A presente pesquisa trata de um estudo experimental da transferência de calor e da perda de carga de fluidos refrigerantes puros e suas misturas em mudança de fase convectiva no interior de tubos lisos e aqueles dotados de ranhuras internas. Para tanto, foi desenvolvido um equipamento experimental cujo componente básico é composto por um tubo horizontal, aquecido por intermédio de uma resistência elétrica do tipo fita, aderida à superfície externa do tubo. As condições de ensaio variaram numa ampla faixa, permitindo cobrir as condições verificadas na maioria das instalações frigoríficas. Os resultados experimentais foram agrupados em duas faixas de velocidades mássicas: elevadas (G > ou = 200 kg/s.m2), onde prepondera o padrão anular de escoamento, e reduzidas (G < 200 kg/s.m2), predominando o padrão estratificado. Os principais parâmetros que afetam o coeficiente de transferência de calor, tais como, velocidade mássica, fluxo de calor, tipo de refrigerante, temperatura de evaporação e diâmetro do tubo foram analisados. O desempenho termo-hidráulico, relativo ao efeito combinado da transferência de calor e da perda de carga dos tubos ranhurados, foi sensivelmente superior quando comparados aos tubos lisos. A análise dos resultados experimentais permitiu a proposição de correlações para a perda da carga, avaliada através do multiplicador bifásico, &#966L, e para coeficiente de transferência de calor, em tubos lisos e ranhurados. As correlações propostas se mostraram adequadas para aplicações práticas, proporcionando desvios reduzidos em relação aos resultados experimentais. Destacam-se as correlações obtidas para o multiplicador bifásico para tubos microaletados e para o coeficiente de transferência de calor para vazões reduzidas em tubos lisos. Diversos registros fotográficos dos principais padrões de escoamento foram levantados, tendo sido importante na análise e entendimento da mudança de fase. / Present research deals with an experimental study of the heat transfer and pressure drop of pure and mixtures of refrigerants undergoing convective boiling inside horizontal smooth and microfin tubes. An experimental apparatus has been developed and constructed whose main component is a horizontal tube electrically heated. Experimental results have been grouped into two mass velocity ranges: the one corresponding to mass velocities lower than 200 kg/s.m2, where the stratified flow pattern is dominant, and that for mass velocities higher than 200 kg/s.m2, where typically the annular flow pattern can be found. Effects over the heat transfer coefficient of physical parameters such as mass velocity, heat flux, diameter, saturation temperature, and refrigerant have been investigated and analyzed. It has been found out that the thermo-hydraulic performance of microfin tubes is better than that of the smooth ones. Empirical correlations have been proposed for both the two-phase flow multiplier and the heat transfer coefficient for different ranges of operating conditions as well as for smooth and microfin tubes. Results from the proposed correlations can be deemed adequate for practical applications given the limited dispersion obtained with respect to their experimental counterpart. Noteworthy are the results obtained from correlations for both the two phase flow multiplier for microfin tubes and the heat transfer coefficient for the lower range of mass velocities in smooth tubes. Finally, worth mentioning is the photographic essay developed in present research involving the flow patterns that occur under convective boiling of refrigerants in horizontal tubes.

