we are to manage the air flow through these two test... 

By developing composites, difficulties of modeling of degradation of properties as stiffness is most considered. The recent advances in the modeling of degradations in stratified composites have led to improved models on all scales. Macro scales methods are good to estimate fracture but not to estimate the failure in micro scale (as microcrack) and moreover, they need many experimental data. Therefore by considering a stratified structure which contains fiber, matrix and intermediate area, mesoscale modeling method is most suitable. In this research Micromechanical Progressive Algorithm (MPA) is used. The method employed is Micromechanic Method of Fracture (MMF). In this work by developing a... 

Presence of emergent vegetation can change the governing forces in flow through such systems and affects the turbulence structure and scalar transport. On the other hand, vertical variation of physical characteristics of stems, which is fairly observed in reality, leads to variation in frontal area and the called vertical density difference. In this study we experimentally investigate the effect of vertical density difference on both flow and vertical transport of mass. The results will be compared with theoretical predictions.
Using rigid emergent model of cylinders as stems with step density variation in depth I simmulate field conditions considering actual variation of frontal area.... 

High-altitude simulation lab of chemical thrusters is one of the most important infrastructures for the development of space thrusters technology. In these laboratories, different sections are designed according to the requirements for simulation of the thrusters at specific pressure and temperature. The purpose of this research is to design a subset of the creation and preservation of vacuum for the purpose of ground testing of chemical thrusters. Vacuum preservation is more comprehensive than the vacuum creation and is usually the bottleneck of design, so the design of this subset is intended in the present study. To illustrate this, after introducing the basic concepts required, two... 

Gas injection is one of the common methods for enhance oil recovery from oil reservoirs. At miscible injection condition, the efficiency of the process is majorly affected by the molecular diffusion coefficient of the gas in the oil. Therefore, the accurate value of this coefficient is an essential for applying in reservoir simulator. However, determination of this coefficient only is possible through experimental methods. In this study, pressure decay method was applied to determine the diffusion coefficient of nitrogen, methane and carbon dioxide gases in crude oil. The reasons for choosing this method are : accuracy in designing the experiment, covering a wide range of pressure... 

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... 

In the present study the production of ferrite-martensite dual-phase (DP) Steel was investigated during the bonding process by transient liquid phase method. The effect of martensite morphologies on mechanical properties of bonding zone were also studied. To make the bonding process and DP steel production heat treatment cycle simultaneously, the step in which the isothermal solidification completed, bonding process, was done simultaneously with austenitising of the steel. Homogenizing of the bond zone, was also done with DP steel making at the intercritical temperature. The St52 steel was utilized for producing DP steel and for bonding process, iron base interlayer with melting point of...