Figure 6 FFT analysis on pressure trace

(d_V = 4 mm, P_H = 0.84 MPa, ΔT = 50 K, l_V = 3.8mm)

　

The result indicates that in flashing in pool water with a short nozzle. Bubbles cannot develop and Phase B occurs. Therefore FO with an alternating flashing location in the pool might be stopped when a long nozzle is used. The maps show that the FO region of a 4 mm and a 5 mm hole diameter vent become smaller as the nozzle length increases. The effects of the experimental settings on the behavior of the flashing in the pool are represented in the maps obtained through this study. Figure 9 shows measured saturated water flow rate. The solid lines in the figure represent Bailey's correlation for the flow rate of discharging saturated water into gas field.

　

　

Equation (3) is expressed as a function of ρ_H (1bm/cu ft). P_H (pst) in the original reference. K and Z are an evaporating coefficient and a function of P_H and P_∞ which are given in a table and a figure in the reference [1], respectively.

As shown in Fig 9, Bailey's correlation can predict well the present result. And subcooling of pool water little affects on the flow rate. These facts indicate that the discharging flow rate into pool water is little affected by the outlet condition except ambient pressure. All of the present data of mass flow rate agree with Bailey's correlation in 20 % deviation (Fig. 10).

　

Linear analysis

　

To assess the effect of the parameters on the duration of FO, a linear analysis was conducted in the same way as simulation of condensation oscillation in pool water [6, 7], using a spherical flashing bubble model and three basic equations: the continuity equation for flashing and condensation the momentum equation for water-steam interface motion and the equations of state for steam and water. When steam is discharged into the pool water, the condensation oscillation (called CO in previous studies), which appears at steam mass fluxes between 30-120 kg/(m²・s), is the pressure oscillation with a control Volume consisting of a steam bubble attached at the vent tube exit. The frequency, components of CO have been well documented in order to prevent a structural resonance in nuclear power plants. The real steam bubble shape in the present experiment is constantly changing and is therefore difficult to represent using a simple shape, as shown in Fig. 4. It was shown in the previous analysis for CO, however, that bubble shape has weak influence on the linear frequency analysis among spherical and cylindrical shapes [6]. Therefore, in this linear analysis, we simply assume the bubble to be spherical, as shown in Fig. 11 and interface motion is represented by the change in the bubble radius caused by the pressure oscillations.

When high-pressure satuated water is discharged into a field where the pressure is lower than that of saturated water, the volume of steam generated by flashing, Q_S, varies with the amount of heat containes in the discharges water.

　

Figure 7 Effect of the experimental settings on the frequency of FO

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