A presente pesquisa envolve um estudo teórico-experimental da transferência de calor e da perda de carga na condensação e no escoamento monofásico de fluidos refrigerantes halogenados no interior de lâminas com micro canais. Os ensaios consideram o fluido refrigerante puro R-134-a e a mistura quase azeotrópica R-410A. As lâminas estudadas envolvem micro canais de seção quadrada de Dh = 1,214 mm e de seção circular de Dh = 1,494 mm. Os ensaios de líquido subresfriado compreendem velocidades mássicas de 390 a 1360 Kg/sm2 para um temperatura de saturação de 40ºC e subresfriamento de 10ºC. Por sua parte, os ensaios foram realizados considerando um fluxo de calor constante de 5 kW/m2, títulos de vapor de 0,1 a 0,9, velocidades mássicas de 410 a 1135 kg/sm2, temperaturas de saturação de 40 a 50ºC e misturas óleo-refrigerante com concentrações de óleo em massa de 0,25 e 0,45%. Para cada condição de ensaio foram avaliados o coeficiente de transferência de calor e a queda de pressão por atrito na lâmina ensaiada. Os resultados para escoamento monofásico apresentaram consistência com relação às correlações típicas aplicáveis a transferência de calor e perda de carga para regime turbulento em tubos convencionais, apresentando, em média, valores de 12% superiores. Na maioria das condições de ensaios de condensação, segundo mapas de escoamento disponíveis na literatura, foi identificado o domínio do padrão estreitamento anular. Este comportamento foi aferido pelos resultados experimentais de perda de carga mostrando dependência quase exclusiva do parâmetro de Martinelli, e o mecanismo conectivo como principal mecanismo de transferência de calor, característico no padrão anular. Os resultados de condensação foram correlacionados a partir de abordagens empíricas em função do parâmetro de Martinelli e o conceito de velocidade mássica equivalente. Assim como, a partir de uma abordagem semi-empírica considerando um modelo anular que permite avaliar os mecanismos principais de transferência de calor e quantidade de movimento, avaliando a espessura do filme de líquido na parede do canal. Finalmente, os resultados experimentais e os obtidos a partir das correlações desenvolvidas são comparados com estudos disponíveis na literatura relativos a lâminas com micro canais. / This project involves a theoretical-experimental study of heat transfer and pressure drop in condensation and single phase flow of halogen refrigerants in microchannel tubes. The tests include the pure refrigerant R-134a and quasi azeotropic mixture R-410A. The microchannel tubes tested include one with square ports of Dh = 1,214 mm and other with circular port of Dh = 1,494 mm. The subcooled liquid tests considered the mass velocities of 390 to 1360 kg/sm2, the saturation temperature of 40ºC and subcooled of 10ºC. The condensing tests considered a constant heat flux of 5 kW/m2, vapor quality of 0,15 to 0,9, mass velocities of 410 to 1135 kg/sm2, saturation temperature of 40 to 50ºC and oil-refrigerant mixtures with oil mass concentrations of 0,25 and 0,45%. For each test condition was evaluated the coefficient of heat transfer and frictional pressure drop in the microchannel tube. The single phase results agree with typical correlations used in conventional tubes to evaluate the heat transfer and pressure drop in turbulent flow, even though the most of experimental date are 12% higher. The most of flow patterns in condensation were identified as annular using the flow patterns maps available on literature. This behavior was verified through pressure drop results, which show exclusive dependence on Martinelli Parameter. The heat transfer results show that the main heat transfer mechanism was convective, typical in annular flow. The results of condensation were correlated from empirical approachs using the Martinelli parameter and the equivalent mass velocity concept. And, also a semi-empirical approach modeling the annular flow to evaluate the mechanism of heat transfer through the liquid film around the wall of the tube. Finally, the experimental results and the results obtained through the models were compared with correlations referred to microchannels available on the literature.

L’érosion est un phénomène d’arrachage et de transport de particules solides par des efforts hydrauliques au sein des ouvrages hydrauliques. Cette pathologie très représentée dans les ouvrages en terre peut conduire à la rupture, aussi, la comprendre et la maîtriser constituent des enjeux sociétaux et industriels très forts. L’érodabilité des matériaux se caractérise au travers notamment d’un essai dit d’érosion de conduit et sa modélisation numérique constitue le pivot de ce travail de thèse. Le phénomène d’érosion est un problème couplé entre le fluide et le solide et nous utiliserons deux codes construits sur des approches particulaires pour aborder le problème : ASPHODEL (ANDRITZLMFA) pour la partie fluide (méthode SPH-ALE Smoothed Particle Hydrodynamics – Arbitrary Lagrangian Eulerian) et YADE (L3S-R) pour la