The gas phase flow patterns in a bubbling column were investigated, using tracer methods to establish the residence time dis­tributive An analogue computer obtained the moments if this distribution directly. The air flow rate and column height were varied. The results showed that as the air flow rate in­creased, although the voidage increased, the mean residence tine decreased. Thus an increasing proportion if the gas phase behaved as a stagnant volume. The results are correlated in terms of a mixed region model. Other work showed that an increase of liquid viscosity, or the inhibition of coalescence, affected only the stagnant volume. The rate of coalescence was investigated and an estimate of its magnitude was obtained. / Thesis / Master of Engineering (ME)

O escopo deste mestrado é de se familiarizar com a chamada {\\it correspondência AdS/CFT}, que tem sido um dos mais importantes desenvolvimentos na física teórica nas últimas décadas. De acordo com essa correspondência, deformações das geometrias do lado da gravidade (ou lado \"AdS\") devem ser mapeadas para operadores das teorias de calibre duais (ou lado \"CFT\"). Em particular, nos temos estado interessados em explorar uma entrada particular no dicionário AdS/CFT, a relação entre os operadores 1/2 BPS em ${\\cal N}=4$ super Yang-Mills, e as chamadas {\\it geometrias bubbling} no lado da gravidade. A fim de fazer isso, apresentamos primeiramente as noções de ${\\cal N}=4$ SYM e soluções de Supergravidade. Portanto, podemos expor mais claramente o sentido da correspondência AdS /CFT, e depois mostrar a derivação das geometrias 1/2 BPS duais a estados 1/2 BPS em ${\\cal N}=4$ SYM como um exemplo. / The scope of this Master program was to get acquainted with the so-called {\\it AdS/CFT correspondence}, which has been one of the most important developments in theoretical physics in the last decades. According to this correspondence, deformations of the geometries in the gravity side (or \"AdS\" side) must be mapped to states of the dual gauge theories (or \"CFT\" side). In particular, we have been interested in exploring a particular entry in the AdS/CFT dictionary, namely, the relation between 1/2 BPS operators in ${\\cal N}=4$ super Yang-Mills, and the so-called {\\it bubbling geometries} on the gravity side. In order to do that, we first present the notions of N=4 SYM and Supergravity solutions. In this way, we can expose the statement of the AdS/CFT correspondence, and later show the derivation of 1/2 BPS geometries dual to 1/2 BPS states in N=4 SYM as an example of this one.

O escopo deste mestrado é de se familiarizar com a chamada {\\it correspondência AdS/CFT}, que tem sido um dos mais importantes desenvolvimentos na física teórica nas últimas décadas. De acordo com essa correspondência, deformações das geometrias do lado da gravidade (ou lado \"AdS\") devem ser mapeadas para operadores das teorias de calibre duais (ou lado \"CFT\"). Em particular, nos temos estado interessados em explorar uma entrada particular no dicionário AdS/CFT, a relação entre os operadores 1/2 BPS em ${\\cal N}=4$ super Yang-Mills, e as chamadas {\\it geometrias bubbling} no lado da gravidade. A fim de fazer isso, apresentamos primeiramente as noções de ${\\cal N}=4$ SYM e soluções de Supergravidade. Portanto, podemos expor mais claramente o sentido da correspondência AdS /CFT, e depois mostrar a derivação das geometrias 1/2 BPS duais a estados 1/2 BPS em ${\\cal N}=4$ SYM como um exemplo. / The scope of this Master program was to get acquainted with the so-called {\\it AdS/CFT correspondence}, which has been one of the most important developments in theoretical physics in the last decades. According to this correspondence, deformations of the geometries in the gravity side (or \"AdS\" side) must be mapped to states of the dual gauge theories (or \"CFT\" side). In particular, we have been interested in exploring a particular entry in the AdS/CFT dictionary, namely, the relation between 1/2 BPS operators in ${\\cal N}=4$ super Yang-Mills, and the so-called {\\it bubbling geometries} on the gravity side. In order to do that, we first present the notions of N=4 SYM and Supergravity solutions. In this way, we can expose the statement of the AdS/CFT correspondence, and later show the derivation of 1/2 BPS geometries dual to 1/2 BPS states in N=4 SYM as an example of this one.

