Κατά τη διαδικασία παραγωγής πλαστικών συμπυκνωμάτων γίνεται ανάμειξη κόκκων πλαστικού με πρόσθετα ώστε να αποκτήσει το πλαστικό ορισμένες επιθυμητές ιδιότητες. Η διαδικασία παραγωγής έχει ως εξής: αρχικά το πλαστικό τήκεται, ομογενοποιείται και οδηγείται στον εκβολέα. Στην κεφαλή του εκβολέα παράγεται το "μακαρόνι" (strand), το οποίο ψύχεται και εν συνεχεία κοκκοποιείται εν ψυχρώ. Ακολουθεί η κοκκοποίηση – ψύξη – ξήρανση του κόκκου. Τέλος έχουμε την συσκευασία – προώθηση και παραγωγή του τροποποιημένου πλαστικού. Η διαδικασία παραγωγής των "μακαρονιών" είναι η ακόλουθη: το ρεύμα του πλαστικού εισέρχεται στον εκβολέα στη συνέχεια εισέρχεται στην κεφαλή του εκβολέα, η οποία στην έξοδο της φέρει αριθμό οπών, κάθε μια από τις οποίες παράγει ένα "μακαρόνι". Ανάλογα με την παραγωγική ικανότητα του εκβολέα και τη διάμετρο των οπών, καθορίζεται ο αριθμός των οπών και άρα ο αριθμός των "μακαρονιών". Η απόσταση των "μακαρονιών" πρέπει να είναι τέτοια ώστε να μη δημιουργούνται συγκολλήσεις μεταξύ γειτονικών "μακαρονιών". Η γεωμετρία της κεφαλής διαφοροποιεί την ποσότητα πλαστικού που εκρέει από κάθε οπή στη μονάδα του χρόνου. Οι διάμετροι των "μακαρονιών" μπορεί να μην είναι ίσες μεταξύ τους με αποτέλεσμα την παραγωγή κόκκων με ανομοιόμορφο μέγεθος, που αποτελεί πρόβλημα. Ένα άλλο πρόβλημα που δημιουργείται κατά την παραγωγική διαδικασία είναι η ύπαρξη συσσωματωμένων κόκκων στο τελικό προϊόν. Η κεφαλή του καλουπιού πρέπει να είναι τέτοια ώστε να ελαχιστοποιούνται τα στάσιμα σημεία της ροής και οι κλειστές ροϊκές γραμμές του τήγματος. Οι οπές πρέπει να είναι τέτοιες ώστε η παροχή διαμέσου αυτών να είναι παρόμοια και εντός των επιθυμητών ορίων. Το σχήμα των οπών πρέπει να είναι τέτοιο ώστε να ελαχιστοποιείται η διόγκωση του παραγόμενου νήματος και η ταλάντωση του πάχους του με δεδομένη την εφαρμοζόμενη τάση εφελκυσμού. Σκοπός της εργασίας είναι η μοντελοποίηση και αριθμητική επίλυση της διαδικασίας εκβολής του τήγματος από την κεφαλή του εκβολέα, τη δίοδό του μέσω των οπών και του σχηματισμού των "μακαρονιών". Η μεθοδολογία που ακολουθήθηκε είναι η εξής: Αρχικά αναλύθηκε το πεδίο ροής του τήγματος μέσα στη κεφαλή του εκβολέα και ταυτοποιήθηκαν τα πιθανά σημεία ανακυκλοφορίας. Παρακολουθήσαμε την εξέλιξη του πάχους των "μακαρονιών" από την έξοδο του εκβολέα. Κατόπιν λύσαμε τις διέπουσες εξισώσεις και κάναμε παραμετρική μελέτη της διεργασίας προκειμένου να βρούμε τις βέλτιστες συνθήκες λειτουργίας. Η αριθμητική επίλυση έγινε με το υπολογιστικό πακέτο FLUENT. Συγκεκριμένα μελετήθηκε το αξονοσυμμετρικό πρόβλημα αλλά και το τρισδιάστατο πρόβλημα μεταβάλλοντας το πλήθος των οπών, το μέγεθός τους καθώς και τη μεταξύ τους απόσταση. Οι παραδοχές που έγιναν είναι οι ακόλουθες: • Θεωρήσαμε πλήρως ανεπτυγμένη ροή στην είσοδο. • Τα τοιχώματα είναι αδιαπέραστα και ισχύει η συνθήκη μη ολίσθησης. • Στο απώτερο άκρο του εκβόλου (έξοδος του πεδίου ροής) έχουμε πλήρως ανεπτυγμένη εκβολική ροή. Η μελέτη του προβλήματος εξόδου του πολυμερούς από τις οπές στη κεφαλή του εκβολέα ήταν προσεγγιστική λόγω περιορισμών του FLUENT. Συγκεκριμένα ήταν λιγότερο ακριβής ο προσδιορισμός των διεπιφανείων με την υποστηριζόμενη από το πρόγραμμα μέθοδο όγκου υγρού (VOF), επειδή οι ιδιότητες των ρευστών (πολυμερές και αέρας) που σχηματίζουν τη διεπιφάνεια διέφεραν σημαντικά. Η παρούσα εργασία επικεντρώθηκε στον υπολογισμό των πεδίων ταχυτήτων, πίεσης, σχήματος "μακαρονιών" από τις οπές εξόδου του ρευστού για τις διάφορες γεωμετρίες με τις οποίες ασχοληθήκαμε. Για να βελτιωθεί η διαδικασία παραγωγής των masterbatches είναι επιθυμητή η παρέμβαση στη διαδικασία εκβολής των πλαστικών καθώς και στη διαδικασία διόδου του τηγμένου μείγματος διαμέσου των οπών της κεφαλής του εκβολέα και στη μετέπειτα ψύξη των παραγόμενων εκβόλων, κυλινδρικού σχήματος μεγάλου μήκους και η ανάπτυξη πιλοτικού συστήματος αυτόματης οδήγησης και ψύξης του παραγόμενου εκβόλου σε κατάλληλο κοπτικό όπου κοκκοποιείται για να δώσει την τελική μορφή των masterbatches. / --

