TS-132
Flashing-condensation Phenomenon in Discharging of High-pressure Saturated Water into Pool Water Tank
Takehiro GOTO* Akira SAITO* Tomoji TAKAMASA*
Abstract
This paper describes our experimental study of a high-pressure saturated water discharge into pool water. Our results revealed that a flashing oscillation (FO) occurred under certain experimental settings. The occurrence of flashing oscillated between a point very close to the vent hole and a point some distance away. Oscillation of the pressure and flashing location might have been caused by a balancing action among the supply of saturated water, flashing in the control volume, and steam condensation on the steam-water interface. A linear analysis was conducted using a spherical flashing bubble model and three basic equations: the continuity equation of flashing and condensation, the momentum equation for water-steam interface motion, and the equations of state for steam and water. The period of the flashing oscillation in the experiments can be explained by theoretical analysis. Flashing phenomena that include FO in the pool was shown in maps.
Key words: Flashing,Condensation, Oscillation, Heat transfer coefficient
Nomenclature
a coefficient
C coefficient of discharge
Ce coefficient of contraction of the liquid cone due to the evaporation
dΓ vent hole (nozzle) diameter, m
g gravity
h heat transfer coefficient, W / (m2 K)
K coefficient of evaporation
L latent heat of evaporation, J / kg
lV nozzle length, m
P pressure, Pa
P∞ ambient pressure,Pa
QH mass flow rate of saturated water, kg / s
QS mass flow rate of steam generated by flashing, kg / s
r radius of steam bubble, m
T temperature, ℃
ΔT degree of subcooling, K
l time
lS volume of steam bubble, m3
Z a function of P and P∞
υ frequency of pressure oscillation or FO, Hz
ρ density, kg / m3
ω angular velocity, rad / s
Subscripts
H Saturated water
L pool water
s steam
Introduction
High-pressure saturated water occasionally contacts low-pressure, low-temperature on cold water in ship's heat plant. For instances, it can be arose when opening a valve which separates high-pressure saturated water and low-pressure, low-temperature-water, discharging high-pressure saturated water from feed water line into a feed water-tank or a distilled water tank during boiler maintenance work, and discharging high-pressure saturated water from a pressure vessel into a containment in a wall-crack accident or loss-of-coolant accident (LOCA) in an advanced marine reactor with water-filled containment. The discharged saturated water causes flashing and generates steam in cold water. Steam is then condensed by cold water. In some cases, peaked and oscillated pressure might be caused by such thermohydraulic action.
The phenomenon of flashing in pool water involves the overlapping phenomena of saturated water flashing and steam condensation in pool water.
The phenomenon of flashing which consists of a flow of saturated water discharged from a nozzle or an orifice into a gas field whose pressure is lower than that of the saturated water, has been the subject of study in the machine industry since the end of the previous century [1-3]. On the other hand, the phenomenon of steam condensation in pool water has also been the subject of study in relation with boiling water reactors (BWRs) using pressure suppression type containment. Containment minimizes the volume of steam by letting it condense, thus preventing large temperature aud pressure increases in the system in the event of a LOCA.
Many theoretical and experimental studies have dealt with both subjects and their mechanisms have been clarified [4-6]. The investigation into the phenomenon of flashing in pool water is essential for verifying the safety and the reliability of new concepts for advanced reactors; however, little data on the phenomena have been available.
This paper describes a fundamental study that we did on high-pressure saturated water discharging into pool water [7-9]. The purpose of the study was to clarify the phenomena that occurs when high-pressure saturated water is blown down from a pressure vessel into a water-filled containment during wall-crack accident or LOCA in advanced reactors. The acquisition of hydrothermal data on the phenomena will be indispensable for the detailed design and development of heat plants or reactors for marine use.
