Despite the many advantages of micro-reactors their application in industry is still limited due to their low throughput. To address this issue, micro-scale porous media are used as inserts in milli-scale tubular reactors. In this work, six different well-structured porous media (WSPM) consisting of cylindrical rods with an outer diameter of 250 mu m are characterized with computational fluid dynamics (CFD). The individual WSPM differ in the rotation of rod layers around the main flow direction, and the orientation of rod layers against the flow direction. The simulation results show that changing the rod layer orientation influences the flow heterogeneity, while the rod layer rotation affects the pore alignment resulting in connected fluid paths. Scalar transport simulations reveal that the WSPM result in a considerable mixing enhancement. This study underlines the potential of integrating WSPM in milli-scale reactors as scale-up approach, and how their geometry affects mixing. (C) 2019 Elsevier Ltd. All rights reserved.