DESIGN OF A PIEZOELECTRICALLY ACTUATED MICROVALVE FOR FLOW CONTROL IN FUEL CELLS

This thesis presents a novel piezoelectrically actuated microvalve for flow control in fuel cells. A fuel cell is an electrochemical device, which directly converts chemical energy stored in a fuel (e.g. hydrogen) and an oxidizer (e.g. oxygen) directly into electrical energy. Poor flow distributions within the cell have been attributed to degraded performance and even damage. In this study, it is proposed to embed microvalves directly into the fuel cells to manage the gas flows and improve efficiency, performance, and reliability. The microvalve has four parts. The actuator is a piezoelectric trimorph which has two piezoelectric layers and one brass layer sandwiched between them and has dimensions of 20000 x 4000 x 290 microns. It also has a valve gate placed on the tip. For a 5-volt input, a deflection of 32 microns can be achieved in the trimorph tip, which is what modulates the flow through the valve.The valve design and analysis are complete. Maximum stress on the bender reaches up to 60 Mpa when the the fluidic and thermal forces are at their maximum. This maximum stress is below the tensile dynamic strength values of piezoelectric and brass layers used. A minimum factor of safety of 1.5 is obtained at 20 degrees C. At the operating temperature, which is about 100 degrees C the factor of safety is higher since the stresses are much lower. The drag and pressure forces are found to reduce the free deflection by only 0.2 microns whereas the thermal expansion forces increases the deflection almost by the same amount. Finally detailed fabrication plan and drawings were completed

The Examining of Relationship between Local People’s Lifestyles and Perceptions towards Socio-Cultural Impacts of Tourism in Antalya

This study mainly examines whether a significant relationship between local people’s lifestyles and perceptions of socio-cultural impacts of tourism. Antalya, one of Turkey's major tourism centers, was preferred as study place. In the study, survey was used as data collection tools. As a result of study, while lifestyleswere divided into six sub-dimensions (Experiencers, Fashion Lovers, Makers, Innovators, Survivors and Unusual People), perceptions of socio-cultural impacts of tourismwere divided into eight sub-dimensions (Social Problems, Social Structure, Acculturation and Cultural Participation, Language and Art, Cultural Heritage, Local Peace, Service Quality and Attractiveness, Religion and Cultural Patterns).Hypothesis that there is a significant relationship between local people’s lifestyles and perceptions of socio-cultural impacts of tourismwas partly accepted. The study has provided important data for tourism planners and politicians. Keywords: Local people, Lifestyles, Perceptions, Socio-cultural impacts of touris

WC tabanlı sert malzemeler nasıl geliştirilir

Tungsten carbide is known to have excellent corrosion resistance and high hardness within carbide ceramics. Due to their superior mechanical properties and wear resistance, tungsten carbide cutting tools containing Co binder have been the subject of many studies. There are a limited number of works regarding the use of Ni and Fe as a binder in tungsten carbide based composites, especially processing with microwave radiation. In this study, a composite cutting tool made of electroless nickel coated tungsten carbide ceramic powder was produced by microwave sintering. Two different tungsten carbide powder sizes of 2 µm and 10 µm were used for the production of composite cutting tool. The microwave sintering was carried out at two different temperatures of 1200 and 1400 ° C for 2 hours. Characterization of composite cutting tools was made by XRD, hardness, compression test and electron microscopy techniques.Tungsten karbür seramikler içerisinde mükemmel korozyon direnci ve yüksek sertliğe sahip olduğu bilinmektedir. Üstün mekanik özellikleri ve aşınma direncinden dolayı, Co bağlayıcı içeren tungsten karbür kesici takımlar birçok çalışmaya konu olmuştur. Tungsten karbür esaslı kompozitlerde, özellikle mikrodalga radyasyonu ile işlem yapan, Ni ve Fe'nin bağlayıcı olarak kullanımıyla ilgili sınırlı sayıda çalışma vardır. Bu çalışmada, elektriksiz nikel kaplı tungsten karbür seramik tozundan yapılmış bir kompozit kesici alet mikrodalga sinterleme ile üretildi. Kompozit kesici alet üretiminde 2 farklı tungsten karbür toz büyüklüğü 2 µm ve 10 µm kullanıldı. Mikrodalga sinterleme, 2 saat boyunca iki farklı 1200 ve 1400 ° C sıcaklıkta gerçekleştirildi. Kompozit kesici aletlerin karakterizasyonu XRD, sertlik, sıkıştırma testi ve elektron mikroskobu teknikleri ile yapılmıştı

