Osvaldo Resende

Análise e descrição matemática da cinética de secagem de folhas de capim-limão

As caracteristicas da secagem de folhas de Cymbopogon citratus (D.C.) Stapf em camada delgada, foram estudadas para a faixa de temperatura de 30-60 oC, utilizando-se modelos semi-teoricos e empiricos. O modelo de Midilli foi o que melhor descreveu as curvas de secagem. Os valores da difusividade efetiva variaram de 4 x 10-12a 3,9 x 10-11 m-2 s-1 para a faixa de temperatura avaliada. Os valores obtidos da difusividade efetiva mostraram uma dependencia de Arrhenius. O valor da energia de ativacao encontrado foi de 63,47 kJ mol- 1.

Coeficiente de difusão efetivo e modelagem matemática da secagem de sementes de crambe

The mechanism of the water diffusion in agricultural products is complex due to the diversity of chemical composition and physical structure of the products. The aim of this work was to fit different mathematical models to the drying process of the crambe seeds (Crambe abyssinica), under varying conditions of air and to determine the effective diffusion coefficient and obtain the activation energy. Crambe seeds harvested with moisture content of 0.26 (decimal d.b.) and dried until 0.09 (decimal d.b.). Drying was carried out under different conditions of controlled temperature 30, 40, 50, 60 and 70 oC and relative humidity of 37.4; 22.3; 14.0; 8.3 and 5.1%, respectively. Among the models that presented the best fit for the experimental data, Wang e Singh was the best fit to the data at different drying conditions. The effective diffusion coefficient increased with increasing temperature with values of 0.88 x 10-11; 1.99 x 10-11; 2.90 x 10-11; 3.48 x 10-11 and 5.85 x 10-11 m2 s-1, for temperatures of 30, 40, 50, 60 e 70 oC, respectively, during crambe drying. The relationship between the effective diffusion coefficient and drying temperature can be described by the Arrhenius equation, which presents an activation energy for liquid diffusion in the drying of 37.07 kJ mol-1.

Isotermas e calor isostérico de sorção do feijão

The equilibrium moisture content of the edible bean was determined using the dynamic-gravimetric method for temperatures between 25 and 55 °C and water activity between 0.20 and 0.75. It was observed that the moisture content decreases when the temperature for a given water activity is increased. Experimental data were adjusted to mathematical models mentioned in the specific literature (Brunauer-Emmett-Teller, Chung Pfost, Copace, Guggenhein-Anderson-de Boer, Modified Halsey, Henderson, Modified Henderson, Oswin, Sabbah and Sigma Copace). According to the results obtained and statistical parameters, the Modified Halsey model was the most effective in representing the hygroscopicity of the edible bean. From the obtained results, the desorption isosteric heats for each equilibrium moisture content was calculated. It was observed that the desorption isosteric heat increases when the moisture content decreases indicating that the reduction in the moisture content increases the energy needed to remove water. The values of isosteric heats for the edible bean in the moisture content are between 10.10 to 21.71 (% b.s.) and they vary from 3961 to 2718 kJ kg-1.

Modelagem matemática para a secagem de clones de café (Coffea canephora Pierre) em terreiro de concreto

The objective of this work was to obtain and evaluate the drying curves for the coffee berry species Coffea Canephora , and to fit different mathematical models into the experimental data of four clones. Coffee berries from the following clones were used: Cpafro 194, Cpafro 193, Cpafro 167 and Cpafro 180, harvested at moisture contents of 1.20; 1.32; 1.51 and 1.46 (decimal d.b.), respectively. The drying continued in a concrete yard until the moisture content of 0.10 (decimal d.b.) was achieved. Ten mathematical models cited in literature were fitted to the experimental data in order to represent the drying process. According to the results and based on the statistical parameters, it can be concluded that the Page model represents well the drying of four coffee berry clones; for the clone Cpafro180, the Verna and other models were also satisfactory in describing the phenomenon. The drying time in concrete yard for coffee berry clones Cpafro 194, Cpafro 193, Cpafro 167 and Cpafro 180, up to the moisture content of 0.10 (decimal d.b.) was 117.5 hours and the diffusion coefficient was 4.50 x 10 -11 ; 5.17 x 10 -11 ; 5.08 x 10 -11 and 5.50 x 10 -11 m 2 s -1 , for analyzed clones, respectively.

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.

Qualidade fisiológica das sementes de soja armazenadas em diferentes condições

Propos-se, neste trabalho, avaliar a qualidade fisiologica das sementes de soja ao longo do armazenamento durante 180 dias em diferentes teores de agua e em duas condicoes de temperatura. Foram utilizadas sementes de soja, cultivar CD 242 RR com teores de agua iniciais de 12, 13 e 14% (b.u.). As sementes foram adquiridas com o teor de agua de 11,0% (b.u.); em seguida, foram umedecidas em câmara BOD a 20 oC e 85% de umidade relativa, homogeneizadas e acondicionadas em sacos plasticos de polipropileno; as embalagens foram mantidas em dois ambientes distintos. Com vista a avaliacao das sementes ao longo do armazenamento foram realizadas as analises de teor de agua, germinacao, primeira contagem da germinacao, indice de velocidade de germinacao e condutividade eletrica. O experimento foi conduzido no delineamento inteiramente casualizado, segundo o esquema fatorial triplo 2 x 4 x 3 (duas condicoes de armazenamento, quatro tempos de armazenamento e tres teores de agua), com tres repeticoes. O teor de agua inicial influencia na qualidade das sementes de soja durante o armazenamento. O ambiente climatizado (20 oC) proporciona melhores resultados em todas as caracteristicas estudadas.

