Effects of hot air assisted radio frequency drying on heating uniformity, drying characteristics and quality of paddy

Abstract

In order to solve the big challenge of cracking during paddy drying, this research revealed the application of hot air assisted radio frequency (HA-RF) drying technology on paddy grains based on its volumetric heating advantage. Drying characteristics and paddy quality were investigated at various combinations of air temperatures (50 °C, 55 °C and 60 °C), air velocities (0.5 m/s, 1.5 m/s and 2.5 m/s) and electrode gaps (100 mm, 110 mm and 120 mm). A comparison between the tempering-intermittent hot air (HA) drying was investigated to demonstrate the applicability of HA-RF drying on paddy grains. Increase in temperature and air velocity, while decrease in electrode gap resulted in increased average heating rate. The RF assistance significantly enhanced the drying rate of paddy grains and reduced drying duration and energy consumption by up to 62.5% and 42.9%, respectively, as compared to HA drying. A higher color and taste value, while a lower crack ratio (CR) without damage in starch granules of microstructure which caused formations of internal fissures were observed in HA-RF dried samples than HA dried ones. The findings of this study demonstrated that HA-RF drying is a good alternative of HA for industrial-scale drying of paddy grains.