This paper describes a theoretical explanation of why the lower phase alway
s goes to the tail end of a coil when the tail is placed at the periphery.
This effect is due to the Archimedean and Hydrostatic influences working to
gether to pump the lower phase towards the tail and the upper towards the h
ead. A combination of the planetary motion, the geometry of the helical coi
l, and the movement of the Interface between the phases generate the pumpin
g effect.