水平管内冷凝流动的稳定性

管内冷凝换热流动在紧凑型两相热控系统中比较常见，本文关注于冷凝两相流中的不稳定性。首先对工质在冷凝器中的热力学过程进行建模，然后利用Lyapunov稳定性理论讨论了冷凝流动过程中流动压降发生振荡的机理。发现失稳区间的质量流量开始点对应的出口工质干度为1，而失稳区间的结束点对应的工质出口干度通常在0.8左右。在大入口过热度、小管径以及低热通量下，冷凝器的压降-流量曲线会出现负斜率，工作流体若进入负斜率区域，会导致压力振荡，使得系统的运行变得不稳定。

Stability of condensing flow in a horizontal tube

The condensing flow widely appeared in compact thermal management system. Thus, this work modelled and discussed the pressure drop oscillation of working fluids to reveal the flow instability of condenser. The mechanism of pressure drop oscillation of condensing flow was analyzed based on Lyapunov instability principle. The flow drift would occur and trigger the flow instability in the condenser channel, when the working fluid operates on the negative slope region of pressure-drop flow curve. The results indicated that the onset-instability of condensing flow with the outlet quality by 1, and flow instability would be ended for the outlet quality of working fluid with the quality of 0.8. In addition, the much higher inlet super, smaller pipe diameter and lower heat flux would be easier to generate the negative slope on the pressure-drop flow curve of the condenser. As a result, the pressure drop oscillation and the unstable operation would be occurred in the condensing flow system.