This study focused on analysis and experiment of hot extrusion of aluminum and magnesium alloys, an extrusion die with an inclination angle leads to non- uniform velocity distribution at the cross-section of the die, and results in different strain and strain rate distributions. This kind of design can make the grain size at the material surface smaller and get a material with larger surface hardness. This study aims to conduct hot extrusion with different die inclination angles, and obtain a material with gradient micro-structures. At first, die with different inclination angles are designed, and the temperature at the die exit and effective strain, effective strain rate distributions are discussed using the finite element analysis. At last, aluminum and magnesium extrusion experiments are conducted and the micro-structures of the materials are observed to understand the effects of the die inclination angles at 15 degrees on the grain size distribution and hardness test at the cross-section of the material. The grain size is about 17.2£gm at around center of the cross-section and hardness is about 68.2HV. The smallest grain size is 4.1£gm at the edge of the cross-section and the highest hardness is 83.8HV.

The problem of the forced film condensation heat transfer of pure steam and steam-air mixture flowing downward a tier of horizontal cylinders is investigated numerically and experimentally. Liquid and vapor-air mixture boundary layers were solved by an implicit finite difference scheme. The effects of the free stream non-condensable gas (air) concentration, free stream velocity (Reynolds number), cylinder diameter, temperature difference and angle of inclination on the condensation heat transfer are analyzed. Inline and staggered tubes arrangements are considered. The mathematical model takes into account the effect of staggering of the cylinders and how condensation is affected at the lower cylinders when condensate does not fall on to the center line of the cylinders. An experimental setup was also manufactured and mounted at METU workshop. A set of experiments were conducted to observe the condensation heat transfer phenomenon and to verify the theoretical results. Condensation heat transfer results are available in ranges from (U&amp / #61605 / = 1 - 30 m/s) for free stream velocity, (m1,&amp / #61605 / = 0.01 -0.8) for free stream air mass fraction, (d = 12.7 -50.8 mm) for cylinder diameter and (T&amp / #61605 / -Tw =10-40 K) for temperature difference. Results show that / a remarked reduction in the vapor side heat transfer coefficient is noticed when very small amounts of air mass fractions present in the vapor. In addition, it decreases by increasing in the cylinder diameter and the temperature difference. On the other hand, it increases by increasing the free stream velocity (Reynolds number). Average heat transfer coefficient at the middle and the bottom cylinders increases by increasing the angle of inclination, whereas, no significant change is observed for that of the upper cylinder. Although some discrepancies are noticed, the present study results are inline and in a reasonable agreement with the theory and experiment in the literature. Down the bank, a rapid decrease in the vapor side heat transfer coefficient is noticed. It may be resulted from the combined effects of inundation, decrease in the vapor velocity and increase in the non-condensable gas (air) at the bottom cylinders in the bank. Differences between the present study results and the theoretical and the experimental data may be resulted from the errors in the numerical schemes used. These errors include truncation and round off errors, approximations in the numerical differentiation for interfacial fluxes at the vapor-liquid interface, constant properties assumption and approximations in the initial profiles. Mixing and re-circulation in the steam-air mixture at the lower tubes may be the other reasons for these deviations.

The objective of this study is to determine the mean heat transfer coefficient and heat transfer rate and to analyse the effect of inclination angles,the effect of subcooling temperatures and the effect of vapour velocity for laminar filmwise condensation of water vapour on a vertical tier of spheres experimentaly and analyticaly. For this purpose, the experimental aparatus were designed and manufactured. In the free condensation experimental study &Oslash / 50mm and &Oslash / 60 mm O.D. spheres were used to analyse the diameter effect . In the experimental studies of free and forced condensation &Oslash / 60mm O.D. spheres on which vapour flows at 2,75 bars were used to analyse the effect of vapour velocity. For the experimental study of the annular condensation in the concentric spheres the effect of vapour velocity was studied by forcing the vapour to flow in the area between two concentric spheres. In the free condensation experiments it is observed that at smaller diameters the heat flux and mean heat transfer coefficients for sphere is higher. In the free and forced condensation experiments increasing the velocity of vapour increases the mean heat transfer coefficient. At the experiments with annular condensation between the concentric spheres high mean heat transfer coefficient values have been obtained compared to the free and forced condansation over the surface of spheres experimental studies.

