Sharif Digital Repository

In this thesis, a numerical analysis of micro chamber filling in centrifugal microfluidics is investigated. In the development of micro total analysis systems, it is often necessary to achieve complete and uniform filling of relatively large micro chambers. With centrifugal devices, these large micro chambers must often be orientated perpendicularly to the direction of centrifugal force and are usually bounded by materials with varying surface properties. On the other hand, the mixing characterization of two fluid by centrifugal microfluidic method has been also conducted. The multiphase flow analyses based on Eulerian-Eulerian approach have been conducted and the VOF method was used for ... 

Pump operating problems may be either hydraulic or mechanical and there is interdependence between the failure diagnoses of these two categories. Consequently, a correct diagnosis of a pump failure needs to consider many symptoms including hydraulic or mechanical causes. Nonlinear, time-varying behavior, and imprecise measurement information of the systems makes it difficult to deal with pump failures with precise mathematical equations, while human operators with the aid of their practical experience can handle these complex situations, with only a set of imprecise linguistic if-then rules and imprecise system states, but this procedure is time consuming and needs the knowledge of human... 

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... 

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... 

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... 

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,... 

Centrifuge is a method in which great gravitational-like forces are used. Gravitational forces which cause molecules to move and are relevant to molecular weight; can cause isotope separation. The separation of light isotope from heavy one is done with a centrifugal field which produces a pressure gradient for the gas mixture. Pressure gradient is different for each of the isotopes due to the dependence of pressure gradient to the mass of the materials. But the separation in this way is very limited. The capacity of separation can be brought up by producing an additional axial flow in the rotor. This rotational flow can be produced with internal or external incitement. Rotational flow with... 

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... 

Industrial centrifuge fans operate in various industries, specifically heavy industries such as pelletizing plants, steel mills, and cement plants. These fans transfer process gas in the production cycle. In some cases, due to their off-design working conditions, asymmetrical wear and failure happen on one side of the impeller's blades more than the other side. The most important reason is the heterogeneity of the entrance fluid's properties. One of the many critical parameters in this issue is the asymmetric distribution of particles between the two entrances of the fan. This research investigates the asymmetric erosion problem of a specific centrifugal fan with a double-suction side... 

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... 

The surge phenomenon, as the most important aerodynamic instability, has caused a severe drop in efficiency and performance in centrifugal compressors, and its prevention and control is considered one of the main concerns of industrialists. The purpose of this study is to design and develop a surge control system in order to improve the stability and safety of the system under the effect of surge. In this research, after simulating the existing control system and working line in Borzouyeh Petrochemical Industry, by designing and adding the piston surge active control system to the above centrifugal compressor and using the combined control system, the flow rate of the bypass path has been... 

In this research, first, the performance map and surge line of 46M6 and 46MB8 multi-stage radial compressors, which have 6 and 8 stages, respectively, have been estimated and invarianted. Invarianting the performance map makes the performance curve and surge line of the compressor, unchanged from input conditions, including molecular weight, which is very important for control systems. Then, the hydrodynamic circuit of Compressor System C-3002 of Nouri Petrochemical Company was modeled according to the characteristics of its components by solving equations in MATLAB software. main working condition of the hydrodynamic circuit is close to Start of Life operating condition which has a... 

A Specific process centrifugal compressor is upgraded. The operating range and efficiency pattern are increased. A one-dimensional performance prognosis tool (CCPP) is developed. The tool uses mean streamline method as the analysis model. Since the working media has various components, a complete equation of state is utilized to model the thermodynamic behavior of the real gas in super critical pressures. The performance of the base-line compressor is deyermined. The performance prognosis tool is validated with available experimental data. Upgrade road map and methodology were introduced in accordance to domestic requirements. The performance of the upgraded compressor is investigated and... 

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... 

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... 

The performance of centrifugal compressors deviates from its best design point and reaches lower efficiencies by time and conversion of input gas properties such as the pressure, temperature, and mixture characteristics. By the fact that each designed compressor should have a wide range of functionality, redesign and optimization processes take place. One of the challenging methods for improving the performance of centrifugal compressors is to modify aerodynamic passage of gas in impellers in order to achieve better pressure ratio and efficiency. The aims of the current study are to evaluate geometry properties of the blades of the first or the second impeller and even the whole compressor... 

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... 

Gas turbines and centrifugal compressors are the preferred means of compressing the gas in pipeline systems. Both gas turbines and centrifugal compressors exhibit performance characteristics that depend on the operating point imposed on them by the pipeline operation. Simulation of gas turbine-driven centrifugal compressors is necessary for a variety of applications in the general area of pipeline simulation. This research focuses on modeling of twin shaft gas turbine dynamic and steady state performance. For this purpose, it was necessary to evaluate the thermodynamic working process of the gas turbine by using an in-house computer code. At design point, the calculations are solely based on... 

Overall performance improvement of gas turbine is available by modifying each component of cycle. The purpose of this research is to improve performance of a micro turbine with 200 KW power, by redesigning compressor set. Considerable increase in performance and stability occurs, by adding individual stage of axial compressor at the entry of centrifugal section. It should be noted that, this improvement occurs without a significant increase in size and without having to change the centrifugal compressor design.In this study, design of one stage axial compressor and three dimensional modeling is discussed after, modeling and preliminary design of centrifugal compressor. Then, after obtaining... 

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...