Simulation and Characterization of Microreactors for Aerosol Generation

This paper shows the application of T-shaped micromixers for the generation of nanoscale aerosols by the mixing of a hot gas-vapor-mixture with a cold gas. The fast mixing within a T-shaped micromixer leads to a quasi-instantaneous and high saturation of the vapor and therefore to homogeneous nucleation. After nucleation, the particles grow to their final size until the vapor is saturated. Different mixer geometries, mixing ratios, and gas temperatures have been investigated by numerical simulation to yield optimum mixing results over a wide range of operational parameters. The main selection parameters are the mixing time, the mixing quality, and the flow regimes in the mixer. Six different microreactor geometries were designed and fabricated in silicon and covered with a Pyrex glass lid for optical observation. Special attention was paid to thermal insulation and particle deposition at the channel walls. This concerns not only the entire mixing chip, but also the design of the fluidic mount with only few bends and corners. First experimental results for particle deposition (prefabricated NaCl nanoparticles in a nitrogen carrier stream,) and aerosol generation (Vitamin E droplets in nitrogen) are presented. High temperature gradients up to 1 Mio. K/s lead to a rapid condensation and forming of nanosized particles with a mean diameter of 20 to 50 nm and a narrow size distribution.