Vertical up-flow of supercritical fluid in the subchannel of a heated rod bundle was numerically simulated using the Computational Fluid Dynamics (CFD) codes ANSYS CFX and ANSYS FLUENT. A total of seven cases from three different sets of experiments were simulated. Three-dimensional steady-state predictions of fluid velocity, pressure, and temperature were made using five versions of two-equation RANS turbulence models with accompanying wall treatments. In addition, the temperature distribution in a solid region comprising a heater and sheathing was also computed in some cases. The k-epsilon turbulence model, implemented using CFX and scalable wall functions, provided the numerical results that have the smallest overall deviation from experimental results for three of the seven cases, and predicts the experimental data of the remaining four cases reasonably well, unlike other turbulence models that severely over-predict the experimental data for wall surface temperature. / February 2016

Volvo Car Corporation (VCC) uses Computational Fluid Dynamics (CFD) and wind tunnel during the aerodynamic development of new vehicles. In the past VCC main focus has been on the drag force correlation to the wind tunnel measurements but in recent years improved methods for lift force correlations has been highly wanted. Three objectives were considered in this study to improve the lift force correlation between the CFD simulations and wind tunnel measurements for geometrical configurations of the V60 and S60 models.Poor mesh resolution for the wall bounded flow existed for the VCC mesh method and therefore prisms layers were considered in this thesis to increase the mesh resolution inside the boundary layer.As slick tyres generally were used in the CFD simulations better geometrical correlation was wanted to be studied as it could improve the lift force correlation between CFD simulations and wind tunnel measurements. Therefore detailed tyres were considered in this study.As the coarsest surface mesh size was used for the underbody and the components inside the engine bay, where some of the highest flow velocities occurred, mesh refinements were investigated for engine bay and underbody in this study.The prisms layers improved the predicted behavior for the boundary layer as it captured the large velocity gradients more accurately. Due to this, the skin friction prediction was also improved. Different flow behavior around the front wheels and rear wake occurred due to earlier separation. The different flow field caused an improved correlation for the lift force but worsened correlation for the drag force due to increased pressure at the rear of the cars. However, the front lift force trend correlation for the considered configurations was improved with the prisms layer mesh method.The detailed tyres caused slight more disturbances for the underbody flow which caused more attached flow around the rear of the car hence lowered pressure. Earlier separation around the front wheels also occurred for the detailed tyre geometry as the disturbed flow around the wheels was increased. Slight improved correlation for the front and rear lift forces to the wind tunnel measurements could be seen with the detailed tyre compared to the slick tyre.The mesh refinements for the engine bay and underbody showed significant differences for the flow at the underbody which had significant impact on the flow at the rear wake for the V60 model. Minor differences could be seen for the aerodynamic forces for the baseline configuration for the V60 model while great differences occurred for the configurations affecting the underbody. Due to this significant improved correlation for the front and rear lift force trends were achieved for the underbody configurations with the refined engine bay and underbody mesh method.Conclusions could be drawn that the prisms layer caused earlier separation due to its increased mesh resolution for the wall bounded flow. However, finer mesh resolution was needed inside the boundary layer to ensure consistent separation behavior for both the considered models. Improved correlation for the front lift force could however be seen. The detailed tyre only had minor effects on the flow field and aerodynamic forces and therefore not so important to include for further studies. The refined engine bay and underbody caused significant improved lift force trend correlation to the wind tunnel measurements and should be considered for future studies. To improve the correlation between CFD simulations and wind tunnel measurements increased mesh resolution for the wall bounded flow should be considered to better capture the large velocity gradients close to the wall.

