how to control vapor bubbles in boilers?
As I recall, boiler feed water is passed through a deaireating heater to remove dissolved gasses before it is pumped into the high pressure boiler.
In most boiler tube surfaces, you do not want steam to blanket the heat exchange surfaces, it does not cool was well as water, so the tube can heat up and fail. If you keep the velocity of water through the tube high enough, the steam vapor bubbles will be swept along with the bulk water to the steam separation drum. This is done by either pumping the recirculated boiler water in controlled circulation boilers or by keeping the tubes large enough to allow natural circulation to keep up the velocities needed. Some boiler manufacturers have also used tubes that are essentially rifled, so the water swirls as it travels upward, sweeping the bubbles along so they do not blanket the tubes' interior surfaces.