Effect of Hot Air Drying on Ultrastructure of Crambe Seeds

This study was conducted to evaluate the morphologic modifications in tissues of the fruit and seed of the crambe (Crambe abyssinica Hochst. Ex R.E. Fr.) after drying at different temperatures. Fruits with a water content of 0.38 kg water/kg dry matter were harvested and manually homogenized. Drying was accomplished at 35, 45, 60, 75, and 90°C and at 21,9,7,5, and 2% relative humidity, respectively. After drying, the structure of the pericarp and tegument of the seed were evaluated and the embryo was removed from the fruit/seed for morphological analysis (structural and ultrastructural and the histolocalization of reserve substances). Drying at different temperatures did not affect the cellular structure of the tissues composing the pericarp of the fruits, but it disorganized the structure of the seed tegument. The cells of the tegument and cotyledons presented a contraction in their volumes. The lowest contractions in the cellular volumes of both the tegument and cotyledons occurred after drying at 35 and 45°C. The cytoplasm of the cotyledon cells contains oil drops and the protein bodies contain protein granules and starch grains. There were no changes in the cellular walls of the embryos of the fruits dried at different temperatures; however, ungluing of the medium lamella occurred. This damage occurred with greater intensity after drying at temperatures above 60°C. The form of the oil drops in the cytoplasm of the cotyledon cells was altered after drying. At temperatures above 60°C, the drops broke up and coalesced. After drying at 45 and 60°C, the form of some protein bodies was altered, whereas at 75 and 90°C coalescence of the protein bodies occurred in some cells. It was concluded that the identified alterations can affect the physiologic quality of crambe seeds.

Isotermas de dessorção e calor isostérico dos frutos de crambe

This study aimed to adjust different mathematical models to experimental data of hygroscopicity of crambe fruits, selecting one that best represented the phenomenon, and obtain the values of the isosteric heat of desorption as a function of equilibrium moisture content. To obtain an equilibrium moisture content, crambe fruit was used with an initial moisture content of 26.0% (dry basis) and static gravimetric method. For each replicate 10 g of fruit were placed surrounded by a permeable fabric to permit air contact with the product and placed within the desiccators. To control the relative humidity inside the desiccators, saturated solutions were used. The desiccators were placed in incubator B.O.D., adjusted to temperatures of 25, 30, 35 and 40 °C. The equilibrium moisture content of crambe fruits is directly proportional to water activity and decreases with increasing temperature for the same value of equilibrium relative humidity. Based on statistical parameters, the models of Copace and Modified Oswin are those that best represent the hygroscopicity of crambe fruits compared to other tested models. The isosteric heat increases with decrease in equilibrium moisture content and requires a larger amount of energy to remove water from the crambe fruit.

Higroscopicidade de sementes de caju-de-árvore-do-cerrado

Studies on conservation and exploitation of the Brazilian Savannah native species are essential to technologies that lead to the rational exploitation of these products . This study aimed at determining the desorption isotherms of Anacardium othonianum seeds for different temperature and water activity conditions, as well as adjusting different mathematical models to the experimental data, by selecting the one that best represents the phenomenon. The hygroscopicity was determined with the aid of the gravity static method, for temperatures of 25oC, 30oC, 35oC and 40oC and water activity between 0.12 and 0.89 (decimal). It was observed that the equilibrium moisture content decreased while the temperature increased, for the same water activity, similarly to what happens with hygroscopic products. The Chung-Pfost model reached the highest determination coefficient and the lowest values ??for relative average error, estimated medium error and chi-square test, being the one selected to predict the hygroscopic equilibrium of Anacardium othonianum seeds. The isosteric heat increased, while the moisture content decreased, i.e., it increased the energy required to remove water, varying from 4,586.35 kJ kg -1 to 2,572.7 kJ kg -1 , for the moisture content of 1.76-6.56 (d.b. %).

Drying kinetics of jatropha seeds

Given the necessity of developing jatropha cultivation equipment, this work adjusted different mathematical models to experimental data obtained from the drying of jatropha seeds submitted to different drying conditions and selected the best model to describe the drying process. The experiment was carried out at the Federal Institute of Goias - Rio Verde Campus. Seeds with initial moisture content of approximately 0.50 (kg water/kg dry matter) were dried in a forced air-ventilated oven, at temperatures of 45, 60, 75, 90 and 105°C to moisture content of 0.10 ± 0.005 (kg water/kg dry matter). The experimental data were adjusted to 11 mathematical models to represent the drying process of agricultural products. The models were compared using the coefficient of determination , chi-square test, relative mean error , estimated mean error and residual distribution. It was found that the increase in the air temperature caused a reduction in the drying time of seeds. The models Midilli and Two Terms were suitable to represent the drying process of Jatropha seeds and between them the use of the Midili model is recommended due to its greater simplicity .