Binary droplet's collision is one important phenomenon, which exists in the two phase flow within some nuclear power plant equipments, such as the steam generator, the steam separator and the vane dryer. Numerical simulation was carried out by using VOF method to study equal-sized binary saturated water droplet's head-on collision in high pressure steam. Two typical collision processes, coalescence and reflexive separation were investigated. Droplets' shapes and internal velocity field during the collision process were observed. The transformation between kinetic energy and surface energy, and the energy dissipation were analyzed to achieve better knowledge about the collision process. By simulating equal-sized head-on collisions with various We number, critical We between coalescence and reflexive separation was found and compared with Qian and Law's model. For collisions at 6.75 MPa (i.e. steam generator and steam separator's operating pressure), Qian and Law's model was revised to achieve better prediction.
