Experimental Validation of Bubble Departure and Lift-off Diameter Models under the Low Heat Flux and Low Flow Velocity Conditions

Bubble departure and lift-off diameters are important parameters to predict the evaporation heat flux at a heated wall. In particular, the boiling in the water pooltype reactor cavity cooling system (WPT-RCCS) of HTGR occurs at a vertical wall under the condition of natural convection with low wall heat flux. Even though the bubble diameter detaching from the heated wall depends on both the wall heat flux and flow condition, most correlations for bubble departure and lift-off diameters were developed under the high heat flux and high flow velocity conditions. Therefore, in order to estimate the bubble diameters under the low heat flux and low flow velocity conditions, it is needed to validate the applicability of existing correlations using the experimental data acquired under the similar conditions