During a rod extrusion process, the oxidation layer and the segregation layer at the billet surface are possibly drawn inside the billet and become one part of the product, which portion with surface-permeation has to be cut off and results in a low productivity of the extrusion process. In this paper, the mechanism of permeation of the oxidation and segregation layers at the billet surface is explored using a finite element analysis. The effects of various extrusion conditions, such as extrusion ratio, inclination angle, billet length, the thickness of oxidation layer, etc., on the length of the portion with surface permeation are discussed systematically. Optimal inclination angles for a free surface-permeation product under different extrusion ratios are found out. An empirical equation for the optimal inclination angles is also proposed. Finally, experiments of extrusion of aluminum rods are conducted to validate the analytical model proposed.

The flow of a liquid film over a rapidly rotating horizontal disk has many applications inmedical, industrial, and engineering fields. A specific example is the heat and mass transfer processes between expanded liquid and surrounded dense gas. Diferent wave regimes of a liquid film depend on a flow conditions such as the properties of a liquid, its initial speed,parameters of environment, etc. Therefore, experimental investigation of the film flow over a spinning disk is needed to both validate theoretical predictions and establish methods for fluid flow monitoring.This thesis presents novel video-based algorithms for detection and tracking wave structural data of the liquid film flowing over a spinning disk reactor. The algorithms are based on the spiral model of wave and the quasi-optimal method for estimation of a wave velocity as ill-posed problem. Their performance is compared with results predicted by the fluid dynamics based on the Navier-Stokes equations in the case of thin film.Using experimental video data, the developed models and algorithms allow investigators to estimate the characteristics of wave regimes such as wavelengths, inclination angles, and the radial and azimuthal velocity components of the fluid. The accuracy of estimated characteristics was analyzed. It was shown that average distance between consecutive two waves,their spiral shapes, and the radial velocities of waves confirm the theoretical results and predictions. In particular, computed wavelength is within 1% and a change of the inclination angles is within 2% of the predicted values.

In a scrap based stainless steel plant the dominant process for carbon reduction is the Argon oxygen decarburisation process (AOD). The process goes through three steps: decarburisation, reduction and desulphurisation where the main challenge is to oxidise carbon to CO without oxidising the expensive chromium. The general practical approach is to inject a mixture of oxygen and an inert gas, like argon or nitrogen, through tuyeres at the converter side starting with a high amount of oxygen gas which followingly is reduced as the inert gas is increased during the decarburisation steps. This allows for a decrease in partial pressure for the CO bubbles which is thermodynamically favourable for carbon oxidation. Recent studies have shown that an aged AOD converter with a worn lining can decarburise the melt faster than a fresh vessel due to favourable thermodynamic conditions occurring since the bath height is lower in the aged converter. The studies show 8-10% savings of oxygen gas which have led to an interest to study the matter. One of two approaches are taken in the present work with the focus to develop a numerical model that simulates a downscaled AOD converter with applied inclinations that is to be validated through physical modelling. A 75-ton industrial converter was downscaled for water-air experiments where three inclination angles namely 0, 5.5 and 14° were studied with focus on mixing time and penetration length. The physical model was replicated for computational fluid dynamics (CFD) modelling using the Euler-Euler approach in ANSYS Fluent. The models show rather good similarities when comparing gas penetration length, flow structure and mixing time however needs some complementary work and final adjustments before upscaling as well as coupling with thermodynamic modelling can be done. / Den dominerande processen för kolfärskning vid skrot baserad rostfri ståltillverkning är AOD- processen (Argon Oxygen Decarburisation). Processen går igenom tre steg, kolfärskning, reducering av krom och svavelrening där de största utmaningarna ligger i att oxidera kol utan att oxidera krom. I praktiken gör detta genom att injicera en blandning av argon och syrgas från sidan av AOD-konvertern för att sänka partial trycket av den kolmonoxid som bildas när kol oxideras. Syftet är att göra det mer termodynamiskt fördelaktigt att oxidera kol i systemet. Den injicerade blandgasen har olika förhållanden under kolfärskning med en hög andel syrgas i början som sedan sänks genom processen tills bara argon injiceras. Tidigare studier har visat att kolfärskningen är en funktion av konverterns ålder där ju äldre en konverter är desto snabbare går kolfärskning. Enligt studierna har det visats att 8-10% mindre syrgas eller användning av reducerings medel kan uppnås i en gammal konverter vilket har väckt ett intresse för vidare studier. I detta arbete har en av två metoder prövats för att undersöka om man kan applicera det som sker i en gammal konverter till en ny. En numerisk modell av en nerskalad AOD-konverter har utvecklats och validerats mot en vattenmodell då konvertern vinklas. En 75-tons konverter nerskalades till en vattenmodell där vinklarna 0, 5.5 och 14° studerades med fokus på blandningstid och penetrations djup. Vattenmodellen gjordes om till en numerisk modell som använde Euler-Euler metoden i ANSYS Fluent. Modellerna visade likheter gällande penetrationsdjup, flödes struktur och blandnings tid men kräver en del justeringar innan en uppskalning samt koppling till termodynamisk modellering kan ske.

