A mathematical model is proposed and validated with experimental data for the estimation of the average diameter attained by the particles that are generated by decomposition of an organometallic precursor in supercritical CO2 (scCO(2)). Experiments have been performed for the synthesis of TiO2 anatase nanoparticles, using diisopropoxititanium bis(acetilacetonate) (DIPBAT) as precursor, ethanol as reactant and scCO(2) as solvent. The model is solved by using computational fluid dynamics (CFD) for the experimental geometry: a tee piece as mixer followed by a cylindrical reactor. Peng-Robinson EOS with Huron-Vidal mixing rule has been used to predict density variations within hydrodynamic equations. A pseudo-first order kinetic (r(TiO2) = kC(DIPBAT), mol L-1 s(-1) with k = 0.0297 min(-1)) has been proposed for mass and population balances. The CFD simulations predict a reduction on particle diameter from 400 to 200 nm when the Reynolds number is increased from 280 to 1500. In this range, deviations with experimental data are lower than 15%. A parametric study of the kinetic constant reveals that for faster reactions (Da >> 10(-3)) the trend of particle size with the Reynolds number is inverse, and particle diameter increases when the Reynolds number is increased. (C) 2009 Elsevier Ltd. All rights reserved.