“…The gas bubbles are sheared off at the gas inlet, due to the velocity gradient; the gas bubble size decreases with increasing rotational disc speed, leading to an increase in gas-liquid mass transfer. 1 The volumetric gas-liquid mass transfer coefficient increases with increasing rotor radius, up to 2.5 m 3 L m À3 R s À1 , at a rotational disc speed of 209 rad s À1 , using a rotor with 0.135 m radius and 1 mm rotor-stator distance (Meeuwse et al, submitted). The energy dissipation rate, however, increases more than the mass transfer rate; scaling up by stacking multiple rotor-stator units in series is therefore, from energetic point of view, preferred over scaling up in rotor size.…”