Sharif Digital Repository

Nowadays electricity power has a key role in developing various aspects of the world. The great importance of fossil fuel power plants come from their large contribution in electricity power generation. Among the different fossil fuel power generation technologies, supercritical power plants have great advantages. They are an advanced power generation technology with high plant efficiency, high coal utilization and low emission. Their complexity and existing many unavoidable uncertainty sources in their dynamic such as changes of ambient temperature, climate condition and wear of components make their control challenging. To overcome mentioned problems and achieving a good performance, a... 

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... 

Presently, a wide range of devices operate at supercritical condition. In fact, supercritical condition refers to a condition in which both temperature and pressure of injected fluid exceed the critical point. In the case of modern internal combustion engine, the temperature and pressure of combustion chamber is high enough that can be considered as supercritical condition, whilst the fuel injected may be subcritical or transcritical.It has been widely accepted that in supercritical state, vaporization enthalpy is vanished and there is no distinction between gas and liquid. Hence, only a single state will remain which is neither liquid nor gas and referred to as fluid. Moreover, many... 

In order to improve performance and optimize design of high pressure combustion devices such as liquid rocket engine, gas turbine engine, and diesel engine there is a need for comprehensive understanding of injection, mixing and combustion in supercritical condition. Under this condition chamber pressure is higher than critical pressure of fuel and oxidizer. The characteristic of supercritical condition, include changing thermophysical properties such as density, CP, and compressibility factor. Therefore under this condition ideal state equation cannot correctly predict the mentioned properties. These characteristics make supercritical combustion different from other combustion regimes.... 

In this research, we focused on demonstration of features and advantages of supercritical fluids technology to formation of fine particles (nano and micro scales) from bulk materials (solid) and synthesized metal oxides nanoparticles. Therefore, using two different fluids, carbon dioxide and water, and two completely different methods, the Rapid expansion of supercritical solution and supercritical hydrothermal, were used to produce fine particles of drug (acetaminophen) and nano metal oxide (zirconium dioxide and bismuth ferrite). The summary of this research are as follows:1. The solubility of acetaminophen in SuperCritical-Carbon Dioxide (SC-CO2) with and without menthol as a cosolvent... 

Pretreatment of nuclear waste for valuable and limited uranium resources in the nuclear industry as well as environmental protection is imperative. Wash the affected parts of the Natanz uranium enrichment plant uranium centrifuges with a standard cleaning solution of citric acid, a liquid waste is generated in this study, the preparation of these residues using supercritical water oxidation (SCWO) and near critical (HTWO1) was studied as a result, the optimum operating conditions, and conditions of solvent extraction has been studied. In the result, the optimum operating conditions, and conditions of solvent extraction has been introduced. Also in the UCF2 as a liquid waste contaminated with... 

Flow analysis in and out of the pressure-swirl injector in supercritical condition is investigated in this thesis. These injectors widely are used in different industries such gas turbine combustion chamber and liquid fuel rockets. Flow simulation in these injectors is so complex because of existence of gas core in axial region and high swirl and axial speeds in injectors. Unlike subcritical condition, droplet and ligament don’t form in supercritical condition so injector performance represents with two parameters including liquid film thickness in vortex chamber and liquid spreading angle. Mass flow, geometric constant, length and the distance between tangential inlet and injector head, are... 

Turbulent combustion at supercritical condition have a considerable effect in modern high performance rocket propulsion systems, gas turbines and diesel engines. In such a reaction conditions, an abrupt changes occur in thermodynamics and transport properties of fluid. So numerically modeling of a real fluid behavior of the cryogenic propellants and the turbulent trans-critical mixing and combustion processes faces serious challenges.In this study, in order to realistically represent turbulence–chemistry interactions, detailed chemical kinetics and real-fluid thermodynamic behaviors related to the gaseous hydrogen and cryogenic liquid oxygen combustion under supercritical pressures, the... 

Thermodynamic properties of supercritical carbon dioxide change near the critical point. High cycle efficiency is realized by having the main compressor to operate near the critical point of CO_2 to benefit from reduced compression work. In addition the high efficiency, compactness, nontoxicity, cheap working fluid and possibility of using dry cooling instead of wet cooling, s-CO_2 has many application such as nuclear, fossil fuel, renewable sources like solar thermal and waste heat. With regards to sCO_2 thermodynamic properties, suitable equation of state with high accuracy has been determined, and then is used in the design modeling. Recompression Brayton cycle with steady state flow is... 

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... 

The arena of supercritical combustion involves a set of unique physical phenomena that are different from what is observed in the spraying and combustion of a subcritical regime. Understand the complex physics of the flow field in transcritical and supercritical operating conditions and discovery of factors affecting them and the extent to which each of these factors affects the structure of the jet and consequently the quality of the mixing and combustion process, is one of the basic steps to optimize of cryogenic liquid fuel engine combustion chamber design. In this thesis, by studying the experimental researches of injection at sub-critical to super-critical conditions, it has been tried... 

