Given the fact that most of the reactions that take place in microreactors occur on the surface, it is crucial to keep the reactants close to the reactive wall. One of the effective techniques presented in this field is single-phase hydrodynamic focusing. But this method has this important drawback that the penetration percentage of reactants into the sheath fluid is high. To solve this defect, the concept of two-phase hydrodynamic focusing is introduced in the present work. The main idea is to use a highly viscous sheath fluid to create a barrier against the penetration of reactants into the sheath flow. To demonstrate the effectiveness of the proposed method, a 3D numerical simulation has been performed using Comsol Multiphysics software considering a parallel plate microreactor with an irreversible first order reaction. The results demonstrate the effectiveness of two-phase hydrodynamic focusing in increasing reaction rates. This effect is particularly pronounced in downstream regions where the Sherwood number can increase by several orders of magnitude, when a highly viscous sheath of liquid is used. Additionally, it was observed that the use of two-phase hydrodynamic focusing improve efficiency, which is defined as the ratio of solute in the sample flow to the total solute in each cross-section.
