Solution of Leakage Problem in a Guarded Hot Plate Device

AbstractThe conduction heat transfer coefficients of the fibrous insulation materials depend on temperature, especially under high temperature conditions. In this study, the device, called guarded hot plate (GHP), measuring the heat transfer performance of insulation materials under high temperature conditions is improved. Circulation of the cooling fluid inside aluminum cold plates is optimized by numerical results. To prevent leakage of the fluid, metal pipes are inserted into the conduits aiming the fluid to circulate throughout these pipes. Following the design, the cold plates are manufactured and the computational results are validated by the experimental ones. By the new designed cold plate, the system operates and achieves validated measurements for the thermal conductivity of the fibrous insulation materials, under high temperature conditions

H2020 STRATOFLY Project: from Europe to Australia in less than 3 hours

As eluded in previous studies, with special reference to those carried out in the European framework, some innovative high-speed aircraft configurations have now the potential to assure an economically viable high-speed aircraft fleet. They make use of unexploited flight routes in the stratosphere, offering a solution to the presently congested flight paths while ensuring a minimum environmental impact in terms of emitted noise and green-house gases, particularly during stratospheric cruise. However, only a dedicated multi-disciplinary integrated design approach could realize this, by considering airframe architectures embedding the propulsion systems as well as meticulously integrating crucial subsystems. In this context, starting from an in-depth investigation of the current status of the activities, the STRATOFLY project has been funded by the European Commission, under the framework of Horizon 2020 plan, with the aim of assessing the potential of this type of high-speed transport vehicle to reach Technology Readiness Level (TRL) 6 by 2035, with respect to key technological, societal and economical aspects. This paper aims at summarizing the main results achieved so far to solve the main issues related to thermal and structural integrity, low-emissions combined propulsion cycles, subsystems design and integration, including smart energy management, environmental aspects impacting climate change, noise emissions and social acceptance, and economic viability accounting for safety and human factors

Multi-fidelity modeling and data-driven design and analysis of a hypersonic engine

Today's rising demand on hypersonic aircraft and cruise vehicles has strongly boosted interest in the research and development of combined-cycle air-breathing engines. They offer not only an efficient operation in terms of specific impulse as compared to their rocket opponents, but also an impeccable propulsion with an extended flight speed range under stratospheric altitude conditions. However, the operation at high speeds has many challenges and requires further complex design and optimization studies of the propulsion systems. The difficulties in the design of the engines used for this purpose vary from figuring out the interaction between multiple cycles to providing optimal fuel-air mixing and flame distributions at the high altitude conditions where the atmospheric conditions are unfavorable enough to impede the supersonic combustion. The numerical simulations in preliminary early design stages are essential to discuss roughly the feasibility of these systems and estimate engine performance for making first guess about the trajectory reliability. In this sense, the accuracy of these critical studies of the hypersonic engines strongly depends on the trustworthiness of the existing low fidelity numerical tools. This doctoral thesis concerns firstly the design and analysis of a combined-cycle air-breathing engine propelling a civil hypersonic transporter mainly at Mach 8 and stratospheric conditions by means of numerical modeling and performing transient simulations with extended version of state-of-the-art tools and analysis methods which are combination of First and Second Laws, secondly develops new generic reduced-order modeling methodologies to improve accuracy of the existing tools in a manner of performing some high-fidelity numerical simulations both for reactive and non-reactive flows and coupling them with advanced machine learning techniques such as Kernel regression, Gaussian Process Regression, and Artificial Neural Network. It also investigates deeply supersonic flow physics via multi-dimensional CFD simulations because the validity of reduced-order modeling relies on proper understanding of the physical phenomena observed in high-fidelity analysis. It is found that the combined-cycle engine performance to highly depend on flow area allocations in nozzle component where the cycles' discharged flows meet. Most of the exergy is generally lost in the nozzle (20-30%). The system efficiency reached its maximum value around mid-supersonic flight speeds corresponding to Mach 2-3. In the reduced-order design and analysis of ramjet engine, optimal range of intake exit Mach number varies between 0.53-0.57 to yield an efficient burning in combustor and favorable system performance. In the reduced-order modeling studies devoted to improve accuracy of the current low-fidelity models by formulating supersonic fuel-air mixing, the regression is found more difficult in the vicinity of fuel struts (due to turbulence/shock effects) and easier further downstream from the struts, but ANN performs generally better than other regression models by computing the thrust of a hypersonic engine with less than 10% error. On the other hand, the regression becomes more challenging in further zones from the struts when the reactions are switched on. This strongly depends on the strength of shock pattern in post strut region and where the ignition takes place which are function of fuel strut configurations (struts location, V-settlement angle, and wedge angle). The sensitivity analysis and detailed discussion show that the strut wedge angle to be the most influencing parameter on the mixing and combustion phenomena and aerodynamic losses.Doctorat en Sciences de l'ingénieur et technologieinfo:eu-repo/semantics/nonPublishe

