A droplet collision model for bouncing–coalescence boundary of droplets under different ambient pressures

Changes in ambient pressure have a significant influence on droplet collision outcomes, especially on the boundary between bouncing and coalescence after collision. Recent experimental findings have demonstrated that an elevation in ambient pressure initially facilitates the bouncing behavior of colliding water droplets, and this facilitative effect essentially plateaus as the ambient pressure continues to rise. In this work, we extended the experimental working fluid from water to glycerol aqueous solutions with different Ohnesorge (Oh) number and verified the universality of this phenomenon in the collision processes of different types of droplets. Furthermore, based on high-resolution droplet collision images, we clarified the variation law of the shape factor ϕ (which characterizes the degree of droplet deformation in Estrade et al.'s model) with the impact parameter B. By introducing empirical coefficients, we completed the fitting of the droplet deformation shape factor with ambient pressure under head-on collision conditions ϕB=0. For the first time, we have developed a droplet collision model capable of capturing the influence of ambient pressure variations on the bouncing–coalescence boundary, specifically for low-viscosity droplets (Oh