Numerical investigation of the process steps in a spray flame reactor for nanoparticle synthesis

The synthesis of titanium dioxide nanoparticles from titanium tetraisopropoxide (TTIP) in a nanoparticle spray flame reactor was investigated. The nanoparticle properties are affected by different processes: (a) the break-up of the liquid jet from the spray nozzle, (b) the combustion of the spray and in the pilot flame and (c) the formation and growth of the nanoparticles. The spray process of the injected liquid was analyzed by volume of fluid (VOF) calculations and validated by shadowgraphy imaging which provided the size distribution and the mean velocity of the droplets. The spray angle was determined by a side illuminated long exposure image of the spray. The resulting spray properties (droplet sizes, velocity, and spray angle) served as injector boundary conditions for the downstream combustion simulations. Spray and gas phase of the flame were simulated using an Euler-Lagrange approach, turbulence was modeled by the RNG k-epsilon model, and turbulent combustion was described as a partially stirred reactor (PaSR). For the formation and growth of the nanoparticles within the synthesis reactor, the population balance equation was solved coupled to the spray combustion using a monodisperse model. The findings from experiment and simulation are discussed in terms of flow, species, temperature, and nanoparticle formation inside the reactor. The effect of the spray droplet properties as droplet size, angle, mean velocity and the dispersion behavior on the nanoparticle synthesis process are investigated and discussed, confirming the observation that this type of spray reactor is a robust design overall. (C) 2014 Published by Elsevier Inc. on behalf of The Combustion Institute.