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Desempenho de filtros cerâmicos na filtração de gases a altas temperaturas
(Universidade Federal de São Carlos, 2008-09-05) Silva, Gracinda Marina Castelo da; Coury, José Renato
The creation of rigorous emission and air pollution control standards has led to a growing interest in developing technologies to clean gases that not only remove pollutants efficiently but also recycle the energy produced by the process. Ceramic filters have been the most frequently utilized to separate aerosol particles in gas streams at high temperatures. The principal characteristics of ceramic filters are low pressure drop and high collection efficiency. This study presents the experimental results on the permeability and filtration efficiency for ceramic filters of different structures and compositions at high temperatures. The filters utilized in the trials were: 0.5mm thick quartz microfiber filters, seven ceramic fiber filters (A1000, B750, B1000, 1A, 2D, 3D and 5A) from 9-12 mm thick and two ceramic filters (A12 and A13) from 9-10mm thick. All the filters were circular (5-6cm diameter) and had an effective runoff area 3cm in diameter. The quartz microfiber filters had a porosity of 0.689 with a fiber diameter of around 1.1μm; the ceramic fiber filters had a porosity of 0.5 to 0.73 and a mean fiber diameter of around 5μm. The ceramic filters had a porosity of 0.62 for the A12 sample and 0.68 for the A13 sample with a mean pore diameter of 0.33 and 0.67μm, respectively. The filters were characterized by porosity (e) determined by a mercury intrusion porosimeter (Quantachrome Poremaster) and fiber diameter was captured by a scanning electron microscope (SEM) and determined by image analysis utilizing Image Proplus for Windows software. The permeability trials were performed at room and 700o C temperatures and at velocities of 0.01 to 1.8 m/s. The equipment utilized in the permeability constant trials consisted of a blower, leak detector, micromanometer (Furness Controls Ltd. FCO14), a furnace (Maitec) and a PID type temperature controller (Flyever). The particulate material utilized in the high temperature filtration tests was concentrated phosphate with a density of 2970 kg/m3 and mean diameter of 4.62mm. The density of the particulate material was determined by a helium picnometer (AccuPyc 1330, Micromeritics). The experimental system consisted of a fluidized bed aerosol generator (TSI-3400), a particle counter (Hiac/Royco Model 5230) and a test chamber inserted in the furnace. Particulates were analyzed in eight granulometric bands: 0.75; 1.5; 2.5; 3.5; 4.5; 6; 8. and 12.5mm. The filtration experiments were carried out at three levels of temperature (room, 300 and 700ºC) at a filtration velocity of 0.05m/s. For the results obtained, there was an increase in the Darcian permeability constant, k1 which elevated the temperature for ceramic filters. For all filters studied, the filtration tests demonstrated a clear dependence between filter efficiency and test temperature: lower filtration efficiency was obtained at higher gas temperatures. The probable thermal expansion of the filter structure temporarily dilated the porous channels for fluid runoff and gas property alterations changing the removal capacity of the filter. Based on the results presented, we concluded that the filters utilized in the study are viable for industrial filtration of hot gases. The correlation proposed for the quartz microfiber was a good representation of the experimental behavior of pressure drop and the efficiency of fractional collection and was a satisfactory fit at the different test temperatures.
Síntese e caracterização de nanopartículas de óxido de ferro e de grafite magnética fluida (GMF)
(Universidade Federal de São Carlos, 2008-09-05) Souza, Nicolau Silva de; Moreira, Fernando Manuel Araújo; https://lattes.cnpq.br/1809254923092721; https://lattes.cnpq.br/6301084663879270
In this work were studied the physical properties of magnetic nanoparticles, based on iron oxide, and magnetic graphite fluid particles. The work was developed in three steps: 1) synthesis of the magnetic nanoparticles of iron oxides by the sol-gel and co-precipitation methods, 2) synthesis of the magnetic graphite fluid particles, 3) structural, microstructural and magnetic characterization of the samples. The morphological properties of the iron oxide nanoparticles, by the MEV-FEG images, showed that the samples obtained by sol-gel technique have a large tendency to create powder agglomerates. By the way, the samples obtained by coprecipitation showed a mean powder diameter 11nm, calculated from the micrographs images. Although, the same value , obtained from the XRD pattern, and diffraction peaks intensity are ~1.5 nm. From the magnetization curves, zero field cooling (ZFC), field cooling (FC), it was possible to see a phase transition for the locked-state at T ( )K B ≈ 39 ±1 for the sample obtained by sol-gel, and at T ( )K B ≈ 179 ±1 for the sample obtained by co-precipitations. The magnetization values as a function of the applied field showed a superparamagnetic behavior, ensured by the electronic paramagnetic resonance (EPR). The morphological characterization of the magnetic fluid graphite, by the TEM images, also showed an agglomerate state, but it was possible to estimate a mean diameter ~10nm. This unpublished value is much smaller than the observed on the literature. The structural characterization of the magnetic fluid graphite, obtained by infrared spectroscopy, showed that the surfactant particles (CTAB) still present on the magnetic fluid graphite surface. The surfactant particles are the responsible for the solution stability; From the magnetization measurements, as a function of the field, the graphite particles showed a typical ferromagnetic behavior. The (ZFC) magnetization measurements showed that the graphite particles have a non-null magnetization at room temperature, and the aqueous suspension doesn`t have influence on the magnetization behavior. The obtained results according to the synthesis way agree with the results showed in the literature. For the iron oxide nanoparticles it has been observed the superparamagnetic behavior in all the samples. The structural properties are ruled according to the synthesis process. On the other hand, for the magnetic graphite fluid particles, the magnetization process was made by the oxi-reduction method controlled on the vapor phase, with controlled atmosphere. After the magnetization process, was obtained by the first time the synthesis of the magnetic graphite fluid, initially on water suspension, with the magnetization properties unchanged.
Presença de dados missing em modelos de regressão logística
(Universidade Federal de São Carlos, 2008-09-05) Ferreira, Natália Manduca; Diniz, Carlos Alberto Ribeiro; https://lattes.cnpq.br/3277371897783194; https://lattes.cnpq.br/2557890621383548
In this work we present a detailed study of the logistic regression model with missing data in the independent variables. Several techniques are considered such as Complete Case, Mean Imputation and Corrected Complete Case. We present a new estimator, denoted EMVGM, given by the combination between the Complete Case estimator and the ML-estimator with the use of Gaussian quadrature. A simulation study is carried out to evaluate the performance of the ML-estimators obtained in each technique above mentioned. In general, the alternative estimador, EMVGM, presents a better performance taking into account the variance, the bias and the mean quadratic error.