Pressure Oscillation in Subcooled Decompression under Temperature Gradient

摘要

In the subcooled decompression experiments of water in a vertical tube under a tem-perature gradient, a violent pressure oscillation was observed. By varying the gradient conditions it was ascertained that this pressure oscillation was due to the existence of the large temperature gradient in the system, and that it occurred in the low tempera-ture region of the system. The generation of the pressure oscillation could be explained by assuming a reflection surface for the pressure wave caused by the blowdown. Two positions of the reflection surface were experimentally obtained from the structure of oscillatory pressure behavior and by computing the autocorrelation function of the pres-sure curve. In the system of a linearly descending temperature distribution, a flashing occurred partially and those two values were in good agreement with the position of the phase boundary generated just after the passage of the decompression wave. The conventional thermal equilibrium model could not completely explain this oscilla-tion. The anomalous pressure peaks appeared in the calculated pressure curve resulting from the prompt flashing in the second supersaturated region. Photographic observation showed that this region was kept in the supersaturated liquid state during the oscillation and that a flashing was delayed. 'Introduction of the flashing delay time into the thermal equilibrium calculation has well succeeded to reproduce the oscillatory pressure behavior.