Experimental Investigation Of Effect Of Pore Diameter And Reentrant Cavity Width On Nucleate Boiling In Micro Structured Surface

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2016Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2016Kaynama en önemli faz değişim yöntemlerinden biri olup fiziksel yapısı oldukça karmaşıktır. Günümüzde enerji dönüşüm sistemlerinde, ısı pompalarından oluşan iklimlendirme sistemlerinde, elektronik soğutmasında ve buhar üretimi yapan ileri mühendislik yapıtlarında sıklıkla tercih edilmektedir. Sistemlerin enerji verimliliği açısından çeşitli kaynama ısı geçiş iyileştirme yöntemleri son yüzyılda birçok araştırmacının ortak çalışma konusu haline gelmiştir. Bu iyileştirme yöntemleri aktif ve pasif olmak üzere ikiye ayrılmaktadır. Dışardan bir etkinleştirme mekanizması ile kaynama ısı geçişine müdahale eden metodlar aktif yöntemler olarak, kaynama yüzey yapısı üzerinde bir takım değişimler yapan metodlar ise pasif yöntemler olarak incelenmektedir. Pasif yöntemlerin kapsamında olan kaynama ısı geçişi iyileştirme yöntemlerinden biri de yüzey üzerine girintili kavite ve tünellerin yapılandırılmasıdır. Bu yapılar gözle görülebilir mertebede olduklarında yüzeyde ısı geçiş alanını arttırmalarının yanı sıra çekirdekli kaynama ısı geçiş mekanizmalarını da doğrudan etkilemektedirler. Birçok çalışma çekirdekli kaynama mekanizmasında kaynama ısı geçiş performansını doğrudan etkileyen çekirdeklenme yoğunluğu, aktif çekirdeklenme bölgeleri sayısı, çekirdeklenme frekansı, sıvının emilimi, buhar kabarcıklarının yüzeyden tahliyesi gibi performans olguları üzerinde iyileştirme sağlayacak yüzey yapıları geliştirmeyi amaç edinmişlerdir. Çekirdekli kaynama ısı geçiş prosesinde buhar kabarcıkları yüzeyden uzaklaştırılırken yerlerine yeteri miktarda sıvı alınması en çok arzu edilen durumdur. Buhar kabarcıklarının yüzeyden uzaklaştırılamaması yüzey üzerinde kuruluğa ve kızdırma derecesinin ani artışına dolayısıyla ısı taşınım katsayısının düşümüne neden olurken fazla miktarda sıvının yüzeyde buhar kabarcığından boşalan yerlere hücum etmesi ısı akısını olumsuz yönde etkiler. Bu amaçla girintili kaviteli ve tünelli yapıların yanında doymuş sıvının veya kızgın buhar kabarcıklarının transportasyonu için gözenekli yapıların da kullanılması kaynama ısı geçişi için pozitif bir etki yaratmaktadır. Gözenekli yapılar bu bağlamda incelendiğinde yüzeye yeterli sıvı emilimi yapmak ve oluşan buhar kabarcıklarını yüzeyde birleşmelerinden önce yüzeyden uzaklaştırmak için uygun oldukları düşünülebilir. Bu çalışmada girintili tünelli ve gözenekli yapıların boyutları parametrik olarak deneysel incelemeye tabi tutulmuştur. 1,5 mm ya da 2,0 mm gözenek çapına, 2 mm, 3 genişliğine sahip 3 kaynama yüzeyi, 3 mm tünel genişliğine sahip gözeneksiz kaynama yüzeyi ve herhangi bir işleme bulunmayan düz kaynama yüzeyi üzerinde ısı akısı, yüzey kızdırma derecesi, ısı taşınım katsayısı, çekirdeklenme davranışlarının belirlenmesi amacıyla havuz kaynama deneyi yapılmıştır. Bu yüzeyler geometrik xxii ölçülerine göre adlandırılmıştır: 1.5G-2.0A-30-30, 1.5G-3.0A-30-30, 2.0G-2.0A-30-30, 3.0A-30-30 ve DUZ-30-30. G harfi gözenek çapını, A harfi tünel aralığını, son iki sayı ise incelenen yüzeyin kesit ölçülerini mm cinsten ifade etmektedir. Tasarlanan kaynama yüzeylerinin kaynamadaki ısı geçişini iyileştirmesi amacıyla gösterdikleri performans literatürde