No description available.

In many energy and process engineering systems where fluids are processed, droplet-laden gas flows may occur. As droplets are often detrimental to the system’s operation, they are required to be removed. According to the state-of-the-art, industrial droplet removal is achieved through a sequential arrangement of several separators followed by droplet collection and discharge. This results in a high-quality gas stream, yet at the expense of bulky and expensive systems that are difficult to retrofit to existing facilities. In addition, the multiple sequential separators produce high pressure drops, further increasing operating costs. Alternatively, a single droplet separation stage and in situ evaporation would provide compact solutions for facilities. However, compact engineering solutions for the removal of entrained droplets are difficult to achieve with conventional flow control and conduction heat transfer approaches such as Joule heating. Joule heating requires a well-defined and homogeneous electrical resistance to ensure uniform heating, which is technically challenging to apply in fine separators and thus compact removal devices are hence often costly and ineffective. Therefore, it becomes necessary to investigate alternative heating approaches to overcome these challenges, such as volumetric heating using microwaves. The research conducted in this thesis aims to analyze the potential of a compact microwave solution approach for droplet removal. The compactness of the approach relies on a novel fine separator structure enhanced by microwave-heat transfer for efficient in-flow droplet evaporation. The investigation targets at fundamental studies of the combined effect of droplet flow filtering and heat transfer from numerical calculations and experimentation. As novel fine separators, solid open-cell foams are a promising alternative for the separation of liquid droplets suspended in gas flows at comparably low pressure drops. Using susceptors, such as dielectric materials, for the skeleton and exposing them to microwaves is an efficient way to use them as heating elements. Silicon carbide (SiC) based open-cell foam samples were considered for the study as they are good susceptor materials. First, pore-scale fluid numerical simulations on representative foam models were used to obtain a deeper insight into the effects of pore size and pore density on the droplet retention time within foams. Numerical findings were reported considering the pressure gradient and the residence time distribution of droplets under different superficial flow velocities, droplet sizes, porosities and pore densities. Next, the temperature-dependent permittivity of SiC-based foam materials was determined by the cavity perturbation technique using a waveguide resonator at a microwave frequency of 2.45 GHz up to 200 °C. The permittivity was of particular interest as it is a crucial parameter for predicting and designing systems utilizing microwave heating. Along the permittivity measurements, electromagnetic wave propagation simulations were used to derive novel mixing relations describing the effective permittivity of foams while considering their skeletal morphology. The derived relations facilitate an efficient and reliable estimation of the effective permittivity of open-cell foams, producing good agreement to experimental data. Using the foams dielectric properties and the fluid characteristics of droplet-laden streams, a microwave applicator was designed to concentrate the electric field on the open-cell foams. The applicator was constructed for carrying out experimental studies on droplet evaporation removal under different flow velocities, microwave power and different SiC-based foams. Measurements of droplet size, velocity, number density and flux at the inlet and outlet streams of the applicator were performed using a 2D-phase Doppler interferometer. Eventually, it was found from the experimental data analysis that the application of open-cell ceramic foams as a filter medium reduced 99.9 % of the volumetric flow of droplets, while additional microwave exposure increased the reduction to 99.99 %. In addition, microwave-heated foams prevent droplet re-entrainment and structure-borne liquid accumulation within foams, thus avoiding water clogging and flooding. Hence, open-cell foams can be used as fine droplet separators as long as microwave heating may effectively evaporate accumulations of liquid. An important factor in designing future devices based on this microwave heating approach is the temperature, as it changes the arcing breakdown voltage of the gas, thus limiting the microwave input power and droplet flow velocity. Although more investigations are needed to develop an applicable and optimal product, the results presented in this thesis provide a first insight into the viability of using microwave heating and fine filtering as a compact solution for droplet removal.

