In recent years there has been a growing interest in production on an industrial scale of particles with size in the sub-micron range (40-200 mn). This can be done by controlling particle formation in order to nucleate very small particles and by tailoring the particle surface in order to avoid particle aggregation and produce stable suspensions. In this work we focus on the role of turbulent mixing on particle formation in confined impinging jet reactors. In particular, we show how computational fluid dynamics and simple precipitation models could be used to derive scale-up criteria for the production of nanoparticles. (c) 2006 American Institute of Chemical Engineers.