Sharif Digital Repository

Energy consumption is considered as one of the key constraints in the design of Embedded Systems. Exploiting abundant ambient energy offers a practical solution for designing embedded systems. In this regard, emerging trends are surging towards replacing battery-powered embedded systems in various different applications such as wearable systems, Internet of Things, and pervasive computing. Also, with the development and ommercialization of emerging Non-volatile memory technologies,the potential to reduce the static energy consumption and the ability to retain data in the absence of input energy, has become practically feasible for Embedded Systems. Consequently, recent researches have... 

In this thesis, a new method has been developed for tuning of fractional PI ( ) and fractional [PI] ( ) controllers for the first order plus dead-time ( ) systems. By using the performance-map method ( ) and based on phase and gain margins' criteria, a formula which is function of fractional order ( ) and normalized dead-time ( ) has been proposed for the proportional and integral coefficients. In addition, an equation has been given for the fractional order of controller to minimize the integrated absolute error ( ) index. Moreover, overshoot and settling-time of the step response of the system have been improved by dynamic setpoint weighting. Simulation results have shown that proposed... 

Thermoacoustics deals with the conversion of heat energy into sound energy and vice versa. This new and emerging technology has a strong potential towards the development of sustainable and renewable energy systems by utilizing waste heat or solar energy. Although thermoacoustic devices are simple to fabricate; however, the design process is very challenging. The thermoacoustic phenomenon is discovered over a century ago; nevertheless, the rapid advancement in this field occurred during the past three decades when the theoretical understanding of the phenomenon is developed along with the prototype devices. There are several advantages of heat engines and refrigerators based on... 

In this thesis, flow-through (or open cycle), standing wave thermoacoustic refrigerator is investigated. The system has the characteristics that the working fluid travels through the system in an oscillatory mode with a mean flow. This type of thermoacoustic refrigerator enables the working fluid to reach the desired cold temperature without passing through the usually required cold heat exchanger. Consequently, the cold heat exchanger subsystem becomes redundant and the entire system becomes less complex and lower in fabrication costs. In this research, while the hot and cold temperatures are fixed, a parametric study is performed to determine the alteration in performance due to the... 

In this research, the principles of design of Heat Exchangers in thermoacoustic systems are developed. The Heat Exchangers as a essential part of thermoacoustic systems, complete the thermodynamic cycle in these systems. In this thesis, principles and algorithms of design for Shell&Tube, Plate and Screen Heat Exchangers are described and these principles are validated for each kind of Heat Exchangers. Then the balance of exergy is studied in thermoacoustic systems and at the end, for every Heat Exchangers amount of exergy destruction is evaluated for oscillating and non-oscillating fluids. Based on fitness functions of exergy destruction, heat transfer area and acoustic pressure drop, Heat... 

thermoacuostic heat pump (THP) is One of the most important thermoacuostic applications which is used for heat lost recovery in industrial applications and civil applications.In this project, we have a quick review on thermoacuostic theory and researches in this field. Also a thermoacuostic heat pump in a lab scale will be designed and analyzed.For achieving this goal, first, mathematical equations of thermoacuostic systems are reviewed; a thermoacuostic heat pump is designed on the base of Tijani method and final model is validated by DeltaEC software. In the next step, after investigating about laboratory equipments which is used in testing process, we generate test matrix and study about... 

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... 

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... 

Axial compressor design is a very complex and expensive process. In general, for design and development of a new axial compressor, manufacturing companies usually intend to employ an existing and successful axial compressor as an starting point and modify and upgrade it. In this regard, dimensional scaling is a common method for derivative axial compressors. The goal of dimensional scaling is to get a different capacitywhile minimizing the development time and cost. In this thesis, theNASA eight stage transonic axial flow compressor is chosen as the base model for dimensional scaling to lower and upper size of its original dimension. The scaled compressor is analyzed with a quasi 2-D code.... 

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... 

Typical thermoacoustic systems deal with the conversion of heat energy to sound energy and vice versa. Recent advances in the field of thermoacoustics have altered the working mechanism of many conventional heating and cooling devices. These systems have three highlighted advantages: first, they have simple structure, no moving parts, low cost of manufacture, and high reliability; second, by using inert gases as working fluid, they are environmentally friendly; and finally, heat driven thermoacoustic devices can be driven by low quality energy sources such as waste heat and solar energy.
The main focus of the present thesis is on the application of the thermoacoustic technology in the... 

In this thesis, a one-dimensional simulation, developed in previous studies, is utilized to study the stability phenomenon in axial compressors of gas turbine engines. The transient and dynamic operation of the axial compressor is determined by solving the conservation equations, expressed as one dimensional and time dependent Euler equations with related turbomachinery source terms. As known, stall and surge are one of the most destructive dynamic phenomenon in gas turbine engine compression systems starting with a flow separation. This occurrence is investigated in detail. In general, while choking phenomenon may occur during engine startup in the first stages, stall... 

The purpose of this thesis is to investigate and identify the performance of a class D gas turbine and improve its efficiency.This thesis contains three parts: first part is to choose a specific engine in class D, for our case “Centaur 40”, then this engine, model and validate by GASTURB with existed data.Second part is tosurvey methods of pgradedemonstrated gas turbine with regard to upgraded Solar Centaur 40 “Taurus 60” using the FORTRAN code base on Stage Stacking method.Finally,the last part of this thesis is to investigate Compressor-Turbine matching. In this part the matching zone of the original and upgraded gas turbines are determined and effect of upgrading on matching zone is... 

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... 

Streaming has some applications in medical and industrial science. This phenomena can increase or decrease efficiency of an acoustic system. Deliberate streaming used to eliminate heat exchanger is an example of desired applications. In the most cases, secondary flow is an undesired issue. Streaming in thermal buffer tube (TBT) of thermoacoustic stirling heat engine (TASHE) has some unwanted effects. The main goal of author is to simulate numerically periodic field in TBT with axisymmetric geometry and study the effects of variating geometry and turbulence on the intensity of streaming. According to inaccessible boundary conditions in TBT of TASHE, firstly, the field is numerically solved... 

Considering the multi-disciplinary aspects as well as the importance of a wide performance map of a propulsion system, this thesis is focused on the preliminary design aspects of an axial flow pump with an inlet guide vane. First, a one-dimensional design algorithm is developed. The code is used to perform a preliminary design of a prototype pump. The results are used to carry on a detailed 3D design by using commercial software. The obtained geometry and performance map are compared with available data. Finally, the finalized code is employed to design and analyze a one megawatt axial pump with and without inlet guide vanes