Estimation of bubble size distribution using spatial digital image correlation

Spatial Digital Image Correlation (DIC) was used to measure the bubble rising terminal velocity to obtain the bubble size distribution generated by a mixing pump. This method provides non-contact and low cost measurement of bubble size. The digital image correlation setup is designed using low-cost line laser-diode as light source, and a consumer pocket digital camera to record the light scattered from the rising bubble inside the chamber. The measured terminal velocity distribution is proportional to the square radius of the microbubble according to the Hadamard-Rybczynski equation. DIC analysis from multiple interrogation windows was performed to obtain the bubble velocity distribution. Therefore the bubble size distribution can be estimated by calculating the radius from the Hadamard-Rybczynski equation. Evaluation of multiple frame pairs over time was performed to see the effect of the geometrical shape of the impeller to the size distribution of the bubble radius.