Heat transfer and melt dynamics of millimetric ice particles impacting a heated water bath
Heat transfer and melt dynamics of millimetric ice particles impacting a heated water bath
复制标题
DOI：
10.1016/j.ijheatmasstransfer.2019.118830
复制
发表时间：
2020
影响因子：
5.2
通讯作者：
Katherine Baskin;K. Flores;Patricia B. Weisensee
中科院分区：
文献类型：
--
作者：
Katherine Baskin;K. Flores;Patricia B. Weisensee
在使用直接能量沉积的金属增材制造中，颗粒和熔池经历复杂的相互作用，包括颗粒冲击、穿透和熔化。这些过程的时空演变决定了凝固材料的微观结构和最终工件的质量。然而，由于金属熔池的不透明性，现场可视化几乎是不可能的。为了模拟这个系统，我们使用高速成像来研究球形冰粒（D = 2 mm）以0.8至2.1 m/s的速度撞击不同温度（23-70 °C）的热水浴的传热和融化动力学。为了可视化熔融冰的流出，代表混合和材料均匀性，用食用染料对颗粒进行着色。我们发现，在冲击后，熔融液体形成一个环形羽流向下移动的浴，直到击中外壳的底部和径向扩大。由于正浮力，未融化的冰粒上升到水浴的顶部，在那里它们完全融化。随着温度的升高，我们观察到随机粒子运动，表明对流的存在。通过视频分析，我们研究了浴温度，冲击速度和传热之间的关系。正如预期的那样，增加浴温度减少了冰粒的总融化时间。有趣的是，撞击速度对熔化时间的影响很小。使用无量纲分析，我们推导出一个表达式之间的相关性Nusselt和Stefan数。这项工作的见解可用于在增材制造过程中匹配特征时间尺度，以定制材料特性。
In metallic additive manufacturing using direct energy deposition, particles and melt pool undergo complex interactions, including particle impact, penetration, and melting. The spatio-temporal evolution of these processes dictates the solidified material microstructure and final workpiece quality. However, due to the opaqueness of metallic melt pools, in-situ visualization is nearly impossible. To model this system, we use high-speed imaging to investigate the heat transfer and melting dynamics of spherical ice particles (D≈ 2 mm) impacting heated water baths of varying temperatures (23–70 °C) with velocities ranging from 0.8 to 2.1 m/s. To visualize the outflow of molten ice, representative of mixing and material homogeneity, the particles were colored with food dye. We show that after impact, molten liquid forms an annular plume travelling downwards in the bath, until hitting the bottom of the enclosure and expanding radially. Due to positive buoyancy forces, unmolten ice particles rise to the top of the water bath, where they fully melt. As temperatures increase, we observe random particle movement, indicating the presence of convective currents. Through video analysis, we examine the relationships between bath temperature, impact velocity, and heat transfer. As expected, increasing the bath temperature decreases the total melt time of the ice particle. Interestingly, the impact velocity has only a minor effect on the melting time. Using non-dimensional analysis, we derive an expression for the correlation between Nusselt and Stefan numbers. Insights from this work can be used to match characteristic time scales during additive manufacturing to tailor material properties.