Análises de sistemas de secagem: solar, elétrico e misto na produção de banana-passa.

Abstract

This paper presents a comparative study of drying systems for the production of dried bananas. An indirect solar exposure dryer with acquisition system and control of the thermodinamic properties of the drying air, and an automatized electric dryer with embedded control and supervision system were used. The drying systems studied in this paper were: solar drying, electrical drying and mixed drying (solar drying followed by electrical drying). The experimental tests were performed at the UFCG in Campina Grande, PB, for the drying of bananas (Musa spp.). The final product obtained by the three drying systems presented good visual aspect, scent and flavour, and moisture percentage at moist base less than 25%, compatible to the resolution RDC nº 272/05 of the ANVISA. The acquisition system a nd data control, added as inovation at the solar dryer, using the Arduino plataform, granted the measurement of the temperature and air relative moisture of drying air, both in the entrance and exit of the solar colector of the drying chamber, and also the activation and control of the forced convection of the drying system to keep the temperature in the drying chamber between 40ºC and 60ºC. As results, the obtained values to the drying system efficiency are presented, specific comsuption of energy (CEE), drying system efficiency and drying time. Through the experiments with the solar and the electric dryers, the curves that represent the drying kinectics of the banana were obtained. The results were compared and showed that Page’s mathematical model is adequate to predict the drying time. The determination coefficient (R²) obtained at the electric dryer was superior to the solar dryer, this shows that the control system of the thermodinamics properties of the drying air is more efficient on the electric dryer. In relation to the CEE, the electric drying showed a CEE of 379.33 kWh per cycle with a temperature of 45ºC and 225.54 kWh per cycle at the temperature of 55ºC . On the other hand, the mixed drying had a CEE of 295.87 kWh per cycle, at a temperature of 45 ºC, and the solar drying a medium CEE of 45.83 kWh per cycle. This shows the great comparative advantage of the solar dryer when compared to the electric dryer. In relation to the massic efficiency to the 3 drying processes, they showed equivalente massi c efficiency around 89%, which was expected. In relation to the thermic efficiencies of the solar dryer, obtained on the experiments with and without temperature control, were respectively 27.85%, 30.65%, these results show that the obtained resulsts are slightly superior to the results reported on the literature, which indicates that the solar dryer under development in the UFCG shows high efficiency to perform the drying of bananas, although its easy to construct and operate.