A microchannel heat exchanger was designed for diesel waste heat recovery and its performance was evaluated. The 21x15x8 cm unit was constructed from diffusion brazed stainless steel lamina and weighed 11 kg. Operating from a 13.4 kW generator with an exhaust temperature of 500 °C the unit delivered 11.1 kW of thermal energy at the design point with an effectiveness of 0.87. If coupled with an organic Rankine bottoming cycle this has the potential of boosting system power output by 35%. Performance was found to be insensitive to cold side flow conditions. Soot accumulation was found to be problematic, which caused a steady exhaust pressure rise at the device but did not affect the thermal performance. / Graduation date: 2012

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[pt] Este trabalho apresenta uma investigação experimental do escoamento induzido pela interação entre uma pluma de bolhas e um escoamento cruzado oscilatório. Condições de escoamento similares podem ser encontrados em processos de aeração artificial utilizados na mitigação da poluição nos rios e na representação de vazamento de gás natural no fundo dos oceanos. No presente trabalho, ondas superficiais controladas foram inseridas em um canal de água para gerar oscilações na corrente do escoamento cruzado. As ondas foram geradas a partir de uma placa móvel na superfície da água e determinadas condições de escoamento instável foram selecionadas para a investigação. O ar foi injetado pelo fundo do canal para formar a pluma de bolhas. A técnica Particle Image Velocimetry (PIV) foi empregada para medir a velocidade do escoamento. Antes da estimativa da velocidade, as imagens foram pré-processadas aplicando-se rotinas desenvolvidas no Matlab a fim de distinguir as partículas traçadoras das bolhas de ar e criar máscaras dinâmicas para as imagens do sistema PIV. Assim, o campo vetorial de velocidade foi estimado utilizando algoritmos padrão do PIV. Além disso, as propriedades das bolhas, como tamanho e velocidade, também foram estimadas a partir das imagens adquiridas. Finalmente, foi analisada a interação entre a pluma de bolhas com o escoamento cruzado instável. / [en] This work presents an experimental investigation of the flow field induced by the interaction between a bubble plume and an oscillating cross flow. Similar flow conditions can be found in artificial aeration processes used for mitigation of pollution contamination in rivers and submarine outfalls in coastal areas. The mixing zone is highly dependent of the flow field near the plume hence the efficiency of aeration processes. In the present work, controlled surface waves were introduced to generate oscillations in streamwise and wall normal components of the cross flow. The waves were excited with a moving paddle and unsteady flow conditions were selected for the investigation. Air was injected in the bottom wall of the water channel to form the bubble plume. Particle Image Velocimetry (PIV) techniques were employed to measure the velocity flow field. Prior to velocity estimation, images were pre-processed using Matlab routines in order to distinguish tracer particles from air bubbles and to create a dynamic mask for the PIV images. Thus, the velocity vector field was estimated using standard PIV algorithms. In addition, properties of the bubbles, such as size and velocity, were also estimated from the acquired images. Finally, the interaction between the bubble plume with the unsteady cross flow was analyzed.

