I was thinking about the "Is the steam wet?" question a bit tonight, and
I realized a couple things. These are just based on gut feel, I haven't
done calculations to back them up (wouldn't even know how to start to
get numeric results), but I think they're interesting gedanken points.
Let's just forget the humidity measurement for a moment.
The steam is passing through what looks like two or three yards of hose,
and it's rather wiggly hose, at least when it's on the floor in the room
rather than stretched over to the door. It's also angled /down/ to the
mouth of the hose.
If the steam is "wet", it contains droplets of water.
Droplets of water don't "corner" very well -- they tend to spin out on
tight turns and crash into the guardrail. That's the principle on which
the steam dryer domes work in a steam locomotive, if I understand them
right.
Asking all the droplets of water to negotiate all the wiggles of the
hose without every skidding off the track and hitting the wall seems
like asking a lot. So, intuitively, I'd expect a a fair number of the
droplets to end up stuck to the inside of the tube. In fact, I'd expect
a lot of the entrained water to fail to make the very first turn, where
the hose comes out the top of the reactor.
So, if the steam is very "wet", I'd expect the inside of at least part
of the hose to also get wet. This would have two likely consequences,
or so it seems to me.
1. Since the hose is angled down to its mouth, one obvious
consequence, if the steam is /very/ wet, would be that the hose
would start drooling. This would be very bad behavior for a hose
carrying "dry steam" and I'd /surely/ expect someone to have
noticed, and commented on it.
Nobody has commented on it, so I conclude it very probably didn't
happen.
2. I would expect steam passing through a wet hose to cool down to
exactly 100% RH pretty darn quick. At or near sea level, that
means 100 C. Now, measuring RH precisely is pretty difficult.
But measure /temperature/ precisely is pretty easy. Levi quotes
the steam temp as being 101.6 C +/- 0.1 degree. That's a
believable level of accuracy for a temperature measurement -- and
it's 1.6 degrees /above/ the temperature I'd expect the steam to
be coming out at, /if/ the hose were wet on the inside.
So, apart from any measurement except the steam exit temperature, and
without any information except the knowledge that it went through a
rather long and flexible hose, I'd tend to conclude that the steam was,
indeed, /dry/.
Discussions of the RH meter seem, therefore, to be a red herring -- the
humidity measurement appears to me to be just belt&suspenders, a double
check of an expected conclusion, not a critical primary check of a
totally unknown parameter.
