Paulo Cesar Corrêa

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.

Modelagem matemática e determinação das propriedades termodinâmicas do café (Coffea arabica L.) durante o processo de secagem

The aim of the present work was to model the drying process and to obtain the thermodynamic parameters of coffee beans (Coffea arabica L.), cultivar Catuai Amarelo, for three different conditions of temperature and relative humidity (35 oC and 32.1 %; 45 oC and 15.7 %; 55 oC and 10.2 %). Coffee beans were hand picked with an initial moisture content of 1.25 (d.b.) and dried to a mean moisture content of 0.13 (d.b.). Six mathematical models commonly used to represent the drying process of agricultural products were fit to the experimental data. Fick’s second law was used to obtain the diffusion coefficients of coffee beans using the drying kinetics. The activation energy for the drying process of coffee beans, as well as the entropy, enthalpy and Gibbs free energy were determined. The modified Midili model best represented the drying phenomenon of coffee beans. The calculated diffusion coefficients were 2.99 x 10 -11 , 2.39 x 10 11 and 5.98 x 10 -11 m 2 s -1 , to the temperatures of 35, 45 and 55 oC, respectively. Enthalpy decreased with the increase in

Sorption Isotherms and Isosteric Heat of Peanut Pods, Kernels and Hulls:

This study was carried out to evaluate the sorption isotherms of peanut pods, kernels and hulls for several temperature and humidity conditions and to fit different mathematical models to the experimental data, selecting the one best fitting the phenomenon. The dynamic method was applied to obtain the hygroscopic equilibrium moisture content. The environmental conditions were provided by means of an atmospheric conditioning unit, in which removable perforated trays were placed to allow air to pass through peanut mass, each one containing 50 g of the product. The mathematical models frequently used for the representation of hygroscopicity of agricultural products were fit to the experimental data. Based on those results, it was concluded that peanut pods, kernels and hulls presented differentiated hygroscopicity. The equilibrium moisture content for peanut pods, kernels and hulls increased with an increase in the relative humidity at any particular temperature and decreased with increase in temperature at constant relative humidity. At a constant water activity, peanut hulls samples had higher equilibrium moisture content than the pods and kernels samples. Based on statistical parameters, the modified Henderson and Chung-Pfost models were found to adequately describe the sorption characteristics of peanut pods, kernels and hulls. Isosteric heat of desorption were evaluated by applying the Clausius—Clapeyron equation to experimental isotherms and decreased with increasing moisture content. The peanut hulls had higher isosteric heat of sorption than that peanut pods and kernels.

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.

Estudo da difusão de umidade em grãos de trigo durante a secagem

The aim of this work was to adjust the liquid diffusion model to the wheat drying curves considering the shrinkage of the grains and to determine the diffusion coefficients under different air conditions. Rough rice with 0.32 (d.b.) moisture content was used in this experiment. The drying procedure was done under different controlled temperatures of 25 to 55 °C with the drying air relative humidity of 55 ± 1%. The shrinkage of the grains was determined by the ratio between the volume of each moisture content and the initial volume. Based on the results, it can be concluded that the liquid diffusion model represents the wheat drying kinetics satisfactorily for experimental conditions in this test, however, the shrinkage of grains was not considered. The diffusion coefficient increases with the increase of the air temperature, with values ranging between 8.6775 x 10-11 and 41.0977 x 10-11 m2.s-1 for the strip of studied temperature. The variation of the diffusion coefficient with the temperature may be described by the Arrhenius expression, presenting an activation energy of liquid diffusion wheat of 42.00 kJ.mol-1.

Modelagem matemática e parâmetros qualitativos da secagem de folhas de capim-limão [Cymbopogon citratus (DC.) Stapf]

The species Cymbopogon citratus, known as lemon grass, is widely used for medicinal purpose and in the pharmaceutical, food, cosmetic and perfumery industries. Due to the need for more specific knowledge of pre-processing management, this work aims to equate and analyze some drying aspects that allow preview the product quality alterations. The leaves from this species were cut at different lengths and dried at different temperatures. Different equations for modeling the drying curves were adjusted to the experimental data. The dried product was also evaluated for color and essential oil content. The results showed that the Modified Page model resulted in the best adjustment for the experimental data. The temperature of 50°C was the best for drying the species leaves, resulting in less essential oil loss and higher green color maintenance.

