An Approach to Optimize the Design of Ultrasonic Transducer for Food Dehydration

Ultrasound-assisted air-drying is considered a useful method to reduce drying time and ensure some agricultural food products' quality. In this study, a practical design method of an Ultrasonic Transducer (UT), which is in the form of a circular stepped-plate, was developed by using Particle Swarm Optimization (PSO) algorithm and Finite Element Analysis (FEA). The numerical calculation is carried out for two different geometric dimensions of the stepped-plate. Based on the obtained results, the smaller UT dimensions were chosen, and its prototypes were fabricated. The prototype's measured resonance frequency is 19.927 kHz compared to calculations getting an error of 0.073 kHz (0.37%). Also, to evaluate the effects of ultrasound on a drying process, the UT is integrated into a heat-pump drying machine for drying foods. The experiments were carried out on Codonopsis javanica using heat-pump drying method at air temperature 45 ± 0.5 °C, air humidity 18-20 %, air velocity 0.5 ± 0.1 m/s with and without ultrasonic intensity while keeping all other conditions and parameters constant. The results showed that the total drying time was reduced in the range of 25% to 42% depending on ultrasonic intensity, compared to heat-pump drying without ultrasonic intensity. The color of the dried products is also considered to testify the quality of the product when using UT in drying processes. The obtained results prove the effectiveness of the proposed approach in design of the UT for food dehydration.