fraction solide (méthode DEM Discrete Element Method). Alors que YADE a été largement utilisé pour modéliser des problèmes géotechniques, ASPHODEL n’a pas encore été évalué dans un tel contexte. Ce travail constituera alors une étude de faisabilité pour l’utilisation d’ASPHODEL dans un contexte du génie civil et donnera les conditions pour espérer obtenir des résultats quantitatifs pour les phénomènes étudiés. Dans un deuxième temps, le couplage entre les deux codes sera construit dans le but d’étudier les phénomènes d’arrachage de particules le long de conduits formés à travers des matériaux granulaires cohérents. La validation du code ASPHODEL à l’échelle de la particule a été effectuée par l’étude de l’écoulement visqueux autour d’un objet 2D (cylindre) fixe et isolé de section circulaire mais aussi carrée ou triangulaire. Les forces de trainée, de portance, le coefficient de pression autour du cylindre et le nombre de Strouhal sont comparés à des résultats issus de la littérature pour différents Reynolds en régime laminaire. La validation du code ASPHODEL à l’échelle de l’échantillon a consisté à étudier un écoulement fluide entre des parois lisses ainsi que des parois constituées de particules solides fixes créant une rugosité. Le coefficient de frottement a été systématiquement calculé et comparé aux résultats issus de la littérature et le torseur fluide sur chaque particule solide des parois a été aussi évalué. Enfin, le couplage partitionné entre les deux codes fluide et solide a été construit et validé qualitativement pour le problème de la sédimentation sous gravité d’un grain solide rigide dans un fluide visqueux. / Erosion is a phenomenon related to the detachment and transport of solid particles by hydraulic efforts in hydraulic structures. This pathology which is common in earth structures can lead to their failure, therefore, the understanding and the prediction of this risk is of paramount importance. Soil erodibility is in many cases characterized through the hole erosion test and its numerical modeling is the pivot point of this thesis. The phenomenon of erosion is a coupled problem between the fluid and solid, and two particle based codes are chosen to address this problem : ASPHODEL (ANDRITZ - LMFA) for the fluid phase (method SPH – ALE Smoothed Particle Hydrodynamics - Arbitrary Lagrangian Eulerian) and YADE (L3S -R) for the solid phase (method DEM Discrete Element method). While YADE has widely been used to model geotechnical problems, ASPHODEL has not been evaluated in this context. This work will constitute a feasibility study for the use of ASPHODEL and its ability to obtain quantitative results for the studied phenomena is addressed. Furthermore, the coupling between the two codes will be carried out in order to study the phenomena of particles detachment along conducts which walls are made with cohesive granular materials. To validate the code ASPHODEL at the particle scale, a study of the viscous flow around a 2D fixed object (cylinder) with different sections (circular, triangular and square) is performed. The drag force, the lift force, the pressure coefficient around the cylinder and the Strouhal number are compared to results obtained from the literature for different Reynolds in the laminar regime. In addition, the coefficient of friction is systematically calculated and also compared with results taken from the literature. The fluid forces on each solid particle are also evaluated. Finally, the partitioned coupling between the solid and fluid codes is developed and qualitatively validated with the problem of sedimentation under gravity of a rigid solid grain in a viscous fluid.

De nos jours, la nécessité d’atteindre la stabilité à long terme et la facilité d'utilisation, en plus d’une plus grande fonctionnalité, implique que de nombreux produits alimentaires et ingrédients liquides ou solides sont déshydratés ou transformés mécaniquement en poudre. Les procédés de fabrication des poudres alimentaires exigent toujours la satisfaction d’une série de critères tels que la performance du procédé et la qualité du produit. La technologie d’atomisation est toujours considérée comme la principale technologie de production des poudres dans plusieurs domaines variés grâce à ses avantages prépondérants. Néanmoins dans quelques cas, l’atomisation se montre moins efficace car les frais d’investissement initiaux et de production sont trop élevés ; le besoin d’aboutir à une grande surface spécifique des poudres entraîne beaucoup de problèmes complexes concernant le transport, le nettoyage, la récupération du produit, les risques d’explosion et la dégradation thermique du produit. Tandis que, de nombreux travaux de recherche sur le phénomène d’autovaporisation par DIC (Détente Instantanée Contrôlée) ont montré que la technologie DIC est capable de résoudre de nombreuses problématiques industrielles, menant par la suite à l’obtention de produits finis de très hautes qualités et à la réduction de la consommation