| Abstract: | The depressurization of a high-pressure vessel initially filled with water heated to below the saturation point is investigated.
After depressurization, the pressure in the vessel drops and the boiling fluid flows out into the atmosphere. The experiments
1–3] showed that, when the first rarefaction wave passes through the fluid and the pressure falls below the saturation point,
a two-phase mixture with a small steam volume fraction (below 20%) is formed in the vessel. Intense boiling starts only after
the arrival of a rarefaction wave traveling at a speed ∼ 10 m/s called the "boiling shock" in 4].
To explain the specific features of this process we developed a mathematical model which takes the difference in the phase
velocities into account. Although in bubbly flows this difference is only ∼ 1 m/s, it is enough to cause bubble fragmentation.
The calculation showed that the fragmentation proceeds like a chain reaction, i. e. one fragmentation event creates the conditions
for the succeeding events. The avalanche-like bubble number growth leads to sharp boiling intensification and the rapid transition
of the non-equilibrium mixture to the equilibrium state. This process occurs in a narrow region, namely, in a slow boiling
wave which, in the numerical calculations, looks like a shock.
The model developed has made it possible to obtain numerical solutions which agree well with the experimental data, to study
the wave structure, and to explain the wave mechanism.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 20–33, July–August, 2000.
The work received financial support in part from the Russian Foundation for Basic Research (project 99-03-32042) and from
INTAS (grant OPEN 97-2027). |
