Abstract: A permeable membrane tube to separate mixed fluids is provided, including a cyclone generator configured to cause fluid entering the permeable tube to flow in a spiral direction. The cyclonic generator may be a plug positioned at the fluid entrance of the membrane tube. The fluid passes through the permeable membrane tube, which has a center axis along a length of the tube, and flows in the spiral direction thereby separating the fluid into first and second portions, wherein the first portion comprises fluid having a greater density than the second portion and the first portion is directed to an inner surface of the tube.