Gas composition measurements in randomly distributed and fast moving gas bubbles in two-phase fluids

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Fluid Dynamics

Background:

• Accurate gas composition analysis is crucial for understanding multiphase flow phenomena.
• Traditional methods struggle with the dynamic and random nature of bubbles in fluid streams.
• Laser-induced breakdown spectroscopy (LIBS) offers a potential optical solution for in-situ analysis.

Purpose of the Study:

• To develop and validate a LIBS-based method for optically measuring gas composition in fast-moving bubbles.
• To investigate and quantify the 'depth' effect of the laser focal point on LIBS plasma emission in two-phase fluids.
• To establish a robust model for extracting accurate gas composition, specifically molecular oxygen, from complex spectra.

Main Methods:

• Utilized laser-induced breakdown spectroscopy (LIBS) by focusing laser pulses into bubble streams to generate plasma.
• Conducted calibration experiments near a liquid-gas interface to analyze the 'depth' effect on plasma emission spectra.
• Employed proper orthogonal decomposition and support vector regression to model spectral variations and correct for liquid interference.

Main Results:

• The 'depth' of the laser focal point significantly influences LIBS plasma emission spectra in two-phase systems.
• A support vector regression model effectively excluded spectral contributions from the interfacing liquid.
• The developed LIBS method accurately measured the molecular oxygen mole fraction in bubbles under realistic conditions.

Conclusions:

• The study successfully demonstrates the feasibility of using LIBS for in-situ gas composition analysis in bubbly flows.
• Accounting for the laser-liquid interface 'depth' is critical for accurate LIBS measurements in two-phase fluids.
• This technique provides a reliable method for quantifying gas components, such as oxygen, in dynamic multiphase systems.