Collapse of steam bubbles in subcooled water
Condensation, of steam bubbles generated at an orifice and rising freely through water, subcooled from 5 K to 36.6 K at pressures of 1 bar and 2 bar, has been analysed theoretically and experimentally. Orifice diameters were 1 mm and 2 mm, and steam flow rates of 0.5, 1 and 1.5 g/min were used. The data indicate a decrease in collapse Fourier number with increase in either Jakob number or steam flow rate, or with a decrease in pressure, while change in orifice diameter does not have a significant effect on collapse Fourier number. Average values of heat transfer coefficient around the collapsing bubbles have been determined to be between 0.15 . 10⁵ - 0.35 . 10·⁵ W/m·²K. The effect of bubble distortion and of local heating of the liquid, close to the orifice, due to condensation of the bubbles, have both been included in the quasi-steady state theory which has been presented. The experimental data is compared with the theoretical predictions. A semi-empirical correlation for bubble rise height has been proposed, which is also based on the quasi-steady theory combined with a correlation for the velocity of steam bubbles condensing in subcooled water.