A mathematical model capable of determining suitable operating conditions to produce TiO2 nanoparticles with specified average diameter is presented. The model consists of mass, momentum and energy conservation equations. Particle dynamics processes under consideration include particle formation by nucleation, growth by both condensation and coagulation as well as the loss of the product particles due to deposition on the reactor wall. The aim of this model is to predict the effect of inlet temperature and reactants concentrations on the average diameter of TiO2 nanoparticle products taking into account particle deposition on the wall due to thermophoresis. Strong non-linear coupling between energy and mass balance equations makes numerical integration of the stiff ordinary differential equations (ODE) a problem. The simulation results obtained provide useful information about the influence of the operational conditions (initial temperature and TiCl4 concentration) and particle wall deposition rate on the average nanoparticle diameter at reasonable computational time. The performance of the present monodisperse model was validated by comparing its predicted results with previously published numerical data. Good correlations between the predicted and numerical results were achieved.