abstract: Proton exchange membrane fuel cells (PEMFCs) run on pure hydrogen and oxygen (or air), producing electricity, water, and some heat. This makes PEMFC an attractive option for clean power generation. PEMFCs also operate at low temperature which makes them quick to start up and easy to handle. PEMFCs have several important limitations which must be overcome before commercial viability can be achieved. Active areas of research into making them commercially viable include reducing the cost, size and weight of fuel cells while also increasing their durability and performance. A growing and important part of this research involves the computer modeling of fuel cells. High quality computer modeling and simulation of fuel cells can help speed up the discovery of optimized fuel cell components. Computer modeling can also help improve fundamental understanding of the mechanisms and reactions that take place within the fuel cell. The work presented in this thesis describes a procedure for utilizing computer modeling to create high quality fuel cell simulations using Ansys Fluent 12.1. Methods for creating computer aided design (CAD) models of fuel cells are discussed. Detailed simulation parameters are described and emphasis is placed on establishing convergence criteria which are essential for producing consistent results. A mesh sensitivity study of the catalyst and membrane layers is presented showing the importance of adhering to strictly defined convergence criteria. A study of iteration sensitivity of the simulation at low and high current densities is performed which demonstrates the variance in the rate of convergence and the absolute difference between solution values derived at low numbers of iterations and high numbers of iterations. / Dissertation/Thesis / M.S.Tech Chemistry 2011

This master´s thesis is focused on aerodynamic analysis of 3D configuration of aircraft TL – 4000 and designing shape modifications to improve flight performances. Modifications are focused on wing – fuselage junction and junction between tail units. In continuation are analyzed the shapes of air intakes to cooling engine. Based on aerodynamic analysis of aircraft TL – 4000 are chosen convenient positions for pitot-static tube and inlets for ventilation of cabin.

abstract: Reynolds-averaged Navier-Stokes (RANS) simulation is the industry standard for computing practical turbulent flows -- since large eddy simulation (LES) and direct numerical simulation (DNS) require comparatively massive computational power to simulate even relatively simple flows. RANS, like LES, requires that a user specify a “closure model” for the underlying turbulence physics. However, despite more than 60 years of research into turbulence modeling, current models remain largely unable to accurately predict key aspects of the complex turbulent flows frequently encountered in practical engineering applications. Recently a new approach, termed “autonomic closure”, has been developed for LES that avoids the need to specify any prescribed turbulence model. Autonomic closure is a fully-adaptive, self-optimizing approach to the closure problem, in which the simulation itself determines the optimal local, instantaneous relation between any unclosed term and the simulation variables via solution of a nonlinear, nonparametric system identification problem. In principle, it should be possible to extend autonomic closure from LES to RANS simulations, and this thesis is the initial exploration of such an extension. A RANS implementation of autonomic closure would have far-reaching impacts on the ability to simulate practical engineering applications that involve turbulent flows. This thesis has developed the formal connection between autonomic closure for LES and its counterpart for RANS simulations, and provides a priori results from FLUENT simulations of the turbulent flow over a backward-facing step to evaluate the performance of an initial implementation of autonomic closure for RANS. Key aspects of these results lay the groundwork on which future efforts to extend autonomic closure to RANS simulations can be based. / Dissertation/Thesis / Masters Thesis Aerospace Engineering 2017

