Abstract:

With the help of high-speed camera, the hydrodynamics of successive droplets impacting on heated cylindrical surface were captured. Under different impact velocities, the local convective heat transfer characteristics along the circumferential and axial directions were obtained by combining the directly measured experimental data with numerical calculation method. The results show that, when the droplet impact velocity is small and liquid film does not splash, due to the anisotropy of cylindrical surface, the convective heat transfer coefficient monotonically decreases in the axis, while in the circumference, the convective heat transfer coefficient firstly decreases and then augments slightly. According to the change of convective heat trasnfer coefficient along the circumference direction, the circumference is divided into impingement zone, heat diffusion zone and tail detachment zone. The improvement of convective heat transfer coefficient by increasing the droplets impact velocity is mainly reflected in the impingement and heat diffusion zones, but not obvious in the tail detachment zone. When the droplet impact velocity exceeds a certain critical value (about 1.53 m/s under the current experimental condition), the liquid film will splash. If continuously increasing impact velocity, the reduction of wall temperature is no longer obvious.

Key words: hydrodynamics, heat transfer, convection, heated cylindrical surface, impct velocity, liquid film splashing

摘要：

借助高速摄像机捕获连续液滴撞击热圆柱壁面后的动力学行为，通过直接测试与数值计算方法相结合，获得了不同撞击速度下沿周向和轴向的局部对流传热特性。结果表明，当液滴撞击速度较小，液膜未发生飞溅时，由于圆柱面的各向异性，沿轴向的对流传热系数单调减小，而沿周向，对流传热系数先减小后略有增大；根据对流传热系数沿周向的变化，将圆周划分为撞击区域、热扩散区域和尾部脱离区域；增大液滴撞击速度主要提高撞击区域和热扩散区域的对流传热系数，而对尾部脱离区域对流传热系数的影响并不明显。当液滴撞击速度超过某一临界值(在本文的实验条件下约为1.53 m/s)时，液膜发生飞溅，此时继续增大撞击速度，壁温的降低不再明显。

关键词: 流体动力学, 传热, 对流, 热圆柱壁面, 撞击速度, 液膜飞溅