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Abstract Microgrids integrating local renewable energy sources at low-voltage level show promising potentials in realizing a reliable, efficient, and clean supply of electricity. Further improvements are expected when such a microgrid is operated based on direct current (dc) instead of alternating current (ac) infrastructure for power distribution commonly in use today. Our study aims to systemically quantify the gap between environmental impacts of microgrids at building level using the case study of power distribution within office buildings. For this purpose, a scalable comparative life cycle assessment (LCA) is conducted based on a technical bottom-up analysis of differences between ac and dc microgrids. Particularly, our approach combines the micro-level assessment of required power electronic components with the macro-level requirements for daily operation derived from a generic grid model. The results indicate that the environmental impacts of employed power electronics are substantially reduced by operating a microgrid based on dc power distribution infrastructure. Our sensitivity analyses show that efficient dc microgrids particularly lead to savings in climate change impact emissions. In addition, our study shows that the state-of-the-art scaling rules of power electronics currently used in LCAs leads to inaccurate results. In contrast, the proposed methodology applies a more technical approach, which enables a detailed analysis of the environmental impacts of power electronic components at system level. Thus, it provides the foundation for an evaluation criterion for a comprehensive assessment of technological changes within the framework of energy policy objectives.

The object of this study was to identify the pro cesses in the production of beet sugar and apply to these processes the first and second laws of therm.0dynam.ic3 to determine the losses and irreversibilities. The sugar industry is dependent on agriculture and for this reason is a preferred industrial sector in deve loping countries because both agricutural and industrial development can be achieved. Furthermore the by-products of sugar factories can be utilised in other agricultural area.3 In parallel with increasing population and national income, it has been necessary to modernise the existing stigar factories and to boild new factories in light of the experience gained. Decrease in the supply of fossil fuels ami environmental considerations have forced industry to take measures for energy recovery and to utilise energy sources at lower temperatures. For this reason/ the mass and energy balances of sugar production processes based on practical estimations of dry substances, sacca rose ratio and purity is inadequate. In the first section of this thesis the first and second laws of thermodynamics and the availability equation are stated and their application to closed and open systems are shown by examples. Information on the properties of the sugar beet and processes related to extraction of sugar from beets is given next. Later the processes are considered separately and the energy and available energy analysis are made for each process. The thermodynamic properties of the substances taking place in this processes are expressed in equation form by using the tables ami graphs available in the literature, BALOH [1], IRVINE and LILEY [2]. The development of sugar industry in Turkey and its present state are also accounted. The capacities and production rates of the sugar factories are given m a table. In the third section of the thesis the operating parameters of the Elazığ Sugar Factory are used as input., to do a first and second law analysis of the production processes in a sugar factory. The processes of sugar production from beets is shown in the diagram below. vi ıWater Beets J L_ JUICE PRODUCTION Water. C02 - Lime - Pressed Molasses.JUICE PURIFICATION Fuel-*- DRYING OF Air - MOLASSES Dried `*` Molasses Sludge.JUICE CONCENTRATION Make-up water Fuel Air _1 L REFINERY Waste water ELECTRICITY AND STEAM GENERATION i r Electrical Stack Energy Gases Molasses Sugar Block Diagram of Processes in a Sugar Factory Processing Beets In the Elasig Sugar Factory 48.79 k¥h (175643 kJ) heat energy and 3.02 kWh (10872 kJ) electrical energy was used to produce 14.83 kg sugar from 100 kg of beets during the 1990 campaign. 100 kg of beets has been used as a reference quantity and referred to as unit beet (BP) in this study. The daily sugar production capacity of the Elasig Sugar Factory is 1650 tons of beets. During the 1990 campaigne the daily production rate of the factory was 165 tons of crystal sugar and 26 tons of cube sugar. The daily average thermal energy used for this production was 628415 k¥h (2262.3 GJ) and the daily average electrical energy requirement was 38898 klh (140 GJ). A steam turbine cogeneration plant was used to supply the heat and electricity requirements. 18 m3/h of steam at 2.5 MPa pressure and 380°C temperature i3 produced in three steam boilers. Electricity is produced by three 1.2 HW five stage turbines. The back pressure in the turbines is between 0.8 and 2.2 bars. The average power output of the turbines during the 1990 campaign was 2. 3 MW. VI 11For comparison., a sugar factory in German uses 11.811 k¥h (42520 kJ) of thermal energy and 6.668 kWh (24005 kJ) of electrical energy to produce 14.46 kg sugar per 100 Kg beets, AUERSWALD [3J. The capacity of this factory is 4440 tons beet per day and the daily thermal and electrical energies used in' this factory are 524000 kWh (1886.4 GJ) and 296000 kWh (1066 GJ) respectively. The reason for the high electric energy usage in this factory compared to Elazığ Sugar Factory is that heat pumps are used to regain heat at low temperatures. The main reason for the low thermal energy usage in this factory is that electiricity used is largely bought from the national grid and therefore, the amount of steam required to generate electricity for the turbines is lowered. In the Elazığ Sugar Factory a total of 51.81 kWh (186516 kJ) of thermal and electrical energy was used to process 100 kg of beets. The reasons for high energy usage