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

Gas composition in randomly distributed and fast-moving bubbles was optically measured aided by laser-induced breakdown spectroscopy (LIBS). Laser pulses were focused at a point in a stream of bubbles to induce plasmas for the LIBS measurements. The distance between the laser focal point and liquid-gas interface, or 'depth,' plays a major role in determining the plasma emission spectrum in two-phase fluids. However, the 'depth' effect has not been investigated in previous studies. Therefore, we evaluated the 'depth' effect in a calibration experiment near a still and flat liquid-gas interface using proper orthogonal decomposition, and a support vector regression model was trained to exclude the influence of the interfacing liquid and extract gas composition information from the spectra. The gaseous molecular oxygen mole fraction in the bubbles was accurately measured under realistic two-phase fluid conditions.