Nanofluids as an innovative class of heat transfer fluids created by dispersing nanometre-sizedmetallic or non-metallic particles in conventional heat transfer fluids displayed the potential toimprove the thermophysical properties of the heat transfer fluids. The main purpose of this study is toinvestigate the influence of the use of nanofluids on two-phase heat transfer, particularly on thethermal performance of the heat pipes. In the first stage, the properties of the nanofluids were studied,then, these nanofluids were used as the working fluids of the heat pipes. The thermal performance ofthe heat pipes when using different nanofluids was investigated under different operating conditionsexperimentally and analytically. The influences of the concentration of the nanofluids, inclinationangles and heat loads on the thermal performance and maximum heat flux of the heat pipes wereinvestigated.This study shows that the thermal performance of the heat pipes depends not only on thermophysicalproperties of the nanofluids but also on the characteristics of the wick structure through forming aporous coated layer on the heated surface. Forming the porous layer on the surface of the wick at theevaporator section increases the wettability and capillarity and also the heat transfer area at theevaporator of the heat pipes.The thermal performance of the heat pipes increases with increasing particle concentration in all cases,except for the heat pipe using 10 wt.% water/Al2O3 nanofluid. For the inclined heat pipe, irrespectiveof the type of the fluid used as the working fluid, the thermal resistance of the inclined heat pipes waslower than that of the heat pipes in a horizontal state, and the best performance was observed at theinclination angle of 60o, which is in agreement with the results reported in the literature. Otheradvantages of the use of nanofluids as the working fluids of the heat pipes which were investigated inthis study were the increase of the maximum heat flux and also the reduction of the entropy generationof the heat pipes when using a nanofluid.These findings revealed the potential for nanofluids to be used instead of conventional fluids as theworking fluid of the heat pipes, but the commercialization of the heat pipes using nanofluids for largescale industrial applications is still a challenging question, as there are many parameters related to thenanofluids which are not well understood. / <p>QC 20170228</p>

The search for new solutions for the generation of energy is becoming more and more important for our future. Big arguments and disagreements on e.g. the questions of gas transport or the dependence on energy supplied by other countries raise demands on the development of new forms of alternative energy resources. Wave power is one of the main sources of renewable energy due to the high power density stored in ocean waves. Nevertheless, the dynamic forces of waves are so large that serious questions popped up on how to design a system which could work even in an unfavourable wave climate or could at least retain working capabilities after big storms without significant damages. This thesis studies the reliability of the mechanical parts of a linear direct driven permanent magnet generator. The results of offshore experiment where strain gauge sensors instrumented on the capsule and the inner framework structure are presented. Stress estimation analyses using strain gauges are carried out. A method for measuring forces and moments in the mechanical structure of the WEC is developed. Evaluation of the lateral force acting on the outer structure is a key factor for the design and construction of the WEC. A method for the measurement of the lateral force acting on the capsule has been developed. A study of the inclination angle between the Wave Energy Converter and the floating buoy has been carried out. The aim of this work is to contribute to the development of wave energy conversion system, and especially to the estimation of structural loads which are important for the survivability of the system under hard sea states. This work is a step that may influence future design of wave energy devices in terms of material aspect, survivability in a hard wave climate and cost-effective renewable energies.

