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Bir Radyal Türbin ve Kompresörlü Hava Çevrim Makinesinin Tasarlanmasi ve Hesaplamali Akiskanlar Dinamigi Analizleri
No full textThe climatization process is still a phenomenon of great importance from the past to the present. Various engineering activities are carried out in many similar areas, from cooling electronic equipment to keeping commercial passenger aircraft and automotive cabins within the defined comfort temperature range. Especially in aerial platforms, the cooling process takes a critical role. Conventional cooling systems, which contain a vapor compression cycle, are rarely used on aerial platforms at present. Air cycle cooling systems have many advantages about air conditioning for aerial platforms. Low power consumption, low weight, ease of maintenance and repair are important advantages of Air Cycle Machines (ACM). Using air as a coolant which is a safe and clean fluid instead of ozone-depleting gases is an additional and important advantage of an ACM. Air cycle machines are the most essential component in air cycle cooling systems. Air cycle machines have many different configurations according to the requirements of aerial platforms such as flight mission profiles, required cooling capacity, pressurization and humidity control. Within the scope of present studies, research was carried out on the cooling of the under-wing pod of fighter jets with a ram powered reverse bootstrap, 2-wheel, air cycle machines. A radial turbine and compressor have been designed for cooling the external pod located under the wing of aerial platforms. First, conceptual design calculation were carried out for a preleminery design of ACM. Three-dimensional blade geometries were obtained by providing input to the ANSYS BladeGen program through the inputs obtained for these calculations and the outputs obtained with ANSYS Vista RTD (Radial Turbine Design) and CCD (Centrifugal Compressor Design). Adding the guidevane geometries to the blade geometries, single-stage (one-blade) three dimensional Computational Fluid Dynamics (CFD) analyzes were performed. In order to carry out more comprehensive numerical studies, three-dimensional Computational Fluid Dynamics analyzes including all system components were run. The geometry used in CFD analysis, which includes all system components, includes turbine and compressor rotors and volutes, guide blade profile and piping. Three Dimensional Computational Fluid Dynamics (CFD) analysis were performed for the detailed design of experiment (DOE). Within the framework mesh independence and turbulence model studies were carried out. CFD compuations were performed using ANSYS CFX solver. Tests were performed on the designed ACM installed at ANOVA ARGE A.Ş. and results were compared with the 3D CFD predictions.İklimlendirme işlemi, geçmişten günümüze halen büyük önem arz eden bir konudur. Çeşitli elektronik cihazların soğutulmasından, ticari yolcu uçakları ve otomotiv kabinlerinin beklenen konfor sıcaklık aralığında tutulmasına kadar birçok benzer alanda çeşitli mühendislik faaliyetleri sürdürülmektedir. Özellikle hava platformlarında soğutma işlemi kritik rol üstlenmektedir. Konvansiyonal soğutma sistemleri, bünyelerinde buhar sıkıştırmalı çevrim içermekle beraber hava platformalarında artık nadiren kullanılmaktadır. Hava platformlarında iklimlendirme işlemi için hava çevrimi içeren soğutma sistemleri birçok avantajından dolayı yer almaktadır. Düşük güç tüketimi ve ağırlığı, bakım onarım kolaylığı, bünyesinde ozon yok edici, sera etkisi yaratan toksik gazların yerine güvenli ve temiz bir akışkan olan havanın bulunması bu avantajlara örnektir. Hava çevrim makinesi (HÇM), hava çevrimi yapılan soğutma sistemlerindeki en temel bileşendir. Hava çevrim makineleri; hava platformlarının uçuş profillerine, gerekli soğutma kapasitesine, basınçlandırma ve nem kontrolü gibi ihtiyaçlarına göre birçok farklı konfigürasyona sahiptir. Bu çalışma kapsamında; ram havası beslemeli ters önyüklemeli, 2 tekerli, hava çevrim makinesi ile savaş uçaklarının kanat altında bulunan podlarının soğutulması üzerine çalışmalar gerçekleştirilmiştir. Deniz seviyesi, 322 K (49 °C) ortam koşulunda, 1 Mach seyir hızında uçan hava platfotmunun, kanat altında bulunan, aviyoniklerin bulunduğu poddaki ısıl yükler aktif iken hava çevrim makinesi