Nowadays the environmental sustainability and the limitation of the energy consumption of buildings is of substantial importance in order to reduce greenhouse gases emissions and mitigate the consequences of climate change. Thermal energy storage (TES) allows to store thermal energy when available in order to use it when and where necessary. The use of insulating materials with TES capability may results in the compensation of energy absorption peaks caused by air conditioning or by space heating with a consequent reduction of energy consumption and related CO2 emissions. This work aims at the development and characterization of composite materials based on polymeric foams and containing a phase change material providing the TES capability. The production procedures were optimized in order to maximize the quality of the samples and the main properties of the resulting materials were then investigated. Different matrices were considered in this work: thermosetting, thermoplastic and elastomeric ones. As thermosetting matrix, a polyurethane foam was considered: this foam was filled, during the production process, with increasing amounts (from 10 to 40 wt%) of a microencapsulated PCM with a melting point of 24 °C. The addition of the PCM caused the disruption of the regular close cell morphology of the foams with a consequent increase of the thermal conductivity and a reduction of the mechanical properties. On the other hand, the addition of the PCM led to interesting TES properties, measured both through differential scanning calorimetry and infrared thermography (up to 54 J/g). Polyethylene was chosen as thermoplastic matrix and the technology of salt leaching was used to obtain foams without the use of chemical foaming agents. Foams containing different amounts (up to 56 wt%) of a microencapsulated PCM with a melting point of 24 °C were prepared. The addition of the PCM led to a decrease of the connectivity and porosity values of the prepared foams with a consequent decrease of the mechanical properties and increase of the thermal conductivity. Despite the rupture of a certain part of the PCM capsules due to the production process, good TES properties (up to 50 J/g) were measured. Elastomeric foams were prepared using an EPDM rubber as matrix and different foaming agents for the expansion process: foams obtained using two different commercial foaming agents were compared with foams obtained using the salt leaching technique. In the first case, a shape-stabilized PCM was added during the production process, while in the second one the foams were impregnated with a liquid PCM without the necessity of a shape stabilization. Salt leaching foams were able to retain higher PCM loads with respect to foams produced using commercial foaming agents and were therefore characterized by higher TES capability (up to 129 J/g). Infrared thermography tests highlighted that the time required to reach a reference temperature during heating/cooling cycles was three times longer for samples with a PCM amount of about 55 wt%. These foams evidenced a general decrease of the mechanical properties upon PCM addition. Moreover, a strong influence of the temperature on the mechanical behaviour of these foams was highlighted, with the PCM acting as softener above its melting point and as hardener below. In order to consider practical applications, elastomeric panels made of an ethylene propylene diene monomer (EPDM) rubber filled with a shape stabilized PCM and covered with a nitrile-butadiene rubber (NBR) envelope were prepared. It was possible to verify the absence of leakage, the uniform distribution of the PCM and the influence of temperature on the mechanical properties of the samples. From rheological tests it was also possible to observe the plasticizing effect of the PCM that hindered the vulcanization process of the EPDM/PCM compound. In the second part of this work larger samples were prepared and used for the internal insulation of wood boxes that were subjected to heating/cooling cycles, simulating thus real summer conditions in north Italy. The beneficial effect of the PCM resulted in a consistent reduction of the temperature peak with respect to a reference box insulated with elastomeric panels without PCM. Moreover, the fire behaviour of the produced samples was studied and the effect of the addition of different flame retardants was deeply investigated. The addition of a flame retardant based on ammonium polyphosphate and aluminium diethyl phosphinate as synergistic agents allowed a strong reduction of the peak of heat release rate measured through cone calorimeter tests, with a significant improvement of the fire behaviour. Fire tests allowed also to point out the significant role, in improving the fire performances of the samples, of the interactions between ammonium polyphosphate and the mineral fillers present in the EPDM/PCM compound (clay) and in the envelope (talc, kaolin and silica). A better comprehension of the combustion mechanisms and of the flame retardant efficacy was achieved through the analysis of the combustion residues. Finally, the specific enthalpy of the different systems was evaluated with respect to the cost of the raw materials used in the production stages in order to classify them on the basis of their melting enthalpy and on the economical aspects.

No description available.

