Mathematical modeling of pequi pulp drying and effective diffusivity determination

Abstract

A B S T R A C TThe aim of this work was to study the drying kinetics of pequi pulp by convective drying at different conditions of temperature (50, 60, 70 and 80 °C) and thickness (0.5, 1.0 and 1.5 cm) at the air speed of 1.0 m s -1, with no addition of adjuvant. The experimental data of pequi pulp drying kinetics were used to plot drying curves and fitted to the models: Midilli, Page, Henderson & Pabis and Newton. Effective diffusivity was calculated using the Fick's diffusion model for a flat plate. It was found that, with increasing thickness, the drying time increased and, with increasing temperature, the drying time was reduced. The Midilli model showed the best fit to the experimental data of pequi pulp drying at all temperatures and thicknesses, presenting higher coefficients of determination (R 2 ), indicating that this model satisfactorily represents the pequi pulp drying phenomenon. There was a trend of increase in the effective diffusivity with the increase in pulp layer thickness and temperature.Modelagem matemática da secagem da polpa de pequi e determinação da difusividade efetiva R E S U M O Objetivou-se, neste trabalho, estudar a cinética de secagem da polpa de pequi por meio da secagem convectiva em diferentes condições de temperatura (50, 60, 70 e 80 ºC) e espessura (0,5; 1,0 e 1,5 cm) na velocidade do ar 1,0 m s -1 , sem adição de adjuvante de secagem. Com os dados experimentais da cinética de secagem da polpa de pequi foram traçadas curvas de secagem cujos modelos ajustados aos dados experimentais, foram: Midilli, Page, Henderson e Pabis e Newton. Calculou-se a difusividade efetiva utilizando o modelo difusivo de Fick para uma placa plana. Constatou-se que, com o aumento da espessura, o tempo de secagem aumentou e com o aumento da temperatura o tempo de secagem foi reduzido. O modelo de Midilli foi o que melhor se ajustou aos dados experimentais da secagem da polpa de pequi, em todas as temperaturas e espessuras, por apresentar maior coeficiente de determinação (R²), indicando que este modelo representa satisfatoriamente o fenômeno de secagem da polpa de pequi. Foi evidenciado que houve tendência de aumento da difusividade efetiva com o aumento da espessura da camada da polpa e com o aumento da temperatura.

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

“…The drying of 'jambu' leaves crushed mass was influenced by layer thickness along the drying time, and the values increased over time as thickness increased. Similar behavior was observed by Sousa et al (2017) studying pequi pulp drying kinetics in convective drying under different conditions of temperature (50, 60, 70 and 80 ºC) and thickness (0.005; 0.010 and 0.015 m).…”

“…leaves, observed no trend in the parameters (a) and (n) for the Midilli model. Sousa et al (2017) did not find a defined trend for the constant (n) of the Midilli model with the increment in temperature and thickness, observing values from 0.949 to 1.148 in the pequi pulp drying. The values found in the present study are within the range described by Sousa et al (2017).…”

“…This fact may have occurred because of the water mass flow generated when a homogeneous mass of material is subjected to drying. Sousa et al (2017) observed an increasing trend in effective diffusivity with the increment in pequi pulp layer thickness and with the elevation of temperature. Diffusivity represents the speed with which the water moves from the inside to the surface of the material, thus being vaporized (Menezes et al, 2013).…”

“…According to Sousa et al (2017), increments of thickness reduce the drying rate and also the constant k.…”

Study of the drying of mesocarp of baru (Dipteryx alata Vogel) fruits

“…The drying times of the mesocarp of baru fruits at temperatures of 40, 50, 60 and 70 °C decreased with increasing drying temperature, thus showing a higher water withdrawal rate (Figure 1). This drying behavior was similar to those of most agricultural products (Costa et al, 2015, Sousa et al, 2017.…”