Ivano A. Devilla

Modelagem matemática da secagem da pimenta Cumari do Pará

Among the processes of food preservation, drying the product stands out for maintaining the nutritional quality and flavor of products. The objective of this study was to determine and adjust the curves of drying of Para Cumari pepper (Capsicum chinense Jacqui), at temperatures of 45, 55 and 65 oC. The Para Cumari peppers were collected in the city of Ceres, GO and transported to UEG - Anapolis, GO. Drying was conducted in fixed bed dryer with temperature control and airflow of 60 m3 min-1 m-2. Experimental data were adjusted to nine mathematical models. The magnitude of the coefficient of determination (R2), the mean relative error (P) and the estimated mean error (SE) were used to verify the degree of fit of the models. It was concluded that: a) the behavior of the drying curves of Para Cumari pepper was similar to most agricultural products; b) the drying time was 4 h; 2 h and 50 min and 1 h and 55 min, respectively, for the drying temperatures of 45, 55 and 65 oC; c) the mathematical model of drying proposed by Midilli et al. (2002) was the best fit to the experimental data; d) values of the diffusion coefficient increased with the increase of the temperature of the drying air, with results between 2.29 10-11 and 2.57 10-11 m2 s-1.

Cinética de secagem de sementes de crambe

ABSTRACT Drying kinetics is fundamental for mathematical and modeling widely used in the project and in the analysis of heat and mass transfer during drying. In this study it was sought to assess the capability of adjustment of nine mathematical models commonly used to describe the seed drying process of Crambe abyssinica Horts. The experimental design was completely randomized, with three replications. The treatments were five water contents (0.11; 0.13; 0.17; 0.25 and 0.28 decimal dry weight) and five drying temperatures (30; 40; 50; 60 and 70 oC). To determine the adjustment of the studied models a non linear regression analyses was performed according to Quasi-Newton method. According to the data obtained it was concluded that: the diffusion approximation method was the model that best adjusted to the drying data obtained; increases in drying temperature promoted higher rate of moisture removal from the seeds; the diffusion coefficient showed values of 0.19 x 10-10 and 3.9 x 10-10 m2 s-1; the activation energy for liquid diffusion during drying of Crambe abyssinica Horts was about 4.97 kJ mol-1.

Cinética de secagem de folhas de manjericão (Ocimum basilicum L.) via infravermelho

The objective of this paper was to model the drying curves of the leaves of basil (Ocimum basilicum L.) in the infrared at temperatures of 50, 60, 70 and 80 oC and to evaluate the influence of drying temperature on the color of dried leaves. Drying was conducted in infrared dryer with temperature and greenhouse air circulation. Experimental data were fitted to eight mathematical models. The magnitude of the coefficient of determination (R2), the mean relative error (P), the estimated mean error (SE) and chisquare test (χ2) were used to verify the degree of fitness of the models. From the study it was concluded that: a) the behavior of the drying curves of basil leaves was similar to most agricultural products, the drying times in the infrared were less than the drying times in an oven with air circulation, b) the mathematical drying model proposed by Midilli et al. (2002) was the one which best adjusted to the experimental data, c) the diffusion coefficient ranged from 9.10 x 10-12 to 2.92 x 10-11 m2 s-1 and d) the color of the samples was highly influenced by drying, becoming darker due to loss of chlorophyll with increasing temperature.

Modelagem matemática das curvas de secagem e coeficiente de difusão de grãos de feijão-caupi (Vigna unguiculata (L.) Walp.)

