Sharif Digital Repository

Off-gas flows in refineries normally consist of hydrogen, methane and heavy hydrocarbons which are burnt in flare. While the demand for hydrogen in refineries is increased and the required hydrogen is provided by steam reforming or partial oxidation of methane or other hydrocarbons, recovering the hydrogen from off-gasses can reduce the refineries losses and optimize it economically. The four main processes for hydrogen recovery unit are the Pressure Swing Adsorption process, Membrane process, Cryogenic process, and absorption process. In the present project besides, considering the process flexibility, reliability, and refinery off-gas properties such as pressure, temperature and mole... 

This thesis discusses design and, simulation procedure of a mono-injector combustion chamber, in order to study and, analyze the ignition and, stable combustion characteristics, for Kerosene and, liquid Oxygen cryogenic propellants. Accordingly, the design and, simulation for the combustion chamber, for Kerosene and, liquid Oxygen propellants is performed. Also, effective parameters on the flame taking place are studied, and finally an algorithm for design and, properties study of cryogenic propellant ignition is presented  

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... 

Heat exchangers are one of the most important components used in liquefaction cycles and overall efficiency of the cycle mainly depends on the heat exchangers effectiveness. It has been shown that the effectiveness of these equipments should be high enough to be able to liquefy a gas. Spiral heat exchangers are used frequently in cryogenic industry and specially in Helium liquefaction industry due to their specific characteristics, however according to literature review it turns out that little study is done in the field of simulation and geometrical parameter investigation of these kind of heat exchangers, so in this study the design and simulation of these cryogenics heat exchangers are... 

The main purpose of this dissertation was to synthesize nanostructured adsorbents based on the sol–gel and electrospinning methods and implement them to the trace determination of the desired analytes from different matrices. In the first and second chapters, a summary of the sol–gel and electrospinning methods along with a glance on extraction methods are presented. Then, the implemented projects are presented in the consecutive chapters.In the first work, third chapter, silica nanofibers were successfully produced using electrospinning method. In this process, sol–gel was formed during electrospinning and then, the backbone polymer was removed by heating. To obtain a thin layer of silica... 

Cryogenic is the study of physical phenomena at temperatures below 123 Kelvin. One of the applications of cryogenic science is the liquefaction of gases. In the liquefaction cycles of gases, such as helium liquefaction, fluidization occurs in the pressure reducing valve but temperature of the gas should be greatly reduced before it enters the pressure reducing valve. For this purpose, high-performance heat exchangers should be used. Spiral Wound is one of the heat exchangers that has ability to achieve over 90% efficiency due to its structure. Researchs in the field of design and simulation of spiral heat exchangers are limited and are done with a lot of simple assumptions such as constant... 

Helium is known as a strategic material due to its unique properties and applications in the development of advanced industries. Currently, natural gas is the only source from which helium can be produced economically. The United States, Qatar, Algeria, and Russia have the largest share of helium production, respectively. In this research, the process of helium extraction from natural gas and its liquefaction, independent of LNG production based on helium in South Pars gas of Iran, which is the largest helium reservoir in the world, were designed and simulated.In the helium liquefaction section, the speed and accuracy of the process simulation were improved by developing a home code based on... 

Spiral-wound heat exchangers have special applications in industry due to their high efficiency, especially in low temperature ranges (cryogenic) such as gas liquefaction cycles; However, due to drastic changes in properties, the mechanism of flow and heat transfer in this type of exchangers has not been fully studied yet. Therefore, accurate modeling of fluid flow on both sides of tubes and shells as well as heat transfer between them can be very important in analyzing and designing this type of exchangers and optimizing them to increase the efficiency of the exchanger and the cycle. In this study, the focus is on the flow and heat transfer of supercritical fluid inside helical tubes of... 

This research aims to develop a numerical tool for design and performance evaluation of spiral wound heat exchanger (SWHE) in the cryogenic temperature range. This type of heat exchangers are used in gas liquefaction cycles due to their compact structure and ability to achieve high effectiveness values. High sensitivity of liquefaction cycles yield to heat exchanger effectiveness, effect of some physical phenomena in cryogenic temperature range, and complicated shell-side flow structure of SWHEs, turns the design and performance evaluation of cryogenic SWHEs into a challenging issue. Consequently, first of all, the geometrical parameters of SWHE were introduced and made dimensionless. In... 

Cryogenic distillation of air is the only method of large-scale production of high-purity oxygen and nitrogen. The falling film column, due to its lower pressure drop and higher heat transfer, is gaining attention. In this method, the heat and mass transfer take place simultaneously on a vertical wall. The present study aims at providing a numerical framework based on a finite volume approach to simulate the falling film distillation column, focusing on the high-pressure column of an air separation unit. Due to the heat integration, filmwise condensation is expected to happen on the surface of the column. An innovative sub-model is developed to evaluate condensation heat transfer... 

This study focuses on path planning for a team of Unmanned Aerial Vehicles (UAVs) involved in efficiently searching a region for early wildfire detection. The primary goal of the path planning algorithm is to identify optimized search paths that maximize the likelihood of detecting wildfires. This optimization considers various factors, including UAV flight time constraints and the locations of the final bases. To improve the algorithm's performance, an initial phase incorporates the utilization of density-based clustering to eliminate noise within the probability map. Furthermore, centroid-based clustering is applied to mitigate the complexity of the optimization problem. Subsequently, an...