Sharif Digital Repository

In this study, a three dimensional model of water-ethylene glycol based aluminum oxide nanofluid in the laminar flow of an automobile radiator has been numerically studied. The passive heat transfer enhancement method of twisted tape insertion in the flat tubes of radiator is used. The effects of different parameters on heat transfer and pressure drop have been investigated. Simulation results show that utilizing twisted tapes is an effective way of enhancing heat transfer in an automobile radiator. Despite the pressure drop penalty of using twisted tapes, the thermal performance factor which is a proper criteria for evaluating the practical use of the twisted tapes and considers the effect... 

According to limitation of fossil fuel consumption and cost, reduction of fuel consumption is very important in internal combustion engine. This requirement becomes twofold in light of the greenhouse effect of CO2 on global warming. Therefore, the use of engines with less fuel consumption is a global success. Diesel engines are among the most productive internal combustion engines. They have a lower fuel economy and carbon monoxide. But unfortunately, these engines respectively in rich and dilute blend have highly soot and nitrogen oxides. One of the methods in the development of the combustion process is the low temperature combustion method, which reduces the production of Knox due to low... 

Today, tissue engineering research is expanding to a large extent, so tissue engineering has the ability to build artificial organs and tissues. In this project, we have used two polymers of polyethylene glycol and polyvinyl chloride, which are used for network irradiation. After irradiation, these polymers were made by drying the freewheeling porous scaffolds and the effect of different parameters on the structure of these scaffolds was investigated. To investigate the effect of different factors on gelation, swelling, tensile test, degradability and finally the conditions of fibroplast cell growth on scaffolds were investigated. The results of the gel test showed that the gel was higher... 

Treatment of critical-size bone defects caused by sport injuries, accidents, trauma, infection, and osteoporosis remains a major clinical challenge. In order to repair or regenerate large bone defects, bioactive three-dimensional scaffolds play a key role due to their multilevel porous structure, high surface area, enhanced mass transport and diffusion. Many studies reported that macropore diameters greater than 500 µm can lead to vascularized bone tissue. In this study, a hierarchically porous composite scaffold was prepared. Hierarchically porous silk fibroin- bioactive glass composite and fibroin scaffold were fabricated with controlled architecture and interconnected structure with... 

Bidirectional axial vortex flow and air enriched with oxygen are used in order to increase solid fuel burning rate in both subsonic and supersonic ramjet engines experimentally. Vortex flow enhances combustion by causing erosive burning on the surface of the solid fuel. Air enriched by oxygen increases the combustion temperature. Therefore, they make the usage of subsonic ramjet engines possible for applications in which a low thrust is need for a long duration. An experimental ramjet engine with the capability of simulating subsonic and supersonic flight conditions was designed and fabricated. Polyethylene and oxygen enriched air are used as solid fuel and oxidizer respectively. ... 

The aim of this research is inroducing appropriate intensity measure to improve the ability of endurance time dynamic analysis to estimate the seismic response of structures and structure response distribution function. In endurance time method, the structure subjected to intensifying artificial accelerograms and we’ll find structure responses at different return periods just by one-time seismic analysis. Also, according to the high computional time of other dynamic analysis’s, the endurance time method is used which decreases the computional time simultaneously the dynamic predicted responses are accurate enough. In this way, we have a concept known as goal time which is duration of... 

So far, several studies have been conducted on the endurance time method. In general, these studies can be categorized into two categories. The first group of studies are based on the theoretical foundations of this methodology and the second group of researches that use the method of endurance time in different engineering issues of earthquake and engineering, and also compare the results of this method with other conventional methods of seismic analysis.The purpose of this study, which is more in the first category of research, is to optimize the acceleration functions using various Transform, such as Fourier and Wavelet, as well as the use of various optimization algorithms. In optimizing... 

Wound healing by engineered scaffolds is a new step in bio-technology and medical studies in recent years. The goal of the current study is to propose a novel structure for a tissue-engineered scaffold to be used in wound healing. Influenced from the multi-layered structure of natural human skin, the fabricated scaffold consists of two layers to maximize similarity with natural skin. This product is comprised of an electrospun layer made of polycaprolactone and polyvinyl alcohol and a hydrogel layer made of chitosan and gelatin. In order to form a porous medium in the hydrogel layer, freeze-gelation was used instead of freeze drying. The evaluation of fabricated scaffolds was performed by... 

The development of novel three dimensional degradable porous scaffolds is of great interest for tissue engineering.silk ibroin has recently received intensive attention as a material for use in fabrication of 3D porous scaffolds beacuse of its excellent biocompatibility, physical and mechanical properties, and easy processibility. However, silk alone has no osteoinductive property and considerebely lower mechanical properties than native bone. In order to overcome this limitation silk fibroin can be combined with other materials.the properties of scaffold can be significantly improved and new features can be endowed by the second ccomposition. The present study deals with fabrication of... 

Studies in recent years show that more than 57% of all suspended particles released from stationary and mobile sources in Tehran are from diesel vehicles. Reducing the release of this pollutant can be very effective in improving the air condition of Tehran. At the moment, Diesel Particulate Filters (DPF) are considered as the most effective and available technology to reduce particulate emissions from diesel engine exhaust. In this research, the results of the tests on two types of non-catalyzed DPFs under Iran’s conditions have been analyzed. In the motor test, the efficiency of the filters is monitored in the state of operation with the engine representing the country's diesel engines and... 

