165
Arşivlenen Tez
2
DOI Atanmış
1%
DOI Oranı
Arşivlenen Tez
Measurement of near-field radiative heat transfer between plane parallel plates at nano-scale gaps
This thesis establishes a methodology and experimental setup for measuring radiative heat transfer between nano-spaced plane-parallel plates. It uses a setup with two plane-parallel substrates, one heated, one cooled, at a fixed distance from one another. The temperature measurements are carried out by temperature probes on each substrate. The heat flux input is provided by an external focused laser source. The measurement of flux is carried out by diverting a percentage of the incoming light to a photodiode. The stabilization of heat flux is achieved by passive cooling. The measured data are to be evaluated based on its comparison with published numerically calculated results, which indicate an exponential increase in net radiation heat transfer as plate spacing decreases from 100 to 1nm.
Experimental investigation on the torque loss of an automobile air conditioning system
An automobile air conditioner (A/C) compressor is usually driven by an engine crankshaft, and thus the A/C system may be considered a device that consumes torque from the engine. In order not to degrade the engine performance, therefore, the torque demand by the A/C system should be predicted and compensated accurately. In the present study, the steady-state A/C compressor torque loss is investigated experimentally. The A/C system is instrumented to measure temperatures of the A/C refrigerant while the vehicle is being driven at several cruise speeds with different outside air temperatures and engine speeds (RPM). Other required data are collected from the sensors that are already implemented to the vehicle. A computer program is written to analyse the data thermodynamically, and thus the compressor torque values are obtained at various vehicle-operating conditions. Finally, the experimental result in the present study is compared with the torque loss map provided by Powertrain Control Module (PCM). The map is re-calibrated based on the present experimental results. In addition, the A/C system performance at different operating conditions is evaluated by examining the isentropic efficiency of the compressor and the coefficient of performance (COP) of the A/C system.
Dynamic modeling of human cardiovascular system and an axial heart pump
Engineering applications are widely used in modern medicine with the progress of technology. Heart pumps are an example to those engineering applications which is used for treatment of cardiovascular system diseases. In this thesis a numerical human cardiovascular system model that includes heart chambers, heart valves, systemic arteries, systemic veins, pulmonary arteries and pulmonary veins was developed. Diseased human cardiovascular system model was obtained by adjusting the parameters of the healthy cardiovascular system model. Numerical models were developed for two types of heart pumps (Heart Turcica axial and Heart Turcica centrifugal). Heart Turcica axial model includes the dc motor dynamics. These models were integrated to diseased human cardiovascular system. Simulations were performed to assess the boundary operating speeds of heart pumps which causes different physiologically significant pumping states. Also pulsatility indexes were defined for pressure difference across the pump, pump flow rate and motor current. These pulsatility indexes are calculated for increasing operating speeds. Studies on control of the pressure difference across the pump and control of pump flow rate were also done.Based on the findings it has been concluded that Heart Turcica axial and Heart Turcica centrifugal may provide sufficient pressure and flow required for the perfusion blood for the tissues.
An investigation of microstructure and mechanical properties of aluminum matrix composite reinforced with b4c particulates manufactured by powder metallurgy method
Currently some composite materials, especially aluminum metal matrix composites with particulate reinforcement and related manufacturing methods are among important research topics because of their low density, high specific stiffness and specific strength, and, high wear resistance. Therefore, there exists a need for investigation of their mechanical properties and microstructures.In this study, microstructure and physic mechanical properties of Al-B4C composites, boron carbide (B4C) particulate reinforcements in 63-µm diameter aluminum matrix, sintered at 550 ºC, are studied. The effects of parameters such as reinforcement particulate size and reinforcement percentage on hardness, compression strength, and microstructure are investigated.Different sizes (22, 77, and 120-µm) and different amounts (3, 6, and 9 wt%) of B4C were added to the base material, and pressureless sintering was conducted at 550 ºC under argon atmosphere. Resulting microstructures, densities, and compression test behaviors are studied.It is observed that particle sizes and percentages of the reinforcement significantly influence the compression strength and hardness values. Visual inspection using SEM (Scanning Electron Microscope) analyses indicates that the microstructure of the composite is also greatly effected by these parameters. In addition, EDS (Energy Dispersive X-Ray Spectroscopy) and X-Ray Diffraction analyses were performed for reliable determination of the chemical composition.