<p>Understanding the behavior of materials with nanoscale features is important because of both the  size  of  engineering  devices  and  the  internal  microstructure  of  more  bulk  materials.  Many electronic  components  have  been  miniaturized  in  recent  years  to  attend  the  high  demand  of technology development. Similarly, new stronger bulk metallic materials use nm-scale grain sizes or  precipitates  to  increase  their  strength  over  more  conventionally  processed  alloys.  Nanoscale testing   also   offers   a   route   for   mechanical   behavior   understanding   at   the   microscale. Nanoindentation  has  been  used  to  find  structure-properties  relationships  of  nanostructured materials due to its high load-depth resolution and versatility of the test. Nanoindentation can be used  to  find  hardness  and  modulus  of  the  materials,  important  characteristics  to  evaluate mechanical  performance.  An  introduction  to  strengthening  mechanism  and  generalities  of nanoindentation is shown in Chapter 1.</p> <p>This thesis explores how traditional strengthening mechanisms for bulk materials, can be  applied  to  nanomaterials  and  how  the  microstructure  could  be  tailored  to  achieve  the  desired outcomes on the specific materials studied. The first one is the study of mechanical properties of Nanometallic  Foams  (NMF)  and  its  relationship  with  the  nanostructure.  NMFs  of  pure  copper, CuNi and CuZn alloys were fabricated and tested to find the predominant structural and chemical parameters  of  the  mechanical  properties.  Research  on  how  to  control  and  tailor  the  structural parameters of NMF with viscosity of the precursors is shown in Chapter 2. The relative density was  the  most  predominant  parameter  among  the  structural  parameters  studied.  However,  when relative density parameter is isolated, NMF  are more susceptible to strengthen by second phase precipitation instead of solid solution. The solid solution strengthening mechanism was validated with  MD  simulation  and  agrees  with  the  experimental  findings  that  showed  the  addition  of  Ni atoms to Cu have a moderate effect on the mechanical properties. Chapter 3 presents these findings The  second  example  presented  shows  the  strengthening  effect  of  precipitates  in  nanometallic multilayer. The precipitation was achieved by aging treatment. High temperature nanomechanical testing is also presented in Chapter 4. The third and final example, presented in chapter 5, shows how  the  second  phase  precipitation  and  dispersion  strengthening  of  lead-free  solder  SAC  305 compares  between  samples  aged  for  nine  years  at  body  temperature  and  an  accelerated  aging treatments.</p>

<div>This body of work examines analytical and numerical models to simulate the response of structures in shock absorption applications. Specifically, the work examines the prediction of cushion curves of polymer foams, and a topological examination of a $\chi$ shape unit cell found in architected mechanical elastomeric metamaterials. The $\chi$ unit cell exhibits the same effective stress-strain relationship as a closed cell polymer foam. Polymer foams are commonly used in the protective packaging of fragile products. Cushion curves are used within the packaging industry to characterize a foam's impact performance. These curves are two-dimensional representations of the deceleration of an impacting mass versus static stress. The main drawback with cushion curves is that they are currently generated from an exhaustive set of experimental test data. This work examines modeling the shock response using a continuous rod approximation with a given impact velocity in order to generate cushion curves without the need of extensive testing. In examining the $\chi$ unit cell, this work focuses on the effects of topological changes on constitutive behavior and shock absorbing performance. Particular emphasis is placed on developing models to predict the onset of regions of quasi-zero-modulus (QZM), the length of the QZM region and the cushion curve produced by impacting the unit cell. The unit cell's topology is reduced to examining a characteristic angle, defining the internal geometry with the cell, and examining the effects of changing this angle.</div><div>However, the characteristic angle cannot be increased without tradeoffs; the cell's effective constitutive behavior evolves from long regions to shortened regions of quasi-zero modulus. Finally, this work shows that the basic $\chi$ unit cell can be tessellated to produce a nearly equivalent force deflection relationship in two directions. The analysis and results in this work can be viewed as new framework in analyzing programmable elastomeric metamaterials that exhibit this type of nonlinear behavior for shock absorption.</div>

No description available.

Acid induced step-growth polymerizations of bis(p-methoxybenzyl) carbonate (pMBC), bis(m-methoxybenzyl) carbonate (mMBC) and difurfuryl carbonate (DFC) have been performed to produce resin-foams, because controlled release of carbon dioxide takes place during polymerization of those organic carbonates. The monomers are polymerized in bulk using p-toluene sulfonic acid (pTS) as a catalyst. The volume development of the foams is assisted by use of an appropriate surfactant and the crosslinking agent 1,3,5-trioxane as co-components. A portion of carbon dioxide release is a function of the carbenium stability of the reactive intermediate derived from the monomer; DFC > pMBC ≫ mMBC. Resins derived from mMBC can be post-treated to release carbon dioxide after polymerization. The molecular structures of the resulting materials are investigated by solid state 13C-NMR spectroscopy and IR spectroscopy. Scanning electron microscopy was used to study foam morphology. The carbon dioxide release was monitored with TG-MS analysis. Finally, the polymer foams have been converted into carbon foams and investigated by means of mercury porosimetry. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

