RESUMO Motores de ciclo diesel são amplamente utilizados em máquinas agrícolas. O biodiesel oferece a possibilidade de substituição parcial ou total do diesel mineral, reduzindo assim a dependência da agricultura desse recurso não renovável e diminuindo as emissões de poluentes. O objetivo deste estudo foi avaliar as emissões de CO, NOx, SO2, CO2 e O2 de várias misturas de biodiesel (B0 = 0%, B7 = 7%, B10 = 10%, B20 = 20%, B30 = 30% e B100 = 100%) em um motor agrícola monocilíndrico a 1000, 1600 e 2400 rpm. Os gases de escape foram identificados usando um medidor de gás. Os combustíveis com maior porcentagem de biodiesel têm as menores emissões de SO2, com a mistura B30 liberando 65,78, 52,47 e 32,25 partes por milhão a 1000, 1600 e 2000 rpm, respectivamente. As emissões de óxidos nitrosos e de dióxido de carbono diminuem com o aumento da velocidade de rotação do motor. Maiores porcentagens de biodiesel resultam em combustíveis menos poluentes.

ABSTRACT Diesel cycle engines are widely used in agricultural machinery. Biodiesel offers the possibility of partial or total replacement of mineral diesel, thus reducing the dependence of agriculture on this non-renewable resource and decreasing pollutant emissions. The objective of this study was to evaluate the emissions of CO, NOx, SO2, CO2, and O2 from various biodiesel mixtures (B0 = 0%, B7 = 7%, B10 = 10%, B20 = 20%, B30 = 30% and B100 = 100%) in a single-cylinder tractor engine at 1000, 1600 and 2400 rpm. The exhaust gases were identified using a gas probe meter. Fuels with a higher percentage of biodiesel have the lowest SO2 emissions, with the B30 mixture releasing 65.78, 52.47 and 32.25 parts per million at 1000, 1600 and 2000 rpm, respectively. Nitrous oxides and carbon dioxide emissions decreases with higher engine rotation speed. Higher percentages of biodiesel result in less polluting fuels.

ABSTRACT This study aimed to assess the drying kinetics of red and yellow chili peppers, “dedo-de-moça” variety, at different temperatures (35, 45, 55, and 70 °C) and model this phenomenon mathematically. We also evaluated the effect of these drying air temperatures on pepper fruit color. Pepper fruits were dried in a forced-air circulation dryer. Ten mathematical models were fitted to the experimental data by nonlinear regression analysis. After drying, pepper samples were analyzed for the following colorimetric parameters: lightness (L*), chroma or saturation (c), and hue angle (h), in order to determine the influence of drying air temperature on fruit coloration. Our findings showed that the higher the air temperature, the faster the drying process. Midilli model fitted well to all temperature data and best represented the drying kinetics of “dedo-de-moça” chili peppers. Moreover, fruit color was affected by the drying air temperatures, in which the higher the drying air temperature, the greater the color variation.

ABSTRACT To maintain seed and soil quality of pumpkin, energy knowledge associated with processing and storage stages is strategic for the optimization of the thermodynamic processes needed for product stabilization. Thus, the objective of this study was to determine isosteric heat, differential entropy, and Gibbs free energy within a temperature range from 20 to 70° C, and relative air humidity levels between 10.75 and 85.11%. The study was based on empirical data for water activity determination. As a result, we verified that as moisture content decreased, the integral isosteric heat of the product increased from 2502.35 to 6231.17 kJ kg-1, differential entropy raised from 1.18 to 12.43 kJ kg-1 K-1, and Gibbs free energy ranged from -243.84 to -432.59 kJ kg-1. Thus, we concluded that the lower the water availability in seeds, the greater the energetic requirement for its removal, as there is a major interaction between water and the product (seeds), indicating an increasingly less spontaneous desorption process.

RESUMO Esta pesquisa focou na determinação do equilíbrio higroscópico e do calor isostérico da pimenta Dedo-de-Moça (Capsicum baccatum) sob diferentes condições controladas de temperatura e umidade relativa do ar. Foi ajustado o modelo que melhor representa o comportamento isotérmico de sorção entre os modelos descritos na literatura, bem como a proposta de um novo modelo e parâmetros que satisfazem com representatividade o fenômeno de higroscopicidade e calor isostérico. As temperaturas utilizadas foram 30, 50 e 70 ºC, com níveis de atividade de água variando de 0.11 a 0.84. O calor isostérico integral de sorção da pimenta Dedo-de-Moça, para o teor de água entre 0.07 a 0.54 (b. s.), variou de 3641.66 a 2614.38 kJ kg-1. O modelo que melhor se representa o comportamento do equilíbrio higroscópico e calor isostérico é o novo modelo proposto no presente estudo, com R2 igual a 0.97.

ABSTRACT This study focuses on the determination of the hygroscopic equilibrium and isosteric heat of the aji chili pepper (Capsicum baccatum) under different controlled temperature and relative air humidity conditions. In addition, the objective was to adjust the model among the existing literature models that best represent the isothermal sorption behavior, as well as propose a new model to represent this phenomenon. Having obtained the mathematical models and experimental data, the best model and parameters that represent the hygroscopicity and the isosteric heat satisfactorily was determined. The temperatures used were 30, 55, and 70 °C, with water activity levels from 0.11 to 0.84. The model that best fit the data had a R2 value of 0.97. The integral isosteric heat of sorption for ‘Dedo-de-Moça’ chili pepper within a moisture content from 0.07 to 0.55 (dry basis) ranged from 3641.66 to 2614.38 kJ kg-1.

Com o intuito de analisar a dinâmica de sorção e a energia necessária para a vaporização da água na desidratação do bagaço da cana-de-açúcar, o presente trabalho teve como objetivo a determinação de seu equilíbrio higroscópico e calor isostérico, a partir de diferentes condições controladas de temperatura (20; 40; 55 e 70 ºC) e umidade relativa do ar (10; 12; 17; 18; 30; 40; 45; 50; 60 e 85%), assim como avaliar, entre diversos modelos descritos na literatura, o que melhor represente o comportamento de sorção. Como resultado, foi verificado que o modelo que melhor se ajustou aos dados empíricos do processo de sorção do bagaço de cana-de-açúcar foi o Modelo de Henderson Modificado, com coeficiente de determinação de 0,972, enquanto o calor isostérico integral de dessorção variou de 2524,09 a 2951,95 kJ kg-1, para os teores de água de equilíbrio de 0,014 a 0,170 b.s., respectivamente.

This study aimed to determine the hygroscopic equilibrium and isosteric heat of sugarcane bagasse to evaluate sorption dynamics and the required energy to vaporize water in the bagasse dehydration. The reaction was assessed at different controlled conditions of temperature (20, 40, 55 and 70 ºC) and air relative humidity (10, 12, 17, 18, 30, 40, 45, 50, 60 and 85%), as well as testing various models described in the literature to identify the condition that better represents sorption behavior. As a result, we found that the model that best fit empirical data of sugarcane bagasse sorption was the modified Henderson with determination coefficient of 0.972; while the integral isosteric heat of desorption ranged from 2,524.09 to 2,951.95 kJ kg-1, for all water contents and equilibrium of 0.014 until 0.170 bs, respectively.