are the low capacity of the factory, the old technology U3ed and design faults such as the unnecessarily long steam supply lines. With today' s technology it is estimated that the total energy requirement to process 100 kg of beets can be lowered` to 40.56 k¥h (146016 kJ), BÂLOH [4]. This represents a energy saving of 21.7 % over the present ene rgy r e qui r emen t s. With the computer program developed in this study it is possible to perform energy and exergy (available energy) analysis for sugar factories. The processes (open systems) and the inlet and outlet streams associated with these processes are identified first and then the entalpies and available energies of these streams are calculated. Application of the first law of thermodynamics and the availability equation to these processes yield the heat transfer, irreversibilities., first and second law efficiencies of these processes. In the analysis of the Elazığ Sugar Factory, the general flow diagram for factories producing sugar from beets was taken as basis.. Ö2KAN [5]. This flow diagram given in section 3.2.2 show very little variations in different factories producing sugar from beets. The computer program that has prepared in this thesis is modular and therefore these variations can easily be incorporated into it. It is also possible, to chance the control volumes so that any portion of a process can be analysed in more detail. By using this computer program it is expected that a first and second law analysis can be made In the planning stage so that the construction and layout of te factory can be optimised. The first law efficiency of the processes concerned has been defined as the ratio of the total enthalpy of the masses leaving the control volume to the sum of the total enthalpy of the masses entering the control volume and the electric energy input to the control volume. This is a measure, of the heat transfer to the IXenvironment. If heat transfer to the environment can be lowered., the first law efficiency can be improved. Equation 2.7 expresses the first law efficiency. The second law efficiency of the processes concerned has been defined as the ratio of the availability of the masses leaving the control volume less the availability of heat transfer to the environment to the availability of the masses entering the control volume plus the electrical energy input. The second law efficiency is a measure of the irreversibilities in the process. Second law efficiency increase as the heat transfer to the environment and the internal irreversibilities in the process are lowered. Equation 2.27 expresses the second law efficiency. Results of the first and second law analysis of the processes in the Elazığ Sugar Factory are summarised below. In the juice, production process the first law efficiency is 95 % and second law efficiency 55 %. In this process third stage steam at 103°C is used as the heating medium. Since the temperature of the water or juice being heated is at least 21°C lower than this temperature, irreversibilities due to heat transfer at a finite temperature difference increase. The use of fourth stage steam at 90°C, by increasing the heating surfaces will lower the irreversibilities. In the jxiice purification process the first law efficiency was calculated as 90 % and the second law efficiency was calculated a3 70 %. In the limed raw juice heating section of this process fourth stage steam at 90°C, instead of third stage steam at 103°C should be used to reduce irreversibilities. For the same reason the third stage steam at 103°C can be used instead of the second stage steam at 115°C in the carbonation heating section. In the juice concentration stage, the first law efficiency was calculated as 96 % and the second law efficiency was calculated as 91 %. The reason for higher efficiencies is that concentration is done in stages and that the vapour seperated from juice in one stage is used to heat juice in the next stage. The frequent cleaning of the heaters to prevent the formation of deposits will decrease the quantity of stream required in the heaters. This will help increase the first and second law efficiencies. In the refining process., the first law efficiency was calculated as 78 % and the second law efficiency was cal culated as 67 %. The reason for higher irreversibilities in the crystalliser is that the vapour separated from the juice i 3 condenced at a high temperature difference inthe condensers and that the low temperature condensates cannot be used for further heating. Furthermore high temperature dif frence s are needed in the vacuum pans. In the drying of molasses, the first law efficiency was calculated as 71 % and the second law efficiency as 20 %. The fuel expenditure for drying molasses in sugar factories that process beets is quite high. In the E la sığ Sugar Factory 3.84 küflı (13424 kJ) of thermal e- nergy is used to obtain 1 kg of dry molasses and 3.29 k¥h (11844 kJ) of thermal energy is used to obtain 1 kg of sugar. The energy balance in the process of drying molasses show that a larger portion of the fuel energy is passed to the evaporating water. The second law analysis show that the ava i lability of the resulting vapours is low due to low temperatures. As a result the loss of available energy in drying molasses is high. The irreversibilities originate from incomplete combustion., mixing of cool air with the drying air and the high temperature difference between the molasses and the drying air stream. The irreversibilities in the mixing chamber can be prevented by using the combustion chamber as a boiler for steam generation. Thus the combustion gases need not be mixed with cool air to attain the proper temperature for drying but are colled to the required tempetarure during the production of steam. The production rate of dry molasses of the factory is 1700 tons per year. The rest of the molasses is given to the livestock growers to be used as animal feed. In the steam generation process the first law efficiency was calculated as 79 H and the second law efficiency was calculated as 35 %. In the process of steam generation 4. 