Heat Flow during Rapid Solidification of Undercooled Metal Droplets
Heat Flow during Rapid Solidification of Undercooled Metal Droplets
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DOI：
10.1007/bf02643312
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发表时间：
1982-02
期刊：
影响因子：
--
通讯作者：
C. Levi;R. Mehrabian
中科院分区：
文献类型：
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作者：
C. Levi;R. Mehrabian
采用牛顿和非牛顿（焓）模型分析了离散熔融温度下过冷球形液滴的凝固过程。建立了雾化参数、生长动力学、界面速度和过冷度以及其他重要凝固变量之间的关系。提出了一种新的数学公式和求解方法，用于模拟在液滴表面发生的单个成核事件在过冷液滴中的凝固过程。焓模型的计算网格是在重叠双球坐标系下定义的。建立了基于焓模型的纯铝液滴凝固的数值解，并将其结果与牛顿模型预测的趋势进行了比较。还讨论了单核与多核事件的意义。总的来说，结果表明，当液滴在成核之前达到大量过冷时，热历史由两种不同的凝固状态组成。在第一种情况下，界面速度高，液滴吸收了大部分释放的潜热，外部冷却通常起很小的作用。第二种状态是生长较慢的状态，并且强烈依赖于液滴表面的热提取。“快速凝固”的程度，由低于某一临界过冷的温度下凝固的材料的比例来确定，是成核温度、颗粒尺寸、动力学参数和传热量（10~4）的函数。
The solidification of undercooled spherical droplets with a discrete melting temperature is analyzed using both a Newtonian and a non-Newtonian (Enthalpy) model. Relationships are established between atomization parameters, the growth kinetics, the interface velocity and undercooling, and other important solidification variables. A new mathematical formulation and solution methodology is developed for simulating the solidification process in an undercooled droplet from a single nucleation event occurring at its surface. The computational mesh used in the enthalpy model is defined on a superimposed bispherical coordinate system. Numerical solutions for the solidification of pure aluminum droplets based on the enthalpy model are developed, and their results are compared to the trends predicted from the Newtonian model. The implications of single vs multiple nucleation events are also discussed. In general, the results indicate that when substantial undercoolings are achieved in a droplet prior to nucleation, the thermal history consists of two distinct solidification regimes. In the first, the interface velocities are high, the droplet absorbs most of the latent heat released, and the external cooling usually plays a minor role. The second regime is one of slower growth, and strongly depends on the heat extraction at the droplet surface. The extent of “rapid solidification”, as determined from the fraction of material solidified at temperatures below a certain critical undercooling, is a function of the nucleation temperature, the particle size, a kinetic parameter, and the heat translow as 10~4.