Hello! I'm advising some residents in the building where I live to change air valves on their one-pipe radiators, and encouraging the board to replace vents on the main, as the ends of the system aren't getting steam (215-205-184F surface temperature drop off in the twenty feet of the main pipe approaching the main vent after boiler had been running for 30min).
Something that has been on my mind as I talked through my understanding of the need to vent air, airlocking etc, is that air and steam are both gaseous, and gases expand to fill available space.
I'm sure that cold air and hot steam would act as separate volumes, and that the boundary between the two would initially see little mixing, but they should equalize after a while and mixing would become easier.
How come after 30 min, half a radiator is (comparatively) cold and the other half is hot? Why doesn't the steam and air mix, and the mixture heat the whole radiator? I know air is an excellent insulator, but it is also a gas...
This instance I wasn't sure steam was even getting to this radiator (it's above the 205F portion of pipe in the basement)...so is this just the pipe heating up via conduction?
This is for a radiator with a drastic slope and a fully open hand valve, so I'm fairly certain condensate is getting out of there.