Mass transport in laminar flow can improve the electrochemiluminescence (ECL) performance at the microchannel electrodes, depending on the device geometry and operating regimes.The known Ru(bpy)$_3^{2+}$/Tripropylamine (TPA) system was selected and studied in continuous microfluidics on semi-transparent platinum electrodes. With this electrode material, ECL is mainly generated via the catalytic pathway. This mechanism was characterized under flow conditions by monitoring the ECL emission in linear sweep voltammetry and chronoamperometry. In parallel, ECL imaging of the electrode surface was conducted in order to characterize the ECL profiles above the electrode in the flow direction. Numerical simulations were carried out and then compared to experimental data to both confirm the ECL mechanism and assess the main kinetic parameters. A good agreement was obtained, demonstrating the influence of the operating regimes of microchannel electrodes on the ECL performances. In the thin-layer regime, due to TPA depletion, ECL is located at the upstream edge of electrode, while it is homogeneously distributed over the electrode surface in convective regimes. These characteristics will necessarily have to be taken into account to design dedicated ECL analytical microfluidic devices operating under continuous flow.