A B S T R A C TThe aim of this study was to evaluate the influence of the initial moisture content of soybeans and the drying air temperatures on drying kinetics and grain quality, and find the best mathematical model that fit the experimental data of drying, effective diffusivity and isosteric heat of desorption. The experimental design was completely randomized (CRD), with a factorial scheme (4 x 2), four drying temperatures (75, 90, 105 and 120 ); however, not affect the final yield of the oil extracted from soybean grains (15.69%).Ajustes de modelos matemáticos e qualidade de grãos de soja na secagem com altas temperaturas R E S U M O O objetivo deste estudo foi avaliar a influência do teor de água inicial da soja e as temperaturas do ar de secagem sobre a cinética de secagem, qualidade do grão e encontrar o melhor modelo matemático que se ajustar aos dados de secagem experimental, a difusividade efetiva e o calor isostérico de dessorção. Foi adotado o delineamento experimental inteiramente casualisado (DIC) com esquema fatorial (4 x 2), quatro temperaturas de secagem (75, 90, 105 e 120 0 C) e dois teores de água inicial (25 e 19% b.s.) com três repetições. O teor de água inicial do produto interferiu no tempo de secagem. O modelo de Wang e Singh mostrou-se mais adequado para descrever o processo de secagem dos grãos de soja para as faixas de temperaturas do ar de secagem de 75, 90, 105 e 120 ºC e teores de água iniciais de 19 e 25% (b.u.). A difusividade efetiva obtida da secagem dos grãos de soja foi maior (2,5 x 10 -11 m 2 s -1) para a temperatura de 120 ºC e teores de água de 25% (b.s.). A secagem dos grãos de soja com temperaturas mais elevadas (acima de 105 ºC) e com maior teor de água inicial (25% b.u.) aumentou também a quantidade de energia (3894,57 kJ kg -1 ), ou seja, o calor isostérico de dessorção necessário para realizar o processo. A temperatura do ar de secagem e dos diferentes teores de água inicial afetou a qualidade dos grãos de soja ao longo do tempo de secagem (condutividade elétrica de 540,35 µS cm -1 g -1 ), no entanto, não interferiu no rendimento de óleo final extraído dos grãos de soja (15,69%).
This study aimed to evaluate the effect of air-drying temperature and initial moisture content on volume shrinkage, physical quality and oil extraction yield of soybean grains. The grains used in this experiment were harvested at two distinct moisture levels of 19 and 25%. Then, these grains were taken to dryness at three different air temperatures of 75 °C, 90 °C and 105 °C, in a forced circulation convection oven of the air. The results showed a drying time reduction with increasing air temperatures. Regarding volume shrinkage, moisture content reductions influenced grain volume and the Rahman's model was the one that best fit the data. Moreover, the higher the air temperature, the greater the effects on soybean grain shrinkage and physical quality. By grain volume reduction effected on oil yield, major impacts were observed when assessing grain initial moisture content were higher. Furthermore, the temperature of 105°C and an initial moisture content of 25% were the factors that most affected soybean grain quality, however not affecting oil extraction yield.
Given the prominence of sunflower on the national scenario and the importance of drying steps in postharvest, this study aimed to evaluate the drying kinetics of sunflower seeds in an oven with forced air convection in different temperatures. Thus, mathematically describe and determine the effects of drying on shrinkage of seeds. The experimental design was completely randomized, factorial (4x3), four air drying temperatures (45, 55, 65 and 75 °C) and three replications. Drying was carried out until the seeds water content reached equilibrium. The air temperature and flow were monitored with a psychrometer, and a hot wire anemometer, respectively. It has been found that the drying time was significantly (P<0.05) reduced with increasing temperature of the air drying. The model of Wang and Sing was that better adjusted to experimental drying data. Effective diffusivity of sunflower seed ranged from 2.83 to 2.93x10 -6 m 2 s -1 , while the isosteric heat of adsorption, 3,725.176 to 3,773.082 kJ kg -1 . Reducing water content influenced the shrinkage of sunflower seeds, with emphasis on temperatures above 55 °C. The model Corrêa was that better adjusted to experimental data of sunflower seeds volumetric shrinkage. KEYWORDS:Dryer, optimization, post-harvest. CINÉTICA DE SECAGEM, MODELAGEM MATEMÁTICA E CONTRAÇÃO VOLUMÉTRICA DE SEMENTES DE GIRASSOL (HELIANTHUS ANNUUS L.)RESUMO: Diante do destaque da cultura do girassol no cenário nacional e da importância da etapa de secagem para a pós-colheita, este trabalho teve como objetivo avaliar a cinética de secagem de sementes de girassol, em estufa com circulação de ar convectivo e forçado em diferentes temperaturas, descrever matematicamente e determinar os efeitos da secagem na contração volumétrica das sementes. O delineamento experimental utilizado foi inteiramente casualizado, fatorial (4x3), sendo quatro temperaturas do ar de secagem (45, 55, 65 e 75 °C) e três repetições. A secagem foi realizada até o teor de água das sementes entrarem em equilíbrio higroscópico. A temperatura e o fluxo do ar foram monitorados com auxílio de um psicrômetro e um anemômetro de fio quente, respectivamente.
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