37 kg of fuel oil with a lower heating value `of 40193 kJ/kg` per 100 kg of beets. The irreversibilities in steam generation result from the combustion process itself. The deposition of layers on steam generating surfaces and the high temperature stack gase3 also in drying molasses decrease the losses and hence the fuel consumption. The results of the first and second law analysis made showed that the second law efficiencies could be much lower than the first law efficiencies and that conclusions based on first law analysis alone could be misleading. Bu çalışmanın amacı pancar işleyen bir şeker fabrikasında üretim süreçlerini belirlemek ve bu süreçlere termodinamiğin birinci ve ikinci kanunlarını uygulamak ol muştur. Çalışmada önce termodinamiğin birinci kanunu, termodinamiğin ikinci kanunu ve kullanılabilir enerji denklemleri açıklanmıştır. Pancardan şeker üretimi süreçleri tek tek ele alınarak, Elazığ Şeker Fabrikası verileriyle enerji ve kullanılabilir enerji çözümlemesi yapılmıştır. Pancardan şeker üreten fabrikaların genel akım şemalarına göre. üretim süreçleri: Şerbet üretimi, şerbetin arıtılması, şerbetin koyulaştırılması, şekerin kristalleştirilmesi ve eldesi, küspe kurutma ve buhar üretimi olarak alınmıştır. Bu çalışmada geliştirilen bilgisayar programında süreçlerin birinci ve ikinci kanun verimleri hesaplanarak karşılaştırılmıştır. Süreçlerin enerji ve kullanılabilir enerji çözümlemeleri modüler biçimde yapıldığından, istenildiğinde bası kontrol hacimleri hesap dışı bırakılabilir. Bundan başka daha dar kapsamlı kontrol hacimleri seçilerek kurulu fabrikalarda yenileştirmeler, kurulacak fabrikalarda projelendirme yönlendirilebilir. Yapılan enerji ve kullanılabilir enerji çözümlemeleri sonucunda şerbet üretimi ve şerbet arıtma süreçlerindeki bası ısıtıcılarda daha. düşük sıcaklıkta ısıtıcı buhar kullanımının mümkün olabileceği saptanmıştır. Şerbetin koyulaştırılması sürecinde ise tüketiciler için çekilen buhar miktarlarının azaltılması ile koyulaştırma için gereken çürük buhar miktarı düşecektir. Küspe kurutma sürecinde tersinmezlikler yanma odasının modernize edilme si, karışım odasının buhar üretici olarak kullanılması ile azaltılabilir. Buhar üretimindeki kullanılabilir enerji kayıpları kazan veriminin düşüklüğünden, yanmanın tam olmamasından kaynaklanmaktadır. Şeker üretiminde nominal çalışma noktasından sapmalarda ortaya çıkan buhar tüketimi fakları veya buhar üreticisinde ısıtıcı yüzeyler üzerinde biriken katmanlar nedeniyle yüksek sıcaklıkta a- tık gazların oluşması, kayıplara yol açar. Bu atık gazların küspe kurutmada kullanılması kayıpları, dolayısıyla da yakıt tüketimini azaltır. Yapılan enerji ve kullanılabilir enerji çözümlemeleri sonucunda enerji çözümlemelerinin, tersinmezlikleri gözönüne almaması nedeniyle, kullanılabilir enerji çözümlemeleriyle tamamlanmadığı zaman yetersiz kaldığı ve hatta yanıltıcı sonuçlar verdiği saptanmıştır. 150

A aviação global contribui significativamente para a mudança climática, representando cerca de 2,5% das emissões globais. Os Combustíveis de Aviação Sustentáveis (SAF) oferecem uma alternativa promissora, emitindo até 80% menos CO2 do que o combustível de aviação convencional. No entanto, espera-se que os preços do SAF superem os preços do querosene fóssil, levando a aumentos de custos para os passageiros. Esta tese estuda como a introdução do SAF influencia os principais fatores de comportamento do cliente na indústria da aviação no mercado europeu e se os incentivos podem efetivamente encorajar uma adoção maior. Uma análise de conteúdo qualitativa usando a metodologia de Gioia foi conduzida com base em 15 entrevistas semiestruturadas com especialistas da indústria da aviação, e foram derivadas descobertas-chave. Utilizando os insights coletados nas entrevistas com especialistas, foi realizada uma pesquisa com o público em geral, com 261 participantes. As entrevistas com especialistas confirmam a literatura existente sobre a importância do SAF e a necessidade de novas estratégias para engajar efetivamente os clientes durante a introdução no mercado. Os resultados da pesquisa demonstram que fatores como sensibilidade ambiental, consideração dos impactos ambientais na reserva, medidas de compensação anteriores, frequência de voos, sexo e idade (associada ao rendimento) influenciam positivamente a disponibilidade para pagar pelo SAF. Os resultados identificam elementos cruciais para alcançar um voo mais neutro em carbono com SAF do ponto de vista do cliente. Eles ilustram como os incentivos podem criar um cenário vantajoso para ambos, beneficiando tanto as companhias aéreas quanto os clientes. Global aviation significantly contributes to climate change, representing about 2.5% of global emissions. Sustainable Aviation Fuels (SAF) offer a promising alternative, emitting up to 80% less CO2 than conventional jet fuel. However, SAF prices are expected to surpass fossil kerosene prices, leading to cost increases for passengers. This thesis studies how the introduction of SAF influences key customer behavior factors within the aviation industry in the European market and whether incentives can effectively encourage greater adoption. A qualitative content analysis using Gioia’s methodology was conducted based on 15 semi-structured interviews with aviation industry experts, and key findings were derived. Utilizing the insights gathered from the expert interviews, a survey was carried out among the general public with 261 participants. The expert interviews confirm the extant literature regarding the significance of SAF and the need for new strategies to effectively engage customers during market ramp-up. The survey results demonstrate that key factors positively influence willingness to pay (WTP) for SAF. Factors include environmental awareness, consideration of environmental impacts when booking, previous compensation measures, frequency of flying, gender, and age (linked to income). Incentives can further increase WTP for SAF, most notably for seats with extra legroom and proportionally, most on short-haul flights. The results identify crucial elements for achieving more carbon-neutral flying with SAF from the customer's perspective. They illustrate how incentives can create a win-win scenario, benefiting both airlines and customers.

