Continuous flow microwave heating of dilute phosphoric acid for dehydration based on a spiral tube under non-cyclic and cyclic heating conditions

Continuous flow microwave heating enables efficient dehydration of dilute phosphoric acid but is limited by a temperature plateau. Cyclic heating offers a potential solution, though its kinetics are unexplored. This paper presents a continuous flow spiral tube microwave heating system designed for both non-cyclic and cyclic heating of dilute phosphoric acid. Multiphysics models for microwave heating of dilute phosphoric acid are developed for both methods and validated through corresponding experiments. The proposed model analyzes electric field, dielectric properties, and temperature distributions during both heating processes, revealing that cyclic heating enables continuous heating of dilute phosphoric acid to the target temperature under limited power, influenced by inlet flow rate and microwave power. Optimal temperature uniformity and heating time can be also achieved by adjusting the inlet flow rate and microwave power. This paper provides theoretical and experimental insights into microwave dehydration of dilute phosphoric acid and dynamic continuous flow cyclic heating.