ile soğutulması için radyal türbin ve kompresör tasarımı yapılmıştır. İlk başta, kavramsal tasarım çalışmaları yapılmış olup bu noktada bir boyutlu hesaplamalar yapılmıştır. Bu hesaplamalar için elde edilen girdiler, ANSYS Vista RTD (Radial Turbine Design) ve CCD (Centrifugal Compressor Design) ile elde edilen çıktılar üzerinden ANSYS BladeGen programına girdi sağlanarak üç boyutlu kanat geometrileri elde edilmiştir. Kanat geometrilerine ve yönlendirici kanatçık profilleri eklenerek tek kanatçık geometrisinin modellendiği üç boyutlu Hesaplamalı Akışkanlar Dinamiği analizleri gerçekleştirilmiştir. Daha kapsamlı sayısal çalışmaların yapılması adına tüm sistem bileşenlerinin yer aldığı üç boyutlu Hesaplamalı Akışkanlar Dinamiği (HAD) analizleri koşturulmuştur. Tüm sistem bileşenlerinin yer aldığı HAD analizlerinde kullanılan geometri bünyesinde, türbin ve kompresör rotorları ve salyangozları, yönlendirici kanatçık profili ve borulamalar yer almaktadır. Tüm sistem bileşenlerinin geometrisinin hazırlanmasındaki temel motivasyon, tasarlanan hava çevrim makinesine ait ANOVA ARGE Teklonojileri A.Ş altyapısında kurulan test düzeneği geometrisinin kurulmasıdır. Üç boyutlu HAD analizleri kapsamında, sayısal ağ ve türbülans modeli çalışmaları gerçekleştirilmiştir. Hesaplamalı Akışkanlar Dinamiği analizleri ticari bir yazılım olan ANSYS CFX çözücüsü ile gerçekleştirilmiştir. Tasarlanan Hava Çevrim Makinesi test düzeneğinde testler gerçekleştirilmiş olup elde edilen sonuçlar HAD analiz sonuçları ile karşılaştırılmıştı
An Evaluation Study of Emd, Eemd, and Vmd for Chatter Detection in Milling
No full text3rd International Conference on Industry 4.0 and Smart Manufacturing (ISM) -- NOV 17-19, 2021 -- Upper Austria Univ Appl Sci, Hagenberg Campus, Linz, AUSTRIAIn modem machining processes, chatter is an inherent phenomenon that hinders efficiency, productivity, and automation. Numerous methods have been proposed using analytical, computational, and artificial intelligence methods to detect and avoid chatter during milling. The vibration signals generated during machining are of non-stationary and non-linearity nature. Hence solely time or frequency domain analysis are not adequate methods for chatter detection. This study investigates the performance of more advanced mode decomposition methods and compares them. Three decomposition methods, namely, empirical mode decomposition (EMD), ensemble empirical mode decomposition (EEMD), and variational mode decomposition (VMD), are used to decompose and identify chatter frequency bands. After decomposition, Hilbert-Huang transform (HHT) was applied for visualization. The comparative results indicate that EEMD or VMD decomposition methods performed better than EMD for intelligent chatter detection. (C) 2022 The Authors. Published by Elsevier B.V.Scientific and Technological Research Council of Turkey (TUBITAK) [118M414]This study was funded by The Scientific and Technological Research Council of Turkey (TUBITAK) through project grant no. 118M414
Benign and Malignant Neoplasms Affecting Periodontal Tissues: a Retrospective Study
No full textIntroduction: Oral neoplasms are the second most common oral lesions after reactive proliferative lesions. The aim of this study is to determine the distribution of the oral neoplasms by gender and age, and briefly discussed the clinical manifestations, diagnosis, and treatments of these lesions. Materials and Methods: To collect the study material, a pathological retrospective archive analysis has been performed and 61 oral neoplasm cases were determined in a total of 423 samples. 61 biopsies and clinical data of patients were studied and classified based on their histopathologic diagnosis, age, gender, and frequency. Results: In our study, a total of 61 neoplastic lesions were examined, and the mean age was 45.5 ±18.2. The most common lesion in the oral neoplastic lesion is leukoplakia (n=15, 24.59%). This is followed by squamous cell carcinoma (SCC) (n =13, 21.31%) and squamous papilloma (n =11, 18.03%). The rest are gingival granular cell tumor, hemangioma, odontoma, lipoma, mucosal nevus, myxoma, ameloblastoma, leukemia, melanoma, lymphoma, and osteosarcoma. Conclusion: This study provided important data on the frequency and histological distribution of oral benign and malign neoplasms. This study also highlights the diagnosis, and management of these oral neoplasms for the dentists
