The controlled technical-scale production of nanoparticles is a very important aspect in nanotechnology. The synthesis of nanoparticles by microemulsion precipitation is a laboratory-scale technique which has to be scaled up to technical use. For a better understanding of this complex process, a numerically efficient process model was derived which is applicable to CFD studies, process control and the analysis of the scale-up behavior. The model contains microemulsion specific nucleation kinetics allowing for the discrete character of the system on a molecular scale, and growth kinetics adopted from bulk phase approaches. The major output of this process model is the computationally efficient and reliable determination of the mean particle diameter as a function of time. A comparison with experimentally obtained data from barium sulfate precipitation showed a qualitatively good agreement.