Sharif Digital Repository

Bonding gravity with Quantum mechanics has always been a challenging issue. So that, accomplishing a theory of quantum gravity is one of the most important research topics in High-Energy Physics.Information paradox in black holes is among such issues which connect quantum mechanics with gravity. Black holes as a natural solution of Einstein equations have a distinction, with other solutions, since there exists an event horizon that imparts space-time into two causally disconnected regions.According to Hawking’s calculations, black holes would evaporate over time by the thermal radiation. This resulting thermal radiation has less information than the initial collapsed matter in a pure state.... 

Optimizing the energy consumption of air conditioning systems has gained great importance in recent years. In addition, maintaining thermal comfort and air quality in buildings is important. The multi-evaporator air conditioning system, which is a direct expansion system, shows the complex and distributed structure of air conditioning systems due to the thermal connection between zones and its large scale. The modeling of these systems is associated with uncertainties. Therefore, designing a suitable control structure for multi-zone systems is very important to achieve optimal energy consumption and maintain comfort conditions in the presence of uncertainty. Model predictive control has been... 

Since physical variables are almost dependent, uncertain and have significant time and spatial changes, nature of hydrological and environmental systems is so complicated, nonlinear and dynamic. Many models have been developed for studying and analyzing various phenomena in these systems. Recently data mining approaches have been used as new methods for modeling of complicated engineering systems. In this study, performance of several data mining tools in analyzing two phenomena in water quality management have been evaluated. These algorithms are Multilayer Perceptron Neural Network (MLP), Radial Basis Function Neural Network (RBFN), Support Vector Machines (SVMs) in the field of Artificial... 

In this thesis, using superstructure concept, a method is presented to synthesize of new structures for thermal desalination processes along with their structural and operational optimization. The proposed superstructure is capable of producing various common (feed forward, backward, parallel cross feed) and non-common structures in evaporators, as well as in combination with flash stages and thermal vapor compressor. By using the GA (Genetic algorithm), the superstructure has been optimized to identify the optimal structures in both Iranian and international economic scales. Also comparisons were made between conventional structures at optimum state, to suggest superior structures at... 

Due to the high cost of the conventional silicon-based circuits, printed electronic introduced as an ultra-low-cost saving techniques which are widely used in RFID tags, displays, sensors and thin film transistors and so on. Unlike the silicon-based devices, Organic materials are used in printed electronic devices, owing to this these devices can be used on large and flexible substrates like glass and plastic. Also in the printing method, there is no demand for expensive and time-consuming processes such as lithography or sputtering. Only by an ink-jet printer or graved cylinders the different layers of a device can be deposited. Besides these advantages of printed electronics to... 

Evaporation is the initial process of losing water and heat from the surface of the lake. There are six well-known methods for estimating the evaporation of water from surface water including: the water balance method,the energy balance method, themass transfer methods, the combined mass transfer and energy balance method, the empirical equation and using pan evaporation. In this thesis, evaporation has been calculated with using different equations, in-site observation and remote sensing data. These results also have been compared with the results of the energy balance method. In addition, we have developed modified empirical equations of fresh water evaporation estimation with the... 

The aim of the work presented in this thesis is deal with some of the aspects in the FEM analysis of sandwich panels containing holes which comprised with foam core. It is a new topic in this field; so the activities that have been done about this case are poor with respect to its performances in engineering. The main emphasis is placed on the treatment of the foam core since the core often is the weakest part of the sandwich and therefore in many ways governs the capacity and lifetime of the whole sandwich structure. Because of increasing application including construction, aircraft and transportation, marine and etc., different load conditions are considered for the analysis and... 

Iin this thesis, evaporation of droplets of a spray from a pressure-swirl injector in a sub-atmospheric combustion chamber is studied. The liquid used in this sudy is a hypergolic oxidizer, Dinitrogen Tetroxide, also known as NTO. The significance of this thesis is its application during the cold startup of a satellite thruster when only oxidizer is injected into the combustion chamber. The most important phenomemon in this stage which is also the focal point for this study, is the ‘Flashing’. In this phenomenon a liquid having a temperature above the boiling point of its own species (for the surrounding gas pressure) is present in the solution field. This state is a non-equilibrium state.... 

Two-dimensional nanostructures can significantly absorb solar irradiation, due to diverse energy levels, large effective surfaces, layered and porous structures with adjustable physical and chemical properties. Mono and multilayers of graphene, as the first isolated 2D materials with special band-structure of a zero-band gap, along with impressive optical properties, tunable light interaction, and adjustable optical properties by chemical doping or structural defects, have great potential for the next generation of nanophotonic devices. So, graphene is an appropriate candidate for absorption, frequent reflection, and energy conversion of electromagnetic waves at the frequency range of the... 

One of the novel methods of stabilization of nuclear waste is the use of vitrification technology. In order to stabilize high level wastes (HLLW) in glass, it is required that the elements are in their oxide form. Therefore, it is necessary to evaporate the waste and turn it into a solid form so that the elements can be converted into oxide form in the calcination furnace. Hence, one of the challenges of stabilization is the optimization of evaporation and calcination conditions. In this research, the parameters affecting evaporation were first investigated. Using laboratory measurements of application: temperature (110 to 180 °C), presence of nitric acid (0.5 to 4 mol/L), ratio of zirconium... 

