Estudo do desempenho de um secador convectivo de bandejas para a secagem de banana: análise da influência das variáveis operacionais.

Abstract

Many kinds of fruits and vegetables are composed of more than 80% of water and are highly perishable. Thus, due to the great deal of losses after harvests, it is very important to study ways of reducing these losses. Studies indicate fruit drying as one of the most economical and efficient conservation methods, when compared to other methods: freezing, canning, and so on. In this work, we made an experimental study of drying bananas slices in a convective tray drier, in order to analyze the effects of operational variables (such as temperature and air drying speed) over the performance of the drier; study the effect of the banana slice thickness above the tray; and analyze the performance of the drier through two criteria: drying air saturation level and global energetic efficiency of the drier. The operational bands used were: input air temperature between 50 and 80° C; air speed between 0,2 and 2,2 m/s; and banana slice layer thickness between 0,6 and 2,0 cm. The evaluation results showed a better utilization of the air and improved energetic efficiency not only when operated with low air drying speed but also in other conditions, such as with thicker banana slice layers over the trays. These results indicate that the air goes out of the drier far from the saturation conditions, making it possible to increase the load and/or the number of trays, in order to have a better efficiency and a better use of the air drying potential. The experimental data were used in a simulator program of a convective tray drier developed by Cavalcante (1999) for comparison of results. The drying model employed was proposed by Sokhansanj (1984). The drying kinetic was simulated using Kiranoudis et alii (1997) equation with empiric coefficients for the estimate of the drying constant. The model and the simulator used correctly represent the experimental behavior observed, not only in predicting fruit moisture evolution, but also air temperature and air humidity.