Research on Microwave Drying Characteristics and Kinetic Model of Green Bananas

Abstract

In order to explore the water diffusion characteristics of green bananas during the microwave drying process, a microwave drying test was conducted to investigate the green bananas drying characteristics under different microwave power densities (3, 5, 7 and 9 W/g), and the microwave drying test model of green bananas was established. Low-field nuclear magnetic resonance (LF-NMR) was used to investigate the internal moisture distribution and change law of green bananas during the drying process. Results showed that drying rate of green bananas in the microwave drying process increased first and then decreased, the effective diffusion coefficient was between 1.082×10−8 and 7.708×10−8 m2/s, and also increased with the increasing of microwave power density. The nuclear magnetic resonance experiments showed that, during the drying process, the free water was removed first, the non-flowing water showed an overall upward trend and then a downward trend, while the combined water showed an overall upward trend. With the extension of microwave drying time, the water peak area of the three states decreased and the total peak moved in the direction of the decrease of relaxation time, at the end of drying, the free water in green banana was basically removed, and the internal water mainly existed in the state of combined water and non flowing water. By fitting green banana drying kinetics model, it was found that the Page model fitted best (R2>0.9), which could provide a basis for effectively describing the variation law of water with time during the microwave drying process of green bananas.

Keywords

• green bananas
• microwave drying
• effective moisture diffusion coefficient
• low-field nuclear magnetic resonance
• drying kinetic models