Providing fresh water for domestic and agricultural purposes has become one of the most pressing issues of the present century. Due to the dependency of conventional desalination on fossil fuels, these methods are associated with carbon dioxide and other greenhouse gas emissions. Therefore, renewable energy-based desalination systems have come to the fore. This study scrutinizes the performance of the solar Humidification-Dehumidification (HDH) desalination systems with subsurface condensers. In this system, solar energy evaporates water, and subsurface condensers condense water vapor into fresh water. Therefore, this system uses two renewable solar and geothermal energy. Due to the lack of... 

In general, the output power of the gas turbines decreases as the ambient temperature increases. One of the ways to deal with such a performance loss is to use a wet compression system, which reduces the air temperature rise throughout the compressor. In this system, the water droplets are injected into the compressor inlet and evaporated throughout the stages. As a result, the work of the compressor decreases, and the power and efficiency of the whole engine increase. Most of the researchers in this field have tried to develop mathematical models to investigate the effects of this system on compressor and gas turbine performance in steady-state conditions. However, it is necessary to... 

This study develops a new framework for the assessment of land subsidence occurrence rate. The proposed framework considers the combined effects of saturated and unsaturated soil behavior. Accordingly, the biot consolidation theory was used for investigating subsidence in the saturated zone while the soil shrinkage curve, i.e., the void ratio-suction curve, was used in the determination of unsaturated zone subsidence. Specifically, groundwater decline and land climate change were used as the main contributing factor in investigating the land subsidence in the saturated and unsaturated zone, respectively. The approach presented in this study is based on using numerical modeling in PLAXIS 2D... 

The study of evaporation of fuel droplet and determination of the rate of vaporization are important in designing combustion chambers. For achieving high performance of a combustor, the evaporation of fuel droplets takes place within a high pressure environment. At these conditions, the use of low-pressure models is not appropriate and many effects that are assumed negligible at low ambient pressures become very important. For example, the solubility of the ambient gas into the liquid phase is increased by increasing the ambient pressure. In addition, the ideal gas assumption is not valid for these conditions and one should use an appropriate equation of state (EOS) that can predict the... 

Injecting several droplets with a known size distribution function in the hot gas environment makes droplets smaller because of evaporation or reaction. Droplets lifetime specification is important in vapor-liquid interactive processes such as chemical or process industries. In previous works, different approximate semi-empirical methods are developed to specify droplets lifetime without considering their size distribution. In this work, governing equations is studiedconsidering a size distribution function for droplets. There is not any analytical method for solving this set of equations, so numerical methods using CFD packages such as Fluent, are applicable in these cases. In this study,... 

Uranium conversion process is one of the most important stages in nuclear fuel cycle. The Uranium Conversion Facilities (UFC) of Iran is located in Isfahan. In this plant, the Yellowcake (impure uranium oxide, U3O8) is converted to Uranium hexa-fluoride, UF6. During the process, considerable amounts of uranium-containing liquid waste are generated. This liquid waste was collected in evaporation pools inside the UCF Plant. In the course of time, a thick layer of precipitated salt form in bottom of the pools which are collected and stored in drums inside a building. This solid waste contains uranium at concentration levels much higher than that permitted for land disposal of the waste.... 

In recent years, there has been the extensive researches on energy and water efficiency due to the increasing stress on these resources. Therefore, the water-energy nexus in large industries, especially power plants, has become very important. In the present study, the water and energy nexus has been analyzed using energy analysis tools, exergy, economic and environmental in a combined cycle power plant. The nexus are observed in the boiler blow-downs, leakage of steam traps, cooling of the air entering the compressor and injection of steam into the combustion chamber, which have been studied in different scenarios to improve water and energy consumption and reduce environmental impact. In... 

Functional design of coating system for the primary mirror of the Iranian National Observatory (INO) is done. This telescope has a 3.4 m primary mirror in diameter, made of Zerodur from Schott. Although similar coating systems are in use since years ago, this is the first attempt to design a system for such a large surface case in Iran. Systematic approach led us first to clarify and identifying the design requirements. Lower limit of 80% for reflectance on all wavelength range from 325-1000 nm, thickness of 100 nm with un-uniformity of 5 nm, adhesion enough to pass the selotape test and surface roughness of less than 8 nm. Study of the available methods for coating and selection of the best... 

Evaporative cooling systems are of most common cooling systems which their electricity consumption is much lower than vapor compression cooling systems. Enhancement of these system’s performance could help to propagate these systems and also decrease the electricity consumption and corresponding emissions in large scale. In this thesis, first a modified cycle is proposed for evaporative cooling. Then, in order to use evaporative cooling in humid climates, a desiccant wheel is implemented in this modified evaporative cooler. As using evaporative cooling will cause high water consumption, a novel cycle is proposed for desiccant based evaporative cooling which is able to cover system water... 

One of the important issues that increasing development of electronic systems has caused is how to transfer the generated heat out of the system. Heat pipes can transfer large amount of heat because of using latent heat of evaporation and condensation. In micro scales using micro heat pipes is popular that in this instrument liquid returns to evaporator by means of surface tension force. So numerical solution is essential for verifying experimental results and increasing performance of this instrument. In this research has been planned to develop a comprehensive model for numerical solution of flow and heat transfer in micro heat pipes. For this reason surface evaporation and …,...