Noninvasive Differential Pressure Technique for Bubble Characterization in High-Temperature Opaque Systems

A novel analytical tool incorporating a differential pressure transducer (DPT) to measure bubble frequency and size in a simple, noninvasive, nonhazardous, and nonoptical-based technique was presented and validated. Bubbles measured in deionized water by an upward facing quartz nozzle and helium gas flow rates up to 50 mL min(-1) ranged from 3.75 to 4.29 mm, with bubble size deviations of 3-8% from the literature correlations considered. The DPT technique was applied to two high-temperature systems, molten tin and molten LiCI-KCl (59-41 mol % LiCl-KCl), over 400-700 degrees C using a u-tube quartz injector. For a 50 mm nozzle tip submersion depth in molten tin at 600 degrees C, preheating stages and bubble frequency measurements were used to demonstrate that the inlet gas temperature at the point of bubble formation, typically assumed at the temperature of the melt, was not in equilibrium and additional gas preheating was required. Calculated surface areas from the bubble diameters obtained from literature correlations and the measured DPT results in molten tin at 600 degrees C showed a maximum deviation from literature correlations of 7.57%. This highlights the accuracy of the DPT applied across a wide range of fluid properties and temperature ranges and its applicability for bubble characterization in applications concerning the kinetics of gas bubble-liquid reactions or mass transfer at the bubble-liquid interface.