Characterizing the dynamics dictating injection and mixing of the coaxial shear and swirl injectors is of central importance in the context of space rockets, diesel and direct injection reciprocating engines, and modern turbine gases. Sophisticated with precise thermo-physical models along with high-fidelity turbulence approaches, a computational platform –based on OpenFOAM open source code– is developed to simulate the practical injectors flow-fields under trans- and supercritical conditions. Aiming at providing a deep insight on the underlying physics, the investigations are conducted in a hierarchical manner; the flow complexities are added step-by-step to eventually construct the... 

Combustion in supercritical conditions (thermodynamic) is one of the most important applications of today's systems. One of the reasons for the increased use of combustion in supercritical conditions is the need to develop high pressure combustion systems, such as liquid fuel engines, gas turbines and internal combustion engines. Combustion is a technique in which the fuel is injected into the combustion chamber with its supercritical state (Any substance at a temperature and pressure above its critical point). Fuels in the supercritical conditions exhibit new features such as low viscosity, high diffusivity and low surface tension, which lead to higher efficiency, high power generation and... 

I-131 isotope is one of the most significant radio medicines for treatments of the thyroid cancer and nuclear tomography of thyroid. As for purification of this radioisotope several methods have been developed among which adsorption-desorption on metallic copper is the most promising. The current study is aimed at elaboration of the kinetics behavior of the different types of metallic copper for adsorption of iodine vapor. The used copper samples included plain and silica-supported Cu nanoparticles as well as micronized copper. The silica-supported Cu nanoparticles were prepared by impregnation of highly porous silica (≈500 m2/g) in Cu(NO3)2 solution, heating of the solution to above... 

Green chemistry seeks to reduce or eliminate the use of hazardous substances in the chemical industry through the development of new products and processes .The replacement of harmful, widely used solvents and reagents is a key part of this approach. Supercritical fluid such as CO2 or water are good solvent for replaceement Exchange reactions involving the displacement of hydrogen bonded to carbon by deuterium are of interest in a broad variety of disciplines, such as the preparative chemistry of isotopically labeled materials, fundamental studies of carbonehydrogen bond activation processes, and studies of the nature of catalysts. The low cost of water and its environmental friendliness... 

Nuclear power is a prominent alternative of fossil fuels that can effectively solve global warming, acid rains and other consequences of air pollutions, caused by combustion. Despite such obvious advantage, this highly compact form of energy suffers from a big problem corresponding to its nuclear waste. Graphene oxide (GO), a lamellar material with wide range of surface functional groups such as epoxy (C-O-C), hydroxyl, and carboxyl offers large surface area as well as high sorption capacity for the metallic cations. This thesis study presents a supercritical, and co-precipitation synthesis of magnetite- graphene oxide (M-GO) in which Fe3O4 nanoparticles are simultaneously formed, surface... 

Milk is One of the most important source s of protein in the world. during the process of cheese the most of these protein remain in whey. There are different methods to separate these protein from whey. The one of advanced method is ultrafiltartion, this method is based on a permeable membranes, with different pore size. There are many research works in this field. In this project we have tried to study the effect ofpressure, temperature, concentration and resistance time on membrane porosity. In order to design the experiment and analyze the results tagochi L 16 methods is used. The PVC membranes were prepaid by gas anti solvent method, experiment showed that changes of temperature and... 

The purpose of the present project is to construct and improve the quality of an absorbable membrane using a supercritical process and study the effects of the operative parameters. Today, usage of biodegradable polymers is intensively increasing and these kinds of polymers are used as drug delivery carrier and tissue engineering medium. A biodegradable membrane is suitable for this goal. In this study Poly Ethylene Glycol (PEG) is used as the biodegradable polymer. Gas anti-solvent (GAS) method was applied for the production of the membrane. The used anti-solvent was Supercritical Carbon Dioxide. In order to study the effects of the operative parameters on the structure of the produced... 

In this study the kinetics of extraction of various hydrocarbons from crude oil using supercritical CO2 has been studied experimentally. The effect of parameters such as temperature (35, 45, 55, 65 °C), pressure (90, 110, 130, 150 bar), initial volume of crude oil (16, 19, 22, 25 mL) were investigated. Flow rate of gas has been recorded dynamically. QUALITECH 4 and MATLAB neural network softwares have been used for designing the experiments and modeling the final results, respectively. Pressure has a direct effect on extraction yield and by increasing it, heavier fractions could be obtained. On the other hand, the effect of temperature is more complicated, by increasing the temperature, the... 

Graphene is pure carbon in the form of a very thin, nearly transparent sheet, one atom thick. It is remarkably strong for its very low weight. Graphene is a novel particle that can improve adsorption properties. We use graphene for Iodine gas adsorption. Iodine-131 (usually in the chemical form of iodide) is a component of nuclear fallout, and is particularly dangerous owing to the thyroid gland's propensity to concentrate ingested iodine, where it is kept for periods longer than this isotope's radiological half-life of eight days. For this reason, if people are expected to be exposed to a significant amount of environmental radioactive iodine (iodine-131 in fallout), they may be instructed...