d’énergie. Cependant, les applications de la technologie DIC dans la fabrication des poudres alimentaires restent encore restreintes, et la comparaison des propriétés de la poudre obtenue grâce à la DIC avec les autres méthodes de production n’est pas encore effectuée systématiquement. Dans un tel contexte, ce travail de thèse est réalisé en vue de contribuer à résoudre quelques problèmes concernant le contrôle et l’amélioration de la qualité de poudre alimentaire ainsi que l’efficacité du transfert de chaleur dans les opérations d’atomisation et d’autovaporisation (traitement DIC). Afin d’atteindre ces objectifs, deux matières premières principales examinées sont la gomme arabique et le soja. Cinq principales recherches effectuées dans cette thèse consistent en : premièrement, l’étude comparative des procédés de production de la poudre de gomme arabique et les impacts du traitement DIC sur les propriétés du produit fini ; deuxièmement, l’optimisation des conditions opératoires de l’atomiseur dans la fabrication du mélange de poudres de gomme arabique (GA) et maltodextrin (MD) en tant qu’un matériau de parois pour la technologie d’encapsulation ; troisièmement, l’étude comparative des procédés de production de la poudre de soja et les impacts du traitement DIC sur les propriétés du produit fini ; quatrièmement, l’optimisation des conditions opératoires de l’atomiseur dans la fabrication de la poudre de soja ; et finalement, les impacts du taux (GA/MD) dans la fabrication de la poudre de soja par atomisation. Les résultats obtenus ont indiqué que la technologie DIC peut être utilisée à la place de l’atomisation pour fabriquer les poudres de haute qualité de la gomme arabique et du soja. Les propriétés de ces poudres ont été contrôlées et améliorées à travers le réglage des conditions opératoires de l’atomiseur et du traitement DIC. Les paramètres opératoires optimaux dans chaque cas ont été trouvés grâce à l’optimisation de processus en termes de qualité du produit fini et d’efficacité de transfert de chaleur dans la chambre de séchage. / Nowadays, the need to achieve long term stability and usability, in addition to greater functionality, implies that many food products and liquid or solid ingredients are dehydrated or mechanically transformed into powder. The manufacturing processes of food powders always require the satisfaction of a series of criteria, such as process performance and product quality. The spray drying technology is always considered the main method used for producing the powders in many varied fields thanks to its preponderant advantages. However, in some cases, the spray drying shows less effective because the initial investment and production costs are too high ; the need to reach a large specific surface area of the powders causes a lot of complex problems relating to the transportation, cleaning, product recovery, explosion risk and thermal degradation of final product. Whereas, many research work on the autovaporization phenomenon by DIC (Instant controlled pressure drop) showed that the DIC technology is able to solve many industrial problems, eventually leading to obtaining the very high-quality finished products and reducing the energy consumption. However, applications of the DIC technology in the manufacture of food powders are still restricted, and the comparison of the properties of the powder obtained by DIC with other production methods is not yet performed systematically. In such a context, this thesis work is performed in order to contribute to solving some problems concerning the control and improvement of the food powder quality as well as the heat transfer efficiency in the spray drying and autovaporization operations (DIC treatment). In order to attain these objectives, two main raw materials consisting of gum arabic and soybean were examined. Five main researches carried out in this thesis consist of : firstly, comparative study of methods for producing the gum arabic powder and the impacts of DIC treatment on the properties of finished products ; secondly, optimization of the spray drying operating conditions for producing the powder mixture of gum arabic (GA) and maltodextrin (MD) as a wall material for encapsulation technology ; thirdly, comparative study of methods for producing the soybean powder and the impacts of DIC treatment on the properties of finished products ; fourthly, optimization of the spray drying operating conditions for producing the soybean powder ; and finally, impacts of ratio (GA/MD) in the manufacture of soybean powder by spray drying. The obtained results showed that the DIC technology can be used instead of the spray drying to produce the high quality powders of gum Arabic and soybean. The properties of these powders were improved and controlled by adjusting the operating conditions of spray dryer and DIC treatment. The optimal operating parameters for each case were found thanks to the process optimization in terms of product quality and heat transfer efficiency in the drying chamber.

