For a given pair of fluid phases, liquid-liquid flows are
generally described in terms of regimes (e.g. stratified, wavy or
dispersed), which are a function of the Reynolds numbers of the
individual phases, the geometry of the flow, as well as the inlet
conditions and the distance from the inlet. Typically, injecting
the heavier phase at the bottom of the channel and the lighter
phase at the top is the common inlet configuration when
establishing a liquid-liquid flow for study in a laboratory
environment. This configuration corresponds to that expected
in a naturally separated flow orientation, on the assumption that
at long lengths the density difference between the two phases
will lead to this arrangement of the two phases. In this study, a
series of experiments were designed to investigate the influence
of injecting the heavier phase at the top of the pipe rather than
at the bottom. This modification introduces the possibility of
phase breakup near the inlet by an additional instability
mechanism (due to the density difference between the two
liquids), which would not appear had the phases been
introduced in the conventional inlet flow arrangement. We
perform detailed flow measurements and observe that this flow
arrangement gives rise to altered flow structures downstream.
Moreover, our results suggest that the effects of this instability
near the inlet may persist along the pipe and influence the
observed flow behaviour even at long lengths.