Sharif Digital Repository

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... 

When we consider Klein-Gordon and Maxwell perturbation fields on the constant gravitational background, the Einstein-Maxwell equations solution will lead to Reissner-Nordstrom black hole which has decreasing mass because of Hawking radiation of bosons from its outer horizon; by reaching this balck hole to extremal case the evaporation will be stoped. The evaporation time is infinite. But String theory equations solution in General Relativity approximation shows that [11] if a Dilaton field ϕ has a exp⁡(-αϕ) coupling with electromagnetic field, the rate of reaching to extremal case will depend on α. We show that by increasing α from 0 to 1, the evaporation time will be initially infinite... 

Two-phase flows are widely used in petrochemical industry, chemical processes, boilers, nuclear reactors, cooling systems and air conditioning equipment. Since the problem of earth’s ozone layer and global warming, the analysis of flow characteristics in evaporators are necessary to improve performance of refrigerating systems and saving the environment. Most of the researchers have been studied the evaporation of two phase flow refrigerant through experimental studies and numerical analysis has less attention in the literature. In this Thesis, a mathematical model based on the two-phase separated flow model is developed to simulate the evaporation of pure refrigerant under constant heat... 

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... 

Developing of electric instruments with high performance needs high capacity heat transfer equipments. Pulsating heat pipes have better performance compared with normal heat pipes and can be used for cooling electronic instruments in near future. Also, one specific kind of heat pipes, which is called rotating pulsating heat pipe, can be used in cooling the turbine blades. Rotating pulsating heat pipe is a mechanism in which the pipes can rotate around the axis perpendicular to the plane of pipes. In this research one rotating heat pipe was built and the effects of heat input, filling ratio and rotational acceleration were examined experimentally. The Innovation in the research was to obtain... 

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... 

Odor caused by the release of volatiles from refinery waste, causing environmental pollution and health hazards may occur. Refinery wastewater project in Saeakhs (Khangiran) has been studied. Contaminated water in evaporation ponds at the plant accumulates due to the large volume of incoming water and slow evaporation in summer the water will smell unpleasant. Odor from the ponds due to wind scattered around the refinery and residents will be put at risk. Several tests to identify the source of the odor was designed and implemented. Among these methods, microalgae growth, the import of oil products such as aromatic compounds or mercaptans, and bacterial growth, for each of the hypotheses... 

The aquatic canopy areas such as wetlands play an important role in ecology of these area. The exchange flow between open water and vegetated area occurs due to sunlight and surface cooling. Wind also causes surface evaporation and create a cold layer at the surface of water. The creation of exchange flow and its magnitude depends on parameters like solid volume fraction and thermal gradient. In this thesis, the goal is to determine the effects of floating vegetation on the hydrodynamic characteristics of exchange flowas a result of surface cooling experimentally. In this research, the PIV method was used to measure velocity profiles. In the experiments, solid volume fraction, depth of... 

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 …,... 

Evaporation and condensation of thin films can rupture or stabilize thin film .We show that evaporation hastens dewetting of a thin film. Dewetting over nanometric downward step causes pinning of the contact line near the step. This phenomena is not permanent and after certain time that contact angle reaches to its critical value depinnnig happens. We also study the effect of the step size, contact angle, film thickness, slip and evaporation on the depinning time of the contact line. We show that depinnig time has a reverse relation with the rate of evaporation  

This study aims to estimate the emission rate of Volatile Organic Components (VOCs) and hazardous air pollutants from the surface of evaporation ponds in oil and gas upstream industries. With respect to the irrecoverable consequences of such emissions, the emission of air pollutants in the oil and gas upstream industries are alarming. Hence, estimation of the pollutants’ emission and surface pollution monitoring are needed for controlling and decreasing of air pollutants in oil and gas upstream industries and also presenting and performing suitable and efficient solutions. The studied ponds in this research include 4 ponds in the oil and gas upstream industries which have been used for... 

Interest in the study of evaporation of liquid droplets is associated with a variety of practical applications, ranging from fuel burning and intensification of heat and mass transfer processes to formation of nanostructures. The study of the evaporation of liquid droplets is a fundamental problem, and it is the subject of a large number of works. However, in droplet evaporation processes, there are still many fundamental issues requiring more in-depth studies. In this study, the effect of the presence of hydrophilic silica nanoparticles and cationic (CTAB), anionic (SDS) and nonionic (TX-100) surfactants separately and in combination on the evaporation rate of water in a pendant droplet... 

Evaporation is one of the main parameters of the mass transfer from earth to the atmosphere, which annually transfers more than 65 billion cubic meters of water. Worldwide, evaporation consumes 25% of the energy input and plays a key role in restoring 60% of the precipitation to the atmosphere. Small changes in the water budget and evapotranspiration (ET) in arid and semi-arid areas can cause a large change in ecosystem health. Lake Urmia Basin has been taken into huge consideration due to steepest decline in lake level in the last three decades. Estimating evapotranspiration of this basin is important for the study of agricultural water consumption, hydrological modeling, water resources... 

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... 

Casting process with foam is a relatively new process which because of having multiple benefits (like elimination of muscle and segregation line, high dimensional precision and using sand without using glue) in recent years has been considered. Considering that during pouring, melt replaces with sand surrounded foam, successfulness of this method depends on complete elimination of foam model during Pouring for preventing formation of some defects like carbon defects in cast irons, or cold work and porosity in aluminum alloys. Parameters like Pouring temperature, alloy type, foam type, density of foam model, type of gating system, and some other parameters are affecting the way of filling of... 

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,... 

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... 

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... 

The Mesoporous Titanium Dioxide film using Sol-Gel method and Evaporation-Induced Self-Assembly technique (EISA) was prepared. In this study, in order to employ the best coatings in anode electrode of dye-sensitized solar cell, different conditions of making this film, the effective parameters in final structure, and various methods of coating were analyzed. After optimizing the conditions of film creating, images of field emission scanning electron microscope (FESEM) proved the formation of a layer of mesoporous structure which thickness after three times of coating is about 1.5 micrometers. In order to increase the energy conversion efficiency of solar cells, a new formulation for... 

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....