Numerical investigation of hemodynamics in the artificial artery-aorta anastomosis and the inflow cannula in ventricular assist systems to prevent complications
Cardiovascular diseases are the most frequent cause of fatality among older populations. Congestive heart failure makes up a considerably large portion of cardiovascular diseases. Ventricular assist devices, which have an increasing success rate in clinical applications, are used to solve these problems. But even with optimized heart pumps fatal complications can occur because of the deformations around the inflow cannula or through the artificial artery ? aorta anastomosis. Due to high rotational speeds of heart pumps, blood cells pass through the pump rapidly and usually without undergoing any deformation. As blood cells flow from the left ventricle into the inflow cannula, flow velocity decreases and reverse flow zones occur, both of which may lead to hemolysis and thrombosis. Similarly, the change in the hemodynamics through the artificial artery ? aorta anastomosis causes deformation of blood cells and endothelium. To investigate the inflow cannula of heart pumps and the artificial artery ? aorta anastomosis and possible clinical consequences, in order to decrease complications and increase the success rate of ventricular assist devices, which is a very difficult and expensive therapy option, computational fluid dynamics analysis were performed using patient-specific geometrical models and boundary conditions. The simulations indicate that the positions of the anastomosis and the cannula have important effects on flow. CFD results provide insight on the altered hemodynamics in the aforementioned regions.
Kalça protezlerinde sürtünmeye bağlı olarak değişim gösteren fiziksel büyüklüklerin ve geometrik özelliklerin ölçüm, analiz ve metrolojik değerlendirilmesi
Günlük aktiviteler boyunca vücut ağırlığının yaklaşık sekiz katı yük altında çalışan kalça implantları oldukça yüksek oranda sürtünmeye maruz kalmaktadır. Gerek vücut içi ortamda gerekse laboratuar şartlarında yapılan deneylerde sürtünmeye bağlı olarak ortaya çıkan sıcaklık artışı kalça eklemindeki malzemelerin ve ortamdaki yağlayıcı sıvının özelliklerinde değişime neden olmaktadır. Sıcaklık artışı ile birlikte bağlantı yüzeyleri ayrışma ve sürünmeye maruz kalmakta, implantı çevreleyen doku da zarar görmektedir. Sonuç olarak implantın aseptik gevşemesi ile birlikte implant ömrü öngörülen süreden daha kısa bir sürede sona ermektedir. İmplant malzemelerinin aşınma ve sürtünme davranışlarının iyileştirilmesi yönünde pek çok çalışma yapılmış olmasına rağmen bağlantı elemanlarının servis ömürlerinin uzatılması konusunda henüz istenen başarı sağlanamamıştır. Bağlantı yüzeylerinde ortaya çıkan sürtünme ve yol açtığı sıcaklık değişiminin ölçülmesi ve malzemelerin aşınma davranışlarının anlaşılması tasarım, malzeme, yağlayıcı ve benzeri faktörler yönünden daha başarılı bağlantıların oluşturulmasına yardımcı olacaktır. Bu amaçdan yola çıkılarak gerçekleştirilen çalışmada, ultra yüksek moleküler ağırlıklı polietilen (UYMAPE), çapraz bağlı UYMAPE, vitamin E karıştırılmış UYMAPE ve vitamin E karıştırılmış çapraz bağlı UYMAPE asetabular insert malzemelerinin ve CoCrMo femur başı malzemesinin aşınma ve sürtünme davranışları incelenmiştir. Malzemelerin aşınma davranışları standart bir pim-disk test cihazında belirlenmiştir. Malzeme yüzeylerinde sürtünmeye bağlı olarak ortaya çıkan sıcaklık değişimi ise kalça ekleminin yürüme çevrimini simüle etmek üzere tasarlanıp, imal edilmiş olan deney düzeneğinde ölçülmüştür. Asetabular insert malzemelerinin yüzeylerinde oluşturulan farklı çaplardaki gözeneklerin, malzemelerin aşınma ve sürtünme davranışları üzerindeki etkisi araştırılmıştır. Sonuçlar matematiksel olarak ve yapay sinir ağları ile modellenmiştir.
