Sharif Digital Repository

During the last 5 decades, the operation of scramjet engines has not been without limitations and technical challenges; i.e., the start-up speed of the engine. Conventional scramjet engines do not have the ability to start from a standstill and even at a flight Mach lower than 5. Therefore, reducing the start-up speed of the scramjet engine is not only very attractive in terms of operation but it will also reduce many technical challenges. The purpose of this research is to identify and analyze the flight speed to start the scramjet engine and the requirements to achieve it. In this regard, first by examining the quasi-one-dimensional equations of gas dynamics, the effect of the static... 

Identification of dynamic behavior and extraction of mathematical model for aerial vehicle is important in design, test and evaluation processes. Due to explosion of unmanned vehicles industry in recent years, many innovative aerial concepts is introduced. Coanda-effect air vehicle is one of these novel ideas which is similar to flying saucers. In this study, an experimental scale model of this air vehicle is designed, built and tested with purpose of identifying the linear dynamic model of the vehicle, using the frequency domain identification methods. Performing the system Identification in hover requires a stable hovering capability in the vehicle. Given the inherent instabilities of... 

The effect of using backpressure of air injection in a microchannel on internal flow pressure drop were investigated in this study. Multiphase flows are commonly encountered in gas and oil industries. Flow fields in production operations are often complex and include multiphase flows of gas and liquid. Previously, because of their complex nature, these flow patterns have been mostly investigated only experimentally and empirical correlations based on the experimental data. From another point of view, it is almost impossible to experimentally realize all the flow conditions for each of the flow patterns. Nowadays computer facilities provide the tool to construct and use large-scale... 

Because of increase in use of cars in recent years, demands for parking spaces have also dramatically grown. To resolve this issue construction of multi-storey underground car parks has sharply increased. Due to the high level of contaminants emitted by cars in parking lots and also the continuous presence of humen within them, the control of pollution level and parking indoor air quality is a vital matter. Type of ventilation systems including modern and conventional used for ventilating parking lots and also exhaust and supply vents locations are the most important factors affecting contaminants distribution. Thus investigation the performance of the conventional and modern ventilation... 

In this study, our objective is to simulate the growth of frost for humid air passing through pressure regulators. The study is carried out in two main stages. First, we use an empirical method to model the formation of frost for a humid-air passing over a flat plate. The model is a semi-2D one and that it is limited to predict the frost growth at a particular station along the plate, considering the local flow heat transfer parameters. We show the validity of results comparing with available experimental data. Second, we numerically simulate the frost formation and growth for a humid air passing between two parallel plates. In this regard, the semi empirical method is suitably coupled with... 

Nowadays, widespread needs for creating low pressure ambient in various industries make vacuum systems have different research and industrial applications. One of these applications is in cooling system of Rankine power cycle. In this case, the performance of the vacuum system has a direct and significant effect on the cooling performance of the condenser and consequently, power production of the steam turbine. Also, a considerable part of deration in thermal power plants industry is due to the thermal deration of the cooling systems. This is mostly because of malfunction of the condenser due to ambient temperature rise. Therefore, by providing suitable solutions to improve the efficiency... 

Using a Numerical simulation approach for modeling multiphase flows is a cost-effective and prevalent method in analyzing the physics of multiphase problems. One of the most applied needs of industry in using gas-particle simulation is the separation of particles using Air Classifiers which are industrial devices that can classify solid inlet particles based on their size using airflow patterns and other mechanisms. The present study focuses on a particular type of classifier using vortex to classify particles. Performance of these classifiers simulated using numerical Eulerian-Lagrangian DDPM model. The two critical studied performance parameters of the classifier are pressure drop and... 

One way to increase the power and efficiency of the gas turbines is to cool their incoming air. There are different methods to cool down the inlet air. One of the most widely used and suitable method is spraying or fogging the water droplets into the air at the gas turbine air inlet. In this research and for the first time, the effect of fogging system on the performance of a combined cycle incorporated with a J-class gas turbine (M-501J) is investigated using the computational fluid dynamics (CFD). There are so many parameters, which affect the amount of achieved efficiency. A few of them includes the average temperature and humidity at the outlet, the evaporation efficiency of the water... 

An important issue in aerospace propulsion systems is the reacting flow analyses, which involve many different concepts and physics including various chemical reactions mechanisms and radiation and convection heat transfer physics. As known, the computer simulation is a powerful tool to analyze the reacting flow physics in various combusting environments. It can suitably provide details of both chemical reaction occurrences and heat transfer physics. In combustion environments, the temperature gradient is noticeably affected by the density gradient. On the other hand, the accurate modeling of density gradients highly affects the computational results. In practice, the density-based methods... 

Electrostatic precipitators (ESPs) are widely recognized for their pivotal role in the collection of dust and particulate matter. ESPs are essential to ensure a particle- and dust-free atmosphere in industrial and non-industrial work environments. With the ever-increasing significance of maintaining air quality at the desired standards, the role of ESPs has gained paramount importance in mitigating airborne pollutants and protecting public health. Achieving higher collection efficiency for particulate matter and attaining cleaner air is of great importance in the design and selection of precipitators. On the other hand, particle collection efficiency is considered as a crucial factor for ESP... 

