Measurement of boiling liquid levels by decomposition of sound waves in a waveguide

•It is a novel application of wave decomposition to measure boiling liquid levels.•Proposed method does not require any sensor to be placed near the boiling vessel.•It is a novel application of nucleate bubbling as a random noise excitation.•Method was applied successfully to 17 cases at an average accuracy of 98.8%.

Many industrial processes require knowledge of the level of hot bubbling liquid in a closed vessel. However, usually conventional instrumentation is unsuitable because of extremely high temperatures, and hot poisonous gases generated by the thermo-chemical processes of the boiling liquid. This paper proposes a novel method to detect such boiling liquid levels by monitoring the boiling/bubbling noise in the vessel using a waveguide. The principle of this method is that the axial modes of the air column and the liquid column in the closed vessel would change with change in liquid height. The sound pressure waves produced in the vessel due to bubbling and propagating along the vessel's axial direction can be captured by decomposition using two microphones in a waveguide co-axially attached to the vessel. These decomposed waves would show peaks at resonance frequencies corresponding to the vessel's axial modes, which would be used to calculate the liquid height. The proposed method was verified through extensive finite element simulations and experiments of boiling water over a wide range of conditions. The boiling water levels were correctly measured in each condition with an average accuracy of 98.8%. Thus, this waveguide system can continuously monitor boiling liquid levels based on the incident wave frequency and amplitude. Such a system has wide industrial applications, particularly in steel plants, where knowing the amount of molten steel during oxygen lancing faces many challenges.