Juarez de Sousa e Silva

Secagem de café em combinação

The general objective of this study was the evaluation of a system for coffee drying, using partial drying in fixed bed dryer and complementary drying in an intermittent concurrent flow batch dryer. The experiment was carried out in the Vegetable Products Processing Area, DEA-UFV. The drying tests were accomplished in completely randomized design. The coffee was harvested on the ground by manual striping process. The fruits were pre-processed by drying of ripe, overripe and greenish cherries. For the preliminary drying, the initial coffee moisture content varied from 68.9 to 71.3% w.b. with the drying being interrupted with moisture content between 44.0 and 47.5% w.b. In the complementary drying phase the final moisture varied between 12.2 and 13.8% w.b. The temperature of the drying air, in the fixed-bed dryer, varied from 50.4 to 76 °C, and in the concurrent flow batch dryer, between 87.2 and 110 °C. The specific enthalpies were 8.4 to 9.1 MJ kg-1 and 7.1 to 16,9 MJ kg-1 for the fixed-bed dryer and concurrent flow batch dryer, respectively. In comparison with the control tests, the final quality of the product presented better commercial characteristics. It was concluded that with preliminary drying in fixed bed dryer and complementary drying in a concurrent flow dryer, besides reducing the total drying time, the combined system contributes to a better preservation of qualities acquired in field.

Variação da temperatura e umidade de grãos armazenados em silos com aeração

The temperature and moisture content variations in corn kernels stored in a bin during an aeration process are presented in this work. The aeration time requirements were determined to obtain a temperature difference of 3 oC between the mass of grains and the external environment. The temperature of the stored grains was increased by submitting the product to a forced flow of moist and pre-heated air before the aeration. Airflow of 0.0157 m3 s-1 m-2 was used in the aeration process. Temperatures were recorded at several points inside the grain mass with the aid of thermocouples connected to a data acquisition system. The points were located radially at different horizontal and vertical distances on the North, South, East and West directions. Samples of the product were collected periodically during the process for moisture content determination. The temperature reduction in the mass of grains depended on the location of the product inside the bin. The largest temperature reductions were detected for the product located at South and East, and the smallest for the product at North and West (initially with lower temperature). The largest reduction in the temperature of the mass occurred between 24 and 48 h of aeration. An aeration time of approximately, 70 h was necessary to obtain a 3 oC temperature difference between the mass of grains and the external environment.