This paper deals with hydrodynamics simulations in an up-flow pre-pilot electrochemical reactor with a stack containing eight cells in a serpentine array. Each cell contains horizontal parallel aluminum plate electrodes, open to the atmosphere at the top of the cell. The single-phase flow was simulated solving the Reynolds-Averaged Navier-Stokes (RANS) equations with k-ε turbulence model via finite element method. The residence time distribution (RTD) simulations were obtained solving the averaged diffusion-convection equation. The influence of mean linear flow velocity, 2.4 ≤ U ≤ 12.1 cm s−1, on the velocity profiles evidenced the presence of jet flow in the first channel of the stack, which is located close to the electrolyte inlet at the bottom of the reactor. Then, the flow pattern became homogeneous in the second and third channels, while the quasi-plug flow profile was developed from the fourth channel to the exit. Streamlines graphs showed that in channel 1 there was very little recirculation of the fluid elements; however, this phenomenon disappears in the subsequent channels. The RTD curves shows the absence of low velocity zones in the reactor, because the electrolyte outlet is open to the atmosphere. The experimental RTD curves showed excellent agreement with simulations. •Simulation of hydrodynamics in a stack of eight cells in a serpentine array.•Horizontal parallel aluminum plate electrodes open to the atmosphere at the top.•The electrolyte velocity was different in each channel due to local turbulence.•The fluid behavior tends towards a plug flow pattern.•Close agreement between simulations and experimental data (95–98%) was obtained.