Engenharia Agrícola - Artigos
URI permanente para esta coleçãohttps://locus.ufv.br/handle/123456789/11739
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Item Experimental characterization of self-heating behavior of charcoal from eucalyptus wood(Fuel, 2019-05-15) Bustos-Vanegas, Jaime Daniel; Martins, Marcio Arêdes; Freitas, Arthur Gomes; Mellmann, JochenThe long cooling time of charcoal produced from eucalyptus pyrolysis is due in part to the heat generation in oxidation reactions at low temperatures. The intensity of this reactions depends on complex interactions between the interstitial gas and the solid matrix. The objective of this paper was to investigate the kinetics of the self-heating phenomena due to charcoal oxidation at low temperatures and at different oxygen concentrations. Samples of 230 g of charcoal were subjected to heating in a steel reactor at constant temperature, from 100 to 300 °C, and oxygen concentrations ranging from 20.9 to 10%. Was evidenced that the rate of oxygen consumption increases with charcoal temperature at rates that depend on the initial concentration of O2. The beginning of the oxidation reactions was observed at 67 °C in atmospheres with 20.9% O2. The overall activation energy for the self-heating phenomenon was 17,790 J mol−1 and its intensity was increased with the temperature and O2 concentration.Item Modelagem matemática da secagem dos frutos de amendoim em camada delgada(Revista Ciência Agronômica, 2017-07) Araujo, Willian Dias; Goneli, André Luís Duarte; Corrêa, Paulo Cesar; Hartmann Filho, Cesar Pedro; Martins, Elton Aparecido SiqueiraEste trabalho teve por objetivo ajustar modelos matemáticos aos dados experimentais da secagem dos frutos de amendoim em camada delgada, submetidos a diferentes temperaturas do ar de secagem. Foram utilizados frutos de amendoim da cultivar IAC 505. Os frutos de amendoim foram submetidos à secagem em estufa de ventilação forçada com diferentes níveis de temperatura (40; 50; 60 e 70 ºC). Aos dados experimentais foram ajustados dez modelos matemáticos tradicionalmente utilizados para representação da cinética de secagem em camada delgada. Baseado nos resultados encontrados, conclui-se que dentre os modelos ajustados aos dados experimentais, o modelo de Page foi o escolhido para representar o fenômeno de secagem em camada delgada dos frutos de amendoim. O coeficiente de difusão efetivo aumenta com a elevação da temperatura, e a sua relação com a temperatura de secagem pode ser descrita pela equação de Arrhenius. As propriedades termodinâmicas entalpia e entropia tiveram seus valores reduzidos com aumento da temperatura do ar de secagem, enquanto que os valores da energia livre de Gibbs aumentam com o aumento da temperatura.Item Modeling of the shrinkage kinetics of coffee berries during drying(Acta Scientiarum. Agronomy, 2011-07) Oliveira, Gabriel Henrique Horta; Corrêa, Paulo Cesar; Botelho, Fernando Mendes; Goneli, André Luis Duarte; Afonso Júnior, Paulo Cesar; Campos, Sílvia CarvalhoThe effects of drying conditions on the shrinkage of Coffea arabica L., cultivar Catuaí Vermelho, were studied. An exponential model derived from the kinetic model was used to describe the shrinkage kinetics. In addition, an equation was proposed to describe the relationship between the superficial areas and weights of the coffee berries. Coffee berries were dried at temperatures (T) of 35, 45, 55 and 65ºC and at relative humidities (φ) of 25, 35, 45 and 55%, forming 16 different sets of conditions, with an initial moisture content for all conditions of 2.27 dry basis (d.b.), dried until 0.11 d.b. Changes in the product dimensions were measured continuously during drying. Surface area-to-volume ratio values increased with moisture content decrease. The model was suitable for representing the shrinkage kinetics, as well the empirical equation for predicting surface area. Temperature had a greater influence over the constant rate of change of the characteristic dimension (k values) than φ. Activation energies were also determined to have magnitudes of 39.31, 37.32, 36.28 and 36.22 kJ mol-1 for relative humidities of 25, 35, 45 and 55%, respectively.