yer alan girintili kaviteli / tünelli ve gözenekli yapılarda yapılan çalışmalardaki sonuçlarla kıyaslanmıştır. En başarılı sonucu 1.5G-2.0A-30-30 yüzeyi göstermiştir. Bu yüzey üzerinde 120,91 kW/m2 ısı akısında yüzey kızdırma derecesi 7,4 C olarak ölçülürken, bu değer düz yüzey için 118,9 kW/m2’de 25,4 C’dir. Bu sonuç girintili tünelli ve gözenekli yapıların etkinliğini ön plana çıkarmaktadır. Kaynama eğrisinde görüleceği üzre yüksek sıcaklıklara çıkıldıkça geçiş ve film kaynama bölgelerinin rejimleri görülmeye başlar. Bu bölgelerde yüzey üzerinde buhar tabakası birleşerek bir buhar yastığı meydana getirir. Sıvı yüzeye ne kadar çok yayılırsa yani temas açısı ne kadar düşük olursa ve sıvıya temas eden sıcak yüzey ne kadar fazla olursa faz değişimi o kadar hızlı gerçekleşir. Havuz kaynamada ulaşılması mümkün olmayan yüzey kızdırma derecelerinde tasarlanan yüzeylerin yüksek sıcaklıkta ısıl performanslarını değerlendirme amacıyla su verme / damla düşüm deneyleri yapılarak yüzey üzerine damlayan damlacığın buharlaşma zamanı ölçülmüştür. TUBİTAK tarafından desteklenen “Buhar Kullanılan Cihazlarda Buhar Üretme ve Aktarma Sisteminin Enerji Verimliliğini Artırmaya Yönelik Tasarımı” adlı 115M403 nolu proje kapsamında incelenen ütü kaynama taban yüzeylerinin performansları ile kıyaslanmıştır. Bu karşılaştırmada ütü taban yüzeylerinden Alüminyum yüzey düşük yüzey sıcaklığında daha iyi sonuç verirken sıcaklık değeri arttıkça tasarlanan yüzeylerin performansları diğerlerinden daha üstün hale gelmiştir.Boiling phase change process is one of the most efficient heat transfer methods and it is hard to understand physics of boiling mechanism. Boiling phase change process is often prefered in various energy conversation units, heat exchange systems, vapor generation mechanisms, heat pumps used in air conditioning systems and cooling of high heat energy density electronic components. In order to increase energy efficiency of the systems, there are a lot of research studies dealing with various boiling heat transfer enhancement techniques. The different enhancement techniques are examined in two groups: Active techniques and passive techniques. Active enhancement techniques involve boiling process externally requiring an external activator or power supply. In passive enhancement techniques, boiling heat transfer is improved by altering boiling surface structure and structure characteristics. Nano/micro structures manufactured in MEMS (microelectro mechanical systems) techniques, covering with woven screens, surface structured with porous media, reentrant cavities and tunnel structures, wettability film covers are the subjects of passive enhancement methods. One of these methods is the structuring boiling surface with reentrant cavities / tunnels and pores. These structures may affect the nucleate boiling process also increase the heat transfer area when they can be seen. Many research studies aims to develop the boiling structures providing an enhancement on the parameter of boiling heat transfer mechanism such as bubble frequency, active nucleation site denstiy, replenishing of saturated liquid into surface and releasing of bubbles. It is very desirable situation that enough amount of liquid is replenished while bubbles are released from boiling surface. When the bubbles cannot move away from the surface merging each other, it results in dry out