Cette étude porte sur l’analyse fondamentale et expérimentale des processus d’extraction des procédés conventionnels et innovants. L’intensification de ces techniques s’est tout d’abord basée sur des approches théoriques. D’une part, nous nous sommes focalisés sur « le paradoxe » généré par l’extraction conventionnelle des huiles essentielles et les issues et solutions que la Détente Instantanée Contrôlée (DIC) ou les Micro-Ondes (MO) peuvent apporter. D’autre part, nous nous sommes intéressés à la problématique d’intensification des opérations d’extraction par solvant des composés non-volatils à partir de végétaux. La spécificité des processus diffusionnels leur donne une importance particulière en raison de la structure propre de la matière, traduisant ainsi une mauvaise aptitude technologique intrinsèque. L’amélioration de l’extraction par l’action de la DIC sur la structure de la matrice, des MO sur le chauffage et des UltraSons (US) sur la micro-agitation, permet d’envisager un couplage, de conduire à une intensification après optimisation souvent multicritères (cinétique, qualité et énergie). La DIC a été appliquée sur des feuilles de romarin et des écorces d’orange afin d’en extraire les huiles essentielles. Ce traitement a permis d’accéder à une expansion et de parvenir à une intensification de l’extraction des molécules antioxydantes. Nous avons donc procédé à une combinaison DIC/MO pour le romarin et DIC/US pour les écorces d’orange. Enfin, la cinétique de l’extraction d’huiles de colza a été intensifiée par un prétraitement DIC et étudiée à travers une modélisation dont l’un des aspects a été une diffusion de type Fick couplée à une solution de Crank / This study focuses on fundamental analysis and experimental work carried out on extraction via conventional and innovative processes. The intensification of these techniques is first based on theoretical approaches. On the one hand, we focused our meditation on examining the "paradox" generated by conventional steam-distillation of essential oils, and suggested solutions from Instant Controlled Pressure Drop (DIC) or Microwave (MW). On the other hand, we were interested in the problematic of solvent extraction operations of plant-based non-volatile compounds. The specificity of the diffusional process gives them a special importance because of the specific structure of the material, reflecting poor intrinsic technological ability. Improving extraction by letting DIC act on the structure of the matrix, MW on heating, and UltraSound (US) on the micro-agitation, allows to coupling technologies leading to a perfect intensification and thus multi-criteria optimization (kinetics, quality and energy). DIC was applied to the leaves of rosemary and orange peel to extract essential oils. This treatment has access to expansion and to achieve increased extraction of antioxidant molecules. We therefore conducted a combination DIC/MW for rosemary and DIC/US for orange peel. Finally, the extraction kinetics of rapeseed oil has been intensified by DIC pretreatment. This kinetics was identified through modeling including Fick diffusion coupled to a Crank solution

Residence time distributions have become an important analytical tool in the analysis of many types of flow systems. Residence time distributions have proven to be effective for analysing trickle bed reactors, as it allows determination of parameters under operating conditions allowing no interference of these conditions. By studying the residence time distribution a great amount of information can be obtained and therefore used to determine a number of hydrodynamic parameters. Due to recent findings that prewetting has a tremendous effect on a number of hydrodynamic parameters such as holdup, wetting efficiency and pressure drop, it is therefore the aim of this study to investigate the effect of trickle flow morphology or prewetting on a trickle bed reactor. The residence time distribution is obtained whereby hydrodynamic parameters are determined and therefore the effect the flow morphology has on various hydrodynamic parameters is highlighted. A number of methods were used to determine these parameters, namely that of the best-fit method, whereby the PDE model was used, and the method of moments. Operating conditions included varying gas and liquid flow rates for porous and non-porous catalyst particles at atmospheric pressure. The different prewetting procedures used during this work included the following: <ul><li>Non-wetted </li> <li>Levec-wetted </li> <li>Super-wetted</li></ul> From this investigation the following conclusions were made: <li>Prewetting has a great effect on the hydrodynamic parameters of trickle bed reactors</li> <li>The differences in prewetting can be attributed to differing flow morphologies for the different prewetted beds i.e. the dominant flow morphology for a non-wetted bed is that of rivulets and for prewetted beds that of film flow</li> <li>It was also found that at low liquid flow rates the flow morphology in prewetted beds changes from film flow to a combination of rivulet and film flow</li> <li>The different flow morphologies for prewetted and non prewetted beds was