La gravité quantique à boucles a fourni un cadre d’étude particulièrement bien adapté aux théories de jauge définies sans métrique fixe et invariante sous difféomorphismes. Les excitations fondamentales de cette quantification sont appelées réseaux de spins, et dans le contexte de la relativité générale donnent un sens à la géométrie quantique au niveau canonique. Les mousses de spins constituent une sorte d’intégrale de chemins adaptée aux réseaux de spins, et donc destinée à permettre le calcul des amplitudes de transition entre ces états. Cette quantification est particulièrement efficace pour les théories des champs topologiques, comme Yang-Mills 2d, la gravité 3d ou les théories BF, et des modèles ont aussi été proposés pour la gravité quantique en dimension 4.Nous discutons dans cette thèse différentes méthodes pour l’étude des modèles de mousses de spins.Nous présentons en particulier des relations de récurrence sur les amplitudes de mousses de spins. De manière générique, elles codent des symétries classiques au niveau quantique, et sont susceptible de permettre de faire le lien avec les contraintes hamiltoniennes. De telles relations s’interprètent naturellement en termes de déformations élémentaires sur des structures géométriques discrètes, telles que simplicielles. Une autre méthode intéressante consiste à explorer la façon dont on peut réécrire les modèles de mousses de spins comme des intégrales de chemins pour des systèmes de géométries sur réseau, en s’inspirant à la fois des modèles topologiques et du calcul de Regge. Cela aboutit à une vision très géométrique des modèles, et fournit des actions classiques sur réseau dont on étudie les points stationnaires. / Loop quantum gravity has provided us with a canonical framework especially devised for back-ground independent and diffeomorphism invariant gauge field theories. In this quantization the funda-mental excitations are called spin network states, and in the context of general relativity, they give ameaning to quantum geometry. Spin foams are a sort of path integral for spin network states, supposed to enable the computations of transition amplitudes between these states. The spin foam quantization has proved very efficient for topological field theories, like 2d Yang-Mills, 3d gravity or BF theories. Different models have also been proposed for 4-dimensional quantum gravity.In this PhD manuscript, I discuss several methods to study spin foam models. In particular, I present some recurrence relations on spin foam amplitudes, which generically encode classical symme-tries at the quantum level, and are likely to help fill the gap with the Hamiltonian constraints. These relations can be naturally interpreted in terms of elementary deformations of discrete geometric struc-tures, like simplicial geometries. Another interesting method consists in exploring the way spin foam models can be written as path integrals for systems of geometries on a lattice, taking inspiration from topological models and Regge calculus. This leads to a very geometric view on spin foams, and gives classical action principles which are studied in details.

Nesse estudo, procurou-se investigar a influência do aumento de carga orgânica em um ASBR operado a 30ºC, agitado mecanicamente e contendo microrganismos imobilizados em suporte inerte. Para tal, foi aplicado um carregamento orgânico volumétrico variando de 1,5 a 6,0 g DQO/L.dia, alimentando-se um reator construído em acrílico (5,4 L) com 2 L de água residuária sintética com concentrações de 500 a 2000 mg DQO/L com fontes de carboidrato/proteína/lipídio, em bateladas de 8 a 12 h. O sistema apresentou eficiências de remoção de material orgânico entre 73% e 88% para as condições estudadas. Entretanto, quando o reator foi alimentado com uma concentração de 2000 mg DQO/L em bateladas de 8 h, verificou-se o acúmulo de ácidos voláteis totais, refletindo na redução da eficiência de remoção de material orgânico para 55%, para amostras filtradas. Os perfis dinâmicos ao longo da batelada permitiram concluir que, para a condição com o mesmo carregamento orgânico, porém com concentrações afluentes e tempos de ciclo diferentes, a produção inicial de ácidos voláteis totais foi mais acentuada para o caso de alimentação com maior concentração. Para condições com concentrações afluentes iguais, o tempo a mais para o ciclo foi fundamental para obter-se efluente de melhor qualidade em termos de remoção de matéria orgânica. / The current study investigated the effect of increasing organic load in an ASBR operated at 30ºC with mechanical stirring and containing immobilized on inert support. Accordingly, volumetric organic loading rates ranging from 1.5 to 6.0 g COD/L.day were used by feeding an acrylic reactor (5.4 L) with 2 L of influent at concentrations of 500 to 2000 mg COD/L from wastewater containing carbohydrates, proteins and lipids in 8 and 12 h batches. Organic matter removal efficiencies between 73% and 88% were observed under the conditions investigated. However, when the reactor was fed at a concentration of 2000 mg COD/L in 8 h batches, accumulation of total volatile acids was detected, leading to a reduction in organic matter removal efficiency as low as 55% for filtered samples. The dynamic batches profiles allowed to conclude that for the same organic loading rates and different concentration influent and cycle times, the initial production of total volatile acids showed to be more pronounced for better quality effluent in terms of organic matter removal.