of the surface. This causes the sudden increase of wall superheat and the sharp decrease of the heat transfer coefficient. On the other hand occupation of excessive amount of liquid occupy the cavities and tunnels in surface affect the performance boiling heat transfer adversely. For heat transfer performance, besides usage of reentrant cavity and tunnel structure for increasing active nucleation site denstiy, it is sensible to use pore structures on tunnels and cavities for transportation of saturated liquid or superheated vapor bubbles. Because it can be considered that pore structures appropriate to release vapor bubbles before merging and replenishing amount of liquid. In this research, the effect of pore diameter and reentrant cavity width were examined in terms of boiling heat transfer in micro structured surfaces. Reference structure geometry was the flat and polished surface. Reentrant cavity width effect and pore diameter effect on the boiling heat transfer performance were examined and compared with the flat surface separately. Five boiling surface structured with pores and reentrant cavities / tunnels were designed, manufactured and investigated to determine pore diameter and width effect on nucleate boiling mechanism. The boiling surfaces are categorized and named according to geometric dimensions: 1.5G-2.0A-30-30, 1.5G-2.0A-30-30, 2.0G-2.0A-30-30. First column is defined as pore diameter in milimetric scale, secound column is reentrant cavity width in milimetric scale, third and fourth column are expressed as geometric dimension of the whole surface. An experimental study was carried out in this study. Although there are many theoretical and numeric study for modelling boiling mechanisms, the studies were inadequate to predict and explain the physics of boiling mechanisms. Experimental studies are always the most reliable method to understand boiling heat transfer. In order to evaluate the performance of boiling heat transfer of the design structured surfaces, pool boiling experimental setup and droplet impingement experimental setup are designed and installed. In pool boiling experimental setup, the boiling surface is heated by two dc power supply units in fully water filled pool. The temperatures in system reach the steady state level in approximately half-two hours and the important measurements, calculations and observations can be held. The measurement can be done by the thermocouples in different location. One of the most important parameter for the performance is wall superheat which can be measured by thermo couples in subsurface. The heat flux transfered to boiling liquid is calculated by one dimension Fourier heat conduction equation. The boiling heat transfer coefficient which is the most important parameter, is calculated by the equation between heat flux and wall superheat. Nucleation behaviour and bubble formation during the boiling is observed by using high speed camera because it is hard to see by bare-eyes. The wall superheat cannot be reach very high levels because of safety and voltage limitation of dc power supply. So the behaviour and effect of the surfaces on the boiling heat transfer can be investigated in droplet impingement experiment setup at high temperature levels. In droplet impingement experimental setup, a liquid droplet is dropped and impinged on heated surface. The evaporation