Biomass is an alternative to fossil fuels that has a lower impact on the environment and is thus of great interest to replace fossil fuels for energy production. There are several technologies to convert the stored energy in biomass into useful energy and this thesis focuses on the process of gasification. The purpose of this thesis is to investigate how the prediction accuracy of gas composition in a kinetic model for fluidized bed gasifier is affected when hydrodynamic parameters are introduced into the model. Two fluidized bed gasifier models has therefore been set up in order to evaluate the affects: one model which only considers the kinetics of a gasifier and a second model which includes both the kinetics and the hydrodynamic parameters for a bubbling fluidized bed. The kinetic model is represented by an already existing kinetic model that is originally derived for a downdraft gasifier which has quite similar biomass gasification processes as fluidized bed gasifiers. Gas residence time differs between the two gasifier types and the model has thus been calibrated by introducing a time correction factor in order to use it for fluidized bed gasifiers and get optimum results. Two sets of experimental data were used for comparison between the two models. The models were compared by comparing the results of the predicted gas composition yield and the amount of unreacted carbon after the reactor at various equivalence ratios (ER). The result shows that the model that only considers reaction kinetics yields best agreement with the experimental data that have been used. One reasons as to why the kinetic model gives a better prediction of gas composition is due to the fact that there are higher reactant concentrations available for chemical reactions in the kinetic, in comparison to the combined model. Less reactant concentrations in the combined model is a result of the bed in the combined model consisting of two phases, according to the two-phase theory of fluidization that have been adapted. Both phases contain gases but the bubble phase is considered solid free, chemical reactions occur therefore only in the emulsion phase since the kinetic model is based on gas-solid reactions. The model that only contains reaction kinetics considers only one phase and all concentrations are available for chemical reactions. Higher char conversion is thus achieved in the model that only contains reaction kinetics and higher gas concentrations are produced.

Zugl.: Clausthal, Techn. Universiẗat, Diss., 1995. / Literaturverz. S. 85 - 94.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-03-30T13:38:45Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese_Mikele Cândida Sousa de Sant'Anna.pdf: 2684133 bytes, checksum: 61e61bb0edcf743d1f2af9c55724a92e (MD5) / Made available in DSpace on 2016-03-30T13:38:45Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese_Mikele Cândida Sousa de Sant'Anna.pdf: 2684133 bytes, checksum: 61e61bb0edcf743d1f2af9c55724a92e (MD5) Previous issue date: 2015-11-18 / CAPEs / O presente trabalho trata da simulação numérica de um gaseificador de leito fluidizado borbulhante fazendo uso da CFD para o sistema composto por gás-biomassa-areia. Inicialmente, simulou-se os sistemas gás-areia e gás-biomassa. O modelo computacional empregado foi validado empregando-se os resultados experimentais de Taghipuor et al. (2005).A seguir, foi realizado um planejamento fatorial 23, onde se variou a massa específica e o diâmetro da partícula e o percentual de biomassa na fase sólida. Para realizar as simulações foram utilizados os softwares ANSYS CFX 15.0 e ANSYS FLUENT 15.0, adotando-se a abordagem euleriana, com a Teoria Cinética de Escoamento Granular. As seguintes velocidades superficiais do gás foram testadas: 0,03, 0,1, 0,38 0,46 e 0,51 m.s-1. Para o sistema gás-areia, o leito permaneceu fixo nas velocidades de 0,03 e 0,10 m.s-1. Aos 2,50 s de simulação transiente, o leito encontrava-se fluidizado para as velocidades maiores ou iguais a 0,38 m.s-1 e assim permaneceu alcançando um estado pseudo-estacionário. No sistema gás-biomassa, o leito manteve-se fixo apenas na velocidade de 0,03 m.s-1. Dois sistemas foram testados com três componentes (gás-areia-biomassa) diferenciando-se entre si pelos tamanhos das partículas de areia e biomassa. Para grandes diferenças entre estes tamanhos, o sistema apresentou segregação durante a fluidização. No sistema com menor diferença nestes tamanhos, a fluidização ocorreu mais facilmente, uma vez que os efeitos de segregação foram atenuados. Foram obtidos perfis de fração volumétrica do gás, areia e biomassa para as 17 condições do planejamento fatorial, bem como um modelo que prediz a expansão do leito em sistemas fluidizados. O ensaio que apresentou maior altura final do leito (0,50 m), mantendo-se em regime borbulhante, foi aquele com 15% de partículas de biomassa com 375 m de diâmetro e 85% de areia, sendo, portanto, uma condição ótima para a fluidização. / This work has studied a bubbling fluidized bed gasifier though numerical simulation using computational fluid dynamics (CFD) for the system composed of gas - biomass - sand. Initially, gas-sand and gas-biomass systems were simulated. The computer model used was validated employing experimental results from Taghipuor et al. (2005) .Then, a 23 factorial design was employed, where the density, the particle diameter and the the fraction of biomass were varied. All simulations were carried out using ANSYS CFX 15.0 and ANSYS FLUENT 15.0. An eulerian approach coupled to the Kinetic Theory of Granular Flow were used. The following gas superficial velocities were tested: 0.03, 0.1, 0.38, and 0.46 0.51 m s-1. For gas-sand system, a fixed bed was obtained for gas velocities of 0.03 and 0.10 m s-1. After 2.50 s of transient simulation, the bed became fluidized for gas velocities greater or equal to 0.38 m s-1 staying in a pseudo-steady state. For the biomassgas system, the bed remained fixed only at the speed of 0.03 m s-1. Two systems were tested using the three components (gas, sand and biomass) differing from each other only by the size of sand and biomass particles. For high differences between these sizes, the system showed segregation during fluidization. In the system with lower size difference, the fluidization occurred more easily, since the segregation effects were attenuated. Volumetric fraction profiles of gas, sand and biomass were obtained for the 17 factorial design conditions used as well as a model that predicts the bed expansion in fluidized systems. The assay that showed higher final height of the bed (0.50 m) staying in a bubbling regime was one with 15% biomass particles with 375 mm in diameter and 85% of sand, being, therefore, a good condition to carry out fluidization.

