Made available in DSpace on 2016-04-01T17:54:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-08-10. Added 1 bitstream(s) on 2016-04-01T18:00:20Z : No. of bitstreams: 1 000505772.pdf: 2673100 bytes, checksum: 0b1ec10e248621594ebb61317344d2af (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este estudo apresenta uma análise numérica dos campos de temperaturas e velocidades d'água durante seu processo de aquecimento via calor sensível no interior de um armazenador térmico cilíndrico, aquecido lateralmente e adiabático em seu topo e base, visando o estudo da condição de operação de um aquecedor de água coletor solar-armazenador integrados (ICSSWH - Integrated Collector-Storage Water Heater). Em uma segunda análise a influência de um defletor interno é estudada pela definição dos campos de velocidades e temperaturas da água. A abordagem numérica é realizada a partir de um modelo bidimensional, transiente, não linear e em coordenadas cilíndricas, discretizada pela técnica de elementos finitos. A construção do modelo é obtida numericamente através de um código computacional desenvolvido em linguagem de programação C. Os resultados numéricos são validados. Análises transientes dos campos de velocidades e temperaturas bem como das temperaturas de mistura e velocidade de carregamento, com e sem parede interna direcionada (defletor interno) são realizadas com a finalidade de estudar a inlfuência da referida parede na convecção livre nessas condições. / This study shows a numerical analysis of the temperature and speed fields of water during the process of heating through sensible heat in the interior of a cylindric thermal storage, heated laterally and with adiabatics top and base, in order to study the operational conditions of an integrated collector-storage solar water heater (ICSSWH). In a second analysis a model with an internal baffle is created and temperature and velocity fields are analysed. The numerical study is done taking into consideration a bidimensional, transient non linear research in cylindric coordenates, discretized by the technique of finite elements. Its solution is obtained numerically through a computational code developed in a C programming language. The numerical results are validated. A transient analysis of the spped and temperature fields so as of the mixing temperatures and the charging speed, with or without the infernal baffle are carried out taking into account the aim of studying the influence of the so called wall in the free convection of those conditions.

La part de consommation d'énergie primaire d'eau chaude sanitaire (ECS) dans des bâtiments à basse consommation (BBC) devient proportionnellement importante quand comparée aux autres postes. Actuellement, l'intégration des systèmes dans les nouveaux bâtiments ne présente pas de difficulté. En revanche, le marché de la rénovation est mal exploité, et une des contraintes importante est le placement du ballon de stockage. Dans le cas où le ballon doit être placé en dehors du bâtiment, les solutions existantes ne sont pas satisfaisantes, ni d'un point de vue thermique (fortes pertes), ni d'un point de vue esthétique (réservoir visible à l'extérieur). Dans le cadre de cette thèse, nous avons étudié une solution innovante visant à intégrer le stockage au capteur, afin de permettre une intégration complète du système au niveau de la toiture. Le critère énergétique nous a conduit à proposer un volume de stockage totalement isolé où l'apport de chaleur se produit en partie basse. Nous réalisons dans le cadre de la thèse une étude expérimentale d'une cavité à haut rapport de forme, qui nécessite la réalisation d'un système de stratification. Ce système, une plaque, a été étudié numériquement pour optimiser le placement du fluide en partie haute. Enfin un modèle global a été conçu pour les simulations de performance annuelle. Ce modèle se montre satisfaisant, et montre que la performance du système est légèrement inférieure aux systèmes classiques (thermosiphon). Les pertes thermiques ont été le facteur le plus pénalisant. Le dimensionnement d'un prototype a été réalisé, et ce dernier sera testé au cours de l'année 2012. / The primary energy consumption of domestic hot water (DHW) in low energy house becomes proportionately large when compared to other energy consumptions. In new buildings, the integration of DHW systems do not present any difficulty. However, the thermal renovation market is poorly operated, with the storage's placement as the main constraint. When the storage must be placed outside the building, nowadays the solutions are not satisfactory, or by a thermal point of view (high losses), or an aesthetic point of view (tank visible from outside). In this thesis we studied an innovative solution of an integrated storage collector, allowing full integration at the roof and completly insulated. The storage is heated at the bottom. A cavity with high aspect ratio has been studied experimentaly and the cavity requires a stratification system. This system, a plate, was numerically studied to optimize the placement of the fluid at the top. Finally a global model was developed for annual performance simulations. This model proves satisfactory and shows that system performance is slightly lower than conventional systems (thermo- siphon). Heat loss was most detrimental factor. The design of a prototype was produced, and it will be tested during the year 2012.