In this work, the effects of the aspect radio and inclination angle in the convection heat transfer inside a square cavity are analyzed through integral transformation. The numerical simulations were made in square and plane cavity in a fluid with constant and variable properties and identifying the effect of the temperature variations. Varying the geometry of the cavity and its inclination it was identified the most sensitive properties at the temperature variations, as well as the geometric combinations which optimize the convection heat transfer. The Generalized Integral Transform Technique (JLWW) was capable to simulate the physical phenomenon successfully, capturing recirculations in critical convective cases numerically. The correlations were established between the rate of convection heat transfer and the aspect radio and the inclination angle of the cavity. / Neste trabalho, serão analisados os efeitos da razão de aspecto e ângulo de inclinação na transferência de calor por convecção via transformação integral, através de simulações em uma cavidade quadrada e plana com um fluido de propriedades constantes e variáveis, identificando a influência à variações de temperatura, bem como as combinações geométricas que otimizam a troca de calor por convecção. A Técnica da Transformada Integral Generalizada (Generalized Integral Transform Technique - JLWW) foi capaz de obter sucesso na simulação do fenômeno físico, sendo capaz de capturar recirculações em casos convectivos críticos do ponto de vista numérico. Foram estabelecidas correlações entre a taxa de transferência de calor por convecção e a razão de aspecto e o ângulo de inclinação da cavidade. / Mestre em Engenharia Mecânica

Η παρούσα έρευνα πραγματοποιήθηκε στο Εργαστήριο Ρευστομηχανικής και Εφαρμογών Αυτής του Τμήματος Μηχανολόγων και Αεροναυπηγών Μηχανικών του Πανεπιστημίου Πατρών και χρηματοδοτήθηκε από το πρόγραμμα «Ηράκλειτος ΙΙ» στα πλαίσια του Επιχειρησιακού Προγράμματος Εκπαίδευση και Δια Βίου Μάθησης, Επένδυση στη κοινωνία της γνώσης. Ο έλεγχος του θερμικού φορτίου στη λειτουργία διαφόρων μηχανολογικών ή ηλεκτρολογικών συστημάτων από συστήματα ψύξης, γίνεται όλο και πιο αναγκαίος στη σημερινή εποχή. Τα συστήματα ψύξης κατηγοριοποιούνται σε ενεργά, που μεταφέρουν ενέργεια υπό μορφή αισθητής θερμότητας μέσω ενός υγρού και σε παθητικά συστήματα ψύξης που χρησιμοποιούν τη λανθάνουσα θερμότητα εξάτμισης του ρευστού λειτουργίας που κυκλοφορεί στην εγκατάσταση, εξαιτίας των τριχοειδών δυνάμεων που αναπτύσσονται από την ύπαρξη πορώδους υλικού. Τα παθητικά συστήματα ψύξης προτιμώνται έναντι των ενεργών, καθώς έχουν τη δυνατότητα να απάγουν περισσότερη θερμότητα, παρουσιάζουν πιο αξιόπιστη λειτουργία, εξαιτίας της έλλειψης κινητών μερών και τέλος, εμφανίζουν μεγαλύτερη διάρκεια ζωής. Μία διάταξη που προσφέρει δυνατότητες ελέγχου του θερμικού φορτίου είναι το κύκλωμα τριχοειδούς αντλίας, Capillary Pump Loop (CPL), που αποτέλεσε και το αντικείμενο μελέτης στην παρούσα διδακτορική διατριβή. Αξιοποιεί τις τριχοειδείς δυνάμεις που αναπτύσσονται στη διεπιφάνεια υγρής-αέριας φάσης του ρευστού λειτουργίας στο πορώδες υλικό που περικλείει ο εξατμιστής στο εσωτερικό του, καθώς και τη λανθάνουσα θερμότητα εξάτμισης και συμπύκνωσης του ρευστού. Με τον τρόπο αυτό, επιτυγχάνει την κυκλοφορία του ρευστού λειτουργίας στην εγκατάσταση, χωρίς την παρουσία μηχανικής αντλίας, και τη μεταφορά των απαιτούμενων θερμικών φορτίων σε μεγάλες αποστάσεις. Ένα κύκλωμα τριχοειδούς αντλίας αποτελείται από έναν εξατμιστή, ένα