Development of a droplet size model for the separated gas–liquid flow in horizontal pipe and its application

Highlights: • Detailed results of droplet diameter in horizontal stratified flow are presented. • A set of non-dimensional numbers that govern droplet size in horizontal pipes has been defined. • The effects of liquid velocity and developing length are considered in the model development. • The application of the developed model into a best-estimated safety analysis code is presented. A new model for droplet size prediction in horizontal pipes under stratified and annular flow is presented. The developed model takes into account the effects of the gas velocity, liquid velocity, pipe diameter, and developing length on the droplet size. Four experimental databases of droplet size in air-water horizontal flow under atmospheric pressure were used in the model development. The experimental flow conditions of the database covered a pipe diameter range of 2.45–24 cm, and gas and liquid Reynolds numbers ranges of 50,519–582,524 and 526–14,728, respectively. Droplet size experimental results were predicted by the proposed model with a root-mean-square error of 19.4% under stratified flow conditions, and 7.8% under annular flow conditions. Finally, the applicability of the suggested model was confirmed by benchmark calculations with SPACE code, a best-estimated safety analysis code for nuclear power plants, with experimental droplet parameters under various flow conditions.