事故容错燃料包壳表面液滴碰撞行为及Leidenfrost现象实验研究

为了研究事故容错燃料包壳表面的液滴Leidenfrost现象，本研究采用高速相机对液滴与事故容错燃料包壳SiC和FeCrAl的碰撞行为进行可视化观测，并与常规包壳材料Zr-4对比。结果表明，液滴碰撞方式有沉积、带二次液滴散射的反弹、带二次液滴散射的碎化、反弹和碎化5种；沉积属于核态沸腾换热，反弹和碎化属于膜态沸腾，带二次液滴散射的反弹和带二次液滴散射的碎化属于过渡沸腾换热；液滴的临界热流密度（CHF）温度与韦伯数（We）无关，而Leidenfrost温度随着We和固体表面蓄热系数的增大而增大；在膜态沸腾阶段，液滴的铺展行为与温度无关，随着We的增大，液滴铺展的更快，且能达到更高的铺展因子。 

Experimental Investigation on Impact Behavior and Leidenfrost Phenomenon of Droplets on ATF Cladding Surfaces

In order to investigate the Leidenfrost phenomenon of droplet impact on ATF (accident tolerance fuel) claddings, the impact behavior of droplet on sintered SiC and FeCrAl is recorded by high-speed camera, and Zr-4 is chosen as a reference. Based on the visualization results, the droplet impact behavior can be categorized into five regimes, i.e. deposition, rebound with secondary atomization, breakup with secondary atomization, rebound and breakup. Deposition corresponds to nucleate boiling. Rebound and breakup correspond to film boiling, and the rest two impact regimes are corresponding to transition boiling. It is found that the CHF temperature is relatively insensitive to Weber number, while the Leidenfrost temperature increases with Weber number and solid thermal effusivity. During film boiling, the droplet spreading dynamics seems to be independent of the surface temperature. As the Weber number increases, the droplet spreads more rapidly, and reaches a larger spreading diameter.