Thermal-Hydraulic Safety Research Division, Korea Atomic Energy Research Institute, 111, Daedeok-daero 989, Yuseong-gu, Daejeon 305-353, Republic of Korea.
Phys Rev E. 2016 Apr;93:043123. doi: 10.1103/PhysRevE.93.043123. Epub 2016 Apr 21.
Film boiling on a horizontal surface is a typical example of the Rayleigh-Taylor instability. During the film boiling, phase changes take place at the interface, and thus heat and mass transfer must be taken into consideration in the stability analysis. Moreover, since the vapor layer is not quite thick, a viscous flow must be analyzed. Existing studies assumed equal kinematic viscosities of two fluids, and/or considered thin viscous fluids. The purpose of this study is to derive the analytical dispersion relation of the Rayleigh-Taylor instability for more general conditions. The two fluids have different properties. The thickness of the vapor layer is finite, but the liquid layer is thick enough to be nearly semi-infinite in view of perturbation. Initially, the vapor is in equilibrium with the liquid at the interface, and the direction of heat transfer is from the vapor side to the liquid side. In this case, the phase change has a stabilizing effect on the growth rate of the interface. When the vapor layer is thin, there is a coupled effect of the vapor viscosity, phase change, and vapor thickness on the critical wave number. For the other limit of a thick vapor, both the liquid and vapor viscosities influence the critical wave number. Finally, the most unstable wavelength is investigated. When the vapor layer is thin, the most unstable wavelength is not affected by phase change. When the vapor layer is thick, however, it increases with the increasing rate of phase change.
水平表面上的膜沸腾是瑞利-泰勒不稳定性的典型例子。在膜沸腾过程中，相变化发生在界面处，因此在稳定性分析中必须考虑热和质量传递。此外，由于蒸汽层不太厚，必须分析粘性流。现有研究假设两种流体的运动粘度相等，和/或考虑薄粘性流体。本研究的目的是为更一般的条件推导出瑞利-泰勒不稳定性的分析色散关系。两种流体具有不同的性质。蒸汽层的厚度是有限的，但从扰动的角度来看，液体层足够厚，可以近似为半无限大。最初，蒸汽在界面处与液体处于平衡状态，传热方向从蒸汽侧到液体侧。在这种情况下，相变对界面增长率具有稳定作用。当蒸汽层较薄时，蒸汽粘度、相变和蒸汽厚度对临界波数有耦合作用。对于蒸汽较厚的另一个极限，液体和蒸汽粘度都影响临界波数。最后，研究了最不稳定的波长。当蒸汽层较薄时，最不稳定的波长不受相变的影响。然而，当蒸汽层较厚时，它随着相变速率的增加而增加。