ÖZET Anahtar kelimeler - Taşıt tahriki, Sıfir emisyonlu taşıt, Alternatif enerji, îçten yanmalı motorlar, Yakıt hücresi Dünya fosil yakıt rezervlerinin tükenmekte olması, günümüz taşıtlarının çevre kirliliğine sebep olması insan yaşamında taşıtların yerinin vazgeçilmez olması gibi etkenler yeni alternatif tahrik sistemleri ve alternatif yakıt sistemleri bulmayı zorunlu kılmaktadır. Bu çalışmada içten yanmalı motorlarda kullanılabilecek alternatif yakıtlardan; biyogaz, bitkisel yağlar, hidrojen ve alkolün fiziksel ve kimyasal özellikleri verilmiş, motor performanslarına etkileri incelenmiştir. Günümüz taşıtların tahrik sistemlerinde köklü değişiklikler meydana gelmektedir. Bunların başlıcalarını elektrikle tahrik edilen sistemler oluşturmaktadır. Bu tür taşıtlarda tahrik amacıyla kullanılan enerji bataryalardan, güneş enerjisinden veya yakıt hücresinden sağlanmaktadır. Gelecekte yakıt hücreleri alternatif tahrik sistemlerinde önemli bir yer teşkil edeceklerdir. Bu açıdan yakıt hücrelerinin maliyetlerinin düşürülmesi ve kapasitelerinin artırılması büyük önem arz etmektedir. Bu çalışmada yakıt hücre tiplerine değinilerek bu konuda yapılan çalışmalar incelenmiştir. VUI ALTERNATIVE ENERGY RESOURCES FOR VEHICLE ENGINES SUMMARY Key Words - Vehicle propelling, Zero emission vehicle, Alternative energy Internal combustion engines, Fuel cell. The usage of alternative fuel systems are required due to the consumption of world fossil reserves, environmental and air pollution occurred by today's vehicles and their vital role in daily life. In this study, the physical and chemical properties of alternative fuels like biogas, vegetal oils, hydrogen and alcohol used in internal combustion engines were introduced and their effects on motor performance were investigated. There are radically changes in propelling systems of today's vehicles. The most important one of them is electrically propelled systems. The energy used in propelling is obtained from energy cells, sun and fuel cell in this kind of vehicles. The fuel cells will be used in propelling systems as an alternative in future. Therefore the costs of them should be decreased and their capacities must be increased. In this study fuel cell types were introduced and relegated studies were investigated. IX 76

ABSTRACT COMPUTER SIMULATION OF A SOLAR ASSISTED HEAT PUMP COŞKUN, A. Ümit M.S. in Mechanical Engineering Supervisor: Prof. Dr. Rüknettin OSKAY Co-Supervisor: Prof. Dr. Faruk ARINÇ August 1993, 130 pages The aim of this study is to examine the performance of a heat pump which is assisted by a solar system. The refrigerant inside the heat pump is heated by the evaporator which is immersed into the storage tank of a solar system. The refrigerant leaves its energy to a space to be heated by its condenser which is located in the space. The tank is filled with water-antifreeze solution as the working fluid of a solar system. The fluid is heated by the solar collectors and this energy is stored in the storage tank due to thermal capacity of the fluid inside the tank. The basic components of the iiiheat pump are a reciprocating compressor, an electrical motor driving the compressor, a compact heat exchanger as the condenser, a capillary tube as the expansion device and a tube in helical coil type immersed into the storage tank as the evaporator. The computer program designs the components according to given design conditions. Then, it simulates the heat pump for off -design conditions (different tank and room temperatures). The program determines the safe operation conditions of the heat pump ( to avoid the liquid in suction or chemical reaction of refrigerant with oil inside the compressor at high temperatures). Finally, it obtains a chart which can be called as heat pump performance chart. It is possible to see the safe operation zone, heat transferred to the room, power consumption of the compressor and COP of the heat pump cycle for specified room and tank temperatures. The program is tested for many off-design conditions and the above performance charts and characteristic are obtained. The input data such as property table of a new refrigerant can easily be incorporated and the program has flexible features to handle new cases efficiently. It is observed that the program is very successful for each case in simulation of the operation of a heat pump assisted by a solar system. ivKeywords : Heat pump. Solar assisted heat pump, simulation and modelling Science Code : 625. 04. 