abstract: This study uses Computational Fluid Dynamics (CFD) modeling to analyze the dependence of wind power potential and turbulence intensity on aerodynamic design of a special type of building with a nuzzle-like gap at its rooftop. Numerical simulations using ANSYS Fluent are carried out to quantify the above-mentioned dependency due to three major geometric parameters of the building: (i) the height of the building, (ii) the depth of the roof-top gap, and (iii) the width of the roof-top gap. The height of the building is varied from 8 m to 24 m. Likewise, the gap depth is varied from 3 m to 5 m and the gap width from 2 m to 4 m. The aim of this entire research is to relate these geometric parameters of the building to the maximum value and the spatial pattern of wind power potential across the roof-top gap. These outcomes help guide the design of the roof-top geometry for wind power applications and determine the ideal position for mounting a micro wind turbine. From these outcomes, it is suggested that the wind power potential is greatly affected by the increasing gap width or gap depth. It, however, remains insensitive to the increasing building height, unlike turbulence intensity which increases with increasing building height. After performing a set of simulations with varying building geometry to quantify the wind power potential before the installation of a turbine, another set of simulations is conducted by installing a static turbine within the roof-top gap. The results from the latter are used to further adjust the estimate of wind power potential. Recommendations are made for future applications based on the findings from the numerical simulations. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2017

Fluid jet polishing (FJP) is a new advanced polishing technology that finds applications in many industries, especially in the optics industry. With the broad application of various surfaces in optics, the sub-micrometric scale and the nanometric surface roughness accuracy are major challenges. Fluid jet polishing is a technology developed from abrasive water jet machining. This technology is a water jet cutting technology, which uses high-pressure flow to cut/remove materials. In this thesis, the working principle, and simulations, as well as verification of fluid jet polishing are thoroughly investigated. The verification of fluid jet polishing in this thesis includes velocity distribution and material removal derivations. The amount of material removed is directly related to the impact velocity of a particle with a surface, which helps define its abrasive particle velocity. During polishing, the particles travel in a solution called slurry. Due to the relatively similar velocity of the particles and the slurry, the particles and the slurry are assumed to be traveling at the same rate. In this thesis, three specific examples are investigated through the creation of an advanced model using FLUENT, a computational fluid dynamics software. The model simulates the particle path during the fluid jet polishing process, and this thesis compares the simulation results to prior analytical and experimental results. The results indicate that the fluid jet polishing erosion area at a particular location is axisymmetric when the 2D cross-section shape is investigated. As the impingement angle of the fluid jet is reduced, the center dead area, where no polishing is observed, approaches zero. vii Additionally, the horizontal component of the velocity vector initially increases then decreases as one moves away from the center stagnation point. Finally, this thesis demonstrates that the erosion depth into the surface that is polished increases when the working pressure of the fluid is increased. This thesis finds that when the distance between the fluid jet and the workpiece is 7 mm, material removal is maximum.

Microbubbles, currently employed in diagnostic ultrasound as a contrast agent, have a potential new application as vehicles for targeted drug delivery, which could revolutionise medicine by eliminating side-effects. A new device is developed which outperforms all existing devices in terms of minimum microbubble size:channel diameter ratio. A numerical model is established to describe the flow behaviour and it is determined that the flow regime and resulting microbubble size are dependent on the ratio of inner- to outer Weber number.

Sebastian Zetterström, Master of Science in energy systems, Mälardalens University in Västerås. Abstract of Master’s thesis, submitted 16th of August. Evaluation of a suction pyrometer by heat and mass transfer methods. The aim of the thesis is to evaluate the cooling of a specific suction pyrometer which is designed by Jan Skvaril, doctorate at Mälardalens University. First part is explained how the balances and correlations are performed before being implemented in MATLAB, after this  a ANSYS Fluent model is constructed and explained, which is used for the comparison of results. The cooling is performed by using water at an inlet temperature of 10°C and an assumed flue gas temperature of 810°C. Sensitivity analysis are performed to test the stability of the models which yield good results for stability, done by adjusting both flue gas temperature and inlet cooling water temperature which are as well presented for observation. From doing further MATLAB sensitivity analysis which show that the model still performs well and is stable. The resulting cooling water is heated to approximately 24, 8°C and the flue gas is cooled to 22, 4°C, in ANSYS Fluent the answer differs approximately 2°C and results in 20, 4°C which can be considered by looking at the flue gas inlet temperature of 810°C that this can be deemed an insignificant change and can therefore conclude that the comparison between the two platforms match each other good and that calculations can be considered accurate. Keywords:  Suction pyrometer, cooling, heat transfer, thermal resistance network, MATLAB, ANSYS Fluent, simulation