A STUDY OF FLASHING PHENOMENA UNDER RAPID DEORESSURIZATION

本课题的目的是阐明闪蒸现象发生的物理判据，并预测在快速降压下容器内汽液相压力和温度的时间历程，实验是用R-113型快速开启电磁阀进行的。本文用照相法观察了液体沸腾过程的行为，用热电偶和压电传感器组成的定量测量系统记录了液体沸腾过程中的温度和压力变化过程。（1）汽-液两相压力瞬变过程中，阀门快速开启后的压力瞬变过程大多数具有指数型压力降的特征，以及在适当的下冲下，液体爆炸汽化引起的压力连续上升，这对应于过热液体的下限压力与初始饱和压力之间的压力差。虽然许多闪蒸过程是从靠近液面的上部区域开始到储层底部，已经观察到，根据汽-液和固-液界面对它们的热物理性质的依赖性的有效性，存在三种类型的压力瞬变模式。(2)在减压速率相对减小的情况下，改进了Alamgir和Lienhard成功地处理过的异相成核理论。在所发展的理论中，即初始降压过程用指数函数来近似，该指数函数以非平衡压力弛豫时间为特征<gamma>。已经发现，这个弛豫时间强烈地影响与气泡产生的开始相关联的物理条件，其估计为Gb数34-40。

The purpose of this project is to clarify the thermodynamical criterion associeted with the inception of vaporization of liquid, so-called the flashing phenomena , and to predict the time history in pressure and temperature of vapor-liquid phase within a vessel under the rapid depressurization.Experiments have been performed with a R-113 by the quick openning of solenoid valve. Behaviors of boiling process of liquid have been made use of photographic observation , and each of their temperature and pressure transients have been recorded by quantative measuring systems using thermocouples and piezoelectric tranducer.The results are summarized as follows;(1) Most of vapor-liquid pressure transients after the rapid openning the valve has been characterized by the sudden exponential-like pressure drops, and the successive pressure rise caused by the explosive vaporization of liquid under the appropiriate undershoot,Hich correspods to the difference in pressure between the lower limit and initial saturated condition of superheated liquid.Although many of flashing process has been initiated from the upper region near a liquid surface to the bottom of reservoir, they have been observed there exists three type patterns of the pressure transients according to the effectiveness of the dependence of both vapor-liquid and solid-liquid interfaces on their thermophysical properties.(2) The heterogeneous nucleation theory that Alamgir and Lienhard have succesfully dealed with, is improved for the case of relatively reduced depressurization rate of this study. In the developed theory,that is, an initial depression process is approximated by an exponential function which is caracterized by non-equilibirium pressure relaxation time <gamma> . It has been found that this relaxation time affects strongly on the thermodynamical condition associeted with the inception of bubble generation, which is estimated Gb Number 34-40.