05 oz GÜNEŞ ENERJİSİ DESTEKLİ ISI POMPASININ BİLGİSAYARLA BENZEŞİMİ COŞKUN, A. Ümit Yüksek Lisans Tezi, Makina Mühendisliği Anabilim Dalı Tez Yöneticisi: Prof. Dr. Rüknettin OSKAY Yardımcı Tez Yöneticisi: Prof. Dr. Faruk ARINÇ Ağustos 1993, 130 Sayfa Bu çalışmanın amacı, güneş enerjisi destekli bir ısı pompasının performansım bilgisayar yardımı ile incelemektir. Bu çalışmada, ısı pomposımn bir depolama tankı ile ısıtılmak istenen bir mahal arasında enerji transferi yaptığı düşünülmüştür. Isı pompasının içindeki soğutucu gaz, enerji depolama tankının içine yerleştirilmiş buharlaştıncı tarafından ısıtılır. Soğutucu gaz enerjisini ısıtılacak mahale yerleştirilmiş yoguşturucu vasıtasıyla bırakır. Depolama tankının içindeki akışkanın antifiriz-su karışımı olduğu kabul edilmiştir. Akışkanın güneş sistemi tarafından ısıtılıp enerjisi depolama tankında ısıl kapasite olarak depolandığı kabul viedilmiştir. Sistemin temel birimleri, kompresör, kompresörü döndüren bir elektrik motoru, yoguşturucu olarak bir eşanjör, genleşme cihazı olarak bir kılcal boru ve buharlaştıncı olarak da depolama tankının içinde helis şeklinde sarılmış boru düşünülmüştür. Bilgisayar programı, önce tasarım şartlarına göre sistem parçalarının tasarımını yapıp boyut landınr. Sonra tasarım şartlarından farklı koşullardaki ( değişik oda ve tank sıcaklıklarında ) çalışmasını inceler. Bu sırada ısı pompasının güvenli çalışma koşullarım belirler. Daha sonra, oda ve tank sıcaklığına bağlı olarak güvenli çalışma bölgesini, ısı transfer miktarını, kompresör enerji harcamasını gösteren ve ısı pompası performans diyagramı diyebileceğimiz bir grafik elde eder. Bunlara ilave olarak, kullanılacak olan soğutucu gazlar da modellenmiştir. Bu gazların özelliklerine denklemler uydurulmuştur. Aynı zamanda farklı soğutucu gazların tablo halindeki değerlerini girip, denklemler uydurup kullanmak mümkündür. Anahtar Kelimeler : Isı pompası, güneş enerjisi destekli ısı pompası, benzeşimi ve modelleme. Bilim Dalı Syısal Kodu : 625.04.05 vii 130

ABSTRACT STEADY-STATE AND TRANSIENT PERFORMANCE ANALYSES OF A DOUBLE OUTPUT INDUCTION GENERATOR OPERATING AT SUBSYNCHRONOUS AND SUPERSYNCHRONOUS SPEEDS ÇADIRCI, Işık Ph.D. in Electrical and Electronics Engineering Supervisor: Prof. Dr. Muammer Ermiş March, 1994, 208 pages This thesis covers the steady-state and the periodic transient performance analyses of a double output induction generator operated at varying shaft speeds in the sub- and super- synchronous regions, by control of both the magnitude and direction of slip power. First, a modified equivalent circuit is used in the analyses in which core losses and, all voltage and current harmonics are ignored. An optimum control strategy, which maximizes the total electrical power output of the double output induction generator is determined, and theoretical results are verified experimentally with particular emphasis on the system including naturally-commutated converters. The limitations of naturally-commutated converters and then- effects on the output power characteristic of the system are also discussed. inFor this purpose, a rigourous performance analysis of the double output induction generator system with two controlled converters is carried out, including also the effects of both the rotor side converter's commutation angles and harmonics as well as the supply side converter's harmonics. This is achieved by using a hybrid mathematical model of the induction machine in which stator variables are transformed onto a reference frame fixed in the rotor whose variables are kept in actual three-phase quantities. This model allows for the changing states of conduction of the rotor side converter's thyristors. 12 sets of first order differential equations with constant coefficients are obtained and solved in an ordered sequence using the fourth order Runge-Kutta technique. Several instantaneous voltage, current, torque and output power waveforms in periodic transient states and for operations at different points in both the sub- and super- synchronous speeds are obtained by the use of the mathematical model. The variations in overlap angle of the rotor side converter is obtained for a wide range of shaft speeds and for various firing control angles under constant rotor current conditions. Also the starting transients of the system are examined under varying speed conditions. The performance of the system in periodic transient state is also obtained experimentally in the laboratory on a special purpose set-up, and presented in the thesis in