Avaliação de modelos matemáticos na descrição das curvas de secagem por convecção de Pectis brevipedunculata (Gardner) Sch. Bip. Assessment of mathematical models for the description of Pectis brevipedunculata (Gardner) Sch. Bip. convective drying curves

O presente trabalho foi realizado com o objetivo de selecionar, dentre cinco modelos matemáticos, aquele que melhor descreve as curvas experimentais de secagem da parte aérea de P. brevipedunculata. Os testes foram realizados em protótipo de secador de leito fixo, em camada delgada, a 30, 40 e 50°C, com fluxo mássico de ar seco de 0,27 e 0,54 kg s-1 m-2. O grau de ajuste dos modelos foi avaliado por meio do coeficiente de determinação, da raiz do erro quadrático médio, do erro percentual absoluto médio, do chi-quadrado reduzido, pela análise de dispersão de resíduos, e considerando o princípio da parcimônia. O modelo exponencial simples de três parâmetros foi o que melhor representou as curvas experimentais de secagem podendo ser utilizado com segurança na simulação do processo em camada espessa. Embora o modelo de Lewis não tenha sido capaz de descrever as curvas de secagem com grau de acurácia satisfatório, observou-se que a relação funcional entre a constante de secagem k e a temperatura, pode ser representada pela equação de Arrhenius.<br>The aim of this study was to select, among five mathematical models, the one that best describes the experimental drying curves of the shoot of P. brevipedunculata. Tests were conducted in a thin-layer prototype laboratory drier, at 30, 40 and 50°C, employing a dry air mass flow rate of 0.274 and 0.542 kg s-1 m-2. The goodness of fit of the models was assessed based on correlation coefficient, root mean square error, mean absolute percentage error, reduced chi-squared, residual plot analysis, and taking into account the principle of parsimony. The model that best described the experimental drying curves was the simple-exponential, three-parameter model, which can be safely used to simulate the deep-bed process. Although the Lewis model was found not to produce accurate predictions of the drying curves, an Arrhenius-type equation represents the relationship between the drying constant k and the temperature

Dielectric properties of papaya seeds from 75 kHz to 5 MHz

The object of this work was to study the dielectric properties of papaya seeds of the Golden cultivar and seeds of two papaya hybrids, Tainung and Calimosa, in the frequency range from 75 kHz to 5 MHz at four levels of bulk density, and with moisture contents ranging from 6 to 23% wet basis. The relative permittivity and the loss factor of the seeds were measured using a precision LCR meter, and their relationship with the variable frequency of the oscillating electric field, the seed moisture content and bulk density, and the cultivar/hybrid type were established. Relative permittivity for each value of the moisture content was reduced regularly as the frequency increased. Abrupt changes in the slopes of the curves demonstrating the relationship between the relative permittivity and the loss factor, and the moisture content were considered an indication of changes in the water sorption mechanisms occurring within the seed. The relationship between the relative permittivity and the loss factor, and bulk density was represented by linear functions with positive slopes. The effect of the cultivar or hybrid types on the relative permittivity and the loss factor revealed that seeds of the Golden cultivar and the Tainung hybrid exhibited similar relative permittivity values in the whole frequency range studied, in contrast to seeds of the Calimosa hybrid