Orientador: Alcides Padilha / Banca: Vicente Luiz Scalon / Banca: Ricardo Fortes de Miranda / Resumo: Este estudo apresenta uma análise numérica dos campos de temperaturas e velocidades d'água durante seu processo de aquecimento via calor sensível no interior de um armazenador térmico cilíndrico, aquecido lateralmente e adiabático em seu topo e base, visando o estudo da condição de operação de um aquecedor de água coletor solar-armazenador integrados (ICSSWH - Integrated Collector-Storage Water Heater). Em uma segunda análise a influência de um defletor interno é estudada pela definição dos campos de velocidades e temperaturas da água. A abordagem numérica é realizada a partir de um modelo bidimensional, transiente, não linear e em coordenadas cilíndricas, discretizada pela técnica de elementos finitos. A construção do modelo é obtida numericamente através de um código computacional desenvolvido em linguagem de programação C. Os resultados numéricos são validados. Análises transientes dos campos de velocidades e temperaturas bem como das temperaturas de mistura e velocidade de carregamento, com e sem parede interna direcionada (defletor interno) são realizadas com a finalidade de estudar a inlfuência da referida parede na convecção livre nessas condições. / Abstract: This study shows a numerical analysis of the temperature and speed fields of water during the process of heating through sensible heat in the interior of a cylindric thermal storage, heated laterally and with adiabatics top and base, in order to study the operational conditions of an integrated collector-storage solar water heater (ICSSWH). In a second analysis a model with an internal baffle is created and temperature and velocity fields are analysed. The numerical study is done taking into consideration a bidimensional, transient non linear research in cylindric coordenates, discretized by the technique of finite elements. Its solution is obtained numerically through a computational code developed in a C programming language. The numerical results are validated. A transient analysis of the spped and temperature fields so as of the mixing temperatures and the charging speed, with or without the infernal baffle are carried out taking into account the aim of studying the influence of the so called wall in the free convection of those conditions. / Mestre

Τα ολοκληρωμένα ηλιακά συστήματα συλλέκτη αποθήκης αποτελούνται από μία δεξαμενή αποθήκευσης, της οποίας τμήμα της επιφάνειας της χρησιμοποιείται σαν ηλιακός συλλέκτης. Συνήθως το ρευστό της αποθήκης είναι το νερό χρήσης. Στο υπό εξέταση σύστημα το νερό χρήσης θερμαίνεται έμμεσα, διερχόμενο μέσα από σωληνώσεις εναλλάκτη θερμότητας που τοποθετείται στο εσωτερικό της παραλληλεπίπεδης δεξαμενής. Για την εντατικοποίηση της μετάδοσης θερμότητας προς το νερό χρήσης, δημιουργείται ανάδευση του ρευστού του δοχείου μέσω κυκλοφορητή, ο οποίος τίθεται σε λειτουργία μόνο όταν υπάρχει ζήτηση ζεστού νερού. Προς αποφυγή παραμορφώσεων τοποθετούνται πτερύγια συγκράτησης που ενώνουν τις δύο μεγάλες επιφάνειες της δεξαμενής. Στην παρούσα διδακτορική διατριβή διερευνήθηκαν τα ροϊκά φαινόμενα στο εσωτερικό του ICS που έχει περιγραφεί προηγουμένως, με στόχο τη μεγιστοποίηση της θερμανταλλαγής μεταξύ των δύο κυκλωμάτων νερού. Για την παρατήρηση του ροϊκού πεδίου καθώς και την λήψη μετρήσεων ταχυτήτων κατασκευάστηκε πειραματική συσκευή με διαφανή τοιχώματα από Plexiglas. Ελήφθησαν μετρήσεις ταχυτήτων και διακυμάνσεων με χρήση συστήματος Laser Doppler διπλής ακτίνας. Για την οπτικοποίηση του ροϊκού πεδίου τοποθετήθηκαν σωματίδια πολυστερίνης στο εσωτερικό της συσκευής. Ελήφθησαν ψηφιακές