comparison with the theoretical results described above. A good agreement between the theoretical and experimental results is observed. IVSince wind electricity generation is considered as a promising field of application for this system, the performance of a wind energy conversion system employing a double output induction generator is optimized on the basis of annual energy production with allowance for the effects of overlap and extinction angles. A comparison is made among alternative induction generator schemes used in wind energy conversion systems on the bases of annual energy production, transfer characteristics and net present worth of these schemes for the same site and turbine. Keywords: Double output induction generator, subsynchronous, supersynchronous, converters, overlap angle, energy conversion, wind energy Science Code: 608.01.02 öz SENKRON ALTI VE SENKRON ÜSTÜ HIZLARDA ÇALIŞABİLEN ÇİFT ÇIKIŞLI BİR ENDÜKSİYON GENERATÖRÜNÜN KARARLI VE GEÇİCİ DURUM BAŞARIM ANALİZLERİ Çadırcı Işık Doktora Tezi, Elektrik Elektronik Mühendisliği Anabilim Dalı Tez Yöneticisi: Prof. Dr. Muammer Ermiş Mart 1994, 208 sayfa Bu tez, kayma gücünün akış yönü ve büyüklüğünü kontrol ederek senkron -altı ve -üstü bölgelerde geniş bir mil hızı değişim aralığında çalıştırılabilen çift çıkışlı endüksiyon generatörünün kararlı ve periyodik geçici durum başarım analizlerini kapsamaktadır. Yapılan analizlerde, ilk olarak çekirdek kayıpları ve bütün akım-gerilim armoniklerinin ihmal edildiği değişik bir eşdeğer devre modeli kullanılmıştır. Çift çıkışlı endüksiyon generatörünün toplam elektriksel çıkış gücünü maksimize edecek bir optimum kontrol stratejisi belirlenmiş, ve teorik çalışma sonuçları, doğal geçişli çevirgeçler içeren sistem ön planda tutularak deneysel olarak sınanmıştır. Ayrıca, doğal geçişli çevirgeçlerin sınırlamaları ve bunların sistemin çıkış gücü karakteristiğine olan etkileri de tartışılmıştır. vıBu amaçla, iki kontrollü çevirgeç ile donatılmış çift çıkışlı endüksiyon generatörü sisteminin, hem rotor tarafına bağlı çevirgecin geçiş açılarını ve harmoniklerini, hem de şebekeye bağlı çevirgecin harmoniklerini dikkate alan ayrıntılı bir performans analizi yapılmıştır. Bunun için, stator değişkenlerini rotorda sabit bir referans eksenine göre dönüştüren, rotorunkileri ise gerçek üç faz değerler halinde bırakan hibrid bir endüksiyon makinası modeli kullanılmıştır. Bu model, rotora bağlı çevirgecin tiristörlerinin değişen iletim durumlarını doğrudan dikkate alabilmektedir. Elde edilen birinci dereceden, sabit katsayılı 12 diferansiyel denklem dizisi dördüncü derece Runge-Kutta tekniği kullanılarak belirli bir sırada çözülmüştür. Bu matematiksel modeli kullanarak, peryodik geçici durumlarda ve senkron altı ve üstü değişik çalışma noktalarında birçok anlık akım, gerilim, moment ve çıkış gücü eğrileri elde edilmiştir. Rotor tarafına bağlı çevirgecin geçiş açısındaki değişmeler sabit rotor akımı koşullarında, geniş bir mil hızı aralığı ve birçok ateşleme açısı için hesaplanmıştır. Aynı zamanda, sistemi başlatma anındaki geçici durumlar değişken mil hızı koşulunda incelenmiştir. Sistemin peryodik geçici durum başarımı aynı zamanda laboratuvarda, özel amaçlı bir deney seti üzerinde pratik olarak da elde edilmiş ve tezin içerisinde yukarıda belirtilen teorik sonuçlarla karşılaştırmalı olarak sunulmuştur. Deneysel sonuçların teorik sonuçlarla aynı doğrultuda olduğu gözlenmiştir. vııBu sistemin rüzgar enerjisi dönüşüm alanında kullanımı ümit verici gözükmektedir. Bu nedenle, çift çıkışlı endüksiyon generatörlü bir rüzgar enerjisi dönüşüm sisteminin performansı, yıllık enerji ürerimi bazında, çevirgeç geçiş ve sönüm açılarının generator performansına etkileri de dikkate alınarak eniyilenmiştir. Ayrıca, aynı konum ve türbin koşullan için, rüzgar enerjisi dönüşüm sistemlerinde kullanılabilecek değişik endüksiyon generatörlü sistemlerin yıllık enerji üretimi, transfer eğrisi ve bugünkü net değerleri açılarından karşılaştırmaları da yapılmıştır. Anahtar Kelimeler: Çift çıkışlı endüksiyon generatörü, senkron altı, senkron üstü, çevirgeç, geçiş açısı, enerji dönüşümü, rüzgar enerjisi Bilim Dalı Sayısal Kodu: 608.01.02 vııı 208