Sintering and characterization of SiC reinforced Ni powders in microwave furnace

In this study, SiC reinforced nickel matrix composites, microwave at different temperatures It is produced by sintering in oven. Nickel deposition on SiC powders was achieved by using electroless nickel plating technique. It is sintered at temperatures between 500°C, 600 °C, 700°C, 800°C and 900°C under Ar atmosphere. XRD, SEM (Scanning Electron Microscope), pressure test and hardness measurements were used to characterize the properties of sintered samples in microwave furnace. The experimental results, maximum compressive strength (σmax) and hardness (HV) were carried out at 800 °C. Microwave sintering of Ni-coated SiC powders without electric current can be a promising technique for producing ceramic-reinforced nickel composites.TUBITAK due to its contributions to this study with project no. 106T744

Investigation of mechanical properties of boronized composites produced by electroless Ni coating

In this study, ceramic-metal composite production and characterization have been made in order to increase the service life of plotter tools used in soil industry. In the study Ni coated (36% AlN + 3% WC) powders were circularly shaped in uniaxial hydraulic press. These samples were sintered at 1000-1100-1200-1300-1400 °C with argon atmosphere in conventional furnaces. The highest hardness value of 112.9 Hv was obtained in the composite samples (36%AlN + 3%WC) at 1400 °C. Powder metallurgy was applied to ceramic-metal composites by using box boring in dry air atmosphere at 950 °C for 4 hours. The samples were characterized by mechanical and metallographic examination. After box boronization, hardness values were measured, their densities were calculated, the current phases were determined by X-ray diffraction (XRD) method and microstructures were examined by scanning electron microscopy (SEM). The highest hardness value of 1150.80 Hv was sintered at 1400 ° C and 61% Ni was obtained in the box boron composite sample (36% AlN + 3% WC). Better mechanical and metallographic results were obtained from the samples by using box boring method. The porosity decreased in the microstructure examination of the sample. Considering the advantages of non-electric Ni coating method in sintering, it can be said that improving mechanical properties is a good method. Boronizing process was effective in reducing surface porosity and increasing surface hardness up to 10 times

Production of Co-Cr-Ti composite and investigation of mechanical properties

Intermetallic materials such as Co2Ti, Cr2Ti are among advanced technology materials that have outstanding mechanical and physical properties for high temperature applications. Especially creep resistance, low density and high hardness properties stand out in such intermetallics. The microstructure, mechanical properties of %64Co– %32Cr and %4Ti powders were investigated using specimens produced by tube furnace sintering at 800–1200 C temperature. A composite consisting of ternary additions, a metallic phase, Ti, Cr and Co have been prepared under Ar shroud and then sintered in tube furnace. XRD, scanning electron microscope, were used to characterize the properties of the specimens. Experimental results carried out for composition %64Co–%32Cr–%4Ti at 1200 C suggest that the best properties as 182.09 HV and 5,584 g/cm3 density were obtained at 1200 C

Production of ni3al-fe composite and investigation of mechanical properties

In intermetallics high resistance to creep and oxidation, high strenght, low density are desired properties. Sintering process was used in this study by adding different amounts of Fe powder to Ni-Al powder mixture. When the properties of the sample after sintering were examined 40% weight Fe added composition was found as the most suitable ratio in terms of mechanical properties. Analyses were conducted metallographically on the samples after sintering, the densities were calculated, hardness and shear strengths were determined. According to the data 40% Fe added composition had 5,82 gr/cm3 of density, 92,8 HB hardness values and displayed 221 MPa shear strength

Posterior fossa epidural hydatid cyst in the adult

Hydatid cyst is an important parasitic disease especially in endemic regions. Hydatid cysts are most commonly found in the liver and lungs and only 1% to 2% of the cysts reach the brain. Intracranial hydatid cysts are usually supratentorial and majority of cases are children and young adults. In this case report, a 55-yearold woman who lives in rural area in Turkey, admitted to our clinic with severe headache, neck pain, gait disturbance, and vomiting. Her neurological examination revealed cerebellar ataxia and left dysmetria. Radiological findings were compatible with hydatid cyst. On the 3rd of antihelmintic therapy, the patient underwent suboccipital craniotomy and epidural cyst was excised using Dowling technique without rupture of the cyst wall. Patient’s symptoms improved postoperatively. Although hydatid cyst in posterior fossa is a very rare entity, it should be kept in mind in patients with intracranial cystic lesions who live in endemic regions

Production of ni3al-cr composite and investigation of mechanical properties

Nickel aluminide intermetallic compounds possess attractive properties that make them good candidates for high temperature structural applications. It is known that Ni3Al intermetallics are commonly used in various application fields with the addition of Cr, in particular as well as elements such as Ti, Co, Mo and Fe which are related to this group for improving properties thereof. Given this information, sintering process was used in this study by adding different amounts of Cr powder to Ni3Al powder mixture. When the properties of the sample after sintering were examined we were able to reveal the effects of Cr on Ni3Al and consider 3% Cr added compositions as the most suitable ratio in terms of mechanical properties. Analyses were conducted metallographically on the samples after sintering, the densities were calculated, hardness and shear strengths were determined. According to the data 3% Cr adde