Radiofrequency assisted hot air drying of corn kernels: Drying characteristics, uniformity, quality, and energy consumption

In order to clarify the applicability of radio frequency assisted hot air drying (RFHAD) for harvested cereals, the drying characteristics, quality, and energy consumption of RFHAD with various air temperatures (40 degrees C, 50 degrees C, 60 degrees C, 70 degrees C) and electrode gaps (90 mm, 100 mm, 110 mm, 120 mm) for corn kernels was investigated by comparing with these of hot air drying (HAD). Results showed that the temperature of corn kernels was higher than that of hot air during RFHAD, hot air mainly played a convective cooling role, and the cooling intensity enhanced with the decrease of air temperature or electrode gap. However, RFHAD inherited the non-uniform characteristic of RF heating, showing a higher temperature at the edges of corn samples, but it could be improved at higher or lower air temperatures than that at 40 degrees C and larger electrode gaps. The drying efficiency, color difference, and crack rate of corn kernels increased with the increase of air temperature or decrease of electrode gap. Especially, for corn kernels with similar temperature by RFHAD (50 degrees C air temperature, 100 mm electrode gap) and HAD (60 degrees C air temperature), the drying time of RFHAD was 25% shorter than that of HAD, meanwhile, the color difference and crack rate were at a smaller level. The energy consumption of RFHAD was reduced at small electrode gaps and high air temperatures since the drying time was significantly shorter than that of HAD. The results provide useful assistance for developing effective strategies for RFHAD of corn kernels.