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  • Artigo de evento
    Possible indirect measurement of diffusion coefficient from migration kinetic essay of food packaging
    (2008-09-10) MANZOLI, J. E.; LEMOS, C.; PANZARINI, L. C. G. A.; FÉLIX, J. S.; MONTEIRO, M.
    Diffusion coefficient is an important quantity that affects any migration process on food or nutritional systems. Special care has to be done to migration of undesirable substances from packaging into foods, if the diffusion is the only process involved in mass transfer. The Fick's equation resolution permits to describe the kinetic of migration from polymer packaging into food or simulant, once it was given the correct contour and initial conditions. Another important quantity is the partition coefficient, which quantifies the relation between the final or equilibrium concentrations in polymer and that in the food or simulant. Here it is proposed a simple procedure, based on numerical resolution of the Fick's equation, where the diffusion coefficient could indirectly be measured, if the kinetic of migration had been measured and the partition coefficient is known.
  • Artigo de evento
    Use of hydrodynamic cavitation as an alternative for biodiesel production
    (2009-08-30) SANTOS, S. L. DOS; FERREIRA, M. S.; Maristhela Passoni de Araújo Marin; Luis Novazzi
    © 2009 by ABCM.Biodiesel is known as an alternative to conventional petrodiesel because of its renewability and better combustion performance, in addition to reducing emissions, harmful to the environment. Biodiesel production consists on the transesterification of triglycerides with an alcohol and the reaction is affected by the alcohol type, temperature, molar ratio of alcohol to oil and catalyst type and amount. Since this reaction is a heterogeneous one, reagent mixing is also of crucial importance and traditionally the blending is carried out by using mechanical mixers. In this work a different approach is proposed, where the mixing is induced by hydrodynamic cavitation provoked by an orifice plate connected to the suction of a centrifugal pump. Biodiesel production was carried out at 45°C with a 1:8 molar ratio of soybean oil to ethanol. It was observed that the method assisted by hydrodynamic cavitation promotes the enhancement of biodiesel yield in comparison to the conventional method that uses mechanical stirring. In comparative tests carried out from 0 to 40 minutes, the hydrodynamic cavitation always showed conversion rates larger than the mechanical agitation. Although specific energy consumption in biodiesel production is slightly higher for hydrodynamic cavitation when compared to conventional mechanical mixing, it was observed that in the alternative approach the equipment employed is simple and has a low acquisition cost, showing that it has a great potential to be scaled up and used in industrial processes.
  • Artigo de evento
    Calorimetric measurement of the interface energy of pure and calcium doped magnesium oxide
    (2009-10-29) CASTRO, R.; Ricardo Torres; GOUVEA, D.
    Interface energetics is of key importance in understanding the evolution of nanoparticles during sintering. During this process, two types of interfaces control the driving forces: the surface and the grain boundary. The knowledge of their energies is therefore of major importance to obtain reliable sintered bodies. The objective of this work was to present a quantitative relationship between the grain boundary energy and the surface energy of MgO and Ca-doped MgO nanoparticles to provide data to better understand the sintering behavior of this system, in particular delineating the thermodynamic basis of using Ca as sintering add. Using a novel and convenient calorimetric procedure, the ratio between the grain boundary energy and the surface energy was determined to be 1.1 for pure MgO and 0.7 for Ca-doped MgO. Based on these, the grain boundary energy of pure MgO and Ca-doped MgO were estimated to be 1.2 J.m-2 and 0.4 J.m-2, respectively. The grain boundary energy decrease caused by calcium doping was attributed to its interface segregation and influenced the sintering behavior by changing the equilibrium dihedral angle in addition to diffusion parameters.
  • Artigo de evento
    Multivariable control of a heat exchanger with bypasses
    (2009-07-15) Delatore, F.; DA CRUZ, J. J.; Fabrizio Leonardi; Luis Novazzi
    A myriad of different multivariable control techniques, ranging from the simplest isolated PID controllers to the most sophisticated model predictive controls, are presented in the literature and applied to chemical plants. This work intends to present an intermediate control solution between the simplest and the most complex control design, with a relative simplicity, in combination with a superior performance when compared to traditional PID controllers. The proposed strategy, based on a Linear Quadratic Regulator (LQR), was applied to a heat exchanger with bypasses, which is a typical equipment in industries' processes. Even though the LQR is relatively straightforward to design, with a simple tuning procedure, some simulations' results demonstrated that the proposed approach leaded to a reasonable control performance, i.e., process variables became almost totally decoupled, no offset was observed and the output responses presented an small time constant.