Transient contact behavior of aqueous polymer solution droplets with transparent hot solid
Transient contact behavior of aqueous polymer solution droplets with transparent hot solid
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DOI：
10.1016/j.expthermflusci.2018.02.026
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发表时间：
2018-09
影响因子：
3.2
通讯作者：
H. Fujimoto;S. Sakane;T. Hama;H. Takuda
中科院分区：
文献类型：
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作者：
H. Fujimoto;S. Sakane;T. Hama;H. Takuda
在金属成形工业中，淬火硬化通常用于通过快速冷却热材料来强化钢产品。淬火硬化工艺中使用的典型冷却剂之一是聚合物水溶液。在硬化过程中，几种现象同时发生，即冷却剂沸腾、聚合物从水溶液中分离以及在固体表面上形成聚合物富集层。冷却过程中冷却剂的流体动力学和传热特性本质上是复杂的，并且仍然不清楚。本研究的主要目的是发展一个实验理解的碰撞和接触行为的聚合物水溶液液滴与热基板。本研究为喷雾冷却淬火工艺提供了基础性的参考。为了实现这一目标，开发了一种三向闪光摄影技术。利用透明蓝宝石棱镜观察了液滴与温度在300 ~ 600 °C之间变化的热固体的瞬态接触行为。使用平均分子量约为20，000的10重量%聚氧乙烯-聚氧丙烯二醇的溶液作为测试液体。在300 °C的基板温度下，在基板上残留有棒状聚合物残留物。在400 ° C和500 °C下，液滴碰撞后不久，在固体基底上暂时出现湿润区域，但由于聚合物的热分解，该区域最终消失。在600 °C下，没有看到潮湿区域。暂时湿润区的寿命随固体温度的升高而降低，但几乎与液滴的冲击惯性无关。此外，在聚合物溶液液滴的情况下，用于形成湿润区域的表面温度的上限为约580 °C，这显著高于水滴的情况。
In the metal forming industry, quench hardening is commonly used to strengthen steel products by rapidly cooling hot materials. One of the typical coolants used in the quench hardening process is an aqueous polymer solution. During the hardening process, several phenomena occur simultaneously, namely, coolant boiling, separation of the polymer from the aqueous solution, and formation of a polymer-enriched layer on the solid surface. The hydrodynamics and heat transfer characteristics of the coolant during the cooling process are complex in nature and remain unclear. The main objective of this study is to develop an experimental understanding of the collision and contact behavior of aqueous polymer solution droplets with a hot substrate. This research will serve as a fundamental reference work for the process of quench hardening using spray cooling. To fulfill this objective, a three-directional flash photography technique was developed. A transparent sapphire prism was used to observe the transient contact behavior of droplets with a hot solid, whose temperature was varied from 300 to 600 °C. A solution of 10 wt% polyoxyethylene-polyoxypropylene glycol with an average molecular weight of approximately 20,000 was used as the test liquid. At a substrate temperature of 300 °C, jellylike polymer residue remained on the substrate. At 400 and 500 °C, a wet area appeared temporarily on the solid substrate soon after the droplet collision, but this area eventually disappeared because of the thermal decomposition of the polymer. At 600 °C, no wet area was seen. The lifetime of the temporary wet area decreased with an increase in the temperature of the solid but was almost independent of the impact inertia of droplets. In addition, in the case of the polymer solution droplet, the upper limit of the surface temperature for forming the wet area was around 580 °C, which was considerably higher than that in the case of a water droplet.