液滴撞击高温梯度表面的动态行为特性

Dynamic behavior of droplets impact on a hot microstructured surface with wetting gradient

以铜片为基底制备了微方孔结构浸润梯度表面,利用高速摄像技术对液滴撞击高温梯度表面的动态行为特性进行了研究。结果表明:在不同表面温度和韦伯数(We)下,液滴撞击在梯度表面上会出现5种不同的撞击模式,即润湿模式、接触沸腾模式、过渡模式、碎裂模式和反弹模式;当表面温度达到Leidenfrost温度时,液滴进入反弹模式,反弹液滴会沿着梯度能方向发生多次连续弹跳行为,且由于弹跳过程中能量的不断衰减,反弹高度逐渐减小直至趋于零。基于表面物理化学理论分析了液滴的定向弹跳行为,并利用图像处理技术,分析了弹跳液滴的动态特征。进一步地,通过液滴以相同We数撞击不同表面温度实验,研究了液滴在弹跳运动过程中反弹高度、铺展因子和运动的水平加速度变化特征,发现三者随反弹次数的增加具有相似的变化过程,即呈现先快速减小、后逐渐稳定的特征。水平加速度的与铺展因子的变化趋势具有一致性,从而验证了理论分析的合理性。

Using copper plates as substrates,the microholed gradient surface was fabricated by the optical etching,and dynamic behaviors of droplets impact on the high temperature microholed gradient surface were studied by high-speed camera. The results showed that when a droplet impacts on the microholed gradient surface,there are five different impact modes. They are wetting mode,contact boiling mode,transition mode,explosion mode and rebound mode. When surface temperature reached Leidenfrost point,the droplet is in the rebound mode and it appears continues rebound behavior along the direction of the wetting gradient. Due to the energy reducing continues in rebound process,the rebound height gradually reduces to zero. Based on surface physical and chemical theories,the directional bouncing behavior of the droplet was analyzed. In addition,the dynamic characteristics of the droplet rebound were analyzed by using image processing technology. Moreover,the rebound height,the spreading factor and the horizontal acceleration of the droplet were discussed by experiments. It was found that they have same characteristics with the increase of rebound numbers. It experienced the same stages：rapid reducing at acceleration. The spreading factor were highly consistent with the theoretical analysis.