Sharif Digital Repository

In the nuclear industry, gas centrifuges are considered of high importance for the purpose of uranium enrichment. Today, with advances in science and technology, the use of gas centrifuges for separating isotopes other than uranium, is so common. With respect to the use of conventional methods such as Pancake equation in calculating the velocity profile in centrifuges, it is needed that A^2=(MV^2)/2RT≫1 (M: Feed molecular weight; V: Peripheral speed of centrifuge; T: Mean temperature of feed; R: The universal constant of gases). While the molecular weight of the feed mixture gets lower, the A2 parameter gets closer to one. So, other methods for modeling the behavior of the gas in the... 

Deoxyribonucleic acid (DNA) extraction, as one of the most important steps in modern molecular diagnostics, is the process by which DNA is separated from intracellular materials like proteins, membranes, and other materials contained in the cell. Microfluidic technology enables sophisticated, time-consuming and costly experiments with minimal use of raw materials, time and cost and acceptable accuracy. The predominant advantages of centrifugal microfluidic systems are utilizing centrifugal force to generate propulsion without the need for a pump, and eliminating the need for experts to run the system. Various fluidic operations such as valving, mixing, metering, heating, and sample... 

In this research, an attempt is made to obtain the geometrical and performance matching between a centrifugal compressor and a pre-designed radial inflow turbine. In this regard, constraints such as the same outer diameters, stagnation pressure, rotational speed, and power are considered. The impeller of the centrifugal compressor is designed by employing one-dimensional design method. The aerodynamic performance of the centrifugal compressor is 3-dimensionally evaluated by the commercial CFX software. A comparison of the 1D and 3D results reveals a maximum deviation of 7% indicating relatively good agreement. A sensitivity analysis on the flow coefficient and tip clearance shows a change of... 

Lipases (Triacyl Glycerol Acyl Hydrolase, EC.3.1.1.3) are multidimensional biocatalysts which have many applications in food industrials, dairy, fats and oils processing, detergents, synthesis of pure chemical and pharmaceutical materials, paper industrial and cosmetics. Generally, industrial enzymes are produced extracellularly, so their separation from a low-cost complex medium (usually used for production) is one of the cost stages in their production process. Filtration is the most economical method of separation in the production of enzymes, but due to the small size of colloidal particles and cell masses present in the fermentation environment, its use is subject to limitations. In... 

One of the challenging issues in Iran's nuclear talks and Group 5+1 countries is the amount of Iran's enrichment capacity and the number of centrifuges needed to meet this demand. In this regard, Iran has recently announced that the basis for determining its enrichment capacity is the supply of fuel for the Bushehr power plant.Modeling and optimizing of gas centrifuge cascade is one of the most important problems in fuel cycle and isotope separation fields. To achieve this goal it is needed to comprehend of single centrifuge operation. Knowing the effectofsingle centrifuge parameters, it is easy to design a desired cascade. Minimizing the number of machines in the cascade is an anticipated... 

The purpose of this study is developing the design means of a high pressure centrifugal compressor impeller for aviational applications i.e. turboshaft engines. The logic and constraints of designing a high pressure centrifugal impeller for a turboshaft engine is different from those of low pressure aerial or high speed industrial ones. This kind of impeller is deployed in a number of advanced generation of aero engines. In this study, the centrifugal impeller design tools are developed using two design methods. Then, the results are compared, validated and corrected with an existing high pressure impeller data. A number of impellers with pressure ratios ranging from 6 to 11 are designed and... 

The present thesis investigates the surge phenomenon of high speed centrifugal compressors. Surge is a highly undesired condition and may cause severe damage to the machine and thus the plant. Traditionally, surge is avoided via a surge avoidance scheme wih recycle valve in discharge at the most common approach. A one dimensional technique is developed where the Greitzer lumped parameter model along with the Gravdahl one dimensional model is considered as the basis. Shaft dynamics, volume dynamics, losses, energy transfer and time lag are imbedded in the present model to improve the prediction of the compressor characteristics beyond the stability region. On the other hand, in order to... 

The purpose of this study is to develop model predictive control approach to control a turbocompressor. The turbocompressor which is consisted of a gas turbine and a centrifugal compressor is manufactured for providing the necessary pressure for gas transport via the gas transmission network. The turbocompressor control system regulates the compressor outlet pressure by controlling the rotational speed of the gas turbine, while preventing the surge phenomenon in the compressor. Surge is a serious instability in the compressor that is associated with periodic fluctuations in system variables and can cause heavy damage to expensive machine parts.In this research, model predictive control has... 

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... 

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... 

Centrifugal Fans are widely used in industrial and commercial applications, from shop ventilation to material handling to boiler applications. They consume extremely high amount of energy each year. Because of this high consumption, even a small efficiency improvement could led to high amount of energy saving. Many projects have been done with this goal up to now, and present work is one of them, with aim to optimize a industrial centrifugal BI fan performance, with wheel diameter about 400 mm. The research has been done based on 3D numerical methods, done by commercial code Fluent 6.3, in steady state. MRF and k-E models have been used to simulate flow around blades, and turbulence... 

