Application Cases

Experimental Name: Application of High-Voltage Amplifiers in Finite Element Analysis and Validation of Ohmic Heating in Soy Milk

Experimental Purpose:
During the ohmic heating process in tofu production, the internal temperature distribution of soy milk significantly affects the uniformity of tofu texture. Studying the distribution and variation of internal temperature during ohmic heating of soy milk is essential for the development of tofu heating and solidification systems.

Experimental Equipment:
Thermocouples, current sensors, data acquisition units, computer signal generators, ATA-4012 high-voltage power amplifiers, electrodes, heating chambers, soybeans, distilled water, glucono delta-lactone, etc.

Experimental Procedure:
The experimental setup consists of an ohmic heating system and a data acquisition system, as illustrated in the figure below:

The data acquisition system includes a computer, data acquisition unit, T-type thermocouples, and current sensors. The data acquisition unit continuously monitors the internal temperature of the soy milk and transmits the data to the computer for storage. Meanwhile, the current during the ohmic heating experiment is measured in real time by the data acquisition unit and stored in the computer.

During the ohmic heating experiment, the computer controls the signal generator to produce a sinusoidal wave with an effective voltage of 2V and a frequency of 1 kHz. This sinusoidal electrical signal is amplified by the high-voltage amplifier to output a voltage with an effective value of 50V and a frequency of 1 kHz, which serves as the power source for ohmic heating. The distance between the electrode plates is 50 mm, and the electric field strength during heating is 10 V/cm. The experiment is conducted by simultaneously starting the ohmic heating system and the data acquisition system (with a sampling interval of 10 seconds). Each experiment is repeated three times, and the average values are taken.

Experimental Results:
During the ohmic heating process, the electrical conductivity of soy milk exhibits a linear relationship with temperature. The heating rate increases as the temperature rises. The internal temperature distribution of soy milk is relatively uniform, with the temperature near the heating chamber walls being lower. As the heating time increases from 50 seconds to 300 seconds, the maximum temperature difference in the soy milk increases from 3°C to 20.2°C. The root mean square error between the simulation results and experimental results is 1.86%. The finite element simulation accurately predicts the internal temperature distribution and variation of soy milk during ohmic heating.

Figure: Comparison of Experimental and Simulated Temperatures

Figure: ATA-4012C High-Voltage Power Amplifier Specifications and Parameters