A k ε model based on the renormalization group theory ( RNG k ε model )is used to predict the turbulent flow field in a liquid liquid hydrocyclone in this work. The new model just has the same form as the standard k ε model, but it includes an extra term that describes the effect of large distortion (shear rate) and incorporates some anisotropy effect.So it can resolve fine details of the flow field better than previous models. The results show that some improvement has been made in predicti...