Validation of top electrode voltage in free-running oscillator radio frequency systems with different moisture content soybeans

• Top electrode voltage was validated by RF treated soybeans with different moisture.
• Voltage increased linearly with increasing moisture and decreasing electrode gap.
• Estimation error of 10% was achieved between anode and measured currents.
• Correlation could be applied to estimate RF top electrode voltage used in simulation.

Precisely estimating the top electrode voltage of a radio frequency (RF) system is important for computer simulation of sample temperatures. The goal of this study was to validate whether the developed equations can be applied to determine the top electrode for RF heated soybeans with different moisture contents. Soybeans with moisture contents of 6.7% and 8.7% (w.b.) were treated in a 27.12 MHz, 6 kW RF system under 5 electrode gaps. The results showed that the top electrode voltage increased almost linearly both with increasing moisture content and decreasing electrode gap. The maximum difference of the estimated top electrode voltages was less than 10% relative error between the anode current and the measured current in the same conditions. The temperature distributions in three representative layers from simulation were in good agreement with those from experiment, as was the average root mean square error (RMSE) of 1.6% for temperature profiles in three selected positions. The validation results demonstrated that the established equation using anode current was suitable for estimating the top electrode voltage when soybeans of different moisture contents were heated in RF systems.