confirmed by the residence time distributions and various parameters obtained there from</li> <li>At low liquid flow rates the flow morphology becomes a more predominant factor in creating the tailing effect present in residence time distribution for prewetted beds</li> <li>The tailing effect in residence time distributions is a result of both internal diffusion and liquid flow morphology, where the liquid flow morphology is the more dominant factor</li> <li>The use of residence time distributions to determine a number of hydrodynamic parameters proved to be very useful and accurate by means of different methods, i.e. method of moments and best-fit method</li> <li>Differences in the liquid holdup determined from the method of moments and the weighing method confirmed that different flow morphologies exist for different prewetted beds</li> <li>An increase in the dispersion coefficient with prewetting was observed indicating that the amount of micro mixing is different for the different prewetted beds</li> <li>Differences in residence times and high values for the dynamic holdup, for the porous packing, confirmed that the PDE model does not model well the porous packing response curves due to the lack of internal diffusion and internal holdup in this model</li> <li>The dynamic-static mass transfer showed that film flow, as in prewetted beds, results in slower mass transfer as opposed to rivulet flow and therefore it is concluded that prewetting results in different flow morphologies.</li></ul> Following this study it is recommended that a residence time distribution model be used or developed that incorporates the effects of internal diffusion and internal holdup as present in porous catalyst particles. In addition, it was found that very few correlations could accurately predict hydrodynamic parameters due to the absence of the effect of prewetting and therefore it is recommended that correlations be developed that incorporate the effect of prewetting. / Dissertation (MEng)--University of Pretoria, 2008. / Chemical Engineering / unrestricted

The subject of this diploma thesis is to design space heating system for building with five floors, where the first above ground floor is used as commercial space. Designed building have one underground floor and four above ground floors. Diploma thesis is designed as project of Building Service, specifically that of Heating. This diploma thesis contains calculations of the design heat load, design of radiators and others heating surfaces, hydraulic balancing, generation of domestic hot water, design of heat source, calculations of safety devices and pumps design. Part of this diploma thesis is also conceptual design of regulation.

Significant maldistribution negatively influences performance of equipment containing dense tube bundles and, moreover, it can cause a wide range of operating issues. This thesis therefore focuses on analysis of fluid flow in complete distribution systems via computational fluid dynamics (CFD). Data obtained from simulations carried out using the software ANSYS Fluent were also statistically analysed. Influence of system arrangement, tube bundle parameters and operating parameters on flow distribution non-uniformity and pressure drop was investigated. According to the results, system arrangement is the crucial differentiating parameter in terms of flow distribution as well as pressure drop. Additionally, data obtained via the classical CFD approach were compared with those yielded by a simplified CFD model for three selected distribution systems. Simplified CFD approach can - given its low computational demand - be utilised in optimization algorithms as well as in the course of the initial stage of equipment design process. Furthermore, this thesis discusses a simulation tool which is based on the simplified CFD approach. Although this tool is still being developed, the results it yields are very promising.

Final thesis, elaborated within the master study field of Foundry technology, deals with determination of some parameters of ceramic foam filters that are necessary for using numerical simulation during foundry practice. Thesis foccuses on defining methodology, manufacturing messuring device and measuring pressure drop on several type sof ceramic foam filters in dependence on flow rate of measuring medium. Measuring medium selected is water, mening this thesis deals also with water simulation in foundry technology.

The diploma thesis describes the design of air conditioning equipment of materni-ty hospital and experimental measurement nanofilters and their subsequent comparison with conventional air filters. The work consists of three parts. The first part describes the types of filters. Nanofilters and nanofiber materials are de-scribed in detail here. In the second part is the topic of air filtration applied to the maternity hospital. Two variants of air conditioning and cooling are designed for the 3rd floor of this building. The third experimental part deals with antibacterial effects of thr silver fiber nanofilter and its comparison with commonly used filters. It also deals with the pressure drop on the filters at different air speeds.