Cinética de secagem de folhas de timbó (Serjania marginata Casar)

Abstract

R E S U M OPropôs-se, neste trabalho, avaliar a cinética de secagem de folhas de timbó (Serjania marginata Casar) e ajustar diferentes modelos matemáticos aos valores experimentais de razão de umidade. As folhas de timbó foram colhidas com teor de água inicial de 2,03 ± 0,10 decimal b.s., sendo submetidas à secagem sob condições controladas de temperatura (40, 50, 60 e 70 °C), até o teor de água de 0,08 ± 0,02 decimal b.s. Aos dados experimentais foram ajustados dez modelos matemáticos utilizados para representação da secagem de produtos agrícolas. Com base nos resultados obtidos o modelo matemático de Midilli é o que melhor representa a cinética de secagem para as folhas de timbó. O aumento da temperatura promove: uma taxa maior de remoção de água nas folhas de timbó durante a secagem; aumento do coeficiente de difusão efetivo sendo que esta relação pode ser descrita pela equação de Arrhenius que apresenta uma energia de ativação para a difusão líquida durante a secagem de 81,39 kJ mol -1 para as folhas de timbó; aumento da energia livre de Gibbs, enquanto a entalpia e a entropia decrescem. Drying kinetics of Serjania marginata Casar leaves A B S T R A C TThis study aimed to evaluate the kinetics of drying of Serjania marginata leaves, as well as to adjust different mathematical models to the experimental values of the moisture ratio. The Serjania marginata Casar leaves were harvested with initial moisture content of 2.03 ± 0,10 decimal dry basis., and submitted to drying process under controlled conditions of temperature (40, 50, 60 and 70 ºC), until the moisture content of 0.08 ± 0,02. Ten mathematical models were fitted to the experimental data and utilized to predict the drying process of agricultural products. Based on the obtained results, the mathematical model of Midilli best represented the kinetics of drying leaves of Serjania marginata. The increase in temperature promotes: an increased rate of water removal in Serjania marginata leaves during drying; the increase of the effective diffusion coefficient, and this relationship can be described through the Arrhenius equation, which presents an activation energy for the liquid diffusion during drying of 81.39 kJ mol -1 for Serjania marginata leaves; an increase in Gibbs free energy, while the enthalpy and entropy decrease.Palavras-chave: modelo de Midilli coeficiente de difusão propriedades termodinâmicas razão de umidade

Thermodynamic properties and drying kinetics of Bauhinia forficata Link leaves

“…Gibbs free energy increase with the increment in temperature, as observed by Martins et al (2015). This behavior is expected, because it establishes the non-spontaneity or spontaneity of the sorption process (McMinn et al, 2005), that is, it is necessary to introduce energy from outside of the product for the process to occur.…”

Drying kinetics of crushed mass of ‘jambu’: Effective diffusivity and activation energy

“…Effective diffusion coefficients between 0.66 x 10 -11 and 12.07 x 10 -11 m 2 s -1 were reported by Martins et al (2015) for the drying of 'timbó' leaves within the temperature range from 40 to 70 °C, respectively. Lower values were obtained for the effective diffusion coefficients of 'jambu' leaves crushed mass, which ranged between 5.79 x 10 -10 and 2.03 x 10 -9 m 2 s -1 for the thicknesses of 0.005 and 0.010 m, respectively.…”

“…The activation energy (E a ) for the drying of 'jambu' leaves crushed mass was equal to 16.61 kJ mol -1 for the thickness of 0.005 m and to 16.97 kJ mol -1 for the thickness of 0.010 m. Goneli et al (2014a), studying the drying of 'erva baleeira' leaves, reported activation energy of 62.89 kJ mol -1 . Rocha et al (2012) found E a of 77.16 kJ mol -1 in the drying of thyme, whereas Goneli et al (2014b) reported 74.96 kJ mol -1 for the drying of aroeira leaves and Martins et al (2015) obtained 81.39 kJ mol -1 in the drying of 'timbó' leaves. Lower E a values in the 'jambu' leaves crushed mass evidenced the need for lower energy to trigger the water diffusion process, in comparison to the leaves of 'erva baleeira' , thyme, aroeira and 'timbó' .…”

“…Martins et al (2015), working with 'timbó' (Serjania marginata Casar) leaves, observed that the Logarithmic and Midilli models showed satisfactory fit to the experimental data for the temperatures of 40 and 50 °C, but only Midilli showed good fit for the temperatures of 60 and 70 °C. These authors recommend the Midilli model to predict thin-layer drying of (12) (13) (14) (18) 'timbó' leaves, because of its good fit to all drying conditions studied.…”

Garlic: kinetic drying and thermodynamic properties

“…The positive value is characteristic of adding energy during the drying process, relating the drying of garlic to an endergonic reaction . OLIVEIRA et al (2015), CORRÊA et al (2010) andMARTINS et al (2015) showed similar values for strawberry, coffee cherry and timbó leaf drying studies, respectively. According to OLIVEIRA et al (2015), a non-spontaneous reaction is related to the enthalpy and entropy values, described above, as these reactions occur only when changes in enthalpy are positive and changes in entropy are negative; the variations of these parameters have a positive effect, but the variations are larger for the enthalpy than for the entropy; the changes in the parameters themselves are negative, and the enthalpy change is smaller than the entropy.…”