How is it possible to filter oil on a long thin slotted pore – doesn it squeeze through?
By careful control of permeate flow. The mechanism for drop passage in to the permeate for oil on a long thin slot is by liquid drag from the permeate over the surface of the oil drop. So long as the drag force is low, and the interfacial tension is high enough, the drop will be retained on the slotted pore and the surface shear will remove it. If the interfacial tension is very low, you have a stable microemulsion and microfiltration will not work. The models for drops deforming, and being dragged, into the permeate are well developed and we have a good understanding of this mechanism, see the microfiltration section.