φωτογραφίες και βιντεοσκοπήσεις του ροϊκού πεδίου. Για την υπολογιστική προσομοίωση χρησιμοποιήθηκε το εμπορικό λογισμικό FLUENT. Αναπτύχθηκε υπολογιστικό μοντέλο και επιλύθηκε με όλα τα διαθέσιμα μοντέλα τύρβης. Στη συνέχεια πραγματοποιήθηκε σειρά υπολογιστικών προσομοιώσεων, στις οποίες διερευνήθηκε η βέλτιστη θέση και το μέγεθος των στομίων ανακυκλοφορίας, η βέλτιστη διάταξη των πτερυγίων συγκράτησης και η βέλτιστη θέση του εναλλάκτη. Επιπλέον προσδιορίστηκε υπολογιστικά και πειραματικά ο χρόνος αποκατάστασης του ροϊκού πεδίου. Τέλος, τα αποτελέσματα συγκρίθηκαν και με πειραματικά αποτελέσματα άλλων εργασιών. Τα συμπεράσματα που εξάγονται έχουν ως ακολούθως: Το μοντέλο τύρβης standard k-ω δίνει τα πιο αξιόπιστα αποτελέσματα. Το υπολογιστικό μοντέλο θεωρείται πιστοποιημένο μετά από πειραματική επιβεβαίωση ταχυτήτων και θερμοκρασιών. Το στόμιο ανακυκλοφορίας δεν πρέπει να τοποθετείται κάθετα στις μεγάλες επιφάνειες της δεξαμενής, ενώ η διάμετρος του πρέπει να είναι 1/2" ή και μικρότερη. Ο χρόνος αποκατάστασης του ροϊκού πεδίου είναι περίπου 35 s. Τα πτερύγια συγκράτησης πρέπει να ακολουθούν τις ροικές γραμμές. Ως βέλτιστη θέση του εναλλάκτη θεωρείται όταν τοποθετείται σε επαφή με το τοίχωμα. / Integrated Collector Storage (ICS) solar systems use part of the hot water storage as collector, i.e. half of the storage surface is used as absorber. Usually, the storage medium serves also as the energy transfer medium (service hot water). In the examined ICS, the service water is heated indirectly, passing through a serpentine heat exchanger placed inside the tank. The heat transfer from the stored water to the service water is intensified by the agitation of the stored water. A simple solution is the recirculation of the stored water by a small pump, which is functioning whenever a request for hot water exists. Fins in suitable positions, connect the front and back surface of the ICS, to withstand the deformation due to pressures by the tank water. In the present PhD thesis, the flow phenomena inside the ICS previous mentioned, are investigated. The aim is the maximization of the heat transfer between the two water circuits. An experimental device was constructed by transparent Plexiglas, for flow visualization and velocity measurements. A dual beam Laser Doppler Velocimetry (LDV) system was used to measure velocities. Polystyrene particles were added in the comprised water, for the visualization of the path lines. Photographs and video films were also taken. The commercial code FLUENT is used for the Computational Fluid Dynamics (CFD) simulations. A CFD model is developed and solutions are obtained using all the available turbulence models. Three main factors that influence the performance are optimized: the position and size of the recirculation ports, the arrangement and size of the interconnecting fins and the heat exchanger placement. The settling time, i.e., the time required for the flow field to be fully developed, is computed both numerically and experimentally. The previous analysis leads to the following conclusions: The standard k–ω model is selected as the most appropriate. The model is validated, with good agreement, against experimental measurements of velocities and temperatures. The placement of the inlet recirculation port perpendicular to the main surfaces of the ICS should be avoided, while its diameter should be 1/2" or less. The settling time is computed about 35s. The interconnecting fins, of the two main ICS surfaces should follow the flow filed path lines. The optimal placement of the tube heat exchanger is in contact with the two major surfaces of the storage tank.