O processo de microfiltração tangencial com membranas tubulares inorgânicas e tubos microporosos, respectivamente de origem importada e nacional, foi investigado tendo-se como objeto de separação as misturas macromoleculares preparadas com os agentes polissacarídeos gomas Xantana e Guar em suspensão aquosa. São evidenciados neste processo os efeitos de sinergia compreendidos nas misturas elaboradas puras e em diferentes proporções, na concentração final de 1000 ppm. A investigação experimental acompanha o comportamento reológico de cada mistura ao longo do processo e os resultados foram investigados a partir de propriedades físico-químicas relevantes como: concentração de carbono orgânico total (Total Organic Carbon - TOC) e análise de absorbância no espectômetro de infravermelho. Resultados de TOC indicaram que em apenas um meio filtrante tubular microporoso (C1T+), o desempenho do processo na retenção dos polissacarídeos foi acima de 90%, em relação ao processo com a membrana comercial importada cuja retenção de TOC foi da ordem de 80%. De acordo com as análises de absorbância, conclui-se que as membranas com tamanho do poro nominal de 0,2 \'mü\'m e 0,4 \'mü\'m tiveram uma retenção mais eficiente do que os tubos microporosos em estudo. A temperatura foi um parâmetro significativo, pois a retenção, na maioria dos casos, foi maior na temperatura de 25ºC, independente da pressão e da velocidade média. Na análise dos procedimentos envolvendo cada mistura, foi constatada a boa sinergia entre as gomas, sem modificação de estrutura (formação de gel) ou fenômenos de superfície que impedissem o processo de microfiltração. A vazão transmembrana das misturas ficou limitada entre os máximos valores para mistura pura de Xantana e mínimos para Guar. Todas as misturas apresentaram comportamento pseudoplástico, sem mudanças na reologia, reforçando a adequada sinergia quanto a este aspecto. / The present dissertation reports cross-flow microfiltration with national and imported inorganic tubular membranes and microporous tubes. The object of separation is the macromolecular mixtures prepared with polysaccharide agents Xanthan and Guar gum in aqueous solution. The process shows the synergism effects in pure and different mixture proportions, with 1000 ppm final concentration. The experiments established the rheologic behaviour of each mixture along the process and significant physical and chemical properties, such as Total Organic Carbon concentration (TOC) and absorbency analysis in infrared spectrometer were analyzed. TOC retention shows that only one microporous tubular filtering medium (C1T+) had better performance (retention 90%) than the imported commercial membrane (retention about 80%). Absorbency analysis show a better retention efficiency of membranes with pore size of 0,2 \'mü\'m and 0,4 \'mü\'m than microporous tube. The temperature was a significant parameter, as the better retention was obtained at 25ºC, independently of pressure and mean velocity. There is good synergism between Xanthan and Guar gums without structure modifications or surface phenomena that would impede the microfiltration process. The transmembrane flux of proportional mixtures has been limited between maximum values of pure Xanthan and minimum values of pure Guar mixtures. All mixtures have pseudoplastic behaviour, without changes in rheology, intensifying the good synergism.

Nesta tese de doutorado é utilizada a técnica híbrida analítico-numérica, conhecida internacionalmente por GITT (Generalized Integral Transform Technique), para modelagem e simulação da equação de conservação das espécies químicas, na investigação do escoamento laminar incompressível, newtoniano e permanente em tubos permeáveis. O escoamento é aplicado ao processo de filtração tangencial com membranas e foram realizados dois estudos relacionados à equação convectiva-difusiva elíptica e parabólica, para as quais são utilizadas as mesmas condições de fronteira. Na modelagem a velocidade na parede permeável é considerada uniforme e os perfis de velocidade para a região de entrada do escoamento são obtidos na literatura. O modelo matemático utiliza originalmente uma expressão para a espessura da camada limite de concentração, com uma metodologia que determina a taxa assintótica, com a qual se estabelece a espessura da camada de concentração. Os resultados são apresentados com análise de convergência através de tabelas e com gráficos para o fluxo transmembrana local e médio, a correlação de Sherwood e a espessura da camada limite de concentração e ainda são comparados com outros resultados e metodologias reportadas na literatura. / In this doctoral thesis, the analytical-numerical hybrid technique, internationally known as GITT (Generalized Integral Transform Technique), is used for the modeling and simulation of the equation of chemical species conservation, in the investigation of the incompressible, Newtonian and permanent laminar flow in permeable tubes. The flow is applied to the cross-flow process with membranes and two studies related to the elliptic and parabolic convective-diffusive equation were accomplished, for which the same boundary conditions are used. In the modeling, the velocity on the permeable wall is considered uniform and the velocity profiles for the entrance region flow are obtained from the literature. The mathematical model originally uses an expression for the concentration boundary layer thickness, with a methodology that determines the asymptotic ratio, establishing the concentration boundary layer thickness. The results are presented with convergence analysis through tables and with graphs for the mean local transmembrane flux, Sherwood correlation and the concentration boundary layer thickness, and they are also compared with other results and methodologies reported in the literature.

