Desenvolvimento de procedimento analítico para determinação de iodato em sal de mesa utilizando sistema com multicomutação e detecção espectrofotométrica

A iodação do sal de mesa é considerada o caminho mais eficiente para controlar os Distúrbios por Deficiência de Iodo. Em países tropicais, o elemento pode ser adicionado na forma de KIO3. Para garantir que os níveis ideais do ânion estejam disponíveis ao consumidor, o controle de qualidade do sal consiste numa estratégia fundamental. Sistemas em fluxo com multicomutação representam uma alternativa versátil para o desenvolvimento de procedimentos simples, rápidos e limpos, minimizando o consumo de reagentes e a geração de resíduos. Nesse contexto, um procedimento analítico utilizando sistema com multicomutação e detecção espectrofotométrica foi desenvolvido para a determinação de iodato em sal de mesa. A reação empregada foi baseada na formação de um composto roxo (540 nm) entre iodato (IO3-) e p-aminofenol (PAP) em meio ácido. O tempo de residência da zona de amostra no percurso analítico foi explorado a fim de favorecer a reação lenta e a frequência de amostragem para a melhoria do desempenho analítico. Foram selecionados 2 pulsos para inserção de amostra, 3 pulsos para reagente (PAP 0,25% (m/v) em HCl 0,025 mol L-1), 7 ciclos de amostragem, 200 pulsos de carregador (água), bolha de ar de 1 s (40 µL), reator de 70 cm (3 mm d.i.) e parada de fluxo de 480 s. Resposta linear foi observada entre 2,28x10-5 e 3,65x10-4 mol L-1, descrita pela equação A = 0,2443 + 2030 C, r = 0,997. Limite de detecção (99,7% de confiança), coeficiente de variação (n = 20) e frequência de amostragem foram estimados em 8,2x10-6 mol L-1, 0,42% e 70 determinações por hora, respectivamente. Houve consumo de 1,05 mg de PAP e geração de 0,70 mL de resíduos por determinação. As principais espécies concomitantes presentes na amostra não interferiram na determinação de iodato em concentrações até 8 vezes maiores que as usualmente encontradas. Estudos de adição e recuperação de iodato foram realizados pelo procedimento proposto, obtendo porcentagens de recuperação entre 88 e 104%. O procedimento analítico desenvolvido apresenta sensibilidade adequada para a determinação de iodato em amostra de sal de mesa e elevada frequência de amostragem quando comparado com procedimentos descritos na literatura

On the development of advanced techniques for mixed-elastohydrodynamic lubrification modelling of journal and sliding bearing systems.

The present thesis is focused on the development of a thorough mathematical modelling and computational solution framework aimed at the numerical simulation of journal and sliding bearing systems operating under a wide range of lubrication regimes (mixed, elastohydrodynamic and full film lubrication regimes) and working conditions (static, quasi-static and transient conditions). The fluid flow effects have been considered in terms of the Isothermal Generalized Equation of the Mechanics of the Viscous Thin Films (Reynolds equation), along with the massconserving p-Ø Elrod-Adams cavitation model that accordingly ensures the so-called JFO complementary boundary conditions for fluid film rupture. The variation of the lubricant rheological properties due to the viscous-pressure (Barus and Roelands equations), viscous-shear-thinning (Eyring and Carreau-Yasuda equations) and density-pressure (Dowson-Higginson equation) relationships have also been taken into account in the overall modelling. Generic models have been derived for the aforementioned bearing components in order to enable their applications in general multibody dynamic systems (MDS), and by including the effects of angular misalignments, superficial geometric defects (form/waviness deviations, EHL deformations, etc.) and axial motion. The bearing exibility (conformal EHL) has been incorporated by means of FEM model reduction (or condensation) techniques. The macroscopic in fluence of the mixedlubrication phenomena have been included into the modelling by the stochastic Patir and Cheng average ow model and the Greenwood-Williamson/Greenwood-Tripp formulations for rough contacts. Furthermore, a deterministic mixed-lubrication model with inter-asperity cavitation has also been proposed for full-scale simulations in the microscopic (roughness) level. According to the extensive mathematical modelling background established, three significant contributions have been accomplished. Firstly, a general numerical solution for the Reynolds lubrication equation with the mass-conserving p - Ø cavitation model has been developed based on the hybridtype Element-Based Finite Volume Method (EbFVM). This new solution scheme allows solving lubrication problems with complex geometries to be discretized by unstructured grids. The numerical method was validated in agreement with several example cases from the literature, and further used in numerical experiments to explore its exibility in coping with irregular meshes for reducing the number of nodes required in the solution of textured sliding bearings. Secondly, novel robust partitioned techniques, namely: Fixed Point Gauss-Seidel Method (PGMF), Point Gauss-Seidel Method with Aitken Acceleration (PGMA) and Interface Quasi-Newton Method with Inverse Jacobian from Least-Squares approximation (IQN-ILS), commonly adopted for solving uid-structure interaction problems have been introduced in the context of tribological simulations, particularly for the coupled calculation of dynamic conformal EHL contacts. The performance of such partitioned methods was evaluated according to simulations of dynamically loaded connecting-rod big-end bearings of both heavy-duty and high-speed engines. Finally, the proposed deterministic mixed-lubrication modelling was applied to investigate the in fluence of the cylinder liner wear after a 100h dynamometer engine test on the hydrodynamic pressure generation and friction of Twin-Land Oil Control Rings.