A newly developed photoelectric optical fiber probe for simultaneous measurements of a CO2 bubble chord length, velocity, and void fraction and the local CO2 concentration in the surrounding liquid

In a bubbly flow, the mass transfer from bubble swarms to the surrounding liquid and the concentration of dissolved gas transported in the liquid are deeply related to time-spatial structures of the gas and liquid phases. Various techniques to measure bubble characteristics or solution concentration in gas-liquid two-phase flows have been developed. However, detailed discussions about the gas absorption process in consideration of the above relations are not found, because there was no instrument to enable simultaneous measurement of bubble characteristics and concentrations of the surrounding liquid. The purpose of the present study was to develop a new type of probe that enables the simultaneous measurement of these features. We have developed a platinum (Pt)-plated optical fiber probe (POFP: Photoelectric Optical Fiber Probe), which can perform the functions of an optical fiber probe and an electrical probe. The POFP is able to simultaneously measure a CO2-included bubble chord length, velocity, and time-series void fraction as well as the liquid-phase local CO2 concentration. The bubble velocities and chord lengths measured via the POFP method satisfactorily agreed with those obtained with high-speed visualization. Based on the theoretical analysis and primary experimental results, the POFP was considered to possess satisfactory accuracy and response speed for the simultaneous measurement of a bubble velocity, a bubble chord length, a void fraction and a CO2 concentration in the surrounding water. We demonstrated the performance of the POFP by examining it in a bubble column. The CO2 concentration fluctuation at the bottom zone of the bubble column correlated rationally with the void fraction fluctuation. The correlation faded out toward the upper zone. The POFP is considered a useful tool for revealing the relations between flow structures of a bubbly flow and concentration transportation.

► We newly developed a photoelectric optical fiber probe (POFP).
► The POFP simultaneously measures bubble characteristics and solution concentration.
► We discuss the measurement accuracy and response speed of the POFP.
► The POFP gave a satisfactory and practical performance for both types of measurement.