Transporte de calor e massa na secagem de tijolos cerâmicos vazados.

Abstract

Drying, thermodynamic process which occurs the reduction of moisture content of solid, through energy supply, comprises one of the most important steps for manufacturing the ceramic part, both by the spent energy and by the undesirable effects that may arise in that phase. In the manufacture of ceramic bricks, for example, structural damages such as cracks, deformations and warping can diminish the quality of the final product, therefore the importance of its study. With the study of computational simulations capable of predicting the behavior of variables such as moisture content, temperature and stresses inside the ceramic bricks, it is possible to obtain a faster and more efficient drying process, avoiding raw material wastage and fuel economy. The main objective of this work is to study the heat and mass transport in the drying of hollow ceramic bricks (eight holes), including thermo-hydro- mechanical stresses, in order to improve the drying process of ceramic bricks. A transient three- dimensional mathematical model is presented to predict the mass and heat transfer, based on the liquid diffusion theory, and for the internal stresses based on the generalized Hooke law, since its numerical solution is obtained by the finite volume method. As results, drying and heating kinetics are presented for temperatures of 50o C, 70o C and 100o C, as well as moisture content, temperature and internal stress distribution graphs for the same conditions. From the results, it is verified that the higher gradients of moisture content, temperature and internal stresses occur on the external and internal surfaces, especially at the vertices. It is also observed that the internal stresses at all times and for all the analyzed temperatures, are predominantly tension, much in function of the loss of moisture and volumetric retraction. In addition, the liquid diffusion model proved to be adequate to represent the drying of hollow ceramic bricks using the effective mass and heat diffusion coefficients, which are of the order of 10 to 10¹¹.