Investigation of the Gas–Liquid–Solid Stirred Tank by Using the Intrusive Image-Based Method

This work investigates the effect of solid particles on bubble size distribution and dispersed phase holdup in a stirred tank with the invasive telecentric photographic measurement system. The bubbles and solid particles are efficiently identified and distinguished with the image processing mainly based on deep learning and two different magnifications of telecentric lenses. The results show that solid particles promote the coalescence of bubbles, particularly at high solid concentrations. However, small bubbles (<1 mm) still dominate in number density, but their volume proportions are less than 3%. The Sauter mean diameter of bubbles (d₃₂) does not always increase monotonously with the increase in solid concentration. For small particles, the increment in d₃₂ is more pronounced due to a better solid suspension and a higher local effective viscosity, which further results in a lower local gas holdup. To summarize, the developed measurement method for the gas–liquid–solid system in this work provides valuable insights into the hydrodynamics in a stirred tank.