Desenvolvimento de um sistema automatizado para medir a variação de massa na câmara de secagem de um secador solar de frutas.

Abstract

Automating the process of measuring the mass variation of the product in a solar dryer is an advance over the currently used procedure which is manual. The objective of this work is to develop this automation using appropriate technology to be incorporated into the developing solar dryer at the Federal University of Campina Grande (UFCG). These dryers need to be simple and inexpensive to be used by the family farming environment. The process used consisted in the construction and testing of a prototype of a drying chamber with rectangular shape, dimensions 32.2 x 43.0 x 34.0 cm, coupled to the solar collector. In the automated measurement system, a scale was used with aluminum tray, measuring 37.0 x 21.0 x 6.0 cm, fixed by a wooden rod to a load cell, type extensometer of sheet, which sends voltage signals, proportional to the mass variation of the product being dried, to a data acquisition platform with Arduino UNO integrated to the equipment. The loading cell attached to the tray was installed inside and, in a subsequent experiment, outside the drying chamber. The data acquisition and processing system was also installed on the outside of the drying chamber. Preliminary measurement tests were carried out with the use of halogen lamps, and the results obtained showed temperatures within the chamber of approximately 45°C ± 5°C, using a standard weight of 100 g. The results obtained during the drying of the silver banana (Musa spp) allowed the construction of the banana mass variation curves and the drying kinetic curve. Curves showing the temperature of the drying air inside the chamber were also obtained. This temperature was in the range of 30°C to 40°C, below that expected to be 50°C ± 10°C as a consequence of the low intensity of solar radiation on the days of experiment. Therefore the banana reached only the value of 44% moisture content on wet basis, above the desirable 25%. Undesirable interferences were observed during the automated measurement process, the strategies used (filters) to reduce interferences were not enough to reduce them completely and will continue to be studied in future works.