The effect of gravity on two-phase flow phenomena depends on the relative magnitude of the gravity force to inertia, viscous, and surface tension forces. Two-phase flow research has investigated heat transfer coefficients, critical heat flux, and flow regimes at different gravity levels and inclination angles, and several researchers proposed threshold flow velocities above which two-phase flow would be independent of the gravity force. This is a promising approach for a safe design of two-phase flow systems employed in microgravity or to build orientation-independent two-phase flow systems operating under the influence of gravity. This paper summarizes the derivation of several proposed approaches found in the open literature and compares their results via a standardized reference velocity. It is found that groups of criteria show similar trends and magnitudes of the reference velocity in parametric studies, despite a generally wide spread of velocities looking at all criteria. A validation of the two-phase flow criteria for two-phase systems is suggested as important future research.

重力对两相流现象的影响取决于重力与惯性力、粘性力和表面张力的相对大小。两相流研究研究了不同重力水平和倾角下的传热系数、临界热通量和流态，一些研究人员提出了阈值流速，高于该阈值流速将与重力无关。这是一种用于安全设计微重力中使用的两相流系统或构建在重力影响下运行的与方向无关的两相流系统的有前途的方法。本文总结了在公开文献中发现的几种提议方法的推导，并通过标准化参考速度比较了它们的结果。发现在参数研究中，标准组显示出相似的参考速度趋势和幅度，尽管在所有标准中速度普遍分布广泛。建议对两相系统的两相流标准进行验证作为重要的未来研究。