The rising velocity of the globules carries them upwards where they become trapped by the under surfaces of plates and （）until the enlarged globules have sufficient rising velocity to travel along the plate surface and break away at periphery.

Humans are still needed to monitor the condition of the...

单项选择题Humans are still needed to monitor the condition of the boiler all the time the latter is operated, （）it is just to acknowledge an alarm buzzer or flashing light in a control room.

The steam boiler is part of a closed loop steam, whereb...

单项选择题The steam boiler is part of a closed loop steam, whereby, after the energy of the steam is used up and it becomes water again, （） is collected and returned back to the boiler for heating up again to steam.

Care must be taken to condition the （）in the boiler to ...

单项选择题Care must be taken to condition the （）in the boiler to prevent scaling, and corrosion, which can weaken the pressure vessel.