Experimental And Numerical Research On Droplet Impact

Re-entrainment phenomena exist in wave-type vane separators used in Nuclear powerplant. The main reasons of this phenomena are that droplet impacts solid surface and the wallfilm to product secondary droplets. Re-entrainment will impact the safety and economical ofNuclear power plant, so carrying out deep study on the process of droplet impact hasprofound significance on nuclear power equipment’s development.In this paper, the high-speed camera was employed to study the process of dropletimpact on solid surfaces. Combination of large eddy simulation model and VOF model, thevelocity and pressure distribution characteristics were analyzed by numerical simulation withOpenFoam. The effects of contact angle, droplet diameter and surface tension coefficient onimpact process were investigated in detail, and based on this calculation model, factorsaffecting the droplet impact liquid process was analyzed, such as droplet impact velocity,impact angle, droplet property, liquid film thickness and so on.The results of the experiments show that:1)When droplets rebound, the Re increasedwith the We.2)Under different impact velocity, same diameter of droplet spent the same timebasically when they reached the maximum spreading coefficient; as the impact velocityincreased, the smaller the asymmetry of droplet, the smaller the oscillation frequency.The results of the numerical simulation show that：1)Droplets with lager surface tensioncoefficient, the sooner the time approached the maximum spreading range, and the smaller themaximum spreading range.2)As the large the contact angle or the smaller the diameter ofdroplets, the smaller the spreading range, the sooner the time approached the maximumspreading range, the greater the oscillation amplitude; the intensity of oscillations increased asimpact velocity decreased, decay rates of oscillations increased and their frequenciesdecreased as surface tension coefficient increased.3)Under droplet impact on liquid film,dynamic process depended the amount of droplets kinetic energy, while the surface tensionand viscosity inhibited the generation of splash; increased the impact angle or the filmthickness, the weaker the splash phenomena.