time of the liquid droplet is very significiant to determine the boiling heat transfer performance. To measure evaporation time, high speed camera can be best option to measure evaporation time of the droplet. Five boiling surfaces were experimentally investigated and the informations about the boiling heat transfer performance of the surfaces were obtained in this study. First of all, it is very obvious that pore structures provided better performance for the boiling heat transfer enhancement when the surface of 1.5G-3.0A-30-30 compared with unpored 3.0A-30-30 surfaces. The decrease of the reentrant cavity/tunnel width increased the heat transfer coefficient when the surfaces having same pore diameter were evaluated. The positive effect can not be explained only by increase of heat transfer area, but also the increment of the reentants provided new active nucleation sites. The increase of nucleation site density was observed in high speed camera medias. In addition, it was seen that bubbles moved to liquid level merging with each other and in the form of turbulent jet. This merging was happened just above the surface with the increase of heat flux. This situation caused the wall superheat increased and colour of surface darkened. 1.5G-2.0A-30-30 boiling surface showed the best heat transfer performance when it is compared with other structured surfaces. Lower reeantrant cavity with and pore structures provided high enhancement in boiling heat transfer. Decrease of reentrant cavity width increased the heat transfer area and active nucleation sides. Pores in surface helped replenishment of the liquid instead of departured vapour and made easier the release of bubbles. The results of pool boiling experiments were compared with the results of reentrant cavity / tunnel structures in literature. The results of other studies are guide for the future studies to obtain better heat transfer performance of studied boiling surfaces such as structuring grooves inside the tunnels, decreasing the pore diameter, using porous media, using vertical tunnels addition to horizontal ones. As it can be seen in boiling curve, transition and film boiling regime are seen at high temperature levels. In this regions, bubbles merge on the surface and create vapor film resulting in the sudden increase of wall superheat. The lower contact angle and the more superheated point to touch liquid cause to decrease evaporation time. In order to investigate heat transfer performance of the surfaces at high temperature levels in which it is hard to reach in pool boiling experimental setup, two selected surfaces were tested in droplet impingement experimental setup. The evaporation time of the droplets impinged on the surfaces compared with that of steam chamber surfaces of iron machine which is being examined as part of a scientific Project namely “Design of Steam Generators and Channels for The Steam Based Devices for Maximum Efficiency” funded by TUBITAK (The Scientific And Technological Research Council of Turkey). The reentrant cavity width effect was examined in these experiments. 1.5G-3.0A-30-30 and 1.5G-2.0A-30-30 were selected for the experiment. In the experiments, while Aluminium iron surface showed better performance at low surface temperatures, the studied surfaces performance were getting higher with the increase of temperature levels.Yüksek LisansM.Sc

