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.