Interesting results represent the oil droplet sizes at high Thoma numbers. At Th¼0.75 the SMD values after the first orifice are considerably smaller than those received in a single stage process. This is a remarkable result since the corresponding pressure loss over the first orifice (Δp1¼25 bar)corresponds to only one quarter of the pressure loss in the single stage process (Δp1¼100bar).According to the cavitation number σ1¼2.8, there is no cavitation at the first orifice, thus cavitation cannot be the reason for a more effective droplet break up. A possible explanation lies in the absence of the tremend ous a mount of vapor in the region of droplet break up as observed in the single stage process. Results on this hypothesis are content of as econdpaper