The production of sustainable fuels for transportation and energy represents an essential technology enabling the transition away from fossil fuel use. Over the past two decades several biological routes for the production of chemically identical molecules to those in fossil fuels (‘drop-in’ fuels) have been discovered and characterized. These have held promise as breakthrough technologies but have yet to reach commercial viability. Industrial scale bioprocess development for drop-in fuel production has been held back by high feedstock prices and inadequate process efficiencies. Currently, bioethanol and biodiesel are produced using crop-derived sugars and oils, so called ‘1st generation’ biofuels. Although their use positively impacts net CO2 emissions, their derivatization from food crops means they compete for arable land. To avoid this ‘food vs. fuel’ issue, alternative carbon sources for bioproduction must be explored. In this thesis the use of two non-sugar substrates, acetate and ethanol, were explored as carbon sources for hydrocarbon biosynthesis. Either carbon source enabled the production of these compounds at titres and product/substrate yields similar to that of glucose. The rate and efficiency of substrate conversion to product largely governs the viability of a bioprocess. These properties are in part defined by the enzymes that make up the relevant metabolic pathways. One of these pathways is the cyanobacterial alkane biosynthesis pathway discovered in 2010, consisting of acyl-ACP reductase (AAR) and aldehyde deformylating oxygenase (ADO). The terminal ADO enzyme is known for its low catalytic efficiency, and as a result many enzyme engineering efforts have targeted this enzyme. This thesis describes the design of growth-coupled approaches for engineering ADO. Growth-coupling involves linking enzyme activity to cell fitness and taking advantage of the principles of directed evolution to select for improved enzyme variants. Several growth-coupling approaches were assessed in this work through a combination of in silico flux balance analysis and experimental work, mostly focussing on the byproduct of ADO – formate. These efforts resulted in functional growth-coupling of ADO activity via the reductive glycine pathway. Another approach to growth-couple ADO activity was based on redox cofactor auxotrophy. An E. coli strain lacking all central metabolic pathways for NAD+ reduction was constructed, dubbed NADHaux, and its growth could be tightly linked to NADH generation by formate oxidation. Taken together, this thesis provides insights into the extremes of E. coli redox metabolism and presents hopeful results regarding the use of non-sugar carbon sources for bioproduction. In addition, it describes valuable novel methodologies for the evolutionary engineering of alkane biosynthesis.

From the British debate on the depletion of coal in 1865 to the First World Power Conference held in London in 1924, scientists, engineers, industrialists, and politicians produced new interpretations of the past, present, and future in terms of the mobilisation of energy resources. This thesis identifies an emerging ‘energy developmentalism’, which called for maximising energy use to maintain or improve a nation’s place in international competition. Energy developmentalism was not a marginal worldview confined to ‘energeticists’, but a coherent set of claims, measurements, and arguments that informed energy governance on an international scale. Rather than focusing on a single resource, energy developmentalism applied a unified schema to all energy sources, including those like solar and tidal energy that were still mostly theoretical. Drawing on sources from across Europe, while staying grounded in political changes in Britain and France, makes it possible to understand how a general formula for transforming raw materials with maximum efficiency was applied differently depending on specific political contexts. This period saw the articulation of problems like the depletion of resources, the difference between renewable and nonrenewable energy, the intermittency of renewables, the overreliance on a single source of energy, and the centrality of energy to modern economies – problems that are often associated with later periods. Scientific measurements of efficiency, horsepower, and kilowatts became operators in political debates centred on questions of national standing and progress. Even as oil became increasingly important in the world economy, the delegates at the First World Power Conference transformed a vision of a renewable energy future into one of a general expansion of energy consumption as the basis of progress. In so doing, they downplayed the continued importance of fossil fuels and equated ‘conservation’ with the fullest possible use of all energy sources, renewable or not.

