Abstract

The injection of air and of a steam-air mixture into water at 60 to 90°C through a downward tube of 50 mm diameter is investigated. Steam at up to 40 l/s and air at up to 24 l/s were injected, leading to the formation and break-up of large bubbles. Instrumentation included video, high-speed video, high-frequency pressure measurement and resistance probes for phase detection.

Air tests show a strong dependence of bubble-formation frequency and thus bubble size on the capacitance or length of the piping. Only at higher flow rates, the equation of Davidson and Schüler (1960) predicts bubble frequency and size well.

For steam-air experiments, total flow-rate, and a maximum-volume-reduction factor are used for defining a test matrix. These parameters effectively describe the fluid dynamics of bubble formation and after break-up, and are useful for visual volume estimations. The pool temperature also has some influence.

Experiments show a very irregular, chaotic, turbulent flow. For some cases, bubble volumes at detachment could be estimated and compared with the given parameters. These tests show that condensation is very strong even before bubble detachment and break-up. The height of complete break-up could be approximately correlated. After complete break-up, uncondensed steam is virtually impossible.

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