Direct contact condensation of steam bubbles in water at high pressure

Experiments have been carried out to investigate direct contact condensation of saturated steam bubbles introduced into a quiescent subcooled water environment. The experiments were performed for a range of pressures from 10.3 to 62.1 bar (150-900 lb in²), for subcooling from 15 to 100°C, and for initial bubble diameters of about 3mm. The data reduction of high speed motion pictures was based on a frame by frame analysis wherein the coordinates of the bubble perimeter were recorded in digital form and subsequently processed to yield quantitative information about the bubble collapse history and heat-transfer coefficient. The photographs showed that the successive shapes of the bubbles during their collapse histories proceeded from a sphere to a hemisphere to an ellipsoid to a sphere to collapse; short-lived bubbles collapsed as ellipsoids. The time to collapse and the height to collapse increased with increasing pressure and with decreasing temperature difference. The rise velocities of the bubbles were essentially constant, with an overall range of 15-22cm/s. The average heat-transfer coefficients were on the order of 10⁴W/m²·°C (1750 Btu/h·ft²·°F), with only modest variations with pressure level and temperature difference. The instantaneous heat-transfer coefficients did not differ appreciably from the average coefficients.