Membrane emulsification with oscillating and stationary membranes

Membrane emulsification of sunflower oil in aqueous solutions of 2% (vol/vol) Tween 20 was performed using a stationary disk membrane with a rotating paddle stirrer and, for comparison, a tubular membrane oscillating normal to the direction of oil flow in an otherwise stationary continuous phase. The oscillation frequency ranged from 10 to 90 Hz. The oil was injected through a sieve-type membrane with a 10 μm pore size and 180 μm between pore spacing at low flux rates to minimise any droplet interference. Using the same membrane material under identical peak shear conditions in both systems, smaller and more uniform drops (30 to 50 μm median sizes) were produced in the oscillating system. In oscillation, the drop size was modelled by a force balance, including a correction for neck formation at the pore surface, but in the rotating paddle system neck formation did not appear to be relevant. Drop size was not found to be frequency of oscillation dependent, apart from its influence on the shear stress at the membrane surface.