Microstructural analysis of pulse gas tungsten arc welding (GTAW) in Ti-6Al-4V alloy
Aerospace manufacturing industry needs high quality, skilled, accuracy work and reliability manufacturing operations. Tungsten Inert Gas (TIG) welding is one of the welding process methods where it is used effectively in aerospace manufacturing applications. Pulse TIG welding is a part of TIG welding and it is preferred to weld Ti-6AL-4V alloy in order to have sound welding. This work investigates the effects of pulse current TIG welding performance on Ti-6AL-4V. Effects of TIG welding parameters, such as pulse and amperage on material grain size (Gs), heat affected area (HAA) and micro hardness of heat affected zone Mh (HAZ) were analyzed throughout the experiment works. The experimental procedure was carried out according to the design of experiment (DOE) and the results were statistically evaluated by using analysis of variance (ANOVA). Response surface methodology (RMS) was used in evaluating the input factors performance with the responses or outputs and mathematical modeling of TIG welding input parameters for Gs, HAA and Mh (HAZ) were established. Gs is adversely affected by increasing amperage on Ti-6AL-4V alloy. On the other hand, Gs is directly proportional to pulsing. HAA is getting wider with increasing amperage on the contrary HAA is getting narrower when the pulsing increases. Mh HAZ shows a significant increase of hardness with the increasing of pulsing, but inversely reacting with the increasing in amperage.
Development of an intelligent fabric defect inspection system
The aim of this study is to design a prototype machine vision system for the fabric inspection machines and develop algorithm for fabric defect detection and classification automatically. The material is selected as `undyed raw denim? fabric. Thus, the fabric inspection process could be achieved in shorter time with higher performances and evaluation of the fabric defects could be performed objectively. The system could be easily adapted on the existing fabric inspection machines. Three different defect detection algorithms were used; Linear Filtering (LF), Gabor Filter (GF) and Wavelet Analysis (WA). These algorithms were applied off-line and real-time over five types of defects; warp lacking, weft lacking, hole, soiled yarn and yarn flow or knot. Defect database was prepared for off-line applications by scanning the fabric samples. Experimental set-up was built for real-time application. User interface was prepared for each real-time algorithm application. The performance and the success rate of the applications were evaluated and discussed. The defective fabric images were then classified by using Artificial Neural Network (ANN) method. A user interface was also formed for this application. The classification rate of the algorithm was evaluated statistically at the end.
Friction stir welding of dissimilar aluminum alloys 2024-T3 To 6061-T6
The importance of aluminum alloys 2024-T3 and 6061-T6 in the aerospace industrial applications push to use a new technology of joining process. The use of fusion welding process for these alloys with the temper conditions ( T3 , T6 ) are not preferred because of the heat generated from the thermal cycle of the welding. Therefore, solid state nature of friction stir welding (FSW) will be very preferable for joining these dissimilar alloys. In the present study, an evaluation for the effect of process parameters on the microstructure and mechanical properties for dissimilar aluminum alloys 2024-T3 to 6061-T6 joint produced by FSW. The experimental work was carried out in the laboratory of mechanical engineering at Gaziantep University and in BCS Metal Company. In this study, FSW joints of good quality have been successfully fabricated from plates with 3mm thickness, using locally made friction stir tool. Four different rotational speed (600, 800, 1000 and 1200 rpm) and three different tool travel speeds (25, 75, and 100mm/min) were used. Experimental results showed that FSW results in fine and equiaxed grain structure at the nugget zone. Better tensile properties were obtained at rotation speed of 1000rpm and traverse speed of 50mm/min. Joint ductility was comparable to that of the base alloys. Tensile failure is found to occur at locations of lower hardness across the welded joints.
Kaynak mikroyapisinin sonlu elelmanlar yöntemi kullanilarak modellenmesi
In the present study, arc welding of the AISI 1045 steel is modelled by using 2D-FEM for three types of welding groove; V, double V and U. The temperature distribution, microstructure, grain growth, and the hardness of the heat affected zone (HAZ) of the welding are simulated. The experimental work is carried out to validate the FE model. The very close value between the simulation and experimental results show that the FE model is very effective for predicting the microstructure, the phase transformation, the grain growth and the hardness. The effect of preheating temperature on the martensite formation is analysed. It is shown that 225oC, 300oC and 350oC pre-heatings eliminate completely the martensite formation for 12 mm thick, V, U and double V-shaped butt welding of AISI 1045 steel. Among the welding grooves, the V-shape is providing the lowest martensite formation and the lowest preheating temperature for martensite elimination.