A Review of the Measurement and Control Technologies for the Critical Parameters of Microwave Drying Processes: Temperature and Humidity

Microwave drying technology is popular in many fields because of its efficient selective heating, fast drying ability, and environmental friendliness. The development of temperature-humidity measurement and control technologies has improved the energy efficiency of microwaves, which will effectively promote the wide application of microwave drying technology. In light of this, this study reviews the recent advances in temperature-humidity measurement and control strategies in the microwave drying process. Furthermore, the advantages and disadvantages of commonly used measurement methods and their application range are systematically summarized. Lastly, the advantages of the joint temperature-humidity control strategy are proposed. The reviews indicate that thermocouples are economical and practical, but susceptible to microwave interference. Optical fiber measurements are accurate and anti-interference, but costly. Infrared thermometers are suitable for dynamic measurements, while internal temperature monitoring is limited. The temperature-humidity accurate detection and control methods are still facing great challenges in the microwave heating process. In the future, the joint monitoring and control strategy of temperature-humidity will be the main direction to promote the development of microwave industrialization. The development of new temperature-humidity detection and control methods is crucial for improving the quality of drying products and energy use efficiency. In particular, online accurate monitoring and feedback technology are expected to accelerate the controllability of parameters of large microwave equipment in industrial applications, thus promoting the industrialization of microwave drying technology.