Precipitation of barium sulphate in an unpremixed feed two-dimensional tubular precipitator is studied experimentally and interpreted theoretically using a closure procedure proposed previously by the authors. The closure employs the presumed beta PDF of the inert type composition variables formed with the local values of Ba2+ and SO42- concentrations and the turbulent mixer model. The flow field is computed using the k-epsilon model. The method enables the particle size and the particle size distribution to be predicted and compared with experimental data.