Numerical study of the separation of two immiscible liquids in helical and straight pipes

Abstract This study reports numerical results for the flow of two initially perfectly mixed but immiscible liquids in helical and straight pipes, with a view toward optimal separation. Different flow orientations were considered, horizontal, upward, and downward. Assuming a perfect mixture at the pipe inlet, the main objective is set on investigating the separation behavior, its location, and finding the optimal Reynolds number for the most efficient separation. A laminar flow was considered, covering a wide range of relevant Reynolds numbers (Re = 10 to Re = 2250). The separation was quantified using the average mixing coefficient of the two liquids. It was found that the horizontal helical pipe leads to the maximum separation, while best mixing occurs in the vertical helical pipe with the downward flow. Additionally, the study revealed that an efficient separation can be always obtained in horizontal helical pipes after two turns. This observation is robust since separation is taking place at the same location for a wide range of water Reynolds numbers (28 to 563), with optimal separation at a water Reynolds number of about 225. It is therefore recommended to use these conditions to effectively separate immiscible liquids and extract one liquid out of the mixture.