The effect of rotor speed n on oil removal efficiency E is shown in Fig. 5. The inlet flow rate and water temperature were 90L/h and 60 1C, respectively. The oil removal efficiency increased with increasing rotor speed until the maximum value was reached at 2100r/min and then began to decrease with the rotor speed. This result is attributed to the increase in centrifugal force with increasing rotor speed, which can enhance oil removal efficiency. When the rotor speed is sufficiently high, however, the EDW is emulsified in the annular zone, thus hindering separation