Modelling the mid-infrared drying of sweet potato: kinetics, mass and heat transfer parameters, and energy consumption

Abstract

This study investigated the drying kinetics, mass and heat transfer characteristics of sweet potato slices (0.4–0.6 cm thickness) during drying based on mid-infrared experimental set-up (intensity of 1100–1400 W/m2). Thin layer drying models were used to evaluate the drying kinetics of sweet potato slices. Two analytical models (Fick’s diffusion model, and Dincer and Dost model) were used to study the mass transfer behaviour of sweet potato slices with and without shrinkage during mid-infrared drying. The heat transfer flux between the emitter and sweet potato slices was also investigated. Results demonstrated that an increase in infrared intensity from 1100 W/m2 to 1400 W/m2 resulted in increased in average radiation heat flux by 3.4 times and a 15% reduction in the overall drying time. The two-term exponential model was found to be the best in predicting the drying kinetics of sweet potato slices during mid-infrared drying. The specific heat consumption varied from 0.91–4.82 kWh/kg. The effective moisture diffusivity with and without shrinkage using the Fick’s diffusion model varied from 2.632 × 10−9 to 1.596 × 10−8 m2/s, and 1.24 × 10−8 to 2.4 × 10−8 m2/s using Dincer and Dost model, respectively. The obtained values of mass transfer coefficient, Biot number and activation energy varied from 5.99 × 10−6 to 1.17 × 10−5 m/s, 0.53 to 2.62, and 12.83 kJ/mol to 34.64 kJ/mol, respectively. The values obtained for Biot number implied the existence of simultaneous internal and external resistances. The findings further explained that mid-infrared intensity of 1100 W/m2 did not significantly affect the quality of sweet potato during drying, demonstrating a great potential of applying low intensity mid-infrared radiation in the drying of agricultural crops.