Compression systems are widely used in industry. Dynamic Modeling is a necessary step in design procedure of a safe compression system. A dynamic model should be adequate and simulate dominant elements of system. One important element of industrial compression systems is downstream pipelines. In this work, a dynamic model including pipeline acoustics is developed. It is accepted that changes of working gas molecular weight can cause inception of instabilities in compression systems. The dynamic model used to study mechanisms of these instabilities. A conventional control system is modeled and tuned for the compression system. The ability of this control system to prevent such instabilities... 

The purpose of this research is providing the preliminary study and designing, fabricating and installing diffuser vanes on the vaneless diffuser compressor to improve its overall performance. To meet the goal, the GT4082 turbocharger centrifugal compressor is chosen as the basis unit. The compressor is fully modeled, to predict the compressor performance curves. One dimensional and three dimensional models are provided, to simulate the compressor with vaneless diffuser as well as vaned diffuser. In one dimensional model, governing equations are continuity, energy, and state and also the empirical components losses coefficients of the compressor are used. In this method, fluid properties are... 

Centrifugal compressors have wide applications in the turbochargers, aircraft propulsion and petrochemical industry. Therefore it is important to design high efficiency centrifugal compressor. Knowledge of compressor performance at different conditions, energy losses and the contribution of each component of compressor in efficiency losses have of great importance.
In this research, different loss models of the centrifugal compressor were reviewed and investigated. Then 1D codes were developed based on the loss models, and performance characteristics of S2B Schweitzer and GT4082 Garret compressors at different conditions were achieved. In order to evaluate the modeling results,... 

Cell lysis, as the first procedure of cell pretreatment, is a process that breaks cell membranes open thereby facilitating access to intracellular substances, such as DNA, proteins, and other components for further analysis to diagnose and treat diseases at early stages. Currently, there are several methods for cell lysis at macroscales. However, the time-consuming and expensive procedures as well as the large scal of the system are the main disadvantages of the systems. Recently, microfluidic systems have attracted considerable attention due to advantages associated with automation, integration and miniaturization of biomedical test protocols. Centrifugal microfluidics (Lab-on-a-Disc) is a... 

Efforts to model and control surge, as the underlying instability of centrifugal compressors, were conducted. Of the three major instabilities in compressors, namely chokage, stall and surge, the latter has a significant role in limiting the available range of operation in centrifugal compressors, which are the most common devices for the transportation of Natural gas. The customary method to circumvent surge, which if occurred, could impose severe, catastrophic and irreversible damages to the machine, is to avoid the zones in which it is likely to develop by means of a recycling system. These often called "surge avoidance" or "surge prevention" schemes have the benefit of high reliability,... 

Increasing the surge margin of compressors and preventing surge and stall phenomena have always been one of the main concerns of gas turbine engines. This research aims to numerically investigate the fluid injection effects on the surge margin in centrifugal compressors. In this regard, the NASA CC3 compressor is selected for validation purposes. Considering the available geometrical data, a simulation is performed by using Ansys software, and results are compared with those available from public literature.After the performance and accuracy of the fluid injection simulation results are validated, fluid injection is implemented in the newly selected location and its impact on the compressor... 

In this thesis, we consider the simulation and active control of a centrifugal compressor in during surge occurrence. Surge, as an aerodynamic instability in compressors, causes to severe decrease of efficiency and loss of energy and with stabilizing the compressor in this condition, efficiency and system reliability increase. Nowadays, anti surge systems are used for surge avoidance in different industrials. They recycle the compressed gas from compressor down-stream to up-stream in instability condition and cause to exit the operation point from unstable zone. In this thesis, at first compression system is modeled based on Greitzer model and governing equation of compressor shaft in surge... 

The purpose of this research is theoretical and numerical investigations on centrifugal compressor. A computer code has been developed to simulate single-zone and two-zone model, based on the revised formulation for real gas, using Peng-Robinson equations. Single-zone modeling, also known as meanline method, established based on 1-D equations of fluid dynamics considering ideal gas relations, empirical loss correlations, slip factors, impeller efficiency and no wake or separation regions. Considering usual significant separated regions in the gas path of impellers, two-zone (jet and wake zone) model has been developed to achieve a more reliable simulation by using fewer correlations based on... 

In this project a centrifugal, microfluidic platform to the end of separation and studying circulating tumor cells is designed, modelled and analyzed. Circulating tumor cells (CTCs) are specific types of cancer cells which leave the original tumor and enter the blood stream. For the separation of CTCs, a novel anti-body separation technic has been used which targets the specific MCF7 CTCs using their corresponding Ep-CAM antibody. First the Ep-CAM antibody is coated on magnetic nanoparticles through a chemical bonding process. Afterwards the CTCs are exposed to their antibodies, through which they will bind together and form CTCs with magnetic characteristics. Finally through exerting an...