Comparação de modelos matemáticos para descrição das curvas de dessorção de sementes de milho-doce

This work had the goal to determine the desorption curves of seeds of sweet corn cultivars Superdoce and Doce Cristal, and to adjust mathematical models to obtained data. Corn seeds were submitted to desorption under different temperature conditions (30, 40, 50 and 60°C), associated with different relative humidity (30, 40, 50 and 60%) until reaching the equilibrium humidity. The following models of regression analysis were adjusted to the experimental data: Henderson-Thompson, Chung-Pfost, Copace, Sigma-Copace, Sabbah and Smith. Seeds of both cultivars showed similar hygroscopic equilibrium. For both cultivars, the equations of Chung-Pfost, Sabbah and Smith, showed the best adjustments to the experimental data, with slight superiority of the first one.

Análise da hidratação do arroz na parboilização

The aim of this work was to study the water uptake phenomenon during soaking of husk rice (IRGA 424) under different temperatures. Grains of husk rice with initial water content of 0.1364 (d.b.) imbibed in distilled water at temperatures of 35, 45, 55, and 75 oC were used. A temperature increase resulted in an increase in the water absorption rate. The Pelegs model fitted satisfactory to the experimental data of water absorption kinetics. The effective diffusion coefficient increased with an increase in temperature ranging from 0.80 to 9.18 x 10-11 m2/s. The dependency of the effective diffusion coefficient on temperature can be described by the Arrhenius relationship for the temperature range studied, activation energy of 33.2 kJ.mol-1.The aim of this work was to study the water uptake phenomenon during soaking of husk rice (IRGA 424) under different temperatures. Grains of husk rice with initial water content of 0.1364 (d.b.) imbibed in distilled water at temperatures of 35, 45, 55, and 75 oC were used. A temperature increase resulted in an increase in the water absorption rate. The Pelegs model fitted satisfactory to the experimental data of water absorption kinetics. The effective diffusion coefficient increased with an increase in temperature ranging from 0.80 to 9.18 x 10-11 m2/s. The dependency of the effective diffusion coefficient on temperature can be described by the Arrhenius relationship for the temperature range studied, activation energy of 33.2 kJ.mol-1.

Tomato Infrared Drying: Modeling and some Coefficients of the Dehydration Process

La deshidratacion por infrarrojo es mas ventajosa que el sistema convectivo, en condiciones similares, y el estudio de este proceso es importante para el desarrollo de equipos y procedimientos. Por tanto, el presente trabajo tuvo como objetivo el estudio del proceso de deshidratacion en tres diferentes estados de maduracion de rebanadas de tomate (Solanum lycopersicum L.) por medio del secado por infrarrojo, usando dos metodos: aproximacion del periodo constante de deshidratacion a la teoria de la transferencia de calor y masa para el termometro de bulbo humedo; y al periodo decreciente de la deshidratacion a la teoria de difusion de liquidos. Se utilizaron frutos de tomate cv. Santa Cruz. Tres estados de maduracion fueron obtenidos: verde (estado 1), naranja (estado 2) y rojo (estado 3). Modelos matematicos usualmente utilizados para representar el secado de productos agricolas fueron ajustados a los datos experimentales del secado de tomate. El coeficiente de difusion efectivo fue obtenido por medio del ajuste del modelo matematico de difusion liquida a los datos experimentales del periodo decreciente de deshidratacion. El modelo Dos Terminos represento mejor el proceso del secado de rebanadas de tomate. La humedad critica para la deshidratacion de tomate fue 2.97 kgw kgdm-1. Existe un periodo inicial de deshidratacion en que la tasa de secado alcanzo el maximo (aproximadamente 1.05 kgw kgdm-1, alrededor de 3 min). Tres diferentes metodos fueron utilizados para obtener los valores del coeficiente efectivo de difusion, incluyendo el metodo de elementos finitos, en que presento los menores valores de la suma de desviaciones minimas al cuadrado, 1.00 x 10-7 m2 s-1. El coeficiente global de transferencia de calor fue 12.45 W m-2 K-1, y el coeficiente global de transferencia de masa fue 0.0105 m s-1.

Periods of constant and falling-rate for infrared drying of carrot slices

The aim of this work was to study the infrared drying process of carrot slices and to determine coefficients related to the heat and mass transfer of the process. Fresh carrots were used, dried until constant weight in a dryer with infrared heating source. Different models were utilized to fit the experimental data of constant and falling drying rate periods. It was verified that the coefficients of heat and mass transfer, during the constant drying rate, significantly increased with temperature on rise. The Diffusion Approximation, Two Terms, Midili and Verna models satisfactory represented the falling period of drying rate of carrot slices. The effective diffusion coefficient increased with temperature and this relationship can be represented by the Arrhenius equation, obtaining activation energy to the drying process of 29.092 kJ mol -1