Analysis of a combined cycle propulsion system for STRATOFLY hypersonic vehicle over an extended trajectory

Hypersonic civil aviation is an important enabler for extremely shorter flight durations for long-haul routes and using unexploited flight altitudes. Combined cycle engine concepts providing extended flight capabilities, i.e. propelling the aircraft from take-off to hypersonic speeds, are proposed to achieve high-speed civil air transportation. STRATOFLY project is a continuation of former European efforts in hypersonic research and aims at developing a commercial reusablevehicle for cruise speed of Mach 8 at stratospheric altitudes as high as 35 km above ground level. The propulsion plant of STRATOFLY aircraft consists of combination of two different type of engines: an array of air turbo rockets and a dualmode ramjet/scramjet. In the present study, 1D transient thermodynamic simulations for this combined cycle propulsion plant have been conducted between Mach 0 to 8 by utilizing 1D inviscid flow transport relations, numerical tools availablein EcosimPro software platform and the European Space Propulsion System Simulation libraries. The optimized engine parameters are achieved by coupling EcosimPro software with Computer Aided Design Optimization which is a differential evolution algorithm developed at the von Karman Institute

Reduced order design and investigation of intakes for high speed propulsion systems

Ramjet propulsion is commonly preferred to power supersonic and hypersonic vehicles for cruising faster than Mach 3. This is an elegant solution owing to the lean architecture which does not embody any rotating parts. Although the geometry of the engine is simple as compared to turbine based configurations, the flow physics through the engine duct is quite complex and the flow speeds modulate between the supersonic and subsonic regimes multiple times. The design and performance analysis of ramjet engines are vital to ensure that propulsion system can satisfy the flight trajectory requirements. Therefore, this study introduces a reduced order holistic approach for design and assessment of the flow development in high-speed propulsion systems composed of generic elements of ramjet/scramjet engine configurations. Accordingly, the intakes designed based on axisymmetric flow templates are used to provide the necessary freestream flow modulation prior to the isolator through which a normal shock assumption is applied. The resultant flow properties are utilized for the combustion module where the flow expansion within the combustor and nozzle components are computed based on 1D steady inviscid flow equations coupled with detailed chemistry approach and JANAF tables. The module was validated and verified with the experimental and numerical data obtained for a dual-mode ramjet/scramjet combustor. Consequently, the parameters such as thrust, fuel consumption and specific impulse are calculated to quantify the engine performance for each design. Finally, the employment of the low fidelity model is demonstrated over a family of ramjet flow paths where the design space is confined based on the requirements of a high-supersonic cruise vehicle

Thermodynamic efficiency analysis and investigation of exergetic effectiveness of STRATOFLY aircraft propulsion plant

info:eu-repo/semantics/publishe

Reduced order design space analysis of for ramjet engines with data mining techniques

info:eu-repo/semantics/publishe

Reduced-order modeling of supersonic fuel–air mixing in a multi-strut injection scramjet engine using machine learning techniques

Dual-mode ramjet/scramjet engines promise extended flight speed range and are the commonly preferred air-breathing propulsion system from within the family of hypersonic aircraft concepts. One of the main challenges that should be hurdled in their design is modeling the fuel–air mixing process to provide optimal fuel distribution and yield the best engine performance. Injecting fuel into high-speed air stream along multiple parallel struts can augment the fuel penetration and improve mixing efficiency. Mixing intensity is increased with turbulence by the shock-expansion waves in post-strut regions. However, this enhancement in mixing can bring about detrimental effects on the aerodynamic performance by increasing losses on total pressure. Designing the optimal working configuration requires testing the interaction between many design variables. This can be a tedious and computationally costly task. Machine learning models thus appear well-suited for multi-objective optimization of design variables that can be elusive to designers. In particular, non-linear regression models can be built over the available sparse simulation data to predict unseen mixing conditions. In the present work, we carry out a detailed investigation of the effect of multi-strut configuration parameters on three objective functions: mixing efficiency, mixing length, and the total pressure recovery (TPR) factor. These objective functions are linked with the most relevant physical phenomena in the supersonic fuel–air mixing flow field. We first generate a CFD database by solving compressible, non-reactive, Reynolds-averaged Navier–Stokes (RANS) filtered flow equations in a 2D scramjet engine domain with three varying design variables: struts location, strut wedge angle and strut V-settlement angle. We then apply various regression models – artificial neural network (ANN), Gaussian process regression (GPR), and kernel regression – to this database and formulate a surrogate model relevant for fuel injection that can be utilized in reduced-order modeling studies that estimate the hypersonic engine performance. We find that regression is generally more difficult in the vicinity of fuel struts (due to turbulence/shock effects) and easier further downstream from the struts, but ANN performs generally better than other regression models. Thus, our reduced-order tool incorporates a mixing efficiency model predicted by the ANN. It computes the thrust of a hypersonic engine with less than 10% error. We also present a detailed discussion of the physical insights gained from our CFD database; we link this discussion with the earlier findings from the machine learning tools. In our sensitivity study, we find the strut wedge angle to be the most influencing parameter on the mixing properties and aerodynamic losses.info:eu-repo/semantics/publishe