Falling film microreactors are ideally suited for fast exothermic reactions due to their large surface to volume ratio (up to 20,000 m2/m3) which greatly intensifies mass transfer. Despite the enhanced mass transfer characteristics of these reactors, mass transfer between the phases can still be the rate limiting step. To improve mass transfer, staggered herringbone structures were incorporated on the microchannel floor of falling film microreactors . It was shown experimentally that reactors with herringbone structures increased CO2 absorption in 1 M NaOH solution by up to 42%. Modelling of this system can be computationally prohibitive. This is due to its three-dimensional nature and the complexity of incorporating gas/liquid absorption and reaction with chaotic flow. For the CO2 chemical absorption system, a pseudo 3D approach has been implemented to account for such a modelling complexity . In this work, the complexity of modelling the effect of herringbone structures was simplified using an effective diffusion coefficient calculated via an eddy diffusivity approach. Good agreement between the experimental data from Ziegenbalg et al.  and the simulations was obtained. The simplification suggested opens the possibility to model complicated systems with minimum computational expenditure.