The efficacy of SPLITT fractionation requires an absence of hydrodynam
ic mixing between laminae constituting the thin liquid film streaming
through a SPLITT cell and it requires structural elements capable of s
plitting the film evenly along streamplanes. These requirements are ex
amined here by both experimental tests and by a numerical analysis of
flow properties near the inlet splitter. The experimental tests, invol
ving dye injection and the injection of pulses of latex particles that
may or may not be driven across flow laminae by gravity, show that SP
LITT cell performance is close to that of ideal theory at low Reynolds
numbers. The computer results verify an absence of mixing under these
conditions, but when the Reynolds number and inlet flow asymmetry are
both high, vortex motion is found near the inlet splitter edge, sugge
stive of mixing. The conditions leading to vortex formation are define
d. It is shown that tapering the splitter edge suppresses vortex forma
tion.