RESUMO - Neste trabalho objetivou-se estudar a cinetica de secagem do feijao-caupi (Vigna unguiculata (L.) Walp.), ajustar diferentes modelos matematicos aos valores experimentais em funcao do teor de agua e, determinar o coeficiente de difusao e a energia de ativacao dos graos durante a secagem. Os graos de feijao-caupi foram submetidos a secagem sob as temperaturas de 25; 35; 45 e 55 ± 1 °C em secador experimental ate o teor de agua de aproximadamente 13% b.s. Realizou-se uma analise de regressao nao linear para o ajuste de 12 modelos matematicos aos dados experimentais de secagem. O coeficiente de difusao efetivo foi obtido por meio do ajuste do modelo matematico da difusao liquida. A variacao do coeficiente de difusao de acordo com a temperatura de secagem foi analisada pelo modelo de Arrhenius, o qual permitiu a determinacao da energia de ativacao. O modelo de Henderson e Pabis Modificada foi o que melhor representou o processo de secagem do feijao-caupi. O coeficiente de difusao apresentou valores entre 8,84 x 10 -8 e 20,17 x 10 -8 m 2 s -1 . A relacao do coeficiente de difusao com a temperatura de secagem pode ser descrita pela equacao de Arrhenius, apresentando uma energia de ativacao de 27,16 kJ mol -1 . Palavras-chave: Cinetica de secagem. Graos-secagem. Graos-armazenamento.

Qualidade fisiológica de sementes de crambe submetidas à secagem

RESUMO - O crambe apresenta potencial de cultivo para as regioes tropicais, sobretudo, para o Centro-Oeste brasileiro, podendo ser considerada como uma opcao a tao limitada lista de especies disponiveis para a safrinha. Contudo, a expansao da area de cultivo desta Brassicacea somente ocorrera com o fornecimento de sementes de qualidade, e para isso os conhecimentos sobre os procedimentos de secagem sao relevantes. Este trabalho foi realizado com a finalidade de avaliar a qualidade fisiologica de sementes de crambe submetidas a secagem. Para tanto, foram avaliadas sementes com cinco teores de agua (10; 12; 15; 20; 22% b.u), submetidas a cinco temperaturas de secagem do ar (30; 40; 50; 60 e 70 oC). Os testes utilizados para analise foram: teste de germinacao, primeira contagem da germinacao, comprimento de plântulas e condutividade eletrica. Conclui-se que a temperatura entre 40 a 60 oC propiciaram melhor desempenho fisiologico nos testes de viabilidade e vigor de sementes de crambe. A temperatura de 70 oC foi prejudicial ao desempenho fisiologico das sementes de crambe. Teores de agua acima de 12% b.u. sob faixas de temperaturas entre 40 a 60 oC, podem interferir positivamente na quebra de dormencia das sementes de crambe. Palavras-chave: Crambe. Secagem. Sementes-qualidade.

Airflow distribution in aerated silos: finite element analysis

In this work the finite element technique was used to obtain the air distribution in a mass of corn kernels submitted to an aeration process. The product (13% w.b.) was stored in metallic bin provided with a circular duct aeration system. The mass of grains was considered as being composed of regions (distributed resistances) that offer different resistances to the airflow in the horizontal and vertical directions. The model for air distribution in the bin was validated through experiments under similar conditions to the simulated ones with 0.0157 m3 s-1 m-2 airflow. The simulated air distribution indicated the existence of zones of low air velocities in the mass of grains located at the base of the bin (close to the center and to the wall of the bin). The simulated and experimental air velocities on the surface of the mass of grains showed a uniform tendency. The use of the finite element technique for the prediction of the airflow distribution in bins with aeration system was satisfactory and it involved a mean relative error of 6.9%..

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.

Physical, thermal and aerodynamic properties of rice grain varieties BR IRGA 409 and BRS Primavera

The rice is a major crop with economical and social importance in many countries. The production systems of this crop promote changes in the properties of the grains. The aim of this work was to characterize the grains of two rice cultivars recommended for the ecosystems: lowland and upland. Hulled rice was used, from the long and thin category, from the lowland BR IRGA 409 cultivar, and, upland BRS Primavera cultivar. Moisture contents of grains was 9,6 (% u.b.), then were determined the sphericity, circularity, apparent and unit specific mass, porosity rest angle, thermal conductivity, specific heat, thermal diffusivity, terminal velocity. The cultivars presented different values for sphericity and rest angle, but did not differ in apparent specific mass, unit specific mass, porosity and thousand grain weight, as well as in the thermal properties and terminal velocity.