Flashing is a classical phenomenon in the discharging process of liquid to the high vacuum environment in space, as well as in nuclear power engineering, chemical engineering, and other engineering fields. To predict the discharge process and ensure the safety of space activities, a better understanding of its laws is needed. In this paper, flashing front propagation in vertical small tubes is experimentally studied under the condition of rapid depressurization. Experiments are carried out with degassed distilled water under different tube diameters and initial temperatures (superheats). The sustainability of flashing front propagation is confirmed to be influenced by superheat, tube diameter and gravity. A correlation is proposed with the Jacob number and Bond number to summarize the sustainability condition. The superficial velocity of flashing front propagation shows to be related to multiple factors such as superheat, tube diameter and downstream pressure. An empirical correlation is proposed to predict the superficial velocity and it agrees well with existing data