This thesis is concerned with modeling of air flow through upper airways of the human lung. Mechanisms of fresh (high Oxygen density) air transportation toward deep lung airways and Alveoli and reverse transport of dirty (low Oxygen density) air to upper airways of lung and moth, particle transport and deposition process, parameters affecting the simulation of flow like: steady and transient simulation, type of geometry including planar and non-planar, structured and unstructured network of airways, respiration pattern and real cycle of inspiration and expiration, inspection of expiration cycle on particle absorption efficiency and other effective parameters in deposition of particles in... 

The ongoing Covid-19 pandemic has driven our attention to a simulation of virus dispersion to complete our understanding of airborne transmission. A myriad of studies have shown that respiratory diseases such as MERS, SARS, and COVID-19 can be transmitted by virus-laden droplets released during coughs, sneezing, and normal breathing. To mitigate and prevent the spread of such infectious diseases, investigation of the transmission routes is of great importance. This study has been fueled to harness the CFD tool to simulate the virus-laden droplets dispersion in hospitals inwards. Because of the limitations intertwined with experimental works such as the risk of infection of experimenters, and... 

For the past few years, increasing the airspace capacity has been one of the most detrimental issues facing air traffic management. Statistically speaking, the demand for aerial transportation has been continuously growing hitting an %8.1 growth in 2017. This growth rate in conjunction with the performance and safety considerations for the ATC systems, clearly indicate the need for a practical and safe solution to the airspace capacity problem. Dynamic Airspace Configuration (DAC), is one of the proposed methods addressing this problem by changing the airspace configuration over time.In this research, we have introduced an intelligent method for airspace configuration given the forecast of... 

One effective way to reduce air pollution created by automobiles is to tax/toll the unfavorable characteristics of the automobiles. This study is an extension of the current literature on taxing visible and measurable aspects of automobile ownership and use, namely engine size, age, fuel used, and technology level. A three sided model, comprising the operator (government), consumers, and automobile producers, has been constructed to control emission by proper taxation. Engine size tax is one-time, age-tax is yearly, and fuel use is usage-based. The model has been built and experimented based on a sample population and the results have been shown to be in the direction of the management... 

Particulate matter (PM) with aerodynamic diameter less than 2.5 micron (PM2.5) is cause of dangerous diseases, like respiratory and cardiovascular and it is one of the main causes of poor air quality in the city of Tehran. Despite the importance of the issue, there is no complete information on the chemical components of the PM2.5 in Tehran. In this study, 24 samples of particulate matter PM2.5 collected during one year in each 6 days at the station of Air pollution monitoring station related to Air Quality Control Company (AQCC) at the Sharif University of Technology. Chemical analysis was performed on samples to determine the composition of particulate matter include organic carbon,... 

In recent years, one of the most important air pollution in Tehran in terms of creating unhealthy air quality is particulate matter and especially PM2.5. Particulate matter in Tehran is released from various sources. Identification of components and estimating the contribution of each emission sources, helps governers to find air pollution control strategies. To find out major components of PM2.5 in Tehran, a one year sampling to collect PM2.5 was conducted from February 2014 through February 2015 in AQM station at Sharif University of Technology located west of Tehran. 24-hour integrated samples collected on a 1-in-6 day schedule on both Teflon and quartz filters. TOT analysis was done for... 

Development of cities as well as population growth causes to development of public transportation especially subway lines. Fire is the one of the most important issues that may occur in subways. The difference in flame size, emission heat, smoke and pollutants generation of subway fires attracts an especial attention of fire investigators. The emergency ventilation of subways in the case of fire should have the ability of discharging heat, smoke and pollutants from passenger escape route and preparing a safe place for a specific duration. The aim of this research is simulating fire in subway stations and defining proper regional fire scenarios to prepare a safe route for passengers escape.... 

In this research, room-temperature flexible humidity sensors using graphene oxide (GO) and partially reduced grapheme oxide (PRGO) are reported. Sensing layer was deposited onto Kapton substrate by spin coating method. Topography of the sensing layer was observed by Optical Microscopy, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Partial reduction of the GO was confirmed by X-ray Diffraction (XRD) data. Humidity sensing properties of the samples that were annealed in different temperatures in the range of 125-200 were measured at room temperature. The sample which was reduced at 125 presented higher response about 106% and shorter recovery time of about 65 s.... 

The air cathode of li-air batteries plays a pivotal role in the overall performance of Li-air batteries. Graphene-based cathodes have been investigated as cathode catalysts for lithium-air batteries due to their extraordinary potential for accelerating and facilitating oxygen reduction reaction (ORR).In this study graphene oxide have been synthesized via modified Hummers’ method. Consequently, the as obtained graphene oxide have been reduced using chemical, electrochemical, and hydrothermal methods. Results of elechtrochemical evaluations demonstrate that the graphene oxide reduced via hydrothermal method possesses the most positive ORR onset potential (+0.55V vs SHE) among the other samples... 

In recent years lithium-air batteries captured worldwide attention because of their high energy density. Solid state electrolytes is one of the main components of lithium-air batteries. Lithium almunium titanium phosphate(LATP) is a nasicon type ion conduction which may be of great potential as solid electrolyte. The object of this thesis was the preparation of LATP solid electrolyte which can be used in a lithium-air battery. To reach this goal LATP powder was synthesized using a solution-based method and an appropriate crystallization temperature was selected based on obtained results of X-ray diffraction analysis. In the next step solid electrolytes was prepared under different pressing...