Análise da secagem em leito espesso com e sem reversão de escoamento usando degraus de aquecimento: ensaios numéricos

Abstract

The drying process may seem mistakenly simple. It includes several complex mechanisms of heat and mass transfer that make the development of mathematical models considerably harder. As a consequence, instantly controlling and optimizing this process has become a well studied challenge. The simplest drying technic is the fixed bed drying, as it occurs when, as an example, the coffee beans are open-air dryed on large cement, bricks or asphalt surfaces. The fixed bed drying is widely used in industries, mainly as packed bed columns. This equipment can be used in small scale batch drying of seeds with seeds that are sensible to mechanical schocks, in cases where the moving dryers are not able to operate. Another alternative to fixed bed drying is through the use of treadmills, that allow a continuous operation. A well-known downside of the fixed bed process is the lack of homogeneity in the product, caused by the high temperature and moisture gradients during the drying phenomenon. The application of timed reversal on the airflow direction through the bed results in a product with higher homogeneity. The present thesis here summarized aims to simulate the dynamic behaviour of the fixed bed drying with and without airflow reversal combined with stepwise temperature changes.