συμπυκνωτή, τις γραμμές υγρού και ατμού καθώς και ένα ρεζερβουάρ. Από τη μέχρι τώρα έρευνα είχαν μελετηθεί πειραματικά αρκετά μοντέλα CPL, δίνοντας ιδιαίτερη έμφαση στη διαδικασία εκκίνησης της διάταξης καθώς και στις συνθήκες μόνιμης λειτουργίας. Σε όλα αυτά τα μοντέλα το θερμικό φορτίο επιβάλλονταν μέσω ηλεκτρικών αντιστάσεων. Στην παρούσα διερεύνηση η διάταξη ενσωμάτωσε τη δυνατότητα η προσφερόμενη θερμότητα να παρέχεται και από την ηλιακή ακτινοβολία αναπτύσσοντας έναν εργαστηριακό ηλιακό προσομοιωτή. Προκειμένου να βελτιώσουμε τη συγκέντρωση της ακτινοβολίας και να επιτύχουμε υψηλότερη θερμοκρασία στον εξατμιστή του CPL χρησιμοποιήθηκε παραβολικό κάτοπτρο σε συνδυασμό με συγκεντρωτικό συλλέκτη. Η πειραματική εγκατάσταση που σχεδιάσθηκε και κατασκευάστηκε είχε ως στόχο τη μελέτη της συμπεριφοράς του CPL σε θερμικά φορτία υπό μεταβλητές συνθήκες πλήρωσης της εγκατάστασης, ενώ εξετάστηκε και η συμπεριφορά της τριχοειδούς αντλίας όταν ο εξατμιστής βρίσκονταν υπό κλίση ως προς το επίπεδο, και έγινε σύγκριση των πειραματικών αποτελεσμάτων που προέκυψαν με τα αντίστοιχα για λειτουργία σε οριζόντιο επίπεδο. Η παραμετροποίηση της πειραματικής διερεύνησης του CPL αφορούσε τέσσερις τιμές θερμοκρασίας εισόδου του ρευστού, 15, 25, 35 και 45 οC, τρεις τιμές πίεσης πλήρωσης του κυκλώματος, 0,05, 0,15 και 0,25 bar, και, τέλος, τρεις γωνίες κλίσης, 8ο, 16ο και 23ο. Η διάρκεια των πειραμάτων ήταν αρχικά δέκα ώρες, ώστε να προσομοιώνει τη λειτουργία της εγκατάστασης σε διάστημα ηλιοφάνειας κατά τη διάρκεια της καλοκαιρινής περιόδου, αλλά και εικοσιτέσσερις, ώστε να αποτυπωθεί η απρόσκοπτη διατήρηση της κατάστασης σταθερής λειτουργίας του κυκλώματος. Στο δεύτερο μέρος της διατριβής παρουσιάζονται τα υπολογιστικά μοντέλα δύο και τριών διαστάσεων, 2Δ και 3Δ, όπως σχεδιάστηκαν στο λογισμικό GAMBIT της Fluent Inc., βάση των διαστάσεων του εξατμιστή της πειραματικής εγκατάστασης. Τα αποτελέσματα της διερεύνησης που πραγματοποιήθηκε αφορούσαν το νερό, την ακετόνη, την αμμωνία σαν ρευστά λειτουργίας, τόσο στο επίπεδο όσο και υπό γωνίες κλίσης, παραμετροποιώντας τόσο το θερμαινόμενο μήκος πορώδους επί του συνολικού μήκους του πορώδους του εξατμιστή, όσο και τη θερμοκρασία κορεσμού. Τα δεδομένα για όλα τα ρευστά συγκεντρώθηκαν σε συγκριτικά διαγράμματα, ώστε να εξαχθούν συμπεράσματα για τα περιθώρια αξιοποίησης αυτών, είτε υπάρχει κλίση είτε όχι. Επιπλέον, τεκμηριώθηκε η επιλογή του νερού σαν καταλληλότερο ρευστό λειτουργίας κάτω από δεδομένες συνθήκες. Στο τρίτο μέρος παρουσιάζεται ο αριθμητικός κώδικας που δημιουργήθηκε για τη μοντελοποίηση ολόκληρης της εγκατάστασης του CPL και παραθέτουμε συγκριτικά διαγράμματα, για τις ίδιες συνθήκες λειτουργίας, με τα πειραματικά, τα αριθμητικά και τα υπολογιστικά αποτελέσματα. Στο τελευταίο μέρος έχουμε σχεδιάσει κυκλώματα, αξιοποιώντας την τριχοειδή αντλία, για τη ψύξη/θέρμανση των χώρων μιας κατοικίας για ολόκληρο το έτος. Μια πρόταση που βασίζεται στην αξιοποίηση της ηλιακής ενέργειας και ανταποκρίνεται στην επιτακτική ανάγκη για εκμετάλλευση των ανανεώσιμων πηγών ενέργειας και τη μείωση της χρήσης ηλεκτρικής ενέργειας, εξοικονομώντας χρήματα και προστατεύοντας το περιβάλλον / Present research was conducted in Fluid Mechanics Laboratory of the Mechanical Engineering and Aeronautics Department, University of Patras, and was financed by the operational programme «Herakleitos II», Education and Lifelong Learning Investing in knowledge society. Modern demands in controlling heating load of the cooling systems of mechanical or electrical