Numerical Investigation of Critical Heat Flux Under the Effect of Different Operating Conditions in Flow Boiling
No full textInternational Symposium on Convective Heat and Mass Transfer (CONV) -- JUN 05-10, 2022 -- Izmir, TURKEYThe influences of inlet mass flux, wall heat flux magnitude and non-uniform wall heat flux profile on the critical heat flux and its location in a vertical round tube are studied numerically. The extended RPI wall boiling model coupled with the two fluid Eulerian-Eulerian multiphase model are utilized. The base case is validated by comparison of obtained wall temperature against the available experimental and numerical data. The obtained results demonstrate that increment in applied wall heat flux leads to generate more vapor in the tube. Thus the wall superheat increases and causes to occurrence of critical heat flux. When the heated wall is subjected to the non-uniform heat flux profile the wall superheat increases and the location of dry-out condition shifts towards the tube inlet compared to uniform wall heat flux case
Kraft Lignin: From Pulping Waste To Bio-Based Dielectric Polymer for Organic Field-Effect Transistors
No full textLignin is an abundant biopolymer deriving from industrial pulping processes of lignocellulosic biomass. Despite the huge amount of yearly produced lignin waste, it finds scarce application as a fine material and is usually destined to be combusted in thermochemical plants to feed, with low efficiency, other industrial processes. So far, the use of lignin in materials science is limited by the scarce knowledge of its molecular structure and properties, depending also on its isolation method. However, lignin represents an intriguing feedstock of organic material. Here, the structural and chemical-physical characteristics of two kraft lignins, L1 and L2, are analyzed. First, several molecular characterization techniques, such as attenuated total reflectance - Fourier transform infrared spectroscopy, elemental analyses, gel permeation chromatography, evolved gas analysis-mass spectrometry, UV–vis, 31P- and 13C- nuclear magnetic resonance spectroscopies are applied to get insights into their different structures and their degree of molecular degradation. Then, their efficient application as gate dielectric materials is demonstrated for organic field-effect transistors, finding the increased capacity of L1 with respect to L2 in triggering functional and efficient devices with both p-type and n-type organic semiconductor molecules. © 2022 The Authors. Advanced Sustainable Systems published by Wiley-VCH GmbH.Università di Pisa, UniPiThis research received financial support from the University of Pisa through the project “BIHO 2021—Bando Incentivi di Ateneo Horizon e Oltre” (D.d. 408, Prot. no. 0030596/2021) and the program “Visiting Fellow.” The authors gratefully acknowledge the support and guidance of Prof. N. S. Sariciftci for this collaboration and his valuable discussions. The authors thank CISUP (Center for Instrument Sharing of the University of Pisa) for the access to the ATR?FTIR and FE?SEM facilities
Two-Dimensional Penta-Like Pdpse With a Puckered Pentagonal Structure: a First-Principles Study
No full textLow-symmetry penta-PdPSe (Pd4P4Se4) with intrinsic in-plane anisotropy was synthesized successfully [P. Li et al., Adv. Mater., 2021, 2102541]. Motivated by this experimental discovery, we investigate the structural, mechanical, electronic, optical and thermoelectric properties of PdPSe nanosheets via density functional theory calculations. The phonon dispersion, molecular dynamics simulation, and cohesive energy mechanical properties of the penta-PdPSe are verified to confirm its stability. The phonon spectrum represents a striking gap between the high-frequency and the low-frequency optical branches and an out-of-plane flexure mode with a quadratic dispersion in the long-wavelength limit. The Poisson's ratio indicates that penta-PdPSe is a brittle nanosheet. The penta-PdPSe is a semiconductor with an indirect bandgap of 1.40 (2.07) eV using the PBE functional (HSE06 hybrid functional). Optical properties simulation suggests that PdPSe is capable of absorbing a substantial range of visible to ultraviolet light. Band alignment analysis also reveals the compatibility of PdPSe for water splitting photocatalysis application. By combining the electrical and thermal transport properties of PdPSe, we show that a high power factor is achievable at room temperature, thus making PdPSe a candidate material for thermoelectric applications. Our findings reveal the strong potential of penta-PdPSe nanosheets for a wide array of applications, including optoelectronic, water splitting and thermoelectric device applications
