A STUDY OF FLASHING PHENOMENA UNDER RAPID DEORESSURIZATION

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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.