The numerical simulation of a batch rotating cylinder electrode (RCE) system for bulk electrolysis was investigated. This study focused on the transient tertiary current distribution and cell configurations for electrolysis of copper sulfate in sulfuric acid. The simulated flow field of an RCE shows one vortex around the axisymmetric cutting plane of the cell when the distance from RCE to container bottom is no more than 5 cm, or double-vortex flow pattern appears. The flow field influences the mass transport of copper ions and then causes the accumulation at the top corner of the cell, proved by the simulated concentration profile. The transient simulation exhibits two-stage development of the concentration distribution between the RCE and anode. In the first stage, the diffusion layer extends with time while the bulk region becomes indefinite in the second stage. Furthermore, hydrogen reduction affects the current density on the RCE, resulting in a decreasing current efficiency with passing time. Although the simulated residual fractions of copper ions slightly deviate from the conventional macroscopic prediction due to the cell configuration and side reaction, the simulated results are consistent with those from the experiments and can provide the information of cell design on the bulk electrolysis. (C) 2014 The Electrochemical Society.