Control of pollutants and emissions has become a major factor in the design of modern combustion systems. The “Liquid Hydrogen Fueled Aircraft - System Analysis” project funded in 2000 by the European Commission can be seen as such an initiative. Within the framework of this project, the Aachen University of Applied Sciences developed experimentally the “Micromix” hydrogen combustion principle and implemented it successfully in the Honeywell APU GTCP 36-300 gas turbine engine. Lowering the reaction temperature, eliminating hot spots from the reaction zone and keeping the time available for the formation of NOx to a minimum are the prime drivers towards NOx reduction. The “Micromix” hydrogen combustion principle meets those requirements by minimizing the flame temperature working at small equivalence ratios, improving the mixing by means of Jets In Cross-Flow and reducing the residence time in adopting a combustor geometry that provides a very large number of very small diffusion flames. In terms of pollutant emissions, compared to the unconverted APU, an essential reduction in emitted NOx was observed, stressing the potential of this innovative burning principle.<p>The objective of this thesis is to investigate the “Micromix” hydrogen combustion principle with the ultimate goal of an improved prediction during the design process. Due to the complex interrelation of chemical kinetics and flow dynamics, the “Micromixing” was analyzed first. Stereoscopic Particle Image Velocimetry was used to provide insight into the mixing process. A “simplified” set-up, that allowed to investigate the flow characteristics in great detail while retaining the same local characteristics of its “real” counterparts, was considered. The driving vortical structures were identified. To further investigate the physics involved and to extend the experimental results, numerical computations were carried out on the same “simplified” set-up as on a literature test case. In general, a number of physical issues were clarified. In particular, the interaction between the different vortical structures was looked into, and a kinematically consistent vortex model is proposed. After demonstrating the development of the mixing, the “cold flow” study was extended to a single injector. The double backward-facing step injector geometry was addressed experimentally and numerically. At design geometry, the flow appeared to behave single backward-facing like, with respect to the first gradation. In terms of varying step configurations, the flow was seen to be dependent on the periodic perturbation arising from the graded series of backward-facing steps. During the second part of the investigation, the “hot flow” was analyzed. Considering combustor similar operating conditions, a test burner was experimented on an atmospheric test rig. NOx emissions were traced by exhaust gas analysis for different working conditions. Particular flame patterns, such as a regular attached flame as well as lifted flames were observed. In parallel with the experimental work, numerical computations on a pair of opposite injectors, permitted to classify the combustion regime and the main factors involved in the NOx formation. Accordingly, NOx emission enhancing design changes are proposed. Finally, the demanding computational effort, worthy of acceptance for academic purposes, is found not agreeable as future design tool and improvements to speed up the design process are projected.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Dans un contexte d’augmentation des volumes de boues résiduaires produits, comprendre et optimiser les processus de déshydratation mécanique est crucial. Leurs performances conditionnent tant le fonctionnement global de la station que son bilan environnemental et économique. En effet, la siccité des boues déshydratées impacte fortement les procédés ou filières permettant leur valorisation à l’échelle des territoires (compostage, valorisation agronomique directe, incinération, …) ainsi que leur bilan environnemental direct et indirect (tonnages à transporter, ...). De plus, les filtrats devront être traités par la station, et leur composition influence significativement le fonctionnement de la filière de traitement des eaux. Les filtres-presses font partie des procédés de déshydratation mécanique les plus utilisés dans les filières boues des stations d’épuration des eaux usées. Leurs performances sont fonction à la fois de leurs paramètres de fonctionnement et des propriétés de la boue à déshydrater. Les connaissances actuelles sont cependant insuffisantes pour permettre (1) d’expliquer pourquoi certaines boues se déshydratent mieux que d’autres et (2) de relier ces phénomènes aux processus mis en oeuvre lors de la déshydratation mécanique. Le poste de déshydratation fonctionne ainsi comme une boîte noire à partir de laquelle il est difficile de prédire les performances d’un outil de déshydratation appliqué à une boue particulière et d’anticiper des dysfonctionnements. Dans ce contexte, l’objectif de ce travail de thèse était de comprendre quels sont les facteurs de contrôle des performances de la déshydratation mécanique des boues d’épuration en filtre-presse et comment ces derniers impactent le fonctionnement du procédé. Dans un premier