Abstract With drastic fossil fuel depletion and environmental deterioration concerns, a move towards a more sustainable bioenergy-based economy is essential. Lately, the application of microwave (MW) irradiation for waste processing has been attracting interest globally. MW-assisted heating possesses several advantages such as the provision of high microwave energy into dielectric materials with deeper penetration for internal heat generation, showing beneficial features in improving the heating rate and reducing the reaction time. Consequently, the most recent literature regarding the applications of MW-assisted heating for biomass pretreatment as well as biofuel and bioenergy production was reviewed and consolidated in this study. An impressive increase in the product yield and improvement of the product properties are reported, with the use of MW-assisted heating in several conversion routes to produce biofuels. Despite being a promising technology for biofuel production, some major fundamental data of MW-assisted heating have not been comprehensively identified. Therefore, the feasibility of this technology for large-scale implementation is still subpar. Understanding the interaction between the feedstock and the microwave electromagnetic field, and the optimization of several operational and mechanical parameters are the two main keystones that would propel the industrialization of MW heating in the near future. This provides key insights leading to increased feasibility and more advanced application of MW heating.

ÖZET Sanayide kullanılan kirli ve sıcak atık suların enerjilerinin tekrar kullanılması, günümüzde enerji tasarrufu açısından önem kazanmaktadır. Sıcak ve kirli atık suların klasik ısı değiştiricilerinde kullanılması, hem işletme zorluklarını ortaya çıkarmakta, hem de enerji kaybına neden olmak tadır. Bu tür olumsuzlukları giderebilmek için, yeni bir ısı değiştiricisinin tasarımı ve performansının belirlenmesi çalışmanın amacını teşkil etmektedir. Ele alınan çalışmada, litaratürde tanımlanan konsantrik, iç içe iki borulu, klasik ısı değiştiricisi modeli esas alınarak, ilave tasarımlarla yeni tip ısı değiştiricisi modeli geliştirilmiştir. Geliştirilen modelde soğuk su, iç boruya, boru cidarına açılan 5mm*10mm boyutlarında, dikdörtgen kesite sahip kanallardan girmekte ve iç boru döndürülmektedir. Dönme etkisi ile boru girişinde, soğuk suya dönme li akış karakteri kazandırılarak, soğuk su tarafındaki ısı taşınım katsayısının iyileştirilmesi amaçlanmıştır. Anular aralıkta akan sıcak ve kirli su tarafında ise, ısı taşınım katsayısının iyileştirilmesi yanında, kirli suyun daha kolay tahliyesi için, iç borunun dış yüzeyi helisel kanatlı imal edilmiştir. îç borunun döndürülmesiyle helisel kanatlar vida taşıyıcı görevi yaparak, kirli sıcak suyu dışarıya tahliye etmektedir. Deneyler soğuk su girişinin iki veya dört kanaldan sağlanması halinde ve iç borunun değişik devir sayılarında, aynı yönlü paralel akışlı ve zıt yönlü paralel akışlı ısı değiştiricisi tiplerinde yapılmıştır. Aynı deneyler iç borunun dış yüzeyindeki helisel kanatların 3 Oram, 20mm, 10mm' lik helis adımaları için tekrarlanmıştır. Soğuk su akışında Reynolds sayısı 4000 ila 30000/ sıcak su akışında ise 3000 ila 20000 arasında değiştirilmiştir. Modelden elde edilen sonuçlar, aynı boyuttaki klasik tipli konsantrik iç içe borulardan oluşan ısı değiştirici sinden elde sonuçlar ile karşılaştırılmıştır. îç borunun tanıtılan giriş kanalı geometrisiyle döndürülmesi halinde, ısı değiştiricisinin toplam ısı transfer katsayısında iyileşmeye neden olduğu görülmüştür ve buna karşılık basınç kayıplarında artışlar olmuştur. Akış gözleme deneylerinde, modelde tanıtılan iç boruda ki dönmeli akışın boru boyunca sönümlenmediği izlenmiştir. îç boru akış alanının teorik hesaplanması, laminer akış için gerçekleştirilerek bulunan sonuçların akış gözleme de neyi sonuçlarıyla uyum içinde olduğu belirlenmiştir. SUMMARY In this thesis, heat transfer and fluid flow in a concentric double pipe heat exchanger of which inner tube rotates are investigated. In industry, day after day, hot and waste water produced by industrial use has been increasing. Employing this water in classical heat exchanger makes some operating diffuculties and causes some energy to be wasted. Improving effectiveness of the heat exchanger is directly connected with the heat transfer coefficients of the hot and cold water sides. In this study, beside improving the heat transfer coefficients of water side, in order to transport hot water more easily, the cold water tube with helical formed finning on the outer surface was designed to rotate, arid resulting the heat exchanger has experimentally been investigated. A wide ranges of Reynolds Numbers for hot water (3000£Re£20000> and for cold water flowing through the inner tube <4000£Re£30000) were covered in the experimental studies. Results recorded from the heat exchanger was compared with experimental results of the heat exchanger without helical finning, but of the same dimensions. The experiments showed that the rotation of the smaller tube was caused to enhance heat transfer for annular flow rather than the pipe flow. As a result of that the total heat transfer coefficent of the heat exchanger was increased comparing with the result of the classical heat exchanger. The flow resistance is also shown to be increased. In addition to that, effectiveness of the heat exchanger was calculated by NTD method and compared with the values in the literature. The comparison showed that the rotation of inner tube causes to increase the effectiveness. 151