A selective combination of the principles of a thermal mass flow meter and constant temperature anemometry was used to develop a solid mass flow meter that improves significantly on the flow meter developed by De Vos et al (2010). The flow meter has a measurement plate that is kept at a constant temperature. Due to conductive heat transfer between the entrained solids and the measurement plate, additional power is needed to maintain the plate at this setpoint temperature value. This additional power was correlated against the average solids flow rate. The calibration curve shows a linear relationship between the power measurement and the entrainment flux for entrainment fluxes between 3.4 x 10-4 kg/(m2.s) and 7.5 x 10-3 kg/(m2.s). Deviation from a linear response at lower entrainment fluxes may be caused by a longer residence time of fine particles on the measurement plate due to lower shear forces. At higher entrainment fluxes the power measurements were unreliable due to poor temperature control. The turndown ratio of the linear section of the calibration curve is approximately 3 times that of the linear part of the calibration curve of the flow meter developed by De Vos et al (2010). Even further improvement is possible with better temperature control. In a case study to test the applicability of the flow meter to measure changes in entrainment rate associated with hydrodynamic properties other than a change in gas superficial velocity, small amounts of ethanol were dosed to the inlet air. The continuously measured entrainment rate increased at lower ethanol dosing rates but decreased as the dosing rate of ethanol was increased. The increase in entrainment rate may be explained by a reduction in static electricity in the bed, while the decrease at higher dosing rates may be as a result of increased powder cohesivity. / Dissertation (MEng)--University of Pretoria, 2012. / Chemical Engineering / unrestricted

No description available.

<p>The inclusions are harmful to the steel cleanliness; process parameters such as stirring and steel and slag oxidation must be controlled to obtain a final number of inclusions in the steel whose size is smaller than the critical size for each steel product.</p> <p>A simple mathematical model was developed to analyze the impact of bubbling, slag and initial oxidation level on inclusion distribution control (quantity and size of them) during the process in a Ladle Metallurgy Furnace (LMF).</p> <p>The initial inclusion size distribution is calculated and adjusted with the samples analyzed by SEM-EDAX, this initial distribution decreases by removal mechanisms such as bubbling and slag and they can increases by reoxidation.</p> <p>The model allows predicting the inclusion removal by bubbling mechanism as a function of gas flow rate and inclusion size and it proves which a softer stirring is better for removal inclusion than stronger one. An interesting point analyzed is the effect of stirring level on small and large inclusions.</p> <p>According to the inclusion number removal by slag, it is possible to appreciate like larger inclusions are removed easier than smaller ones. This mechanism is the most important to remove inclusions calculated by this model.</p> / Master of Science (MSc)

Yes / Ultrasmall SnO2 nanocrystals as anode materials for lithium-ion batteries (LIBs) have been synthesized by bubbling an oxidizing gas into hot surfactant solutions containing Sn-oleate complexes. Annealing of the particles in N2 carbonifies the densely packed surface capping ligands resulting in carbon encapsulated SnO2 nanoparticles (SnO2/C). Carbon encapsulation can effectively buffer the volume changes during the lithiation/delithiation process. The assembled SnO2/C thus deliver extraordinarily high reversible capacity of 908 mA.h.g(-1) at 0.5 C as well as excellent cycling performance in the LIBs. This method demonstrates the great potential of SnO2/C nanoparticles for the design of high power LIBs. / National Natural Science Foundation of China (21103039), Anhui Province Natural Funds for Distinguished Young Scientists, https://bradscholars.brad.ac.uk/browse?order=ASC&rpp=20&sort_by=-1&etal=-1&offset=6150&type=authorResearch Fund for the Doctoral Program of Higher Education of China (20110111120008), Beijing National Laboratory for Molecular Sciences (BNLMS), and Deutsche Forschungsgemeinschaft Grant (DFG): H1113/3-5. C.Y. acknowledges the support from the “Thousand Talents Program” and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).