【摘要】 黑斑是一种宏观通道偏析,由于其在横截面上为黑褐色斑点而得名。它产生于糊状区富溶质液体对流。Rayleigh数很好的描述了糊状区液体流动而被作为通道偏析形成的判据。本文分析和总结了近年来文献中出现的主要通道偏析形成机制及其判据,给出了它们之间的联系和相应的应用条件,发现W．Yang提出的Rayleigh判据能够全面考虑影响黑斑形成的各个因素,可作为黑斑形成的通用公式,在实际应用中可根据实际情况选取合理的黑斑判据以简化计算。更多还原

【Abstract】 Freckles are kind of macro channel segregation for its brown spots morphology in the transverse section. Freckles originate from the solute rich liquid convection in the mushy zone. Rayleigh number accurately describes the liquid convection in the mushy zone and was selected as the criterion for channel segregation. The prevailing channel segregation theories and their criteria proposed in lectures in recent years were analyzed and summarized. The relationship between them and their application condition were presented. A universal freckling criterion constructed by W. Yang was found to include all the conditions affection channel segregation and it can be simplified by considering the application condition.更多还原