Fernando Mendes Botelho

Influência da temperatura do ar de secagem sobre o teor e a composição química do óleo essencial de Lippia alba (Mill) N. E. Brown

Leaves of Lippia alba were submitted to six different drying treatments, using air at ambient temperature and heated up to 80 °C. The essential oil was extracted by steam distillation and analyzed by GC-MS. For the dried leaves, the oil content was reduced by 12 to 17% whenxa0compared with the fresh plant (0.66%). The major oil component was citral, representing 76% for the fresh plant, and varying from 82 to 84% for the dried material. These results showed that L. alba can be submitted to a drying process of up to 80 oC without degradation and/or loss of the major, [LC1] active component.

Modelagem matemática para a descrição do processo de secagem do feijão (Phaseolus vulgaris L.) em camadas delgadas

The objective of this work was to obtain and to evaluate the drying curves of edible bean (Phaseolus vulgaris L.) and to fit different mathematical models to different experimental data of moisture content and drying air conditions. Edible beans harvested at moisture content of 0.92 (d.b.) were dried until achieving the moisture content of 0.14 (d.b.) under controlled drying air temperatures (35; 45 and 55xa0°C) and relative humidity of 40 ±2%. Twelve mathematical models cited in the 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 half of the tested models represent well the edible bean drying phenomena. Within themxa0the classic Page model was selected due to its simplicity and widely use within researchers to describe the agricultural product drying kinetic. xa0The relationship between the drying constant k and the drying air temperature can be described through Arrheniusx92s equation presenting activation energy of 10.08 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

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

Determinação e modelagem das propriedades físicas e da contração volumétrica do trigo, durante a secagem

The objectives of this work was to evaluate the effect of variation of water content on the physical properties of wheat grain and to adjust different mathematical models to the obtained experimental values as a function of moisture content. Also two different methodologies for determining bulk density and the real density were analysed. Based on the obtained results it may be concluded that the reduction of the moisture content affects the physical properties of wheat grain promoting the decrease of porosity and increase of both the bulk density and the specific gravity. Also the wheat grain bulk density and specific and real gravity values found through the chemical composition of grain were lower than the experimental data. However, the differences in values found between the two methodologies decreased as the moisture content decreases. The adapted Bala & Woods model fits best the individual wheat grain shrinkage as well as the bulk grain volume shrinkage. The grain shape (sphericity and circularity) did not vary for the moisture content range in this experiment.

Mathematical modeling of dehydration of ‘Fuji’ and ‘Gala’ apples slices using infrared

The objective of this work was to determine and model the infrared dehydration curves of apple slices - Fuji and Gala varieties. The slices were dehydrated until constant mass, in a prototype dryer with infrared heating source. The applied temperatures ranged from 50 to 100xa0°C. Due to the physical characteristics of the product, the dehydration curve was divided in two periods, constant and falling, separated by the critical moisture content. A linear model was used to describe the constant dehydration period. Empirical models traditionally used to model the drying behavior of agricultural products were fitted to the experimental data of the falling dehydration period. Critical moisture contents of 2.811 and 3.103xa0kgwxa0kgs-1 were observed for the Fuji and Gala varieties, respectively. Based on the results, it was concluded that the constant dehydration rates presented a direct relationship with the temperature; thus, it was possible to fit a model that describes the moisture content variation in function of time and temperature. Among the tested models, which describe the falling dehydration period, the model proposed by Midilli presented the best fit for all studied conditions.

Pear Drying: Thermodynamics Studies and Coefficients of Convective Heat and Mass Transfer

Abstract The objective of this work was to study the convective drying process used for cylindrical samples of two different pear varieties, one originating from Europe (Pyrus communis) and the other from Asia (Pyrus pyrifolia), submitted to two blanching treatments, as well as determine some coefficients referring to heat and mass transfer and thermodynamic parameters of the process, being: enthalpy (ΔH*), entropy (ΔS*) and Gibbs energy of activation (ΔG*). All samples were dried in a forced air oven at temperatures of (62, 76, 84 and 92)°C until reaching a constant mass. The heat and mass transfer coefficients referring to the constant and falling-rate drying periods were obtained by adjusting the experimental data to wet bulb temperature and liquid diffusion models, respectively. The heat and mass transfer coefficients varied linearly with temperature. Blanching altered the drying behavior of the two varieties in relation to the non-blanched samples, mainly at the elevated drying temperatures of 84°C and 92°C. ΔH* and ΔS* decreased while ΔG* increased with the elevation of drying temperature; therefore, it was possible to verify that variation in the diffusion process in pears during drying is dependent on energetic contributions of the environment.

Propriedades térmicas de grãos de trigo: determinação e modelagem

Objetivou-se com o presente trabalho, avaliar as propriedades termicas dos graos de trigo, de uma variedade nacional (Alianca), durante o processo de secagem em estufa e ajustar modelos matematicos que representem satisfatoriamente as variaveis estudadas em funcao do teor de agua. Foram utilizados graos de trigo com teor de agua inicial de 26 %b.s. secos ate o teor final de 11 %b.s. em estufa com ventilacao forcada a 40 oC e umidade relativa de 45%. As variaveis estudadas foram o calor especifico, obtido pelo metodo das misturas; a condutividade termica, obtida por meio de um cilindro teoricamente infinito considerando a hipotese da conducao unidimensional na direcao radial; e a difusividade termica, determinada indiretamente utilizando-se os valores experimentais da massa especifica aparente, calor especifico e condutividade termica do trigo. Com base nos resultados obtidos, pode-se concluir que o calor especifico e a condutividade termica do trigo aumentam, enquanto a difusividade termica apresenta reducao dos seus valores com a elevacao do teor de agua e que estas propriedades termicas do trigo variam linearmente com o teor de agua, sendo satisfatoriamente representadas pelo modelo linear simples, para a faixa de umidade estudada.

INFLUÊNCIA DA TEMPERATURA DE SECAGEM SOBRE AS PROPRIEDADES FÍSICAS DOS GRÃOS DE SOJA - DOI: 10.13083/1414-3984/reveng.v23n3p212-219

The objective of this study was to evaluate the effect of drying temperature on physical properties of soybeans. To evaluate the effect of temperature, soybean samples with an initial moisture content of 0.244 (db) were dried in an standard hot air oven at temperatures of 40, 50, 60, 70 and 80 °C until reaching the final moisture content of 0.136 (db), followed by determining the physical properties: angle of repose, bulk density, real density, one thousand grain weight, color and electrical conductivity of the solution of the soybean exudates. It was noted that the drying temperature significantly influenced the physical properties of soybeans, resulting in increased angle of repose and electrical conductivity of the exudate solutions. The bulk and real densities, one thousand grain weight and the characteristic color of soybeans decreased with increasing drying temperature. It was concluded that as the drying temperature increase there was a decrease in quality of the grains analyzed.