André L. D. Goneli

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.

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.

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

Propriedades mecânicas dos grãos de soja em função do teor de água

This work aimed to determine the effect of the soybean grain moisture content in the maximum compression force values for a fixed deformation (2 mm) and the proportional deformity modulus under different compression positions. Soybean grains varying from 0.58 to 0.093 (d.b.) of moisture content were compressed uniaxialy between two parallel plates towards its three main dimensions under compression speed of 0.001 m s-1. According to the results it was concluded that the compression force and the proportional deformity modulus decrease with the increasing of the moisture content. Also the soybean grains presented higher resistance to its compression when submitted to the repose position (P1) and presented similar compression force and proportional deformity modulus values when compressed in the position P2 (on the hilum) and P3 (in the vertical).

Análise da variação das propriedades físicas dos grãos de soja durante o processo de secagem

The present work was accomplished with the objective of evaluating the drying effect on soy grain physical properties and to analyze different methodologies for determining bulk density and specific gravity. Also, the soy grain shrinkage was evaluated during the drying and different mathematical models were fitted to the experimental data in order to analyze the properties in connection with their moisture content. Based on the obtained results it can be concluded that the reduction in the moisture content promotes the linear decrease in the porosity in the range from 0,31 to 0,15 (b.s.) and increase of both the bulk density and specific gravity. Also the soy grain bulk density and specific gravity values found through the grain chemical composition were lower than the experimental data. The adapted BALA & WOODS [2], RAHMAN, linear and exponential models are appropriate for description of the soy bulk grain shrinkage, while only the adapted BALA & WOODS [2] model is the most appropriate for description of the soy unitary grain shrinkage.

Propriedades físicas do feijão durante a secagem: determinação e modelagem

As propriedades fisicas dos produtos agricolas sao influenciadas diretamente pela secagem. Assim, buscou-se com o presente trabalho avaliar o efeito do teor de agua nas propriedades fisicas dos graos de feijao da cultivar Vermelho Coimbra, e ajustar diferentes modelos matematicos aos valores experimentais. Analisaram-se duas metodologias para a determinacao da massa especifica aparente e da massa especifica unitaria. A massa especifica aparente e a porosidade da massa foram determinadas utilizando-se uma balanca de peso hectolitro e um picnometro de comparacao a ar, respectivamente. A massa especifica unitaria foi determinada em funcao da porosidade e da massa especifica aparente. Os dados experimentais da massa especifica aparente e unitaria foram comparados com os obtidos pelo calculo a partir da composicao quimica media dos graos de feijao. Concluiu-se que a reducao no teor de agua pela secagem influencia as propriedades fisicas dos graos, proporcionando a diminuicao da porosidade e o aumento das massas especificas aparente e da massa especifica unitaria. A metodologia de determinacao das massas especificas pela composicao quimica media dos graos de feijao apresenta limitacao quanto a precisao dos resultados. As variacoes das propriedades fisicas analisadas em funcao do teor de agua sao adequadamente representadas pelo modelo linear.

MATHEMATICAL MODELLING OF THIN-LAYER DRYING KINETICS OF WHEAT

The thin-layer drying characteristics of wheat grains were studied in this work. The experimental data were obtained in order to fit to semi-theoretical models widely used to describe thin-layer drying behavior of agricultural products. The effect of the air temperature on drying kinetic was also evaluated. The drying kinetics of wheat in a thin-layer dryer was investigated for a temperature range of 35 to 55°C and relative humidity of 55 ± 1%. The time required for wheat dying from an initial moisture content of 32 % in dry basis to the final moisture content of 13 % was 24.25, 7.0 and 3.5 h for drying temperatures of 35, 45, and 55°C, respectively. Eight mathematical thin-layer model were used to fit the drying data. The best fit was verified for the Page model to describing thin-layer drying process. It was verified that the temperature dependence of the model parameter could be predictable by Arrhenius-type relationship. The activation energy was found to be 26.829 kJ mol-1.

MOISTURE SORPTION HYSTERESIS OF ROUGH RICE

The objective of this work was to determine the sorption isotherms for rough rice for different temperatures and relative humidities environments, and also to evaluate the hysteresis phenomenon. In order to obtain the rough rice equilibrium moisture content through the desorption and adsorption, it was used a static method where samples were kept in desiccators with saturated salt solutions stored in the controlled temperature chamber and fixed from 10 to 50°C. The experimental data were adjusted to mathematical models for representing the agricultural product hygroscopicity. Based on the obtained results, it could be concluded that the Equilibrium moisture content of the rough rice decreases as the temperature increases, for the same relative humidity, following the tendency of most agricultural products. Based on statistical parameters, the Chung Pfost model better represents the rough rice hygroscopicity when compared to the traditional methods used to describe the hysteresis. It was verified that hysteresis values for the same relative humidity values decrease as the temperature increases.