components are increasing. Cooling systems are divided in active and passive systems. In active systems energy is transported due to sensual heat. While in passive systems due to working fluid latent heat of evaporation because of capillary forces developed in the porous wick inside the evaporator. Passive systems are preferred compared to active systems because they can transfer larger amount of heat, are more reliable, since there are no moving parts, and, finally, lifetime period is longer. The Capillary Pumped Loop (CPL) is a device proper for thermal management control, and was investigated in the present PhD study. The CPL operating principle is based on capillary action, developed in the liquid-vapor phase interface of the working liquid in the porous wick inside the evaporator, and working fluid evaporation and condensation latent heat. The result is that the working fluid is displaced inside the loop without any mechanical pump and heat load is transported in large distances. CPL main components are an evaporator, a condenser, a liquid line, a vapor line and a reservoir. Research regarding the CPL experimental models so far concentrated in the evaporator start-up and steady working state conditions. For all those cases heat load was applied through electric resistances. In the present study heat load was alternatively applied through solar radiation using a solar simulator, designed for this purpose. In order to achieve higher temperature in the evaporator external wall and increase solar radiation exploited, a parabolic mirror was used in combination with a solar collector. The experimental installation was designed in such a way to study the behavior of a CPL when heat load was imposed under different loop charging pressures and for several evaporator inclination angles. Experimental results where compared to the results acquired for evaporator operating at zero inclination angle. The initial values of the working fluid temperature were 15, 25, 35 and 45 oC, of the charging pressure 0,05, 0,15, 0,25 bar and of the inclination angle 8, 16 and 23o. The duration of the experiments was initially ten hours, in order to simulate CPL operating during a typical summer day, and then increased to twenty four hours to investigate continuous operation during all day. In the second section of this study two and three dimensions, 2D and 3D, computational models are presented designed in Gambit, Fluent Inc., based on the exact dimensions of the experimental ones. Computational results were derived for water, acetone and ammonia, as working fluid, for zero inclination and the three values of angles mentioned above. Models were customized for different porous wick heated length and working liquid of different saturation temperature. Comparative figures for all working fluids are presented whether evaporator was under inclination angle or not. Moreover, those comparative figures reviled that water was more suitable as working fluid under steady operating state. In the third section the numerical model simulating the overall CPL function is presented and comparative figures between experimental, computational and numerical results are given, for the same operating conditions. In the last section a potential solar CPL heating/cooling system for domestic use is presented. This potential system could meet the demands for using renewable energy sources in order to reduce electrical energy consumption, save money and protect the environment at the same time.