A conditional quadrature method of moments (CQMOM) was developed to solve turbulent mixing problems associated with population balance equations (PBE) by approximating the evolution equation of the composition probability density function (PDF) for the moments of the PBE. The well-established Interaction-by-Exchange-with-the-Mean (IEM) model was used to close the PDF evolution equation. The new CQMOM methodology was coupled to a quadrature-based PBE solver for univariate problems, which relies on the extended quadrature method of moments (EQMOM). The two procedures were implemented into the OpenQBMM framework, which leverages the OpenFOAM® CFD toolbox. The CQMOM approach for mixing problems was first tested considering two consecutive-competitive reactions to verify the implementation and validate the proposed approach. The coupled turbulent mixing-PBE approach was then used to investigate polymer aggregation in a multi-inlet vortex reactor (MIVR), typically used to perform flash nano-precipitation for the production of nanoparticles used in pharmaceutical applications. Results showing the predicted mixture fraction, reactant and product concentration fields and the polymer particle size distribution are shown.