temps, l’impact des paramètres de fonctionnement des filtres-presses sur leurs performances a été étudié en cellule de filtration tangentielle (cellule de laboratoire reproduisant les processus d’un filtre presse industriel). Ce travail a permis de hiérarchiser les paramètres opératoires selon leur impact sur les performances de déshydratation. Cette étude a permis de mettre en évidence que le paramètre le plus sensible est l’épaisseur de gâteau suivi de la pression. L’impact de ces paramètres est en partie lié à celui du gradient de pression sur les équations de la filtration même si ce dernier doit être considéré en 3D pour expliquer les résultats observés. Dans un second temps l’étude de l’impact des propriétés des boues sur les performances de déshydratation a été réalisée. Pour ce faire, ce travail s’est focalisé sur l’impact d’un des procédés qui modifie le plus les propriétés des boues : la digestion anaérobie. L’objectif de ce travail était d’identifier comment le temps de séjour hydraulique (TSH) appliqué dans le digesteur influence les propriétés physicochimiques des boues et les performances de déshydratation évaluées au travers d’essais de déshydratation en cellule de filtration tangentielle. Cette phase a permis de montrer que quand le TSH augmente de 0 à un TSHcritique, la déshydratabilité de la boue diminue. Au-delà de ce TSHcritique, cette dernière s’améliore sans pour autant atteindre celle de la boue brute. Ces phénomènes ont pu être reliés à une modification des équilibres osmotiques entre les flocs et le milieu interstitiel couplée à une modification de la matrice d’exopolymères solubles des flocs. Enfin, un modèle numérique permettant de simuler la déshydratation des boues résiduaires a été implémenté sous COMSOL multiphysics®. Au travers des processus modélisés, il prend en compte les principaux facteurs de contrôle des performances identifiés auparavant. Après ajustement des paramètres sur un unique essai de déshydratation à une pression donnée, le modèle permet de prédire la siccité du gâteau pour une pression comprise entre 3 et 15 bars. / As more and more sewage sludge are generated, understanding and optimization of mechanical dewatering processes is crucial. Their performances affect both plant management and its environmental and economic impacts. Indeed, dryness of dewatered sludge strongly impacts processes for agronomic and energetic recovery (composting, direct agricultural recycling, incineration ...) and their direct and indirect environmental impacts (volumes to transport...). In addition, the filtrates have to be treated by the wastewater treatment plant, and their composition significantly affects its operating. Filter presses are one of the most common mechanical dewatering processes operated for sludge treatment in wastewater treatment plant. Their performance depends on their operating parameters and sludge properties. However, current knowledge is insufficient (1) to explain why some sludges are easier or harder to dewater than others, and (2) to link these phenomena to processes that carry out during the mechanical dewatering. Hence, dewatering works like a black box from which it is difficult to predict the efficiency of a dewatering tool performed with a particular sludge and to anticipate operating problems. In this context, the objective of this thesis was to understand witch factors drive the efficiency of mechanical dewatering of sewage sludge in the filter press and how they impact the process. First, the impact of operating parameters of filter presses on their efficiency was investigated in cross-flow filtration cell (lab-scale cross-flow filtration cell reproducing processes that occur in an industrial filter press). This work allowed the classification of the operating parameters according to their impact on the dewatering performances. This study highlighted that the most sensitive parameter is the cake thickness followed by pressure. The impact of these parameters is partially linked with their influence on the pressure gradient even if it should be considered in 3D to explain the results. Secondly, the study of the impact of sludge properties on dewatering performances was carried out. In this thesis, this work focuses on the impact of one of the processes which modifies most significantly sludge properties: anaerobic digestion. The objective of this work was to identify how hydraulic retention time (HRT) in the digester affects physicochemical properties of sludge and dewatering performance. Results demonstrated that when the HRT increases from 0 to a critical HRT (HRTcritical), sludge dewaterability decreases. Beyond this HRTcritical, it increases without reaching cake dryness of the raw sludge. These phenomena could be linked to a change in osmotic balance between the flocs and the bulk solution, combined with a modification of the soluble exopolymer matrix of flocs. Finally, a numerical model, allowing the simulation of sludge dewatering was implemented with COMSOL multiphysics®. Equation system takes into account the main factors that affect performances previously identified. After parameter calibration on a single dewatering experiment at 8 bars, the model allows the prediction of cake dryness for any pressure between 3 and 15 bars.

