In microfluidic reactors designed for the synthesis of nanomaterials, hydrodynamics and mixing performance play a crucial role in the characteristics of the synthesized nanoparticles. In the current study, CFD simulation is utilized to shed light on flow characteristics inside a spiral microfluidic device and the way it affects the mixing during ZnO synthesis. Before microfabrication, the optimal number of spiral loops and flow rate in the microfluidic reactor was determined through mixing index calculation according to the CFD results in terms of the concentration distribution. Furthermore, this synthesis method is compared with batch nanoparticle fabrication techniques. In the microfluidic system, the concentrations of precursors were 50 times more diluted rather than batch methods. The droplet-based microfluidic ZnO synthesis was eight-fold faster than batch synthesis. The ZnO nanoparticles were characterized by XRD, SEM, and FTIR techniques. The outcomes of the FTIR analysis demonstrated that both the batch and microfluidic samples exhibit identical vibrational peaks. The experiments showed that the microfluidic system is reliable for controlling size. Besides, the CFD results indicated that a spiral micromixer with five loops provides sufficient mixing. The acquired findings from the characterization analyses can lead us toward a clue that once the ZnCl2/NaOH concentration ratio is greater than unity, a narrower size distribution of ZnO particles is probable. Consequently, the microfluidic reactor can be an efficient method for nanomaterial construction owing to the minimization of energy consumption and independence of the operational synthesis temperature.