Numerical study on drying uniformity of bulk corn kernels during radio frequency-assisted hot air drying

Non-uniform heating is a main obstacle to the application of radio frequency (RF) energy in food thermal processing, which will cause uneven drying when combined with hot air drying. This research focused on developing a three-dimensional numerical model to study the drying uniformity of bulk corn kernels during radio frequency assisted hot air drying (RFHA) with various conditions, and to improve the drying uniformity using a new convection strategy. The simulated temperatures and moisture contents matched the experimental data well with the maximum relative errors of less than 5.1% and 7.7%, respectively. During RFHA, the non-uniform electric field acting on corn sample caused non-uniform heating and hence non-uniform drying. The largest electric field intensity appeared in the corn kernels in vertical state, resulting in the highest temperature, followed by the corn kernels in side standing, oblique and horizontal states. The drying uniformity was improved with increasing air velocity and decreasing electrode voltage. Reducing the temperature of hot air passing through the edge of sample was an effective strategy to improve drying uniformity of RFHA, for RFHA with 55 °C hot air, the drying uniformity was the best when the temperature of hot air passing through the edge of sample reduced to 48.70 °C.