Biomass liquefaction by fast pyrolysis is considered to be a key technology in future biorefineries for the production of low-carbon renewable liquids. These liquids may be used as a fuel for heat and power, as an intermediate for catalytic upgrading to distillate transportation fuels (such as renewable diesel or biojet) and as a raw material for advanced bioproducts. With the estimated supply of bioenergy required to meet international GHG reduction targets, the use of high ash (mineral-containing) biomass sources, such as harvest residues, hog fuels, and other unmerchantable wood sources is also expected to increase. However, the elevated presence of suspended char particulate (solids), as well as minerals and other ash components contained in pyrolytic liquids resulting from the conversion of these lower quality biomass residues may create new challenges for end-users. In light of this, two treatment pathways were investigated in this work: biomass pretreatment through sieving and acid washing, and post-condensation microfiltration of fast pyrolysis bio-oils. Selection of these two pathways was prioritized based on scarcity of published data, as well as the technical potential of both approaches for suspended char particulate and ash reduction in fast pyrolysis bio-oils. For biomass sieving and acid washing carried out at pilot scale, it was found that removing up to 80% of the ash contained in a hog fuel feedstock was possible by sieving out a fraction of the fines and subsequently washing with 0.1M nitric acid provided up to 40% increase in organic liquid yield after fast pyrolysis. Reaction water in the product was minimized when acid leaching was performed, while the solids content and ash content of the produced liquids were reduced by up to 80% and 87%, respectively. Cross-flow microfiltration of fast pyrolysis bio-oils produced principally from non-pretreated mill and harvest residues in the 1-40 µm range was performed. Microfiltration was found to remove between 80-95% of suspended solid particles, while only removing 4-45% of ash, presumably in the solid phase. To achieve high ash removal (>90%), microfiltration was combined with use of solid-phase adsorbents, such as Amberlyst 15, to remove cationic ash elements such as magnesium, calcium, iron, etc. The flux profiles from bio-oil cross-flow microfiltration were analyzed and consistently demonstrated a transient rapid and intermediate decline operating region, followed by a pseudo steady-state operating region. It was found that the initial flux of permeate in the transient operating region ranged from 100-1000 L m-2 h-1, while the pseudo steady-state flux ranged from 20-50 L m-2 h-1 for the experimental trials included in this study. It was determined that bio-oil temperatures of 50-60 ˚C, transmembrane pressures less than 1 bar and the addition of diluent solvents provided the highest pseudo steady-state fluxes of such a process. To improve the throughput of the process, different fouling remediation strategies were experimentally evaluated. The use of permeate, solvent and air backflushing confirmed that on-line cleaning strategies are suitable for active flux remediation, as fouling was found to be reversible over continuous operating periods up to 10 hours. Furthermore, it was found that the use of non-optimized on-line air backflushing resulted in increased throughput of low solids fast pyrolysis bio-oil from cross-flow microfiltration by 100%. Ultimately, the data produced from this work is intended to be used to generate design parameters and associated cost estimates for biomass washing and post-condensation microfiltration as processing strategies to generate high quality bio-oils from low cost biomass feedstocks.

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