The synthesis of aluminum (an energetic material) nanoparticles in a plasma reactor is simulated. The effects of flow-field mixing on nanoparticle growth are investigated via direct numerical simulation. The flow consists of high temperature argon/aluminum jet impinges on a low-temperature argon jet. To analyze the influence of fluid dynamic mixing on nanoparticle growth, the momentum ratio of the two jets is varied. The flow-field is obtained by solving the compressible Navier-Stokes equations while the evolution of the particle field is obtained by using a nodal approach to represent the aerosol general dynamic equation. The results indicate that increasing the momentum of the cooler jet increases dilution of the aluminum jet and increases flow-through time of nanoparticles (the time required by particles to travel the length of the domain).