Due to increasing of internal combustion engine applications in metropolitan, reduction of emission is one of the challenging issues for engine companies. Natural gas is a promising fuel for the strict legislation of emission in many countries. Vast variety of natural gas sources in Iran and also lower carbon to hydrogen content of natural gas motivates us to use this fuel for engine application. Using natural gas also helps to increase the variety of fuel basket in Iran. Present research has focused on mixture formation and injection characteristics of natural gas direct injection engine. Injection and mixture formation in direct injection engines is very important for good combustion and... 

During the past decade the ever increasing volume of greenhouse gases due to fossil fuels consumption have made humans to seek for alternative, non-polluting fuels as an effective strategy to reduce pollution and prevent environmental issues thereof. Electric cars are today known as one of the most effective solutions for this purpose. Of course, transition from gasoline-powered cars to electric cars in a wide scale is not technically possible in short term due to technological and infrastructural limitations. As a result, this lengthy process would lead to emergence of a combinational transportation system including both gas and electric-powered vehicles. The major differences between these... 

Thermo-acoustic sience is the conversion of heat to power through the sound wave. Thermoacoustic engines for different reasons like easy making, not having moving parts and so high reliablibility of system is in attention for researchers. Also looped-tube thermoacoustic engines are very new in the world and sience and thechnology of them belong to a few companies and for different reasons are replacing different kinds of thermoacoustic engines.They have higher efficiency than other types. They can be made in large scales. They have a larger thermal range. In this research, the numerical study of one, two and four stage looped-tube thermoacoustic engines has investigated with the help of... 

Platelet Rich Plasma (PRP) is a blood-derived product containing concentrate of platelets, which are a rich source of autologous growth factors. PRP injection has been used clinically as a therapeutic method for cartilage repair. However, clinical efficiency of this method is unpredictable, maybe as a result of burst release of growth factors then fail cell-stimulating potential as most biomolecules are cleaned before they can exert a therapeutic effect. The aim of this project was to prepare a suitable scaffold for PRP delivery to regenerate cartilage injuries. In order to resemble polysaccharide-protein nature of the cartilaginous extracellular matrix, in this study, we developed an... 

Rotating detonation engines are capable of reaching a higher efficiency in comparison with ordinary engines, due to utilizing pressure gained combustion wave. In this study, the feasibility of a laboratory sample RDE with an annular geometry of diameter of 76 mm has been studied and then designed and constructed. In this sample, hydrogen and standard air were separately injected into the combustion chamber of detonation. The injection of fuel flow and air flow are axial and radial, respectively. The designed geometry is flexible in terms of changing the injection geometry and detonation channel wide, which provided the possibility of testing for a variety of injection and detonation... 

Assessment of the probability of collapse or exceeding other limit states is one of the major goals of Performance-Based Earthquake Engineering. Moreover, other beneficial materials such as estimation of loss of money and downtime, which make it convenient for decision makers to judge the condition of a structure and take wise steps about it, can be drawn from the results of such an assessment.Current work investigates the probability of collapse and also immediate occupancy limit states at three discrete hazard levels of 50%, 10% and 2% in 50 years and also by utilizing mean annual frequency approach for three archetypes of steel special moment-resisting frames of 4, 8 and 12 stories.Ten... 

Energy management in vehicles is ann important issue, because it can significantly influence the performance of the vehicles and component sizing., Although the bbatteries have been widely used in electric vehicles (EVs), However the large current impact of battery cycle life is still a difficult problem that remains to be resolved and because of that, Hybrid Electric Vehicles (HEVs) areis the way that allows to to achievinge the advantages of both engines.Hybrid cars uses both an electric motor and internal combustion engine (ICE) used together, so, itwhich can benefit from the advantages of both engine types. ImprovImprovement ofing energy management in (HEVs) can providedeliver important... 

Diesel particulate filters (DPFs) are used in active and passive regeneration exhaust systems in order to reduce the soot emission of diesel engines. Soot regeneration process initiates at a certain minimum temperature. In Compression Ignition (CI) engines, the intake is not throttled usually, and load control is carried out by adjusting the amount of fuel injected into the cylinders. Consequently in low load working condition, as the fuel mass decreases, the air to fuel ratio increases that results in lowered exhaust gas temperature. On the other hand, passive regeneration strategies alone are not enough and it should be backed up by an active regeneration system in order to guarantee... 

Education has become a crucial issue worldwide, and it needs new techniques and technologies to create and raise interest and motivation towards learning. Serious games are gaining acclaim as viable solutions for enhancing educational processes; Serious games are interactive computer applications that use a challenging and amusing context to transfer a practical skill, knowledge or attitude to their users. Organizations and companies need an effective way for teaching their business processes to their employees. There are many business-related serious games. but few of them focus on business processes, most of which are business-specific and no precise approach is used in their development,... 

However “The Social Construction of Technology (SCOT)” is the title of a thesis in the domain of Science and Technology Studies (STS), it has an important effect on the philosophy of technology. In this paper I try to elaborate and criticize SCOT’s approach. For this purpose we need to answer the question “what is Technology exactly?”. So in the first chapter, I defined Technology. After reviewing some of it’s famous definitions, I defined the joint of technologies based on the “Dual nature of technical artefacts” thesis. Because of the wide range of technologies, I have concentrated on “Technical Artefacts”, although I was not inattentive to other meanings of technology, especially...