Abstract The present study reports a study of water droplets impacting on cold thin water films on a superhydrophilic surface. A thermal infrared imager was used to record the surface temperature distribution after the droplet impact on the liquid films. A ring-shaped high temperature zone was found after impact with the temperature first increasing and then gradually decreasing in the radial direction. Numerical simulations were then used to study the velocity distribution and the droplet motion inside the liquid film. The droplet spreading motion was restricted by liquid in the film for lower We which then reduces the heat transfer in that area and causes the formation of a ring-shaped high temperature distribution. The ring structure shape then changes with the increasing of We. This hot ring becomes wider and the temperature difference between the ring and the impact center decrease with the increasing of We. As We continues to increase, the ring-shaped temperature distribution disappears with the highest temperature at the center and the temperature in radial direction monotonically decreasing from the center to the edge. The initial film thickness also affects the temperature distribution after droplet impact. A thicker film causes the ring-shaped hot region to gradually move inward until it reaches the center and forms a hottest region in the impact center. Thus, the ring-shaped temperature distribution only occurs for lower We and thinner films. The shape and position of the temperature distribution after droplet impact on the cold, thin liquid films can then be precisely controlled by regulating the impact We and the initial film thickness. These results will greatly facilitate the design of precision spraying processes.

中文翻译：

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液滴撞击超亲水表面超薄冷膜的温度演化的精确调节

摘要 本研究报告了水滴影响超亲水表面上的冷薄水膜的研究。使用热红外成像仪记录液滴撞击液膜后的表面温度分布。撞击后发现一个环形高温区，温度在径向上先升高后逐渐降低。然后使用数值模拟来研究液膜内的速度分布和液滴运动。液滴扩散运动受到较低 We 薄膜中的液体的限制，从而减少了该区域的传热并导致形成环形高温分布。环结构形状随后随着 We 的增加而变化。随着 We 的增加，该热环变宽，环与冲击中心的温差减小。随着 We 继续增加，环形温度分布消失，中心温度最高，径向温度从中心到边缘单调递减。初始膜厚也影响液滴撞击后的温度分布。较厚的薄膜使环形热区逐渐向内移动，直到到达中心并在撞击中心形成最热区。因此，环形温度分布仅出现在较低 We 和较薄的薄膜中。水滴撞击冷后温度分布的形状和位置，然后可以通过调节冲击 We 和初始膜厚来精确控制薄液膜。这些结果将极大地促进精密喷涂工艺的设计。