Drying kinetics of crushed mango stone: analysis of effective moisture diffusivity and drying rate for any drying condition

• A methodology is developed to obtain the mass transfer coefficients for any drying condition. • The methodology is based on two new variables, modified drying rates and modified effective diffusivity. • Effective moisture diffusivity is obtained as a function of velocity, temperature, sample thickness and moisture ratio. • Drying rate is obtained as a function of velocity, temperature, sample thickness and moisture ratio. • This methodology can only be applied within the range of the design experiments. Mango stone is positioned as one of the most abundant biomass in the world, with a high net calorific value to help reduce the CO 2 emissions in the atmosphere. Its high moisture content implies a drying treatment to improve its fuel properties. In this work, the drying of crushed mango stone in a convective dryer was studied using a design experiment based on fifteen isothermal drying experiments. Tests were carried out at different drying air temperatures, 100 °C, 125 °C, 150 °C, 175 °C and 200 °C, drying air velocities, 1 m/s, 2 m/s and 3 m/s and a sample thickness of 1.8 cm. Drying curves, drying rates and effective moisture diffusivity have been analysed. Drying times were drastically reduced, ranging from 35 minutes (the fastest test) to 2 hours and 25 minutes (the most extended test), compared to the drying of entire mango stone pieces carried out in a previous study. Drying rate values were obtained between 0.5·10 -4 s -1 and 9·10 -4 s -1 , and the effective moisture diffusivity presented values between 6.88·10 -9 m 2 /s and 35.9·10 -9 m 2 /s. Two new variables are obtained by using an adequate association of parameters, namely modified drying rate and modified effective moisture diffusivity, which were derived from experimental data through regression analysis using polynomial surfaces with excellent fit results. The use of these new variables enables the determination of the drying rate and effective moisture diffusivity for various parameters, including temperature, sample thickness, moisture ratio, and velocity, through a single overall function.