Sharif Digital Repository

In this research, a novel quasi-3D design method is developed for the centrifugal compressor impeller on the blade-to-blade plane. In this method, an iterative inverse design method called Ball-Spine Algorithm (BSA) is incorporated into the quasi-3D analysis code solving the Euler equations on the blade-to-blade and meridional planes at each shape modification step. In design procedure, the difference between the target and current pressure distribution along the suction or pressure sides of the impeller causes the blade-to-blade profile to be changed and the target pressure distribution to be satisfied. In order to validate the quasi-3D analysis code, the centrifugal compressor of a gas... 

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,... 

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 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... 

Radial Flow compressors have broad applications in aero-space, transport, gas and oil industries and etc. This type of compressor is a better choice in meeting constraints on weight and space, especially when continuous high pressure stream in low volumetric rate is of interest.
Through main components of radial flow compressors, many investigations have been performed on design and optimization of the impellers and the diffusers, but the optimum design and optimization of compressor volute have received less attention.Volute design has direct and strong influence on compressor performance and its stable operating range.
In this research numerical and experimental investigations is... 

The present work has been planned to elaborately investigate the key parameters which affect the formation of shrinkage porosities during centrifugal casting of ductile cast iron pipes. The porosity defects can be mostly found in the Hot Mould centrifugal casting products and adversely affect the final mechanical properties of ductile iron pipes namely Ultimate Tensile Strength and Elongation.
In the first point of view, the created defects were detected through microstructural observations and the corresponding responsible mechanisms were also discussed. The results showed that the inner porosity is produced because solidification occurs from both the inner and outer surfaces... 

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... 

Centrifugal compressors are vastly implemented in the industry due to their higher pressure ratio per stage. So, researches are still going on to improve the performance of these devices. On this way, the current project is defined to perform geometrical optimization in the impeller of a centrifugal compressor using numerical and experimental methods. In this research, the design process of centrifugal compressors is first discussed according to methods and guidelines provided in several references. Then the compressor of the GT4082 turbocharger is redesigned using these theories. It is shown that overall available rules are enough to design an acceptable centrifugal compressor. Experimental... 

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... 

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,... 

The heart is a powerful muscle whose primary function is to pump blood into the body. many cardiac patients reach a stage that can no longer be kept function of their heart to a satisfactory level by using medication thus doctors undergo surgery. The common problem occurs to most patients undergoing cardiac surgery is that after the surgery, the patient's heart during a short period of time is unable to supply blood with the flow rate and pressure required for all organs, especially the end organs of the body. In this conditions, ventricular assist device help the patients. These devices are used parallel with patient’s heart and supply the large portion of blood that patient’s body needs.... 

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... 

In this project, two centrifugal microfluidic platforms with the goal of separation and genetical study of circulating tumor cells have been designed, simulated and fabricated. Circulating tumor cells are the ones that are detached from the cancer tumors, entered the blood and disseminated the danger of cancer through other parts of the body. Both passive and active methods of separation are investigated in this study. The passive method is based on the inertial effects of the fluid and the active method is based on the magnetophoretic force exerted from an external magnetic field. In order to use the active method, the magnetic nanoparticles are attached to the breast cancer cells by the... 

Diabetes mellitus is a global endemic that is rapidly increasing prevalence in both developing and developed countries. Recently, the American Diabetes Association has recommended the hemoglobin A1c as a possible substitute to fasting blood glucose for diagnosis of diabetes because it is an indicator of long-term glycemic control. Also, centrifugal microfluidics systems have a good potential to be used in the point of care testing systems. In this study, two centrifugal microfluidic discs were designed and manufactured in order to separately measure the hemoglobin and hemoglobin A1c in the whole blood. In the first part of the study, the hemoglobin measurement disc consists of two chambers... 

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... 

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... 

Cancer diagnosis area has recently been in the limelight of the medical research and there exist an unremitting focus on the devices & technologies which enable cancer detection in its victims. Lately a genius diagnostic method based on isolation and entrapment of circulating tumor cells has been developed which pave the path for cancer identification. These circulating cells which are detached from the primary tumor are carried out through body by means of circulation system. They play key role in phenomenon called metastasis. Separating these rare cells from multifarious background blood cells, assessing their quantity can supply valuable information on the stage of disease as well as its... 

Duct Inverse design problems usually involve finding the wall shape associated with a prescribed distribution of wall pressure or velocity. In this investigation, a novel iterative inverse design method is presented and developed for internal flows. In the proposed method, the duct walls shape is changed under a novel algorithm based on the deformation of a virtual flexible string in flow. The deformation of the string due to the local flow conditions resulting from changes in wall geometry is observed until the target shape satisfying the prescribed wall’s pressure distribution is reached. The flow field at each step is analyzed to obtain the current pressure distribution along the wall.... 

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... 

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...