2008 Küresel Ekonomik Kriz Sonrası Türk Bankacılık Sektöründe Nakit Tutma Oranlarının Seçili Finansal Göstergeler ile İlişkisi
No full textCash holding behavior is the most obvious application of risk avoidance and prudence in organizational terms. Cash holding, which refers to the use of a cash or cash-like asset to be protected or to make a profit at an uncertain time in the future, shows sectoral and temporal differences, and one of the most important of these differences is the periods of before and after the economic crises. In this study, cash holding behaviors in the Turkish banking sector after the 2008 period were examined with the regression model and it was determined that the banking sector indicators such as total assets, loans, non-performing loans and debts to banks, and inflation and gross domestic product, which are macroeconomic indicators, have an effect on the cash holding rate.Nakit tutma davranışı organizasyonel anlamda riskten kaçışın ve ihtiyatlı davranmanın en belirgin uygulaması olmaktadır. Nakit veya nakit benzeri bir varlığın korunmak veya gelecekte belirsiz bir zamanda kar etmek amacıyla kullanılmasın ifade eden nakit tutma sektörel ve zamansal olarak farklılıklar göstermekte ve bu farklılıkların en önemlilerinden bir tanesi ekonomik krizlerin öncesi ve sonrası dönemler olmaktadır. Bu çalışmada ise Türk bankacılık sektöründe 2008 dönemi sonrasında nakit tutma davranışları regresyon modeli ile incelenmiş ve bankacılık sektörü göstergelerinden toplam aktifler, krediler, takipteki krediler ve bankalara borçların ve makroekonomik göstergelerden enflasyon ile gayrisafi yurtiçi hasılanın nakit tutma oranı üzerinde etkisi olduğu tespit edilmiştir
Evaluation of Amine Functionalized Thermal Power Plant Solid Waste for Industrial Wastewater Remediation
No full textMicro/nanoparticles generated after the combustion of coal/lignite in the thermal power plants were modified with amino groups of (3-aminopropyl) triethoxysilane (APTES). These silane-based functional particles were applied in textile dye (xylenol orange, XO and methyl orange, MO) removal process to deal with an industrial wastewater problem. The maximum adsorption efficiencies of APTES coated micro/nanoparticles for MO and XO dye molecules were calculated to be around 98% and 75%, respectively. The adsorption behavior of the LCFA against dyes is also assessed by investigating the effect of adsorbent dosage, contact time, pH, and temperature. The optimum dye removal was observed at a pH of 4.0, and the equilibrium was achieved within 5 min. The maximum uptake capacities of LCFA-APTES for MO and XO dye molecules were calculated to be around 17.91 and 14.72 mg g-1, respectively. This value is approximately 3 - 5 times higher than the similar adsorbent in the literature. The uptake mechanism of MO and XO dyes onto LCFA-APTES is governed by electrostatic interaction and hydrogen bonding between dye molecules and APTES. The surface chemical modifications and the nature of functional groups were ascertained by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray fluorescence (XRF), and X-ray photoelectron spectroscopy (XPS). The application of recovered micro/nanoparticles from solid wastes and their utilization for wastewater treatment is important not only for economy of developing countries but also for protecting the environment.Max-Planck-Gesellschaft (MPG); Borcelik Steel Industry Inc.H.D. gratefully acknowledges Max-Planck-Gesellschaft (MPG) for the financial support of the MPIP-TOBB ETU Partner Group Program (Soft Matter in Nanoconfinement). We are grateful to members of the UNAM, Bilkent University, for their enduring support and helpfulness. Also, Thanks are due to Borcelik Steel Industry Inc. for their support to use SEM and EDX analyses. Gratefully acknowledges Eczacibas ; imath; Building Products (Vitra) for their support to obtain textile dyes