Steam radiator heating rate

Steamhead

down-firing the boiler slightly and see if that helps. I'll bet you get some short-cycling too, down-firing will also help here.

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michael_15

some mind exercise

Not a totally serious question/puzzle, just an interesting one. For some reason, I tend to think of frivolous things.

Anyway, I was sitting in front of my 2-column (4-section, one-pipe steam, nippled on top and bottom) radiator today reading and noticed something interesting about the way it heats up. I had expected that the tops of each section would get hot first, going across the sections to the air vent, and then the heated part of the radiator would expand downward, with the section near the inlet getting hot earlier. Instead, I noticed the following.

1) The inlet tube, of course, gets hot first.
2) By the time the tops are warm (but not too hot to touch), the second section is too hot to touch from top to bottom. The rest of the sections are still cold except for the very tops, which are warm.
3) The next section to get hot is the section is the last one. At some intermediate stage, the 2nd and last sections, then, are fully hot while the other two are only hot about halfway down.
4) The 1st and 3rd sections heat up at about the same time.

The radiator has the proper pitch and size pipes and all that good stuff. The air vent, however, is misplaced; someone apparently put a bunch of bushings on the top nipple and jammed an air vent there. I'm sure there are all sorts of potentially partially correct explanations (heck, I've got a few already) to support why the radiator heats the way it does.

This doesn't bother me, but I thought it was fun to think about.

-Michael

Dean_7

radiator

Funny, I had a radiator that heated about the same way. It too had the air vent installed in the top nipple with a bunch of bushings. when I restored our radiators the bushings were removed and a plug installed. the boss was drilled and tapped for the new vent and now it heats evenly. What would be interesting is to have a thermograph done while the radiator is heating and you could see exactly where the steam was going.

thfurnitureguy_4

Rad heating

I think that the steam is blowing past the first few sections of the radiator during the initial start up. steam is a gas with some mass. If it has velocity it would stand to reason that it could blow past the first sections and fill them later as the radiator becomes filled. There is a section in the library that describes "short circuiting of steam" or somthing like that. A smaller (slower vent) may change things What do you think?

Steamhead

I've seen this too

FurnitureGuy is right, the steam entering the rad is moving fast enough that it travels along the bottom of the first few sections. In a rad with a small number of sections this can result in the steam reaching the last section earlier than usual, closing the air vent.

Usually everything heats up as the steam rises to the top and the air drops to the bottom, which allows the vent to cool down and open to allow more air to escape. But if the vent is installed at the top it won't reopen since that's where the steam is.

Drill and tap the boss on the last section to 1/8-inch pipe thread and move your vent there. You'll see the difference right away.

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michael_15

well,

I can see the boss on the last section and thought about moving the vent, but actually, this radiator heats very quickly and that's not a problem. It has one of those Dole/Ventrite adjustable vents on it, I set it to a very low venting rate (it's the smallest radiator and closest to the boiler and was always heating first) and I haven't had any problems with it. It definitely heats fully without problems.

I think it was actually moved up since given where the radiator sits with regard to the walls/etc., it is actually fairly susceptible to having an air vent kicked accidentally if placed too low. Of course, that's just wild conjecture.

I guess I tried to imagine the rate at which air was leaving the air vent (not very fast) and couldn't imagine that corresponded to steam moving fast enough to just "skip" the first section and heat the second one. Also, the fact that the second section heats all the way through (top to bottom) before the tops of the sections even get fully hot is a feature that I found. . . interesting.

-Michael

Steamhead

There's still enough velocity in there

to make the steam skip that section initially. I wonder if your main vents are sized properly? Or if the boiler is oversized?

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michael_15

I guess it would be fun

to actually watch the steam move along the pipes. Except that dry steam is mostly invisible, and I can't see through metal anyway. Maybe I should get some thermal coating which changes color when it gets hot. That would be pretty cool.

Main vents should be fine. I've got 2 Gorton#1's for about 25 feet of 2" supply main. Boiler is about 50-70% bigger than it should be (86k DOE but only 160sqft of radiation)

-Michael