Dinâmica da impregnação a vácuo em meios porosos
AUTOR(ES)
Bruno Augusto Mattar Carciofi
DATA DE PUBLICAÇÃO
2009
RESUMO
Vacuum impregnation technology (VI) is a process that consists of removing internal air of a porous medium, through the application of vacuum in a hermetic container with the sample immersed in an impregnating solution, followed the recovery of the atmospheric pressure, leading to the solution penetratation into the sample porous space. In food processing, VI is useful to accelerate osmotic dehydration, addition of vitamins, probiotic and prebiotic compounds in foods, to accelerate salting and to improve solid-liquid extraction processes. The mathematical models often applied to VI of foods are equilibrium models, i.e., they do not allow determining the dynamics of the VI process. In this way, the main goal of this study was to evaluate the phenomena related to this mass transfer mechanism and to propose a physical-mathematical model to describe VI dynamics of porous foods. Homogeneous model and volume of fluid (VOF) methods were used to formulate the VI model. In order to solve numerically the model, a computational routine was implemented. Besides, an experimental device was built in order to supply data on the dynamics of VI. The experiments were carried out using two different kinds of porous medium, a non-deformable model (refractory ceramics samples) and a porous food (apple samples, var. Fuji), which can undergo small volume variations with pressure variations observed during VI processes. The experimental device allowed determining the apple samples deformation, sample mass variations through the VI experiments, the times necessary for evacuation and impregnation, and the time evolution of sample volumetric fraction impregnated by the liquid. From experiments of VI performed with water and with glycerol, it was verified the influence of the characteristic length and of the viscosity of the impregnating solution on the process dynamics. The equilibrium experimental results were compared to the results predicted by a literature model, while the dynamics of VI determined experimentally was compared with the developed model. This model allowed to follow the interface, which was well defined, for simulations of classic geometries and for the nonclassic ones, showing robustness. The results from the mathematical model agreed well with the experimental results, including the prediction of the dynamics of the VI process. On the other hand, the experimental device was a very useful tool for investigating VI dynamics. As waited, the kinetic was fluid viscosity and sample characteristic length dependent. The kinetic data allowed esteeming the relevant process parameters that can be used to improve VI processes.
ASSUNTO(S)
engenharia de alimentos alimentos - - embalagens engenharia de alimentos tecnologia de alimentos vacuo - - tecnologia escoamento bifasico
