Measurement of forced convection subcooled boiling flow through a vertical annular channel with high-speed video cameras and image reconstruction

ABSTRACT

In order to develop models regarding subcooled boiling flow and its heat transfer, we conducted subcooled boiling experiments to investigate subcooled bubble formation and measured development process of the bubbles using a test loop with a vertical annulus flow path under atmospheric conditions. Two-phase flow parameters regarding subcooled boiling, such as instantaneous bubble velocity, turbulent velocity components, void fraction, onset of nucleate boiling (ONB) and onset of significant void (OSV), were obtained with two high-speed video cameras in high resolution in temporally and spatially. The identical bubbles were identified from the two video images taken by the high-speed video cameras, and the trajectories were reconstructed in three-dimensional. The instantaneous bubble velocities and turbulence velocity components regarding bubble transport were quantified with the trajectory data. It was observed that the bubbles were rising along the surface of the heater rod moved largely in the circumferential direction, and it was found from the result that velocity component for circumferential direction was enough large compared with that for radial direction.

KEYWORDS:

• Subcooled boiling
• bubble dynamics visualization
• three-dimensional reconstruction
• particle tracking velocimetry

Acknowledgments

This study was financially supported by the Agency for Natural Resources and Energy of the Ministry of Economy, Trade and Industry and conducted as part of the Infrastructure Development Project to Enhance Safety Measures at Nuclear Power Plants “Research and Development for Understanding Two-Phase Flow Behavior inside a Fuel Bundle.” The authors would like to thank to the Agency, Dr. Hiroki Takiguchi, Mr. Yoshiyuki Shiratori, Mr. Yuuki Miyazawa and Mr. Shinya Ueno of Denryoku Techno-Systems, Co. Ltd.

Nomenclature

Dh	=	hydraulic diameter of flow region of the annular
Di	=	diameter of heater rod, inner diameter of flow region of the annular
Do	=	outer diameter of flow region of annular
Hl,in	=	inlet enthalpy [J/kg]
Hl,sat	=	liquid saturated enthalpy [J/kg]
Hfg	=	inlet enthalpy [J/kg]
jL	=	volumetric flux of liquid phase [m/s]
q	=	heat flux [kW/m2]
uz	=	bubble velocity component for vertical direction [m/s]
$u{ }_r^{\prime }$	=	turbulent velocity component for radial direction [m/s]
$u{ }_{\theta }^{\prime }$	=	turbulent velocity component for circumferential direction [m/s]
Xe	=	thermal equilibrium quality [-]
y	=	boundary layer thickness [mm]
z	=	axial position [m]
Δt	=	frame rate of high-speed video camera [s]
ΔTsub	=	subcooled temperature [K]
τp	=	time constant of the fluorescent particle