An experimental and theoretical study on the size of bubbles formed between a rotating disc and a stationary wall

• Experimental and theoretical study on bubble size between a rotor and a stator.
• Liquid properties: 1000–1150 kg m−3 (density), 0.81–1.70 mPa s (viscosity).
• Bubble sizes are calculated via a force balance on the bubble and gas feedflow.
• The azimuthal liquid velocity is the single fitting parameter.
• The model correctly describes all bubble diameters (range: 3.32–15.3 mm).

This paper comprises an experimental and theoretical study on gas bubble formation in a liquid in a spinning disc device. Measurements were done in a device with a rotor radius of 0.135 m and a distance of 2×10−3 m between the rotating disc and the stationary wall. Experiments have been performed at rotational velocities where the Von Kármán boundary layer at the rotor and the Bödewadt layer at the stationary wall interfere. It was found that the highest angular velocities resulted in the smallest average bubble diameters (3.32±0.662 mm), while at the highest gas mass flow rate and lowest rotational velocities, the largest bubbles were produced (15.3±1.89 mm). Variation of liquid density from 1000 to 1150 kg m−3 and liquid viscosity from 0.81 to 1.70 mPa s appeared to have a negligible effect on the bubble size. A model was derived from a mass and momentum balance, which incorporates the unsteady effects of added mass, gas momentum, bubble growth rate, drag force and centrifugal buoyancy. The general trends in calculated average bubble size are in agreement with the experimental results and the model calculations were able to simulate average bubble diameters within a single experimental standard deviation.