In this paper, the hydrodynamics in the FM01-LC electrolyzer is studied by flow visualization and residence time distribution (RTD). Divided and undivided modes are studied by direct visualization, with two injection points. The use of foams instead of turbulence promoters as well as that of electrodes without turbulence promoters is tested. In the membrane-partitioned-mode configurations, radial and axial dispersions are observed. Dispersion is drastically extended in case of empty channel flow. A high-flow asymmetry is generally induced by the flow distributors. RTD is implemented in the whole cell and in the reaction area. The reactor working with a plane plate alone gives a rather constant, low Peclet number, Pe, whatever the tested flow rates. The low Pe values denote an important axial dispersion. The use of turbulence promoters or foams induces a significant increase of Pe, giving plug flow character.